I I I

IlBLACKWELL

I I I

IlBLACKWELL

Copyright C Andrew Goudie and Heather Viles 1997

The right of Andrew Goudie and He1Iher Viles 10 Ix identified as authors of this workhas been werted in accordance with the Copyright Designs and Patents Act 1988

First publishcd 1997Reprinted 1998 2000 and 2003

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A CIP catalogue record tor this book is availablt from tht British Library

librllr] of Congrus Cllttdogirtg-irt-Publi(Jloll Datil

Goudie AndrewThe Oarth tramformed an introduction 10 human impacts on th

enironmentby Andnw Goudie and Heather Vilesp em

Indudes bibliographical rderences and indexISBN 0-631-19464-9 -ISBN 0-631-19465-7 (pbk ~Jk p~pcr)

J Naturc-Effict of human beillgs 011 I ik~ Heather Ar1 TitleG75G677 199730428-DC20 96-26798

ellgt

CONTENTSPart I

Pan IIPan IIIPan IVPart VPart VIPart VII

Introduction to the DevelopingEnvironmentallrnpactThe BiosphereThe AtmosphereThe WatersThe Land SunaceOceans Seas and CoastsConclusion

11781

123163203237

GlossaryReferencesIndex

245254264

PART I

Introduction to theDevelopingEnvironmentalImpact

1 Early DY 32 Developing Populations 33 Agricultural Revolutions 44 Urban and Industrial Revolutions 55 The Modem Scene 76 Undersunding Environmental

Transfonruuions 14Key Tenns wd ConceplS 16Points for Review 16

1 EARLy DAYS

In this book we explore the many ways inwhich humans have transformed the faceof the Earth We stan by placing th~

mnsformations into an historical contextand ~dng how they have changed throughrime

Human life probably first appeared onEarth during the early part of the lee Agesome 3 million years ago The oldesthuman remains have been found in eastshyern and southern Mrica For a very longtime the numbers ofhumans on the planetwere small and even as recently as 10000years ago the global population was probshyably only about one-thousandth of its siutoday Also for much of that time hushymans had only modest technology andlimited capacity to harness energy Thesefactors combined to keep the impact of

Developing Populations 3

humans on the environment relativdysmall Nonetheless urly humans were nottorally powerless Their stone bone andwood tool technology developed throughtime improving their efficiency as humshyers They may have caused marked changesin the numbers ofsome species of animalsand in some cases even their extinction(see pan II section 13) No less imporshytam was the deliberate use of fire (see partII section 2) a technological developmentthat may have been acquired some 14million years ago Fire may have enabledeven smaU human groups to change thepattern of vegetation over large areas

2 DEVEWPING POPULATIONS

There Ire It least three interpretationsof global population trends over the llSt3 million years (Whitmore et aI 1990)

Plate 11 The OJduvai Gorge in Tanzania is one of a group of sites in the RiftValley of East Africa where some of the earliest remains of humans and their stonetools have been found ltA S Goudie

4 Introduction

Plate 12 A grass fire in the high grasslands of Swaziland southern Africa Firewas one of the first ways in which humans transfonned their environment andwas probably used deliberately in Africa over a million years ago (A S Goudie)

The first described as the arithmeticshyexponential view sees the history ofglobalpopuJation as a two-stage phenomenonthe first stage is one ofslow growth whilethe second stage related to the industrialrevolution (sec section 4 below) displaysa staggering acceleration in growth ratesThe second view described as ltIogarithmicshylogistic sees the last million or so yearsin terms of three revolutions - the toolagricultural and industrial revolutions Inthis view humans have increased thecarrying capacity of the Earth at leastthree times There is also a third viewdescribed as arithmetic-logistic whichsees the global population history over thelast 12000 years as a set of three cyclesthe primary cycle the medieval cycleand the modernization cycle These threealternative models are presented gnphishycally in figure 11

3 AGRICULTURAL REvOLUrIONS

Until the beginning of the Holoceneabout 10000 years ago humans wereprimarily hunters and gatherers After thattime in various parts of the world inshycreasing numbers of them started to keepanimals and grow plants Domesticationcaused genetic changes in plants and anishymals as people tried to breed more usefulbetter-tasting types Domestication alsomeant that human populations could proshyduce more reliable supplies of food froma much smaller area than hunter-gatherers(table 11) This in turn created a moresolid and secure foundation for culturaladvance and allowed a great increase inpopulation density This phase of developshyment is often called the first agriculturalrevolution

As the Holocene progressed many other

Urban and Indwtrial ~olutions 5

lOllllOk 5000

pastoralism (the use of land for keepinganimals) had a profound effect on manyenvironments in many parts of the world

A further significant ~eldopmcnr inhuman cultural and technological life wasthe mining of ores and the smelting ofmetals begun around 6000 years agoMetal artefacts gave humans greater powerto alter the environment The smeltingprocess required large quantities of woodwhich caused local deforestation

4 URBAN AND INDUSfRIAL

REVOLlTfIONS

The processes of urbanization and indusshytrialization are two Olher fundamentaldevelopments that have major environmenshytal implications Even in ancient timessome cities evolved with considerable popushylations Nineveh (the Assyrian capital)may have had a population of 700000Augustan Rome may have had a populashytion of around 1 million and Carthage(on the North African coast) at its ft11 in146 BC had 700000 inhabitants Suchcities would have exercised a considerableinOuence on their environs but this influshyence was never as extensive as that of citshyies in the last few centuries The modemera especially since the late seventeenthcentury has witnessed the transformationof culture and technology through the demiddotvelopment of major indwtries (table 12)This industrial revolution like the agrishycultural revolution has reduced the spacerequired to sustain each individual and hasseen resources utilized more intensively

Part of this indwtriaJ and economictnnsformation was the development ofsuccessful ocean-going ships in the sixshyteenth and seventeenth centuries As aresult during this time countries in verydifferent parts of the wond became inshycreasingly interconnected Among otherthings this gave humans the power to

fl iJ

i i I 0

sect

j

Figure 11 Three interpretations ofglobal population trends over themillennia (a) the arithmetic-exponential(b) the kgtgarithmic-Iogistic (c) thearithmetic-logisticSource Whitmore et aI (1990) figure 21

technological developments occurred withincreasing rapidity AU of them served toincrease the power of humans to modifythe surface of the Eanh One highJy imshyportant development with rapid and earlyeffects on environment was irrigation1bis was intrrouced in the Nile Valleyand Middle East over 5000 yevs agoAt around the same time the plough was~t used disturbing the soil as neverbefore ArUmals were used increasingly [0

pull ploughs and caru to lift water andto carry produce Altogether the introducshytion of intensive cultivation and intensive

6 Introduction

Table 11 Five stages of economic development

Economic stage Dates and characteristics

Hunting-gathering and early agriculture Domestication first fully established insouth-western Asia around 7500 BeE

hunter-gatherers persisted in diminishingnumbers until today Hunter-gatherersgenerally manipulate the environmentless than later cultures and adaptclosely to environmental conditions

Riverine civilizations Great irrigation-based economies lastingfrom c4000 Be to 1st century AD inplaces such as the Nile Valley andMesopotamia Technology developed toattempt to free civilizations from someof the constraints of a dry season

Agricultural empires From 500 BC to around 1800 AD anumber of city-dominated empiresexisted often affecting large areas ofthe globe Technology (eg terracingand selective breeding) developed tohelp overcome environmental barriers toincreased production

The Atlantic-industrial era From c1800 AD to today a belt of citiesfrom Chicago to Beirut and around theAsian shores to Tokyo form aneconomic core area based primarily onfossil fuel use Societies haveincreasingly divorced themselves fromthe natural environment through airconditioning for example Thesesocieties have also had major impactson the environment

The Pacific-global era Since the 1960s there has been ashifting emphasis to the Pacific Basin asthe primary focus of the globaleconomy accompanied by globalizationof communications and the growth ofmultinational corporations

Source Adapted from Simmons (1993) pp 2-3

The Modern Scenc 7

Plate 13 A simple irrigation system in use in the drier portions of Pakistan Suchirrigation was probably introduced in the Old World drylands around 5000-6000years ago (A S Goudie)

introducc planes and animals to puts ofthe world whert they had not previouslybeen Thc steam engine was invented inthe late eighteenth ccntury and the intershynal combustion engine in the late nineshyteenth century both these innovationsmassivdy increased human need for andaccess to energy and lessened dependenceon animals wind and water

5 THE MODERN SCENE

Modern science and modern medicine havecompounded the effects of me urban andindustrial revolutions leading to accelershyating popuJation incrtasc even in nonshyindustriaJ societies Urbanization has goneon speedily and it is now recognized thatlarge cities have their own environmentalproblems and produce a multitude of

environmental effects If present trendscontinue many citics in the less dcvdopcdcountries will become unimaginably largeand crowded For instance it is projcctedthat by the year 2000 Mexico City willhave more than 30 million people shyroughly three times the present populashytion of the New York metropolitan areaCalcutta Greater Bombay Greater CairoJakarta and Seoul are each expected to bein the 15-20 million range by that timeIn all around 400 cities will have passedthe million mark by the end of me twenshytieth century and UN estimatcs indicatethat b) then over 3000 million peoplewill live in cities compared with around1400 million people in 1970

Modern science technology and indusshytry have also been applied to agricultureIn recent decades some spectacular proshygress has been made Examples include

8 Introduction

Plate 14 A limestone pavement developed on the Carboniferous limestone ofnorth-west England Although they were formed in giadaI times by gladalabrasion they may be exposed at the surface today because of soil erosionproduced by forest dearance since the Mesolithic (A S Goudie)

the use of fertilizers and the selectivebreeding of plants and animals Biotechshynology has however immense potentialto cause environmental change (see partII section 14)

We can recognize cenain trends inhuman manipulation of the environmentduring the modem era First the numberof ways in which humans are affectingthe environment is growing rapidly Forexample nearly all the powerful pesticidespost-date the Second World War The sarJK

applies to the increasing construction ofnuclear reactors to the usc of jet aircraftand to many aspectS of biotechnologySecondly environmental issues that onceaffected only particular local arus havebecome regional or rven global problems

An instance of this is the appeanncc ofsubstances such as DDT (a major pestishycide) lead and sulphates at the North andSouth Poles far removed from the indusshytrial societies that produced them Thirdlythe complexity magnitude and frequencyof impacts are probably increasing Forinstance a massive modern dam like thuu Aswan in Egypt has a very diffcrentimpact from a small Roman darn Finallya general increase in per capita consumpshytion and environmental impact is comshypounding the effects of rapidly expandingpopulations Energy resources are beingdrveloped at an ever-increasing rate givinghumans enormous power to transform theenvironment One measure of this is worldcommercial energy consumption which

The Modem Scene 9

Table 12 Energy technology and environmental impact time line

Time Global Daily Energy Technological Environmentallone population energy source discoveries impacts

use perperson(kcals)

1 million lt 10 2000-5000 Food Tool local andto 5000 million human production short-termyears BC muscle fire animal kills

andvegetationchange

5000 BC 10 million 2ltXXl- Animals Cultivation Local andto AD -1 billion 26000 agricultural building longer-term1800 crops transport natural

wind irrigation vegetationwater coal removal soil

erosionurban airpollution

AD 1800 1 billion- 50000 Fossil fuels Industry Localto 1950 4 billion electricity regional and

steam permanentmajorlandscapechanges airand waterpollutioncommon

1950 to gt4 billion 300000 Internal Industry localpresent combustion cultural regional

engine globalization globalelectricity permanentnuclear and perhapsfossil fuels irreversible

add rainglobalwarming

10 Introduction

Plate 15 The power of humans to transform the lands surface in the modern erais illustrated by the size of the giant open-cast uranium mine at Rossing NamibiaModern technology allows humans to harness energy resources as never before(A S Goudie)

trebled in size bet1een the 1950s and1980

The importance of the harnessing ofenergy can be clearly seen in the contexrof world agriculture At the beginningof the twentieth century more or lessthroughout the world farmers relied upondomestic animals to provide both pullingpower and fertilizer They were largely selfshysutlicient in energy However in manyareas the situation has now changed Fosshysil fuels are eXhnsively used to carry outsuch tasks as pumping (or in many casesmining) water propelling tractors andmanufacturing synthetic fertilizers (whichin many cases cause pollution) The worldstractor fleet has quadrupled since 1950and as much as two-thirds of the worldscropland is being ploughed and compactedby increasingly large tractors

Above all as a result ofthe huge expansionof environmental transformation it is nowpossible to talk about global environmentalchange There are two aspectsofthis (TurnerKasperson et aI 1990) systemic globalchange and cumulative global changeSystemic global change refers to changesoperating at the global scale and includesfor example global changes in climatebrought about by atmospheric pollmioneg the greenhouse effect (see part III)Cumulative global change refers to thesnowballing effect of local changes whichadd up to produce change on a worldwidescale or change which affects a significantpart of a specific global resource eg acidrain or soil erosion (sec parts III and V)The two types ofchange are closely linkedFor example the burning of vegetationcan lead to systemic global change through

The Modem Scene II

Table 13 Systemic and cumulative global environmental changes

Type of change

Systemic

Cumulative

Charaderistic

Direct impact onglobally functioningsystem

Impact throughworldwide distributionof change

Impact throughmagnitude of change(share of globalresource)

Examples

(a) Industrial and land-use emissionsof greenhouse gases

(b) Industrial and consumer emissionsof ozone-depleting gases

(c) Land cover changes in albedo

(a) Groundwater pollution anddepletion

(b) Spelties depletiongenetic alteration(biodiversity)

(a) Deforestation(b) Industrial toxic pollutants(c) Soil depletion on prime agricultural

lands

Source Turner Clark et aL (1990) table 1

processes such as carbon dioxide releaseand albedo modification and to cumulashytive global change through its impact onsoil erosion and biodiversity (table 13)

Figure 12 shows how the human imshypact on six component indicators of thebiosphere has increased over time Thisgraph is based on work by Kates et aI(1990) For each component indicatorthey defined the total net change dearlyinduced by humans to be 0 per cent for10000 years ago (before the presentBI)and 100 per cem lor 1985 They thenestimated the dates by which each commiddotponent had reached successive quartiles(that is 25 50 and 75 per cent) of itstOtal change at 1985 They believe thatabout half of the components havechanged more in the single generationsince 1950 than in the whole of humanhistory before thar date

Human activities arc now atusing envirshyonmental transformation on the localregional continental and planetary scalesThe following examples both give an indishycarion of what is currently being achieved

and provide a sample of some of rhe issueswe cover in rhis book

Large areas of tcrnperate forest havcbeen c1eartd in the past few centuries Nowfarmers and foresters art removing forestsfrom the humid tropics at Idtes of aroundII million hectares (ha) per ycar This isexposing soils to intense and erosive rainshyfall and increasing Idtes of sediment yieldby an average of six times The worldsrivers are being dammed by around 800major new structures each year transformshying downstream sediment loads Hl1gereservoirs held behind dams as high as 300mctres are generating seismic hazardsand catastrophic slope failures Some ofthe worlds largest lakes most notably theAnI SCa in the fOrmer Soviet Union arcbecoming desiccated because the watcris being taken for irrigation usc and transshyferred to other water basirn at a nearmiddotcontinental scale Fluids both water andhydrocarbons (eg oil and gas) arc beingwithdrawn from beneath cities and farmmiddotlands leading to subsidence of up to 8-9metres Recreational vehicles and trampling

12 Introduction

1700~m~I~---Itmiddot-Imiddot50--2000YUI (0)

Figure 12 Percentage change (fromassumed zero human impact at 10000BP) of selected human impacts on theenvironment

feet are damaging many popular touristareas Development on tundra areas isdisturbing the thermal equilibrium ofpermafrost leading to more and moreinstances of thermokarst Coastlines arcbeing protected and reclaimed by theusc of large engineering structures oftenwithout due thought for the possible conshysequences We art pumping at least SOOmiUion tonnes of dissolved material intorivers and oceans around the world eachyear We arc acidifying precipitation tothe extent that some of it has the pHof vinegar or stomach fluid therebyaltering rates of mineral release and rockweathering

These human impacts are having greatdirect and indirect effects on vegetationtable 14 shows the amounts of vegetation(in terms of net primary production)ustd dominated or lost by humans

We shall return to these and other issuesin subsequent sections In this book wehave chosen to focus on specific environshymental issues as they affect the biosphere(part II) atmosphere (part III) surfacewaters (part IV) land surface (part V)and oceans seas and coasts (part VI)However you will notice through all of

these sections that a range of importanthuman activities play key roles and canhave a range of different impacts on manyst(tors of the environment

Even in the modern world economyhunting and gathering activities still havean important effect on the environmentlargely through the biological impacts offishing and the shaming of game Theseactivities arc becoming increasingly largeshyscale and mechanized Agricultureaquaculshyture and other forms of fOod productionnow occupy vasr areas of the Earthssurface and have a wide variety of eirmiddotonment1 efl~cts including soil erosionnutrient depiction changes in speciesdivesiry and genetic changes to crops 2ndanimals Forestry and quarrying as extracshytive industries are creating whole newbndscapes and releasing large amountsof sediment in parts of the globe rangingfrom the humid tropics to the ArcticHeavy industries (such as oil refining andchemical manufaetwC) power generationplants (from coal-fired to nuclear) andlight and high-technology industries havemany different environmental imp2cts andcontribute to pollution of land water 2ndair on the locaI and regional scales

Transport and urbanization have pershyhaps some of the most dr2matic localimpacts on the environment They createwhole new 12ndscapcs dominated by conshycrete add to pollution and affect plantand animal distributions and the circulashytion and distribution of w2ter Tourismwhich is now a booming global industryalso has considerable impacts on the envirshyonment In recent years there has beenmuch interest in the notion of ltccotourshyism or tourism which attempts to minishymize environmental damage

One of the consequences of all thesedifferent human interactions with the enshyvironment is the production of waste Thisitself hu had major environmental effectsThere arc problems of waste disposal and

------TorTlSlriII-brN oiotnily

--- COzmun------ 1lIpab--bull bull WaIftidaIl_- _ Nrdrun

100

The Modem Scene 13

Table 14 Terrestrial net primary production of vegetation used dominated or lostthrough human activities

Category

NPP usedconsumed by humansconsumed by domestic animalswood used by humans

Total

NPP dominatedcroplandsconverted pasturestree plantationshuman-occupied landsconsumed from little-managed areasland-clearing

Total

NPP lost to human activitiesdecreased NPP of croplanddesertificationhuman-occupied areas

Total

Total NPP dominated and lost

bull 1 Pg or Petagramme bull 1 x 10 gSource Vitousek (1994)

waste management Big issues like nuclearwaste disposal have potentially long-termenvironmental implications So do lesscontentious matters such as disposing ofdomestic and industrial waste on landfillsites

Human societies do not always runsmoothly War civil strife and smaller-scaledisruptions such as vandalism and crimehave their own environment1l conseshyquences Indeed some wars au pardymotivated by disputes over environmentalresources for example over water suppliesRecent conflicts in the Arabian GulfBosnia and Mglunistan have had bothshort-term and long-term environmentalconsequences induding pollution andsoil erosion In the 19605 and 19705 the

Amount (Pg per year)-

08222452 (4 of total global NPP)

151026043

1041 (31 of total global NPPl

104526

17 (8 of total global NPP)

58 (39 of total global NPPl

Vietnam War had widely publiciud effectson the mangrove vegetation of theMekong Delta The use of defoliantchemicals there has had long-term impacuon biodiversity from which the envirshyonment is only just recovering Evenwithout war political systems can imposeadditional stress on the environment Theapartheid system in pre-I994 South Africafor example forcibly distributed popushylation and wealth in a highly unhir wayleading to huge environmental pressureson marginal land The planned socialisteconomies of the fanner Soviet Union andmany East European states appear now tohave had particularly damaging environshymental impacts And capitalist enterprisewhich now dominates the global economy

14 Introduction

has often had a tendency to plunder anddespoil the environment

These many negative environmentalimpacts have generated in response a longshyterm and growing focus on conKrvationand improving human management of meenvironment Conservation and manageshyment themselvcs have environmental imshypacts as in the creation of nature reservesthere may also be less desirable impactswhere management schemes go wrongThe ideas of sustainable development arethe most recent attempt to combine remiddotsource exploitation with conservation anda concern for the environmental futureAs our scientific understanding of how theenvironment works has advanced we havegained a better view of how serious ourhuman impacts can be On the other handwe have also learnt that there is muchreason for hope The environmental fumiddotture is not all doom and gloom as westress in part VII of this book

6 UNDERSfANDING

ENVIRONMENTAL

TRANSFORMATIONS

We have already shown in this chapter thathuman impacts on environmental processeshave had a long and complex historyand now take on many complex and intershylinked forms The environment itself is alsonot a static simple entity but has a comshyplicated history of its own We now reashylize that the environment changes naturallyover a range of different time-scales as aresponse to a number of natural forcingfactors such as the varying position ofthe Earth Iithin its orbit around the sunOn shorter time-spans we know that theenvironment can work in abrupt and chalshylenging ways producing what are callednatural hazards such as volcanic erupshytions earthquakes floods and hurricanesSo putting together human and naturalfactors influencing the environment to

explain any single environmental transforshymation can be a hugely difficult usk It isimportant to realizc that there is still a lotof scientific uncertainty and debate overthe causes and consequences of many ofthe environmental issues we look at in thisbook

Understanding the role of human activmiddotities in environmental transformations isnot a completely hopeless task howeverThere arc several useful concepts whichwe can adopt to help us untangle whatis going on First it is useful to think ofthe environment (of which of course wearc a part) as being a series of interlockedsystems These systems arc affected by awhole series of stresses (which can behuman or natural in origin) The Stressesproduce some changes in the system orresponses these arc what we sec as environmiddotmenw transformations or environmentalissues Because the systems arc interlockedstresses on one system may produce linkedeffecu on other systems Some of the sysshytems arc more able to resist stresses thanothers and so some can be suessed greadybefore they show any response Others arcmore sensitive to stresses

As an example to clarify the ideas preshysented above we could look at a drainshyage basin (or watershed as it is knownin the USA) Drainage basins arc primashyrily hydrological systems with interlinkedvegetation communities Cutting downtrees (a stress) will produce a range ofresponses soil erosion increased floodingand changes in the way water is distributed(hydrological pathways) The severity ofthese outcomes will depend on the climateand topography of the area Normally amixture of natural and human-inducedstresses will affect the environment toshygether complicating the picture One wayof understanding such multi-causal situashytions is to identify different types ofstreSSeSor causal factors A uscful frameworkwhich has blaquon used in various ways inthe foUowing sections of this book is to

split causal faCtors into three typc=S that ispredisposing inciting and contributingfactors Pndisposing factors are those feashyturc=s of the natural or human environshyment which make a system vulnerable tosuess inciting factors are thosc= stressesthat trigger otT a change in the systemand conrributiJg factors are the whokrange of additional strc=sses which makethe rc=sponse more noticeable and acuteLct us apply this frtmc=work to the case ofa drainage basin The predisposing factorswhich may make it vulnerable to changefoUowing tree-cutting would lx the toshypography and climate and pcrhaps alsopast forest management pnctices Theinciting factor would lx the tete-euningitself The contributing factors could bethe health of the trees the sc=ason whenthe trees were felled the weather at thetime and over a longer time-span whatvegetation grows in place of the trees

FURTHER READING

Environmental Transformations IS

The concepts of stressc=s raponses anddifferent types of causal poundactors are veryuseful in trying to understand how humiddotmans are influencing thdr environmentSuch understanding is vital in any attemptsto solve or manage the resultant environshymental problems However to arrive atsolutions it is also necessary to have adeeper understanding of the human socishyeties involed in such environmental isshysuc=s as many of our subsequent examplesillustrate For example just knowing howtree-cutting can produce soil erosion andhydrological changes within a drainagebasin does not mean that we can solve theproblem We need also to know why peoshyple arc cutting down the trees Before wecan effect any great changes we need moreunderstanding of the economic conditionstechnological capability cultural organizashytion and political systems of the peopleinvolved

Freedman B 1995 Environmenral Ecowgy 2nd edn San Diego Academic Prc=ssAn enormously impressive and wide-ranging study with a strong ecological emphasis

Mannion A M 1995 Agriculture and Enpironmental Change London WikyA new and comprehensive study of the important rok that agriculture plays in landtransformation

Meyer W B 1996 Human Impact on the Earth Cambridge Cambridge UniversityPressA good point of entry to the literature that brims over with thought-provoking epigrams

Middleton N J 1995 The Gwbal Quino London EdWdrd ArnoldAn introductory text by a geographer which is wdl iIIustrated and clearly wrinen

Ponting c 1991 A Gnen History of the World London PenguinAn engaging and informative treatment of how humans have transformed the earththrough time

Simmons I G 1996 Changing the FRee of the EArth Cultl4re Environment andHistory 2nd edn Oxford BlackwellA characteristiCally amusing and perceptive review of many faceu of the tole ofhumansin transforming the earth from an essentially historical perspective

16 Introduction

KEy TERMS AND CONCEPTS

agricultural revolutionbiosphereglobal environmental changeHolocenehunter-gatherer

POINTS FOR REVIEW

industrial revolutionpredisposing inciting and contributing

factorsstresses and responsessystems

How much environmental change was achieved in prehistoric times and how much inthe last three centuries

To what extent are environmental changes the result of both natural and humanshyinduced stresses

What do you understand by the phrases global environmental change andsustainability

PART II

The Biosphere1 Introduction 19

2 Fire 20bull The YeDowsrone fires of 1988 24

3 Desertifiallion 26bull Desertification in north centr1l China 30

4 Oeforestuion 32bull Managing tropical rain forest in Cameroon 36

5 Tropical Secondary Forest Fonnacon 386 Grasslands and Heathlands The Human Role 39

bull Recent human impacts on subalpine grasslandand heathland in Victoria Australia 43

7 Temperate Forests under Stress 44bull Forest decline in Bavaria Germany 47

8 Urban Ecology 48bull Chicagos dunging vegetation 51

9 Wetlands The Kidneys ofme undsclpe 53bull Wetlands management in the Niger

Inland Delt 5710 Biodivmity and Extinctions 58

bull Pandas plants and parks conservingbiodiversity in China 62

The Biosphere11 Introductions Invasions and Explosions 64

bull Alien plant species invading KakaduNational Park Australia 68

12 Habitat Loss and Fragmentation 69bull Texas Gulfcoast habitat chages and the

Lesser Snow Goose 7213 Extinctions in the Past 7314 Biotechnology Genetic Engineering

and the Environment 7615 Conclusions 77

Key Tenns and Concepts 78Points for Review 79

1 INTRODUCTION

In this part of the book we look at someof the main ways in which humans havemodified the biosphere and the conseshyquenccs of these impacts

Humans have changed the biosphere invery many ways with wide-ranging andlong-lasting effects As soon as peoplediscovered how to use fire at a very earlystage in human development they obshytained tremendous power to modify thevegetalion cover of the Earths surfaceAlso during the Stone Age humans gradushyally developed the technology to enablethem to bccome ever more effecrive huntshyers Early people may have contributed tothe extinction ofsome of the worlds greatmammals Since the Mesolithic as passhytonlism and agriculture have becomewidespread modification of habitat hascontinued rapidly Humans also gainedthe ability to manipulate the genetic comshyposition of plants and animals - a majorpart of the process generally called domcs-

Introduction 19

ticarion This has been one of the mostdirect ways that humans have changed thebiosphere

As the human population of the Earthhas expanded in numbers and spread tomore and more parts of thc globe Ccrmore environments havc been modifiedThese include tundra anas deserts forshyests and wetlands The total area ofsurviving natural habitat has stcadil dimiddotminished and wilderness arcas are 110W

relatively few Figure 111 shows an attemptto mark out the areas of the planet thatcan still bc defined as wilderness Howshyever no part of the Earths surtacc call beconsidered entirely free from the imprintof human activities Air pollution and clishymatic changes causcd by human action arcevident even at the poles As it has beshycome easier for humans to move from oneplace to another so plants and animalshave been introduced to many new areasSometimcs the numbers ofthcsc= newcomerspecies have exploded damaging the comshymunity struetu~ of existing plants andanimals

bull

bullbulleJC1)-

~ )

Figure 111 Global wilderness remaining in the 1980sSource McCloskey and Spalding (1989)

20 The Biosphere

Table 111 Biomass burning in the tropical regions

Region Forest Savanna Fuel Agricultural Regional Regionalwood waste total total

(Tg dmlyr) (Tg dmlyr) (Tg dmlyr) (Tg dmlyr) (Tg dmlyr) (Tg Oyr)

America 590 770 170 200 1730 780Africa 390 2430 240 160 3210 1450Asia 280 70 850 990 2190 980Oceania - 420 8 17 450 200

Total tropics 1260 3690 1260 1360 7580 3410

Tg dmlyr = teragrammes of dry matter per yearTg elyr = teragrammes of carbon per yearSource Andreae (1991) table 13

2 FIRE

Fire is one of the earliest means that hushymans used to modifY the natural environshyment It is also one of the most powerfulFires do of course occur naturally andhave done so during the entire history ofme Earth For example they arc causedby volcanic eruptions by spontaneouscombustion oforganic materials by sparksfrom falling boulders and above all bylightning which on average strikes me landsurface of the globe 100000 times eachday However in some environments megreat majority of fires arc now caused byhumans either deliberately or accidentally

There arc many good reasons why hushymans from our early Stone Age ancestorsonwards have found fire useful

bull to clear forest for agriculturebull to improve the quality of grazing for

game or domestic animalsbull to deprive game of cover or to drive

them from coverbull to kHi or drive away predatory ani-

mals insects and other pestsbull to repcl or attack human enemiesbull to make travel quicker and easierbull to provide light and heatbull to enable them to cook

bull to transmit messages by smoke signsbull to break up stone for making tools or

pottery smelting ores and hardeningspears or arrowheads

bull to make charcoalbull to protect settlements or camps from

larger fires by controlled bumingbull to provide spectacle and comfort

Fire has been central to the life of manygroups ofhunter-gatherers pastoralists andfarmers (including shifting cultivators inthe tropics) It was much used by peoplesas different from one another as the Aborishyginals of Australia the cattle-keepers ofAfrica the original inhabitants of TIerradel Fuego (the land of fire) in the farsouth ofSouth America and the Polynesianinhabitants of New Zealand It is still muchused especially in the tropics and aboveall in Africa Biomass burning appears tobe especially significant in the tropicalenvironments of Africa in comparisonwith other tropical areas (table 111) Themain reason for this is the great extentof savanna which is subjected to regularburning As much as 75 per cent of Afrishycan savanna areas may be burned each year(Andreae 1991) This is probably an anshycient phenomenon in the African landscapewhich occurred long before people arrived

on the scene Nevenhelcss humans havegready increaKd the role of fire in thecontinent where they may have uKd it forover 14 million years (Gowlen et al 1981)

Naturally occurring fires break out withvarying frequency in different global en~

vironments Over a century may passbetween one firc and the next in tundraenvironments and ecosystems dominatedby thc spruce uec In areJs ofsavanna andMcditerranean shrubland on the otherhand the interval may be only five to

fifteen years and in semi-arid grasslandsless than five years

Fira can extend over huge areas In1963 in Parana Brazil no less than 2million hectares of forest were consumedin JUSt three weeks while the fire of 1987in China and the neighbouring SovietUnion destroyed around 5 million hecshytares over the same length of time

Fires can also cause some very highground surnce ttmperarures up to 800Cor higher The temperature reached deshypends very much on the size duration andintensity of the fire Some fires are relashytivdy quick and cool-burning and onlydestroy ground vegetation Other firessuch as crown fires affect whole forestsup to the Icvd of tree crowns and gcncrshyate very high temperatures In generalforest fires arc hotter than grassland firesIt is significant for forest management thatwhcre fires occur very often they do notattain the highest temperatures becausethcre is not enough flammable material tokeep them going However humans oftendeliberately prevent fires as part of normalpolicy in forest areas When this is donclargc quantities of flammable materialsaccumulate so that when a fire docs breuOut it is of the hot crown type that canbe ecologically disastrous There is nowmuch debate therefore about the wisdomof suppressing the fircs that in many forshyests would occur quite regularly under soshycalled natural conditions

fire 21

Recent studies have indicated that rigidpolicies of protecting habitats against firehave often had undesirable results Conseshyquendy many foresters now suess the needfor prescribed burning or environmenshytal restoration burning For example inthe coniferous forests of the middle andupper levds of the Sierra Nevada mounshytains of California protection from firesince 1890 has made the srands densershadier and less park-like and Slquoiaseedlings hae decreased in llumber as aresuh Ukeise at lower leels the charshyacter of [he semi-arid shrubland calledchaparrll has changed The lgetationhas bt-come denser the amount of flamshymable material has increased and fireshysensitive species have encroached Thevegetation has become less diverse witholder trees predominating instead of amosaic of trees at different stages ofgrowth In the Kruger National Park inSouth Africa fires have become less freshyqucnt since the game reserve was estabshylished when local hunters and farmerswere moved out AJ a rcsult bush hasencroached on areas that werc formerlygrassland and the carrying capacity forgrazing animals has declined Controlledburning has been reinstituted as a necesshysary element of game management

Fire has many positive ecological conseshyquences Fire may assist in seed germinashytion For example many investigatorshave reported the abundant germinationof dormant seeds on recently burnedchaparral in areas like California with aMediterranean climate and it Kerns thatsome Keds of chaparral species requirescarification by fire to germinate effecshytively Fire alters seedbeds and even thoseKeds not requiring scarification maygerminate better after a fire because fireremoves competing seeds litter and somesubstances in the soils which are toxic toplants If substantial amounts of litter andhumus arc removed large areas of rich

22 The Biosphere

ash bare soil or thin humus may becreated Some trees such as the Douglasfir and the giant sequoia benefit fromsuch seedbeds Fire sometimes triggers therelease of seeds from cones (as with Jackpine Pinus banlujana) and seems to stimushylate the vegetative reproduction of manywoody and herbaceous species Fire cancontrol forest insects parasites and fungi- a process termed sanitization - andseems to stimulate the flowering and fruitshying of many shrubs and herbs It alsoappears to modifY the physiochemical enshyvironment of plants with mineral elementsbeing released both as ash and throughfaster decomposition of organic layersAbove all areas subject [0 fire often showgreater species diversity which tends tofavour the Hability of the habitat over thelong term

Fire is also crucial to an unders[andingof some major biome types and manybiota have become adapted to it Forexample many savanna trees are fireshyresistant The same applies to the shrubvegetation (mafuis) of the Mediterraneanlands which contains certain species (egQuercus io and Quercus cocciera) whichthrive after burning by sending up a seriesof suckers from ground level Mid-latitudegrasslands (eg the prairies of NorthAmerica) were once thought to have deshyveloped in response to drought conditionsduring much of the year Now howeversome have argued that this is not necesshysarily the case and that in the absence offire trees could become dominant Thefollowing reasons are given to support thissuggestion

bull planted groves and protected trees seemable to flourish

bull some woodland species notably junishypers are remarkably drought-resistant

bull trees grow along escarpments and indeep valleys where moisture is conshycentrated at seeps and in shaded areas

and where fire is least effective theeffects of fire are greatest on flat plainswhere there are high wind speeds andno interruptions to the course of thefire

bull where fires have been restricted woodshyland has spread into grassland

Fire rapidly alters the amount formand distribution of plant nutrients in ecoshysystems and has been used deliberatelyto change the properties of the soil Boththe release of nutrients by fire and thevalue of ash have long been recognizednotably by those involved in shifting culshytivation based on slash-and-burn techshyniques However once land has beencultivated the loss of nutrients by lcachshying and erosion is very rapid This is whythe shifting cultivators have to move onto new plots after only a few years Firequickly releases some nutrients from thesoil in a form that plants can absorbThe normal biological decay of plant reshymains releases nutrients more slowly Theamounts of phosphorus (P) magnesium(Mg) potassium (K) and calcium (Ca)released by burning forest and scrubvegetation are high in relation to both thetotal and the available quantities of theseelements in soils

In forests burning often causes the pHvalue of the soil to rise by three units ormore creating alkaline conditions whereformerly there was acidity Burning alsoleads to some direct loss of nutrients fromthe soil by volatilization and by causingash to rise up into the air or by loss ofashto water erosion or wind deflation Wherefire removes trees soil temperatures inshycrease because of the absence of shade sothat humus is often lost at a faster ratethan it is formed

Concern is now being expressed aboutthe role of biomass burning in alteringatmospheric chemistry and contributingto the greenhouse effect by adding carbon

dioxid( (COl) to m( aunosph(r( (Levin(1991) About 40 per c(nt of m( worldsannual production ofCOJ may r(Sult from

FURTHER READING

Fire 23

th( destruction of biomass by fir( Firesalso produc( (missions ofsmok~ and nitricoxide

Crutzen P and Goldammer G 1993 Fire in the Environment Chicheu(rWileyThis book considers some of th( potential global dfects of fir~s including effects onatmospheric chemistry

Kozlowski T T and Ahlgren C C (eds) 1974 Fire 1 aosyrtems New YortAcademic PressAlthough relatively old this provides a very useful picture of the effects of fir~ on faunaand flora

Pyn~ S 1982 Fire in America A Cwlrural HiJrory of Wildnd and Rwral FinPrinceton Princ(ton Univ(rsity PressA massive and scholarly survey of how fires hav( been fundamental to und(rstandingmuch of the veg(tation of America

Plate 111 Forest burnt in the Yellowstone fires of 1988 (EPLRob Franklin)

u INO

I MONTANA OAKOTA

f-tN I

~i----IDAHO f r IIMWIJe1J SOVln

I OAKOTA-- I---- WYOMING ---___

L _ NtRIlASKAT-----___ LlJrAll I --I COLORAOO J

I 0 kl 2laquolI ~

24 The~iosphert

The Yellowstone fires of 1988

In the summer of 1988 wideshyspread fires ravaged the Yellowshystone National Park in theAmerican West Forest fires beshygan in June and did not die outcompletdy until the onset ofwinter in November Somcwherebetlcen 290000 alld 570000hectares burned in by tar theworst fire sinc Yellowstone wasestablished as the worlds firstnational park in the 1870s

Was this inferno the result of apolicy of fire suppression Without suh a policy the torest would burn at intershyvals of 10 or 20 years because of lightning strikes Could it be that the suppresshysion of fires over long periods of say 100 years or more allegedly to protect andpreserve the lorest led to the build-up of abnormal amounts of combustible fuelin the torm of trees and shrubs in the understory~ Should a programme ofprescribed burning be carried out to reduce the amount of available fueH

Fire suppression policies at Yellowstone did indeed lead to a critical build-upin flammable material However other factors must also be examined in explainingthe severity of the fire One of these was the fact that the last comparable firehad been in the 1700s so that the Yellowstone forests had had nearly 300 yearsin which to become increasingly flammable In other words because of the wayvegetation develops through time (a process called succession) very large firesmay occur every 200-300 years as part of the natural order of things (figureII2) Another crucial factor was that weather conditions in the summer of 1988were abnormally dry bringing a great danger of fire

Rommc and Despain (1989 p 28) remark in conclusion to their study of theYellowstone fires

It seems that unusually dry hot and windy weather conditions in July andAugust of 1988 coincided with multiple ignitions in a forest that was at itsmost flammable stage of succession Yet it is unlikely that past suppressionefforts were a major factor in exacerbating the Yellowstone fire If fires occurnaturally at intervals ranging from 200 (0 400 years then 30 or 40 years ofeffective suppression is simply not enough for excessive quantities of fuel tobuild up Major attempts at suppression in Yellowstone forests may have merelydelayed the inevi(able

Further reading

Remme W H and Despain D G 1989 The Yellowstone fires ScientifteAmerican 261 21-9

Fire 25

The old fomt

~i t~rfti (

---

Figure 112 EcotogicaJ succession in response to fire in Yellowstone NationalParle USASource After Romme and Despain (1989) pp 24-5

26 The Biosphere

3 DESERTIFICATION

The term desertification was first used bythe French forester Aubreville in 1949 buthe never formally defined it Since thenover 100 definitions have been publishedThe United Nations Environment Proshygramme (UNEP) has recently defineddesertification as land degradation in aridsemimiddotarid and dry sub-humid areas resultshying mainly from adverse human impacts(Tolba and EI-Kholy 1992 p 134) Othershowever suggest that climatic change mayalso play an important role

There are fundamental problems relatshying to how extensive the problem ofdesertification is how quickly it is takingplace and what the main causes are UNEP(Tolba and EI-Kholy 1992 p 134) hasno doubts about the significance of theproblem Desertification is the main envirshyonmental problem of arid lands whichoccupy more than 40 per cent of the totalglobal land area At present desertificationthreatens about 36 billion hectares shy70 of potentially productive drylands ornearly one-quarter of the total land areaof the world These figures exclude naturalhyper-arid deserts About one sixth of theworlds population is affected

UNEP recognizes the following seriesof symptoms of desertification that relateto a fall in the biological and economicproductivity and therefore value of a pieceof land

bull reductlon of crop yields (or completefailure of crops) in irrigated or rain-fedfarmland

bull reduction of biomass produced byrangeland and consequent depletionof feed material available to livestock

bull reduction of available wood biomassand consequent increase in the disshytances travelled to obtain fuelwood

bull reduction of available water due to

decreases in river flow or groundwaterresources

bull encroachment of sand bodies (dunessheets) that may overwhelm producshytive land settlements or infrastructures

bull social disruption due to deteriorationof life support systems and the associshyated need for outside help (relief aid)or for havens elsewhere producingenvironmental refugees

It is however by no means clear howextensive desertification is or how fast it isproceeding In a recent book called Desertshyification Exploding the Myth Thomas andMiddleton (1994) have discussed UNEPsviews on the amount of land that isdesertified They state

The bases for such data are at bestinaccurate and at worst centered onnothing better than guesswork Theadvancing desert concept may have beenuseful as a publicity tool but it is notone that represents the real nature ofdesertification processes (Thomas andMiddleton 1994 p 160)

There are indeed relatively few reliablestudies of the rate of desert advance orencroachment Lamprey (1975) attemptedto measure the shift of vegetation zonesin the Sudan and concluded that the Saharahad advanced by 90-100 km between1958 and 1975 an average rate of about55 km per year However on the basisof data amassed by remote sensors andground observation Helldcn (1984) foundlittle evidence that this had in fact hapshypened One problem is that biomass proshyduction may vary very substantially fromyear to year This has been revealed bysatellite observations of green biomassproduction levels on the southern side ofthe Sahara

The way in which desert-like conditionsspread is also [he subject of some controshyversy Contrary to popular rumour this

D~rtification 27

ADVANCE Of DtSmTflpoundATlOS OFDfS(RT-UKf CO~I)Jl1OIiS

lniptioa

Figure 113 The causes and development of desertificationSource Kemp (1994) figure 312

does not happen over a broad front likea wave overwhelming a beach Rather itis like a rash tending to appear in localpatches around settlements This distincshytion is important because it influences pershyceptions of how to tickle lhe problem

Another point made by Thomas andMiddleton (1994 p 160) is that drylandsmay be less fragile than is often thought

We should bear this controVersy in mindas we consider some of the undoubtedpressures that are being placed on aridenvironments (figure 113) It is gefKrallyagreed that the massive increase in humanpopulation numbers during the twentieth

century has been of fundamental imporshytance This demographic explosion has hadfour key consequences for dryland areasovercultivation overgrazing deforestationand salinization of irrigation systems

There arc two aspects ofovercuhivationmore intensive usc of land already undercultivation and the inuoduetion of agrishyculture into areas where conditions arc notsuitable to it primarily because of theiraridity or because their soils are fragile andinfertile Crops are now grown in areas ofthe Sahel of West Africa where annualrainhll is as low as 250 mm and in partsof the Near East and Nonh Africa which

28 The Biosph~re

SOUTIlERNKORDOFAN

bull 00~

Figure 114 The expanding wood andcharcoal exploitation zone south ofKhartoum SudanSource From Johnson and Lewis (1995)figure 62

have only 150 mm of rainfall a year Someof these areas hav~ friable soils d~vdopcdon lat~ Pleistocme dun~ fidds This makesth~m highly prone to water ~rosion andwind reactivation

Ov~rgrazing is rclat~d to ov~rcultivashy

tion for in many ar~as increasing numbersof humans r~quire incrusing numbers ofdomestic animals Larger tr~e-ralging stockherds r~duc~ th~ amount of pasturdandavailable and mean that the pastures thatremain have to support even mor~ animalsTh~ carrying capacity of the land may thenbe exceeded Thcr~ may also be conflictsbetw~~n pastoralists and cultivators Asthe fronti~r of cultivation is pushed outshywards into ever mor~ marginal ar~as itencroaches more and mort on th~ grazshying lands of the pastoralists In this waynomadic pastoralists many of whom haddeveloped sophisticated ways of keepingmarginal areas in productive use have oftenKen their traditional systems disintegrateThis has disrupted the equilibrium betweenpeople and land For nampie the nomads

Kasonal or annual migrations may havebc~n resuict~d by delibcrat~ policies ofscd~ntarization (making peopl~ setde inone place) imposed by central governshyments The same restrictive eff~ct resuJtsfrom th~ est2blishm~nt of national boundshyaries wh~re non~ previously existed

Another cause of overgrning has beenthe installation of boreholes and the digshyging out of wat~rholes These have mademor~ water available for domestic animalswhich thus rapidly increase in number Thisin turn leads to overgrazing Vegetationin ~fTect r~places water as the main factorlimiting stock numbers

The third human cause ofdesertificationis d~forestation and the removal of woodymaterial Many pwpl~ depend on woodfor domestic uses (cooking heating brickmanufacture ~tc) and th~ ccUection ofwood for charcoal and firewood is anespecially serious probl~m in the vicinityof urban c~ntres This is illustrated forKhartoum in Sudan in figure 114Th~ fourth prim~ cause ofdesertification

is salinization This kiUs plants destroysth~ soil struetur~ and reduces plant growthSalinization oft~n occurs where irrigationis introduc~d without making proper proshyvision for drainag~ It can howev~r alsobe an unwant~d consequ~nce of v~getamiddot

tion cl~arance Th~ r~moval of plantsr~duc~s the amount of moistur~ lost fromthe soil as a result of int~rccption of rainshyfall by leav~s and evapotranspiration Asa result groundwater levels rise and salin~

water is allowed to seep into lowmiddot lyingareas like valley bottoms This is a seriouscause of salinization both in the prairies ofNorth Am~rica and in the wheat belt ofW~st~rn Australia It is so important thatwe tr~at it in a separate section (part Ysection 5 below)

As we saw ~arli~r som~ obKrv~rs hav~

suggested that a naturaJ d~terioration inth~ climate may contribut~ to the damshyage don~ to drytand and the spread of

desen-like conditions When we examinerainfall data for recent deades we see thatfor some arid areas there is relatively clearevidence fur a downward trend while inother areas rainfall appears to be stable orto be increasing A downward trend hasbeen established for the Sudan and Sahelzones of Mrica This has had a range ofconsequences including a subslantial risein dust-storm activity and a severe reducshytion in thc area and watcr volumc of LakcChad By COntrast the latest analyscs ofsummer monsoon rainfall for the RajasthanDescrt in India show a modest upwardtrend between 1901 and 1982 Data fornorth-cast Brazil much of Australia andCalifornia and Arizona in the USA showno dear trend in either direction

Attempts to reduce damage to drylandcan be dividcd into twO types (1) technoshylogical methods and (2) fundamentalchanges in societies economies and polishytics For exampic a nnge of technologicalsolutions is available to control blowingsand and mobile dunes (see part V secshytion 3) It is much more difficult howshyever to make changes in the humanconditions that are the real rOOt causes ofthe problcm Population growth povertypolitical instability poor planning theattitudes of urban clites and the prevenshytion of traditional nomadic migration areamong the long-term basic issues thatneed to be addressed

FURTHER READING

Desertification 29

Land degradation is not however aninevitable result of rapidly growing humanpopulations Excellent proof of this isprovided by TifTen et als (1994) study ofthe semi-arid Machakos District in KenyaAround sixty years ago this area hadsevere fumine problems and was sufferingfrom sevcTe land degradation and soil eroshysion Photographs from the 1930s show agullied and impoverished landscape Sincethat time the population of the districthas increased more than fivefold but theenvironmcnt is now in a vcry much bcltcrcondition than it was then Slope terracshying has reduced the extent and rltc ofsoilerosion and gully formation A fuclwoodcrisis has been averted by planting a largenumba of farmed and protected trees Inaddition agricultural output has increasedTiffen e( al argue that high rates of popushylarion growth can be combined with susshytainable environmental management InMachakos District the local Akamba peoshyple have proved very adaptable Labouris plentiful and they have invested bothlabour and capital in land improvementand development They have added to theiragricultural incomes by doing much morenon-furm work and the huge growth inthe output of non-subsistence prodUCTS hasled to a development of jobs and skillsin marketing and processing In shorthumans can manage the landscape to goodeffect even when their numbers increase

Goudie A S (ed) 1990 Techniques for Desert Rulmarion Chichester WileyThis edited work looks at some of the solutions that arc available for dealing with theproblems of d~rt environments

Graingtt A) 1990 TJIt TbrtRuning DtJnt Controlling DesertifURtjon LondonEanhscanA very readable and wide-rIDging review of desertification

Middleton N J 1991 DeserrifitlltU1fl Oxford Oxford University PressA weU-illustrated simple introduction designed for usc in secondary eduation

30 The Bi06phere

Desertification in north central China

--

OIlNA

~

WuboII

Deserts and desertified lands coversome 149 million sq km of Chinaamounting to approximately 155per cent of the total land area of thecountry There are 12 named desertswithin China and it is estimated that 35W

various human and natural forces are ri-J------~

combining to produce desertificationof some 1560 sq km per yeararound these deserts (see table 112)Three main types of desertificationarc found in China the spread ofdesert-like conditions on sandy steppe reactivation of vegetated dunes (sandylands) and encroachment of mobile dunes on to settlements and farmland Studshyies within China suggest that such desertification is a blistering process ie thatit occurs in blister-like localized patches of rangeland away from the desert marginThese blisters then gradually grow and coalesce to produce large patches ofdescrtified land According to Fullen and Mitchell (1994) Chinese desertification

Plate 112 Encroaching sand dunes on the edge of the Gobi DesertDunghuang China The dunes are invading fields and many methods arebeing used to try to stabilize them (TripJ Batten)

Daertification 31

Table 112 Types causes and extent of desertlfted lands In China

Causes Area affected(sq km)

Overcultivation on steppe 44700Overgrazing on steppe 49900Overcollection of fuetwood 56000Misuse of water resources 14700Encroachment of dunes 9400

Source Adapted from Fullen and Mitchell (1994)

of totaldesertified land

252833188355

is mainly a result of land mismanagement encouraged by climatic factors whichproduce droughts and encourage sand movements

The severity of desertification and land degradation in China has prompted theInstitute of [kscrt Research of Academia Sinica (IDRAS) to set up research intocombating desertification IDRAS has nine research stations in desertified areasat which various reclamation techniques are practised At the Shapotou ResearchStation in Ningxia Autonomous ~gion established in 1957 to discover methodsof protecting a major railway line from sand movements the following techshyniques have been used

bull planting windbreaks of pines poplars and willows parallel to the railway linebull levelling dunes with bulldozersbull installing drip irrigation systems to aid topsoil development on levdled dune

sandsbull constructing straw checkerboards to stabilize surfaces and (ncourag( plants to

grow on shifting dunes to help stabilize them this produces an artificialecosystem on the dllOes increasing vegetltioll cover from less than 5 per cenl10 between 30 pc=r cent and 50 per cent and stopping dune movement

Irrigation land enclosure and chemical treatments arc also being lIs(d in this ar(ato help turn descrtified lands into productive rangdands According to r(c(ntstudies such reclamation efforts must be maintained and monitof(d over at kastsix y(ars b1=forc significant improv(ments can be seen

Further reading

Fullen M A and Mitchell D 1994 Desertification and reclamation in northcentrl1 China Ambjo 23 131-5

32 The Biosphere

4 DEFORESTATION

Clearing middotforests is probably the mostobvious way in which humans have transshyformed the face of the Earth It was theprime concern of George Perkins Marshwhen he wrote his pioneering book callshying for the conservation of nature Manatld Nature in 1864 (see part IV section3) Forests provide wood for construcshytion for shelter and for making toolsThey are also a source of fuel and whencleared provide land for fOCK productionFor all these reasons they have been usedby humans sometimes to the point ofdestruction

Forests however are more than aneconomic resource They play severnl keyecological roles They arc repositories ofbiodiversity (see section 10 below) theymay affect regional and local climates andair quality they playa major role in thehydrological cycle they influence soil qualshyity and rates of soil formation and preshyvent or slow down soil erosion

We do not have a dear view of how fastdeforestation is taking place This is partlybecause we have no record on a globalscale of how much woodland there is toshyday or how much there was in the pastIt is also because there are disagreementsabout the precise meaning of the worddeforestation For example shifting culshytivators and loggers in the tropics oftenleave a certain proportion of forest rnesstanding At what point does the proshyportion of trees left standing permit oneto say that deforestation has taken placdAlso in some coumries (eg India) scrubis included as forest while in others it isnot

What we do know is that deforestationhas been going on for a very long timePollen analysis shows that it started inprehistoric times in the Mesolithic (around9000 years ago) and Neolithic (around5000 years ago) urge traCts of Britain

had been deforested before the Romansarrived in the islands in the first centuryBC Classical writers refer to the effectsof fire cutting and the destructive nibbleof goats in Mediterranean lands ThePhoenicians were exporting cedars fromLebanon to the Pharoahs and to Mesopomiddottamia as early as 4600 years ago A greatwave of deforestation occurred in westernand central Europe in medieval times Asthe European empires established themshyselves from the sixteenth and seventeenthcenturies onwards the activities of tradersand colonists caused forests to contract inNorth America Australia New Zealandand South Africa especially in the nineshyteenth century Temperate North Americawhich was wooded from the Atlantic coastas far west as the Mississippi River whenthe first Europeans arrived lost morewoodland in the following 200 years thanEurope had in the previous 2000 At thepresent time the humid tropics arc undershygoing particularly rapid deforestationSome areas are under particularly seriousthreat including South-East Asia WestMrica Central America Madagascar andeastern Amazonia (figure II5)

The effects of deforestation can be seenespecially vividly in the Mediterraneanlands of the Old World As Ponting (1991p 75) puts it

Modern visitors regard the landscapeof olive trees vines low bushes andstrongly scented herbs as one of themain attractions of the region It ishowever the result of massive environshymental degradation brought about notby the creation of an artificial systemsuch as irrigation but by the relentlesspressure of longmiddotterm settlement andgrowing population The natural vegshyetation of the Mediterranean area wasa mixed evergreen and deciduous forshyest of oaks beech pines and cedarsThis forest was cleared bit by bit fora variety of reasons - to provide land

Deforestation 33

Figure 115 Estimated annual forest change rates 1981-1990Source World Resources Institute (1994) figure 71

for agriculture fuel for cooking andheating and construction materials forhouses and ships

Other processes linked to humans inshycluding grazing and fire have preventedforest from returning over wide areas Inplace of forcst a kind of vegetation calledmalfuis has become widesprcad This conshysists of a stand of xerophilous evergrecnbushes and shrubs whose foliage is thickand whose trunks arc normally obscuredby low-level branches It includes suchplants as holly oak (~ercu iJex) kermesoak (QuercllS coccim) tree heath (Ericaarbona) broom heath (Erica coparill) andstrawberry trees (Arbutus unedo) There isconsidenble evidence that malfuu vegetashytion is in part adapted to and in part aresponse to fire One efTeet of fire is toreduce the numbers of standard trees andto favour species which after burningsend up suckttS from ground level BothQJlercUI ita and Q1Iercus cocciera seemto respond to fire in this way A numberof species (for example Cistus albidllS

Erica arbona Pinu hlllepenJis) seem to

be encouraged by fire This may bc bccallS(it suppresses competing plants or perhapsbecause a short burst of heat encouragesgermination We have already noted thishappening in the chaparral of the southshywc=st USA an environment similar tomaluis (sce section 2 above)

Sinee premiddot agricultural times approxishymately one-fifth of the worlds forests havebeen lost The highest losses (about a thirdof the toul) have been in tcmperatc areasHowever deforestation is nO( an unstoppshyable or irreversible proceSS For examplea rebirth of forest has taken place in theUSA since the 19305 and 19405 Manyforests in developed countric=s are sJowlybut steadily expanding as marginal agrimiddotcultural land is abandoned This is hapshypening both ~causc of replanting schemesand because of fire suppression and conshytrol (see section 2 above) Also in somecases the extent and consequences ofdeforestation may have ~en exaggeratedA classic example of this is provided bythe mountains of parts of Nepal It was

34 The Biosphere

generally believed that rapid deforestationand changes in land use here had contrishybuted to higher flood runoffs floods soilerosion and increases in river sedimentloads The effects were thought to extendas far as the Ganges Delta in BangladeshA detailed study by Ives and Messerli(1989) however has cast doubt on thisargument by showing that little reductionin forest cover has taken place in theMiddle Mountains of Nepal since the1930

Many of the phenomena noted inNepal - flood runoffs soil erosion etc shymay be natural and inevitable consequencesof the presence of steep mountains rapiduplift by tectonic forces and monsoonalstorms Nonetheless the loss of moist rainforests in some of the worlds humid tropishycal regions is a very major concern Theconsequences are many and serious (tableII3) The causes are also diverse and inshyclude encroaching cultivation and pastorshyalism (including cattle ranching) miningand hydroelectric schemes as well as logshyging operations themselves

Views vary as to the present ratc of rainshyforest removal Recent FAO estimates(Lanly et aI 1991) put the total annualdeforestation in 1990 for 62 countries(representing some 78 per cem of thetropical forest area of the world) at 168million henares This figure is significandyhigher than the one obtained for thesesame countries for the period 1976-80(92 million hectares per year) Myers(1992) suggests that there has been an 89per cent increase in the tropical deforestashytion rate during the 1980s This contrastswith an FAQ estimate of a 59 per centincrease Myers believes that the annualrate of loss in 1991 amounted to about2 per cent of the total forest expanse

Plainly therefore rain forests whichMyers (1990) describes as these mostexuberant expressions of nature are underthreat A very significant proportion of

them will disappear in the next few decshyades unless some form of action is takento prevent this

Possible solutions to the tropical deforesshytation problem are as follows

bull research training and education to givepeople a better understanding of howforests work and why they arc imporshytant and to change public opinion sothat more people appreciate the usesand potential of forests

bull land reform to teduce the mountingpressures on landless peasants causedby inequalities in land ownership

bull conservation of natural ecosystems bysetting aside areas of rain forest asNational Parks or nature reserves

bull restoration and reforestation ofdamagedforests

bull sustainable development namely develshyopment which while protecting thehabitat allows a type and level of ecoshynomic activity that can be sustained intothe future with minimum damage topeople or forest (eg selective loggingrather than clear felling promotion ofnon-tree forest ptoducts small-scalefarming in plots within the forest)

bull control of the timber trade (eg by imshyposing heavy taxes on imported tropishycal forest products and outlawing thesale of tropical hardwoods from nooshysustainable sources)

bull rdebt-ormiddotnature swaps whereby debtshyridden tropical countries set a monshyetary value on their ecological capitalassets (in this case forests) and Iitetallytrade them for their internationalfinancial debt

bull involvement oflocal peoples in managingand developing the remaining rainforests

bull careful control of international aid anddevelopment funds to make sure theydo not inadvertently lead to forestdestruction

Deforestation 3S

Table 113 The consequences of tropical deforestation

Type of change

Reduced biological diversity

Changes in local andregiooal environments

Changes in global environments

Source Grainger (1992)

Examples

Species extinctionsReduced capacity to breed improved crop

varietiesInability to make some plants economic

cropsThreat to production of minor forest

products

More soil degradationChanges in water flows from catchmentsChanges in buffering of water flows by

wetland forestsIncreased sedimentation of rivers reservoirs

etcPossible changes in rainfall characteristics

Reduction in carbon stored in the terrestrialbiota

Increase in carbon dioxide content ofatmosphere

Changes in global temperature and rainfallpatterns through greenhouse effects

Other changes in global dimate due tochanges in land suriace processes

Thc situation is complex but it is alsourgcnt No simplc or singlc solution willbe adcquatc The time-bomb of ecologi-

FURTHBR READING

cal environmental climatic and humandamage caused by dcforestation continuesto tick (Park 1992 p 162)

Aiken S R and Leigh C R 1992 Vanishing Rainorens Their poundCologieRI Trlmsitionin Mallllysia Oxford Oxford University PressA case study from a threatened area

Gl2inger A 1992 Controlling Tropical DeforntatUm London EuthsanAn up-to-date introduction with a global perspective

Park C C 1992 Tropical Rainforuu London RoudedgeAnother relatively simple introduction to many aspccts of the rainmiddotforest environment

Williams M 1989 Americans anti their Fortm Cambridge Cmibridge UniversityPressA very fuU and scholarly discussion of the historical geography of American fomts

36 The Biosphere

n~anaging tropical rain forest In Cameroon

Cameroon in West Atiica is only 1ft

the 23rd largest country on the JhN

I continent but it contains the fitth r---------if---A---~I highest number of mammal md I p]lllt species as well as populations Loges

I of oer 40 globally thleUllled ani- ~I I 1 amp1 mals (Alpert 1993) It is pan of an f J ~+ (

illllJOrtant hlartland ofdiwrsit (on- -_ lllgt1 c~ II bull VIOImdP taining many endemic species III the

lowland forests of Clmeroon and - -somh-east Nigeria there aft oer8000 endemic plant spedcs as wdlas endemic animals such as theCameroon woolly bat (KfrivollfalUIscilla) Jnd pygmy squirrel(My(scillrtS pumifju) Lowland evergreen tropical loresr covers 34 per cenr ofrhecountry Sixty per cent of this total is classed as degraded and 4 per cent asprotected According to Stlfwys in the mid-1980s some 17 million hClrares havebeen ddorested out of an original area of neltlrly 38 million hectares In thedecade 1976-86 06 per cellt of the toral torest was lost each year

Plate 113 The landscape of Rumsiki Cameroon (Panos PicturesNictoriaKeblemiddotWilliams)

Deforestation 37

Figure 116 National parks and reselVes inCameroonSource After Kingdon (1990) pp 272-3

Exploitation of tropical forshyests in this part of Mrica hasgradually spread inland fromthe west coast Cameroonhas more forests left than anycoastal West Mrican countrybut less than any CentralAfrican country such as ZaireThe major cause of deforestashytion at me moment is fellingfOr fudwood and charcoal butmere are also increasing indusshytrial demands for timber andforest products Out ofa totalofover 14 million cu metres ofwood produced by Cameroonin 1989-91 more than 11million cu metres was roundshywood for fuel and charcoalHunting is also a major threatto animal life in the tropicalforests

Cameroon established lawsto manage and protect itstropical forests in 1981 Thislegislation decreed mat 20per cent of national territoryshould be designated as state forests Most of these are to be productive notprotected forests However several protected areas have been established withinthe forests an example is the Korup National Park which covers 1260 sq kmand has IS staff Maintenance is supported by the WFN (Worldwide Fund torNature)WWF (World Wildlife Fund) and other international bodies

Figure II6 illustrates the distribution of protected areas withill north-westCameroon many of which arc found in tropical forests At present forest reservesin Cameroon are poorly funded This may put their long-term protection at risk

Further reading

Alpert P 1993 Conserving biodiversity in Cameroon Ambia 22 44-8

Kingdon J 1990 bJRnd AfrieR The Evolution of Africa$ Rare AnimRu nndPlsmn London Collins

Williams M 1994 Forests and tree cover In W B Meyer and B L Turner(cds) O1aga in lAnd Use and LAnd CoP A Global Penpectipe 97-124Cambridge Cambridge University Press

38 The Biosphere

5 ThOPICAL SECONDARY

FOREST FORMATION

The clearance cultivation and subsequentabandonment of forests in the moist tropshyics has resulted in the development ofincreasing expanses of what is called secshyondary forest In a large and steadilyincreasing proportion of the tropics secshyondary forests make up most or all of theremaining forest

It is difficult to define precisely what wemean by secondary forest Some foresterswould define it as a type of forest thathas suffered some form of disturbance asa result of human actions This could beslight (eg hunting of animals or collecmiddottion of foodstuffs) or massive (eg clearfclling) Other forestcrs believe it is nowuseful and logical to restrict the use of theterm secondary forest to describe forestthat has regrown after clearance

Secondary forest development is oneconsequence of the practice ofshifting culshytivation Peasant farmers clear small plotsof just a few hectares cultivate them for afew years and then abandon them whensoil fertility and crop yields decline Theabandoned plots are then colonized byherbs shrubs and a canopy of pioneertrees This kind of tree grows rapidly needsa lot of light and has low-density woodand sparse branching These trees are typishycally short-lived with life-spans of one ortwO decades There are not many differshyent species As the process of successioncontinues the forest progressively apshyproaches its primary state However it maylake 500 years or even longer for the forshyest to recover its full diversity of species

Exactly how the forest recovers willdepend on the degree of initial disturbanceTraditional shifting cultivation employsonly small plots so that recolonization

Plate 114 Tropical secondary forest and slash-and-burn fields in the rainforestzone of Ghana (Rod Mcintosh)

from neighbouring primary forest is relashytively easy Whtn larger areas are clearedor when prolonged cultivation and freshyquent burning takes plate (leading tosevert soil degradation) the process willbe much slower However on sites whichhave not been seriously damaged thebiomass of leaves and fint roots (thoughnot total biomass) is restored to that ofprimary forest within as little as five to ten

FURTHER READING

Grasslands and Heathlands 39

years by which time net primary producmiddottion (NPP) is equal to or greatcr thanthat of primary forest Thus secondaryforest is probably highly effective at promiddotviding what are called laquoosystem Krvices- that is at preventing soil erosion andregulating runoff It also has some consershyvation value in that it provides a refugtfor some forest fauna and a habitat forsome Aora

Corlett R T 1995 TropicaJ secondary forests Progress in Physical Geography 19 159-72

Ellenberg H 1979 Mans influence on tropical mountain ecosystems in South AmericaJournal of ampoloDY 67 401-16

6 GRASSLANDS AND

HEATHLANDS

THE HUMAN ROLE

In the highlands of Africa there are largeareas of what are called AfTomontaneGrasslands Thty extend as a series ofismiddotlands from the mountains of Ethiopia tothose of the Cape area ofSouth Africa Arethey the result mainly of forest clearanceby humans in the recent past Or are theya long-standing and probably namral comshyponent of the pattern ofvegetation (Meadshyows and Linder 1993) Arc they causedby frost seasonal aridity excessively poorsoils or an intensive fire regimd This isone of the great controversies of Africanvegetation studies

Almost certainly a combination of facshytors has given riK to thesc grasslandsOn tht one hand currtnt land manageshyment pralaquoicts including tht usc of fireprevent forest from expanding Thtre hasundoubtedly been extensivt defortstationin recent centuries On the other handpollen analysis from various sites in southshytm Africa suggests that grassland waspresent in the area as long ago as 12000BP This would mean that much grassland

is not derived from forest through veryrtcent human activities

Similar argumtnts relate to many othtrof the worlds grtat areas of grasslandConsider for example the savannas oftropical rtgions which covtr about 18million sq km Grasses and sedges makeup most of the Vtgttation in savannaalthough woody plants arc present invarying proportions As with mOSI maorvegetation types a large number of intershyrelated factors are involved in causingsavanna It is important to distinguish clearlypredisposing causal resulting andmaintaining factors For instance aroundthe periphery of the Amazon Basin itappears that the climate predisposes the vegshyetation toward the development ofsavannarather than forest Tht geomor-phologicalevolution of the landscape and the formashytion of heavily leached old trosion surmiddotfaces may Ix a muml factor increaKdlaterite (iron crUSt) development a nIultshyinB factor and fire a maintaining factor

Originally savanna was belitved to bea predominandy natural vegetation typedevdoped to suit particular climatic conmiddotditiaRS (figure II7) It was thought thatsavanna is bentr adapted than other

40 The Biosphere

DtfOI~$tation

Dtsrrtifimion

Grudaflls

Aridshrubshygrlllslaoos

PrectpitatiOll

Figure 117 An idealized relationbetween the biomass density andproductivity of five major vegetationtypes (biomes) and precipitation Asprecipitation increases so doesproductivity and therefore biomasswith the two extremes being the lowsparsely shrubbed grasslands of thedeserts and the tall dosed forests bethey tropical temperate or borealSource Graetz (1994) pp 125-47

plant formations to cope with the greatfluctuations in rainfall during the year inthe seasonal tropics Rain torests could notresist the long wimer droughts while dryforests could not compete successfully withperennial grasscs during the lengthy periodof water surplus in the summer months

Other workers havc emphasized the imshyportance of edaphic (soil) conditions Theyargue that the development of savanna isencouraged by poor drainage soils witha low water-retention capacity in the dryseason soils with a shallow profile due tothe development of a lateritic crust andsoils with a low nutrient supply This lastcondition may arise because the soil hasdeveloped on a nutrient-poor parent rocksuch as quartzite or because the soil hasundergone an extended period of leachshying over millions ofyears on surfaces which

have been exposed to the elements for allthat time

A third group of researchers take theview that savannas are the product of drierconditions in former times such as thelate Pleistocene In spite of a moisteningclimate in the Holocene the savannas havebeen maintained by fire They point tothe fact that the patches of savanna insouthern Venezuela occur within areas offorest where the levels of humidity andsoil infertility are similar This suggests thatneither soil fertility nor drainage norclimate can be pinpointed as the cause ofsavanna Moreover the present islandsof savanna contain plant species which arcalso present elsewhere in tropical Amerishycan savannas This suggests that the isshylands were once part of a much largercontinuous expanse of savanna

The importance of fire in creating andmaintaining some savannas is suggested bythe fact that many kinds of tree that growin savanna are fire-resistant Controlledexperiments in Africa demonstrate thatsome tree species such as Burkea africanaand Lophira lanceoMa withstand repeatedburning better than others It has also beennotld that for example African herdsmenand agriculturalists frequently use fire overmuch of tropical Africa to maintain grassshyland Certainly the climate ofsavanna areasis conducive to fire

Some savannas are undoubtedly naturalPollen analysis in South America showsthat savanna vegetation was present beforethe arrival of human civilization Noneshytheless even natural savannas change theircharacteristics when subjected to humanpressures For example many studies fromwarm parts of the world have shown thatgrass cover cannot maintain itself underheavy grazing pressure Heavy grazingtends to remove the fuel (grass) from muchof the land surface This means that fireshappen much less often allowing trees andbushes to invade the savanna

Grasslands and Heathlands 4)

Plate 115 Savanna landscape in the west Kimberley region of northmiddotwesternAustralia The use of fire may be important in controlling both the nature and thedistribution of this extensive biome type (A S Goudie)

Whatever the fac[Ors that determine theorigin of savannas there arc others thathelp to determine some of their particularcharacteristics One example we can giveof this is the role of elephantS in Mricansavannas We do this partly because it isa good illustration of the interdependenceof vegetation and animals and partly bcshycause if elephant numbers arc reduced byhuman prcssures then the whole charaC[crof the savanna ecosystem may change Eleshyphants arc what is known as a keystonespecies because they cxert a strong influshyence on many aspects of the environmentin which they live They divcrsify the ecoshysystems which they occupy and create amosaic of habitats by browsing tramplingand knocking over bushes and trees Theyalso disperse seeds through their eatingand defecating habits and maintain orcreate water holes by wallowing All these

roles arc of benefit to other sptcies Conshyversely where human interference prcvcntsekphants from moving freely within theirhabitats and leads to their numbers exceedshying the carrying capacity of the slvannatheir etTen can be environmentally catamiddotstrophic Equally ifhumans redme dephuInumbers in a particular piece ofsavanna thesavanna may become less diverse and lessopen and its water holes may silt up Thiswill be to the detriment of other species

The mid-latitude grasslands (the prairiesof North America for example) are also thesubject of controversy as to their originsAs we discussed in section 2 above on firethere has been a debate as to whether theprairies arc ~ntially the result of lowprecipitation and high evapotranspirationlevels or whether they result from fires

Hcathland is another fascinating vegetashytion type It is characteristic of temperate

42 The Biosphere

oceanic conditions on acidic substratesIt is composed of cricoid (or heather-like)low shrubs which form a closed canopyat heights usually less than 2 metres Treesand tall shrubs are either absent altogetheror scattered Some heathlands are naturalThese include areas at altitudes abovethe forest limit on mountains and thoseon exposed coaSts There are also wellshydocumented examples of heathlands whichappear naturally in the course of plantsuccession This can happen for examplewhere Catuna vulgaris (heather) replacesgrasses like Ammophila arenana and CR-rexarenana on coastal dunes

However extensive areas of heathlandalso occur at low and medium altitudeson the western fringe of Europe betweenPortugal and Scandinavia The origin ofthese heathlands is strongly disputed Somewere once thought to have developedwhere there were appropriate edaphicconditions (for example well-drainedloess or very sandy nutrient-poor soils)but pollen analysis showed that mostheathlands occupy areas which were forshymerly tree-covered This evidence alone didnot settle the question whether the changefrom forest to heath was more likely tohave been caused by Holocene climaticchange or by human activity Howevertwo other factors suggest that humanactions established and then maintained

FURTHER READING

most of these heathland areas The first ofthese is the presence of human artefactsand buried charcoal the second is the fuctthat the replacement of forest by heathhas occurred at many different times beshytween the Neolithic and the late nineteenthcentury Fire is an important managementtool for heather in locations such as upshyland Britain since the value of CalJuna asa food for grazing animals increases if it isperiodically burned

The area covered by heathland in Westmiddotern Europe reached a peak around 1860Since then there has been a very rapiddecline Reductions in Britain averaged 40per cent between 1950 and 1984 and thiswas a continuation of a more long-termtrend In England the Dorset heathlandsthat were such a feature of Thomas Harshydys Wessex novels are now a fraction oftheir former size There are many reasonsfor this decline They include unsatisfacshytory burning practices the removal ofpeatdrainage fertilization replacement by immiddotproved grassland conversion to forest andthe quarrying of sand and gravel

Thus human activities over a very longtime can combine with natural changesboth to produce and to remove grasslandsand heathlands Many scientific debates arccontinuing on how such plant communshyities react to stress The box opposite givesan example from Australia

Gimingham C H and de Schmidt I T 1983 Heaths and natural and semi-naturalvegetation In W Holzner M J A Werger and I Ikusima (eds) Mtms Impact onVegetation 185-99 The Hague JunkThe best general review of the worlds heathlands

Harris D R (cd) 1980 Human Ecology in SRPanna Environments London Acashydemic PressA useful collection of papers on savannas in their human context

Grasslands and HeathJands 43

Recent human impacts on subalpine grassland andheathland in Victoria Australia

C]lndllYfflooornbullCattle grazing began in the 1850sin the Bugong High Plains alpinegrassland in what is now the Victoshyria Alpine National Park (created in1980) Eer since there have beendehates over the degradation ofgrassland and soil erosion In 1939there were disastrous hush fires heremd in the 19405 soil erosion beshycame very Knous u stock numbersincreascd Since the 1950$ there hasbeen an overall decline of about 60per cent in both stock numbers andthe area graud and by 1991 onlyabout 3100 cutle were grazing thearea benvc-en December and April

These changes in grazing densishyties have been echoed by an incretse in the area of shrub cover In 1945 pershymanent study plou were established by ecologists to monitor the changing vegshyetation cover on grazed and ungrazed land The rlaquoords produced from theseplots over five decades enab]( scientists today to test the relationship benveengrazing fire and the maintenance of grassland (Wahren et al 1994) It hu beensuggested that cattle grazing reduces shrub cover (therefore maintaining grassshyland) and also fire risk But the Bugong study docs not back this up as grazedplots have more bare patches than ungrazed (Ke table IlA) although by 1994old shrubs on some ungraud plots were beginning to die back In this areaalpine vegetation seems slow [0 recover after dislUrbance (such as fire) and evenslower where grazing is present

Table 114 Comparisons of percentage cover of different vegetation on grazed andungrazed grassland plots Bugong High Plains Victoria Australia 1982-1994

Cover 1982 1982 1989 1989 1994 1994dassmiddot Ungrazed Grazed Ungrazed Grazed Ungrazed Grazed

1 76 53 71 61 66 722 21 31 24 20 31 173 3 16 5 19 3 10

bull Cover class 1 = thick litter and dense vegetationCover class 2 thidc or thin litter sparse vegetationCover class 3 thin litter sparse to no vegetation

Source Adapted from Wahren et al (1994)

44 The Biosphere

7 TEMPERATE FORESTS UNDER

STRESS

Forest decline is an environmental issuethat came to the fore in the 1980s It hasmany symptoms including the discolorashytion and loss of needles and leaves reshyduced rates of grovlth abnormal growthforms and in extreme cases tree death

Germany is probably the Europeancountry most seriously affected by lorestdedine In 1985 55 per cent of the foreststands in West Germany were reponedto be damaged The decline is howeverwidespread in much of Europe (see tables115116) The process is now also undershymining the health of eastern NorthAmericas high coniferous forests In Gershymany it was the white fir Abies alba whichwas afflicted initially but since then the

symptoms have spread to at least ten otherspecies in Europe induding Norwayspruce (Picea abies) Scots pine (Pinussylvestris) European larch (Larix decidu)and seven broad-leaved species

In 1982-3 the German governmentadopted a comprehensive clean air legislashytion package However the data presentedin table II6 indicate that German forestsarc still suffering from decline In 1994at the Oslo international meeting Gershymany agreed to reduce sulphur emissionsby 83 per cent (from 1980 levels) by 2000In 1986 the Federal Environment Minisshytry concluded that there is no single typeof forest damage and no single cause Wearc dealing with a highly complex pheshyn0l111non which is difficult to untangle andin which air pollutants playa decisive rolc

Many suggested explanations for thisdieback have been put forward They

Table 115 Reported percentage of different tree species affected by forest declinein West European countries 1984

Species W Germany E France Switzerland Austria Italy (5 Tyrol)

Norway spruce 51 16 11 29 16Silver fir 87 26 13 28 35Scots pine 59 17 18 30 6Beech 50 3 8Oak 31 6 9Others 31 6 9

Source Goudie (1993)

Table 116 Results from German forest damage surveys 19B6-1993 percentage oftrees in classes 2-4 (ie defoliationgt 25) for all species

Area 1986 1987 1988 1989 1990 1991

EG 138 164 359WG 189 173 149 159 159G 252

bull EG = former East GermanyWG = former West GermanyG = Germany after reunification

Source Acid News 1995

1992 1993 1994

260 242 244

includ~ poor for~st manag~m~ntpracticesag~ing of strnds climatic chang~ sev~re

climatic events (such as the sev~re sumshym~r droughts in Britain during 1976 and1995) nutri~nt d~fici~ncy viruses fungalpathogens and pest infestations Howeverparticular attention is being paid to therol~ of pollution This may tak~ variousforms including gaseous pollutants suchas sulphur dioxid~ (SOl) nitrogen oxides(NOx) or ozone acid deposition on kav~s

and needles soil acidification and the assoshyciat~d probl~ms of aluminium toxicity and~xc~ss kaching of nutri~nl$ (for ~xampl~

magnesium) over-fertilization by d~posit~d

nitrog~n and the accumulation of trac~

metal or synth~tic organic compounds (~g

pesticides or herbicides) as a r~sult ofatmosph~ric d~position

In many cases forest d~clin~ may miuhfrom a combination of Strcsscs For ~X2m-

T~mpcrat~ For~sts und~r Str~ss 45

pk long-term climatic chang~ may cr~at~

a pmtisposing stTtSS (see pan I section 6)which ov~r a long period weakens a treesability to resist other forms of str~ss Thenth~r~ ar~ ineiling SlnJJeJ that operat~ overshort~r rime-spans for exampk droughtS(v~r~ frost or a short-li~d pollution ~pishy

sod~ These damage trees that are alr~ady

weaken~d by the predisposing str~sses

Thirdly w~ak~ned tr~~s ar~ then morepron~ to a scri~s of contributing SlrelJes(eg attack by insect pests or root fungi)

There may also be different causes indifferent ar~as Thus widespread for~st

death in Eastern Europe may r~sult fromhigh concentrations of sulphur dioxidecombined with extr~me winter stress Thisis a much less likely ~xplanation in Britainwh~r~ sulphur dioxide concentrationshav~ shown a mark~d d~cr~~ in r~c~nt

years Indeed Innes and Boswell (1990

Plate 116 Acid rain damage at Szkalrska Poreba south-west Poland Much ofthe pollution here comes from the burning of low-quality coals and lignites inGermany and the Czech Republic (Richard Baker Katz Pictures)

Figure 118 Estimates of total quantityof de-icing salt purchased annually inmainland Britain during the period1960-1991 Arrows represent yearswhen significant crown dieback ofLondon plane has occurred In the early1960s highway departments changedfrom using saltabrasive mixtures tousing pure rock salt This may accountfor some of the increase in salt usageSource Dobson (1991)

Ivgt with many environmental problemsinterpretation of forest decline is hamperedby a lack of long-term data and detailedsurveys Forest conditions vary fromyear to year in response to fluctuations inclimatic stress (eg drought frost windthrow) This means that it is dangerousto infer long-term trends from short-termdata (Innes and Boswell 1990) The probmiddotlem may well have been exaggerated inthe 1980s by some observers who fJiled to

recognize that stressed trees may be a morenormal phenomenon than they believed

46 The Biosphere

p 46) suggest that the direct effects ofgaseous pollutants in Britain appear to bevery limited

It is also important to recognize thatsome stresses may be especially significantfor a particular tree species In 1987 asurvey of ash trees (Fraxinus excelsior) inGreat Britain showed extensive diebackover large areas of the country Almostone-fifth of all ash trees sampled wereaffected Hull and Gibbs (1991) identifieda link between dieback and the way theland is managed around the tree Theynoted particularly high levels of damagein trees next to arable farmland They sugshygested this might be associated with unmiddotcontrolled stubble burning the effects ofdrifting herbicides and the consequencesof excessive nitrate fertilizer applicationsto adjacent fields However the primecause ofdieback was seen to be the disturshybance of tree roots and the compaction ofthe soil by large agricultural machineryAsh has shallow roots if these are damshyaged repeatedly the trees uptake of waterand nutrients might be seriously reducedBroken root surfJces would be prone toinfection by pathogenic fungi

Trees growing alongside roads which arcregularly salted to reduce ice problems incold winters may also become damagedThis may be a growing problem becausethe use of salt on roads has increased inrecent years (figure 118)

FURTHER READING

II I I II

Boehmer-Christiansen S and Skea ] 1991 Acid Politics Environment and EnergyPolicies in Britain and Germany London Belhaven

Innes ] 1 1992 Forest decline Progress in Physical Geography 16 1-64An impressive overview of the competing hypotheses that have been put forward toexplain forest decline

Schulze E-D Lange O L and Oren R 1989 Forest Decline and Air PollutionEcological Studies no 71 New York Springer-Verlag

Templ=rate FOrc5ts under Stress 47

Forest decline in Bavaria Germany

I AVARIA (--

--MwBdIbullhypotheses have been

to explain the apparent

Forest decline in Germany became amajor environmental issue during the1980s Many conifers and broadshyleaved trees showed signs of Stressranging from yellowing of needlesto death In the mountains of theFichtelgebirge in north-east Bavariamost forests at altitudes over 750metres currentlyshow signs ofdcdincBy 1986 30 per cent of Bavarianforests were cla~d as moderatelyor seriously damaged by unknownfactors

Severaladvanceddecline

bull natural climatic causes andepidemics

bull direct effects of air pollutionbull mineral deficiency and imbalances as a consequence of acid deposition and

soil acidificationbull a combination of some or all of the above factors

The forests in Bavaria grow on acid poor soils above granite and metamorphicgneiss and schist bedrocks In the sixteenth century beech was the major speciesBeech and sycamore together accoumed for 60 per cent of the canopy and firformed the remaining 40 per cent Over the following 400 years the forests weredepleted by mining smelting and agriculture During the ninetccnth centuryreforestation took place producing a difierent mix of trees Now there an~ 96 percent spruce 2 per cent beech and 1 per cent fir (Schulze et aI 1989)

During the twentieth century episodes of ozone sulphur dioxide and nitrogenoxide pollution have been very $Cvere It now appears that air pollution coupledwith a past history of polluted air and planting is a major problem lor these verysensitive forests Much of the pollution occurs in winter and comes trom steeland chemical industries and power plants in eastern Germany and the CzechRepublic The effects of air pollution are compounded by mble winter air conshyditions which encourage temperature inversions and the production of smogAmmonia produced by nearby cattlc and other Iarmed animals also adds to thenitrogen pollution

bull

bull

48 The Biosphere

8 URBAN ECOWGY

The world is becoming increasingly urshybanized In 1980 here were 35 cities withpopulations of over 4 million by 2025135 cities will probably have reached hissize Over the period 1950-90 the totalpopulation of the worlds cities has in~

creased tenfold and is now more than 2billion Cities thus contain around half theworlds population They also contributemost global pollution Funhermore urbanpopulations are concentrated into a rela~

tively small area for example only 34 percem of he Iand in the USA is urbanizedThis makes the urban impact upon theenvironment even more imense

The impacts ofurban areas on the envicshyonmem and ecology can be devastatingProblems have been felt for a long timein many countries where industrial citiesdeveloped early In many less developedcountries huge expansion in populationhas occurred relatively recently leading to

burgeoning environmental problemsWhat impacts do cities have 011 the

environment And how do these affectecology Cities do all of the following

bull produce a major dem3nu tor naturalresources in the surrounding arC3

bull obliterate the llatur3l hydrological sysshytem on the site of the dtyreduce biolll3SS and alter the speciescomposition 011 the site of thl cityproduce waste products which canalter the environment in and aroundthe city

bull create new land through reclamationand landfill

Together these impacts make up theecological footprint of a city that is thearea affected by pollution resource extracshytion devdopmem and transport causedby the city irsclf Cities demand raw matershyials such as tim bet coal and oil these must

be extracted from the surrounding areaor transported into the city They alsorequire agricultural products energy andlabour As the variow parts of the worldbecome increasingly interconnected theecological footprints of major cities beshycome bigger and bigger This means thata vast proportion of the Earths surface isbeing sucked intO the urban system oneway or another

On he site of cities the entire entershyprise of urbanization leads to dnsticchanges in geomorphology climate h)liroshylogy and ecology Urbanization is oftenseen as evidence of societys success intaming and overcoming nature Increasshying urban pollution problems howevetshow that this success has been limitedCities replace natural foteSts grasslandand other vegetation with vaSt swathes ofconcrete brick and nrmac as well as garshydens parks ponds and derelict land Thesechanges in vegetation rebound upon anishymal life they also affect the hydrologicalresponse Trees grassland and the soilsin which they grow act as butTers slowingdown the movement of water through adrainage basin As explained more fully inpart IV section 4 urbanization reducessuch butTers It acce1ciltes and streamlinesthe flows of water by reducing the diffuseflow below the land surface and replacingit by flows over the surtacc lnd throughpipc=s

Species diversity may be increased incities despite the great disruption causedby building work Gardens parks pondsand street plantings introduce a range ofexotic plants The urban climate also enshycourages growth and diversity favouringspecies which tolerate wanner 1css variableconditions than those found in neighbourshying rural areas The urban environmentalso produces behavioural changes in manyanimals For example animals which usushyally hibernate in winter in temperate counshytries can live normally throughout the year

Urban Ecology 49

Plate 117 A kestrel sitting on a street lamp in a British city These raptors andmany other organisms have proved their ability to adapt to the urbanenvironment (NHPNMichael leach)

in large cities where there is year-roundwarmth and food Street lighting confusesbirds and extends the hours of daylightfor them The vast amount of waste tOadfound in urban areas encourages scavenging animals such as racoons and foxesMany urban-dwelling species have nowcome to be regarded as pests Pigeons inmany British and American dty centres arean example their droppings arc a greatnuisance Many species arrie in cities alongrivers and canals Communications nctshyworks in general provide a major route formany animals and plants seeking to coloshynize new areas In Britain for examplemink which have escaped from fur farmsare now found on urban riverbanks inOxford

On the other hand the pollution anddereliction present in many citia depletethe ecology High levels ofsulphur dioxide

in the atmosphere for example kill offlichen species growing on trlaquo bark Manytrees themselves a~ threatened by air andsoil pollution Similarly urban and indusshytrial pollution of aterways depletes theaquatic ecology For example in Shangmiddothai China the Huangpu River is nowthought to be biologically dead as a resultof the 34 million cu metres of industrialand domestic waste dumped in it each daySome derelict land is highly contaminatedwith heavy metals and Other toxins thwmaking recolonization impossible Howshyever other derelict land areas provideopportunities for wildlife colonizationand conservation In Britain large areas ofurban allotments (small plots ofland rentedout for domestic food production) are nolonger cultivated and native and exoticspecies are colonizing the abandoned land

Increasingly city dwellers are becoming

50 The Biosphere

committed to improving the ecology ofcities A range of strategies is employed

bull reducing poUution to encourage desirshyable organisms to return

bull removing undesirable species throughcareful extermination programmes

bull reducing the use of lawn fertilizers andpesticides

bull planting trees in streetSbull cstablishing urban nature reserves city

forests and conservation areasbull undertaking backyard compostingbull developing urban farms thus bringing

food production back into cities

Such schemes are part ofa general trendtowards improving the urban environmentthrough managing pollution and immiddotproving stmdards of housing and healthSustainable development of cities is apopular phrase at prescnt However vastdisparities in wealth between inhabiuntsof different cities and between differentparts of anyone city make the goal ofsustainability hard to reach In manydeveloping countries squatter settlementson the outskirts oflarge cities are growingat an alarming rate as more and more poorinhabitants of outlying rural areas are atshytracted to the opportunities in cities These

FURTHER READING

settlements arc very destructive of theenvironment and also severely affected byenvironmental poUution and hazards Theyusually grow up on land which is dereUetbecause it is least suitable for developmentThey lack even basic services such as elecshytricity or running water Trees arc removedso that dwellings can be put up on steeptropical hillslopcs this can result in accelshyerated landslides (see part V section 6)Wastes produced in squatter settlementscannot be removed effectively because ofthe lack of sanitation and services Thiscauses pollution of land air and watermiddotcourses In South Africa for exampleSoweto (which has a population of around25 million according to some estimates)has horrendous air poUution from sulphurdioxide produced by coal burning becausethe electricity supply is completely inadshyequate The natural ecology has beenwiped out and human health is suffering

All round the world it is clear thatthe ecological impacts of cities are justone manifcstation of a deep problem withpresent-day urbanization A5 RichardRogers the architect put it in 1995 Inthe beginning we built cities to overcomeour environment In the future we mustbuild cities to nurture it

Bridgman H Warner H and Dodson J 1995 Urban Biophysical EnvironmentsMelbourne Oxford University PressA concise introduction with an Australian flavour

Hardoy J E Midin D and Satterthwaite D 1992 Environmental Problems inThird World Cities London u([hscanLike most Earthscan books this provides a clear introduction to the crucial issuesaccompanied by many short case studies

White R 1994 Urban EinmmentRI MRn4gement Chichester WdcyA modern general trcaonent of how city environments can be managed

Urban Ecology 51

Chicagos changing vegetation

CANADA

USA

In the 1840s ~fore urban development really began the flat gladated plainnext to Lake Michigan in the USA was dominated by natural forest and prairievegetation (figure 119) Low prairie grasslands occupied most of the area Deshydduow forests of oaks (such as the Bur oak Q4ercllS mlicroclirplI) ashes andcIms were common on sand ridges and the edges of streams By 1860 thepopulation of Chicago city had riscn to 50000 and by 1990 the metropolitanarea conDined over 8 million people

This urban explosion has been accompanied by an almost total loss of naturalvegetation apart from some large tracts designated as forest prescrves Severaldirect and indirect cawes of this loss of natural vegetation can be recognized Thefirst direct causc is the dearing of land for development Interestingly howeverindividual trees survived some trees identified in the 18305 by the original landsurveyors were still present in the 19705 (Schmid 1975) Studies of the forestvegetation in and around Chicago show that removing the dosed canopy bycreating clearings for building favours trees which cope well in the drier andlighter conditions (such as Bur oak) Other moisture-loving species such assugar maple and red oak suffer Indirectly construction has disturbed the soilsaffecting particularly trees such as red and white oaks Oil spills gas leaks thesalting of icy roads and digging to lay pipes have all had direct impacu on naturaland introduced vegetation in some parts of the dry

New kinds of trees and other vegetation have been introduced into ChicagoThcsc incorner species have had a key impact on the citys vegetation They havealso suffered from the urban environment Interestingly there has been an inshycrease in the proportion of Chiago covered by trees since urbanization This isbecause trees have been planted on upland sites which would naturally have beendominated by prairie

52 The BiosphereJ

~1lt1- N -

t laquo

-

-

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bull bull U U Range

Figure 119 The distribution of forest (black) and prairie (white) in theChicago region during the 1840s as recorded by the General land SurveySections formed by the townshiprange grid are 1 mile squareSource Schmid (1975) figure 3

Air pollution has had an indir~ct ~ff~ct on veg~tation In 1913 a study foundthat trees in Chicago near th~ railway stations w~re aff~ct~d by smoke and th~

vegetation around sted mills was reduc~d to a f~w w~~dy annuals Mor~ recentlythe mainly d~ciduous tr~~s in Chicago have shown much less damag~ from airpollution than th~ ev~rgreens in other North American cities A much moreserious ~vent for the urban vegetation of Chicago was the outbreak of Dmch elmdisease from the late 1950s Until 1950 American elm was the most commonlyplanted tree species her~ Dutch elm disease destroyed the great majority of them

Housing brings grass and shrubs planted for decorative purposes in gardensChicago residents especially in the wealthy suburbs have planted many exoticshrub and herb species but few native ones Of the native plants opportunisticherbs from flood plains have been the most successful These plants thrive onwasteland and abandoned plors The vegetation pattern of Chicago is now con-trolled by economic social and cultural factors The number and mix of speciesnow vary according to the age and social characteristics of different neighbour-hoods Natural ecological factors are no longer so important as they were

-

ltshyi

9 WETLANDS ThE KJDNEYS

OF THE LANDSCAPE

In th~ 19805 w~tlands becam~ a lOpic ofgr~al ~nvironm~nral conc~rn Th~y w~r~

pcrcdv~d to be vitally important ~cosysshy

t~ms as is mad~ dear in the followingintroductory remarks to Mitsch and Gosseshylinks pione~ring book WetlandJ

Wetlands are among the most imporshytant ecosystems on the Earth In thegreat scheme of things it was theswampy environment of the Carbonifshyerous P~riod that produced and preshyserved many of the fossil fuels on whichwe now d~pend On a much shortertime scale wetlands are valuable assources sinks and transformers of amultitude of ch~mical biological andg~netic materials Wetlands are someshyrimes described as the kidneys of thelmdsca~ for the functions they rtr-

Table 117 Threats to wetlands

W~dands 53

form in hydrologic md chemical cycl~s

and as the downstream rec~ivers ofwast~s from both natural and humansources Th~y have been found tod~anse pollut~d waters pr~middot~nt floodsprot~ct shor~lin~s and rechargegroundwat~r aquif~rs Furthermoreand most important to som~ w~tlands

play major roles in the landscape byproviding unique habitats for a widevariety of flora and fauna While thevalues of wetlands for fish and wildlifeprotection have be~n known for severaldecades some of the other benefitS havebeen id~ntified more rec~ndy (MitSchand Gossdink 1986 p 3)

W~t1ands arc also percdvcd to be underthreat mOSt notably from draining ditchshying dredging filling pollution and chanshyn~lization According to some sources theworld may have lost halfof all itS wetlandssince 1900 md the USA alone has lost54 rtr cent of its original w~t1and area

Human Indirect

Source Type

Human Direct

Examples

Drainage for crops timber mosquito control

Dredging and stream channelization

Filling for waste disposal and land claim

Construction of dykes dams and sea walls forflood control and storm protection

Discharge of materials (eg pesticides nutrientsfrom sewage sediments) into waters and wetlands

Mining of wetland soils for peat coal gravel andother minerals

Sediment diversion by dams and other structures

Hydrological alterations by canals roads etc

Subsidence from extraction of groundwater oiletc

Natural Direct and indirect Subsidence (including natural rise of sea leve)droughts hurricanes and other storms erosion andbiotic effects

Sourc~ Adapted from Maltby (1986) p 92

54 The Biosphere

Table 118 Wetland terms and types

Name Definition

Swamp Wetland dominated by trees or shrubs (US definition) InEurope a forested fen (see belowgt could easily be called aswamp In some areas wetlands dominated by reed grassare also called swamps

Marsh A frequently or continually inundated wetland characterizedby emergent herbaceous vegetation adapted to saturated soilconditions

Bog A peat-accumulating wetland that has no significant inflowsor outflows and supports acid-loving mosses particularlySphagnum

Fen A peat-accumulating wetland that receives some drainagefrom surrounding mineral soil and usually supports marshlikevegetation

Peatland A generic term for any wetland that accumulates partiallydecaying plant matter

Mire Synonymous with any peat-accumulating wetland (Europeandefinition)

Moor Synonymous with peatland (European definition) A highmoor is a raised bog while a low moor is a peatland in abasin of depression that is not elevated above its perimeter

Muskeg large expanses of peatland or bogs particularly used inCanada and Alaska

Bottomland

Wet prairie

Reed swamp

lowlands along streams and rivers usually on alluvialfloodplains that are periodically flooded

Similar to a marsh

Marsh dominated by Phragmites (common reed) term usedparticularly in Eastern Europe

Source Modified from Gleick (1993) table F1

primarily because of agricultural developshyments The pressures on wel1ands are listedin table 117

What precisely are wel1ands~ There isno single Wliversally recognized definitionbecause they take a variety of forms andoccur in a considerable range ofconditions(table IIB) However Maltbys (1986)definition is a useful one He defines wet-

lands as ecosystems whose formation hasbeen dominated by water and whose proshycesses and characteristics are largely conshytrolled by water A wetland is a place thathas been wet enough for a long time todevelop specially adapted vegetation andotherorganismsbull Wetlands therefore includeareas ofmarsh mire swamp fen peatlandor water whether natural or artificial per-

Wetlands 55

HlQIWATEl

Figure 1110 Diagram showing the hydrological and ecological characteristics ofwetlands which act as ecotones between dry terrestrial ecosystems andpermanently wet aquatic ecosystemsSource Mitsch and Gosselink (1986) figure 14

manent or temporary The water may lxstatic or flowing fresh brackish or saltyincluding marine water whose depth at lowtide does not exceed 6 meues

Wetlandscoversignificant areas In all theyaccount for about 6 per cent of the Earthsland surface This is not much less than theproportion orland under uopicaJ rain forestThey also account for as much as a quarterafthe Earths total net primary productionNotable wetlands include the Evergladesin Florida the Sudd and Okavango swampsof Mrica the Fens and Broads of EastAnglia in England and the mangroveswamps of South and South-East Asia

Wetlands are what are known as ccotonesthat is transitional zones They occupythe transitional space bt=tween largely dryterrestrial systems and deep-water aquaticsystems (figure 1110) This transitionalposition in the landscape allows them toplay valuable roles for example as nutrientsources or nutrient sinks It also causesthem to have high biodiversity for theyacquire and contain species from bochterrestrial and aquatic systems

Why are wetlands important and deservshying of careful management Because

bull they are fertile and highly productiveecosystems

bull they support fisheries of great valuebull they absorb and store carbon which has

implications for the greenhouse effectbull they sift dissolved and suspended mashy

terial from floodwaters thereby cncourshyaging plant growth and maintainingwater quality

bull they absorb and store floodwater(thereby mitigating flood peaks) andaCI as barriers against storm surgesetc

bull they are vital breeding and nurserygrounds for waterfowl animalsand plamsand provide refuges in times ofdrought

bull they provide staple food plams(eg rice)bull they provide fuel (eg peat)bull they provide building materials (eg

mangrove wood reeds for malch etc)bull they have recreational uses

Because of the great value of wetJands in 1971 many countries signed the Conshyvention on Wedands of International Imshyponance especially as Waterfowl HabitatAs this was signed at Ramsar in I~ it isotien more eonveniendy known as the

56 The Biosphere

Plate 118 The Niger River of West Africa creates a great wetland itsso-called inland delta This photograph shows an area flooded by the annualinundation near Jenne Mali (Rod Mcintosh)

Ramsar Convention Those states that havesigned the Convention which now amountto over 90 agree to designate at least oneof their national wetlands for inclusion ina List of Wetlands of International Imshyportance They also agree to formulateand implement their planning so as topromote the conservation of the wetlandsincluded in the List to establish wetlandnature reserves and to co-operate in themanagement ofshared wetlands and sharedwetland species

FURTHER READING

International collaboration is ofcourseessential It is no use conserving a wetlandin one country to provide a refuge forspecies that spend one particular season ofthe year at that wetland if another counshytry destroys the refuge which they use inanother season of the year Full details ofinternational environmental conventions ofthis type are listed each year in the GreenGlobe Yearbook which is prepared by theFridtjof Nansen Institute of Norway andpublished by Oxford University Press

Maltby E 1986 Waterlogged Wealth Why Waste the Worlds Wet Placet LondonEarthscanA very useful statement of why wetlands are important and the stresses they face

Williams M (ed) 1990 Wetlands A Threatened Landscape Oxford BlackwellA more advanced collection of papers that deals with many different types of wetlandsfrom an international perspective

Wt=tlands 57

Wetlands management in the Niger Inland Delta

Tht= Niger Inland Delta in MaliMrica is in the Sahel zone It formsan important seasonally flooded wetshyland environment in an area whereevaporation vastly exceeds precipitashytion It covers some 20000-30000sq km in me flood season and 4000sq km at low water and supportsa population of around 550000JKople (Adams 1993) Fishinggrazing and cultivation of rice andsorghum are all important activitiesSeventy-five JKr cent of me fishcaught along the entire River Nigerare caught hcre half the total rice area in Mali is found here Over 2 millionsheep and goats and around 1 million cattle graze on the delta in the dry seasonThcsc numbers make up around 20 per cent of all thcsc animals found in Mali

The key to the complex and abundant agricultural production of the delta isthe timing of the floods The high flow in the delta does not coincide with thelocal rainfall peak This means that there is frequent variation in environmentalconditions throughout the year The floodwaters JKak betwt=en September andNovember and recede between December and February rains ft11 between Juneand September and the delta is dry between April and June Different activitiesdominate the delta under these different hydrological conditions Rice is planttdas the waters rs( in July and August and harvested as they recede in Decemberto February Sorghum is planted on the fulling flood in January and the delta isextensively used for grazing from December to July

This wetland is also of international importance Migrating birds visit it and thedelta provides an important stop for them on the routes from the Arctic to otherparts of Africa

Failure of the rains and alterations to the flow of the Niger River may haveserious consequences for the rich natural and human ecology of the Niger InlandDelta Dams further up the Niger River are likely to remove about 12 JKr centof inflow to the delta in a dry year which could have impacts on fishing andagriculture Damming of rivers tends to affect both the quality and the quantityofwater and to detract from the significant economic uses ofdownstream wetlandsOne solution on regulatt=d rivers may be controlled flooding with artificial proshyduction of floodwaters from hydroelectric dams In this way the dams arc madeto work pith the natural river environment nther than replacing it

Further reading

Adams W M 1993 Indigenous usc of wetlands and sustainable developmentin West Africa Geographic1 jOJ4nuli 159 209-18

S8 The Biosphere

10 BIODIVERSITY AND

ExnNcrIONS

Wlut is biodiversity It has recently beendescribed as an enormous cornucopia ofwild and cultivated species dive~ in fonnand function with beauty and usefulnessbeyond the imagination (litis 1988 p98) Biodiversity has recently become amajor environmental issue With environshyments being degraded at an acceleratingrate much diversity is being irretrievablylost through the destruction of naturalhabitats At the same time science is disshycovering new uses for biological diversity

The fundamental concern is the finalityof the loss of biodiversity Once a specieshas gone it cannot be brought back Thedodo (a bird) is dead and gone and willnever be seen again

Biodiversity has five main aspects

bull the distribution of different kinds ofecosystems which comprise communshyities of plant and animal species andthe surrounding environment andwhich are valuable not only for thespecies they contain but also in theirown right

bull the total number of species in a regionor area

bull the number of endemic species (speshycies whose distribution is confined to

one particular location) in an areabull the genetic diversity of an individual

speciesbull the sub-populations of an individual

species that is the different groupswhich represent its genetic diversity

The Earths genes species and ecosysshytems have evolved over a period of 3000million years They form the basis forhuman survival on the planet Howeverhuman activities arc now leading to arapid loss of many of the components of

biodiversity Human self-interest arguesthat this process should be stemmed forecosystems playa major role in the globalclimate arc a source of useful productspreserve genetic strains which crop breedshyers use to improve cultivated varieties ofplants and conserve the soil

We have no clear idea of the totalnumber of species of organisms that exislon the face of the Earth Therefore it isdifficult to predict what numbers ofspeciesmay be lost in the coming decades Howshyever according to Myers (1979 p 31)during the last quarter of this century weshall witness an extinction spasm accountshying for one million species This is a conshysidenble proportion of the estimatednumber of species living in the world toshyday which Myers puts at between 3 and 9million He has calculated mat from AD

1600 to 1900 humans were causing thedemise of one species every four yearsthat from 1900 onwards the rate increasedto an average of around one per year matat present me C2te is about one per dayand that within a decade we could Ixlosing one every hour By the end of thecentury our planet could have lost anyshything between 20 per cent and 50 percent of its species (Lugo 1988) It isobvious from even this brief look at thequestion that the need to maintain bioshydiversity has become one of the crucialissues with which we must contend

Some environments are particularly imshyportant for their species diversity Suchbiodiversity hot spots (figure IIII) needto be made priorities for conservationThey include coral reefs (sec part VI secshytion 7) tropical forcst5 (which support weUover half the planets species on only about6 per cent of irs land area) and somt ofthe Mediterranean climate ecosystems (inshycluding the extraordinarily diverse Fynbosshrublands of me Cape region of SouthAfrica) Some environmtnts are crucial beshycause of their high levels ofspecies diversity

bull

i

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-Figure 1111 Forest and heathland hot spot areas Hot spots are habitats with many species found nowhere else and ingreatest danger of extinction from human activitySource Wilson (1992) pp 262-3

60 The Biosphere

or endemic species others are crucial beshycause their loss would have consequenceselsewhere This applies for example towetlands which provide habitats for mishygratory birds and produce the nutrientsfor many fisheries

Reduction in habitat area can lead to adecline in the population of each speciesas well as in the number of differentspecies that the habitat can hold Lowpopulations make species highly vulnerableto inbreeding disease habitat alterationand environmental stress If a species hasbeen reduced to one population in onesmall area a single fire a single diseasethe loss of a food source or any othersuch demographic accident can kad toextinction

Human demographic success has proshyduced the biodiversity crisis As E OWilson noted in his remarkable book TheDiversity of Life

Human beings - mammals of the 50shykilogram weight class and members ofa group the primates otherwise notedfor scarcity - have become a hundredtimes more numerous than any otherland animal of comparable size in thehistory of life By every conceivablemeasure humanity is ecologically abshynormal Our species appropriates beshytween 20 and 40 per cent of the solarenergy captured in organic material byland plants There is no way that wecan draw upon the resources of theplanet to such a degree without drastishycally reducing the state of most otherspecies (Wilson 1992 p 272)

With the human population expected todouble or treble by the middle of thetwenty-first century and the material andenergy demands of developing countrieslikely to accelerate at an even faster rateeven less habitat will be left for otherspecies

What needs to be done~ Wilson suggests

five enterprises that need to be undertakento save and use in perpetuity as much aspossible of the Earths diversity

1 Survey the worldJsfauna andflora Weknow very little about how many speshycies there are and even less about theirqualities or where they are Threatenedhabitats need to be paid particularattention

2 Create biological wealth As our reshycords of species expand they open theway to what is called bioeconomicanalysis - the broad assessment of theeconomic potential of entire ecosysshytems An aim will be to protect ecoshysystems by assigning to them a futurevalue We need for example to searchamong wild species (possibly using ethmiddotnographic sources) for useful medicalor chemical products

3 Promote sustainable development Aswith desertification (see section 3above) the root cause of the problemlies in society The solution lies thereas well As Wilson (1992 p 322) exshyplained it The rural poor of the thirdworld are locked into a downwardspiral of poverty and the destructionof diversity Lacking access to marshykets hammered by exploding popushylations they turn increasingly to thelast of the wild biological resourcesThey hunt out the animals withinwalking distance cut forests that canshynot be regrown put their herds onany land from which they cannot bedriven by force They use domesticcrops ill suited to their environmentfor too many years because they knowno alternative Their governmentslacking an adequate tax base andsaddled with huge foreign debtscollaborate in the devastation of theenvironment

4 Save what remains Seed banks boshytanical gardens zoos and the like (the

so-called ex sitw methods) may havesome limited scope to preserve geneticmaterial However the key issue is thepreservation of nantral ecosystems Weneed large areas of reserves to includeas many of the undisturbed habitats as

Biodiversity and Extinctions 61

possibk Priority shouJd be given tobiodiversity hot spots

S Restore tbe wild lAnds Existing ecoshysystems need to be salvaged and remiddotgenentcd

Plate 119 A giant panda Ailuropoda melanoleuca feeding on bamboo atWolong Sichuan China The panda has become a symbol of the worlds wildlifeconservation movement (Heather Angel)

FURTHER READING

Myers N 1979 Tht Si1lkilJg Ark A Ntw Look at thtlrobJem ofDif(Jpp((Jrin~q SpainOxford Pergamon PressOnt of [ht classic statements about txtinctions and biodivtrsity loss by one ofthc= mostpc=rsuasivt tnvironmental wriltrs

Wilson E 0 1992 nJt Dipersity of Lift London PtnguinA beautiful piece of science writing for the Ia)middot person by a kading biologist

62 The Biosphere

Pandas plants and parks conserving biodiversityin China

China is both the worlds most populous country and an important storehouseof global biodiversity The country is home to around 30000 species of plantsand around 400 species of mammals Exact statistics are hard to obtain but wedo know that there are many unique endemic species found in China such asthe well-known giant panda (Aiuropoda melanoleuca) In 1965 there were 19nature reserves covering 6500 sq km (007 per cent of the toral land area ofChina) In 1991 there were 708 reserves covering 560000 sq km or 583 percent of the total land aru

The history of nature conservation and the preservation of biodiversity inChina reflects the changing social economic and political conditions prevailingin the country Before 1944 China had a patchy history of nature conservationas rulers established parkland hunting grounds gardens and temple areas Manytemple lands and sacred sites acted as biodiversity reserves

The first modern nature reserve in China was established in 1956 in theDinghu Subtropical Mountain Forest in Guandong Province (Freedman 1995)The mountain was the sice of an ancient Buddhist temple and so had alreadyreceived much protection Two-thirds of the reserves 1200 hectares had beenplanted with pine or subjected to other land usc modifications In 1980 it wasincorporated into the International Biosphere Network It is now a major touristdestination with up to 700000 visitors a year

Table 119 shows that most nature reserves were not established until after1980 when Chinas nature conservation laws began to multiply By 1989 379vertebrate species and 389 plant species received official protection in China Bythe early 1990s 13 nature reserves were devoted to the conservation and protecshytion of the giant panda and even more are planned

Hunting poaching and traditional medicine are great threats to biodiversityconservation in China In 1990 the country was the worlds largest exporter ofcat and reptile skins and live orchids Immense indirect threats are also posedto biodiversity by the development of industry agriculture transport and urbanareas Although China has made great attempts to conserve biodiversity like allcountries its nature conStrvation programme faces many problems

bull The distribution of nature reserves is uneven (figure ILIl)bull Administration is of uneven qualitybull Many nature reserves arc too small to be ecologically effectivebull Nature conservation laws are not rigorously enforcedbull Environmental education in people living near nature reserves is low and

planners do not consider the economic concerns of these people sufficientlybull Tourism has placed an additional stress on many nature reserves

Biodiversity and Extinctions 63

Table 119 Nature reserves In the Peoples Republic of Chinbullbull 1965-1991

Year No of reserves

1965 191978 341980 721983 2621985 3101987 4811991 708

Total area of reserves(000 sq km)

6512616

156167237560

of totaf area ofcountry covered by reserves

007013017162174247583

Source Edmonds (1994) table 82

Figure 1112 The distribution of nature reserves in ChinaSource Edmonds (1994) figure 83

Further reading

Edmonds R L 1994 Parterns ofChjnas Lost Harmony A Survey of the Counshytrys Environmental Degradation and Protection London Routledge

64 Th~ Biospher~

11 INTRODUCfIONS

INVASIONS AND

EXPLOSIONS

Humans are gr~at transporters of otherorganisms whether deliberately or accidenshytally Thus many organisms hav~ arrivedin areas where they did not naturally occurThis applies both to plants and to animals

Di Castri (1989) has identified thr~e

main stages in the process of biologicalinvasions stimulated by human actions Thefirst stage covers several millennia lip toabout AD 1500 During this periodhuman historical events favoured invasionsItld migrations primarily within the OldWorld The second stage began aboutAD 1500 At this time the explorltion

discovery and colonization of new territorshyi~s began in earnest and the globalizationof ~xchang~s got under way During thisphase which lasted for about 350 y~ars

invasions occurred from to and withinth~ Old World The third stage whichonly covers the last 100 to 150 years hasseen a rapidly increasing rate of exchangesand an even more extensive multifocalglobalization with Europe taking a lesscentral place

Plants that have been deliberately introshyduced to a new location can be dividedinto two groups (I) an economic groupwhich consists of crops timber trees andcover plants for control of erosion~ and(2) an ornamental or amenity group whichconsists of plants introduced out of curishyosity or because of their decorative value

Plate 1110 The remarkable Fynbos heathland of the Cape Province of SouthAfrica is rich in species many of which are endemic A major threat to the Fynbosis posed by the spread of invasive plants introduced from Australia In thisexample it is being encroached upon from the rear by Acacia cyclops(A S Goudie)

Introductions Invasions Explosions 6S

Table 1110 Allen plant species on oceanic Islands

Island No of naUve No of alien of alienspecies spedes species in flora

New Zealand 1200 1700 586Campbell Island 128 81 390South Georgia 26 54 675Kerguelen 29 33 532Tristan da Cunha 70 97 586Falklands 160 89 357TIerra del Fuego 430 128 230

SOUfce From data In Moore (1983)

A major role in such deliberate introdshyuctions was played by botanic gardensboth th~ in Europe and those in thecolonial territories from thc sixteenthcentury onwards

Mants that have becn accidentally disshy~rsed have arrived in a variety of waysby adhercnce to individual people or theirmeans of transport among crop seedfodder or packing materials and as a comshyponcnt of transponed soil ballast roadmetal or minerals

Introduccd plants are capable of inshyvading areas to which they have beenintroduced cven to the extent of causingso-called ecological explosions Theyprove to be so successful in their newhabitat that they expand in range andnumbers to the detriment of the nativespecies The same applies to introducedplant pathogens In Britain for instancemany elm trees have died sincc the 1970sbecauS( of the accidental introduction ofthc Dutch elm disease fungus on timberimportcd through certain ports in southshycrn England In thc USA thc Americanchestnut was almost eliminated in less thanSO years following the introduction ofthe chestnut blight fungus from Asia latein the 1890$ In western Australia thegreat jarrah fOteSts have been invaded anddecimated by a root fungus which was

probably introduced on diseased nurserymaterial from eastern Australia

Occan islands have oncn been particUshylarly vulnerable to invasions The simplicshyity of their ecosystems inevitably Icads tolower stability Introduced species oltenfind that the relative lack of competitionenables them to spread into a wider rangeof habitats than they could on the continshyents Moreover because the naturl1 speshycies inhabiting remote islands have cometo be there primarily because of their abilshyity to disperse over large distances theyhave not necessarily been dominant or evcnhighly successful in their original continshyental setting Therefore introduced speshycies may be more vigorous and effectiveThere may also be a lack of indigenousspecies to adapt to conditions such as bareground caused by humans This enablesintroduced weeds to establish themselves

Table 1110 illustrates dearly how prominshyent alien specics have become among theflora of some islands The percentage ofintroduced plants varies between aboutone-quarter ilnd two-thirds of the tOtalnumber of species present

Another type of ecological explosioncan be cauS(d by human-induced habitatchange Some of the most striking examshyples are associated with the establishmentof artificial lakes behind dams in place of

66 The Biosphere

rivers Riverine species which cannot copewith the changed fluvial conditions tendto disappear Others that can exploit thenew sources of food and reproduce thcmmiddotselves under thl new conditions multiplyrapidly in the absence ofcompetition Vegshyetation on land flooded as the lake watersrise decomposes to providc a rich supplyof nutrients This allows explosive outshygrowth of organisms as the new lake fillsIn particular floating plants may formdense mats of vegetation which in turnsupport large populations of invertebrateanimals These may cause fish to die bydeoxygenating the water and can create aserious nuisance for turbines naviguorsand fishermen On Lake Kariba in CentralAfrica the communities of the SouthAmerican water fern (SAvinia molestll)bladder-wort (UtriJ4iAria) and the Afrishycan water lettuce (Pittill stratious) grewdramatically and on the Nile behind theJebel Aulia Dam there was a huge increasein the number of water hyacinths (Eihshyhornill musipes)

Various human activities including dearshying foresr cultivating depositing rubbishand many others have opened up a wholerange of environments which are favourshyable to colonization by a particular groupof plants Such plants which arc notintroduced intentionally arc generallythought of as weeds

Animals have been deliberately introshyduced to new areas for many reasons forfood for sport for revenue for sentimentfor control of other pests and for aesmiddotthetic purposes Such dclibcrare actionsprobably account for insunce for thewidespread distribution of trout

There have also been many accidenulintroductions especially since the develshyopment of ocean-going vessels These arcbecoming more frequent for whereas inthe eighteenth century there were fewocean-going vessels of more than 300tonnes today there arc thousands Because

of this in the words ofC S Elton (1958p_ 31) we arc seeing one of the greathistorical convulsions in the worlds faunaand flora Indeed many animals arc inshytroduced with vegetable products for justas trade followed the flag so animals havefollowed the plants

A recent example of the spread of anintroduced insect in the Americas is promiddotvided by the Mricanizcd honey bee Anumber of these were brought to Brazilfrom South Mrica in 1957 as an experishyment and some escaped Since thenthey have moved northwards to CentralAmerica and Texas (figure 1113) spreadshying at a rate of 300-500 kIn per year andcompeting with established populations ofEuropean honey bees

Some animals arrive accidenrally withother beasts that arc imported deliberatelyIn nonhern AusmIia for instance waterbuffilo were introduced They brought withthem their own bloodsucking fly a specieswhich bred in cattle dung and transmittedan organism sometimes fatal to caweAwtralias native dung beetles accustomedonly to the small sheep-like pellets of thegrazing marsupials could not tackle thelarge dung pats of the bufhlo Thw unmiddottouched pats abounded and the flies wereable to brecd undisturbed EventuallyMrican dung beetles were introduced tocompete with the flies

Domesticated plants have in most casesbeen unable to survive without humanhelp The same is not so true of domesshyticated animals There arc a great manyexamples of cattle hones donkeys andgoats which have effectively adapted to newenvironments and have become virtuallywild (feral) Frequently pigs and rabbitsthat have esublished themselves in this wayhave owted native animals Feral animalsmay also panicularly on ocean isJandscause dcscni6cation Fern goats for exmiddotample have degraded the Channel Islandsoff the California coast

Introductions Invasions Explosions 67

Figure 1113 The spread of the Africanized honey bee in the Americas between1957 (when it was introduced into Brazilgt and 1990Source Modified after Texas Agricultural Experiment Station in Christian Science MonitorSeptember 1991

Aquatic life can be spread accidentallythrough human alteration of waterwaysand by the construction of canals whichenables organisms to spread from onesea or one lake to another This processis called Lessepsian migration after thename of the man who built the Suez Canal

FURTHER READING

The construction of that great watershyway has enabled the exchange of animalsbetween the Red Sea and the easternMediterranean The migrants include amenacing jellyfish which has now inshyvaded beaches on the eastern shore of theMediterranean

Drake] A (ed) 1989 Biological Invasions A Global Perspective Chichester WileyAn advanced collection of edited papers

Elton C S 1958 The Ecology ofInvasions by PiRtI ad Animals London MethuenThe classic monograph on this theme

68 The Biosphere

Alien plant species invading Kakadu National ParkAustralia

N

tNORTHERN fERRlTORY

bull 10

The Kakadu National Park is a UNESCO World Heritage Site in the monsoonaltropical north of Australia containing most of the catchment of the South Alshyligator River The natural vegetation is mainly savanna woodland and open forestdominated by eucalyptus There are also extensive alluvial floodplains seasonshyally water-covered where herbaceous wetland vegetation grows Out of 1526plant species found here some 58 per cent (89 species) are considered to beinvasive (Corrie and Werner 1993) Most of these are weedy annuals from theNew World tropics Although this percentage of introduced species is low comshypared with the figure for the whole of Australia (10 per cent of all plant speciesare invasive) it is clearly a cause of worry for a nature reserve which is attractingan increasing number of visitors

Invasions have increased by an average of 16 species per year since 1948 astourism and mining have increased bringing in more habitat disturbance Mostalien species are found around camp-sites car parks roads and mines One of thebiggest problems is a fast-growing shrub (MimoJa pjgra) This plant was introshyduced deliberately into the Northern Territory from South America and was notrealized to be a serious nuisance until around 80 years later It has spread overthe alluvial floodplains changing herbaceous swamps into shrublands This inturn affects wildlife There has been a major effort to control the plant

There are also many other indirect ways in which alien plant species are spreadhere Feral water buffaloes for example make a major contribution to invasionsnear floodplains as they disturb the ground

Further reading

Kirkpatrick J 1994 A Continent Tramformed Melbourne Oxford University PressA concise discussion of human impacts on the natural vegetation of Australia

12 HABITAT Loss AND

FRAGMENTATION

One of the conscquences of human activshyitia is that many naturaJ habitats bc=comereducro in extent and also bc=come ampagshymented into isolated patches Figure 1114shows how both these processc=s haveoccurred in the forest cover of a part ofcentraJ England in the last 1500 yearsWhereas at the end of Romano- Britishtimes (AD 400) there were still large exshypanses of forest there are now only verysmall islands of forest in a sea of agriculshytural land

Certain types of habitat may be lostbecausc= of changes in agriculturaJ pracshytica In Britain for example the botanishycal diversity of much pastureland has been

Figure 1114 Forest fragmentation inWarwickshire England from AD 400 to1960 Forested areas are shown inbladeSource Wikove et aI (1986) figure 1

Habitat loss and Fragmentation 69

reduced as many old meadows have bunreplaced with fields planted solely withgrass (leys) or treated with selective hershybicides and fertiliurs This treatment cantake out of the habitat some of the basicrequirements essc=ntial for many speciesFor exampk the larva of the commonblue bunerfly (Polyommatus jcarus) feedsupon birds-foot trefoil (Lotus cornjeulshyaoo) This plant disappears when pastureis ploughed and converted into a grassfidd or when it is treated with a selectiveherbicide Once the plant has gone thebutterfly vanishes too because it is notadapted to feeding on the plants grown inleys of improved pasture Likewise numshybers of the large blue butterfly (Maculjneaarion) have decreased in Britain Its larvaelive solely on the wild thyme (Thymustiruul a plant which thrives on doseshycropped grassland Since the decimarionof the rabbit by myxomatosis conditionsfor the thyme have been less favourable50 that both the thyme and the large bluebutterfly have declined

Another major land-usc change of reshycent decades has been the replacement ofnatural oak-dominated woodlands in Britshyain and e1sewhere by conifer plantationsThis also has implications fOr wildlife Ithas been estimated that where this changehas totken place the numbc=r of species ofbirds found has been approximately halvedLikewisc the replacement of upland sheepwalks with conifer plantations in southern$corland and northern England has led toa sharp decline in numbers of ravens Theraven (Corvus eorax) feeds on carrionmuch ofwhich it obtains from open sheepcountry Other birds mat have sufferedfrom moorland areas being planted withforest trees are scera1 types of waderthe golden eagle peregrine falcons andbuzzards

Many species of birds in Britain havedeclined in numbers over the last twO deshycades because of habitat changes resulting

70 Thc Biosphere

from more intensive fuming methodsTheS( include no longer leaving fallowsless mixed farming ncw crops modernfarm management uS( of biocides andhedgerow removal

Reducing the areas of land covered byparticular habitats has a direct impact onthe fortunes of species It is usdul to secthe remaining fragments of habitat asislands We know from many of the classicstudies in true island biogeography thatthe number of species living al a particularlocation is related to its area Islands supshypurt fewer species than do similar areasof mainland and small islands have fewerspecies than do large ones Thus it maywell lollow that if humans destroy thegreuer part of a vaSI belt of natural forestleaving just a small reserve initially it willbe middotsupemnlrated with species containshying more than is appropriate to its areaunder nuural conditons Since there willbe tCwer individuals of each of the speciesliving in the forest now the extinction rat(will increase and the number of specieswill decline For this reason it is a soundprinciple to make rescrves as large as posshysible A large reserv( will support mor(species by allowing the existence of brgerpopulations and keeping extinction rateslower Size of course is not everythingand other factors such as the shape ofreserves and the existence of links betweenreserves arc also important

Reduction in area of habitat leads to

reduction in numbers of organisms Thisin turn can lead to genetic impoverishmiddotment through inbreeding with particuJarlymarked effect on reproductive performshyance [nbrttding degenention is howevernot the only effect of small populationsize In the longer term the depletion ofgenetic variety is more serious since itreduces the capacity for adaptive changeIt is therefore very important to provideenough space especially for th~ animalsthat require large expanses of territory For

example the population density of the wolfis arout one adult per 20 sq km and ithas been caJculaled thal for a viable popushylation to exist one mighr need 600 indishyviduals ranging over an area of 12000sq km The significance of this is apparentwhen onc realizes that most narure reshyserves art small 93 per cent of the worldsnational parks and reserves havc an arealess than 5000 sq km and 78 per centcover less than 1000 sq km

Habitat fragmentation has SOffiC othtrmajor clTects One of these is loss of habimiddottat heterogeneity In other words indiovidual fragments may lack the full rangeof ditlcrcnt habitats found in the originalblock For insnnce a small patch ofwoodmay not contain a reliable water supplyLikewise sollle species - certain amphibshyians for example - require two or morehabitat lypCs Habitat fragmtntation maymake it impossible for these animals tomove between habitats

A second effect of fragmentation is thatthe new landscape that replaces the orishyginal habitat such as human setdementsor agricultural land may act as a barrierpreventing colonization and interchangebetween groups Also the new landscapesmay enable populations to build up ofanimals that arc harmful to species withinthese fragments

A third consequence of fragmentationis what are called edge effects Some anishymals do well in edge habitats that is theboundary areas around the rim of theisland but others suffer For examplemany nest predators occur in higher denmiddotsities around forest edges

A fourth effect is secondary extinctionsFragmentation disrupts many of the imshyporum ecological interactions of a comshymunity For example small woodlandwands in the eastern USA contain few ifany of the large predators (eg mountainlions) that would nonnally regulate thenumber ofsmaUcr omnivorous species (eg

racoon) Th~ omnivores can thus preyunhindered upon the eggs and young of

FURTHER REAoING

Habitat Loss and Fragmentation 71

the forest songbirds and may wi~ themout

Wilcove D S McLellan C H and Dobson A P 1986 Habitat fngmemation inthe temperate zone In M E Soule (cd) OmserJl4tion Biology The Science ofSc4rcityand DiJlenity pp 251-6 Sunderland Massmiddot Sinauer AssociatesA short but useful chapter in an advanced book

Plate 1111 A flock of Lesser Snow Geese (NHPARobert Erwin)

_72 The Biosphere

Texas Gulf coast habitat changes and the LesserSnow GooseThe changing fortunes of the LesserSnow ~ (Chen caeruJescenscRerulmens) population in Tnasshow interesting links betweenhabitat changes and wildlife Presshyently around 600000-850000Lesser Snow Geese winter here everyyear (Robertson and Slack 1995)Until the 1920s the Lesser SnowGeese wintered mainly on coastalmarshes but now they arc found onthe inland prairie as well

During the twentieth century theTexas Gulf coast has secn the rise ofpetroleum rdining and oil extractionindustries coupled with the spreadof rice cultivation and a boom inpopulation Nearly 50 per cent ofthe entire USAs chemical producshytion is bascd in the Houston areaand 73 per cent of the US petroshyleum industry is there Rice cultivashytion peaked at 254800 hectares in1954 and now covers an a~a ofaround 141000 hectares These diverse changes to the landscape have causedsome areas to become more suitable for the Lesser Snow Goose while other areashave become less attractive in terms of availability of food and water

The wintering grounds of the Lesser Snow Goose spread to the prairies beshytween the 1920s and the 19505 following the spread of rice cultivation althoughthe movement of the birds lagged behind the expansion of the ricefields by someyears These changes may also have been encouraged by alterations to the coastalmarsh areas as urban and industrial development from the 1940s onwards led tomarsh drainage and pollution

The changes in wintering range were accompanied by a growth in populationnumbers the Lesser Snow Goose population peaked at around 813000 in theearly 1980$ Since then numbers have declined in association with declining riceproduction (the area sown with rice declined by a third from 1978 to 1991) Thisdecline in rice cultivation was in tum related to the lack of federal price supportSfor rice growers which made other crops more economicaUy viable

An airpon planned for construction on Katy Plains would afkct 1168 hecuresdirectly and 16)00 hectares indirectly This project will have further impacts onthe distribution and population numbers of the Texan Lesser Snow Geese

Extinctions in the Past 73

13 EXTINcrIONS IN THE PAST

Extinctions are nothing new They are apart of evolution and spasms of extincshytion have recurred through geologicaltime There have been five major massglobal extinctions over the last 600 milshylion years (figure IU5) The last of theseoccurred at the boundary between theCretaceous and Tertiary periods about66 million years ago This was when theextinction of the dinosaurs took placepossibly because of the environmentalimpact ofa massive meteorite crashing intothe Earth or perhaps because of somemajor volcanic eruptions The other massextinctions took place in earlier periodsthe Ordovician (440 million years ago)the Devonian (365 million years ago) thePermian (245 million years ago) and theTriassic (210 million years ago)

We arc now living in a sixth spasm ofmass global extinction This started toshywards the end of the Icc Age (round about11000 years ago) and is accelerating at

the present time Humans are implicatedin this sixth spasm though for prehistorictimes there is a major controversy as towhether the wave ofextinctions might havea natural (ie essentially climatic) cause

We have discussed present-day exshytinctions and their causes in section 10above on biodiversity In this section wewill explore the role of our prehistoricforebears in causing the decline and exshytinction of many species of animal

Over the last 30 years Paul Martin andco-workers have argued that Late Pleisshytocene extinctions closely followed thechronology of the spread of prehistorichuman cultures and the development ofbig-game hunting technology They wouldargue that there are no known continentsor islands in which accelerated extinctiondefinitely pre-dates the arrival of substanshytial numbers of humans They would alsoargue that the temporal pattern ofextinctions of large land mammals (themegafauna) follows in the footsteps ofStone Age humans They suggest that

~

Iz Iz z z

~~ ~ gt

~ lt I~

I~ ~

sect ~ ~ i ~~bull ii bull6 0 ~

I~pound ei~

~

B~ ]z

~ bull 500 bullMiI1iom of)laI1 ago

Figure 1115 Graph shOWing the five mass global extinctions of marine organisms(indicated by lightning flashes)Source Wilson (1992)

74 The Biosphere

Plate 1112 A reconstruction of mammoth being hunted in Europe at the end ofthe Ice Age Mammoths were one of the megafauna that became extinct at thetransition from the Pleistocene to the Holocene Was climatic change the cause orthe hunting activities of our ancestors (Natural History Museum london)

Mrica and parts ofsouthern Asia were firstaffected in this way with substantial lossesaround 200000 years ago North andSouth America were stripped of large hershybivores between 12000 and 10000 yearsago Extinctions extended into the Holoshycene (ie the last 10000 years or so) onocean islands where humans arrived lateon the scene (figure IIl6)

There were three main types of humanpressure involved in what is sometimescalled Pleistocene overkill

bull the blitzkrieg effect when humanpopulations with big-game huntingtechnology spread rapidly so that anishymal populations decline very quickly

bull the innovation effect when longshyestablished human population groupsadopt new hunting technologies andwipe out fauna that have already beenstressed by climatic changes

bull the attrition effect when extinctiontakes place relatively slowly after a longhistory of human activity because ofloss of habitat and competition forresources

What are the arguments that can bemarshalled in favour of this anthroposhygenic hypothesis First in areas like theHigh Plains of America the first massiveextinctions appear to coincide with thearrival of humans who were numerousenough and who had sufficient technoshylogical skills to be able to kill large numshybers ofanimals Secondly the vast numberof bones at some Late Pleistocene archaeoshylogical sites attests to the efficiency of themore advanced Stone Age hunters Thirdlymany animals unfamiliar with people areremarkably tame and naIve in their presshyence rendering them easy prey Fourthlyin addition to hunting animals to death

~~~~~lOllOOOO JOOOOO 10000 1000 100

YtlllUIO

Figure 1116 The percentage survival oflarge animals and flightless birds overthe last million years in four differentareas The extinction of these organismscoincided doseo with the arrival ofhumans in North America MadagascaIand New Zealand and less decisively inAustralia In Africa where humans andanimals evolved together for millions ofyears the damage was less severeSource Wilson (1992)

humans may also have competed withthem for particular food or water suppliesFifthly the supposed extinction of thelarger rather than the smaller mammalscould be related to thc= effc=cLS of humanprc=dation Large mammals havc= smallnumbers of offspring long gaution pc=rishyOOs and long periods before manlrity isreached This means that populations ofthese animals can survive only a very lowrate of slaughter ~en against primitivehunters

In addition cc=rtain objections havc= beenlc=velled against the climatic change model

Extinctions in the Past 75

which tend to support the anthropogenicmodel It has been suggested for instancethat changa in climatic zones arc gc=nershyally gradual enough to allow bcasLS to folshylow the shifting vegetation and climaticzones of their choice Similar environmentsarc available in North America today aswere present in different locations amiin different proportions during lIt(Pleistocene times Sccondl~ it can beargued that the climatic changes associmiddotated with the multiple glaciationsintugladals pluvials and interpluvialsearlier in the Icc Age do not seem [0 h3Ccaused the same striking degree of sjXcklgtelimination as the changes in the LattPleistoc~n~ A third difficulty with thec1imati cause theory is that animals likethe mammoth occupied a broad range ofhabitats from Arctic to tropical latitudesso that it is unlikely that all would perishas a result of a climatic chang~

However thc=re is some support for thealt~rnative climatic hypoth~sis namely thatrapid and substantial climatic change atthe end of the last Icc Age led to th~

extinction of the great mammals lik~ themammoth The migration of animals inresponse to the npid climatic change atthe cnd of the Pleistocene could bc haludby geographical barriers such as highmountain ranges or seas According to thispoint of view Africa is rclativc=ly rich inbig mammalian fauna because thc Africanbiota is not or was not greatly r~stricted

by any insupc=rable geographical barrierAnother way in which climatic chang~

could cause extinction is through its influshyence on the spread of disease It has beensuggested that during g1acials animalswould bc split intO sepal2te groups CUtoff from one another by ice sheets Theseisolated groups might lose immunity tocertain diseases to which they werc= nolonger exposed Then as the ice melted(before 1lOOO years ago in many areas)contacts bctwcen group5 would once again

76 The Biosphere

be made enabling any diseases to whichimmunity had been lost to spread rapidly

It has also been noted recently that insome areas it was not only the greatmegafauna that became extinct Some smallanimals and birds that would not have beenhunted by humans also died out Moreshyover as the radiocarbon dates for earlysocieties in some countries like Australiaand Brazil are pushed back it becomesincreasingly clear that humans and severalspecies of megafauna were living togethertor quite long periods This is underminshying the idea of rapid overkill Mso ifhumans were primarily responsible for thewaves of extinction how does one explainthe survival of many big game species in

FURTHER READING

North America well imo the nineteenthcemury~

The Late Pleistocene extinctions mayof course have been caused by bothclimatic and anthropogenic mechanismsor by a combination of the two types Forexample animal populations reduced andstressed by climatic change would be morevulnerable to increasing levels of humanpredation Nonetheless the rapidity withwhich extinctions took place in Madagasshycar New Zealand and the Pacific islandsafter they wete first settled in the Holoceneis striking evidence ofhow even quite smallnumbers of technologically not vetyadvanced people can cause major environshymental change

14 BIOTECHNOLOGY GENETIC

ENGINEERING AND THE

ENVIRONMENT

Biotechnology is the manipulation of livshying organisms and their components (eggenes or gene components) for specifictasks Genetic engineering is one form ofbimechnology involving the isolation ofgenes and gene components that conferdesired traits and their transfer betweenspecies It is also sometimes called recomshybinant DNA technology This branch ofscience has now reached a level where it ispossible to transfer genes between unnshylated species or types of organisms

There are many applications of biotechshynology that arc ofenvironmental relevancein agriculture resource recovery and re-

Ehrlich P R and Ehrlich A H 1982 Extinetiol London GollanczAn accessible treatment for the general reader

Martin P S and Klein R G 1984 Pleistocene Extinctions Tucson University ofArizona PressA massive advanced tome from two of the leading scientists involved in the study ofthe possible role of humans in causing extinctions in prehistory

cycling pollution abatement and the proshyduction of renewable energy resources

In agriculture biotechnology can helpto maximize energy and nutrient flowsfor example by increasing crop yield andby engineering resistance to disease inshysects and herbicides Nitrate levels can beenhanced by seeding the ground withnitrogen-fixing bacteria Stress tolerance(eg to frost) can be engineered

Biotechnology is also being developedto undertake the recovery of resourcesMineral orcs can be recovered through aprocess called biomining which exploitsthe ability of specific types of bacteria toobtain their energy supply by breakingdown certain types of ore-bearing deposmiddotits Certain micro-organisms can be emshyployed to scavenge metals from wastewaterso that the metals can be re-used

Biotechnology can also contribute topollution aba~ment Bioscnsors areorganisms that can be used to identifY critishycal levels of poUution Other organismscan be uscd to extract pollutants such asheavy metals from wastewater to neutralshyize hazardous substances in the environshyment (bioremediation) or to break downscwage

Another usc of biotechnology is to produce renewable energy resources For exshyample it is possible to extract alcohol fromsome plants this call be used as fuel forautomobiles Protein-rich animal feeds canbe obtained by using algae fungi (indudshying yeasts) and some bacteria to producecellular protein from energy and nutrientsources such as carbon dioxide methanolethanol sugars and carbohydrates

Biotechnology is potentially ofenormousvalue and it may have many environmenshytal benefits For example the environmenshytal advantages of using biotechnology inagriculture include

FURTHER READING

Conclusions 77

bull reduced need for fuelbull reduced usc of pesticidesbull reduced usc of artificial fertilizer thus

also lessening pollution by phosphatesand nitrates

bull increased food supply which could leadto less pressure on marginal lands andon remaining natural ecosystems

Similar types of advantages can apply tothe other uses of biotechnology which wehave described

On the other hand there are possibledisadvantages These include

bull the potential to create invasive organshyisms - as for instance when genesescape into the wild relative of an enshygineered crop creating potential pests

bull the potential to create organisms whichare toxic or contain toxic components

bull the potential to create organisms espeshycially bacteria that could profoundlyalter the nature of global biogeoshychemical cycles

Mannion A M 1991 Global Environmental Change Harlow LongmanA very general but useful treatment of all aspects of global change both natural andanthropogenic

Mannion A M) 1995 Agriculture and Enviroilmental Change Chichester WileyA more detailed treatment by the same author of biotechnology as one aspect of theagricultural impact on the environment

15 CONCLUSIONS

In this chapter we have demonstrated thathumans have had effects on the biospherefor a very long time For many good reamiddotsons our early ancestors developed the useof fire This powerful technological toolhas had many positive ecological conseshyquences It may also have had a majoreffect on some of the worlds biomes andvegetation types induding savannas andMediterranean shrublands The manage-

ment of fire is an important tool for themanagement ofsome major environmentsAs the Yellowstone study has shown firesuppression policies can have adverseeffects

Other major changes in the state of theworlds biomes include desertification anddeforestation Both phenomena are diffishycult to define and to quantifY There arcvarious ways in which desert margins andrain forests can be managed so that theseprocesses can be kept under control Even

78 The Biosphere

secondary forests which result from humanuse of tropical moist forests have positivevalue

With many such changes however wehave to recognize that very many proshycesses both anthropogenic and naturalmay have played an important role Thisis evident from a consideration of theorigin of tropical savannas heathlands andmid-latitude grasslands Indeed we haveseen recently how complex causes can bein the case of forest decline in Europe Aswe point out thete is no single type ofInrest damage and no single cause Equallywe should not necessarily equate urbanshyization with a reduction in biodiversity Thegrowth of dties as illustrated by Chicagohas major ecological consequences bur notall of them have negative impacts

Nonetheless there are some major habishytats and particular habitat types that deshyserve particular attention and protectionbecause of their importance for the preshyservation of biodiversity These indudewetlands and other crucial ecological hotspots such as the Fynbos heathlands ofsouthern Mrica or the forests inhabited

KEy TERMS AND CONCEPTS

biodiversiry biodiversity hot spotsbiomass burningbiotechnologydeforestationdesertificationecological explosionecosystem servicesecotonesedaphic conditionfufire suppressionforest decline and diebaekhabitatheathland

by the Giant Panda in China Many habishytats arc being considerably modified bythe spread of organisms introduced byhumans These organisms may then invadesusceptible habitats of which oceanicislands are a notable example Many otherhabitats are being greatly reduced in areaand continuity This creation of smallltislands of habitat increases the likelihoodof species extinctions Extinction is an irshyreversible process which results from bothnatural and anthropogenic causes It is oneof the great challenges we face in comingdecades

We are emering a new era in the humanmanipulation of the biosphere Biotechshynology and genetic engineering both offergreat opportunities and raise a great needlor prudence

The many case studies discussed in thispart of the book show how complex hushyman impacts on the biosphere are howscience cannot as yet answer all the quesshytions and how the many different presshysures on human societies affect the waysin which they use and abuse the resourcesof the biosphere

invasionskeystone speciesLessepsian migrationmegafaunaovercultivationovergrazingPleistocene overkillprescribed burningsalinizationsavannasecondary focestspecies diversityurban ecologywetlandswilderness

Points for Rl=view 79

POINTS FOR REVlEW

hat do you undefSlilnd by the term biosphete~

Why was fire one of humankinds first technological achievements~

ShouJd fires Ix suppresscd~

How would you identify if desertification was raking place~

How might you aim 10 reduce the effects of desertification~

In what ways might tropical deforestation rates be reduceJ~

gtltscss the role of predisposing causal resulting and maintaining tactors ill thedevelopment of grasslands savannas and heathlands

Discuss the many different factors that could account for lorest declinc

What characteristics of cities determine their impact on the environment

Why and how should wlt1ands be conserved

What do you understand by the term biodiversity~

What arguments would you use to support the view that biodiversity lgthOlild Illmaintained

Why should we be interested in ecological invasions and explosions~

What do you understand by the term habitat~

Did climatic change or human impact cause Pleistocene eXlinctions~

Consider the potential role of biotechnology in environmental prorCluon JnJdegradation

PART III

The Atmosphere1 Inrroduction 832 Amhropogenic Climate Change

bull The Role ofAerosols 83The dust bowl ifI

bull The GulfWar oil lites hype and reality 883 Anthropogenic Climate Change

bull The Role of Land Cover Changes 904 The Enhanced Greenhouse Effect

and Global Warming 92bull Global warming and UK agrigculture 97

5 Urban Climates 98bull The implications ofsome urban heat islands 100

6 Urban Air Pollution 102bull Air pollution in South African cities

the legacy ofapanheid 1087 Ozone Depletion and Ozone Pollution 1108 Acid Deposition 1169 Conclusion 120

Key Tenus and Concepts 121Points for Review 121

Aerosols 83

2 ANTHROPOGENIC CLIMATE

CHANGE ThE ROLE OF

AEROSOLS

Let us first consider the possible effects ofaerosols An aerosol is defined as an intimatemixture of two substances one of whichis in the liquid or solid state disperseduniformly within a gas_ The tcnn is normallyused to describe smokecondensation nuclei

and nitrous oxide (the greenhouse gases)play in global wurning There are howeverother mechanisms by which humans maycause global or regional climatic changeThey are not yet fully understood and inthe long term they may not have so greatan impact as the greenhouse gases Nevcrshytheless they may have a significant role toplay In some cases morcovn they couldscrve to counteract the greenhouse ctrect Incertain specific localities they may alreadybe producing a decipherable climatic trend

The mechanisms so far idenrificd thatmay be related to human innuenccs onglobal and regional climates and their maineffeclS can be summarized as follows

Greenhousegases

bull Gas emissionsCarbon dioxideMethaneChlorofluorocarbonsNitrous oxide

bull Aerosol BeneratwnDustSmokeSulphates

bull Therntal poUuti01lUrban heat generation

bull Albedo changeDust addition to icc capsDeforestation and afforestationOvergrazingExtension of irrigation

bull Altrltion of watr flow il rivers andoceansWater vapour changeDeforestationIrrigation

bull

When me gn~at American geographer andconservationist George Perkins Marshwrote Man and Natllr in 1864 (~e partIV section 3) in which he surveyed theways in which humankind had transformedthe Earths surface he scarcely consideredthe various ways in which humans mightaffect the quality of the atmosphere andthe nature of the Earths climate Howshyever just over 100 years later it is thisvery area that is the cause of greatest conshycern to many scientists and to others inshyterested in environmental matters To besure loatl air pollution was a major conshycern at the time Marsh wrote but for themost part broader-scale human impactson the atmosphere and climate were notgiven very much attention

Since the mid-nineteenth century whenMarsh wrote his book world industrialproduction and energy consumption haveaccelerated dramatically All sorts of newtechnologies including noably the intershynal combustion engine have been inuoshyduced As a consequence a cocktail ofgases that is growing in quantity and varishyety has been emitted into the atmosphereThis has created problems of poor airquality which can affect not only humanhealth but also the state of whole ecosysshytems (for example by acid rain) and alsoof global climatic conditions (for exampleby the greenhouse effect) It is also apparshyent that changes in land use (such as deforshyestation) of the type discussed in part IIarc causing changes at the Earths surfacewhich may have impacts on the climateGreat unceruinty still surrounds many ofthese issues but there is no denying thatmatters such as global wanning oronedepletion and acid rain have very greatimplications that deserve intensive study

Recent years have ~en a great concenshytration of interest in the so-called greenshyhou~ effect (section 4 below) and therole that gases like carbon dioxide methane

1 INTRODUcrlON

84 The Atmosphere

freezing nuclei or fog contained within theatmosphere or other pollutants such asdroplets containing sulphur dioxide ornitrogen dioxide (Encyclopaedic Dictionshyary of Physical Geography 1985 p 6)Many atmospheric aerosols (eg thosederived from volcanoes sea spray or naturalfires) were not placed there by humansHowever humans have become increasshyingly capable of adding various aerosolsinto the air For example one consequenceof the industrial revolution has been theemission of hugely increased quantities ofdust or smoke particles into the loweratmosphere from industrial sources Thesecould influence global or regional tempershyatures through their impact on the scanershying and absorption of solar radiation

The exact effects of aerosols in the atmoshysphere are still not dear however yenhemeradded aerosols cause heating or cooling ofthe Earth and atmosphere systems dependsnot only on their intrinsic absorption andbackscatter characteristics but also on theirlocation in the atmosphere with respect tosuch variables as cloud cover cloud reflecshytivity and underlying surface reflectivitySo for example over ice caps grey aerosolparticles would warm the atmosphere beshycause they would be less reflective than thewhite snow surfuces beneath Over a darkersurface on the other hand they wouldreflect a greater amount of radiation leadshying to cooling Thus it is difficult to assessprecisely the effects of increased aerosolcontent in the atmosphere

Uncertainty is heightened because of thetwo contrasting tendencies ofdust the backshyscattering effect producing cooling andthe thermalmiddot blanketingeffect causing warmshying In the second of these dust absorbssome of the Earths thermal radiation thatwould otherwise escape to space and thenre-radiales a portion of this back to theland surface raising surface temperaturesNatural dust from volcanic emissions tendsto enter the stratosphere (where backshyscattering and cooling are the main con-

sequences) while anthropogenic dust morefrequently occurs in the lower levels ofthe atmosphere where it could cause thershymal blanketing and warming

Industrialization is not the only source ofparticles in the atmosphere nor is a changein temperature the only possible conseshyquence Intensive agricultural exploitationof desert margins such as in RajasthanIndia can create a dust pall in the atmoshysphere by exposing larger areas of surfacematerials to deflation in dust storms Thisdust pall can change atmospheric tempershyature enough to cause a reduction in conshyvection and thus in rainfall Observationsof dust levels over the Atlantic during thedrought years of the late 1960s and early1970s in the Sahel suggest that the deshygradation of land surfaces there led to athreefold increase in atmospheric dust atthat time It is thus possible for humanshyinduced desertification to generate dustwhich in turn increases the degree ofdesertification by reducing rainfall levels

Dust storms generated by deflation fromland surfaces with limited vegetation coveroccur frequently in the worlds drylandsThey happen naturally when strong windsattack dry and unvegetated sandy and siltysurfaces Their frequency also varies fromyear to year in response to fluctuations inrainfall and wind conditions At presenthowever in some parts of the world thedust entering the atmosphere as a result ofdust storms is increasing because of theeffects of human activity In particular proshycesses such as overgrazing which are partof the phenomenon of desertification (seepart II section 3) strip the protective vegetashytion cover from the soils surface Elsewheresurfaces may be rendered more susceptibleto wind attack because of ploughing ordisturbance by wheeled vehicles

Atmospheric aerosols can be an imporshytant source of cloud-condensation nucleiOver the worlds oceans a major source ofsuch aerosols is dimethylsulphide (DMS)This compound is produced by planktonic

algae in seawater and then oxidizes inthe atmosphere to form sulphate aerosolsBecause the albedo of clouds (and thusthe Earths radiation budget) is sensitiveto the density ofcloud-condensation nucleiany factor that has an impact on planktonicalgae may also have an important impacton climate The production ofsuch planktoncould be affected by water pollution incoastal seas or by global warming Charlsonet al (1992) believe that anthropogenicallyderied sulphate aerosols could significantlyincrease plamtary albedo through theirJirect scattering of shon-wavelength solarradiation and their modification of theshort-wave reflective properties of cloudsThus the~ could eXtTt a (Ooling influenceon the planet Charlson et al maintainthat this eflect could be as great as thecurrent hllmanmiddotillduccJ global warmingbut acting of coursc in the opposite waya~ global cooling

A nuckar conflict could produce the mostcatastrophic dlects of anthropogenic leroshysols in the atmosphere Explosion tire andwind might generate a great pall of smokellld dust in the atmosphere which wouldmake the world dark and cold It has beenestimated that if the exchange reached alevd of several thousand megatons a nushyclear wimer would occur in which temshyperatures over much of the world wouldbe depressed ro well below freezing point

Fears were also expressed that the heavysmoke palls generated by oil-well fires inthe Gulf War of 1991 might have seriousclimatic impacts The actual ctlccts arc stillnotckar Howevt=r preliminary studies havesuggested that because most of the smokegenerated by the oil-well fires stayed in thelower troposphere and remaineJ in the airfor only a shon time the eflects (some coolshying) were local rather than global It alsoseems that the operation of the South Asianmonsoon was not significantly affected

Although some of this discussion of theeffects of aerosols in the atmosphere isspeculative at the global scale this is not

Aerosols 85

so at the more local scale where it is clearthat human actions can change levels ofvisibility This is especially true in urbanareas where the concentration of Iightshyscanering and light-absorbing aerosols inthe atmosphere is greatest For examplebefore the Clean Air Acts (most notablythose passed in 1956 and 1968) LondonsuHered some severe smogs that reductJvisibility to a few metres and killed thoushysands of people (eg in the winter of1952) Reduced burning of coal since theClean Air Acts has cut down smoke emisshysions improving visibility in many pans ofBritain Fogs have become much rarer overthe last three decades

Sulphate emissions ftom cOlI-fired powerstations have also btin riduced An analvshysis ofchanges in visibility at a largi numberof sites in the UK shows that oetwecn1962 and 1990 the median atmosphericisioility has improved ti-om 109 kill to

260 km (Lee 1994) Figure IIIl showsthe number of days per ~ear when tl)goccurred in Britain over the period 1950shy83 It is clear that although the ti-equellcyof fogs has not changed a great deal incoastal areas (where they arc largely anatural phenomenon) ill the inland inshydustrial heartland they have declined verysubstantially as a result of Clean Air legismiddotlation and changes in industrial technology

The total suspended particulates (TSP)is the total mass of aerosol particles pervolume of air (usually measured in Ilg perCll metre of air) or this TSr much recemconcern has IOclised on the respirable susshypended particulates (RSP) panicles withdiameters of less than 10 11m (also knownas PM10s) These small particles arc theonly ones which can be deposited in therespiratory system - lungs and bronchialtubes - as larger particles are filtered outby the nose mouth and throat In manyurban areas concentrations of RSP havebecome worryingly high The build-up ofparticles in lungs can contribute to branmiddotchitis and other respiratory diseases

86 The Atmosphere

bull

~[ -i ~o 19~~ 30 OI~0 lll96S-9c 2(1 bullJ97O-4C 10 ~ilm9

iTll93lgt-3o OJU(l~) -M~III00

fidays widfog (lhitk fos)1974-83

~ lJO(~6)

- Finningl~

bull 20HU)Widdingtl)Jl

_ ~1~ alnall2Q8(72)

llHU)

133(27)

1ltmiddotilL

H28)fjloo

~G18l(U)

bullRiIIgll)

Sllllwburybull

i 1lt

lU(~6)

bull Wick~J 100(20)

bull1 Tumhoo~

tu1h89(10)

11111U1h66(17)

SquimG~tt

Eslubllflluir L10HI7)

~H51 Mlwpn lLLU

us (1)

Figure 1111 The spatial variation of fog over Great Britain 1950-1983Source After Musk (1991) fig 66

Aerosols 87

The dust bowl

Tht= dust bowl of tht= 1930s in tht= Grt=at Plains of tht= USA is pt=rhaps tht= bestknown and most oftt=n quott=d t=umpk of largt=-sca1t= wind t=rosion and dU$[stonn activity anywht=rt= in tht= world Tht= most KVt=rt= storms (black blizzards)occurr~d in th~ dust bowl betw~~n 1933 and 1938 and wt=r~ most frc=qu~nt

during th~ spring of th~se y~an At Amarillo T~xas at th~ h~ight of the periodon~ month had 23 days with at I~ast 10 hours of airbocn~ dust and in on~ infiv~ storms visibility was z~ro For comparison th~ long-t~rm average for this partof T~xas is just six dU$[ storms a year

The reasons for this most dramatic of ~cological disast~rs have been widelydiscussed Blame has largely been laid at the feet of the pioneering farmers andsod busters who ploughed up the plains for cultivation For although duststorms are fr~quent in the area during dry years and the 1930s was a droughtperiocl the 5CaI~ and extent of the 1930s events wen unpr~cedented

Plate 1111 In the 19305 (the dirty thirties) the Great Plains of the USAexperienced many black blizzards (dust storms) caused by a combination ofa run of dry hot years and the ploughing up of large tracts of land forgrain production Similar phenomena occur at the present day in the Sahelzone of West Africa This example occurred in Mali in 1977 (Rod McIntosh)

Further reading

Goudie A S and Middleton N J 1992 Tht= changing fnqut=ncy of duststornu through time CJjti( Clmnge 20 197-225

88 The Atmosphere

The Gulf War oil fires hype and reality

I

I KUAlT

I---~----

I SAOOI ARABIA c-i-~)

Following the Iraqi invasion ofKuwaiton 2 August 1990 deliberate oil spillsand oil-well fires were used by the Iraqileader Saddam Hussein as a weaponof war In January 1991 Iraqi torcesdetonated over 800 oil wells (out ofatoal ofaround 1116 wells in Kuwait)ofwhkh 730 exploded Most of these(656) burned lor several monthsmd tht rtlllainder gushed om oilAround I billion barrels of cmde oilwere lost reprtsenting 15-2 per(ellt of the entire Kuwliti oil reserve

Immediately atter this cpisode scishycntists and environmental activistsspcculated that the fites kt alone the spilled oil would have serious local regional1Ild global climatic impacts Doomsday scenarios were slggested including dramati(global (ooJillg similar to thl nuclear winter hypothesis slIplr-acid rain diversionof the Asian summer monsoon and rapid SIlOW melt from talls of bla(k snow

Liter however scientific studies involving remote scnsing ground-level monimiddottoring and computer modelling studies showed that the global climatic impactshad heen exaggefltted The smoke was not injccted high enough to spread overlarge areas of the Northern Hemisphere most of it was confined to an altitudeof between I km and 3 km Reneath the plume of smoke daylight and daytimetemperatures were reduced Simulation modds suggested a decrease in surfacedaytime air temperaures of between 4middotC and 10C (Bakan et aI 1991 Browninget aI 1991) There has been no permanent winter no major diversion of themonsoon and no super-acid rain

Scientific studies have shown however that the months of burning producedemissions of sulphur dioxide carbon monoxide hydrogen sulphide carbon dioxshyide and nitrogen oxides (estimates are showll in table 1Il1) Particulates containshying partly burned hydrocarbons and metals such as vanadium and nickel were alsodischarged into the atmosphere These emissions may have severe local impactsFor exalllple monitoring of inhalable particulate matter (PM IOs) in the EasternProvince of Saudi Arabil during and after the Kuwaiti oil fires found high conshycentrations at various phlCes higher than the maximum permissible level of340 ~g pel- Cl1 metre (Husain and Amin 1994) Other studies in Kuwait itselfin tne April to early May 1991 showed high levels of total airborne particulatematter (soot organic carbon sulphate and chloride) but rather low levels ofsulphur dioxide nitrogen dioxide and carbon monoxide

The local health and ecological impacts of such elevated pollution levels arenow of major concern Some of the compounds released may Ix carcinogenicThe inhalable PMIOs may cause severe health problems Hospital studies inKuwait in 1991 showed a moderate rise (about 6 per cent) in lung and heartcomplaints (Hoffman 1991) Clearly long-term health issues need monitoring

Aerosols 89

Plate 1112 In the Gulf War of 1991 large quantities of oil were burnt ashere at the AI Burgan oil field Fears were expressed that this could have asevere climatic impact In the event these fears were to a large extentmisplaced (EPLJim Hodson)

Table 1111 Predicted annual production of kuwaltl 011 flres in 1991

Type of emission Amount Comparison with current(Tg per year) gfobal emissions

Fine particulate black smoke 5 Roughly onemiddotthird of carbonparticles produced by tropicalbiomass burning

Sulphur (as S oxides) 2 Slightly more than current UKannual S emissions

Nitrogen (as N oxides) 05

Carbon (ultimately as CO2) 60

Tg Teragramme I x 101lg

Source Browning et al (1991)

1988 UK emissions of nitrogenoxide were 075 Tg

About 1 of current globalannual CO2 emissions from Jfossil fuel combustion _

90 The Atmosphere

3 ANTHROPOGENIC CLIMATE

CHANGE ThE ROLE OF

LAND COVER CHANGES

Another major possible human-inducedcause of climate change is change in thereflectivity (albedo) of the ground surfaceand the proportion ofsolar radiation whichthe surface reflects Land-use changescreate differences in albedo which haveimportant effects on the energy balance ofan area Tall rain forest may have an albedoas low as 9 per cent while the albedo ofa desert may be as high as 37 per centThere has been growing interest recentlyin the possible consequences of deforestashytion on climate as a result of the associshyated change in albedo Ground deprivedof vegetation cover as a result of deforshyestation and overgrazing (as in parts ofthe Sahel) has a very much higher albedothan ground covered in plants This couldaffect temperature levels Satellite imageryof the Sinai-Negev region of the MiddleEast shows an enormous difference inimage between the relatively dark Negevand the very bright Sinai--Gaza Strip areaThis line coincides with the 1948-9armistice line between Israel and Egyptand results from different land-use andpopulation pressures on either side of thatboundary Otterman (1974) has suggestedthat the albedo affected by land use hasproduced temperature changes of the orderof SoC

Charney et al (1975) have argued thatthe increase in surface albedo resultingfrom a decrease in plant cover would leadto a reflection outwards of incoming radiashytion and an increase in the radiativ( coolmiddoting of the air Consequently they arguethe air would sink to maintain thermalequilibrium by adiabatic compressionand cumulus convection and its associatedrainfall would be suppressed A positivefeedback mechanism would appear at this

stage namely the lower rainfall would inturn adversely affect plants and lead to afurther decrease in planr cover

This view was disputed by Ripley(1976) He suggested that Charney andhis colleagues when considering the imshypact ofvegetation changes on albedo failedto consider the effect of vegetation onevapotranspiration He pointed out thatvegetated surfaces are usually cooler thanbare ground since much of the solar enshyergy absorbed is used to evaporate waterHe concluded from this that protectionfrom overgrazing and deforestation mightin contrast to Charneys views be expectedto lower surface temperatures and therebyreduce rather than increase convectionand precipitation

The models used by some scholars sugshygest that removal of the humid tropicalrain forests could also have direct climaticeffects Lean and Warrilow (1989) used ageneral circulation mood (GCM) whichsuggested that deforestation in the Annshyzon basin would lead to reductions in bothprecipitation and evaporation as a resultof the changes in surface roughness andalbedo The surface roughness effect occursbecause rain forest has quite a jaggedcanopy and this in turn affects wind flowlikewise a UK Meteorological OfficeGCM shows that the deforestation of bothAmazonia and Zaire would cause precipishytation levels to fall by changing surfacealbedo (Mylne and Rowntree 1992)

Budyko (1974) believes that the presentuse of irrigation over about 04 per centof the Earths surface (13 per cent of theland surface) is decreasing the albedo ofirrigated areas possibly on average by 10per cent The corresponding change in thealbedo of the entire Earth--atmosphere sysshytem would amount to about 003 per centenough according to Budyko to mainshytain the global mean temperature at a levelnearly OlC higher than it would othershywise be

Land Cover Changes 91

Figure 1112 Predictions of the change in climate following a conversion ofAmazonian rain forest to grassland (a) Temperature increase rC) (b) Evaporationdecrease (mm per year) (c) Rainfall decrease (mm per year) (d) Evapotranspirationdecrease (mm per year)Source After Shukla et al (1990)

A change in land use can also lead to achange in the moisture content of theatmosphere It is possible for example thatif humid tropical rain forests arc cut downthe amount of moisture transpired intothe atmosphere above them will be reshyduced This would reduce the potentialfor tain (figure m2(e)) The spread ofirrigation could have the opposite effectleading to increased atmospheric humiditylevels in the worlds drylands The HighPlains of the USA for example are normshyally covered with sparse grasses and havedry soils throughout the summer Evapo-

transpiration there is very low In thelast four decades however irrigation hasbeen developed throughout large partsof the area This has gready increasedsummer evapotranspiration levels Thereis strong statistical evidence that rainfall inthe warm season has been increased bythe use of irrigation in two parts of thisarea one extending through Kansas Nemiddotbraska and Colorado and a second in theTexas Panhandle The largest absolute inshycrease was in the latter area Significandyit occurred in June the wettest of the threeheavily irrigated months The effect appears

92 Thc= Armosphc=rc=

to bc= espc=cially important whc=n stationaryweathc=r fronts occur This is a situationwhich allows for maximum intc=racrionbc=twc=en the damp inigatc=d surface andthc= atmosphc=re Hail stonns and tornashydoes arc= also significantly morc= prc=valc=ntover irrigated dun ovc=r non-irrigated reshygions (Nicholson 1988)

Although wc= have discussc=d albc=doChUlgc= and atmospheric moisture changesas two separate dassc=s of processc=s thc=yneed to be seen as working togc=thc=r Uld

also in association with other mechanismsFor an example of why this is importantwe an look at tropical rain-forest removalThis causa albedo change reduction inmoisture loss by evapotranspiration and achange in surftce roughness The comshybinc=d effects may be considerable (figurem2) They include an increase in temshyIXrature a major dc=crease in loss of moisshyture into the atmosphere and a very majordecrease in rainfall

FURTHER REAoING

Kemp D D) 1994 GlobRl Environmental fuuu A Qimatological Approach 2nd ednLondon RoutledgeA well-iUustratc=d clnr and accessiblc= introduction to many areas of global climaticchange

Figure iII3 (a) The greenhouse effectin the atmosphere (b) A diagramshowing how a greenhouse acts as aradiation blanketSources (a) Houghton et aJ (1990)figure 1 (b) Houghton (1994) figure 22

s-fIl bull -w_IC~ lIt-r-bullbull__ rcc shy

ln6gt radWionis nnintd amp011I

tht eartl

MOll tgtdUIion bull~bytht

urthlltIIfxwi_it

b

4 ThE ENHANCED

GREENHOUSE EFFECT AND

GWBAL WARMING

Planet Earth rcccivcs warmth from thc= sunRadiation from the sun is pardy trappedby the atmosphc=re It passes through thc=atmosphere and heats the Earths surfacc=Thc= warmed surface radiates c=nergy butat a longer wavdength than sunshineSome of this cnc=rgy is absorbed by theatmosphere which as a result warms upThe rest of thc= c=nc=rgy c=scapes to spaceWe call this procc=ss of warming thc= greenshyhouse effc=ct because the atmosphere ispercdved to act rather like glass in a grec=nshyhouse (figure 1113) Although the atmosshyphere consists primarily of nitrogen andoxygen it is some of thc= so-called tracegases which absorb most of the heat inspite of the fact that they occur in verysmall concentrations These are called thegreenhouse gases

Various grc=cnhouse gases occur natushyrally - water vapour (HlO) carbon dioxshyide (COl) methane (CH) ozonc= (OJ)

and nitrous oxide (N20) In recent censhyturies and decades however the quantitiesof some of these greenbouse gases havestarted to increase because of humanactiviues In addition a new type ofgreenshyhouse gas the chloroflurocarbons (CFCs)has been introduced to the atmosphere inthe las[ fifty years

Since the start of the industrial revolushytion humans have been taking stored carshybon om of the earth in the form of fossilfuels (coal oil and natural gas) They burnthese fuels releasing CO2 in the processThe pre-industrial level of CO2 in the atshymosphere may have been as low as 260shy270 parts per million by volume (ppmv)The present level exceeds 350 ppmv andis still rising as is evidem in records ofatmospheric composition from variousparts of the world Fossil fuel burningand cement manufacture release over 6gigatonnes of carbon [Q the atmosphereas CO2 each year Burning of forests andchanges in the levels of organic carbon insoils subjected to deforestation and cultishyvation may also contribute substantially toCO2 levels in the atmosphere perhaps byaround 2 gigatonnes of carbon each year

Other gaslts as well as Calgt will probshyably contribute to the accelerated greenshyhouse effect The dTect ofeach on its ownmay be relatively small but the effects ofall of them combined may be considershyable Moreover molecule for moleculesome of these other gases may be moreeffective as greenhouse gaslts than CO2

This applies to methane (CH4 ) which is21 times more effective than COlgt tonitrous oxide (N20) which is 206 timesmore effective and [Q the CFCs whichare 12000-16000 times more effective

Where do these other gases come fromand why are amounts of them increasingConcentrations of methane are now over1600 parts per billion by volume (ppbv)compared to eighteenth-century backmiddotground levels of 600 ppbv Methane has

Global Warming 93

increased as a result of the spread of ricecultivation in waterlogged paddy fieldsenteric fermentation in the growing numshybers of belching and flatulent domesticcattle and the burning of oil and naturalgas Nitrous oxide levels have increasedbecause of the combustion of hydroshycarbon fuels the uslt of ammonia-basedsynthetic fertilizers deforestation andvegetation burning The increase in CFCsin the atmosphere (which is also associshyated with ozone depletion in the stratoshysphere - see section 7 below) results fromtheir use as refrigerants as foam makersas fire control agents and as propellantsin aerosol cans Use of CFCs is now beingrestricted by various international agreeshyments

The Earths climate has become genershyally warmer over the last century or soand the 1980s saw an unprecedentednumber ofwarm years This has promptedsome scientists to propose that globalwarming as a result of the acceleratedgreenhouse effect has already startedHowever the complexity of factors thatcan cause climatic fluctuations leads manyscientists to doubt that the case is yet fullyproven Most however believe that ifconcentrations of effective greenhousegases continue to rise and attain doubletheir natural levels by around the middleof the twenty-first century then temperashytures will rise by several degrees over thatperiod The Intergovernmental Panel onClimate Change (IPCC) which reportedin 1990 suggested that global mean temshyperature might increase during the nextcentury at a rate of 03degC per decade TheIPeC report of 1996 suggested a bestestimate of20degC increase in temperatureby 2100 (with a range of 1-3SdegC) Thisis somewhat lower than previous predicshytions because of improvements in inforshymation and modelling techniques Coolingeffects of aerosols are taken into accountin this prediction The rise in temperature

94 Thc= Atmosphere

I

Figure 1114 Change in global surface temperature following a doubling of CO2

(a) December January and February (b) June July and AugustSource Kemp (1994) figure 78 using data in Houghton et al (1990)

will not howevc=r bc= thc= samc= across thc=g1obc= In particular high latitudc=s (egnorthern Canada and Eurasia) will showeven morc= pronounced warming perhapstwo to three times the global average(figw-e III4)

Such increasc=s in tc=mperaturc= if thc=yoccur will undoubtedly causc= majorchanges in the general atmospheric circushylation These in turn will cause changc=sin precipitation patterns Overall levels ofprecipitation ovc=r the g1obc= will increasc=as morc= moistl1laquo is relc=ased by higher ratesofevaporation from the oceans However

some areas will get wetter while some willgc=t drier Thc=re is still considerable uncershytainty about what precise pattern precipishytation will take as a result of these changc=sThe very cold dry areas of high latitudesmay well become moister as a warmeratmosphw= will be able to hold moremoisture Some tropical areas may receivemore rain as the vigour of the monsoonalcirculation and of tropical cyclonc=s is inshycreasc=d Some mid-Iatitudc= areas like theHigh Plains of America may becomemarkedly drier

Therc= is however great uncertainty as

to how far the climate may change as aresult of me greenhouse effect The reashysons for this uncertainty include

bull doubts about how fast the global ecoshynomy will grow

bull doubts about what fuels will ~ usedin the future

bull doubts about the speed at which landshyuse changes are taking place

bull uncertainty regarding how much COlwill be absor~d by the oceans and bybiota

bull uncertainties about the role of omeranthropogenic and natural (eg volshycanic) causes of climatic change

bull the assumptions that are built intomany of our predictive general circulashytion models (eg about the role ofdouds)

bull the role of possible positive feedbacksand thresholds that may mean changesare more sudden than anticipated ordo not happen at all

The degree of global warming that IS

proposed for the coming decades does notat first sight appear enormous Howeverit may over a period that is very short ingeological terms produce warmer condishytions than have existed for several millionyears and set up a series of changes thathave important implications both for theenvironment and for humans Some ofthese implications may be benign (eg

Global Warming 95

warmer conditions will enable new cropsto be grown in Britain) but some of themwill be malign (eg more frequent andlonger droughts in the High Plains ofAmerica) Among the possibeenvironmenshytal consequences are

bull more intense widespread and frequenttropical cyclones

bull the melting of alpine glaciersbull the degradation of permafrost in tunshy

dra areasbull the wholesale displacement of major

vegetation belts such as the borealforests of the Northern Hemisphere

bull rising sea levels and associated floodshying of coral reefs deltas wetlands etcand accelerated rates of beach erosion

bull decreased flow of water in streams as aresult of increased loss of moisture byevapotranspiration

bull reduction in the extent of sea ice inpolar waters

bull shifts in the range of certain vectorshyborne diseases (eg malaria)

Many scientists and politicians believe thatthe case has now been made that globalwarming will occur and that the resultingchanges are likely to be so significant thataction needs to be taken In some countriesa policy of no regrets is being promotedThis is a policy under which the reductionof greenhouse emissions is also justifiableon other grounds (see table 1112)

Table 11I2 Examples of no regrets climate-warming policies

Policy

Tree planting

Energy conservation

Energy efficiency

CFC emission control

FURTHER READING

Effect on greenhouse gases

Increased biosphere sinkstrength to absorb CO2

Reduced CO2 emissions

Reduced CO2 emissions

Reduced CFC emissions

Other benefidal effects

Improved microdimate

Improved habitat for manyspedesReduced soil erosion

Reduced seasonal peak riverflows

Conservation of nonshyrenewable resources forcurrent and futuregenerations

Conservation of nonmiddotrenewable resources forcurrent and futuregenerations

Reduced stratospheric ozonemiddotlayer depletion (see section7)Reduced surface UV-S andassociated skin cancer andblindn~s

Houghton J T 1994 Global Warming The Camplere Briefing Oxford Lon BooksA useful clearly written introduction by a leading expcrt that summarizes the keyfindings of the worlds scientific community in this area

Houghton] T Jenkins G J and Ephraums]] (eds) 1990 Climate Change TheIPCC Scientific Assessment Cambridge Cambridge University PressHoughron J T Callander B A and Varney S K (eds) 1992 Climate Change 1992T1Jt Supplementary Report of the IPCC Scientific Mesrmet Cambridge CambridgeUniversity PressHoughton J T Meira Filho L G Callander B A Harris N Kaltenberg A andMaskell K (eds) 1996 Qimau OJtlnge 1995 The Stience of Climate OJange Camshybridge Cambridge University PressThree reports from the global bod) the Intergovernmental Panel on Climate Change(IPCq established to look at the causes and consequences of global warming

Kemp D D 1994 Global Enpironmental Imm A QimatoloBical Approach LondonRoutledge

- -

Figure 1115 The potential distributionof grain maize in the UK underdifferent warming scenariosSource After Parry in Jones (1993) fig 11

Global Warming 97

Global warming and UK agricultureA5 a result ofglobal warming the temshyperltu~ in Britain could rise by severaldegrees Celsius during the coune ofthe next 50-100 yean A change in theclimate of this magnitude would belikely to shift the thermal limits of agshyriculture by around 300 kin oflatitudeand 200 m of altitude per degree Celshysius Several crop species such as wheatmaize and sunflowers have their conshytemporary northern limits in the UKAn increase oftempcrltu~ could thereshyfore assuming that soil conditions ~resuitablelead to a substantial northwardshift of cropping zones This couldtransform the British agricultural landshyscape British 6dds and rural areas mightcome to resemble those currcndy foundfurther south in mainland Europe Foeexample the northern limit of grainmaize which currendy lies in the CIshy

treme south of England (see figureIlLS) could be shifted Kross centnlEngland by a OSmiddotC inclUSC in temshyperature across nocthern England bya lSmiddotC inclease and into the north ofScodand by an increase of 3C

A rise in temperatule apart fromtruufonning the range over which parshyticular CIOP types could be growncould be significant for the agriculshytural sector in other ways For example higher temperatures and more frequentsummer droughts migh[ Ieduce crop yiclds The occurrence of certain plant pestsand diseases could change for better 01 worse

Further reading

Jones D K C (ed) 1993 Earth surface resources management in a warmerBritain GeoIJr4phittd ]owNId 159 124-208

98 The Abnosphere

5 U RJlAN CLIMATES

Climate Stltistics for recent decades showthat many cities have become warmer thanthe countryside around them Climatoloshygists have long spoken of the urban heatisland in the cool rural sea The boundshyary between countryside and city forms asteep temperature gradient or difT to theurban heat island Much of the rest of theurban area appears as a plateau of warmair with a steady but shallower gradient ofincreasing warmth towards the city censhytre The urban core or central businessdistrict with its high-density buildings isa peak where the maximum temperatureis found The difference between this peakvalue and that in the rural sea defines theintensity of the urban heat island

There are various reasons why cities maybe relatively warmer than the fUJa1 areasthat surround them (figure 11I6) Firstcity surfaces absorb significantly moreradiation from the sun than rural surfacesThis is because a higher proportion of the

ttgtlto

Figure 1116 Mechanisms of urban climates

reflected radiation is retained by the highwaIls and dark-coloured roofs and roadsof the city environment These city surshyfaces have both great thermal capacity andhigh conductivity so that heat is storedduring the day and released by night Bycontrast vegetation cover gives plantshycovered rural areas an insulating blanketso that they experience rdatively lowertemperatures both by day and by nightThis effect is enhanced and compoundedby the evaporation and transpiration thatoccur from plant-covered surfaces Secshyondly cities are relatively warm becausethey generate a large amount of artificialheat Energy is produced and then usedby industrial commercial transport anddomestic usen

The heat island effect is nO the onlyway that towns and cities affcd theclimate HDWaCf the effects ofurban areason other aspects of climate are less easilymeasured and explained There is someevidence that rainfall induding that proshyduced by summer thundemorms can be

t t

bull

higher over urban than ruraJ areas Thereart various possible ccasons for this

bull the urbm hcat island generates conshyvection (ie thermally induced upwardmovement of air)

bull the presence of high-rise buildings anda mixture of building heights inducesair turbulence and promotes increasedvertical motion

bull cities may produce large amounts ofwater vapour from industrial sourcesand power stations and also variouspollutant aerosols that act as condenshysation nuclei

The London area provides an interestshying but by no means unique example ofthe effects of large chies on prccipitationlevels In this case it seems that the meshychanical dreer of the city was the maincause of local peak precipitation It hadthis effect by being a mechanical obstacleto air flow on the one hand and by causshying frictional convergence of flow on theother A long-term analysis of thundershystorm records for south-east Englandshows that thunderstorms arc mort freshyquent over the urban area than elsewherein the region (Atkinson 1968) The simshyilarity between the shape of the thundershystorm isopleth and that of the urbanarea is striking Moreover Brimblecombe(1977) found that thunderstorms havebecome steadily more frequent as the cityhas grown

Winds arc another aspect of the urban

Ft1IlTHBR READING

Urban Climates 99

climate There arc twO main aspects to theeffect that cities have on winds first therougher surface cities prescnt in comparishyson with rural areas and secondly thefrequently higher temperatures of the ciryBuildings especially those in cities with avery varied skyline exert a powerful mcshytional drag on air moving over and aroundthem This creates turbulence with rlpidand abrupt changes in both direction andspeed The average speed of the winds islower in built-up areas than over ruralareas However Chandler (1976) foundthat in London when winds arc lightspeeds arc greater in the inner city thanoutside whereas when winds arc strongspeeds arc greater outside the city centreand lower within it Overall annual windspeed in centraJ London is about 6 percent 10000er than outside but for the highershyvelocity winds (more than 15 metres persecond) the reduction is more than twicethat

Studies in two English cities Leicesterand London have shown that on calmdear nights when the urban heat islandeffect is at its greatest there is a surfaceinflow of cool air towards the warmestzones These so-called country breezesare low in velocity and arc quickly sloweddown further by intense surface friction inthe suburban areas One effect of thesebreezes is to transport pollution from theouter parts of an urban area into the citycentre accentuating the pollution probshylem during periods with photochemicalsmogs

Landsberg H E 1981 The Urba Ciuatt New York Academic PressThe classic study

OU T J 1987 amp LAyer Cliatu 2nd cdn London RoudedgeA thorough review of Iocalmiddotscale climates which includes an authoriativc study ofurban clinutes

100 The Atmosphere

Ghe implications of some urban heat islandsI ~ cities grow so does their heat island effect In Columbia Maryland USA for

example when the town had only 1000 inhabitants in 1968 the maximumtemperature difference between residential areas and the surrounding countrysidewas only ImiddotC By 1974 when it had grown to a town with a little over 20000inhabitants the maximum heat island effect had grown to rc

Thus the annual average temperatures over the hearts of great cities can besubstantially higher than those over the surrounding countryside This is dearfrom the temperature map of Paris (figure 1I17(araquo) The outlying weather stashytions have mean annual temperatures of 106-109middotC whereas in cennal Paristhe value is 123C about lSC higher These values have all been reduced toa uniform elevation of 50 metres above sea level to correct for possible orographiceffects

Urban climates are often characterized by different precipitation characteristicsfrom rural areas For example it is remarkable that there tends to be more rainin Paris during the week than at weekends (figure III7(b)) There is a gradualincrease in average rainfall from Monday to Friday (when factories art producingmore heat and aerosols) then a sharp drop for Saturdays and Sundays Theweekend average for May to October was 147 mm whereas the workday averagewas 193 mm - a decrease of 24 per cent for the weekend

In winter months the consequences of urban heat islands can be particularlysignificant in cold regions For example the average date of the last freezingtemperatures at the end of winter in Washington DC in the USA is about threeweeks earlier than in the surrounding rural areas (figure 1I17(c)) In aurumn thecity has on average the first freezing temperature on about 3 November whereasin the outlying suburbs OC will usually be observed about two weeks earlierThus in all the frost-free season will be about 35 days longer than it is in thecountryside Similar figures have been obtained for some other great cities Datafor Moscow Russia suggest an increase of around 30 days without freezingwhile those for Munich in Germany suggest an increase that can be as g~at as61 days

In summer months the urban heat island effect can lead to an increasingdemand for air conditioning and because the energy requirements of air conshyditioning are greater than those of heating the savings in winter heating bills aremore than offSet Moreover air conditioning can aggravate the heat island effectbecause air conditioning plant discharges heat to the outside air where it mixeswith air that has already been warmed up by the hot air forming adjacent to sunlitwalls and pavements

Further reading

Landsberg H E 1981 The Urban Climate New York Academic Press

Urban Climates 101

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Figure 1117 The impact of urban areas on climate (a) Annual isotherms inthe Paris region (b) Precipitation in Paris averaged by day of the week(c) Average date of last freezing temperature in spring in Washington DC(A = International Airport B =White House)Source Landsberg (1981) figures 55 86 525

102 The Atmosphere

6 URBAN AIR POLLUTION

The concentration of large numbers ofpeople factories power stations and carsmean that large amounts of pollutantsmay be emitted into urban atmospheresIf weather conditions permit the level ofpollution may build up The nature of thepollutants (table 1113) has changed astechnologies have changed For examplein the early phases of the industrial revoshylution in Britain the prime cause of airpollution in cities may have been the burnshying of coal whereas now it may be vehishycular emissions Different cities may havevery diffennt Icvels of pollution dependshying on factors such as the level of techshynology size wealth and anti-pollutionlegislation Differences may also arise beshycause of local topographic and climaticconditions Photochemical smogs for

Table 1113 Major urban pollutants

example are a more serious threat in areassubjected to intense sunlight

The variations in pollution Icvels beshytween different cities arc brought out infigure IIIB which shows data for twotypes of pollution for a large range of citytypes The data were prepared for the years1980--4 by the Global Environment Monishytoring System of the United NationsEnvironment Programme (UNEP) Figshyure IIIB(a) shows concentrations of totalparticulate matter Most of this comes fromthe burning of poor-quality fuels Theshaded horizontal bar indicates the rangeof concentrations that UNEP considers areasonable target for preserving humanhealth Note that the annual mean levelsrange from a low of about 35 lig percu metre to a high of about 800 ligper cu metre a range of about 25-foldThe higher values appear to be for rapidly

Type

Suspended particulate matter(characteristically 01-25 11m indiameter)

Sulphur dioxide (5deg2)

Photochemical oxidants ozoneand peroxyacetyl nitrate (PAN)

Oxides of nitrogen (NOx)

Carbon monoxide (CO)

Toxic metals lead

Toxic chemicals dioxins etc

Some consequences

Fog respiratory problems carcinogens soilingof buildings

Respiratory problems can cause asthmaattacks Damage to plants and lichenscorrosion of buildings and materials productionof haze and acid rain

Headaches eye irritation coughs chestdiscomfort damage to materials (eg rubber)damage to crops and natural vegetation smog

Photochemical reactions accelerated weatheringof bUildings respiratory problems production ofacid rain and haze

Heart problems headaches fatigue etc

Poisoning reduced educational attainments andincreased behavioural difficulties in children

Poisoning cancers etc

1

()

)

Urban Air Pollution 103

(For caption see overleaf)

104 The Atmosphere

growing cities in the developing countriesSome cities however such as Kuwait mayhave unusually high values because Qf theirsusceptibility to dust storms from deserthinterlands The lower values tend to comefrom cities in developed areas (eg Westshyern Europe Japan and North America)

Figure III8(b) shows concentrations forsulphur dioxide Much of this gas probshyably comes from the burning of highshysulphur coal Once again the horizontalshaded bar indicates the concentrationrange considered by UNEP to be a reashysonable target for preserving human healthThese data indicate that the concentrationsof sulphur dioxide can differ by as muchas three times among different sites withinthe same urban area and by as much as30 times between different urban areas

In some cities concentrations of polshylutants have tended to fall over recentdecades This can result from changes inindustrial technology or from legislative

changes (eg clean air legislation restricshytions on car use etc) In many Britishcities for example legislation since the1950s has reduced the burning ofcoal Asa consequence fogs have become lessfrequent and the amount of sunshine hasincreased Figure IlL9 shows the overalltrends for the United Kingdom and highshylights the decreasing fog frequency andincreasing sunshine levels The concentrashytions of various pollutants have also beenreduced in the Los Angeles area of C~lishy

fornia (figure 11110) Here carbon monshyoxide non-methane hydrocarbon nitrogenoxide and ozone concentrations have allfallen steadily over the period since thelate 1960s

However both of these examples ofimproving trends come from developedcoumries In many cities in poorer counshytries pollution is increasing at present Incertain countries heavy reliance on coaloil and even wood for domestic cooking

Figure 1118 (a) The range of annual averages of total particulate matterconcentrations measured at multiple sites within 41 cities 1980-1984 Eachnumbered bar represents a city as follows 1 Frankfurt 2 Copenhagen 3 Cali 4Osaka 5 Tokyo 6 New York 7 Vancouver 8 Montreal 9 Fairfield 10Chattanooga 11 Medellin 12 Melbourne 13 Toronto 14 Craiova 15 Houston16 Sydney 17 Hamilton 18 Helsinki 19 Birmingham 20 Caracas 21 Chicago22 Manila 23 lisbon 24 Accra 25 Bucharest 26 Rio de Janeiro 27 Zagreb28 Kuala lumpur 29 Bombay 30 Bangkok 31 Illigan City 32 Guangzhou 33Shanghai 34 Jakarta 35 Tehran 36 Calcutta 37 Beijing 38 New Delhi 39Xian 40 Shenyang 41 Kuwait City (b) The range of annual averages of sulphurdioxide concentrations measured at multiple sites within 54 cities 1980-1984Each numbered bar represents a city as follows 1 Craiova 2 Melbourne 3Auckland 4 Cali 5 Tel Aviv 6 Bucharest 7 Vancouver 8 Toronto 9 Bangkok10 Chicago 11 Houston 12 Kuala lumpur 13 Munich 14 Helsinki 15lisbon 16 Sydney 17 Christchurch 18 Bombay 19 Copenhagen 20Amsterdam 21 Hamilton 22 Osaka 23 Caracas 24 Tokyo 25 Wrodaw 26Athens 27 Warsaw 28 New Delhi 29 Montreal 30 Medellin 31 St louis 32Dublin 33 Hong Kong 34 Shanghai 35 New York 36 london 37 Calcutta38 Brussels 39 Santiago 40 Zagreb 41 Frankfurt 42 Glasgow 43Guangzhou 44 Manila 45 Madrid 46 Beijing 47 Paris 48 Xian 49 SioPaulo 50 Rio de Janeiro 51 Seoul 52 Tehran 53 Shenyang 54 MilanSource Graedel and Crutzen (1993)

and hating Imam that their levels ofsulphur dioxid~ and suspend~d particulatematter (SPM) ar~ high and climbing Inaddition rapid economic d~velopment is

Urban Air Pollution lOS

bringing increased emissions from indusshytry and motor vehicles which are g~nershy

ating progressively more serious air-qualityproblems

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bull - Figure 11I9 Trends in atmospheric quality in the United Kingdom (a) Sulphurdioxide emissions from fuel combustion and average urban concentrations(b) Smoke emissions from coal combustion and average urban concentrations ofoil smoke (c) Increase in winter sunshine (10-year moving average) for londonand Edinburgh dty centres and for Kew outer london (d) Annual maximumhourly ozone concentrations at selected sites in the Los Angeles basin1958-1989 (e) Annual fog frequency at 0900 GMT in OxfOfd central England1926-1980Sources (a)-(c) Figures from Depa~nt of Environment (d) After Elsom (1992) figure211 (e) After Gomez and Smith (1984) figure 3

o lSU 70 72 74 Jf 11 ID a 14

in (ie smaller than 10 Jffi and so oftenknown as PMIOs) Also of great conc~min terms of human health ar~ elementalcarbon (for example from diesel vehicles)polynuclear aromatic hydrocarbons (PAHs)and toxic b~ metals (eg arsenic leadcadmium and mercury) in part becauseof their possible role as carcinogens

Urban air pollution V3S particularlysevere in the former Communist states ofEastern Europe Carter and Turnod(1993 p 63) described this problem andits political background in the comext ofCzechoslovakia (now the Czech ~public

and Slovakia)

Environmental quality has clearly detemiddotriorated as a result of human activitythe major cause is an excessive 3ndinconsiderate extraction of naturalresources extensive waste emissionsand failur( to observ( ecological andaadKtic laws These were compoundedby an inefficient economy which conshysumed inordinat( amounts of raw mashyterials and energy based on outmodedtechnology which produced manufacshytured goods with little respect for theccologicaJ consequences This ud situshyation was further aggravated by inadshyequate financial reoourcc allocation forenvironmental protection which was ofa rem~dial chancter rath~r than one ofdamage prevention Much of the blamefor this state of affairs must be laid uponthe Communist government over thepast fony years when legislative execushytive and political pow~r was concenshytlared in the hands ofa small controllinggroup (lIomenilRtJlrll) who did little tocorren adv~rse effects on the ~nvironshy

men( cauSoCd by their policies Addedto this dctrimentll domestic attitude wasthe significant contribution made bytrlrUboundary pollution from neighshybouring states particularly along thenorthern and western boundaries of thecountry

The problem was cncerbated by the uscof lignite (brown coal) in some of the East

Particular attention is being paid at thepreKnt time to the chemical compositionof SPMs and particularly to those partishycles that are snull enough to be bruthed

Figure 11110 Air quality trends in losAngeles and its environs have beenmeasured continuously and averagedover each hour The highest of thehourly averages is then selected fortrend analysis Part (a) shows thedownward trend in carbon monoxide(CO) concentrations this trend isconsistent with vehicular emissioncontrol measures part (b) shows thetrend for oxides of nitrogen (NOx) andozone (OJ Both are expressed in partsper billion by volume (ppbv)Source Modified from kun~ and Chang(19Sn copyright 1987 by Air PollutionControl Association

106 The Atmosphere

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Urban Air Pollution 107

Plate 1113 Some of the worst urban air pollution occurred in the former SovietUnion A particularly gruesome pollution hot spot was the Magnitogorsk steeshymaking area (Katz Pictures)

European states Such col is of low qualshyity so disproportionatdy large quntiticshve to be burnt it can also have bull veryhigh sulphur content Cuter and Turnock(1993 p 189) refer to the dedly plI ofsulphurous smoke tht this fud source

FURTHER READING

has hdped to promote They point outthat even in the late 1980s over threeshyquarters of Polnds energy orne frombrown coal as did two-thirds of the enmiddotergy in Czechoslovakia and the fonner EastGermany

Brimblecombe P 1987 The Big Smoke London MethuenA diverting history of air pollution with particular reference to London

Carter F W and Turnock D (eds) 1993 Environmental Problems in Eastern EuropeLondon RoutledgeAn edited collection of papers on the kgacy of dtcadful air polJution problems inEastern Europe

Elsom D 1996 S418 Alert Mtma8in8 UrbAn Air ~AH London EanhscanA very readable and informative guide

108 The Atmosphere

Air pollution in South Mrican cities the legacy ofapartheidSouth Mrica produces the worldscheapest electricity but for manyyears it has only been available toaround 30 per cent of the populashytion This bald statement sums upthe major causes of South Africanurban air pollution Around 83 percent of South Africas electricity isgenerated by coal-fired power stashytions which burn coal with a sulshyphur content of around 12 per centSuch high sulphur content (relativeto many other types of coal) proshyduces high levels of polluting gasesMany of these plants are located inthe eastern Transvaal which suffersgreatly from air pollution and acid deposition Apartheid the system of governshyment which dominated South Africa from 1948 to 1994 and forced differentracial groups to live apart produced highly unequal distributions of access toenergy resources and of pollution conditions Apartheid forced black and Colshyoured populations into poor townships usually without electricity and withsevere pollution problems

The background air pollution in many parts of South Africa is increased inurban environments where coal paraffin and wood are burnt as important domesticenergy sources By 1985 about 57 per cent of the entire South African populashytion lived in cities many of them in squatter settlements and townships whereelectricity supply was limited Soweto for example some 15 Ion from Johannesshyburg covers nearly 60000 sq Ion and had a population in 1990 of around 25million according to some tstimates Electricity was brought into Soweto in1981 but coal is still widely used as it is cheaper and the supply more reliable

Sulphur dioxide pollution is now a critical health problem for Sowetan inhabshyitants In Soweto mean annual sulphur concentrations are up to 60 ~g percu metre whereas in the unpolluted north-west of Transvaal mean annual conshycentrations are on average only about 7 ~g per cu metre There are also highlevels of nitrogen oxides and carbon monoxide in Soweto

The air pollution problems of Soweto are exacerbated by climate andtopography North and north-westerly winds transport pollution here fromJohannesburg city centre and winter temperature inversions help trap the polshylution The South African Department of Health now believes coal smoke intownships to be the most serious national air pollution problem Air pollution isa problem indoors as well as outdoors especially in areas where open fires orinefficient stoves are used for cooking Suspended particulate matter carbon

Urban Air Pollution 109

Plate 1114 Air pollution in Cape Town South Africa Much of the pollutionis caused by the burning of low-quality fuel in the densely populatedtownships that surround the city At some times of year the pollutingsmoke and gases are trapped by climatic conditions called inversions(A S Goudie)

monoxide oxides of sulphur and nitrogen hydrocarbons and a range of otherpollutants are produced by stoves and fires The accumulation of indoor andoU[door pollution in Sowew and many other towns is leading to severe respirashytory problems especially in the poorest and most vulnerable members of societyAsbestos also poses an air pollution problem in South Africa where blue asbestosis mined in the northern Transvaal and northern Cape Asbestos can cause lungand other cancers and urbanized areas near mining operations are particularlyvulnerable to wind-blown asbestos

Further reading

Ramphele M 1991 Restoring the Land Environme1Jf and Change in PostshyApartheid South Africa London Panos

Vogel C H and Drummond J H 1995 Shades of green and brownenvironmental issues in South Africa In A Lemon (ed) The Geographyo[Changein South Africa 85-98 Chichester Wiley

110 The Atmosphere

7 OZONE DEPLETION AND

OZONE POLLUTION

Ozone (03) was discovered in 1840 It isa naturally occurring form ofoxygen whichconsists of three oxygen atoms rather thantwo It exists throughout the atmospherein very low concentrations never exceedshying around one molecule in every 100000present It is especially abundant in thestratosphere between 10 and 40 km abovethe ground This ozone layer containsabout 90 per cent of atmospheric ozoneand is important because it provides athin veil which absorbs ultraviolet (UV)radiation from the sun Indeed the ozonelayer prevents about 97 per cent of W-Blight from reaching the Earths surfaceToo much ultraviolet radiation can damshyage plants including the phytoplanktonthat live in the oceans In humans it cancause skin cancers it may also cause eyecataracts and damage the bodys immunesystem Thus it is clear that any reductionin the thickness and concentration ofozone in the ozone layer is worrying

In the 1980s satellite observationsground measurements and readings frominstruments on balloons and in aircraftbegan to suggest that the ozone layer wasbecoming thinner especially over theAntarctic More recent measurements haveindicated that the ozone layer is also thinshyning over America and northern Europe(see table III4) Here ozone decreasedon average by around 3 per cent in the1980s In the 1970s concern was expressedabout possible damage to the ozone layerby high-flying supersonic aircraft such asmilitary jets or Concorde However curshyrent concern among scientists is focusedon a range of manufactured gases ofrecent origin These include chloroflushyorocarbons (CFCs) and halODS Thesegases have been extremely useful in manyways - for example as refrigerants for

extinguishing fires for making foams andplastics and for use in aerosol spray cansThis is because they have some valuableproperties they are stable non-flammableand non-toxic Unfortunately their stabilshyity means that they can persist a long timein the atmosphere and can thus reach theozone layer witham being destroyed Oncethey are in the ozone layer UV radiationfrom the sun starts to break them downThis sets olf a chain of chemical reactionsin which reactive chlorine atoms arereleased These act as a catalyst causingozone (03) to be converted into oxygen(0) (figure IIUl)

Global production of CFC gases inshycreased gready during the I960s 1970sand 1980s from around 180 million kgper year in 1960 to nearly 1100 millionkg per year in 1990 However in responseto the thinning of the ozone layer manygovernments signed an international agreeshymenl called the Montreal Protocol in1987 This pledged them to a rapid phasshying out of CPCS and halons Productionhas since dropped substantially Howeverbecause of their stability these gases willpersist in the atmosphere for decades oreven centuries to come Even with themost stringent controls that are now beshying considered it will be the middle ofthe twenty-first century before the chloshyrine content of the stratosphere falls beshylow the level that triggered the formationof the Antarctic ozone hole (see below)in the first place

Some thinning of the ozone layer mayresult from time to time from naroralrather than anthropogenic processes Apossible factor may be the pollution of thestratosphere with particulate material (aeroshysols) emitted by volcanic eruptions suchas that of Mt Pinatubo in June 1991

The most drastic decline in stratoshyspheric ozone has been avec AntarcticaThis has led to the formation of theozone hole which expanded to an area

Ozone Depletion Ozone Pollution 11

()

Plate 1115 (a) The Antarctic Olone hole from space 8 October 1995 overleaf(b) the Northern Hemisphere ozone hole 12 March 1995 The colours representozone concentrations in Dobson units (NOAAScience Photo Library)

Table 1114 Trends in stratospheric Olone 1979-1991 ( per decade)

December-March May-August September-November

Satellite-derived data45degNEquator455

-56 35+03 plusmn 45-52 plusmn 15

-29 plusmn 21+01 plusmn 52-62 plusmn 30

-17 plusmn 19+03 plusmn 50-44 plusmn 32

Land-based data26middotN-64middotN -47 z 09 -33 z 12

Sour~ Tolba and E1middotKhoIy (eels) (1992) tabJe 2 p SO

-12 t 16

112 Th~ Atmosph~rc

(b)

Figure 11I11 opposite (a) The naturally occurring chemical processes leading tothe formation and decomposition of ozone in the atmosphere in the presence ofultraviolet radiation (b) The decomposition of ozone initiated by chlorine atomsreleased dUring the breakdown of a commonty occurring anthropogenicaUygenerated CFC believed to be harmful to the atmosphere (CFCll ) Not all thetwo-atom (diatomic) molecules of oxygen combine to form ozone and the freechlorine atoms that are liberated are potentially capable of initiating furtherreactions that lead to the breakdown of ozone (c) Schematic diagram to show theprindpaJ sources of atmospheric ozone and the main reactions that cause ozonedepletion in the stratosphereSource Pickering and Owen (1994)

Ozone Depletion Ozone Pollution 113

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114 The Atmosphere

of 24 million sq km during SeptembershyOctober 1992 and again in the same monthsof 1993 Record low ozone levels of lessthan 100 ozone units were registeredduring a few days in October 1993 Thesecompare with values from years before theozone hole (1957-78) of 330-350 units

The deS[ruction of ozone is grC=3[estover the Antandc because of the uniqueweather conditions during thc long darkwimer of the south polar regions Strongwinds circulate in a great vortex above theAntarctic essemially isolating the polarstratoshysphere from the rest of the atmosphereUnder the vcry cold conditions with ternmiddotperatures below -SOmiddotC icc clouds formcalled polar stratospheric clouds Theseprovide ideal conditions for the transforshymation ofchlorine (derived from the breakshydown of CFCs ampOd halons) into potentiallyreactive compounds When sunlight reshyturns in the spring months UV radiationfrom the sun triggers the reaction betweenthese chlorine compounds and ozonethereby leading to ozone destruction

No such clear ozone hole develops overthe Arctic becau$C the more complexarrangement of land and sc-a here leads toa less weU devel~d vortex system ofwinds In addition the winter stratosphereat the North Pole tends to be warmerthan its southern coumerpart This meansthat polar stratospheric clouds arc usuallyless abundant Nonetheless ozone depIcshytion docs seem to have occurred producshying an ozone crater rather than a hole

Paradoxically while ozone levels may be

FURTHER READING

dropping in the stntosphere at lowerlevels in the atmosphere they arc increasmiddoting This tropospheric ozone is producedb) the action of sunlight on the nitrogenoxides and hydrocarbons that are emittedin fossil fuel exhaust gases Such photoshychemical reactions as thcy arc caJlcd arcparticularly serious in some great citieslike Los Angeles where the high densityof chicles the frequent occurrcncc ofsunshyshine and the favourable topography leadto high concentrations ofa soup ofphotomiddotoxidant gases Rcscarch in both Americaand Europe has established that extensiveformation of tropospheric ozonc also freshyquently occurs in Northern Hcmispheremid-latitudes in thc summer in non-urbanareas most noticeably downwind of citksand major industrial regions The problemis fegional rather than mcrdy urban

High levels ofozone conccnrration havesc-vcral ~rious consequences Humanssuffef from eye irritation respiratory comshyplaints and headaches Ozone is also poshytcncally toxic to many species ofconiferoustrces herbaceous plants and crops at conmiddotccntrations nOt far above the natural backmiddotground le-d Rigorow controls on vehicleemissions can grcatly reduce thc problemSuch mcasures arc now being implementedin California Indeed as figure m12 showsin spite of a hefty increase in both popumiddotlation and the number of mOtOf vehicles inthc Los Angeles area since 1970 peak ozonclevels havc declincd vcry markedly and thearea subjected to high ozone concenmshytions has shrunk (Lents and Kdly 1993)

Gribbin J 1988 Tnt Hole in the sq MRns TbreRt to the Ozone lAyer London CorgiBooksAn introductory trcatment for the gencral public by a well-known scientific journalist

Minrur I M and Miller A S 1992 Stratospheric ozone depletion can wc savc thesky~ In Green GlDbe naboo 1992 83-91 Oxford Oxford Univcnity PressA morc rccent gcncra1 discussion of thc causes and consequences of the ozone hoIcand what can be done to deal with it

Ozone Depletion Ozone PoUution 115

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116 The Atmosphere

pH

Figure 11113 The pH scale shOWingthe pH level of add rain in comparisonwith that of other common substancesSource Kemp (1994) figure 41

As a result ofair pollution precipitationin many parts of the world has pH valuesfar below 565 Snow and rain in thenorth-east USA have been known to havepH values as low as 21 In the eastern

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8 ACID DEPOSITION

Rain is slightly acid under natural conditionsbecause it contains some dissolved gasesincluding carbon dioxide (COl) sulphurdioxide (SOl) and nitrogen oxides (NOx)The~ gases are naturally pre-sent in theair Under natural conditions rain has apH of around 565 (figure 11113) Theterm acid rain was introduced as longago as the 1850s for rain which has a pHof less than 565 Such rain has becomemore than usually acid because of air polshylution Two of the chemical reactions inshyvolved are shown in figure IIIl4

Some scientists prefer the term aciddeposition to acid rain for not all envirshyonmental acidification is caused by acidrain in the narrow sense Acidity can reachthe ground surface without the assistanceof water droplets as particulate matter orgases This is termed dry deposition Furshythermore there are various different typesofwet deposition mist fog hail sleet andsnow as well as rain itself

(t) SuIplunlU$ Ind sulphuric acids

~ il tlDimd ampom lWurlllnd whropogtnic sourm Ind dissoIm in cloud _to pnld~ IUIphurous Kid

SuJphlllOU$lcid Cln b oxidimi in the pi or ~ueouI plwe by IlIrious oxidants

~ amp ~

AqUtltlll$ sulphur lrioxidt fonm IlIIpburil acid

(2) Nilrow lind nilric arids

NO alldN~ (rolIecliVlly known as Nih) art ptoduced by combuslion prornseI and lightnillshyNilric and nil10llS acids may b produced

Figure 11114 Chemical reactions producing acid depositionSource Modified after Mannion (1992) fig 112

Acid Deposition 117

Table 1115 Main sources of acid gases in the UK In 1990

Nitrogen oxidesRoad transportPower stationsIndustry

Sulphur dioxidePower stationsIndustry

Annual emissions(000 tonnes)

1400780270

2700710

of UK total

51289

7219

Source Department of Environment figures

USA as a whole the avcrage annual acidityvalues of precipitation tend to be aroundpH4 The pH scale is logarithmic so adecrease of one pH unit represents a tenshyfold increase in acidity Thus pH4 is tentimes more acidic than pHS The maingases responsible for this state of afhirsare the sulphur oxides and nitrogen oxshyides emined from fossil fuel combustion(see table ilLS) As a general rule sulshyphur oxides have the greatest effect andare responsible for about two-thirds of theproblem However in some regions suchas Japan and the west coast of the USAthe nitric acid contribution may well be ofrelatively greater importance

Whichever of these gases is most impormiddottant most acidification has occurred in theindustrialized lands of the Northern Hemishysphere It is here that emissions of sulphurand nitrogen oxides arc highest becauseof high rates of fossil fuel combustion bya range of sources notably industries carsand power stations However the polshylutants that cause acidification can berransponed over long distances by thewind The acidifiC2tion ofScaodinavia forexample has been attributed in part toemissions from Britain Similarly Canadareceives much of i[S acid deposition fromthe industrial heartland and tlK Ohio River

Valley region of the USA Recent estimatesof global emissions ofsulphur suggest thatanthropogenic sources now account for55-80 per cent of the combined total(anthropogenic and natural) and that over90 per cent of emissions from anthroshypogenic sources originate in the NorthernHemisphere

The effects of acid deposition arcgreatest in tho~ areas which have highlevels of precipitation (causing more acidshyity to be transferred to the ground) andthose which have base poor (acidic) rockswhich cannot neutralize the depositedacidity

Some of the most persuasive evidencefor long-term increases in acid deposishytion is provided by what is called thepalaeolimnological approach In this apshyproach past environmental information isobtained by looking at the changes in thefaunal and floral content of cores of sedishyment taken from the floors of lakes Therecord provided by diatoms is especiallyuseful for these algae are excellent indicashytors of water chemistry The compositionof fossil assemblages retrieved from datedcores can be used to reconstruct changesin water pH In Britain at sensitive sitespH values oflakc WlIters were close to 60before 1850 but since then pH declines

118 The Atmosphere

SipIilinlionrJaquotit

lnllIbilily1

Figure 11115 Pathways and effects ofacid precipitation through differentcomponents of the ecosystem showingsome of the adverse and beneficialconsequences

have varied between 05 and 15 unitsoverall

Acid precipitation has many ecologicalconsequences (figure IIUS) One harmfuleffect is a change in soil character Thehigh concentration of hydrogen ions inacid rain causes accelerated leaching ofessential nutrients making them less availshyable for plant usc Furthermore aluminiumand some heavy metal ions become moresoluble at low pH values and may havetoxic effects on plants and aquatic organshyisms Forest growth can also be affectedAcid rain can damage foliage increase susshyceptibility [0 disease affect germinationand reduce nutrient availability (figureIII16)

Particular fears have been expressedabout the possible effects of acid deposishytion on aquatic ecosystems especially on

fish populations Many fish are intoleranrof low pH values (table 1116) Fishlesslakes are now common in areas like theAdirondacks in the north-east USA Fishmay also be adversely affected by the inshycreasing amounts of toxic metal ions (egaluminium) in surface waters

Changes in land use can also make surmiddotface waters more acid Modern forestrypractices for example contribute to theproblem with drainage clear felling andthen the planting of monocultures of fastshygrowing species such as conifers In theseconditions acidic leaf litter builds up morespeedily than might be the case naturallyThis can add to the nutrient leachingeffects ofacid rain Tall trees are also moreeffective at scavenging airborne pollutshyants from douds than say upland grassshyland This serves to increase the amountof pollution deposited

Another adverse effect of acid rain isthe weathering of buildings particularlythose made from limestone marble andsandstone For example sulphate-richprecipitation reacts with limestone tobring about chemical changes (eg theformation ofcalcium sulphate or gypswn)which cause blistering while the low pHvalues encourage the dissolution of thelimestone Many of the great cathedrals ofEurope have been attacked in this way

Various methods are used to try to reducethe damaging effects ofadd deposition Oneof these is to add powdered limestone tolakes to increase their pH values Howshyever the only really effective and practicallong-term treatment is to curb the emisshysions of the offending gases This can beachieved in a variety of ways by reducingthe amount of fossil fuel combustion byusing less sulphur-rich fossil fuels byusing alternative energy sources that donot produce nitrate or sulphate gases (eghydropower or nuclear power) and byremoving the pollutants before they reachthe atmosphere For example after comshybustion at a power station sulphur can be

Acid Deposition 119

Figure 11I16 The impact of acid precipitation on the terrestrial environmentSource Various sources in Kemp (1994) figure 411

Table 11I6 Ecological effects of water pH on European freshwater fish

pH range

30-35

35-40

40-45

45-50

60-65

Effects

Unlikely that any fish can survive for more than a few hours

This range lethal to salmonids Tench roach pike and perch cansUlVive

likely to be harmful to salmonids tench bream roach goldfishand common carp Fish can become acclimatized to these levels

likely to be harmful to adults eggs and fry of salmonids Canharm common carp

Unlikely to harm fish unless free carbon dioxide concentrationgreater than 20 mgtl or water contains iron salts

Unlikely to harm fish unless free carbon dioxide in excess of 100mgI

Harmless to fish

100-105

90-95

95-100

likely to harm salmonids and perch if present for a long time

lethal to salmonids over prolonged periods

Can be withstood for only short periods by roach and salmonids

Rapidly lethal to salmonids Prolonged exposure lethal to carptench goldfish and pike

110-115 Rapidly lethal to all species of fish

Source Gleick (1993) table F2

120 The Atmosphere

removed (scrubbed) from flue gases by aprocess known as flue gas desulphurization(FGD) in which a mixture of limestoneand water is sprayed into the flue gas whichconverts the sulphur dioxide (502) intogypsum (calcium sulphate) NOx in flue

FURTHER READING

gas can be reduced by adding ammoniaand passing it over a catalyst to producenitrogen and water (a process called selecshytive catalytic reduction or SCR) NOxproduced by cars can be reduced by fittinga catalytic converter

Park C C 1987 Acid Rain Rhetoric and Reality London MethuenA general introduction that provides a useful overview

Wellburn A 1988 Air Pollution and Acid Rain The Biological Impact LondonLongmanA more advanced treatment with a strong biological emphasis

9 CoNCLUSION

Changes in the composition of the Earthsatmosphere as a result of human emissionsof trace gases and changes in the natureof land cover have caused great concernin recent years Global warming ozonedepletion and acid rain have become cenmiddottral issues in the study of environmentalchange Although most attention is oftenpaid to climatic change resulting fromgreenhouse gases there is a whole seriesofother mechanisms which have the potenshytial to cause climatic change Most notashybly we have pointed to the importance ofother changes in atmospheric compositionand properties whether these arc causedby aerosol generation or albedo change

However the greenhouse effect andglobal warming may prove to have greatsignificance for the environment and forhuman activities Huge uncertainties remainabout the speeddegree direction and spatialpatterning of potential change Nonetheshyless if the Earth warms up by a couple ofdegrees over the next hundred or so yearsthe impacts some negative and some posishytive are unlikely to ~ trivial The box inthis part on the effects of warming onagriculture in the UK indicates this clearly

For many people especially in citiesthe immediate climatic environment has

already been changed Urban climates aredifferent in many ways from those of theirrural surroundings The quality of the airin many cities has been transformed by arange of pollutants and we have pointedto the particularly serious levels of polshylution that developed in Eastern Europeand in South Africa Conversely we havepointed out that under certain circumshystances clean air legislation and othermeasures can cause rapid and often rcmiddotmarkable improvements in this area

The same is true of twO major pollutionissues - ozone depletion and acid deposishytion Both processes have serious environshymental consequences and their effects mayremain with us for many years but bothcan be slowed down or even reversed byregulating the production and output ofthe offending gases

The human impacts on the atmospherediscussed in this part of the book showclearly how different the impacts can beon different parts of the population andalso how impacts can spread widely oftenaffecting people a long way from thesource of the problem Furthermore imshypacts on the atmosphere show forcefullythe interlinked nature of environmentalsystems and the knock-on effects of manyatmospheric changes on the biospherefresh waters and land surface

Points for Rtview 121

KEy ThRMS AND CoNCEPTS

acid rainaerosolsalbedodust bowlglobal warminggreenhouse effect

POINTS FOR REVIEW

land coverozone holesUatospheric ozonethermal pollutiontropospheric ozoneurban heat island

What forces could (a) cause future climate to cool and (b) cause future climate tobecome wanner~

Can humans change regional and global precipitation patterns

Is global warming an important environmental issue and if so why~

Ozone concentrations are increasing in many cities but decreasing in the stratosphereWhy should this bd

Is acid rain an increasingly important or decreasingly important environmental issueDefend your answer

PART IV

The Waters1 Introduction 1252 River Regulation 125

bull Modification ofthe Colorado River USA 1333 Forests and River Row 136

bull George Perkins Marsh - pioneer investigatorofhuman impam on forests and hydrology 138

4 The Hydrological Response to Urbanization 1405 LutdDnimge 1426 Water Pollution 145

bull Past and present pollution ofthe River ClydeScotland 148

7 Eutrophication ISObull Controlling eutrophication Lake Bim Japan 153

8 Thennal pollution 1549 Inter-basin Water Transfers and the

Death ofthe Arll Sea 15510 Groundwater Depletion and

Groundwater Rise 15911 Conclusion 161

Key Terms and Concepts 162Points for Review 162

1 INTRODUCTION

In a recent review of the worlds freshshywater resources Gleick (1993 pl) summedup the importance of water in a few clearsentences

fresh water is a fundamental resourceintegral to all environmental and societalresponses Water is a critical componentofecological cycles Aquatic ecosystemsharbour diverse species and offer manyvaluable services Human beings requirewater to run industries to provide enshyergy and to grow food

Because water is so important to humanaffairs humans have sought to controlwater resources in a whole variety ofwaysAlso because water is such an importantpart of so many natural and human sysshytems its quantity and quality have undershygone major changes as a consequence ofhuman activities Again we can quoteGleick (1993 p 3)

As we approach the 21st century wemust now acknowledge that many ofour efforts to harness water have beeninadequate or misdirected Riverslakes and groundwater aquifers are inshycreasingly contaminated with biologishycal and chemical wastes Vast numbersof people lack clean drinking water andrudimentary sanitation services Millionsof people die every year from watershyrelated diseases such as malaria typhoidand cholera Massive water developshyments have destroyed many of theworlds most productive wetlands andother aquatic habitats

In this chapter we look at some of theways in which the quantity and quality ofwater have been modified in some ofthe worlds freshwater systems - riversgroundwater and lakes Table IVI sumshymarizes some of the hydrological effects

River Regulation 125

of land-usc change and demonstrates theirgreat number and diversity

2 RIvER REGULATION

In recent decades human demand for freshwater has increased rapidly Global wateruse has more than tripled since 1950 andnow stands at 4340 Cll km per year shyequivalent to eight times the annual flowof the Mississippi River Annual irretrievshyable water losses have increased aboutsevenfold this century

One major way of regulating rivers is tobuild dams Many new large dams havebeen built in the twentieth century espeshycially between 1945 and the early 1970sand there are now more than 36000 damsaround the world As table IV2 showslarge dams (ie more than 15 metres high)arc still being constructed in substantialnumbers especially in Asia In the late1980s some 45 very large dams (more than150 metres high) were being built Inshydeed one of the most striking features ofnewly constructed dams and reservoirs isthat they have ~come increasingly large(table IV3)

Most dams achieve their aim which isto regulate river discharge They arc alsohighly successful in meeting the needs ofsurrounding communities millions of peoshyple depend upon them for survival welmiddotfare and employment However dams havemany environmental consequences thatmayor may not have been anticipated(figure rvl) Some of these arc dealt within greater detail elsewhere (eg salinity inpart V section 5)

The River Nile before and after theconstruction of the great Aswan High Damin Egypt (table IVA) provides a goodexample of how dams retain sedimentUntil the dam was built concentrationsof silt were high in the late summer andautumn period of high flow on the NileSince the dam has been finished the silt

126 The Waters

Table IV1 Summary of the major hydrological effects of land-use changes

Land use change Hydrologicalcomponentaflected

Afforestation Annual flow(deforestation hasthe opposite Seasonal floweffects in general)

Floods

Water quality

Erosion

Climate

Agricultural Water quantityintensification

Water quality

Principal hydrological processes involved

Increased interception in wet periodsIncreased transpiration in dry periods

Increased interception and increased dryperiod transpiration reduce dry season flowDrainage improvements associated withplanting may increase dry season flowsCloud water (mist and fog) deposition ontrees will augment dry season flows

Interception reduces floods by removing aportion of the storm rainfall and allowingsoil moisture storage to increaseManagement activities such as drainageconstruction all increase floods

Leaching of nutrients reduced as surfacerunoff reduced and less application offertilizerDeposition of atmospheric pollutantsincreased because of larger exposed surfacearea of trees

High infiltration rates in natural mixedforests reduce surface runoff and erosionSlope stability enhanced by reduced soilpore water pressure and binding effect oftree rootsWind throw of trees reduces slope stabilityManagement activities (constructiondrainage) all increase erosion

Increased evaporation and reduced sensibleheat fluxes from forests affect climate

Alteration of transpiration rates affectsrunoffTiming of storm runoff altered through landdrainage

Application of inorganic fertilizers addsnutrientsPestidde application poses health risks tohumans and animalsFarm wastes pollute surface andgroundwater where inadequate disposal oforganic and inorganic wastes

Table continues opposite

River Regulation 127

Table IV1 Continued

Land use change Hydrologicalcomponentaffeded

Erosion

Principal hydrological processes involved

Cultivation without proper soil conservationmeasures and uncontrolled grazing increaseerosion

Draining wetlands Seasonal flow lowering of water table may induce soilmoisture stress reduce transpiration andincrease dry season flowsInitial dewatering on drainage will increasedry season flows

Annual flow Initial dewatering on drainage will increaseannual flowAfforestation after drainage will reduceannual flow

Floods Drainage method soil type and channelimprovement will all affect flood response

Water quality Redox potentials altered leading to peatdecomposition acidification and increasedorganic loads in runoffNew drainage systems intercepting mineralhorizons will reduce acidity

Carbon balance Accumulating peat bogs are sink foratmospheric CO2

Source Adapted from Calder (1992) table 1311

Table IV2 Number of large dams (over 15 metres high) 1950 and 1986

Continent 1950 1986 Under construction31 Dec 1986

Africa 133 885 58Asia 1562 23555 615

of which in China 8 18820 183AustralasiaOceania 151 497 25Europe 1323 4077 230North and Central America 2099 6663 39South America 885 69

TOTAL 5268 36562 1036

Source Data provided by UNEP

128 Th~ Waters

Table IV3 Worlds 20 largest reservoirs by reservoir volume

Namemiddot Country Capacity Year completed(million cu metres)

Owen Fallsb Uganda 204800 1954Bratsk FSUlt 169000 1964High Aswan Egypt 162000 1970Kariha Zimbabwe-Zambia 160368 1959Akosombo Ghana 147960 1965Daniel Johnson Canada 141851 1968Gun Venezuela 135000 1986Krasnoyarsk FSU 73300 1967W A C Bennett Canada 70309 1967Zeya FSU 68400 1978Cahara Bassa Mozambique 63000 1974La Grande 2

Barrage Canada 61715 1978La Grande 3

Barrage Canada 60020 1981Ustmiddotllim FSU 59300 1977Boguchany FSU 58200 under constructionKuibyshev FSU 58000 1955Serra da Mesa Brazil 54400 under constructionCaniapiscau

Barrage K A 3 Canada 53790 1980Bukhatarma FSU 49800 1960Ataturk Turkey 48700 1990

bull All these reservoirs have been constructed Since the Second World Warb Owen Falls capacity is not fully related to construction of a dam the major part of it is anatural lakelt Former Soviet Union

Source Modified from GJeick (1993) table G9

load is lower throughom the year and theseasonal peak is removed The Nile nowonly transports abom 8 per cent of itsnatural sediment load below the AswanHigh Dam This figure is exceptionally lowprobably because of the great length andsize of Lake Nasser the reservoir behindthe dam Other rivers for which data areavailable carry between 8 per cent and 50per cent of their natural suspended loadsbelow dams

The removal of sediment from the Nilehas various possible consequences These

include a reduction in flood-depositednutrients on fields less nutrients for fishin the south-cast Mediterranean Seaaccelerated erosion of the Nile Delta andaccelerated riverbed erosion since less sedishyment is available to cause bed aggradationThe last process is often called clearshywater erosion It may speed up the rate atwhich streams cut back into their banks inan upstream direction It may also causegroundwater tables to become lower andundermine bridge piers and other strucshytures downstream of the dam On the

River Regulation 129

WaIn chrmillry IIIImdS1mm Row ClIIIIIIllIrdIwponolicllllou IncmJtdGround _ aImecI(t bJ~)WJtor ltmptealurt ohanpI

diaurc_-shysalinity

Figure rV1 Generalized representation of the possible effects of dam constructionon human life and various components of the environment

Table IV4 Slit concentrations In the Nile at Gaafra before and after the construemiddottlon of the Aswan High Dam (ppm)

Jan Feb March April My June July Aug Sep Od Nov Dec

Before (averages for the period 1958-63)64 50 45 42 43 85 674 270 242 925 124 77

After44 47 45 50 51 49 48 45 41 43 48 47

Ratio of before to after15 11 10 08 08 17 140 600 591 215

Source AbumiddotAtia (1978) p 199

258 163

other hand in regions such as northernChina where modern dams trap silt thecutting-out of the river channel downshystream may alleviate the strain on leveesand so les~n the expense of strengthenshying or heightening the levees

However clear-water erosion does notalways follow from dam construction In

some rivers before a dam was built thesediment brought into the main streamby steep tributaries was carried away byfloods Once the dam is built these floodsno longer happen and so the sedimentaccumulates as large fans of sand or gravelbelow each tributary mouth The bed ofthe main stream is raised and any water

130 The Waters

Plate IV1 The Sagan River in southern Ethiopia The dark brown colour of thisriver is caused by its large load of sediment derived from accelerated erosionupstream This renders the river much less suitable as a source of drinking water(A S Goudie)

intakes towns or other structures thatlie alongside the river may be threatenedby flooding or channel shifting across theaccumulating wedge of sediment

Some landscapes are almost dominatedby dams canals and nservoirs Probablythe most striking example of this is thetank landscape of south-east India wheremyriads of linle streams and areas of overshyland flow have been dammed by smallearth structures to produce what Spate(Spate and Lcarmonth 1967 p 778) haslikened to a surface of vast overlappingfish-scales

In the northern part of the Indian subshycontinent in Sind the landscape changesbrought about by hydrology are no lessstriking Here the mighty snow-fed IndusRiver is controlled by large embankments(bunds) and interrupted by great damsIts waters are distributed over thousandsof square kilometres by a network ofcanals that has evolved over the past 4000years

Another direct means of river manishypulation is channelization This involvesconstructing embankments dikes lev~es

and floodwalls to confine floodwaters andimproving the ability of channels to transmiddotmit floods by enlarging their capacitythrough straightening widening deepenshying or smoothing

Some of the great rivers of the worldare now lined by extensive embankmentsystems such as those that run for morethan 1000 krn alongside the Nile 700km along the Hwang Ho in China 1400km by the Red River in Vietnam and over4500 km in the Mississippi Valley Likedarns embankments and other such strucshytures often fulfil their purpose but mayalso create environmental problems andhave some disadvantages For examplethey reduce natural storage for floodwatersboth by preventing water from spillingon to much of the floodplain and whereimpermeable f100dwalis are used by not

River Regulation 131

allowing water to be stored in the banksThe flow of water in tributaries may alsobe constrained Occasionally embankmentsmay exacerbate the flood problem theywere designed to reduce This can happenwhere the barriers downstream ofa breachprevent floodwater from draining back intothe channel once the peak has passed

Channel improvement designed to imshyprove water tlow may also have untoreshyseen or undesirable effects For examplethe more rapid movement of water alongimproved sections of a river channel canaggravate Rood peaks further downstreamand cause excessive erosion The loweringof water tables in the improved reachmay cause overdrainage of adjacent agrishycultural land In such cases sluices needto be constructed in the channel to mainshytain levels On the other hand channelslined with impermeable material mayobstruct soil water movement (interflow)and shallow groundwater flow therebycausing surface saturation

Channelization may also have variouseffects on fauna These may result fromfaster water flow reduced shelter in thechannel bed and reduced food suppliesdue to the destruction ofoverhanging bankvegetation If channelization of rivers werecarried out in large swamps like those ofthe Sudd in Sudan or the Okavango inBotswana where plans to do so exist itcould compktely transform the whole charshyacter of the swamp environment

Another type of channel modification isthe construction of bypass and diversionchannels either to carry excess floodwateror to enable irrigation to take place Thewe of such channels may be as old asirrigation itself They may contribute tothe salinity problems encountered in manyirrigated areas (see part V section 5)

Deliberate modification ofa river regimecan also be achieved by long-distance intershybasin water transfers (Shiklomanov1985and see section 9 below) Such transfers

132 The Waters

are necessitated by the unequal spatialdistribution of water resources and by theincreasing rates of water consumption Atpresent the world water consumption forall needs is 4340 cu km per year ninetimes what it was at the beginning of thetwentieth century By the year 2000 it isexpected to be 6000 sq km per year The[Ota volume of water in the various transshyfer systems in operation and under conmiddotstruction throughout the world at presentis about 300 sq km per year The greatestvolumes of transfers take place in Canadathe former USSR the USA and India

It is likely that many even greaterschemes will be constructed in future deshycades Route lengths of some hundreds ofkilometres will be common and the waterbalances of many rivers and lakes will betransformed (See section 9 below for whathas already happened to the Ami Sea)

A human activity that affects manycoastal portions of rivers or estuariesis dredging The effects of dredging canbe as complex as the effects of dams andreservoirs upstream (La Roe 1977) Dredshyging may be performed to create andmaintain canals navigation channels turn-

FURTHER READING

ing basins harbours and marinas to laypipelines and to obtain a source of matershyial for filling or construction The ecoshylogical effects of dredging are various Inthe first place filling directly disrupts habishytatS like salt marshes Second the largequantities of suspended silt generated canphysically smother plants and animals thatlive on river and estuary beds smotherfish by dogging their gills reduce photoshysynthesis through the effects of turbidityand lead to eutrophication by releasinglarge quantities of nutrients Ukewise thedestruction of marshes mangroves and seagrasses by dredging and filling can resultin the loss of these natural purifYing sysshytems (see part II section 9 on wetlands)The removal of vegetation may also causeerosion Moreover as silt deposits stirredup by dredging accumulate elsewhere inthe estuary they tend to create a falsebottom The dredged bonom with itsshifting unstable sediments is recolonizedby fauna and flora only slowly if at allFurthermore dredging tends to changethe configuration of currents and the rateof freshwater drainage and may provideavenues for salt-water intrusion

Brookes A 1985 River channelization traditional engineering methods physicalconsequences and alternative practices Progress in Physical Geography 9 44-73An advanced review by a leading authority

Gleick P H (ed) 1993 Water in Crisis A Guide to the World)s Freshwater ResourcesNew York Oxford University PressAn invaluable compendium of information on all aspects of water use and misuse Itcontains many useful tables of data

Gregory K J 1985 The impact of river channelization Geographjcal ]ournalI5153-74A useful overview in a relatively accessible journal

Petts G E 1985 Impounded Rjvers Perspeujves for Ecological Management Chichshyester WileyAn advanced textbook that looks at the large range ofconsequences ofdam construction

River Regulation J33

Modification of the Colorado River USA

Plate IV2 The Hoover Dam on the Colorado River Arizona USA The flowof the river and its sediment load are now almost totally controlled(TripM lee)

The Colorado River in the American WeSt (figure IY2(araquo which Aows throughthe Grand Canyon has been at several points dammed to control Aoods generateelectricity and provide water for irrigation Among the major dams are the Hooshyver and Glen Canyon dams both over 200 m high (figure JV2(b)) They havecaused radical adjustments in the hydrological regime Flood peaks are reducedas a flood control strategy and water is released at times of low Aow Dischargevaries rapidly in response to fluctuations in the need for hydropower during thecourse of a day The high dams trap most of the sediment carried by the riverSO that downstream discharges are largely sediment-free In the Colorado Riverthis combination of impacts has changed a natural river with very large springfloods lower summer flows and little daily variation ofsediment-laden waters intoa highly controlled system with only modest flood peaks in spring relatively highsummer flows and drastic daily variation of discharges of clear water Indeed atits seaward end the Colorado has been totally transformed Prior to 1930 beforethe dams were built it carried around 125-130 million tons of suspended sedishyment per year to irs delta at the head of the Gulf of California (figure IV2(c))Now the Colorado discharges neither sediment nor water to the sea Upstream

134- The Waters

(j

o ISO kmI

NEVADA

(AUFQRNlA

WYOMING

COlORADO

NEW MEXICO

----~IP~--~

1750

6000 g

]bull ]bull

3000 -g

River Regulation 135

PREmiddotDAM

~

f~~

-I ~-

rO$TmiddotDAM

bullwbull

bull bullr~1

--J-t-J

z-~hj~

~middot~oo-~11---~~lJ

(d)

w

1961l 197019lt40 1950

Walfrynr

Water discllarge (m~IiOllI ofam-ftetJyr)

()

1910 1920 1930 l~ 1950 116O 1910 1400 Suspmdeltktdiment dischargt (milliorui of lonlyr)

Figure IV2 (a) The Colorado River basin (b) Profiles of the Green andColorado Rivers showing locations of dams reservoirs and whitewatercanyons (c) Historical sediment and water discharge of the Colorado River(d) Pre- and post-dam riparian vegetation in the Grand Canyon downstreamfrom Glen Canyon dam Vegetation lones 1 stable desert vegetation2 stable woody vegetation 3 unstable lone 4 new riparian vegetationphreatophytesSources (a) After Schwarz et al (1990) (b) After various sources in Graf (1985)fig 13 (c) After Schwarz et al (1990) (d) After Graf (1985) from original byS W Carothers

in the vicinity of the Grand Canyon riparian vegetation communities have beencompletely changed since the construction of the Glen Canyon dam (figurelV2(d))

Further reading

Graf W L 1985 The Colorado Rifler Instability and Basi Management Washshyington DC Association of American Geognphers

136 The Waters

3 FORESTS AND RIvER FLOW

When George Perkins Marsh wrote hisremarkable book Man and Nature in1864 one of the main themes which conshycerned him was the consequences of forshyest removal In the early twentieth centuryscientists in America began to measurethe effects of forest removal on streamdischarges To do this they used what issometimes called the paired watershedtechnique First they compared the flowsOUt of two similar watersheds (catchments)over a period of years Then they c1earshyfelled one of the watersheds to see howthat basin responded in comparison withthe unchanged control valley The pioneershying study at Wagon Wheel Gap in ColoradoUSA in 1910 revealed that the clear-felledvalley yielded 17 per cent more waterflowthan would have been expected if it hadremained unchanged like the control valleySubsequent studies in the tropics haveindicated that dear-felling can lead to meanannual stream flow increases equivalent toabout 400-450 mm of rainfall

There are many reasons why the removalof a forest cover and its replacement withpasture crops or bare ground have suchimportant effects on stream flow A mashyture forest probably intercepts a higherproportion of rainfall tends to reduce fatesof overland flow and promotes soils witha higher infiltration capacity and bettergeneral structure All these factors ill tendto produce both a reduction in overallrunolT levels and less extreme flood peaksthough this is not invariably the case

Reforestation of abandoned farmlandsreverses the elTects of deforestation inshycreased interception of rainfall and higherlevels of evapotranspiration can cause adecline in water yield to rivers This cancause problems for human activities

Reviews ofcatchment experiments frommany parts of the world have pointed totwo conclusions

bull Pine and eucalypt forest types cause anaverage change of 40 mm in annualflow for a 10 per cent change in coverwith respect to grasslands that is a10 per cent increase in forest cover ongrassland will decrease annual flow by40 mm and a 10 per cent decrease incover will increase annual flow by thesame amount

bull The equivalent effect on annual flowof a 10 per cent change in cover ofdeciduous hardwood or scrub is 10shy25 mm that is if 10 per cem of agrassland catchment is converted tohardwood trees or scrub vegetation theannual runoff will decrease by 10-25mm

The increase in annual flow that resultsfrom tree or scrub removal tends to bemost marked in two particular environshyments those with very high rainfall andthose with very low rainfall In the formerevaporation from forest will tend to behigher than that from other land usesbecause of high levels of rainfall intercepshytion In the latter evaporation from forestis likely to be higher than that from otherland uses because forests composed oftrees that have deep root systems arebetter able to make use of soil andgroundwater reserves

Having discussed changes in annualflows now let us turn to a considerationof how forest removal influences low seashyson flows and flood peaks The higherlosses from forests in wet seasons fromrainfall interception and increased lossesin dry seasons from transpiration (becauseof trees deeper root systems) both tendto increase soil moisture deficits in dryseasons compared to those under otherland uses On the other hand in forests athigh altitudes whete there is a lot ofwaterdeposition on to trees from clouds thismay provide a significant component ofthe dry season flows in rivers and also

Forests and River Flow 137

Plate IV3 A well-managed tea and rubber plantation in the Nilgiri hills southernIndia (A S Goudie)

increase runoff The same applies in areaswith high-intensity storms where highshyintensity rainfall may lead to high 1Celsof surfolce runoff The higher infiltrationrates under indigenous forest comparedwith other land usa may help soils andtheir below-ground aquifers to rechargethemselves In steeply sloped areas forestsmay have the additional benefit of reducshying landslips (see part V section 6) andpreserving the soil aquifer which may bethe source of dry season flows Boththese effecLS of afforestation may there-

FURTHER READING

fore benefit stream flows in the lowseason

When it comes to flood peaks there isstill a great dcaJ of controversy as to howimportant forest cover is with respect tothe largest types of event Some authorssuggest that management practices assoshyciated with forestry (eg the building ofroads culverts and drainage ditches) orsubsequent activities (eg grazing) whichpromote the flood by causing compactionof the soil and reducing its infiltrationcapacity increase this type of hazard

1 R Calder 1992 Hydrologic e(fects ofland-usc change In D R Maidment (ed)HRndbool of Hydrology pp 131-1350 New York McGraw HillA Iengthy and detailed summary of the available Iiterature

138 The Waters

George Perkins Marsh pioneer investigator ofhuman impacts on forests and hydrology

George Perkins Marsh (1801-82) was born in Vermont USA and can be reshygarded as one of the most important pioneers of the conservation movcment In1864 he wrote Man and Nature This book was the product of two majorinfluences on him first his upbringing in New England and secondly his expeshyriences working for the US government in Turkey and elsewhere around theMediterranean basin In it he recognized how human occupation of the land hadtransformed it This brief extract from Man and NRture in which he deals withthe consequences of forest destruction gives a good indication of his clear anddirect style

With the disappearance of the forest all is changed At one season the earthparts with its warmth by radiation to an open sky - receives at another animmoderate heat from the unobstructed rays of the sun Henee the climatebecomes excessive and the soil is alternately parched by the fervors of summerand seared by the rigors of winter Bleak winds sweep unresisted over itssurface drift away the snow that sheltered it from the frost and dry up itsscanty moisture The precipitation becomes as regular as the temperature themelting snows and vernal rains no longer absorbed by a loose and bibulousvegetable mould rush over the frozen surface and pour down the valleysseaward instead of filling a retentive bed of absorbent earth and storing upa supply of moisture to feed perennial springs The soil is bared of its coveringof leaves broken and loosened by the plough deprived of the fibrous rootletswhich hold it together dried and pulverized by sun and wind and at lastexhausted by new combinations The face of the earth is no longer a spongebut a dust heap and the floods which the waters of the sky pour over it hurryswiftly along irs slopes carrying in suspension vast quantities of earthly partishycles which increase the abrading power and mechanical force of the currentand augmented by the sand and gravel of falling banks fill the beds of thestreams divert them into new channels and obstruct their outlets The rivushylets wanting their former regularity of supply and deprived of the protectingshade of the woods are heated evaporated and thus reduced in their summercurrents but swollen to raging torrents in autumn and spring From thesecauses there is a constant degradation of the uplands and a consequentelevation of the beds of the watercourses and of lakes by the deposition of themineral and vegetable matter carried down by the waters The channels ofgreat rivers become unnavigable their estuaries are choked up and harborswhich once sheltered large navies are shoaled by dangerous sandbars Theearth stripped of its vegetable glebe grows less and less productive andconsequently less able to protect itself by weaving a new carpet of turf toshield it from wind and sun and scouring rain Gradually it becomes altogetherbarren The washing of the soil from the mountains leaves bare ridges ofsterilerock and the rich organic mould which covered them now swept down intothe dank low grounds promotes a luxuriance of aquatic vegetation that breedsfever and more insidious forms of mortal disease by its decay and thus theearth is rendered no longer fit for the habitation of man

~t i

Forests and River Flow 139

MARSH 186r PHOTOGRAPH BY BRADY

Courtesy of Frederick H Meserve

Plate IV4 George Perkins Marsh author of Man and Nature (1864)and one of the major proponents of nature conservation

Further reading

Marsh G P18M Man and Nture (quoted from edition by D Lowenthal 1965Cambridge Mass Belknap Press of Harvard University Press pp 186-7)

140 The Waters

4 ThE HYDROLOGICAL

RESPONSE TO

URBANIZATION

The remarkable growth of the number andsize of cities in recent decades has createdmany new impacts on water resources anddistribution For example cities modify theprecipitation characterinics of their imshymediate environs (see par[ III section 5)They aso can cause changes in waterquality through thermal pollution (seesection 8 below) and chemical pollution(see section 6 below) Moreover the deshymand for water by city populations maybe so great that groundwater is mined fromcity aquifers (see section 10 below) andlarge amounts are brought in by inter-basinwater transfers Los Angeles for examplereceives water from distant parts of northshyern California In this section howeverwe will concentrate on the effect of urshybanization on river flow characteristics

Research in various countries has shownthat urbanization influences flood runoffFor example figure IV3 shows in a scheshymatic way the hydrological changes resultshying from urbanization in a part ofCanadaThese changes are caused mainly by theproduction of extended surfaces of tarmactiles and concrete Because these impershymeable surfaces have much lower infilshytration capacities than rural vegetatedsurfaces they generate a rapid response torainfall This response is further accelershyated by sewers storm drains and the likewhich are very efficient at catching andtransporting city rainfall In general thegreater the area that is sewered the greateris the discharge that will occur in any givenperiod of time In other words the intershyval between flood events becomes progresshysively shorter Moreover peak dischargesare higher and occur sooner after runoffstarts in basins that have been affectedby urbanization and sewer construction

Indpilllion

URBAN

Figure IV3 Hydrological changes inOntario Canada caused byurbanizationSource After OECD (1986) p 43

Table IV5 shows the impact of differentinfluences resulting from the urbanizationprocess

Some workers have found that urbanishyzation has a proportionately greater effecton smaller flood events than on larger oncsIn other words the effects of urbanizashytion appear less important as the size ofthe flood and the interval between floodsincrease A probable explanation for this isthat during a severe and prolonged rainmiddotstorm a rura catchment may become sosaturated over large areas and its channelnetwork so extended that it begins tobehave almost as if it were an imperviousurban catchment with a dense storm drainnetwork Under these conditions a ruralcatchment produces floods rather similarto those of its urban counterpart Alsoin very large floods subsurface drains indties may not be large enough to takethe volume ofwater resulting in less rapidand lower discharge

Urbanization 141

Table IVS Potential hydrological effects of urbanization

Urbanizing influence

Removal of trees andvegetation

Initial construction of housesstreets and culverts

Complete development ofresidential commercial andindustrial areas

Construction of storm drainsand channel improvements

Source KIbler (1982)

Potential hydrological response

Deltreased evapotranspiration and interceptionincreased stream sedimentation

Decreased infiltration and lowered groundwatertable increased storm flows and decreased baseflows during dry periods

Decreased porosity redUcing time of runoffconcentration thereby increasing peak dischargesand compressing the time distribution of the flowgreatly increased volume of runoff and flooddamage potential

Local relief from flooding concentration offloodwaters may aggravate flood problemsdownstream

I~middottPtKtfWIOO

ggt~i~f~~~

Lokinl waltlt mailgtl alwo)$

diJcha1 alrr II undu ~

Rrduetioniolrrfor e-apol1llUpirgttion

SfwI disltllgtrging 0--Stwm akiosn 8wllrr

I+---------III( in rn-------_ 11__ 0lt rrhllgr-----+-j

Figure IV4 Urban effects on groundwater rechargeSource After Lerner (1990) fig 2

Different dties different constructionmethods and other variable factors willall affect the response to rainfall inputsand we should avoid overgeneralizationUrban groundwater provides an exampleWe have suggested that surface runoff isincreased by the presence of impermeable

surfaces One consequence of this wouldbe that less water went to recharge groundshywater However there is an alternatiwpoint of view namely [hat groundwaterrecharge can be accelerated in urban areasbecause of leaking water mains sewersseptic tanks and soakaways (figure rv4)

142 The Waters

In cities in arid areas there is often noadequate provision for storm runoff andthe (rare) increased runoff from impermeshyable surfaces will infiltrate into the permeshyable surroundings In some cities rechargemay result from over-irrigation of parks

FURTHER READING

and gardens Indeed where the climate isdry or where large supplies of water areimported or where pipes and drains arepoorly maintained groundwater rechargein urban areas is likely to exceed that inrural areas

urner D 1990 Groundwater Rechatge in Urban Areas 59-65 IAHS Publicationno 198A cogent account of the role of groundwater in the urban environment

5 LAND DRAINAGE

The drainage of wet soils has been one ofthe most successful ways in which ruralcommunities have striven to increase agri~

cultural productivity It was for examplepractised centuries ago by the EtruscansGreeks and Romans

Large areas of marshland floodplain andother wetlands have been drained to hushyman advantage When water is led awaythe water table is lowered and stabilizedproviding greater soil depth for plant rootshying Moreover well-drained soils warm upearlier in the spring and thus permit cropsto be planted and to germinate earlierFarming is easier if the soil is not too wetsince the damage to crops by wimer freezshying may be reduced undesirable salts arecarried away from irrigated areas and thegeneral physical condition of the soil isimproved In addition drained land tendsto be flat and so is less prone to erosionand more amenable to mechanical cultivashytion It will also be less prone to droughtrisk than certain other types of land Byreducing the area of saturated grounddrainage can alleviate flood risk in somesituations by limiting the extent ofa drainshyage basin that generates saturation excessoverland flow but this is an issue we shallreturn to later

The most spectacular feats of drainageare the arterial drainage systems involv-

ing the construction of veritable rivers andnetworks of large dikes seen for examplein the Netherlands and the Fenlands ofeastern England These have received muchanention However more widespread thanarterial drainage and sometimes independshyent of it is the drainage of individual fieldsThis is done either by surface ditching orby underdrainage with tile pipes and thelike In Finland Denmark Great Britainthe Netherlands Hungary and the fertileMidwest of the USA the majority ofagricultural land is drained

In Britain underdrainage was promotedby government grants and in the 1970s inEngland and Wales reached a peak ofabout1 million hectares per year More recentlygovernment subsidies have been cut andthe uncertain economic future of farminghas led to a reduction in farm expenditureBoth tendencies have led to a reductionin the growth of field drainage which isnow being extended by only about 40000hectares per year (Robinson 1990)

Drainage is a widespread practice whichhas many advantages and benefits Howshyever it can also have environmental costsThe first of these is related to a reductionin the extent of highly important wetlandwildlife habitats (see part II section 9)Marshes fens and swamps are of majorecological significance for a wide range ofspecies

Secondly the drainage oforganically rich

Land Drainage 143

Plate IVS Drainage maintenance on agricultural land in the Fenlands of easternEngland at Spalding in lincolnshire (EPLRichard Teeuw)

Similar subsidence has taken place followshying drainage of portions of the Florida

Figure IVS The subsidence of theEnglish Fenlands peat in Holme FenPost from 1842 to 1960 followingdrainageSource After Goudie (1993) fig 68 fromdata in Fillenham (1963)

sa-kYt1 (OrdnanCf Datum)

bullbull0

-

soils (such as those that contain much peat)can lead to the degradation and eventualdisappearance of peaty materials which inthe early stages of post-drainage cultivashytion may be highly productive for agriculshyture The lowering of the water table makespeats susceptible to oxidation and deflashytion (removal by wind) so that their volshyume decreases One of the longest recordsof this process and one of the clearestdemonstrations of its efficacy has beenprovided by the measurements at HolmeFen Post in the English Fenlands Approximiddotmately 38 metres of subsidence occurredbetween 1848 and 1957 with the fastestrate occurring soon after drainage had beeninitiated (figure IVS) The present rateaverages about 14 em per year At itsmaximum natural extent before the Midshydle Ages the peat of the English Fernandcovered around 1750 sq Ion Now onlyabout one-quarter (430 sq km) remains

144 The Waters

Everglades there rates of subsidence of32 cm per year have been recorded

The moisture content of the soil canalso affect the degree to which soils aresubjected to expansion and contractioneffects which in turn may affect engineershying structures in areas with expansivesoils Particular problems are posed by soilscontaining smectite clays When drainedthey may dry Out and shrink and the soilmay crack damaging the foundations ofbuildings

In Britain there has been considerabledebate about the effects on river Oowsand in particular on flood peaks of drainshying upland peat areas for afforestationThere appear to be some cases where floodpeaks have increased after peat drainageand others where they have decreased Ithas been suggested that differences in peattype alone might account for the differenteffects Thus it is possible that the drainshyage of a catchment dominated by theSphagnum moss would lead to increasedflooding since drainage compacts Sphagshynum reducing both its storage volume andits permeability On the other hand in thecase of peat where Sphagnum moss didnot grow there would be relatively lesschange in structure but there would be areduction in moisture content and an inshycrease in storage capacity thereby tendingto reduce flood flows The nature of thepeat is however just one feature to beconsidered The intensity of the drainageworks (depth spacing etc) may also beimportant In any case there may be two(sometimes conflicting) processes operatshying as a result of peat drainage the inshycreased drainage network will encouragerapid runoff while the drier soil condishytions will provide greater storage for rainshyfall Which of these two tendencies isdominant will depend on local catchmentconditions

The impact of land drainage upon theincidence of floods downstream has alsolong been a source of controversy This

impact depends on the size of the areabeing considered the nature of land manshyagement and the character of the soil thathas been drained Robinson (1990) conshyducted a detailed review of experience inthe UK and found that the drainage ofheavy clay soils that are prone to prolongedsurface saturation in their undrained stategenerally led to a reduction of large andmedium flow peaks He attributed thisto the fact that their natural responsewith limited soil water storage availableis flashy whereas their drainage largelyeliminates surface saturation By contrastthe drainage of permeable soils which areless prone to such surface saturationimproves the speed of subsurface flowthereby tending to increase peak flowlevels

As with so many environmental issuesit is not always easy to determine whetheran increase in flood frequency or intensityis the result of land-use changes of thetype we have been discussing or whethersome natural changes in lOlinfall have playeda dominant role In central and southernWales for example there is some clearevidence of changes in the magnitude andfrequency of floods over recent decadesThis has sometimes been attributed to theincreasing amount of afforestation that hasbeen carried out by the Forestry Commis~

sian since the First World War and to thedrainage of upland areas that this has neshycessitated While in the Severn catchmentthis appears to be a partial explanation inother river basins the main cause of morefrequent and intense floods appears to havebeen a marked increase in the magnitudeand frequency of heavy daily rainfalls Forexample in the case of the Tawe Valleynear Swansea of 17 major floods since1875 14 occurred between 1929 and1981 and only 3 between 1875 and 1928Of 22 widespread heavy rainfalls in theTawe catchment since 1875 only 2 occurshyred during 1875-1928 but 20 bccween1929 and 1981 (Walsh et aI 1982)

Water Pollution 145

FURTHER REAoING

Robinson M 1990 Impact of Improved Land Drainage on River Flows Institute ofHydrology Wallingford UK Report no 113A state-of-the~art review produced by the UKs leading institute for the study ofhydrology

6 WATER POLLUTION

The activities of humans have begun todominate the quality of natural riverwaters both locally and increasingly at aregional scale The ever-increasing humanpopulation and its growing wasteload havebegun to overtax the recycling capabilitiesof rivers The water pollution challengesthat the world faces are enormous Theycan be categorized according to sourceinto three main groups

bull Municipal waste This is composedprimarily of human excreta While itcontains relatively few chemical conshytaminants it carries numerous pathoshygenic micro-organisms

bull InduseriRI wastes These are of veryvaried composition depending uponthe type of industry or processingactivity and they may contain a widevariety of both organic and inorganicsubstances

bull AgriculturRl wastes These are comshyposed of the excess phosphorus andnitrogen present in synthetic fertilmiddotizers and in animal wastes as well asresidues from a number of pesticidesand herbicides

It is also possible to categorize waterpollutants according to whether or notthey are derived from point or nonshypoint (also called diffuse) sources (figshyure N6) Municipal and industrial wastestend to full into the former category beshycause they are emitted from one specificand identifiable place (eg a sewage pipeor industrial outfill) Pollutants from nonmiddot

- ~--~~~~~~---

Figure IV6 Diffuse and point sourcesof pollution into river systemsSource After Newson (1992) fig 77

point sources include agricultural wastesmany of which enter rivers in a diffusemanner as chemicals percolate into groundshywater or are washed off into fields as wellas some mining pollmants uncollectedsewage and some urban stormwater runoff

Possibly the most useful way to categorshyize pollutants is on the basis of their chemishycal physical or biological composition andthis is the framework we shall use for therest of this section We will not cover thewhole range of waste pollutants but conshycentmte on three groups

bull nitrates and phosphatesbull metalsbull synthetic and industrial organic

pollutants

146 The Waters

Nitrates and phosphates are an importamcause of a process called eutrophication(see section 7 below) Nitrates normallyoccur in drainage waters and are derivedfrom soil nitrogen from nitrogen-richgeological deposits and from Mffiosphericdeposition Anthropogenic sources includesynthetic fertilizers sewagl and animalwastlS from feedlots Land-use changes(Ig logging) can also increasl nitrateinputs to streams Perhaps 3S much as oneshythird of the total dissolved nitrogen in riverwaters throughout the world is the resultof pollurion Indeed Peierls et ai (1991)have demonstrated that the quantity ofnitrates in rivers worldwide now appearsto be closely linked to the density ofhuman population nearby Using publisheddata for 42 major rivers they found ahighly significant correlation between nishytrate concentration and human populationdensity that explained 76 per cent of thevariation in nitrate concentration for the42 rivers They maintain that human acshytivity clearly dominates nitrate export fromland Nitrate levels in English rivers arenow clearly rising Current levels (1990s)are between 50 per cem and 400 per centhigher than a quarter of a century ago

Phosphate levels are also rising in someparts of the world Major sources includedetergents fertilizers and human wastes

MetalJ are another major class of pollutshyants Like nitrates and phosphates metalsoccur naturally in soil and water Howshyever as the human use of metals hasburgeoned so has the amount of waterpollution they cause Other factors alsocontribute to water pollution from metmiddotalso Some metal ions reach river watersbecause they become more quickly mobishylized as a result of acid rain (sec part IIIsection 8) Aluminium is a notable examshyple of this From a human point of viewthe metals of greatest concern arc probshyably lead mercury arsenic and cadmium

all of which have adverse health effectsOther metals can be toxic to aquatic lifeand these include copper silver seleniumzinc and chromium

The anthropogenic sources of metalpollution include the industrial processingof ores and minerals the use of metalsthe leaching of metals from garbage andsolid waste dumps and animal and hushyman excretions Nriagu and Pacyna (1988)estimated the global anthropogenic inputsof trace metals into aquatic systems (inshycluding the oceans) and concluded thatthe sources producing the greatest quanshytities were in descending order the folshylowing (the metals produced by eachsource are listed in parentheses)

bull domestic wastewater effluents (arsenicchromium copper manganese nickel)

bull coal-burning power stations (arsenicmercury selenium)

bull non-ferrous metal smelters (cadmiumnickel lead selenium)

bull iron and steel plants (chromium molybshydenum antimony zinc)

bull the dumping ofsewage sludge (arsenicmanganese lead)

However in some parts of the worldmetal pollution may be derived from othersources There is increasing evidence forexample that in the western USA waterderived from the drainage of irrigated landsmay contain high concentrations of toxicor potentially toxic trace elements suchas arsenic boron chromium molybdenumand selenium These can cause humanhealth problems and poison fish and wildshylife in desert wetlands (Lently 1994)

Synthetic and industrial ollInic polutllnnhave been manufactured and released invery large quantities since the 1960s Thedispersal of these substances into watershycourses has resulted in widespread envirshyonmental contamination There are manytens of thousands of synthetic organic

compounds currendy in use and many arethought [Q be hazardous [Q human healthand to aquatic life even at quite low conshycemratiolls - concentrations possibly lowerthan those that can routinclr be measuredby commonl~ available analytical methodsAmong thesl pollutants are syntheticorganic pesticides including chlorinatedhydrocarbon illst([icides (eg DDT) Someof these can rlach harmful concentrationsas a result of biological magnification inthe food chain Other important organicpollutams include PCBs which have beenused extensively in the electrical industry

FURTHER READING

Water Pollution 147

as di-electrics in large trl11stormers andcapacitors PAHs which result ti-om thlincompkte burning of I(lssil fuels variousorganic sohcnrs mcd in industrill anddomestic processes phth~IIltlmiddotS which Ireplasticizers used Illr exunpk in Ih proshyduction of polyvil1~1 chloride rlsills andDBPs which arl a mngc of JisinlcCliollby-products The long-term hlalth tttl-ctsof cumulativc exposure 10 such substancesare difficult to qlanti~ However somework suggests that rhey may be implicatcdin the development of birth detects andcertain types of cancer

Nash L 1993 Water quality and health In P H Gldck (ed) Water in Crisis AGuide to the WorJdJs Freshwater Resources 25-39 New York Oxford University PressAn excellent summary of pollution characteristics and effects

148 The Waters

Past and present pollution of the River ClydeScotlandThe River Clyde which runs woughGlasgow in Scotland has a mean disshycharge of 41 cu mecres per secondh is tidal in its lower sections up [Q

the Tidal Weir upstream of the AlbertBridge It has had a long hiswry ofpollution In 1872 the Royal RiverPollution Commission found theClyde to be the most pollU[ed riverin Scotland Parts were described asa foul and stinking flood Until thebeginning of the nineteenth centurythe river was probably quite deaneven in the heart of Glasgow Howshyever by 1845-50 fish populationshad been eliminated from the upperestuary Poor oxygen conditionsprevented them from returning until1972 (McLusky 1994) In 1872the Clyde through Glasgow was deshyscribed thus its water is loaded with sewage mud fould with sewage gas andpoisoned by sewage waste of every kind - from dye works chemical worksbleach works paraffin oil works tanyards distilleries privies and water closets(quoted in Hammerwn 1994)

This alarming pollution had come about because of the enormous boom inpopulation and industry in the area In summer many of the lower tributarieseg the Black Cart and White Cart were no more than open sewers conveyingsewage and industrial wastes to the main river By the 1930s over fifty years afterthe Commissions report the river was if anything in a worse condition Progressin cleaning it up was hindered by the two world wars and it was only in 1965that effective legislation began [Q improve things In 1968 when the first bioshylogical surveys of the Clyde were done (figure IV7(araquo no fish were foundwithin the boundary of Glasgow nor in the lower reaches of the North CalderSouth Calder Kelvin Black Cart and White Cart By autumn 1983 Atlanticsalmon (Salmo samar) had returned to the Clyde and some fish are now foundin all the river areas shown in figure IV7 Since 1972 dissolved oxygen levels inthe Clyde estuary have improved markedly The greatly improved pol1ution situ~

arion achieved by 1988 is shown in figure rv7(b) The number offish speciesin the upper estuary has steadily increased to 18 in 1978 34 in 1984 and 40in 1992 Thus even rivers with a long history of dire poUution can be cleanedup and their fauna and flora restored

Wat~r Polllltioll 149

Plate IV6 The River Clyde in Central Glasgow (Graham BurnsEnvironmental Picture library)

Figure IV7 The changing pollution of the River Clyde Scotland based onbiological classification of pollution (a) 1968 (b) 1988Source After Hammerton (1994) figs 201202

150 The Waters

7 EUTROPHICATION

The process ofeutrophication can be wellillustrated by the case of the Black Sea

The Black Sea is a very large body ofwater surrounded by land except for itsnarrow shallow connection to the Medishyterranean Sea called the Bosporus It reshyceives river discharge from a land area fivetimes greater than its own and coveringparts of nine different countries Two ofEuropes largest rivers the Danube andthe Dneiper flow into it Over 162 milshylion people live within the catchments ofthese rivers (Mee 1992) Therefore polshylution generated by all these people headsfor the Black Sea The Danube for examshyple currently introduces 60000 tons ofphosphorus per year and some 340000tons of total inorganic nitrogen into theSea

As a result and in spite of its size theBlack Sea shows many of the classic sympshytoms of a process caUed eutrophicationThe symptoms include

bull A gradual shallowing right across thebasin of the so-called euphotic zone(the surface layer ofwater in which thelight level is sufficient for net biologishycal primary production) In otherwords the lake is becoming more turshybid or cloudy thereby reducing theamount of light available to supportlife The decreased light penetration hasresulted in the massive loss oflarge shalshylowmiddotwater plants

bull Dense blooms of a single species ofnanoplankton have developed drashymatically modifying the base of themarine food chain

bull Widespread hypoxia (reduction ofoxygen levels) resulting from the enorshymollS increase in organic matter fallingto the shelf floor from blooming anddecaying organisms Thishas led to the

complete elimination of a large proshyportion of macrobenthie organismsand the demise of formerly rich comshymercial fisheries

What precisely is eutrophication Funshydamentally it is the enrichment of watersby nutrients Among these nutrientsphosphorus and nitrogen arc particularlyimportant as they regulate the growthof aquatic plants The process does occurnaturally - for example when lakes getolder - but it can be accelerated by hushyman activities both by runoff from fertilshyized and manured agricultural land andby the discharge of domestic sewage andindustrial effluents This amhropogenicallyaccelerated eutrophication - often calledcuJmraI eutrophication - commonly leadsas in the case of the Black Sea to excesmiddotsive growths of algae serious depletion ofdissolved oxygen as algae decay after deathand in extreme cases to an inability tosupport fish life It can affect all waterbodies from streams to lakes to estuariesand coastal seas Coastal and estuarywaters are sometimes affected by algal foamand scum often called red tides Someof these blooms arc so toxic that consumshyers of seafood that has been exposed to

them can be affected by diarrhoea someshytimes fatally

The nature of red tides has recently beendiscussed by Anderson (1994) who pointsout that these blooms produced bycertain types of phytoplankton (tiny pigshymented plana) can grow in such abundshyance that they change the colour of theseawater not only to red but also to brownor even green They may be sufficientlytoxic to kill marine animals such as fishand seals Long-term studies at the localand regional level in many parts of theworld suggest that these so-called red tidesare increasing in extent and frequency ascoastal pollution worsens and nutrientenrichment occurs more often

Eutrophication 151

Figure IV8 The natural process of lakeeutrophicationSource After Mannion (1991) fig 63

NIIIritnl input iaIioninm

with

L

Mlt- tnaltllI ftIlICn Iho mInml_ so t1u1 nulritnts IIoOlnodily Igtlibbk (intK) lG

oqwlic 1oninns

INCJWING Nl1T1UENT uvwbull HYDJOSW IJEVELOPS

~iIIP

bull LOW NUTlIOO IllPUTSmiddot1tlGlt DISSOLVW OXYGEN LpoundVpoundlS

bull HIGH NUTIIENT IlVpoundLSbull MAY HAVE lEDUCEDOXYQN UVFLS

Figure IV9 The major components ofthe drainage basin nutrient cycleleading to cultural eutrophicationSource After Newson (1992) fig 74

-

Initially coral productivity increases withrising nutrient supplies At the sametime however corals are losing their keyadvantage over other organisms theirsymbiotic self-sufficiency in nutrientshypoor seas As eutrophication progressesalgae start to win out over corals fornewly opened spaces on the reef beshycause they grow more rapidly than corshyals when fertilized The normally dearwaters cloud as phytoplankton begin tomultiply reducing the intensity of thesunlight reaching the corals furtherlowering their ability to compete At acertain point nutrients in the surroundshying waters begin to overfertilize thecorals own zooxanthdlae which multishyply to toxic levels inside the polypsEutrophication may also lead to blackband and white band disease twodeadly coral disorders thought to becaused by algal infections Throughthese stages of eutrophication thehealth and diversity of reefs declinespotentially leading to death

Eutrophication also has adverse effectson coral reefs This has been explained byWltbe (1993 p 49)

The natural process of eutrophication isshown in figure IVS using the exampleof how a lake ages What has happenedparticularly since the Second World Waris that various human actions have speededup the natural process (figure IV9) Thegrowth in fertilizer usage in the last fivedecades has been increasingly rapid Inspite of the increasing costs of energysupplies and hydrocarbons (from whichmany of the fertilizers are derived) in the1970s world fertilizer production hascontinued to rise inexorably and fertilizershyderived nitrates reach groundwater andrivers For example the mean annual nitrateconcentration of the River Thames whichprovides most of Londons water supplyincreased from around 11 mg per litre in1928 to 35 mg per litre in the 1980s

152 The Waters

Plate IV7 lake Tempe Sulawesi Indonesia (Frederic Pelras)

However it is necessary to point Olltthat the application of fertilizers is not theonly possible cause of rising nitrate levelsSome nitrate pollution may be derivedfrom organic wastes Intensive cultivationmay cause a decline in the amount oforganic matter present in the soil and thiscould limit a soils ability to assimilatenitrogen so that more is lost to waterThe pattern of tillage may also affect theliberation of nitrogen The increased areaand depth of modern ploughing accelershyates the decay of residues and may changethe pattern of water movement in thesoil Finally the area of England coveredby tile drainage has greatly expanded inrecent decades This has affected themovement of water through the soil

FURTHER REAnING

accelerating the flow of leached nitratesand other materials into streams

What can be done to control culturaleutrophicationl Preventive measures mayinclude the introduction oflaws to limit thetype and quantity of permitted dischargesfrom industrial sources Water companiesmay be forced to treat effluent to reduce itsnutrient content Bans can be introducedon detergents containing phosphates as hasalready been done in some areas The mostsevere problems however are posed bynutrients derived from agriculrural sourcesSteps may need to be taken to make agrishyculrure less intensive and to control the apshyplication offertilizers and sludge in locationsfrom which they can easily be washed intostreams and rivers such as floodplains

Mannion A M 1991 Global Environmental Change Harlow LongmanThis useful general review contains some perceptive information on eutrophication

Newson M 1992 Patterns of freshwater pollution In M Newson (cd) Man4gingthe Human Imp4t on the Natural Environment 130-49 London Belhaven PressA hydrological approach to understanding the pathways taken by pollutants

Eutrophication 153

Controlling eutrophication Lake Biwa JapanThe largest freshwater lake in Japancovering 674 sq lon is Lake Biwain Shiga Prefecture Honshu It isone of the oldest lakes in the worldand has a maximum depth of over100 metres The catchment area ofthe lake is less than five times thesurface area of the lake itself andthe lake is fed by high annual preshycipitation and in8ow Until around1950 Lake Biwa was oligotrophic(Le containing low nutrient loads)but since then has become eutrophic(ie containing high nutrient loads)with algaJ blooms first noticed ill1959 and red tides occurring everyyear since 1977

The causes of eutrophic conditionsare linked to the explosive economicdevelopment of the Shiga PrdectureLake Biwa today meets the waterneeds of 13 million people and all their industry The lake also provides animportant freshwater fishery and is of immense cultural and spiritual value Fiftyshytwo per cent of the catchment remains forested although Japanese red pines havereplaced the natural broadlcafforestj 173 per cent of the catchment area is nowurbanized The quality of the lakes water has declined as industry and agriculturehave expanded and domestic wastes have not been managed effectively (Petts1988) Eutrophication peaked in 1978 Since then the lake has shown signs ofimprovement as water quality has responded to a number ofmanagement strategies

A ten-year voluntary use soap campaign among local residents reduced drashymatically the 18 per cent of the toal phosphorus load that had been coming fromdomestic detergents In 1980 a Shiga Prefecture government ordinance regulatedindustrial domestic and agricultural discharges ofphosphorus and nitrogen Sincethen nitrogen and phosphorus concentrations in streams Howing into Lake Biwahave declined by 20 per cent even though population and industry have continshyued to grow Phosphorus levels in the southern part of the lake have also fallenby 30 per cent The Shiga Prefecture government has introduced conservationplans to ensure the monitoring of water quality conservation and environmentaleducation over the long term

Further reading

Petts G E 1988 Water management the case of Lake Biwa Japan Geo8aphishycRI Journal 154 367-76

154 The Waters

8 THERMAL POLLtTTlON

Thermal pollution is the pollution ofwater by increasing its temperJtun AsnlJllY orgJnisms arc SlnsitiC to tempershyature this lorm of pollution In haeconsiderable cologkal significane

Where docs the heat that produces thethermal pollution come from~ One of thelllJin sources in industrialized countries isthe condenser cooling water released frompower stations If there are large concenshytrations of big electricity generating plantsalong one stretch of river as for examplealong the River Trent in the midlands ofEngland the amount of water involvedcan be quite large River water dischargedalter it has been used for cooling may besome 6-9C warmer than it was beforebeing taken out of the river At times oflow flow this can raise river water temshypcntures downstream considenbly

The process of urbanization is anotherfactor that needs to be considered It has

a range of effects changes produced bythe urban heat island effect (see part IIIsection 5) changes in the temperature ofstreams brought about by the presence ofreservoirs changes in the volume of stormrunoff and changes in the nature of urshyban stream channds - how much they arecovered ou or shaded by egct3tion andhow their width and dcpth compare- withnatural channds

The-rmal pollution can also occur in ruralareas Large reservoirs will modify downshystream river temperatures Deforestationwhich removes shade cover may increasewater temperatures particularly in the sumshymer months

Thennal pollution has many ecologicaleffects Tempc=rilture increases can be harmshyful to temperature-sensitive fish such astrout and salmon and an disrupt spawnshying and migration patterns (figure IVIO)An increase in water tempentuce caU$C$a decr~ in the solubility of oxygenwhich is needed for the oxidation of

00~

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29~

24~

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j]1_ G_ _ 1 1_ G_ _ II j- GlllWlbrLpikt prrch WI1le)otsmaIlmoothbass 1tI1- SplIWllinl IIld II~IopmmtIicadbh buffalo shadI j __ Spawning Ind II lkoielopmmt oIlarzrmouth whik ytllow Ind lpotttd baniii i-- Egg dtvdoplllflli ofptrch Ind llIlal1mouth btu I1I__ Spawning~ II dMIopmmt of~ aDd mosllrout1-_ - _ tlJ_ w ~

FIgure JV10 Maximum temperatures for the spawning and growth of fishSouru After Giddings (1975) fig 13-2

biodegradable wastes At the same timethe tate of oxidation is accelerated deshymanding more and mote oxygen from thesmaller supply and thereby depleting theoxygen content of the water still furtherTemperature also affects the lower organshyisms such as plankton and crustaceans Ingeneral the higher the temperatun is theless desirable the types of algae in water

FURTHER READING

Inter-basin Water Transfers 155

In cooler waters diatoms are the predoshyminant phytoplankton in water that is notheavily eutrophic at higher temperatureswith the same nutrient levds green algaebegin to become dominant and diatomsdecline At the highest water temperaturesblue-green algae thrive and often developinto heavy blooms

Langford T E L 1990 Ecological Effects of Thermal Discha1lJes London ElsevierApplied ScienceThe most authoritative advanced treatment of thermal pollution

9 INTER-BASIN WATER

ThANSFERS AND THE

DEATH OF THE ARAL SEA

Increasing rates ofwater consumption andthe unequal distribution ofwater resourcesfrom one region to another mean tharin many parts of the world long-distancetransfers of water are made between riverbasins AJso in the worlds drylands largequantities of water are abstracted fromrivers to supply irrigation schemes One ofthe results of such large-scale modificashytions of river regimes is that the dischargesof some rivers have declined very substanshytially This in turn means that the extentand volume of any lakes into which theyempry have been reduced

Perhaps the most severe change to amajor inland sea or lake is that taking placeto the Aral Sea in the southern part of theformer Soviet Union (figure IVII) Untilvery recently this was the worlds fourthlargest lake with a high level of biologishycal activity and a rich and distinctive aquaticfauna and flora It had considerable comshymercial fisheries and was used for transshyport as weU as sporting and recreationalactivities It was also a refuge for hugeflocks of waterfowl and migratory birdsIt may also have exerted a favourable

climatic hydrological and hydrogeologicaleffect on the surrounding area

However since the 1960s a dramaticchange has taken place The inflow of waterinto the lake has decreased markedly (seefigure lV12) and it has now lost morethan 40 per cent of its area and about 60per ceO( of its water volume The lakeslevel has fallen by more than 14 rneuesIts saliniry has increased threefold Its faunaand flora have been desuoyed so that onlya small number of aquatic species hassurvived The climate around the lake mayalso have been affected The increasingareas ofexposed desiccating and salty lakebed provide an ideal environment for thegenesis of dust storms Such storms nowevacuate some tens of millions of tons ofsalt each year and dump them on agriculshytural land reducing crop yields The hushyman population also seems to be sufferingfrom poorer-quality water supply and fromrespiratory disorders caused by the blowshying salt and dust It is not surprising thereshyfore that the Aral Sea is now regarded asthe greatest ecological tragedy of theformer Soviet Union

Why has the inflow ofwater to the AralSea declined so extraordinarily The mainreason was that in the 1950s and early1960s a decision was taken to expand

156 The Waters

Plate IVS Inter-basin water transfers are vital for the survival of los AngelesThis large canal transports water from inland California (east of the Sierra Nevadamountains) to satisfy the needs of the sprawling conurbation hundreds ofkilometres away (A S Goudie)

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Figure IV11 Irrigation and the Aral Sea

Inter-basin Water Transfers 157

~C- ----1

19M 966I Ilnnow

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J965 JS7C 1m WIO J980 I JFigure IV12 (a) Changes in the Aral Sea 1960-1989 (b) The past and predictedcontraction of the Aral Sea as its level falls50urces (a) After Kotlyakov (1991) (b) Modified after Hollis (1978) p 63

irrigation in Central Asia and Kazakhstanso that crops like rice and conon whichconsume a great deal of water could becultivated in the middle of a desert Largevolumes of fertilizers and herbicides werealso used in growing these crops and thesehave contributed to the deterioration inwater quality In many cases too the irrishygation systems themselves were of poordesign construction and operation

Scientisrs economists and politicians arenow seeking solutions to the Aral tragedySome proposed ideas are

bull The local population should for healthreasons be provided with supplies ofsafe non-polluted piped water

bull The policy of growing cotton in thedeserts of Central Asia needs to bereconsidered

158 The Waters

Plate IV9 The rapid desiccation of the Arat Sea following the extraction of waterfrom the rivers that feed it to supply irrigation schemes has left these boats highdry and redundant (Marcus Rose Panos Pictures)

bull Agriculture needs to be made moreefficient by reducing the very subshystantial losses caused by inadequatestorage and transport infrastructure

bull A fundamental restructuring of theregions economy should be orientedtowards developing products thatdo not require the imensive usc ofwater

bull Irrigation systems need to be reconshystructed to reduce water losses and

FURTHER READING

application of water should be rationmiddotally controlled

bull A policy of expanding the arca of irrishygated agriculture should be replacedby more intensive use of existing irrimiddotgated tracts through better crop rotashytions technologies and the growth ofimproved varieties of crops

bull Attempts should be made to revegetatedesiccated areas to reduce dust stormactivity

MickJin P P 1988 Desiccation of the Aral Sca a water managellHnt disaster in theSoviet Union Science 241 1170-5One of the key papers that drew attention to the situation around the An Sea

Micklin P P 1992 The AnI crisis introduction to the special issue Pon-StnielGgraph] 33 (5) 269-82A coUection of papers on all aspects of tk AnI ampa problem

10 GROUNDWATER

DEPLETION AND

GROUNDWATER RISE

In some parts of the world groundwater isthe main source of water for industrialmunicipal and agricultural use Some rocksincluding sandstones and limestones havecharacteristics that enable them 10 holdand transmit large quantities of waterwhich (an be reached by installing pumpsand boreholes In some cases largeamounts of water can be abstracted withshyOut severe environmental effects This isparticularly true of areas where a combishynation of favourable climate topographygeological structure and rock compositionenables the water-bearing body - theaquifer - to recharge itself rapidly In suchcases the water is a renewable resourceHowever in other cases the rate ofexploishytation may greatly exceed the capacity ofthe aquifer to be recharged In these casesboth the quantity and the quality of thewater supply may deteriorate markedly overtime In such cases it is more appropriateto refer to the extraction ofwater as minshying of a largely non-renewable resource

Let us take m extreme example theexploitation of groundwater resources inthe oil-rich kingdom ofSaudi Arabia Mostof Saudi Arabia is desert so that climaticconditions are not favourable for rapidlarge-scale recharge of aquifers Also muchof the groundwater that lies beneath thedesert is a fossil resource created duringmore humid conditions - pluvials - thatexisted in the Late Pleistocene between15000 and 30000 years ago In spite ofthese inherently unfavourable circumshystances Saudi Arabias demand for wateris growing inexorably as its economy deshyvelops In 1980 the annual demand was24 billion cubic metres (bern) By 1990it had reached 12 bern (a fivefold increasein just a decade) and it is expected to

Changes in Groundwater 159

reach 20 bem by 2010 Only a very smallpart of the demand can be met fromdesalination plants or surface runoff overthree-quarters of the supply is obtainedfrom predominantly non-renewablegroundwater resources The drawdown onaquifers is thus enormous rt has been calshyculated that by 2010 the deep aquitcrswill contain 42 per cent less water than in1985 Much of the water is used ineffecshytively and inefficiently in the agriculturalsector (AI- Ibrahim 1991) to irrigate cropsthat could easily be grown in more humidregions and then imported

Saudi Arabia is not alone in its orashycious appetite for groundwater In manyparts of the world such problems havegrown with increasing population levelsand consumption demands together withthe adoption of new exploitation techshyniques (for example the replacement ofirrigation methods involving animal orhuman power by electric and dieselpumps)

Considerable reductions in groundshywater levels have been caused by abstrac~

tion in other areas The rapid increase inthe number of wells tapping groundwaterin the London area from 1850 until afterthe Second World War caused substantialchanges in groundwater conditions Thepiezometric surface in the confined chalkaquifer has fallen by more than 60 metresover hundreds of square kilometres Likeshywise beneath Chicago Illinois USApumping since the late nineteenth centuryhas lowered the piezometric head by some200 metres The drawdown that has takenplace in the Great Artesian Basin of Ausshytralia exceeds 80-100 metres in someplaces The environmental consequencesof excessive groundwater abstraction inshyclude salinization of coastal aquifers (seepart V section 5) and land subsidence (seepart V section 7)

Some of the most serious reductions inwater levels are taking place in the High

160 The Waters

Plate IV10 A major cause of groundwater depletion is the use of centre-pivotirrigation schemes The Ogallala aqUifer of the High Plains of Texas where thisphoto was taken is a major example of this phenomenon (A S Goudie)

Plains ofTexas threatening the long-termviability of irrigated agriculture in that areaBefore irrigation development started inthe 1930s the High Plains groundwatersystem was in a state of dynamic equilibshyrium with long-term recharge equal tolong-term discharge However the groundshywater is now being mined at a rapid rateto supply centre-pivot and other schemesIn a matter of only fifty years or less thewater level has declined by 30-50 metresin a large area to the north of LubbockTexas The aquifer has narrowed by morethan 50 per cent in large parts of certaincounties and the area irrigated by eachwell is contracting as well yields arc falling

In some industrial areas recent reducshytions in industrial activity have led to

less groundwater being taken out of theground As a consequence groundwaterlevels in such areas have begun to rise a

trend exacerbated by considerable leakagefrom ancient deteriorating pipe and sewersystems This is already happening in Britshyish cities including London Liverpool andBirmingham In London because of a 46per cent reduction in groundwater abstracshytion the water table in the Chalk andTertiary beds has risen by as much as 20metres Such a rise has numerous implicashytions both good and bad

bull increase in spring and river flowsbull re-emergence of flow from dry

springsbull surface water floodingbull pollution of surface waters and spread

of underground pollutionbull flooding of basementsbull increased leakage into tunnelsbull reduction in stability of slopes and

retaining walls

bull reduction in bearing capacity of founshydations and piles

bull increasedhydrostaticupliftandswelJingpressures on foundations and structures

bull swelling of clays as they absorb waterbull chemical attack on building foundations

There are various methods of rechargshying groundwater resources providing thatsufficient surface water is available Wherethe materials containing the aquifer arepermeable (as in some alluvial fans coastalsand dunes or glacial deposits) the techshynique of water-spreading is much usedIn relatively flat areas river water may bediverted to spread evenly over the groundso that infiltration takes place Alternativewater-spreading methods may involve reshyleasing water into basins which are formedby excavation or by the construction of

FURTHER READING

Conclusion 161

dikes or small dams On alluvial plainswater can also be encouraged to percolatedown to the water table by distributing itinto a series ofditches or furrows In somesituations natural channel infiltration canbe promoted by building small check damsdown a stream course In irrigated areassurplus water can be spread by irrigatingwith excess water during the dormant seashyson In sediments with impermeable layshyers such water-spreading techniques are noteffective and the appropriate method maythen be to pump water into deep pits orinto wells This last technique is used onthe heavily setded coastal plain of Israelboth to replenish the groundwater reshyservoirs when surplus irrigation water isavailable and to attempt to diminish theproblems associated with salt-water intrushysion from the Mediterranean

Downing R A and Wilkinson W B (eds) 1991 Applied Groundwater HydrologyA BririJh Pmpecrive Oxford Clarendon PressAn advanced textbook on all aspects of groundwater in the British context

11 CoNCLUSION

Freshwater resources are of vital imporshytance Their quality and quantity have unshydergone major changes as a consequenceof human activities Human demand forfreshwater has grown inexorably in reshycent decades As a result ever-increasingproportions of river flow are being conshytrolled or modified by deliberate humanmanipulation most notably by the conshystruction of dams the channelization ofstreams and by long-distance inter-basinwater transfers As our case study of theColorado River in the USA shows thedegree of control that can be achieved isradical

EquaUy important are changes in thehydrological cycle resulting unintentionshyally from changes in land use and land

cover The replacement of forests withfarms and of countryside with cities aretwo particularly important mechanisms inthis respect Also significant are the conshysequences - some anticipated some not shyof land drainage activities

Humans have modified not only thequantity of river flow but also its qualityMany water resources are polluted by arange of both point and non-pointsources River pollution can lead in turnto eutrophication of lakes and inland andmarginal seas However water pollutionand lake eutrophication as our case studiesof the River Clyde and Lake Biwa showare reversible if proper management stratshyegies are adopted Nonetheless as is shownin the case of the rapid desiccation ofthe AraI Sea the required solutions maybe extremely complex and technological

162 The Waters

change is seldom the only solution Wholeshysale changes in a regions economic andpolitical structure may be required

Finally we have pointed to the imporshytance of groundwater reserves and showedthat in some countries these resources arcbeing exploited at an unsustainable rateIn many areas the water table Ius beendrawn down too fur and too tast We havealso pointed out that in other parts of the

KEy TERMS AND CONCEPTS

aquiferbiological magnificationchannelizationdear-water erosioneutrophication

POINTS FOR REVIEW

world the reverse process is happening andthat groundwater levels are rising

The issues discussed in this part of thebook indicate how problems of humanimpacts on water are complicated by thelinks between bodies of water by themutual interaction of ditlcrent stressesand by the links between water and otheraspects of the environment such as theatmosphere biosphere and land surface

inter-basin water transterspoint and non-point sources of pollutionred tidesthermal pollution

Are dams a good or a bad thing

If you were in charge of providing large quantities of clean water in an area would youseek to increase or decrease the amount of forest in your catchments

How do humans increase the risk of river floods

What is the difference between point and non-point sources of water pollution

What do you understand by the term eutrophication

How do humans change the state of groundwater bodies

PART V

The Land Surface1 Introduction 1652 Soil Erosion by Water 165

bull Soil erosion on the South Downssouthern England 170

3 Wind Erosion and Dune Reactivation 172bull Controlling sand at Walvis Bay Namibia 186

4 River Channel Changes 1785 Salinization 1826 Accelerated Landslides 185

bull Slope erosion in the Pacific nolth-wcstof North America 188

7 Ground Subsidence 1898 Waste Disposal 1919 Stone Decay in Urban Buildings 197

bull Venices decaying treasures 20010 Conclusion 201

Key Terms and Concepts 202Points for Review 202

1 INTRODUCTION

This part of the book focuses on humanimpacts on the land surface - primarilysoils and landforms Humans havt modishyfied soils in many ways Most serious of allhas been the impact of land-use changeson the rates at which soils art eroded bywind and water The quality of soils hasalso been transformed At present fortxample many soils in irrigated regionsare being affected by salinization but atother times and in other places changtsin soil quality have included the formashytion of peat layers podzols and lateritehardpans Soil conditions are atfected bymodern farming practices heavy farmmachintry causes soil compaction andchemical changes are brought about bythe application ofsynthetic fertilizers Thtwhole impact of humans on soils is oftentermed metapedogenesis (table VI)

As well as soils the skin of the earth iscomposed of its landforms Here again thehuman impact can be considerable (tableY2) In particular humans can destabilizehillside slopes and cause wholesale groundsubsidence The range of human impactson landforms and landforming processesis considerable Some landforms may beproduced by dirtct anthropogenic processes Examples are landforms producedby constructional activity (eg tipping)excavation mining and farming (eg tershyracing) Landforms produced indirecdy byhuman activities while less easy to recogshynize are of particular importance Indeedthe indirect and unintentional modificashytion of processes by humans is the mostcrucial aspect of what is called anthropomiddotgeomorphology The geomorphologicaleffects of removing vegetation are anexample of this type of change Sometimeshumans deliberately try to change landshyforms and landforming processes but setin train a series of events which were notanticipated or desired As is noted in part

Soil Erosion by Water 165

VI section 3 for instance many attemptshave been made to rtduce coastal erosionby building impressive-looking and expenshysive engineering structures which have infact exacerbated the trosion rather thanhalting it

2 SOIL EROSION BY WATER

Soil erosion is a natural geomorphologicalprocess which takes place on many landsurfaces Under grassland or woodland ittakes place slowly and apptars to be moreor less balanced by soil formation Accelshyerated soil erosion takes place wherehumans have interfered with this balanceby modifYing or removing the natural vegshyetation cover Construction urbanizationwar mining and other such activities areonen significant in accelerating the probshylem However the main causes of soilerosion are deforestation and agriculture

Forests protect the underlying soil fromthe direct effects of rainfall generating anenvironment in which rates oferosion tendto be low The canopy plays an importantrole both by shortening the fall of rainshydrops and by decreasing the speed atwhich they hit the ground There art exshyamples of ctrtain types of trees (eg beech)in certain environments (eg maritimetemperate) creating large raindrops butin general most canopies reduce the eroshysive effects of rainfalls The prestl1ce ofhumus in forest soils may be even moreimportant than the canopy in reducingerosion rates in forest Humus in the soilboth absorbs the impact of raindrops andleads to soils with extremely high permeshyability Thus forest soils have high infiltrashytion capacities Another reason why forestsoils allow large quantities of water to passthrough them is that they have many largemacropores produced by roots and theirrich soil fauna Forest soils arc also wellaggregated making them resistant to boththe effects of wetting and water drop

166 The Land Surface

Table V1 Metapedogenesls human impacts on the main factors Involved in soilformation

Factor

Parent material

Topography

Climate

Organisms

Time

Human impacts

Beneficial adding mineral fertilizers accumulating shellsand bones accumulating ash removing excess amounts ofsubstances such as saltsDetrimental removing through harvest more plants andanimal nutrients than are replaced adding materials inamounts toxic to plants or animals altering soilconstituents in a way which depresses plant growth

Benehcia checking erosion through surface rougheningland forming and structure building raising land level byaccumulation of material land levellingDetrimental causing subsidence by draining wetlands andby mining accelerating erosion excavating

Beneficial adding water by irrigation rainmaking byseeding douds removing water by drainage diverting windsDetrimental subjecting soil to excessive insolation toextended frost action or to wind and rain

Beneficial introducing and controlling populations ofplants and animals adding organic matter loosening soilby ploughing to admit more oxygen fallowing removingpathogenic organisms eg by controlled burningDetrimental removing plants and animals reducingorganic content of soil through burning ploughingovergrazing harvesting adding or encouraging growth ofpathogenic organisms adding radioactive substances

Beneficial rejuvenating soil by adding fresh parentmaterial or through exposure of local parent material bysoil erosion reclaiming land from under waterDetrimental degrading soil by accelerated removal ofnutrients from soil and vegetation cover burying soilunder solid fill or water

Source Modified from Bidwell and Hole (15)

impact This high degree of aggregation isa result of the presence of considerablequantities of organic material which is animportant cementing agent in the formashytion of large water-stable aggregatesEarthworms also help to produce wellshyaggregated soil Finally deep-rooted treeshelp to stabilize steep slopes by increasingthe total shear strength of the soils

It is therefore to be expected that withthe removal of forest for agriculture orfor other reasons rates of soil loss will riseand mass movements (landslides debrisflows etc) will happen more often andon a larger scale Rates of erosion will beparticularly high if the deforested groundis left bare under crops the increase willbe less marked The method ofploughing

Soil Erosion by Water 167

Table V2 Major anthropogeomorphologlcal processes

Type of process

Dired anthropogenic processes

Constructional

Excavational

Hydrological interference

Indired anthropogenic processes

Acceleration of erosion andsedimentation

Subsidence

Slope failure

Earthquake generation

Source After Goudie (1993)

Examples

Tipping moulding ploughing terracing

Digging cutting mining blasting of cohesiveor non-cohesive materials cratering trampingand churning

Flooding damming canal constructiondredging channel modification drainingcoastal protection

Agricultural activity and vegetation clearanceengineering (especially road construction andurbanization)Incidental modifications of hydrological regime

Collapse and settling related to mininggroundwater pumping and permafrost melting(thermokarst)

landsliding flow and accelerated creep causedby loading undercutting shaking andlubrication

loading by reservoirs lubrication along faultplanes

the time of planting the nature of the cropand the size of the fields will all have aninfluence on the severity of erosion

Many fires are started by humanseither deliberately or accidentally Becausefires remove vegetation and expose theground they also tend to increase rates ofsoil erosion The burning of forests forexample can lead to high rates ofsoil lossespecially in the first years after the fireRates ofsoil loss in burnt forests are oftenup to ten times higher than those in proshytected areas

Soil erosion can also be caused by conshystruction and urbanization A number ofstudies have been done which illustrateclearly that urbanization can create signifishycant changes in erosion rates The highest

rates of erosion are produced in theconstruction phase when there is a largeamount of exposed ground and a lot ofdismrbance from vehicle movements andexcavations The equivalent of many decshyades of natural or even agricultural eroshysion may take place during a single year inareas cleared for construction Howeverconstruction does not go on for ever andeventually the building work is completedThen the disturbance ceases roads aresurfaced and gardens and lawns are culshytivated Rates of erosion fall dramaticallyperhaps to the levels prevailing under natshyural or pre-agriculrurai conditions

Soil erosion by water takes on a varietyof forms Splash erosion and sheet ftowmay occur in some areas Elsewhere rills

168 The Land Surface

Plate V1 Soil erosion at St Michaels Mission in central Zimbabwe A large donga(or erosional gully) has formed as a result of overgrazing and other land-usepressures (A S Goudie)

(small channels) may develop Under moreextreme conditions for example wheresoils are highly erodible large gullies mayform and these may coalesce to form abadlands topography Slopes can becomedestabilized so that mass movementsoccur

Concern about accelerated erosion foshycuses on two main categories of impactThe first of these relates to the threat itposes to our ability to grow crops and tofeed the worlds growing population Soilerosion reduces soil depth and often meansthat the most fertile humus- and nutrientshyrich portion of the soil profile is lost Thesecond category of impact is what aretermed off-farm impacts These include

bull accelerated siltation of reservoirs riversdrainage ditches etc

bull eutrophication of water bodies by the

transport of nutrients attached to soilparticles

bull damage to property by soil~laden waterand debris flows

There is some evidence that soil erosionis becoming a more serious problem inparts of Britain in spite of the fact thatthe countrys rainfall is much less intenseand so less erosive than in many parts ofthe world The following practices mayhave caused this state of affairs

bull Ploughing on steep slopes that wereformerly under grass in order to inshycrease the area of arable cultivation

bull Usc of larger and heavier agriculturalmachinery which tends to increase soilcompaction

bull Use ofmore powerful machinery whichpermits cultivation in the direction of

maximum slope rather than along thecontour Rills often develop along thewheel ruts (wheelings) left by tracshytors and farm implements and alongdrill lines

bull Use of powered harrows in seedbedpreparation and the rolling of fieldsafter drilling

bull Removal of hedgerows and the associshyated increase in field size Larger fieldscause an increase in slope length andthus a higher risk of erosion

bull Declining levels oforganic matter resultshying from intensive cultivation and relishyance on chemical fertilizers which inturn lead to reduced aggregate stability

bull Widespread introduction of autumnshysown cereals to replace spring-sowncereals Because of their longer growingseason autumn-sown cereals producegreater yields and are therefore moreprofitable The change means that seedshybeds with a fine tilth and little vegetashytion cover are exposed throughout theperiod of winter rainfall

Several measures can be used to reducethe rate at which soil is lost from agriculshyturalland In some parts of the world thesetechniques have been practised for sometime and have been quite successful Theyare

FURTHER READING

Soil Erosion by Water 169

bull Revegetation(a) deliberate planting(b) suppression of fire grazing etc

to allow regenerationbull Measures to stop stream bank erosion

(eg stone banks and rip-rap)bull Measures to stop gully enlargement

(a) planting of trailing plants etc(b) weirs dams gabions etc

bull Crop management(a) maintaining cover at critical times

of year(b) rotation of crops(c) growing cover crops(d) agroforestry

bull Slope runoff control(a) terracing(b) deep tillage and application of

humus(c) digging transverse hillside ditches

to interrupt runoff(d) contour ploughing(e) preservation ofvegetation strips (to

limit field width)bull Prevention of erosion from point

sources such as roads and feedlots(a) intelligent geomorphic location of

roads feedlots etc(b) channelling of drainage water to

non-susceptible areas(c) covering of banks cuttings etc

with vegetation

Boardman J Foster I D L and Dearing J A (cds) 1990 Soil Erosion on Agrishycultural Land Chichester WileyAn edited series of advanced reseatch papers providing some useful case studies

Hudson N 1971 Soil Conservation London BaufordA general introductory level textbook

Morgltln R P C 1995 Soil Erosion and Conservation 2nd edn Harlow LongmanA general introduction that is especially strong on methods of controlling erosion

Pimental D (cd) 1993 World Soil Erosion and Conservation Cambridge CambridgeUniversity PressA series of advanced edited papers that look at soil erosion in a regional context

170 The Land Surface

Soil erosion on the South Downs southernEnglandThe South Downs are a rAnge of L3chalk hills in south-east England ~~--J

which rise to an altitude of around todM200 metres They are deeply dis-sccted by a network of dry valleysIn the early Holocene the Downswere wooded and their soils weremuch thicker than they are now Soilsarc now typically shallow and stonyrendzinas with A horizons usuallyless than 25 cm thick Since thexcond World War the dominantland usc in the area has been farmshying of wheat and barley In the 1970s a major change of fuming practice ocmiddotculTed with the adoption of autumn-grown cereals (eg winter wheat) in prefshyerence to lower-yielding spring-sown varieties Farming has also become moreintensive fields have increased in size with the removal ofhedgcs and grass bankswhile larger and more powerful tractors have enabled farmers to cultivate slopesas steep as 25

Plite V2 Sotl erosion and flood runoff on the South Downs southmiddoteastEngland Uohn Boardman)

Soil Erosion by Water 171

figure V1 Typical location and form oferosion on agricultural land on the SouthDowns EnglandSource After Boardman (1992) fig 21

v

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525middot

CHALK

Valleyoonom riU and fan

As a result there has been anincrease in soil erosion by wateron the Downs especially betweenSeptember and December on landprepared for or drilledmiddot with wintercereals This is because large areasof smooth ground with minimalvegetation cover are exposed durshying the wettest months Rills developin hillsides (figure Vl) especiallyalong tractor wheel ruts (wheelshyings) and some gullies havedeveloped along valley bottomsSediment-laden runotT can causeserious problems for nearby housesLocalized erosion and flooding were recorded in 1958 and 1976 but there arefew records of such events earlier in the twentieth cenrnry Frequent and someshytimes serious erosion occurred in the 1980s especially during the wet autumnsand winters of 1982-3 1987-8 and 1990-1 John Boardman has monitoredabout 36 sq km of agricultural land in the area during this time (see table V3)and found that peak soil erosion in the 1987-8 winter season was accompaniedby serious flooding of roads and properties

Further reading

Boardman J 1995 Damage to property by runoff from agricultural land SouthDowns southern England 1976-1993 Geographieal Journal 161 177-91

Table V3 Rainfall and soil erosion on a monitored site in the eastern SouthDowns England 1982-1991

Year Total rainfall1 Sep-1 Mar (mm)

Total soilass(01 metres)

1982-31983-41984-51985-61986-71987-81988-91989-901990-11991-2

724560580453503739324621469298

181627

182541211

135292

9401527

112Source Modifled from Boardman (1995)

172 The Land Surface

3 WIND EROSION AND

DUNE REACTIVATION

In the drier parts of the world or onparticularly light soils wind erosion maybecome a major cause of accelerated soilloss As in the case of accelerated soilerosion by water the key factor is the reshymoval of vegetation cover

Possibly the most famous case of soilerosion by deflation was the dust bowl ofthe 1930s in the USA This was caused inpart by a series of hot dry years whichdepleted the vegetation cover and madethe soils dry enough to be susceptible towind erosion The effects of this droughtwere made very much worse by years ofovergrazing and unsatisfactory farmingtechniques However perhaps the primarycause of the dust bowl was the rapid exshypansion of wheat cultivation in the GreatPlains The number of cultivated hectaresdoubled during the First World War astractors (for the first time) rolled out onto the plains in their thousands In Kansasalone wheat cultivation increased fromunder 2 million hectares in 1910 to alshymost 5 million in 1919 After the warwheat cultivation continued apace helpedby the development of the combine harshyvester and government assistance Thefarmer busy sowing wheat and reapinggold could foresee no end to his land ofmilk and honey but the years of favourshyable climate were not to last and overlarge areas the tough sod which exaspershyated the earlier homesteaders had givenway to friable soils which were very susshyceptible to erosion Drought acting ondamaged soils created the black blizzardsthat carried dust as far as the Atlantic seashyboard (see box in part III section 2)

The dust bowl was not solely a featureof the 1930s and dust storms are still aserious problem in various parts of theUnited States For example in the San

Joaquin Valley area ofcentral California in1977 a dust storm caused extensive damshyage and erosion over an area of about2000 sq kIn More than 25 million tannesof soil were stripped from grazing landwithin a 24middothour period While the comshybination of drought and a very high wind(as much as 300 kIn per hour) providedthe predisposing conditions for the stripshyping to occur overgrazing and the genshyeral lack of windbreaks in the agriculturalland played a more significant role Inaddition broad areas of land had recentlybeen stripped of vegetation levelled orploughed up prior to planting Othercontributory factors albeit quantitltltivdyless important included the stripping ofvegetation for urban expansion extensivedenudation of land in the vicinity of oilshyfields and local denudation of land byrecreational use of vehicles One interestshying observation made in the months afterthe dust storm was that in subsequentrainstorms runoff occurred faster fromthose areas that had been stripped by thewind exacerbating problems of floodingand creating numerous gullies Elsewherein California dust yield has been considershyably increased by mining operations in drylake beds

A comparable acceleration ofdust stormactivity has also occurred in the formerSoviet Union After the Virgin Lands promiddotgramme of agricultural expansion in the1950s dust storms in the southern Omskregion became on average two and a halftimes more frequent and in some localareas five or six times more frequent

We can see how drought and humanpressures can combine to produce accelershyated wind erosion by considering themeteorological data for dust-storm freshyquency at Nouakchott in Mauritania westshyern Africa (figure V2) Since the 1960sthe number of dust storms has gone updramatically from just a few each year toover 80 a year This is partly caused by the

Wind Erosion 173

Plate V3 Gully erosion by water near luyengo central Swaziland southemAfrica (A $ Goudie)

]

l l )

bullo

Figure V2 Annual frequency of duststorm days and annual rainfall forNouakchott Mauritania Africa1960-1986Source After Goudie and Middleton (1992)fig 8

low rainfall of the Sahel drought that hasaftlicted the area bU[ also by human popushylation growth and increased disturbanceof the dcsert surface by vehicles

Wind erosion is also active in certainparts of Britain Dust storms have lxenrecorded in the Fen1ands the BrecklandsEast Yorkshire and Lincolnshire since the1920s and they seem to be happltningmore often in recent years The s[Qrmsresult from changing agricultural practicesincluding the usc of artificial fertilizc=rs inplace of farmyard manure a reduction inthe process of ltc1aying whereby day wasadded to the peat to stabilize it the reshymoval of hedgerows to facilitate the useof bigger farm machinery and perhapsmost importantly the increased cultivationof sugar beet This crop requires a finetilth and tends to leave the soil relativelybare in early summer compared with othercrops

174 The Land Surface

When and where wind erosion of soilstakes place is determined by two sets offactors wind erosivity and surfaceerodibility (table VA) Wind erosion willnormally be reduced if those variablesmarked in the table with a (+) are increasedand if those marked with a (-) are reshyduced (Those marked with a plusmn can haveeither effect) These are important pointsto be considered when selecting consershyvation methods which have to focus onimproving the stability of the soil and reshyducing wind velocities at the soil surface

Table V4 Key factors influencing winderosion of solismiddot

Erosivity Wind variablesVelocityFrequencyDurationMagnitudeShearTurbulence

Erodibility Debris variablesParticle size plusmnSoil clods andcohesive properties +AbradabilityTransportabilityOrganic matter +

Surface variablesVegetation residue +

height +orientation +density +fineness +cover +

Soil moisture +Surface roughness +Surface length(distance from shelter) shySurface slope plusmn

bull See text above for explanation

Source After Cooke and Doomkamp (1993)

Soil conservation measures can be dishyvided into three types

bull agronomic measures which manipulatevegetation to minimize erosion by proshytecting the soil

bull soil management methodJ which focuson ways of preparing the soil to proshymote good vegetative growth and imshyprove soil structure in order to increaseresistance to erosion

bull muhanicaJ methods which manipulatethe surface topography in order toreduce wind velocity and turbulence

Agronomic measures use living vegetationor the residues from harvested crops toprotect the soil Wind erosion problemsoccur on croplands only when the soil isexposed because the crop is not matureenough to provide adequate protectionHence stubble mulching which involvestilling but not to the extent whereby thefield is left dean has become a widelyused method of protection from erosionSoil management techniques are concernedwith different methods of soil tillage thefarmers methods of preparing a suitableseedbed for crop growth and of helpingto control weeds Mechanical methodsinclude the creation of protective barriersagainst the wind such as fences windshybreaks and shelter belts

Another aspect of wind erosion is dunereactivation This occurs on the marginsof the great subtropical and tropical deshyserts and is one facet of the process ofdesertification (see part II section 3)Dune reactivation arouses some of thestrongeS[ fears among those combatingdesertification The increasing populationlevels of both humans and their domesticanimals brought about by improvementsin health and by the provision of boreholeshas led to excessive pressure on the limitedvegetation resources As ground coverhas been reduced so dune instability has

Wind Erosion 175

Plate V4 The use of palm frond fences to reduce sand movement at Erfoudsouthern Morocco (A S Goudie)

increased The problem is not so muchthat dunes in the desert cores are relemmiddotIcssly marching on to moister areas morethat fossil dunes laid down during themore arid phase peaking around 18000years ago have been reactivated in litu bythe removal of stabilizing vegetation

Many methods are used in the attemptto control drifting sand and moving dunesIn practice most solutions to the problcmof dune instability and sand blowing haveinvolved establishing a vegetation coverThis is not always easy Plant species usedto control sand dunes must be able to

FURTHER READING

endure undermining of their roots buryshying abrasion and often severe deficienciesof soil moisture Thus the species selcctedneed to have the ability to recover afterpanial burying to have deep and spreadmiddoting roots to have rapid height growthin the seedling srages to promote rapidliner development and to add nitrogento the soil through root nodulcs Duringthe early stages of growth they may needto be protected by fences sand trapsand surface mulches Growth can also bestimulated by the addition of syntheticfertilizers

Goudie A S (ed) 1990 Techniques for Desert Reclamation Chichester WileyThis edited work contains several chapters on the control of dunes and dust hazards

176 The Land Surface

Controlling sand at Walvis Bay NamibiaThe movement of sand can be aserious problems for the inhabitantsof the worlds drylands Sand stormsreduce visibility on roads whileencroaching dunes can overwhelmhouses farms canals and transportlinks For this reason humans havedeveloped a range of techniques totry to control drifting sand andmoving dunes (table vS)

One location where moving sandhas proved to be a severe problemand where many of these controltechniques have been attempted isthe port town of Walvis Bay on thecoast of Namibia in southern Africa(figure V3) Here the annual rainshyfall is so low (around 2S mm) thatvegetation cover is minimal allowshying sand to move when windvelocities reach critical levels (as theyoften do) Many of the dunes nearWalvis Bay are individual crescentshyshaped dunes called barchans Theseare highly mobile travelling sometens of metres per year From timeto time they have blocked roadsthey have also caused the relocationof the main railway link with theinterior The local authority is tryshying to stabilize the sand by suchmeans as planting (and irrigating)shrubs and building sand fences (seeplates V4 V5)

PfiwI ~

- ir i WaMII Bay i

i Y - - - - - - - - - - - - - - - - - - 23S

ProbIelll$lronl dtiftirlJ wld dunA

it i t--AncicoldiltrigtIIwJolKuiKb iiu

~~ flood proIecion dun

N

I

~WIlI __

Figure V3 The coastal zone nearWalVis Bay Namibia The main coastroad is often blocked by sand whilethe main raHway line has had to berelocated inland

Tll

~

~

Wind Erosion 177

Plate V5 A road has been blocked by a migrating barchan dune nearWalvis Bay Namibia Sand fences have been constructed in an attempt toslow the process down (H A Viles)

Table VS Control technlque$ for drifting sand and mobile dunes

Problem

Drifting sand

Moving dunes

Control methods

Enhancement of deposition of sand through creatinglarge ditches vegetation belts and barriers and fencesEnhancement of sand transport by aerodynamicstreamlining of surface or changing surface materialsReduction of sand supply by surface treatmentimproved vegetation cover or erection of fencesDeflection of moving sand by fences barriers orvegetation belts

Removal by mechanical excavationDestruction by reshaping trenching through dune axis orsurface stabilization of barchan armsImmobilization by trimming surface treatment andfences

178 The Land Surface

4 RIvER CHANNEL CHANGES

River channels developed in alluvium(sediments deposited by the river itself)adjust their shape slope and velocity offlow in response to discharge sedimentload the calibre of the bed and bank sedishyment the banks vegetation and the slopeof the valley Humans have intervened innatural channel systems by building damsrealigning channel courses constructinglevees and embankments and in manyother ways (see part IV section 2) Howshyever they have also altered channel charshyacteristics unintentionally (table V6) forexample by modifYing the amounts ofdisshycharge the amount of sediment beingcarried and the nature of vegetation onthe river bank Sometimes too deliberatechanges have set in train a series of unshyintended changes

Let us consider channel straighteningFor purposes of navigation and flood conshytrol humans have deliberately straightenedmany river channels The elimination ofmeanders contributes to flood control intwo ways First it eliminates some floodsover banks on the outside ofcurves wherethe current is swiftest and where the water

Table V6 Accidental channel changes

surface rises highest Second and moreimportandy the shorter straightenedcourse increases both the gradient andthe velocity of the stream Floodwaterscan then erode and deepen the channelthereby increasing its flood capacity Deshyliberate channel-straightening causes varishyous types of adjustment in the channelboth within and downstream from straightshyened reaches The types ofadjustment varyaccording to such influences as stream grashydient and sediment characteristics (figureVA) Brookes (1988) has recognized fivetypes of change within the straightenedreaches (types WI to W5) and twO typesofchange downstream (types Dl and D2)

bull Type WI is degradation of the channelbed This happens because straightenshying shortens the channel path andtherefore increases the slope This inturn increases the efficiency ofsedimenttransport

bull Type W2 is the development of anarmoured layer on the channel bed bythe more efficient removal of finematerials as described under Type WI

bull Type W3 is the development of a sinushyous thalweg in streams which are not

Phenomenon

Channel incision

Channel aggradation

Channel enlargement

Channel diminution

Channel diminution

Cause

Clear-water erosion below dams caused by sedimentremoval

Reduction in peak flows below damsAddition of sediment to streams by mining agricultureetc

Increase in discharge level produced by urbanization

Discharge decrease following water abstraction or floodcontrol

Trapping and stabilizing of sediment by artificiallyintroduced plants

River Channel Changes 179

Plate V6 A completely artificial stream channel in Maspalomas Gran CanariaCanary Islands (A S Goudie)

Figure V4 Principal types of adjustment in straightened river channelsSource After Brookes (1987) fig 4

180 The Land Surface

only straightened but also widened beshyyond the width of the natural channel

bull Type W4 is the recovery of sinuosityas a result of bank erosion in channclswith high slope gradients

bull Type W5 is the development of a sinushyous course by deposition in streamswith a high sediment load and a rclashytivcly low valley gradient

bull Types 01 and 02 result from deposishytion downstream as the stream tries toeven out its gradient The depositionmay occur either as a general raisingof the levcl of the bed or as a series ofaccentuated point bar deposits

Another influence on channel form isthe growth ofsettlements It is now widclyrecognized that the urbanization of ariver basin results in an increase in thepeak flood flows in a river (see part Nsection 4) It is also recognized that themorphology of stream channels is relatedto their discharge characteristics and esshypecially to the discharge at which bankfull flow that is a complete filling of thechanncl occurs As a result of urbanizashytion the frequency ofdischarges which IiIlthe channcl will increase This will meanthat the beds and banks of channcls inerodible materials will be eroded so as toenlarge the channel This in turn will leadto bank caving possible undermining ofstructures and increases in turbidity

Similarly important changes in channelmorphology result from the lowering ofdischarge caused by flood-control worksand diversions for irrigation This can beshown for the North Platte and the SouthPlatte Rivers in America where both peakdischarge and mean annual discharge havedeclined to 10-30 per cent of their preshydam values The North Platte 762-1219metres wide in 1890 near the WyomingshyNebraska border has narrowed to about60 metres at present The South PlatteRiver 89 kIn above its junction with the

1m

Figure VS The configuration of thechannel of the South Platte River atBrule in Nebraska USA (a) in 1897and (b) in 1959 Such changes inchannel form result from dischargediminution caused by flood controlworks and diversions for irrigationSource After GoudIe (1993) fig 615(a)

North Platte was about 792 metres widein 1897 but had narrowed to about 60metres by 1959 The tendency of bothrivers has been to form one narrow wellshydefined channel in place of the previouslywide braided channels The new channclis also generally somewhat more sinuousthan the old (figure VS)

The building of dams can lead to chanshyncl aggradation upstream from the resershyvoir and channcl deepening downstreambecause of the changes brought about insediment loads The overall effect of th~

creation of a reservoir by the constructionof a dam is to lead to a reduction in downshystream channel capacity of about 30-70per cent

Equally far-reaching changes in channclform are produced by land-use changesand the introduction of soil conservationmeasures Figure V6 is an idealized repshyresentation of how the river basins ofGeorgia USA have been modified throughhuman agency between 1700 (the time ofEuropean settlement) and the presentClearing of the land for cultivation (figureV6(b)) caused massive slope erosion which

lbi

1lt1

Xvcdy erodeduplmds

Partial to cOOIpkttc~ndfilliJIg

~tlk lWmank ckposition

River Channel Changes 181

Trees lilJcd by thensing aler bd

Ltvm wIUky fillofmodern itdimenll

BloCm=p

Regrowth d lOmuprcdOOlinaody pine

Accumulation of~nt1y miggttiogsedirncnt ClwInol

Rill aggrading

Drained badslIolmpI I Suem iJlcised in modltrn lCdirncnt

Intensive coomaINm IcticQT- broad-based [(rrmspntUfC in Bermuda gr1Sl

Trees in bonomlands nor SoolI for darilf

SW oflm-kswoImp increasing

Figure V6 Changes in the evolution of the fluvial landscapes of the Piedmont ofGeorgia USA in response to land-use change between 1700 and 1970 (a) at thetime of European settlement c1700 (b) after the clearing and erosive cultivationof uplands (c) after the checking of erosion and the consequent incision of theheadwater streamSource After Trimble (1974) p 117

182 The Land Surface

resulted in large quantities of sedimentbeing moved into channels and floodplainsIntense erosive land use continued and wasparticularly strong during the nineteenthcentury and the first decades of the twenshytieth century Thereafter (figure V6(c))conservation measures reservoir construcshytion and a reduction in the intensity ofagricultural land use led to further chanshynel changes (Trimble 1974) Streamsceased to carry such a heavy sediment loadand became much less turbid As a resultthey cut down imo the floodplain sedishymems of modern alluvium lowering theirbeds by as much as 3-4 metres

Anmher causc of significant changes inchannels is the accelerated sedimentationassociated with changes in the vegetationgrowing alongside the channels In thesouthern USA the introduction of a bushytree the salt cedar has caused significant

FURTHER READING

floodplain aggradation In the case of theBrazos River in Texas for example theplants encouraged sedimentation by theirdamming and ponding effect Theyclogged channels by invading sand banksand sand bars and so increased the areasubject to flooding Between 1941 and1979 the channel width declined trom 157metres to 67 metres and the amount ofaggradation was as much as 55 metres(Blackburn et al 1983)

Finally mining can lead to very majorchanges in channel morphology The reashyson for this is that mining often requiresthe use of large quantities of water andproduces large quantities of waste Thewaste tends to lead to the aggradation ofthe channel bed and if the waste materialis coarse then there may be a tendency fora natural meandering pattern to be reshyplaced by a braiding one

Brookes A 1988 Channelized Rivers Chichester WileyAn advanced research monograph with broad scope

5 SALINIZATION

Salinity is a normal and natural feature ofsoils especially in dry areas Howevervarious human activities are increasing itsextent and severity

Salinity in soils has a range of undeshysirable consequences For example asirrigation water IS concentrated byevapotranspiration calcium and magneshysium components tend to precipitate ascarbonates leaving sodium ions dominantin the soil solution The sodium ions tendto be absorbed on to colloidal clay parshyticles deflocculating them and leavingthe soil structurdess almost impermeableto water and unfavourable to root develshyopment Poor soil structure and toxicitylead to the death of vegetation in areas ofsaline patches This creates bare ground

which is vulnerable to erosion by windand water

Probably the most serious result ofsalinization is its impact on plant growthThis takes place partly through its effecton soil structure but more significantlythrough its effects on osmotic pressuresand through direct toxicity When a watersolution containing large quantities ofdisshysolved salts comes into contact with a plantcell it causes the cells protoplasmic liningto shrink This is due to the osmoticmovement of me water which passes outfrom the cell towards the more concenshytrated soil solution The cell collapses andthe plant dies

This toxicity effect varies with differentplants and different salts Sodium carbonshyate by creating highly alkaline soil condishytions may damage plants by a direct caustic

effect high nitrate may promote undesirshyable vegetative growth in grapes or sugarbeets at the expense of sugar contentBoron is injurious to many crop plants atsolution concentrations of more than 1 or2 ppm

There are a variety of reasons why soilsalinity is spreading The most importantof these is the growth in the area ofirrigated land which has increased fromabout 8 million hectares in 1800 to 250million hectares in the 1990s (Thomasand Middkton 1993) The extension ofirrigation and the use of a wide range ofdifferent techniques for water abstractionand application can lead to a build-up ofsalt levels in the soil This happens beshycause water abstraction raises the groundshywater level so that it is near enough to theground surface for water to rise to thesurface by capillary action Evaporation

Salinization 183

then leaves the salts in the soil In the caseof the semi-arid northern plains of Victoshyria in Australia for instance the water tablehas been rising at around 15 metres peryear so that now in many areas it is linlemore than 1 metre below the surfaceWhen groundwater comes within 3 memiddottres of the surface in day soils - less forsilty and sandy soils - capillary forces bringmoisture to the surface where evaporationtakes place leaving salts behind

Second many irrigation schemes spreadlarge quantities of water over the soilsurface This is especially true for ricecultivation Such surface water is readilyevaporated so that again salinity levelsbuild up

Third the construction of large damsand barrages to control water flow and to

give a head ofwater creates large reservoirsfrom which further evaporation can take

Plate V7 A satanic mockery of snow Waterlogged and salinized land in SindPakistan The white surface is not snow but salt a major cause of decliningagricultural yields (A S Goudie)

Source Grelck (1993) table E5

Table V7 Salinization of irrigated cropshyland In selected countries

an increase in recharge rates of groundshywater and to an increase in the salinity ofstreams as salty groundwater seeps outfrom the ground and into stream flowReplanting has been shown to reverse theprocess (Bari and Schofield 1992)

Salinity can also be increased by salinematerials transferred from lake beds thathave dried up because of inter-basin watertransfers Around 30-40 million tonnesof salty soils are blown off the Aral Seaevery year (see part IV section 9) forexample and these add to the salt contentof soils downwind

It has been estimated (table V7) thatsalt-affected and waterlogged soils accountfor 50 per cent of the irrigated area in

184 The Land Surface

place The water gets saltier This saltywater is then used for irrigation with theeffects described in the previous paragraph

Fourth water seeps laterally from irrishygation canals especially in highly permeshyable soils so that further evaporation takesplace Many distribution channels in agravity irrigation scheme are located onthe elevated areas ofa floodplain or riverineplain to make maximum use of gravityThe elevated landforms selected are natushyral levees river-bordering dunes and tershyraces all of which arc composed of siltand sand which may be particularly proneto loss by seepage

In coastal areas salinity problems arccreated by seawater incursion broughtabout by overpumping of fresh groundshywater from aquifers If the aquifer is opento penetration from the sea salty watertends to replace the freshwater that hasbeen extracted This is a particularly sershyious problem along the shores of the Pershysian Gulf where bccallS( of the dry dimatethe freshwater can only slowly be replenshyished by rainfall However it can be aproblem for any coastal aquifer

Increases in soil salinity are nm restrictedto irrigated areas In some parts of theworld salinization has resulted fromvegetation clearance (Peck 1978) Theremoval of native forest vegetation allowsmore rainfall to ~netrate into deeper soillayers This causes groundwater levels torise creating seepage sometimes of salinewater in low-lying areas Through thismechanism an estimated 200000 hectaresof land in southern Australia which atthe start of European settlement in thelate eighteenth century supported goodcrops of pasture is now suitable only forhalophytic species Similar problems existalso in North America notably in Manishytoba Alberta Montana and North Dakota

The clearance of the native evergreenforest (predominantly Eucalyprusforest) insouth-western Australia has led both to

Country

AlgeriaAustraliaChinaColombiaCyprusEgyptGreeceIndiaIranIraqIsraelJordanPakistanPeruPortugalSenegalSri lankaSpainSudanSyriaUSA

of irrigated landsaffected by salinization

10-1515-2015202530-40

727lt30501316lt401210-1510-151310-152030-3520-25

Iraq up to 40 per cent of all Pakistan 50per cent in the Euphrates Valley of Syria30-40 per cent in Egypt and up to 30 percent in Iran In Africa however wherether~ are fewer great irrigation schemesless than 10 per cent of salt-affected soilsare so affected because of human action(Thomas and Middleton 1993) Lookingat the problem on a global basis the calshyculations of Rozanov et al (1990) makegrim reading They estimate (p 210) From1700 to 1984 the global areas of irrigatedland increased from 50000 to 22000001on2

while at the same time some 500000kIn2 were abandoned as a result ofsecondshyary salinization They believe that in thelast three centuries irrigation has resultedin I million sq km of land destroyed plus1 million sq kID of land with diminishedproductivity due to salinization

Given the seriousness of the problem arange of techniques for the eradicationconversion or control of salinity have beendeveloped These have been reviewed byRhoades (1990) and include the following

FURTHER READING

Accclerated Landslides 185

bull provision of adequate subsoil drainshyage to prevent waterlogging to keepthe water table low enough to reducethe effects of capillary rise and to reshymove water that is in excess of cropdemand

bull leaching of salts by applying water tothe soil surface and allowing it to passdownward through the root zone

bull treatment of the soil (with additions ofcalcium magnesium organic matteretc) to maintain soil permeability

bull planting of crops which do not needmuch water

bull planting of crops or crop varieties thatwill produce satisfactory yields undersaline conditions

bull reduction ofseepage losses from canalsand ditches by lining them (eg withconcrete)

bull reduction in the amounts of waterapplied by irrigation by using sprinkshylers and tricklers

bull storage of heavily salted waste waterfrom fields in evaporation ponds

Worthington E B (ed) 1977 Arid lAnd Irrigation in Dneloping Countries Envishyronmenttd ProblemJ and Effects Oxford PergamonA collection of papers that was among the first and most persuasive considerations ofthe problem caused by the rapid spread of irrigation schemes

6 ACCELERATED LANDSLIDES

In 19632600 people were killed in Italywhen a great landslide fell into a reservoirand caused a mass of water to spill overthe dam and cascade downstream Threeyears later at Aberfan in South Wales amassive debris flow killed over ISO peoplewhen it destroyed a school and houses asit rID down from a steep coal-waste tipThese are just two of the worst examplesof how human actions have created hazshyardous mass movements on slopes

Human capacity to change a hillside and

to make it more prone [Q failure has beentransformed by engineering developmentExcavations are going deeper buildingsand other structures are larger and manysites which are at best marginally suitablefor engineering projects are now beingused because of increasing pressure onland This applies especially to some ofthe expanding urban areas in the humidparts of low latitudes - Hong Kong KualaLumpur Rio de Janeiro and many othersMass movements are very seldom deshyliberately accelerated by human agencyMost are accidentally caused the exception

186 The Land Surface

possibly being the delibcrate triggering ofa threatening snow avalanche

The forces producing slope instabilityand landsliding can usefully be divided intodisturbing factors and resisting propertiesSome disturbing factors art natural othersmarked with an asterisk in the followinglist are caused by humans

bull Removal of lateral or ulld(rlyjn~q supshyportundercutting by wattr (tor exampleriver waves) or glacier icewcathering of weaker strata at the tOCof the slopewashing out of granular material byseepage erosionmiddothuman cuts and excavations drainmiddotage of lakes or reservoirs

bull Increased disturbing forcesnatural accumulations of water snowtalusmiddotpressure caused by human activity (forexample stockpiles of are tip-heapsrubbish dumps or buildings)

bull Transitory earth stressesearthquakesmiddotcontinual passing of heavy traffic

bull Increased internal pressurebuildmiddot up of pore-water pressures (forexample in joints and cracks especiallyin the tension crack zone at the rear ofthe slide)

Factors leading to a decrease in the reshysisting properties (shear strength) of thematerials making up a slope can also besummarized as follows Again those reshysulting from human activity are markedwith an asterisk

bull Materialsbeds which decrease in shear strengthif water content increases (clays shalemica schist talc scrpentine) for exshyample middotwhen local water table is artishyficially increased in height by reservoir

construction or as a result of stressrelease (vertical andor horizontal)following slope formationlow internal cohesion (tor example conshysolidated clays sands porous organicmatter)In bedrock faults bedding planesjoims foliation in schists ceaagebrecciated zones and pre-existingshears

bull Weathering changesweathering reduces effective cohesionand to a lesser extent the angle ofshearshying resistanceabsorption of watcr leads to changesin the fabric of days (for exampk lossof bonds bcrween particles or the forshymation of fissures)

bull Pore-JVater pressure jncreaseHigh groundwater table as a result ofincreased precipitation or middotas a resultof human interference (for example-dam construction) (see under Matershyials above)

Some mass movements are created byhumans piling up waste soil and rock intounstable accumulations that fail spontaneshyously The disaster at Aberfan in SouthWales referred to at the beginning of thissection occurred when a pile ofcoal waste180 metres high began to move as an earthflow The pile had been constructed notonly with steep slopes but also upon aspring line

In the case of the Vaionr Dam disasterin Italy (also referred to at the begilUlingof this section) heavy rainfall and the presshyence of young highly folded sedimentaryrocks provided the necessary predisposingconditions for a slip to take place Howshyever it was the construction of the VaiontDam itself which changed the localgroundwater conditions sufficiently toaffect the stability of a rock mass on themargins of the reservoir The result wasthat 240 million ell metres of ground

Accelerated Landslides 187

Table VS Examples of methods of controlling mass movements

Type of movement Method of control

Falls Flattening the slopeBenching the slopeDrainageReinforcement of rock walls by grouting with cementanchor boltsCovering of wall with steel mesh

Slides and flows Grading or benching to flatten the slopeDrainage of surface water with ditchesSealing surface cracks to prevent infiltrationSubsurface drainageRock or earth buttresses at footRetaining walls at footPilings through the potential slide mass

Source Dunne and leopold (1978) table 1516

slipped with enormous speed into thereservoir producing a sharp rise in waterlevel which spilled over the dam causingflooding and loss of life downstream

It is evident from what has been saidabout the predisposing causes of the slopefailure triJ8eretl by the Vaiont Dam thathuman agency was only able to have suchan impact because the natural conditionswere broadly filVourable to such an outshycome

Although the examples of acceleratedmass movements that have been givenhere are associated with the effects ofmodern construction projects more long-

FURTHER READING

established activities including deforeshystation and agriculture arc also highlyimportant For example Innes (1983) hasdemonstrated on the basis of the size oflichens developed on debris-flow depositsin the Scottish Highlands that most ofthe flows have developed in the last 250years He suggests that intensive burningand grazing may be responsible Presentshyday deforestation can generate spectacularmass movements

Because of the hazards presented bymass movements a whole series of techshyniques have been developed to attempt to

control them (table VB)

Cooke R U and Doornkamp J c 1993 Geomorphology in Environmental Manageshyment 2nd edn Oxford Oxford University PressThis general text contains useful material on slope problems and their control

Dikau R Brunsden D Schrott L and Ibsen M-L 1996 Landslide RecognjrionChichester WileyAn edited text rich in European examples which describes and classifies the main typesof landslides that pose hazards to human activities

188 The Land Surface

Slope erosion inNorth America

the Pacific north-west of

The mountainous regions of Oregon Washington British Columbia and Alaskaare areas with steep slopes high rainfall and active tectonics They are thus areasof high potential erosion rates Heavy forest vegetation and the high infiltrationcapacities of many forest soils protect the slopes however the removal of forestin the area and road-building to take the timber out have had a series ofprofoundeffects Studies by Swanston and Swanson (1976) have shown a dramatic increasein the occurrence of violent debris avalanches flows and slides (table V9) Theseshallow mass movements leave scars in the form of spoon-shaped depressionsfrom which up to 10000 cu metres of soil and organic material have moveddownslope They may move as fast as 20 metres per second Clear-cutting offorest results in an acceleration by two to four times of debris avalanche erosionwhile road construction could accelerate debris avalanche erosion by between 25and 340 times the rate under undisturbed forest

Table V9 Debris-avalanche erosion in forest c1eapcut and roaded areas

Site Period ofrecords(years)

Area(sq km)

No ofslides

Debris-avalancheerosion(cu metressq kmyr)

Rate of debrisshyavalancheerosion relativeto forested areas

Stequaleho Creek Olympic PeninsulaForest 84 193 25Clear-cut 6 44 0Road 6 07 83Total 244 108

Alder Creek western Cascade Range OregonForest 25 123 7Clear-cut 15 45 18Road 15 06 75Total 174 100

718o

11825

4531171

15565

x 10o

x165

x 10x 26x344

Selected drainages Coast Mountains south-west British ColumbiaForest 32 2461 29 112Clear-cut 32 264 18 245Road 32 42 11 2825Total 2767 58

H Andrews Experimental Forest western Cascade Range OregonForest 25 498 31 359Clear-cut 25 124 30 1322Road 25 20 69 1n2Total 642 130

x 10x 22x 252

x 10x 37x 49

7 GROUND SUBSIDENCE

Like many of the environmental issuesdiscussed in this book ground subsidencecan ~ an entirely natural phenomenonFor example climatic change may causepermanently frozen subsoil (permafrost) todecay in tundra areas this will produceswampy depressions called thermokarstLikewise in limestone areas true karsticphenomena such as swallow holes maydevelop when the ground surface collapsesinto a subterranean cavity produced by thesolution of limestone over a long period

Nevertheless humans are now causingground subsidence to occur at an accelermiddotating rate and with dramatic consequencesin certain sensitive areas The main mechshyamsms are

bull the transfer and removal of subterrashynean fluids such as oil gas and water

bull the removal of solids either throughunderground mining (eg coal andother minerals) or in solution (eg salt)

bull the disruption of permafrostbull the compaction or reduction of

sediments (especially organic-rich ones)by irrigation and land drainage

bull the construction of reservoirs

Ground subsidence is often a relativelygentle progress but sometimes it can besudden and catastrophic This is particushylarly the case in areas where the bedrockis limestone and where overpumping hasgreatly drawn down the level of the watertable A sensitive area of this kind is theFar West Rand of the Transvaal ill SouthAfrica when gold mining has requiredthat the local water table be lowcred bymore than 300 metres The tall of thewater table has caused clay-rich materialsfilling the roofs of large underground cavesto dry Out shrink and collapse This inturn has caused large depressions to deshyvelop at the ground surface In densely

Ground Subsidence 189

populated urban areas this is a considershyable hazard In another limestone areaAlabama in the southern USA groundshywater pumping has caused over 4000sink-holes or related features to formsince 1900 Fewer than 50 natural sinkshyholes developed in that area over the sameperiod

More gentle but in geological termsstill very rapid has been ground subsidshyence caused by oil abstraction The classiccase is the Los Angeles area where over 9metres of subsidence occurred as a resultof the development of the Wilmingtonoilfield between 1928 and 1971 Considerthat 9 metres is more than the averageheight of a two-storied house Even morewidespread is the subsidence caused bygroundwater abstraction for industrialagricultural and domestic purposes InMexico City subsidence of more than 75metres has occurred while in the CentralValley of California the figure exceeds 85metres In Tokyo Japan subsidence hasbrought some areas below sea level In1960 only 35 sq km of the Tokyo lowshyland was below sea level By 1974 thisfigure had almost doubled exposing atotal of 15 million people to major floodhazard Bangkok is suffering from a simshyilar problem

Perhaps the most familiar example ofground subsidence caused by humans isthat resulting from mining It causes damshyage to houses roads and other structuresas well as disrupting surface drainage 1l1dcausing flooding

In permafrost areas ground subsidenceis associated with thermokarst deeJopshymem Therl1lokant is the irregular humshymocky terrain produced by the melting ofground ice permafrost The developmentof thermokarst is due primarily to the disshyruption of the thermal equilibrium of thepermafrost and an increase in the depthof the active layer (the layer subjected toannual thawing) Consider an undistur~d

190 The Land Surface

tundra soil with an active layer of 4S emAssume also that the soil beneath 4S emis supersaturated permafrost and uponthawing yields (on a volume basis) SO percent water and 50 per cent saturated soilIf the top 15 em were removed the equishylibrium thickness of the active layer underthe bate ground conditions might increaseto 60 em As only 30 em of the originalactive layer remains 60 em of the permashyfrOSt must thaw before the active layercan thicken to 60 em since 30 em ofsupernatant water will be released Thusthe surface subsides 30 em because ofthermal melting associated with thc= deshygrading permafrost to produce an overalldc=pression of 4S em

Thus the kc=y factors involvc=d inthermokarst subsidence are the state of theactive layc=r and its thermal relationshipsWhen surface vegetation is cleared forpurposes of agriculture or construction forexample the dc=pth of thaw will tend to

increase as the ground will no longer beinsulated from the effects of dirc=et sunshylight The movement of uackc=d vehicleshas been particularly harmfuJ to surfacevegc=tation and deep channels may soonrc=sult from permafrost degradation wherethe$( have been used Similar c=ffects maybe producc=d by siting hc=atc=d buildings onpermafrost and by laying oil sewer andwater pipes in or on thc= active layer

Some subsidence is creatc=d by a processcalled hydrocompaction This occurs beshycause moisture-deficient unconsolidatedlow-density sediments tc=nd to have suffishycic=nt dry strength to support considenbleeffective stresses Vtithout compacting

FURTIIER READING

However when such sediments which mayinclude alluvial fan materials or loess art

thoroughly wetted for the first time (forexample by percolating irrigation water)the inter-granular strength of the depositsis diminished Rapid compaction resultsand subsidence of the ground surface folshylows Unequal subsidence can crate probshylems for irrigation schemes

Land drainage can promote subsidenceof a different type notably in soils rich inorganic matter The lowering of the watertable makes peat susceptible to oxidationand deflation (being blown away by thewind in dust storms) so that its volumedecreases We discuss this in the context ofthe English Fenlands in part IV section S

A further type of subsidence sometimesassociated with earthquake activity rcsultsfrom the effects on the earths crust oflarge masscs of water impounded behinddams Seismic effects can be generated inareas with susceptible fault systems Thismay account for eanhquakcs recorded at

Koyna (India) and elsewhere The processwhereby a mass of water causes crustaldepression is called hydro-isostasy

It is clear from this discunion thatground subsidence is a diverse but imporshytant facet of the geomorphological impactof human activity The damage caused ona worldwide basis can be measured in bilmiddotlions of dollars each year We have menshytioned some of the forms such damagetlkes in this section They include brokendams cracked buildings offset roads andrailways fractured well casings deformedcanals and impeded drainage among manyothers

Johnson A T (ed) 1991 LAnd SubJidmu IAHS Publication no 200A large collection of research-level papers

Waltham A C 1991 LAnd Subsithnu Glasgow BlackicA lower-level inuoductory study which is particularly strong on the effects of miningon subsidence

WaS[( Disposal 191

8 WASTE DISPOSAL

Waste can be loosely defined as all unshyused unwanted and discarded materialsincluding solids liquids and gases (Costaand Baker 1981 p 397) Alternatively itcan be defined as something for which

(Il tllUlllPJamptd WUQ

we have no further use and which we wishto get rid of However it is defined thereis no doubt that waste is generated in largequantities by humans that the amount ofwaste generated develops as societies bltshycome greater consumers of materials andthat the control and disposal of waste is a

tJ -A-

(~~

~-~

H ~-~aSlltS Rcoolltl of Runoff (fOOl urban lltiddquitioll TUJi spiJLampltllI fmnbnd ldltIiriva rmllJld tnJ other Ivtd rK khgcI

-8 ttltmM~ t B lilli ft- HolINtiIliun hydfQIrigttgtts gt011 W)

p(flriiti

~_-----Dmmilt nd 0001TlCrltial9

r8 PtMpwlIpoundIhpWttrgt

Demolition and llIUQuoon 8B Irbk rMJ fIa~iP

-- bull------------~

(tl DispouJ motIwllb for~ WUltl

(UKdl - toulfOO millioo ton)

~ -------UodIiU 57 -8 _Mew

-riIeI illIItgtUII W bullbullUI

--Ii I

SCi dlllllping 1~54_4yullllilriamps__IJIlliIIUIi

itWlIriM fMjiulJ

Figure V7 The main sources of and disposal strategies for wastes that canpollute land and water early 19905Source After Woodcock (1994) fig 161

192 The Land Surface

Table V10 Wastes arising In Englandand Wales late 19805

Source House of Commons EnvironmentCommittee Second Report Toxic Waste(19889)

major environmental issue Furthermorethe disposal of waste can substantiallymodify surface conditions and produce anarray of environmental impacts

Wastes can be divided into those thatare unmanaged and those that arc manshyaged (figure V7(a) and (braquo)

Table VIO shows the amounts of difshytcrcllt cangories of waste produced in Engshyland and Wales In terms of sheer wdghtliquid industrial etfhunt is the largest comshyponent but the production of emucntfrom the agricultural sector is also imporshytant Significant amounts of primarily solidwaste arise trom mining and quarryingindustrial sources the domestic seerorsewage sludge power station ash blast furshynace slag and the building ami cOllStrucshytion industries In the USA an average dtywith 250000 inhabitants has to collecttransport and dispose of 450 tonnes ofrefuse every day In general about 2-3 kgof municipal waste and 3-4 kg of industrialwaste are produced in the USA per person

Waste type

liquid industrial effluentAgriculturalMining and quarryingIndustrial

HazardousSpecial

Domestic and tradeSewage sludgePower station ashBlast furnace stagBuildingTotal

Quantity(mtlyr)

2000250130

503915

28241463

2505

per day In the UK about 137 million tonnesofcontrolled waste (waste which is eitherincinerated or disposed of to a landfill) areproduced every year Landfill takes 90-95per cent of the controlled waste

In this section we are mainly concernedwith solid waste a category which includesmaterials from a wide range of sources(table VII) There are a number of disshyposal options for solid waste (figure V7(c)) As we have already noted the mostimportant of these in the UK is so-calledsanitary landfill (table Vl2) The relashytive importance of different methods varshyies from country to country (table VI3)For example whereas most municipal solidwaste in the UK and Australia goes to

landfills in Switzerland nearly half is inshycinerated and in Japan about two-thirds isincinerated

The content of waste is also highly varishyable Some types contain contaminants thatcan pose a series of hazards to health andproperty (table VI4) For example inshydustrial waste may contain dangerous heavymetals building waste may contain asbesshytos and household food waste may genshyerate potentially explosive methane gasIf sites are not carefully controlled wastedraining from the site (leachate) may beheavily polilited Other problems are posedby the bct that landfill ma~ graduallycompact through time

Landfilling is a cheap means of disposalIn countrie~ where there are manr oldquarries and gravel pits it may be a conshyenient way not only to dispose of wastebut also to reclaim such land lor otheruses Such sites are not always availablehowever in cloS( proximity to sourcesAlso if the~ are badly managed they canproduce environmental problems of rhetypes just discussed

There may be advantages in reducingthe amount of landfill capacity that is reshyquired A range of methods is available

Waste Disposal 193

Table V11 Refuse materials (solid waste)

Type

Garbage

Rubbish

Ashes

Street refuse

Dead animals

Abandonedvehicles

industrial wastes

Demolition wastes

Constructionwastes

Special wastes

Sewage treatmentresidue

Composition

Wastes from preparation cookingand serving of food marketwastes wastes from handlingstorage and sale of produce

Combustible paper cartons boxesbarrels wood shavings treebranches yard trimmings woodfurniture bedding

Residue from fires used for cookingand heating and from onmiddotsiteincineration

Sweepings dirt leaves catch-basindirt contents of litter receptacles

Cats dogs horses cows

Unwanted cars and trucks left onpublic property

Food-processing wastes boilermiddothouse cinders lumber scraps metalscraps shavings

lumber pipes brick masonry andother construction materials fromrazed bUildings and other structures

Scrap lumber pipe otherconstruction materials

Hazardous solids and liqUidsexplosives pathological wastesradioactive materials

Solids from coarse screening andfrom grit chambers septic-tanksludge

Sources

Households restaurantsinstitutions storesmarkets

Same as garbage

Same as garbage

Streets Sidewalksalleys vacant lots

Same as street refuse

Same as street refuse

Factories power plants

Demolition sites to beused for new buildingsrenewal projectsexpressways

New constructionremodelling

Households hotelshospitals institutionsstores industry

Sewage treatmentplants septic tanks

Source Costa and Baker (1981) table 13-1 Data from Institute for Solid Wastes of theAmerican Public Works Association and Bureau of Solid Waste Management 1970

Incineration

Sanitary landfills

Method

Open dumps

194 The Land Surface

Table V12 Methods of solid waste disposal

Description

Practices vary from indiscriminate piles to periodic levellingand compacting

little effort taken to prevent rodents flies odours andother health hazards

Often located with little planning where land was available

Consists of alternating layers of compacted refuse and soiLEach day refuse is deposited compacted and covered withsoilDaily operation and a final cover of at least 70 em ofcompacted soil prevents many health problems

Requires planning for economical operation and for suppliesof topsoil for cover Operations vary depending ontopography and supplies

Reduces combustible waste by burning at 1700F to aninert residue Ash and noncombustibles dumped or placed inlandfills

Air pollution is a problem with poor management

Increasing in use and often combined with a sanitary landfilland salvage operation

Onmiddotsite disposal Small-scale incinerators and garbage disposals

Incinerators are expensive and require considerablemaintenance

Garbage disposals are increasing rapidly in use with wastetransferred directly to the sanitarymiddotsewer system

Swine feeding A decreasingly used method which involves collection ofgarbage for swine food (pig swill)

Composting Biochemical decomposition of organic materials to a humusshylike material usually carried out in mechanical digesters

Increasingly used method with a useful end product whichis often sold

Source Costa and Baker (1981) table 13-3 from Schneider (1970)

Waste Disposal 195

Tabe V13 Selected solid waste material statistics for various countries

Country Annual per capita disposed disposedprodudion (kg) by landfill by incineration

Australia 681 98 2Austria 216 57 19Canada 642 94 6Denmark 420 64 32France 289 33 32Germany (W) 447 83 9Italy 246 38 20Japan 342 28 67Netherlands 502 66 19Sweden 300 52 38Switzerland 336 13 49UK 332 80 6USA 744 nla nla

Source UNEP (1990)

Table V14 Some commonly encountered contaminants the sites on which theyare likely to occur and the principal hazards they produce

Underground fires

Principal hazards

Harmful to health ofhumans or animals ifingested directly orindirectly May restrictor prevent the growthof plants

Explosions within orbeneath buildings

Chemical attack onbuilding materials egconcrete foundations

Contamination of watersupplies by deteriorationof service mains

Dangerous jf inhaled

Likely to occur

Metal mines iron and steelworllts foundries smeltersElectroplating anodizing andgalvanizing works

Engineering works egshipbuilding Scrap yards andshipbreaking sites

Gasworks power stationsrailway land

landfill sites filled dockbasins

Made ground includingslags from blast furnaces

Other metals egcopper nickel zinc

Type of contaminant

Toxic metals egcadmium lead arsenicmercury

Combustiblesubstances eg coaland coke dust

Flammable gases egmethane

Aggressive substanceseg sulphateschlorides acids

Oily and tarrysubstances phenols

Chemical worllts refineriesby-products plants tardistilleries

Asbestos Industrial buildings Wastedisposal sites

Source Attewell (1993) table 41

196 The Land Surface

Plate VS Landfill is one way of disposing of waste but the choice of sites to usecan be a problem This site is filling in old gravel pits near Didcot central England

bull Incineration can greatly reduce thevolume ofwaste However incineratorsare expensive to construct and maycreate pollutant emissions to the auConcerns have been expressed forexample about dioxin emissions Onthe positive side incinerators can proshyduce usable energy

bull Compaction can also reduce wastevolume Powerful hydraulic rams canbe used to compress waste

bull Shredding and baling can also reducewaste volume

FURTHER READING

However it may be mort desirable toreduce the amount of waste produced inthe first place This can be achieved by

bull substituting durable goods for dispos-able ones

bull composting garden wastebull generating less wastebull reusing materials and extending their

lives (eg by using rechargeable batshyteries and refillable bottles)

bull recycling paper glass etcbull recovering materials from waste (eg

magnetic separation of ferrous metals)

Douglas T 1992 Patterns of land water and air pollution by wastes In M Newson(ed) Managing the Human Impact on the Natural Environment Patterns and Promiddotcesses 150-71 London Belhaven PressA very useful review chapter in an introductory textbook

9 STONE DECAY IN URBAN

BUILDINGS

The natural materials we use for buildingare just as prone to weathering and alterashytion as are natural rock outcrops Simishylarly manufactured building materials suchas bricks concrete and plastics also decayand change once in contact with theatmosphere Usually such decay processesare of no real concern as they act veryslowly and produce only slight changes tothe appearance of buildings monumentsand engineering structures and do notaffect their strength safety or economiclife-span However where decay processesbecome accelerated and altered usually asa result of air pollution they can oblitershyate priceless carvings prcxiuce unsightlydecay features and lead to structural weakshyness Many buildings and monuments areat risk from the historic basilica of StMarks in Venice to Lincoln Cathedral inEngland the Parthenon in Athens and theMerchants Exchange Building in Pniladelshyphia In many cities whole groups of buildshyings and monuments are under attackExamples are the historic university townof Oxford in England and the lxautifulcity of Prague in the Czech Republic

Buildings in the urban environment areparticularly vulnerable to decay because ofthe following factors

bull urban microclimatic changes such aswarming and increased local rainfall orhumidity

bull air pollution such as increased conshycentrations of sulphur dioxide andnitrogen oxides

bull increased urban traffic levels which conshytribute to air pollution lead to applishycation of de-icing salts in winter inmany temperate-zone cities and causevibrations affecting roadside buildings

Stone Decay in Urban Buildings 197

~ DStQIttff

3 C~~ ) cpm~~ r~lt ~ Lichtns

- ron surfacfWi

)

0) () (d) () if) disroloralKln

Figure VS Some common forms ofbUilding stone decay (a) sooty andgypsum encrustations on shelteredparts of a building (b) blistering andexfoliation of gypsum crusts from (a)(c) cracking (d) pitting blistering andexfoliation of porous stone which hasbeen affected by salts (e) lichengrowths on stone with biologicalweathering underneath (f) surfacelowering and roughening by add rain

bull increased human contan with buildshyings leading to abrasion graffiti etc

Cities on coasts and within the arid zonesuffer particularly from highly corrosiveenvironments because of high concenshytrations of salt in the atmosphere andgroundwater

These environmental conditions inurban areas produce the following effectson building and monument surfaces (seefigure VS)

bull gypsum crusts produced by directchemical reaction of sulphur dioxidewith calcium carbonate-rich stone

bull soiling of building materials by sootyparticulates commonly prcxiuced by coaland oil combustion and diesel engines

bull accelerated lowering of surfaces proshyduced by acidified rainfall hitting calshycium carbonate-rich stone

198 The Land Surface

Plate V9 Decaying bUildings in Venice The sheltered portion of the columnshows the development of a black crust which contrasts sharply with the lightcolour of the portion of the column that is washed by rain (Dr 8 Smith)

bull exfoliation and blistering produced bysalt crystallization and hydration inporous materials

bull cracking produced by vibration andother stresS(s

bull pitting and surface growths producedby organic colonization especially bymicro-organisms and lichens possiblyencouraged by nitrogen oxides actingas fertilizers

Vast changes in pollution and environshyment have occurred in many cities overrecent years These changes have had conshysequent impacts on the weathering anddecay of buildings and monuments Thusa rapid increase in urban traffic andphotochemical pollution in Athens seemsto have been reflected in increasing stonedamage on the many ancient marblemonuments in the city In other cities suchas those in Britain and the USA legislamiddottion to combat air pollution has resultedin sharp decreases in sulphur dioxide andsmoke pollution over the past 40 yearsbut not in nitrogen oxides Measurementsfrom St Pauls Cathedral in London howshyever indicate that the rate of decay inbuilding stone has not yet declined Inshydeed stone decay may worsen in someplaces as nitrogen oxides act as a fertilizerfor organic growths such as bacteria andlichens which are important agents ofstone decay

How serious a problem is urban stonedecay and what can we do about it Interms of cost stone decay can be a seriousproblem for the owners of buildingsespecially when it has turned into a longshyterm problem In Oxford England forexample by the middle of the twentiethcentury 200 years or so of air pollutionfrom domestic and industrial coal burninghad produced intense damage to buildshyings constructed from the rather vulshynerable Headington Freestone (a locallimestone which weathers badly in pollutedatmospheres) Restoration work costing

FURTHER READING

Stone Decay in Urban Buildings 199

over pound24 million was carried out in the1950s and 1960s More recently trafficand other sources ofair pollution arc damshyaging these restored buildings as well asnew ones and soiling paintwork withinthe city centre Stone decay is particularlyserious when it affects monuments ofgreatcultural and spiritual significance especiallythose which attract large numbers of tourshyists and their associated income Decaycan also be hazardous as when it affectsbridges or causes bits ofstone to fall fromhigh towers In most cities however buildshying stone decay is just one symptom ofincreasing urban pollution and environshymental despoliation The impacts of airpollution on human health and urbanecology in cities are also of great concern(as discussed in paC[ II section 8 and paC[III section 6)

Suategies for combating urban buildingstone decay include

bull removing the causes of accelerateddecay by reducing air pollution stopshyping the application ofddcing salts to

roads etcbull removing vaJuable and vulnerable sculpshy

tures and carvings from the aggressiveurban environment putting them inconuolled museum environments andreplacing them with copies

bull cleaning and repairing soiled and damshyaged buildings

bull preventing future -decay by applyingprotective treatments on new or newlycleaned and repaired stone

Winkler E M 1975 Stone Properties Durability in Mans Environment ViennaSpringer-VerlagContains much information about many aspects of stone weathering

Cooke R U and Gibbs G 1994 Crumbling Heritage Studies of Stone Weatheringin Polluted Atmospheres Report for National Power picA useful summary of the recent worries over stone decay in Britain and results fromresearch aimed at elucidating the problem

200 The Land Surface

Venices decaying treasures

Venice in Italy contains many imporshytant buildings and monuments whichform a key part of the European culshytural heritage and which are underthreat from decay accelerated by airpollution and rising u=a levels Thereare also over 2000 pieces ofoutdooran mainJy stone carvings and sculpshytures within the city Studies of oldphotographs have revealed that moSdeay has occurred since the SecondWorld War The cause seems to bethe high sulphur dioxide levels resultshying from rapid post-war industrialshyization of the surrounding area (DelMonte and Vittori 1985) Since1973 laws have banned the use ofoil within the city itself replacing itwith methane However pollutionstill drifts in from elu=where and much u=rious decay has already occurred Smokeand sulphur dioxide react with marble limestone and calarcous sandstones toproduce the blackened gypsum crusts vhich now coat many ampmoos buildings inVenice These crusts are not only unsightly they are also damaging the undershylying stone A local relative sea-level rise has been a problem over the past centuryin Venice This has been caused by a combination of natural subsidence andextraction of groundwau~r (which has now ceased) As well as creating floodingsuch higher u=a levels have had a less visible impact on Venices environmentthrough encouraging the penetration of water and salts into vulnerable buildingmaterials The humid environment also encourages the transformation ofcalciumcarbonate into gypsum in the presence of sulphur dioxide

Major research is currently under way into stone decay in Venice coupled withmany schemes to restore damaged buildings and outdoor art Estimates of thecosts of restoration suggest that all the sculptures and carvings in Venice couldbe restored at a cost of some $US9S million Grime accounts for IS per centof the damagt requiring conservation corrosion or decay accounts for 35 percent and structural problems for the remaining SO ~r ctnt (Carrera 1993)

Considerable care has to be taken in attempting to clean and restore valuableobjects and buildings It is essential first to diagnose the major causes of decaycorrectly Only then can the most appropriate solutions be proposed The Churchof Santa Maria dei Miracoli for example has marble decoration slabs which arcbadly damaged Surveys revealed that salts from rising damp were the major causeof decay and techniques to remove the salts were develop=d before any restotamiddottion began

10 CONCLUSION

In this part of the book we have considshyered the impact that humans have had onthe soil on geomorphic processes and onlandforms We have drawn attemion tothe unintended acceleration of rates ofsoilerosion by water caused by a range ofhuman actions including deforestation theuse of fire and urban growth Acceleratedsoil erosion threatens soil fertility andagricultural productivity It also has otheroffarm impacts which indude a lowershying of water quality While this has oftenbeen seen as a particular problem in dcmiddotveloping countries where it has been idenshytified as onc facet of desertification andland degradation we have also shown thatit is a problem demanding attemion inthe British context Likewise acceleratedsoil erosion by wind has been a majorproblem not only in the Sahel zone ofAfrica and China but also in the techshynologically advanced farmlands of theUSA and the lowlands of Britain Thereare however a wide range of soil conshyservation measures that can be adoptedto counter both water and wind eroshysion caused by land-use and land-coverchanges

Land-use and land-cover changes arealso responsible for many other geoshymorphological changes They affect theform of river channels and the nature ofmass movements (including landslides)on slopes As is the case with soil erosionnumerous methods arc available to try tostabilize slopes and so reduce the hazardsposed by slope failures

Soil erosion and accelerated landslidesare not the only serious ways in which theEarths surface materials are transformedIn particular the spread of irrigation andthe removal of trees can lead to one ofthe most pernicious forms of soil transshyformation or metapedogenesis acceler-

Conclusion 20 I

ated salinization This is a major problemfor agricultural production especially inthe drier parts of the world Again a rangeof techniques for the eradication conshyversion or control of salinity have beendeveloped

Another form of accelerated geoshymorphological change that we hac idenshytified for a range of environments fromthe tundra regions to the worlds greatdeserts is ground subsidence However inmany parts of the world it is not so muchthe subsidence of the ground that is theproblem but where to put the cvcrshyincreasing quantities of waste which weproduce Landfill is one solution but therearc other options including incinerationcompaction shredding and baling A morefundamental solution is to reduce theamount of waste produced in the firstplace

Finally we draw attention to the factthat humans alter the weathering environshyment particularly by subjecting rocks andother building materials to corrosive airStone decay whether in Venice or Oxshyford Prague or York Athens or Agra is aserious threat to our cultural heritage Eventhough the process is slow compared withthe accelerated soil erosion mentionedearlier in this part it can have a seriousimpact on buildings and monuments

Overall the human impacts on the landsurface discussed in this section are a rathermixed bag often spatially limited in exshytent and often inadvertently caused Theyare nevertheless serious and show linkshyages with human impacts on the bioshysphere and atmosphere Many technologishycal solutions have been developed to dealwith these problems Nevertheless asseveral of our case studies have shownthe success of such schemes depends onthe willingness and ability of the peopleinvolved at all levels to implement andmaintain them

202 The Land Surface

KEy ThRMS AND CONCEPTS

accelerated landslidesaccelerated soil erosiondune reactivationforest soilshydrocompactionlandfillmass movementspermafrost

POINTS FOR REVIEW

salinitysand controlseawater incursionsoil conservatonsubsidencethetmokarstwaste

Why shouJd we be concerned about soil erosion

How would you seek to control rates of soil erosion by (a) wind and (b) water

What are the main ways in which humans unintentionally cause river channel characshyteristics to change

Why is salinization such an important issue in the worlds drylands

What are the main geomorphological hazards that are being accelerated by humanactivities

How in your own life could you reduce the need for waste to be disposed of aslandfill

Is there are evidence in your own home area that buildings are suffering from severeweathering Why might this bd

PART VI

Oceans Seas andCoasts1 lncroduction 2052 Sea-level Rise 206

bull Sea level rise and the Essex coast marshesEngbnd 208

3 Coastal Erosion 210bull Erosion at Victoria Beach Nigeria 213

4 Coastal flooding 215bull flooding at Towyn North Wales

February 1990 2165 Coastal and Marine Pollution 218

bull Pollution in the Mediterranean Sea 2206 Coastal Dune Management 222

bull Muuging dunes on the lancashire coast

England 2257 Coral ReefDegradation 226

bull Threatened reefS ofthe Red Sea 2308 Aquaculnue and Coastal Wedands 232

bull Pond culture in the Philippines 2349 Conclusion 235

Key Tenns and Concepts 235Points for Review 236

1 INTRODUCTION

Today almost 3 billion people (about 60per cent of the worlds population) livenear coasts often in large cities Furthershymore coastal popuJations are rapidly increasshying In the USA for example populationdensity is growing faster in coastal statcsthan inland ones Nearly half of all buildshying in the USA between 1970 and 1989occurred in coastal regions which accountfor only 11 per cent of the countrys totalland area Similar trends are found in manyother countries

Human activity is contributing to arange of local and regional environmentalproblems in coastal areas The main envirshyonmental impacts along the worldscoastline involve disruption to coastal sedishymentation pathways through erosion andaccelerated deposition increased floodhazard through sea-level rise and encourshyagement of local subsidence disruption ofcoastal ecology through reclamation of

Introduction 205

land and changing land uses and coastalpollution Historically attempts to manmiddotage the coastal ecosystem have involvedtrying to make the coast more stable andfixed These have made many environmenshytal problems worse In recent years an extradimension has been added to concerns overcoastal environmental problems with thethreat of accelerated sea-level rise in thefuture as a result of global warming

The worlds oceans and seas cover over70 per cent of the Earths surface and playa vitaJ role in the biosphere These vastbodies of water are also being affectedby a range of human impacts Pollution isthe major worry Some pollutants comefrom ships and oil platforms but most arefrom onshore sources reaching the sea viathe atmosphere rivers or coastal outfallsFishing and harvesting of marine resourcesaJso have adverse consequences for the mashyrine environment leading to more pollushytion and also damaging ecosystems About53 million toones ofmarioe fish are caught

TropIc ofCIJm

Tropic ofCprirom

bull~

-- CltWIII KltgtIog ltiMply inJIutllCfd by pollution

Aniflri1 lt1115S (diktbullbull hubows lind ttbmgttion tic) ofloogtr atto

Figure VI1 World distribution of major coastal problemsSource After Kelletat (1989)

206 Oceans Seas and Coasts

worldwide for human consumption everyyear with an additional 22 million tonnescollected for processing into fish mealoil etc (Taiba and EI-Kholy 1992) Atpresent the most severe problems are reshystricted to enclosed seas such as the Medishyterranean and Baltic Seas surrounded bydense populations However the evershyincreasing load of pollution entering theworlds oceans is likely to cause wider proshyblems in the future

Coastal areas particularly vulnerable toenvironmental problems include estuariesdeltas and other low-lying coasts especiallyin highly populated areas Figure Vllshows the global distribution of suchareas Parts of the Mediterranean BalticNorth Sea and Bangladesh coasts arcparticularly vulnerable to a whole range of

FURTHER READING

problems Natural and human-inducedprocesses combine to create coastal proshyblems In most cases these do not occurin isolation but rather interact to producea complex web of stresses on the environmiddotment Thus salt-marsh erosion may beexacerbated by pollution which interfereswith the plant-sediment relationship vitalto marsh development where such eroshysion occurs it may encourage floodingStresses on one part of the coastline mayaffect other parts For example deforestashytion can cause mangrove swamp erosionwhich in turn leads to downdrift degradashytion of coral reefs as they become chokedby the extra sediment load The destrucshytion ofcoral reefs in turn encourages stormdamage to the coastal zone behind thereefs that once sheltered it

GESAMP 1990 The State of the Mnrine Environment Oxford Blackwell ScientificAn authoritative global survey of marine pollution

Bird E C F 1985 Coastline Changes Chichester WileyA counrry-by-country survey of the erosional state of the worlds coastline

Viles H A and Spencer T 1995 Coastal Problems London Edward ArnoldA textbook which surveys with many examples the range of ways in which humansinteract with the natural coastal processes

2 SEA-LEVEL RISE

Sea level is perhaps a misleading termfor the relative positions of land and oceansare continually changing on a variety oftime-scales These fluctuations range fromdaily tidal cycles to vast changes in oceanvolume related to glacial and interglacialcycles over periods of thousands and milshylions of years However a practical definishytion of mean sea level is the long-termaverage (usually over 19 yean at least) ofhigh and low tide levels at a particularplace This level is affected by changes inthe volume or mass of water (eustatic orglobal changes) and movements of land

(tectonic and isostatic changes) or a comshybination of the two Over the past 18000years since the peak of the last Ice Agethe rising volume of ocean water as theicc on land melted coupled with complexisostatic changes has produced a generallyincreasing mean sea level over the world

Individual areas however have experishyenced very different sea-level histories(Clark et al 1978) Over the past 1000or so years sea level has risen (accordingto a range of evidence) at 01-02 mm peryear During the last 100 years sea-level risehas accelerated to l0-25 mm per yearaccording to many estimates This accelershyation is mainly due to climatic factors such

S~a-l~v~1 Ris~ 207

as th~ thermal ~xpansion of oc~an watersand the melting of ice on land E

bullIt is predicted that over the next 50 to -100 years global warming will lead to a tfurther acceleration of the rat~ of sea-level lris~ through a combination of two effects

bull

bull increased volume as ocean warer warmsup (call~d the steric effect)

bull addition of water to the oceans fromth~ melting of small glaci~rs and largeic~ she~ts

Th~ direct impact of human actions on sealevel may also provide an additional accelshyeration These actions and their conseshyquences include the following

extraction of oil and groundwater mayencourage coastal subsidence

bull d~forestation may encourage incrtasedfreshwater runoff to oceans

bull groundwater extraction for irrigationand damming of rivers to produce resshyervoirs may encourage evaporation ofthis water which will eventually r~turn

to the oceans (Sahagian et aI 1994)bull w~dand drainage reduces the water holdshy

ing capacity ofw~dand soils and thereshyfore adds more wat~r to the oceans

It is very difficult to predict how suchinfluenc~s might combine to aff~ct seashylevel ris~ in the futur~ The b~haviour ofsom~ of th~ compartments of the system(eg ice sheets) is not well understoodand the magnitude of global warming in

High

Middlt

1-

Y - -- ---- 1-

----- -

00Yo

Figure VI2 Best estimate high middleand low projections of sea-level riseto the year 2100 under the IPCCemissions scenario IS92aSource After Wigley and Raper (1992)fig 4

the next few decades is itselfthe subject ofmuch debate Howewr the most recentestimates suggest an average sea level riseof about 5 mm per year over the nextcentury within a range of unc~rtainty of2-9 mOl per year This will produce a totalincrease ofabout 50 cm by 21 00 as shownin the middle curve in figure VI2 andm~ans that sea level will rise two to fivetimes fast~r than over th~ last 100 years(Watson ~t aI 1996) This rat~ althoughhigh is much lower than some ~arlier

estimates which predicted wid~spread

drowning of many coastal ar~as Whatev~r

its precise magnitude future s~amiddotlevel ris~

in association with a whol~ host of small~rhuman-induced and natural disturbancesis likely to provid~ a complex seri~s of~ffects on th~ coastal ~nvironment

208 Oceans Sus and Coasts

Sea-level rise and the Essex coast marshes England

bull

N

I

ESSEX

bull

FIgure VI3 The Blackwater estuaryEssex and its associated marshes andmudflatsSource After Pethick (1993) figs 1 2

=

Much of the eastern and southerncoasdine of England is already undershygoing rdative sea-Ievd rise Isostaticreadjustments to the removal of theicc cap over northern Britain at theend of the last lee Age (some 11000yurs ago) arc causing the north ofBritain to risc forcing the southernpart down as a consequence TheEssex coast has been experiencingrelative sea-level rise of 4-5 mm peryear over the past few decades as aresult of such a process The coast-line of Essex is dominated by lowshylying estuarine and open coastmarshes which play a valuable rolein coastal protection acting as bafflesto wave energy and protecting thesea walls on the landward side Reshycent sea-Ievd risc coupled with 10-eaI human activities has led toerosion ofmany of the marshes here

The Blackwater estuary (figureVI3) provides a good example ofthe problems faced by the Essexcoast It has 680 hectares of saltmarsh and 2640 hectares of inter- ~

tidal mudflats around it and isbacked by agricultural land TheBradwell nuclear power station islocated on its margins Much ofthe coastal marshland around theestuary has been reclaimed over thecenturies to increase the area offarmland Flood embankments nowline 95 per cent of the estuary Theselimit the ways in which the marshes can react to seamiddotkvel rise Studies show thatbetween 1973 and 1988 23 per cent of the total salt marsh area around theestuary was lost to erosion (Pethick 1993) Over the past 150 years sea-level risehere has lxen accompanied by an increase in width of the main estuary channeland a decrease in its depth John Pethick an eIpcrt on this particular area of thecoast thinks that accelerated sea-Icvd rise in the future will lead to erosion ofmarshes in the outer estuary and their replacement by sand and gravel habitltsFurther inland marshes will ~come less brackish as salt Wllter penetrates further

Sea-Icvel Rise 209

Plate VI1 The salt marshes at Tollesbury Essex Marshes such as these willbe modified by any future sea-level rise Marshes nearby are the site of ascheme to stimulate marsh development (H A Viles)

up the estuary The extensive coastal defences behind the Blackwater marshesmean that unless humans intervene sea-level rise will eventually lead to thedestruction of these marshes

As the marshes help to protect the sea walls tram coastal erosion there havebeen strenuous efforts [0 help save the marshes A pilot scheme on NortheyIsland (whose location is shown in figure VI3) for example has pioneered theuse of set-back techniques to stimulate new marsh growth by removing an oldbroken-down sea wall and allowing the sea to reclaim the land behind it AtTollesbury on the northern shore of the estuary similar experiments are takingplace Here 21 hectares of arable land bought by EngJish Nature specially for thepurpose is being flooded in a policy of managed retreat There is a danger thatsuch piecemeal schemes will make the problems worse for the rest of the estuaryunless they are carefully managed John Pethick suggests that a much biggeresmary-wide project is necessary to manage these vital coastal wetlands in the faceof future sea-level rise Such a scheme would involve allowing the outer estuarinechannel to widen coupled with a general retreat of flood embankments

Further reading

Pethick J 5 1993 Shoreline adjustments and coastal management physical andbiological processes under accelerated sea level rise GeographictJl Journal 159162-8

210 Oceans Seas and Coasts

3 COASTAL EROSION

Coastal erosion is a natural processpowered by wave energy and vital tothe maintenance of a dynamic coastlineHuman activity however has increasinglybeen responsible for accelerating coastalerosion Increasing human settlementnear the coast and use of the coastal zonehave also created a serious environmentalissue which requires sensitive long-termmanagement

Recent surveys have produced somestark statistics For example net erosionhas occurred on over 70 per cent of theworlds sandy coastline over the past fewdecades However such erosion does notonJy affect sandy coastlines There havebeen spectacularly high losses of land onthe Niger delta Here 487 hectares ofcoastal plain were lost as a result of subshysidence caused by oil and gas extractionfrom the delta and mangrove deforestamiddottion Where high rates of erosion howshyever localized they may be (see table VlIfor Britain) coincide with dense humansettlement and intensive coastal useserious problems result Along the midshyAtlantic coast of the USA for example

barrier islands have retreated at about 15metres per year as sediment from the oceanside is eroded and washed over the top asa response to locally rising sea level Manysuch barrier islands are now highly builtup for example places such as AtlanticCity and Ocean City arc built almost litershyally on the beach This restricts the naturalinland migration

Cliff erosion is often linked to beacherosion as removal of protective beachesexacerbates erosion of the cliffs Clifferosion is a serious problem along partsof the developed southern California coastwhere cliffmiddottop apartment buildings havehad to be demolished Here eliffi havefailed because of tectonic activity coupledwith groundwater seepage and waveundercutting of the cliffs In Britain therehave been many instances of buildingscollapsing as a result of cliff failure Arecent example was Holbeck Hall hotel inScarborough on the north-east coast ofEngland In most such cases naturally highrates of erosion on failure-prone e1iffi havebeen exacerbated by building which hasaltered the cliff hydrology

What causes coastal erosion Erosion isproduced by the interaction of natural and

Table VI1 Rapid rates of coastal retreat at sites In Britain

Area

North YorkshireHoldernessNoriolk (Cromer-Mundesley)Essex (The Naze)

Kent FolkestoneEast Sussex Seaford HeadEast Sussex Beachy HeadEast Sussex Cliff EndDorset Ballard DownDorset Kimmeridge Bay

Cliff geology

Glacial driftGlacial driftGlacial driftGlacial drift London Clay

and cragGault ClayChalkChalkSandstone (Hastings Beds)ChalkKimmeridge Clay

Average retreat rate(metres per 100 years)

2812096

11-88

281261061082339

Source After Goudie (1990 1995)

Coastal Erosion 211

Plate VI2 The jetty at West Bay Dorset southern England has plainly modifiedthe drift of sediment along the coastline In the foreground sediment hasaccumulated but in the background the beach is starved of sediment and erostenrs occurring neussrtating coastal protection engineering schemes (A S Goudie)

human hctotS both acting to increase waveenergy andor reduce sediment 2vail2bilshyity The rate of erosion depends upon theinterpl2Y between the erosive action of thewaves and other agents of erosion andthe etodibility of the rocks and sedimentsbeing affected Natural increases in thetendency of the coastal environment toerode arc caused by storms BI Ninoevents and longer-term increases in sealevd All these herotS increase wave enshyergy at the coast LocaJly human impactsmay be increasing the erodibility of coastsby the following means

bull reducing the availability ofsediment forprotection and accelenting erosion byaJtering the wave energy field and sedishyment stores with graynes breakwatersand cliff protection schemes

bull removing vegetation which stabilizes

coastal wetlands thus making the sedishyment more erodible

bull reducing the sediment supply by otTmiddotshore and onshore mining and by trapmiddotping sediment behind dams on riversthat enter the ocean

bull replacing the coastal plain over whichbarrier islands can migrate withbuilt-up areas which restrict sedimentmovements

bull reducing the stability of coastal cliffsthrough building and aJtering groundmiddotwater levels

The fact that sediment moves betweendifferent parts of the coast means thatattcrnpts to reduce erosion in one area canhave the opposite effect on areas downdriftIn New Jersey USA for example tenninalgroyncs at Sandy Hook at the southernend of Long Beach Island have encouraged

212 Oceans Seas and Coasts

Plate VI3 A sea wall and cliff stabilization measures at Weymouth Dorsetsouthern England Such engineering solutions are expensive and are not alwayssuccessful (A S Goudie)

accelerated erosion downdrift Beach nourshyishment that is feeding the beach bybringing in sediment has been utilized toovercome such problems with some success

It is clear then that managing coastalerosion can ~ a very difficuh task To besuccessful it requires understanding bothof what factors are causing erosion in aparticular area and of how remedial techshyniques will themselves affect the situationFor example a highly developed barrierisland where future sea-level rise inducedby global warming threatens to exacerbate

FURTHER READING

erosion on a naturally subsiding coast willrequire a very different management stratshyegy from a small beach where erosion canbe rdated to a specific episode of offshoresand mining Clearly the threat of afuture acceleration in sea-level rise becauseof global warming (see section 2 above) ismaking coastal erosion an increasinglyserious problem In many places managedretreat where coastal erosion is allowedto occur relatively naturally and settlementsmiddotmoved inland is perhaps the only feasiblelong-term solution

Nordstrom K F 1994 Developed coasts In R W G Carter and C D Woodroffe(eds) Coastal Evolution 477-509 Cambridge Cambridge University PressA wide-ranging review of the problems faced by coasts with large concentrations ofpeople in an edited collection of advanced papers

Bird E C E 1985 Coastline Changes A GJobfll Reliew Chichester WileyA survey of erosion and accretion on coasdines in various countries

Coast1l ElQ5ion 213

Erosion at Victoria Beach Nigeria

Around the port of Lagos is a 200kin long sttttch ofbarrier island coastcharaeteriud by a sandy barrierbacked by a mangrove-mnged lashygoon It appears to have grownseawards over the Holocene Nowhowever the coast is eroding atsometimes spectacular rates (Ibc1988) Wave energy is high in thisenvironment the coast is poundedby waves coming all the way acrossthe Adantic and there is a generaltrend from west to east in movementof material along the shore

The port and former capital cityof Lagos has a population of over 6million Much of its economic prosperity is based on the extraction of oil fromthe Niger Delta Lagos is situated where ~ere is a break in the coastal barrierand expanded rapidly in the nineteenth and early twentieth centuries on landreclaimed from mangrove swamps behind the barrier As the port developedimprovements were made to the harbour starting with dredging in 1907 Majorharbour works began in 1908 These involved the construction of two breakshywaters and a training wall or jetty to provide a safe deep-water entry for largeships These breakwaters interrupted the west-to-east longshore drift The conshysequence has been a long-term erosion problem on Victoria Beach (on the westside of the harbour) and accumulation of sand on Lighthou~ Beach to the eastVictoria Beach has eroded by up to 69 metres per year since then (by 2 km inall) and an estimated 25 sq km of beach has been lost (figure VIA)

Victoria Beach is an important recreational arca for Lagos Also its erosion wasstarting to threaten housing built on low-lying reclaimed land behind the beachwhich protects the coast under natural conditions Beach nourishment by bringshying in sediment has been used to try [Q solve the problem starting in 1976Although it was successful in the shott tetm dramatic erosion occurred in 1980necessitating further emergency nourishment using 21 million cu metres of sandbetween 1980 and 1981

The erosion problems of Victoria Beach are particularly hard to solve becausethe Lagos port must be kept open The sand accumulating on Lighthouse Beachis also proving to be a problem as eventually it will extend past the weslernbreakwater and be washed around into the harbour Long-term integrated manshyagement of the entire coast here is necessary This may involve pumping sandaround from wcst to east (mimicking the natural longshore drift) and preventingfurther development on vulnerable low-lying land

Erosion ofVictoria Beach must be set in the context of more general erosionaltrends along the Nigerian coast Altogether Nigeria has some 800 km ofcoasdineand there is much evidence of widesprcad erosion within the past few decades

214 Oceans Seas and Coasts

Figure VI4 Since breakwaters were built erosion and accretion haveresulted along the beaches around Lagos harbour NigeriaSource After Usoro (1985)

Along the Niger Delta coast which is situated to the east of the Lagos areaerosion - coupled with environmental problems related to the oil extractionindustry - is a serious problem and several schemes (usually involving beachnourishment like that at Victoria Beach) have been implemented with limitedsuccess Table VI2 below shows some recent typical erosion rates along barrierbeaches of the Niger Delta coast for comparison with those at Victoria Beach

Table VI2 Erosion on the Niser Delta cout

Location

OgboiodoEscravos(western part of the Niger Delta coast)Forcados(western part of the Niger Delta coast)Brass(central part of the Niger Delta coast)Kulama(central part of the Niser Delta coast)Bonny(eastern part of the Niger Delta coast)ImoOpobo(eastern part of the Niger Delta coast)

Erosion rate (metres per year)

18-24

20-22

16-19

15-20

20-24

10-14

4 COASTAL FWODlNG

Simply put coastal flooding is a result ofsubstantially increased water levels on thecoastal plain above high ride levd Floodsoccur therefore as the Ka level riKS orthe coast sinh or where a combination ofthe two happens The possibility of globalwarming raising sca levels worldwide ismaking coastal flooding an cver morcserious issue Currently flooding affectslow-lying coasts such as the MississippiNile and Ganges dehas the Thames estushyary Venice Bangkok and the NetherlandsIn many areas expensivc flood protectionstructures and schemes have been impleshymented usually after a serious flood Anexample is the Thames Barrier completedin 1982 In Bangladesh storm surges proshyduced by cyclones in the Bay of Ikngalhave produced particularly dcvasntingfloods such as that in April 1991 which isestimated to have killcd morc than100000 pltrople

The major causa of coastal floodingarc storm surges EJ Niio events hurrishycanes tidal waves (tsunamis) and subsidshyence through abrupt tectonic movementsThe size and severity of flooding are influshyenced by the tidal regime and the phaseof the tide when the flood event suikesIn esruanes peak river flows can also makematters worse

Factors which make places more proneto flooding by lowering the land include

bull natural compaction of delta sedimentswhich promotes subsidence

bull oil gas and groundwater extractionwhich promotes subsidence

bull removal of mangrove and marsh veg-

FURTHllR READING

Coastgtl Flooding 215

etation which reduces coast2l protecshytion for backshore areas

bull building on low-lying subsidingland

bull fli1ure of flood defences such asdikes

There are severa stages in managementof the coastal flood hazard The initialstages include understanding the majorcauses of flooding in the area buildingstructures and flood defence schemes andimproving prediction and disaster planningIn Bangladesh for example mangrovetrees have been planted on a large scale [0

encourage the stabilization and development of mangrove swamps These helpto provide a buffer and so to preventflooding inland Also the Coastal Embankmiddotment Project has been established to buildembankments and a series ofsluices to proshytect against flooding Flood hazard warnshying improvements and increased provisionofemergency shelters on high land are alsovital elements in flood management here

The management of coastal flooding inBritain is in the hands of the Ministry ofAgricuJrure Fisheries and Food (MAFF)Since 1985 MAFF has also managedcoastal protection works for example [0

control erosion The Environment Agencyformerly the National Rivers Authority alsohas an important role to play in floodwarning and flood defences The floodson the east coast in 1953 provided a majorstimulus to planning and defences in Britainin East Anglia most of the sea defencestructures date from the decade after 1953A national network of tide gauges and theStorm TIde Warning System (STWS) wasalso set up about this time

Perry A H 1981 EPiroflMnltlJl HtuImu i the British klu London Allen andUnwinWard R C 1978 FlHds A GeogrRphiuJ Perrpectipe London Macmillan

216 Oceans Seas and Coasts

Flooding at Towyn North Wales February 1990Towyn and the surrounding Clwyd coastal lowlands covering about 20 sq kmaltogether support a population of around 14000 people On 26 February 1990the sea wall at Towyn was breached as a result of a storm surge The floodwatersrose to over 5 metres above normal sea level or Ordnance Datum (00) in thecentre ofTowyn Over 64 sq km ofland was flooded including all ofTowyn andmuch of the adjacem settlement of Kinmel Bay (figure VIS) Many housesbungalows and caravans were destroyed Over 750 domestic and commercialproperties were ruined in Towyn alone The floodwaters reached up to 2 Ioninland covering much agricultural land

What caused these floods and why were the floodwaters so patchily distribshyuted Storm surges are a major cause of coastal flooding around the British coastTheir low barometric pressure and strong winds act to raise tide levels abovethose predicted When a strong depression occurs over the sea falling barometricpressure acts to suck up the water surface producing a rise of about 1 cm forevery 1 millibar (rob) drop in pressure

On 22 February 1990 there was a large anticyclone situated over central EUJopeand a strong depression over south-west Iceland Between 23 and 25 Februshyary this depression deepened and moved towards southern Scandinavia By 26February it was JUSt west of Denmark and a second related depression haddeveloped to the sourn-east of Iceland These depressions had low-pressure cores

Plate VI4 A flooded caravan and trailer park beind the sea wall at TowynNorth Wales in March 1990 (Richard SmithKatz)

~f ~

Coastal Flooding 217

bullo flood wmr in dilrhes C--

_ Roilwi) _ Majolt road

Figure VI5 (a) location of Clwyd lowlands (b) The extent of flooding westof the River Clwyd near Towyn North Wales in February 1990Source After Englefield et aJ (1990) fig 3

of between 950 and 960 mb and major storms with high winds occurred acrossthe UK between 2S and 26 February Rain hail gale-force winds and lowpressure occurred in the Clwyd lowlands coupled with exceptionally high sealevels (assisted by the storm surge conditions) This combination of circumstancesled to the floods

The Clwyd lowlands were particularly vulnerable to flooding as they are exshytremely low-lying situated on reclaimed land ranging from 35 metres 00 to 7metres 00 most of it below 5 metres Along much of the coast there is a naturalprotective shingle ridge this reaches a height of up to 7 metres at Kinmel Baybut dies out at Towyn

The history of land use and human intervention in the area also had a crucialrole to play in the flooding In 1847 the Chester to Holyhead railway wasopened running along the coast (figure VI5) This has interfered with coastalsediment movements ever since resulting in long-term coastal erosion problemsFor example between 1872 and 1899 along one section the coast eroded by 60metres in frOnt of the railway line During the nineteenth and early twentiethcentury sea defences were built to help overcome these problcms including a seawall and groynes at Towyn Very little sediment ever accumulated in front of thewall and on 26 February 1990 it faced the full force of the ocean breaking ataround 11 am

Studies carried out after the flood by Englefield et al (1990) showed theextent of the damage and explained that the pattern of flooding was controlledby microtopography and the road layout within settlements Roads and higherareas acted as flood barriers Interestingly the old bungalows nearest (0 the seaat Kinmel Bay escaped the worst 800ding as they were located on the shingleridge at 6-7 metres 00

218 Oceans Seas and Coasts

5 CoASlAL AND MARINEPOLLunON

A report in 1990 by the Group of ExpertSon the Scientific Aspects of Marine Pollumiddottion concluded that most of the worldscoasts are polluted while many parts ofthe open ocean arc still relatively cleanCoastal pollution is an important environshymental issue affecting human health andthe diversity of fisheries and coastal ecoshysystems Recent attention has focused onliner and sewage pollution on Britishbeaches red tides (algal blooms caused byan excess of nutrients sec part rv section7) in the Mediterranean and elsewhereand oil spills such as that resulting fromthe WTeck of the Braer tanker ofT the Shetshyland Islands in January 1993 and the SeaEmpress off West Wales in February 1996

Most marine and coastal pollution (over75 per cent) coma initially from landshybu4=d sources It is brought down to thesea by rivers dumped in sewage outfalls orarrives via the atmosphere The rest comafrom dumping by ships and from offsho~

mining and oil production To we oilpollution as an example a surprising 344per cent of a total of 32 million tonnaper year which reaches the sea coma fromland via urban runoff etc another 343per cent comes from marine tnnsport (oilshipment) the rcst comes from atmoshyspheric fail-out offshore oil production(only 16 per cent) and natunl sources

The major types and sources of coastalpollution are

bull nutrients from sewage agriculturalrunoff aquaculture

bull pathogenic organisms from sewagebull litter especially plastics from land and

shipsbull metals eg admium and lead from

mining and indwuybull sediments from deforestation soil

erosion mining and dredging which

may be contaminated with syntheticorganic compounds

bull orpnochJoride pesticides from agrimiddotcultural and industrial runoff

bull PCBs (polychlorinated biphenyls) fromindustry

bull oil from land and oil tanker dischargesbull radionuclides from discharges from

nuclear reactors and reprocessing plantsand naNral sources

The amounts involved can be hormiddotrifying In 1985 at least 450000 plasticcontainers were dumped by th~ worldsshipping fleet The impacts on humanscoastal ecosystems and coastal stability canbe devastating The effects can also belong-lasting Oil spilt from the Isla Payardioil refinery in Panama in 1986 for examshyple came ashore on to a mangrove coastand killed many shellfish as well as beshycoming absor~d in mangrove muds Fieyears later the oil was recycled as thesesediments eroded and started to threatennearby coral reefs

Other pollutants have more immediateand shortmiddotlived effects For examplenutrients whieh trigger algal blooms causedeoxygenation of the water killing otherspecies These algal blooms may also betoxic poisoning shellfish and affectinghuman health Many synthetic organiccompounds such as PCBs have a sinisterlong-term effect They tend to accumushylate in living organisms gradually gettingmore concentrated as they are passed upthe food chain and seriously affectingmarine mammals and sea birds

Some areas ofthe coastal and marine envirshyonment arc particularly prone to such polshylution Espccially vulnerable are areas wheretidal and wave acrion encourage the conshycenmrion of pollutants and where sedishyments can act as a sink Thus sheltued baysestuaries and coastallagoons are key areasaffected by pollution Enclosed seas such asthe Mediterranean and Baltic are now alsoseriouslyaffected by pollutionover vast areas

Coastal and Marine Pollution 219

Plate VI5 Beach pollution at Bahrain Arabian Gulf (A S Goudie)

What can we do to reduce coastal polshylution~ Great strides have already beenmade in limiting the influx of pollutantsthrough a number of international agreeshyments In 1987 for example eight counshytries bordering the North Sea agrccd tophase out the incineration of chemicalwastes at sea by 1994 Dumping of radioshyactive waste at sea was stopped worldwidein 1982 The United Nations EnvironmentProgramme (UNEP) has coordinatedmany attempts to tackle pollution in parshyticular areas such as the south-east Pacificand the Black Sea (which has already sufshyfered serious ecological damage from toxic

FURTHER READING

chemicals pathogens and eutrophication- see part IV section 7) Agriculture inshydustry urbanization maricu1turc marinetransport dumping oil extraction miningand war are all important polluters Allmust be addressed if the problem is goingto be tackled successfully In many areasit is still difficult to get accurate infonnationon coastal pollution and its effects Duringand after the Gulf War for example disshyagreements raged about how much the warhad increased coastal pollution (throughdeliberate sabotage of oil fields) or deshycreased it (through preventing oil shipshyments and their associated pollution)

GESAMP 1990 The State of the Marine Enronment Oxford Blackwell ScientificA general report by an authoritative international group on pollution of the oceans andthe coastal seas

Clark R B 1989 Mllrine Pollution 2nd edn Oxford Clarendon PressA very good overview

220 Oceans Seas and ~ts

Pollution in the Mediterranean Sea

It is estimated that the population ofcountries around the Mediterranean will riseto 430 million by 2000 CB These countries and especially their coastal zonesalso attract large numbers oftounsts 100 million visited the area in 1984 Thereare huge disparities between the economies of countries on the northern andsouthern sides of the Mediterranean but pollution is getting worse everywhere

The major types of pollution are

bull oilbull domestic wastebull industrial and urban wastewaterbull organochlorine pesticidesbull heavy metalsbull PCBs

All these harm wildlife affect human health and may lead to long-tenn damageto the entire Mediterranean ecosystem Oil pollution is now a chronic problemover most of the Mediterranean as a result of tankers discharging ballast and bilgewaters in the network of shipping lanes which criss-cross the sea carrying some250 million tonnes of oil per year Sewage is a severe problem especially aroundthe Italian Spanish and French coasts (see figure VI6) The costs of reducingsuch sewage pollution may be very high In 1990 GESAMP suggested it wouldcost USS150 per person to construct sewage treatment and disposal facilities forall the 132 million inhabitants of the coastal settlements around the Mediterrashynean That would amount to US$lS billion overall at 1990 prices Sewage polshylution can make swimmers ill and can also contaminate seafood In 1973 acholera epidemic broke out in Naples Italy because of contaminated molluscsand hepatitis can also be transmitted by seafood Organochlorine pesticides PCBsand heavy metals are a problem in particular areas such as the Venice lagoonwhere lack of flushing allows them to accumulate in bottom sediments Sewageleads to algal blooms and red tides under extreme circumstances which firstposed a problem in the Gulf of Venice in 1972 Eutrophication is a seriousproblem in the western Adriatic Sea where rivers coming from Italy bring around29000 cu metres of phosphates and over 120000 cu metres of nitrates everyyear Like acid rain this results in a transnational problem beaches along thecoast of Croatia are affected as seriously as Italian beaches

i

CoOStal and Marine Popution 221

shyFigure VI6 Sewage and industrial waste discharges into the MediterraneanSea (BOD = biological oxygen demand)Source After Clark (1989) fig 93

Some pollution problems affect only small areas and arc easily solved Anexample is the discharge of tannery wastes contaminated with chromium into theGulf of Geras on the Isle of Lesbos The impact of this was lessened in 1983when an effluent treatment plant was installed (Papathanassiou and Zenclos1993) Some pollution problems however are less easily solved and some areassuch as the Vcnice lagoon appear to be polluted beyond acceptable limits

In 1979 as a response to concerns about many oftheslt issues the Blue Planset up with the help of UNEP was adopted by the Mediterranean countries Thisplan aimed to help both economic development and environmental protectionand to limit pollution from land-based sources As always however dealing withinternational environmental problems is a difficult task and implementing susshytainable development and tourism has so far proved very hard amp tourism is oneof the major industries of the Mediterranean and is affected by pollution as wellas contributing to it perhaps the initiation of ecotourism would make a starttowards solving the poUution problems here

222 Oceans Seas and Coasts

6 COASTAL DUNE

MANAGEMENT

Coastal dunes provide an important bufferbetween land and sea and act as a storefor sediment They arc dosdly linked withbeaches as there is a regular interchangeof sediment nutrients and organismsbetween beach and dune systems Coastaldunes arc a common component of mostcoasdines and arc often of very impresshysive height and extent Notable examplesarc found on the west coast of Americawhere the Coos Bay dunes arc 72 kID longand reach heights of 50 metres In Eurshyope high dunes occur along the CocoDonana in southern Spain where theyreach 90 metres Coastal dunes unlikemany descrr dunes tend to be vegetatedHardy salt-tolennt plants grow on themnearest the sea as dune environments getmore sheltered and better soils occur furshyther inland and over time other plantsfollow

Coastal dunes provide many attractionsfor human society Because of this as wellas their natural dynamism and role asagents of coastal protection their successshyful management has become an irnporuntissue especially as most sandy coastlinesarc undergoing erosion As cliffs areprevented from eroding so the supply oferoded material going to beaches anddunes is reduced In Britain for exampledunes on the East Anglian coast probablynow have a diminished supply of sandbecause of coastal protection works covershying about 60 per cent of the coast hereDunes themselves are eroded by both windand waves

Sand dunes provide a harsh environshyment colonized at first by hardy plantsthat can tolerate salt and sand such as searocket (CiJtie mllritimll) and salt won(SIIsoJ4 W) whose seeds can tolente longperiods soaked in seawatec As these plants

grow they trap sand and help the dunesto grow Grasses such as A1fJmophili4llrettllrill (marram grass) and sand couchshygrass (Aaropyrtm jmuitmfIU) are themajor sand-accumulating species Gradushyally plant succession creates a diverse ecoshysystem which is attractive to birds insectsreptiles and small mammals For examplehalf the flowering plants of Britain can befound in coastal dune areas around thecountry

Important human uses ofdunes include

bull golf coursesbull sand and water extractionbull afforestation and grazingbull recreation such as horse-riding walkmiddot

ing biking and off-road vehiclesbull military training and exercisesbull housing camping and caravan parksbull transport such as coods and airfieldsbull pipelines

Most of these uses however inoledisrurbing the narura ecosystem Suchdisrurbance often encourages dune mobilmiddotiution and destabiliution and the develmiddotopment ofblowouts This can lad to sandmigrating inland ovec valuable agriculturalland or housing it also removes the coastalprotection afforded by the dunes Otherimpacts affect the groundwater level ofdunes which in turn affects the ecologyIn the Netherlands for example coastaldunes provide an important source ofdrinking watec Other human uses ofdunescan fossilize them removing any chanceof natunl dynamism through such thingsas planting grass and trecs for golf courscsFinally some human impacts affect dunesindirectly removing sand from beachesdamming rivers offshore sand mining andpoUution can aU tip the balance betweensedimentation and erosion

Because of the many and vuloW usesand abuses of coastal dunes considenblemoney and time have been invested in

trying to conserve and protect dunes inorder to save them and the wildlife theysupport Dune management schemes usushyally involve all or some of the following

bull aiding deposition of sand on beachesthrough groynes sea walls and beachnourishment

bull shaping dunes using bulldozers tomove sand

bull planting and watering dunesbull using biofabrics mulches etc to help

stabilize fragile dune surfacesbull fencing to restrict accessbull providing walkways to channel people

away from sensitive areas and preventdamage to the underlying dune

Coastal Dune Management 223

bull providing signs information displaysand education to involve the public indune conservation

However overmanagement can also be aserious problem Most coastal dunes unshyder natural circumstances are not fixedand movement ofdunes and blowouts areperfectly natural occurrences Some eleshyment of disturbance needs to be includedin successful dune management schemesFigure Vl7 shows how dune managementis also affected by natural coastal erosionon the Baltic coast of Poland a catastrophicstorm in January 1983 led to severe eroshysion of beach and foredunes which thenthreatened the stabilized dunes behind(Piotrowska 1989)

Plate VI6 Footpaths causing erosion patterns across coastal sand dunes atWinterton Norfolk eastern England This is a dear example of the effects ofrecreational pressures on the landscape (University of Cambridge Air Photographcollectlon)

224 Oceans Seas and Coasts

18th Ctntury Browndulll m

SI 8mh Fortmlll Yellow dun~ Grt)dune S v 0

EIymo-Ammophiletum HeUehryraquo-jasionetum Em~ro-Pinetum

IS

19th20th Century 10

S

0Bnch JgtuJtrd gmsn He~dllp(l-Jasionum Pine lIlQIlocult=

2nd halfof2Oth Century

After 1983 rommon slate

lkach Young pinrmonocullUn

After 198310cat slates

I Btach

IS

10

S

0Old pine monocultun

IS

10

S

0Old pi~ llJOIlocuhun

Figure VI7 The history of dune management and coastal erosion on the Balticcoast of PolandSource After Piotrowska (1989) fig 5

FURTHER RBAoING

Ranwell D S and Boar R 1986 Coast Dune Management Guide HuntingdonInstitute of Terrestrial EcologyA useful practical guide to management techniques with plenty of C~ studies

Goasral Dune Management 225

Managing dunes on the Lancashire coast EnglandThe Ainsdale-Forrnby dunes cover 800 hectares of which 490 hectares is aNational Nature Reserve The coast here faces north-west and the dunes form asuite of more or less parallel ridges with low-lying areas called dune slacks inbetween Behind these are more irregular dunes Erosion has dominated at thesouth end of the area since the beginning of the twentieth century The coast isprotected in the north towards Stockport by wide sand flats The sand here is richin calcium carbonate so dune soils are not very acidified The area is rich in plantspecies with marram dune scrub and woodland including Anm and BetultlHippophae rhamnoides (sea buckthorn) was introduced here and has spread conshysiderably over the dunes (Boorman 1993) In 1959 myxamatosis arrived decishymating the rabbit population and aiding the spread ofscrub (by preventing rabbitgrazing which maintains grass) Now the Formby dunes to the south of thenature reserve are threatened by both public pressure and coastal erosion

Detailed studies by the geomorphologist Ken Pye have revealed the long-termimportance of human activities to the dunes here (Pye 1990) Marram grass wasintroduced into the area at the start of the eighteenth century when strict lawswere introduced to encourage planting indeed planting was obligatory until1866 Marram favours the development of hummocky sand hills as found tomiddotwards the back of todays dune system In the late nineteenth and early twentiethcentury brushwood fencing and backshore planting were wed to encouragedune development resulting in the parallel dune ridges found over most of thedune system

By the late 1920s recreational pressure was causing severe erosion and producmiddoting much blown sand Other activities which have affected these dunes include

bull excavation of flat-floored depressions for asparagus cultivationbull sand miningbull waste dumpingbull development of caravan and car parksbull road-buildingbull development of golf courses

These pressures have led to dune management and restoration schemes such asthe Sefton Coast Management Scheme established in 1978 This scheme beganto restore the dunes using brushwood fencing marram planting and woodenfencing and restricting access by vehicles and pedestrians Covering some 17 kmof coast the Sefton Coast Management Scheme provides a framework for natureconservation projects within an area which includes several different landownersA Coast Management Officer has been appointed who promotes co-operationbetween the different landowners and ensures integrated management of thissensitive coastal environment

226 Oceans Seas and Coasts

7 CORAL REEF DEGRADATION

ConJ reefs arc some of the worlds mostdiverse ecosystems containing a bewildershying array ofcorUs fish and other organismsAlthough mey cover only 017 per cent ofthe ocean floor (an area roughly the sizeofTexas) they are home to perhaps 25 percent of all marine species One hundredand nine countries have bctween them over100000 km of reefs and many of theseare threatened by a series of natural andhuman-induced stresses (figure VI8)

Coral reefs require very specific envirshyonmental conditions Reef-forming coralsonly grow in waters with temperatures of2S-29degC where there is a suitable relashytively shallow platform less than 100 meshytres below sca level to grow on and wheresediment and pollution do nOt kill themof[ Thus meir growth is restricted to suitshyable tropical and subtropical shores Onesuch is the north-eastern coast ofAustraliawhere the Great Barrier Reef forms thelargest agglomeration of reefS in the worldstretching for over 2000 km and comshyprising ova 2500 individual reefs Othermajor reefs are found along the Gulf coastof Belize and around many South Pacificislands

As Charles Darwin explained in the nineshyteenth century there arc three main typesof reefS related in a genetic sequence First

there are fringing reefS which connectdirectly with the shore Then there arcbarrier reefs which arc separated from theshore by a lagoon Finally when such reefSarc growing around a gently subidingoceanic island atoUs arc produced Anaroll is a ring of coral reefs around a lashygoon in the centre ofwhich was once theisland Sand and gravel islands accumulatshying on the margins of such atolls providea precarious home for flora fauna andhumans as in the Maldives

Reefs arc remarkable in that their entiregeological structure is formed from bioshylogical growths now dead covered by athin veneer of living corals Despite thename coral reefs most reefs arc in factcomposed of a number of important reefmiddotbuilding species including coralline algaeas well as a range of corals

Stresses affecting coral reefs in todaysworld include

bull storms and hurricanesbull EJ Nino eventsbull scamiddotlevel rise and other effects ofglobal

warmingbull outbreaks of disease and preduors

(such as the Crown ofThoms starfish)bull increased sedimentation produced by

deforcstation on landbull eutrOphication produced by sewage and

other pollutants

Figure VI8 A generalized map of threatened coral reefs around the worldSource After C R Wilkinson personal communicationUnivmity of Guam

bull onshore and offshore mining producshying scdimcntenrichcd with heavy metals

bull trampling and physical damage fromboats and divers

bull overfishing and the usc of damagingfishing techniques such as dynamiting

bull direct quarrying and removal of coralsfor building or curios

bull oil pollution from land and shippingbull nuclear weapons testing and other

military activitybull pollution and damage from landfill

(used for example to create new landfor airports and sometimes constructedwith toxic waste)

Natural disturbances such as hurricanescan damage fragile corals and fling themup on to the reef flat However the imshypact of such events is probably short-livedand may in fact be good for the overallhealth of reefs providing a disturbancewhich may increase species diversity andgrowth in the long term El Nino eventswhich occur every two to ten years andinvolve widespread changes in ocean curshyrents and temperature have a potentiallymore scrious effect They temporarily warmthe water around reefs this can causecoral bleaching when the corals expel thezooxanthellae the tiny algae that livesymbiotically with them In severe casesbleaching can cause mass death of coralsGlobal warming may mue such bleachingepisodes more frequent and more seriousas it will heat the oceans and may providefurther stresses by accelerating the rate ofsea-level rise forcing corals to grow fasterin order to keep up with sea level Locallysome corals have been badly affected byoutbreaks of pests and diseases Crownof Thorns starfish for example eat coralsthese predators spread rapidly across manySouth Pacific reefs in the 19605 In 1993South Pacific reefs were first observed tobe suffering from another biological probshylem CLOD (coralline lethal orange dis-

Coral Reef Degradation 227

ease) which affects coralline algae anotherimportant part of reef frameworks (Littlerand Uttler 1995) The causes of suchbiological disturbances arc unknown andmuch-debated but they may be at leastpartly due to environmental pollution

Other stresses on coral reefs can dearlybe blamed on human impacts both dishyrectly on the reefs themselves (from divshying and fishing for example) or indirectlyfrom activities on land or offshore Inshycreased sediment load pollution fromsewage agriculture and industry and deshystructive fishing techniques all damage thereef ecosystem by upsetting the balance ofspecies At the Green Island resort on theGreat Barrier Reef sewage has led to anincrease in the area of seagrasses largelyat the expenS( of corals Thcsc seagrassestrap sediments which usually circulate freelyaround the beaches of the island Thuspollution here is damaging both reef andbeach environments Deforestation inThailand and conversion of forest to rubshyber and cocoa plantations has had severeimpacts on the reefs on southern PhuketIsland producing excessive sedimentationand killing corals

Many of these stresses on reefs are nowacting together and many reefs are goinginto the twenty-first century in an increasshyingly unhealthy state (table VI3) If gloshybal warming continues some reefs may beunable to cope How serious is the proshyblem and what can we do about it~

Reefs have many uses and roles for society

bull they are agents of coastal protectionproviding a natural sponge absorbingwave energy

bull they are major tourist attractionsbull they arc an important focus for bioshy

diversity and conservation of marinespecies

bull they contain living and nonmiddotliving reshysources ofgreat elaquogtnomic value such asfish crustaceans coral rockand sediment

228 Oceans Seas and Coasts

Plate VI7 The destruction of a coral reef by draglines used to build a new porton the island of Taketoni off Okinawa Japan (Panos PicturesJim Holmes)

Most counrries cannm afford to lose theirreefs In terms of fishing alone Pacificislanders get up ro 90 per cent of theirprotein requirements from reef fish andworldwide reefs are home ro a toral fishcatch of 4-8 million ronnes per year (Weshyber 1993)

Furure sea-level rise will affecr reefs asreef-building corals and algae only growwithin relatively shallow water Three majorreef strategies have been identified (figureVI9) Keep-up Catch-up or Give-updepending on he balance between therelative rate of sea-level rise and the growthrate of the corals involved Ifsea levels risevery fast most reefs will be unable ro keepup Given the receor predictions of 4-5mm per year mean sea-level rise over thenext 50-100 years (see section 2 above)most reefs will keep up or catch up Unshyhealthy reefs however are less able to keeptheir growth rates up and are more likelyto give up

- ---_ _-$fa~ ___~ _ - bull r

~ Z4 -- _~ampJt)

RftfswflKe

~lnb_~--~Rftfiuface (tl

--$fIlM rise -Rffi growth

Figure VI9 Coral reef growthscenarios (a) keep-up reef growthproceeds at roughly the same rate assea-level rise (b) catch-Up sea levelinitially rises faster than reef growththen reef growth catches up (c) giveshyup sea level rises too fast for slowshygrowing or unhealthy coral reefs

Area

Coral Reef Degradation 229

Table VI3 Summary of the health of coral reefs In various parts of the world

worlds reefs Reef healthfound in the area

South-east Asia 30 60-70 reefs sick Deforestation miningand fishing problems

Pacific Ocean 25 Mainly good condition because of lowpopulations

Indian Ocean 24 20 reefs lost Mining fishing and coastalpollution problems

Caribbean Sea 8 Deforestation and tourism problems

Atlantic Ocean 6 Coastal development and tourism problemsBermuda has good reef reserves

Middle East 6 low runoff low population and littletourism aid reef health oil spills a problem

Source Adapted from Weber (1993) table 3-2

Currently many reefs are protected tovarying degrees in an attempt to reducethe suesses on them The Great BarrierReef Marine Park in Australia was createdin the 19705 It contains five sectionswith different reef uses allowed in eachOil drilling and mining are prohibitedthroughout the park and in some secshytions only scientific research and traditionalfishing are permitted Where relatively poorcountries have vulnerable reefs which arealso major touriSt attractions there can bemany conflicts involved in successful reefmanagement and marine parks can be hardto monitor and control If reef manage-

FURTHER READING

ment and protection is to be successful itis necessary to understand how reefs workmanage the various human uses of themand plan onshore land use (0 reduce damshyage from external sources The problemhas many dimensions as Weber (1993p 53) explains Ultimately the forcesbehind reef dedine are hard to untangleOverexploitation and coastal pollutionstem from business interests wealthy conshysumers the growing numbers of coastalpoor and governments trying to balanceconflicting development goals No singlegroup is the cause of reefs precipitousdecline yet all contribute to the tragedy

Guilcher A 1988 Coral Reef GeomorphokJgy Chichester WileyA general clearly written study of coral reefs with a useful section on human pressureson reefs

230 Oceans Seas and Coasts

Threatened reefs of the Red Sea

The Red Sea which extends from 13 N to 30 N has fringing reefs along almostall of its coastline Reefs are especially well developed along the north and centralcoasts Conditions arc particularly suitable for reef growth here There are nopermanent rivers flowing into the Red Sea from its arid hinterland andphytoplankton productivity is low both of which encourage clear water Thereare few storms and no tropical cyclones Reefs along the northernmost part of theRed Sea however are affected by occasional extremely low tides and sea temshyperatures here are near the minimum level acceptable for reef-building coralsMost countries bordering on the Red Sea are arid and sparsely populated andthere have therefore been few onshore threats to the reefs Pollution from thebusy Red Sea shipping lanes is a problem and oil pollution from oil explorationin the Gulf of Suez is especially serious

Tourism is a growth industry here most concentrated in the northern counshytries of Israel Egypt and Jordan Studies estimate that 19 per cent of Egyptsreefs are now affected by tourism and this figure is expected to rise to 73 percent by the year 2000 The Egyptian resort of Hurghada provides a good examshyple of the actual and potential impacts of tourism on Red Sea reefs The townof Hurghada was founded in 1909 to supply the oil industry It did not start toamact many tourists until the late 1970s Now it has huge tourist complexesstretching some 20 km along the coast and many more are planned (figureVIlO) Diving is a major attraction for tourists here What damage does tourismcause to these reefs~

First construction creates dust which in the dry Red Sea climate gets blownon to reefs creating a sediment nuisance Secondly construction often involvescreation of new coastal land from landfill This can cause major damage to reefsAlso enhancement of tourist beaches through beach nourishment etc can upsetregional sediment dynamics Thirdly sewage disposal desalination irrigation andrubbish disposal all pose problems At Hurghada sewage is treated before itenters the sea but observations of high algal growth on reefs nearest the shoresuggest that high nutrient inputs may still be a problem (Hawkins and Roberts1994) Fourthly tourism may encourage overfishing and the collection of coralsand shells for sale Fifthly diving and boat anchoring have been shown to damagereefs over small areas Finally it should be noted that tourism has positive benefitsfor neighbouring reefs as it reduces the industrial development in the area andbrings an added awareness of the value of natural reef habitats

A Marine Station was established at Hurghada in 1931 which has providedinvaluable data on marine biology A national park has been proposed to helpprotect the reefs Oil pollution remains a serious problem For example in 1982fresh oil was found over a wide area affecting turdes white shark spoonbill andosprey (Wells 1988)

Further north around the tourist resort of Sharm-el-Sheikh the Ras Mohamshymed Marine Park was set up in 1983 to aid reef conservation Here there is a

Coral lkef Dt=gradarion 231

WI e-J

DpIo

N

j -----

EGYPT

Figure Vl10 Present and planned coastal tourist development aroundHurghada EgyptSource After Hawkins et al (1993)

high density and diversity of corals as well as sharks giant clams green turtlesand many interesting bird species

According to a recent scudy tourism is causing worrying rather than alarmingdamage to Red Sea ~efs However the situation could easily worsen as touristnumbers grow and global warming and natural stresses compound the problemsNatural stresses include outbreaks of sea urchins and other grazing organismsSea urchins can reach high population densities on the coral reefs here Theygraze on coral and can inflict damage on the reefs Several areas of reefs alongthe Ikd Sea coast have shown signs of urchin damage in the past and similarproblems may recur in the future

Further reading

Hawkins] P and Roberts C M 1994 The growth of coastal tourism in theRJd Sea present and future effects on coral reefs Ambio 23 503-8

232 Oceans Seas and Coasu

Io 0

19t5 1986 1917 1911 1919 1990

8 AQUACULTURE AND

COASTAL WETLANDS

Figure VI11 Global aquacultureproduction 1985-1990Source After UNEP (1993) fig 310

ments where wave energy is low andwhere tidal processes dominate such asestuaries deltas and bays In the upperintertidal zone and above salHolerant vegshyetation may grow In the temperate zonesalt marsh communities such as SpRrtin4grasses dominate grading into mangrovetrees (eg speeies of Rbiuphora andApUnR) in the tropics At lower tidallevels there are mudflat surfaces which lookbare but actually support large numbersof algae and mud-dwelling animals

Coastal wetlands have often been seenas wastelands but 1ikc other wetlands (seepart II section 9) they play some veryuseful roles These include acting as anatural agent of coastal protection buffshyering the land behind them from the seaand acting as a purifying agent by removshying roxic wastes from the water enteringthem They are also invaluable in preservshying biodiversity for example they provideimportant stopping-off points for numershyous migrating birds In mangrove swampsthe mangrove trees themselves are a useshyful source of timber and firewood for manylocal communities

There arc many large areas of coastalwetlands such as nearly 600000 hectaresof salt marsh on the Atlantic coast ofthe USA and an estimated 22 millionhectares of mangrove swamps worldwideMany coastal wetlands are threatened bydevelopment Agriculture industry andurban expansions can all lead to landreclamation and the removal of naturalmangrove ecosystems Aquaculture alsoleads to disruption of the natural coastalwetland as trees and other natural vegetashytion are cleared ponds dug and filled withwater and nutrients and waste productsdischarged into the water Eutrophicationcan become a problem as a result of theinflux of nutrients The species mix maybe affected and total biodiversity reduced

In Indonesia for eumple brackish waterfishponds (locaUy known u tRmbu) nowoccupy over 269000 hectares or 65 per

Aquaculture is the water-based version ofagriculture where plants and animals aregrown and harvested for food and otherproducts Since the 1970s aquaculture hasdeveloped enormously and now accountsfor about IS million tonnes or 17 per centof world fisheries production (figureVIll) Aquaculture can take place inlandon freshwater lakes and ponds but a largeproportion of aquaculture takes place inbrackish water or seawater ponds in coastalwetlands Along tropical coasts for examshyple it is estimated that about 765000hecrares of land are currently in usc forshrimp production Shrimps oysters catshyfish tilapia salmon rainbow trout andtiger prawns among a wide range ofotherspecies are regularly farmed throughaquacultural techniques

Why are coastal wetlands commonlyconverted to aquacultural use~ And whydoes it matter Coastal wetlands whichinclude salt marshes mangrove swampsand mud flats arc found along low~lying

sheltered coastlines with a large sedimentsupply In general they form in environ-

ED] Ra1I olWoridlMOllr Dlnltil

olloulfuh (Itch

IlJ~f

I~ uoo-

-Aquaculture and Coastal Wetlands 233

---~--

Plate VI8 Aquaculture is expanding rapidly in South-East Asia These fish pondsare located on Java Indonesia The creation of fish ponds can destroy importantnatural coastal vegetation and contribute to coastal pollution (Panos PicturesJeremy Hartley)

cent of the total former mangrove areaConversion to tambak is often unsuccessshyful as erosion and pollution can becomeserious problems if the sites are not choshysen correctly As with agriculture on landaquaculture will only succeed in the longterm without causing ecological damageif there is a good understanding ofhow the natural environment works andaquacultural techniques are developed thatavoid disturbing these environmental sysshytems too much In the Far East whereaquaculture has been practised for thoushysands ofyears technological improvements

FURTHER READING

and more sensitive management techniquesare helping to reduce environmental probshylems associated with aquaculture Technoshylogical improvements include better diseasecontrol and nutrition and genetic enhanceshyment Technological advances also enablemangroves to be planted on dikes aroundponds The mangroves provide useful fuelshywood and fertilizer (from decaying leaves)and protect the ponds from erosion Moresensitive management techniques involveensuring that aquaculture ponds andmangrove forests are not seen as mutuallyexclusive

Beveridge M C M Ross L G and Kelly L A 1994 Aquaculture and biodiversityAmfri 23 497-503An introductory review in a journal that is full of important case studies on many topicscovered in this book

234 Oceans Seas and Coasts

Pond culture in the PhilippinesThe Philippines consist ofsome 7100islands in all Between 1920 and 1990the area of mangroves around theseislands shrank from 450000 hectaresto 132500 hectares Over the sameperiod the area covered by ponds in~

creased to 223000 hectares Around50 per cent of mangrove loss in thePhilippines can be ascribed [Q theconstruction ofbrackish water pondsBy 1991 27 ~r cent of the totalPhilippines fish production (some26 million tonnes) came from suchaquaculture

Brackish water pond aquaculturein south-east Asia started in Java Inshydonesia in the fifteenth century andspread to the Philippines whereponds were first constructed on theshores around Manila Bay (Primavera 1995) There have been several phases ofbrackish water aquaculture in the Philippines and several effects

bull In the 1950s and 1960s the government sponsored fishpond developmentespecially for milkfish production for local consumption

bull The 1970s was declared a conservation decade andbull The 1980s saw shrimp fever with a boom in production of shrimps and

especially tiger prawns mainly for export and the urban macket

The notable effects of brackish water pond aquaculture in the Philippines havebeen mangrove loss pollution of coastal waters and decline in production ofdomestic food crops

The loss of mangroves affects coastal stability removes protection against the20 or so typhoons which affect the Philippines each year and removes some veryversatile plants There ace 26 mangrove tree species found here many of whichhave a wide range of traditional meso The most seriously affected areas arewestern Visayas and central Luzon

The ecological damage inflicted by pond aquaculture has prompted the Philipshypines government and others to take action Rtforestation has been carried outfor example in 1984 when 650 hectares in central Visayas were replanted As of1990 8705 hectares of mangroves have been successfully planted

9 CoNCLUSION

The worlds coastlines and their immedishyate hinterlands are the focus of a greatdeal ofhuman activity They are thus undersevere pressure from humankind By conshytrast the worlds oceans which are enorshymous have so far been much less affectedby anthropogenic changes Their sheer sizeoffers them some protection from theeffects of pollution and waste disposalHowever the depletion ofworld fish stocksis an increasingly serious issue Halfwaybetween coastlines and the great oceansare the marginal seas - water bodies likethe Mediterranean the Baltic and theNorth Sea These do show the dear imshypacts of a wide range of human activities

The worlds coastlines are experiencingslowly rising sea levels (There arc someexceptions such as those areas undergoshying rapid uplift because of isostatic responseor tectonic activity) If the enhanced greenshyhouse effect causes global warming to takeplace the nHe ofsea-level rise will increaseover the coming decades Many of theworlds coastlines are also being subjectedto accelerated fates of erosion or retreatbecause of a range of human impactsSome are also being flooded more oftenpartly because of sea-level rise but alsobecause of a combination of local humanand natural stresses

Many types of coastal terrain are bothdynamic and fragile Dunes deltasbeaches reefS swamps and marshes comeinto this category They all offer many

KEy ThRMS AND CoNCEPTS

aquaculturecoral blachingcoral reefsEl Ninoeustatic changeisostatic change

Conclusion 235

ecological services to humankind Forexample they act as agents of coastal deshyfence or as highly productive ecosystemsThus we need to treat them with particushylar care and respect

Overall the issues covered in this partof the book illustrate that there are a wholerange of immediate environmental probshylems affecting many parts of the worldscoastline resulting from a combination ofhuman and natural stresses Future seashylevel rises if they do occur will be affectshying coastlines which are already stressedand therefore unlikely to be able to reshyspond as they would naturally to suchchanges Furthermore as we have showncoasts arc naturally dynamic over a rangeof time-scales and any attempts at coastalmanagement must take this into aCCOUD[We cannot fossilize the coast Because ofthe many attractions of coastal environshyments a multitude of people are involvedina wide range of activities within thecoastal zone Effective coastal zone manshyagement must involve and consider thesepeople Finally several of the examplcs wehave used show the many links betweencoastal environments and those on landand in the oceans There are also manylinks between different segments of thecoastline and between the different comshyponents of the coastal enviroment (ecolshyogy sediments water) In orGa to copesuccessfully with all these componentsand interlinkages coastal zone manageshyment schemes must be truly integratedprogrammes

salt marshessea levelsediment circulation celissurgestectonics

236 Oceans Seas and Coasts

POINTS FOR REVIEW

Why arc coastal areas being placed under increasing pressure

Why might sea levels rise in some areas in coming decades

Why are so many stretches of the worlds coastlines showing signs of erosion

How would you aim to reduce the impacts of coastal flooding

What marine environments are especially prone to [he effects of pollution

Which coastal types do you think are especially fragile and dynamic

Why should we aim to conserve coastal wetlands and coral reefs

PART VII

Conclusion1 Introduction 2392 The Complexity ofthe Human Impact 2393 Towards a Sustainable FUlUre 239

Key Tenns and Concepts 244Points for Review 244

1 INTRODUCTION

The human transformation of nature hasbeen going on for a very long time andhas been very pervasive The Earths surshyface still has areas ofsome size which showlittle obvious manifestation of the impactof humans (c=g the deep oceans pans ofthe polar regions some of the tropical rainforests) and we talk of wilderness areasin which very little human activity occursHowever there is no place on the face ofthe Earth which is not to some extentaffected by the changes in the chemicalcomposition of the atmosphere and assoshyciated changes in climate and levels ofpollution

2 THE COMPLEXITY OF THE

HUMAN IMPACT

We have demonstrated in this book thatdifferent types of human activity causedifferent types of land transformation Forexample at the one extreme we have disshycussed some of the changes in the envirshyonment that have been caused in andaround cities by the process of urbanizashytion At the other we have demonstratedhow even hunters and gatherers livingin scattered groups have contributed tosuch processes as deforestation anddesertification We have selected our casestudies to illustrate this theme We haveshown how some changes in the environshyment are made deliberately by humans butalso how many others are accidental byshyproducts of human activity Often it takessome time for the environments responsesto such impacts to become apparentOften too their exact causes are hard toidentify In many cases human impactsarc increasingly becoming interlinked andaccompanied by natural fluctuations toproduce massive and often unpredictablechanges in the environment We have idenshytified a whole spectrUm of different types

A Sustainable Future 239

of environmental response to stress Theserange from short-term fluctuations whichcan be easily reversed to long-term poshytentially irreversible changes which poseintractable problems for environmentalmanagement Our case studies have alsoillustrated the wide variety of types of atmiddottempted solutions to environmental probshylems These range from technologicalquick-fix solutions such as engineeringstructures to control coastal erosion tosofter and more ecologically friendlyinterventions such as replanting riparianbuffer zones to lessen the amount ofnitrate pollution that enters rivers fromagricultural slopes Increasingly any suchschemes need to be integrated That isenvironmental problems should nO[ beconsidered in isolation but should beviewed as linked parts of the same seriesof problems Inevitably any such schemeswill work only if the additional complexshyities of human society economy cultureand politics arc also taken into account

3 TOWARDS A SUSTAINABLE

FUTURE

It is likely that in coming decades many ofthe transformations we have described anddiscussed will become even more imporshytant and the need for effective environshymental management even more pressingHuman population levels arc increasingnew technologies are emerging and evershyincreasing quantities of energy and reshysources are being produced and consumedespecially in countries that aspire to thelevels of development achieved by someof the worlds richest nations There mustbe severe doubts as to whether these trendsarc sustainable Will the world be transshyformed by global warming Will we cutdown all our rain forests1 Will a large proshyportion of the worlds flora and faunabecome extinct Will many of the worldsdryIands tum into dust bowls Will urban

240 Conclusion

Table VII1 Some potential adverse Impacts of global warming on resources

Resource Possible effects

Agriculture Lower crop yieldsSpread of pestsSoil erosion

Forests

Conservation areas and naturereserves

Coastal areas

Fisheries

Water resources

Human health

Energy demand and production

Change in rate of growthChange in species compositionShifts in geographical distribution

Disruption or loss of habitatInvasion of new species

Inundation of land and accelerated erosion byrising sea levels

Changes in composition of stocks and theirlocation

Droughts floods changes in amount of supply

Heat stressShifts in prevalence of infectious diseases

Increases in need for summer aiHonditionlng

atmospheres continue to become morepoUuted and more health-threatening Willour water supplies dwindle in quantity anddeteriorate in quality~ These are some ofthe many questions that we can ask aboutthe future They form the basis of muchof the environmental concern that is deshyveloping throughout the world

Arc such massive and unwelcometransformations of the face of the Earthinevitabld Is human life sustainable Canhuman energies be harnessed over thecoming decades to improve rather than to

degrade the environment We arc notwithout hope We have indicated in manyof our cast studies that there are waysmeans and opportunities to overcomesome of the undesirable processes that wehave identified Each and everyone of usin our daily life has the power to makesure that the generations to come have asustaUnable future

There is now very great interest in howwe might adapt to global warming shouldit occur Such adaptations would be necshyessary if we could not limit emissions ofgreenhouse gases sufficiently to rule outthe possibility ofsignificant warming Theywould also be necessary because of thevery great range of environments activshyities and resources that might be modifiedas a result of global warming (table VIIl)It is onen said that there are two types ofadaptation that may be necessary The firstof these is reactive adaptation wherebywe respond to climatic change aner itoccurs The second is anticipatory adapshytation in which we take steps in advanceofclimatic change to minimize any potenshytially negative effects or to increase ourability to adapt to changes rapidly andinexpensively

Reactive adaptation may well be feasibleand effective In many parts of the world

A Sustainable Future 241

Table VII2 Examples of no-regrets policies In response to possible global warming

Policy area and measures

Coastal zone management

Wetland preservation andmigrations

Integrated development ofcoastal datasets

Improved development ofcoastal models

land-use planning

Water resources

Conservation

Market allocation

Pollution control

Benefits

Maintains healthy wetlands which are morelikely to have higher value than artificiallycreated replacements Maintains existing coastalfisheries that are difficult to relocate

Integrated data allow formation ofcomprehensive planning and identification ofregions most likely to be affected by physicalor social changes Allows effects of changes tobe examined beyond the local or regional scale

Improved modelling allows more accurateevaluation of how coastal systems respond toclimate change and also to other shocks

Sensible land-use planning such as the use ofland setbacks to control shoreline developmentbetter preserves the landscape and alsominimizes the concerns of beach erosion fromany cause

Reducing demand can increase excess supplygiving more safety margin for future droughtsUsing efficient technologies such as dripirrigation reduces demand to some extentPreserving some flexibility of demand is usefulas less valuable uses allow reduced demandduring droughts

Market-based allocation allows water to bediverted to its most efficient uses in contrastwith non-market mechanisms that can result inwasteful uses Market allocations are able torespond more rapidly to changing supplyconditions and also tend to lower demandconserving water

Improving water quality by improving thequality of incoming emissions prOVides greaterwater quality safety margins dUring droughtsand makes water supply systems lessvulnerable to declines in quality because ofclimate change

Table continues overleaf

242 Conclusion

Table VII2 Continued

Policy area and measures

River basin planning

Drought contingency planning

Human health

Weatherhealth watch warningsystems

Improved public health andpest management procedures

Improved surveillance systems

Ecosystems

Protect biodiversity and nature

Benefits

Comprehensive planning across a river basincan allow for imposition of cost-effectivesolutions to water quality and water supplyproblems Planning can also help cope withpopulation growth and changes in supply anddemand from many causes induding climatechange

Plans for short-term measures to adapt todroughts These measures would help offsetdroughts of known or greater intensity andduration

Warning systems to notify people of heatstress conditions or other dangerous weathersituations will allow people to take necessaryprecautions This can reduce heat stress andother types of fatalities both now and if heatwaves become more severe

Many diseases which will spread if climatechanges are curable or controllable and effortsin these areas will raise the quality of humanlife both now and if climate change occurs

More and better data on the incidence andspread of diseases are necessary to betterdetermine the future patems of infection anddisease spread This information is helpfulunder any scenario

Biodiversity protection maintains ecologicaldiversity and richness preserves variety ingenotypes for medical and other research Amore diverse gene pool proVides morecandidates for successful adaption to climatechange One possibility is to preserveendangered species outside of their naturalhabitat such as in zoos

Table continues opposite

A Sustainable Future 243

Table VII2 Continued

Policy area and measures

Protect and enhance migrationcorridors

Watershed protection

Benefits

Such policies help maintain an ecosystem andanimal and tree species diversity Corridors andbuffer zones around current reserve areas thatinclude different altitudes and ecosystems aremore likely to withstand climate change byincreasing the likelihood of successful animaland tree migration

Forest cover provides watershed protectionincluding protection from bank erosionsiltation and soil losss All of these functionsare extremely valuable whether climatechanges occur or not

Agriculture

Irrigation effiCiency Many improvements are possible and efficientfrom a cost-benefit standpoint Improvementsallow greater flexibility to future change byreducing water consumption without reducingcrop yields

Development of new crop types Development of more and better heat- anddrought-resistant crops will help alleviatecurrent and future world food demand byenabling production in marginal areas toexpand Improvements will be critical as worldpopulation continues to increase with orwithout climate change

Source After Smith et al (1995) table 3

we may well be able to adapt to the mostlikely ways in which the climate maychange For example we could substituteheat- and drought-resistant crops for thosewhose yields are reduced Infrastructure isgenerally replaced on a much faster timeshyscale than climatic change so it could beadapted to changes in climate It can alsobe argued in favour of reactive adaptashytion that it does not involve prematurelyspending money in advance of uncertainchanges

On the other hand one can argue thatrapid climate change or significant in-

creases in the intensity and frequency ofextreme events such as floods storms ordroughts could make reactive adaptationsdifficult and could pose immediate probshylems for large numbers ofpeople Equallysome policies would have significant beneshyfits even under current environmentalconditions and would be valuable from acost-benefit perspective even if no climaticchange toolc place These types of anticishypatory policies are often called no regretspolicies because they will succeed whetheror not climatic change takes place meaningthat policy-makers should never have to

244 Conclusion

regret their adoption No regrets policiesmay none the less be expensive TableVII2 illustrates a selection of these policies

One can argue that the central challengefor policy-makers in coming decades willbe to find ways of allowing the globaleconomy to grow at a moderate rate whileat the same time maintaining or enhancingthe protection of wilderness the prevenshytion of pollution and the sustenance ofecological resources We cannot be sure

KEy TERMS AND CoNCEPTS

anticipatory adaptationno-regrets policiesreactive adaptation

POINTS FOR REVIEW

that we will find policies that enable thisto happen Governments and society willinevitably need to make difficult trade-ofTsbetween economic growth and environshymental protection We cannot envisage asituation where there is indefinite growthin the human population and indefinitegrowth in the consumption of resourcesWe need to ensure to use Sir CrispinTickells phrase (Tickdl 1993) that hushymans are nOt a suicidal success

Which environmental issues wiU become increasingly important in coming decades

Can human energies be harnessed over the coming decades to improve rather than todegrade the environment

How might we adapt to global warming should it occur

GLOSSARYIn each definition any words that themselves ap~ar in the glossary are printed in iudieltyplt

adiabatic compression The process bywhich as a parcel of air falls the internalenergy is increased and its temperature israisedacid rain Rain which because of the preshysence ofdissolved substances derived fromair pollution has a pH of less than 565aerosol (atmospheric) An aggregation ofminute particles (solid or liquid) suspendedin the atmosphere The term is often usedto describe smoke condensation nucleifreezing nuclei or fog or pollutants suchas droplets containing sulphur dioxide ornitrogen dioxideaggradation The building upwards oroutwards of the land surface by the deposhysition of sedimentalbedo A measure for the reflectivity ofabody or surface defined as the total radiashytion reflected by the body divided by thetotal radiation falling on it Values are exshypressed on a scale ofeither 0-1 or 1-100alluvial floodplain A flat-lying area comshyposed ofsedim~nts (sands silts clays gravshyels etc) deposited by riversamphibian A creature that can live onland or in wat~r

anthropogenic Caused by human activshyitiesanthropogeomorphology The study ofthe human impact on landforms and landshyforming processesaquaculture The cultivation or rearingof plants or animals that grow or live in ornear wateraquifer An underground water-bearinglayer of porous rock through which watercan Row

arid Dry with limited vegetation rainshyfall less than about 250 mm and a greatexcess of evaporation over precipitationarterial drainage A system of majordrainage channels into which numeroussmall channels feedatoll An irregular annular (ring-shaped)coral algal reef enclosing or almost enclosmiddoting a central lagoon The reefS are oftenbreached by channelsbackscatter To send back rather thanlet through incoming radiation from thesunbadlands Areas that have been erodedby deep systems of ravines or gulliesbarrier island An elongated mainlysandy ridge feature running parallel to thecoast and separated from it by a lagoonbase levd The lower limit down to whicherosion on land may operate usually deshyfined with reference to the role of runshyning water For example sea level acts asa general base level though there can bea wide range of local base levels above andbelow sea levelbasin The area that drains into a partishycular river It has the same general meaningas catchment (British usage) or watershed(American usage)biodegradable A term used to describea substance that can be rendered harmlessor be broken down by natural processesbiodiversity A term used to describe thevariety of species both floral and faunalcontained within an ecosyrtembiofabrica Fabrics made of organicmaterialbiological magnification The increased

246 Glossary

concentration of toxic material at consecushytive higher trophic levels in an ecosystemToxins such as heavy metals and persistentpesticides become incorporated into livshying tissue from the environmentbiomass The total mass of biologicalmaterial contained in a given area of theEarths surface (expressed as dry weightper unit area)biorne A major ecological community orcomplex ofcommunities that extends overa large geographical area and is charactershyized by a dominant type ofvegetation (egtundra desert rain forest)bioremediation The use of microshyorganisms to restore the qualities of enshyvironments contaminated by hazardoussubstancesbiosphere The interlinked communitiesofanimals plants and micro-organisms thatlive on the land and sea of the Earthbiota The animal and plant life of aregionbiotechnology The manipulation ofliving organisms and their components(eg genes or gene components) for speshycific tasksbloom A scum produced by algae on thesurface of standing waterblowout An area of dune that has beenbreached by wind excavationboreal Of northern regions A termapplied both to a climatic zone charactershyized by cold snowy winters and shortsummers and to the coniferous forests ofthe high mid-latitudes in the NorthernHemisphere also known as taigabrecciate Break lip into angular fragmentscarbon budget The balance between theamount of carbon which accumulates in asystem and the amount that is releasedcarcinogen Any substance that producescancercarrying capacity The maximum popushylation of a given organism which a parshyticular environment can sustain without atendency to decrease or increase

catalyst A substance that without itselfundergoing any permanent change setsoff a change or increases the rate at whicha change occurscatchment The area that drains into ariver It is bounded by a drainage divideor watershed (British usage)centre-pivot irrigation The artificialdistribution of water to land for agriculshytural use in which Broundwater is pumpedand from a central point is dispersed in acirclechannelization The modification of riverchannds for the purpose of flood controlland drainage navigation and the reducshytion or prevention of erosionchaparral A type of stunted (scrub)woodland found in temperate regions withdry summers It is dominared by droughtshyresistant evergreen shrubschlorofluorocarbons A range of synshyrhetically manufactured chemically inertcompounds containing atoms of carbonfluorine and chlorine They have beendeveloped and widely used as solventsrefrigerants and aerosol propellanrs and inrhe manufacture of foam plasticscolloidal Composed of ultramicroscopicpaniclesconvection The transfer of heat in theatmosphere by the upward flow of hot airor the downward flow of cold airdeflation The removal of dry unconshysolidated material eg dust or sand froma surface by winddeflocculate To disperse or break up anaggregate so that particles become susshypended in a solution This may be achievedby the presence of sodium cationsdefolianr An agent tha[ removes foliage(eg leaves) from a plantdeforestation The permanent removal ofuees from an area of forest or woodlanddesertification The spread of desenmiddotlikeconditions in arid or semi-arid areas dueto human interference or climatic changeor both

desiccation Drying up of the environshymentdiatom A microscopic single-celled algawith a siliceous cell walLdieback A diseased condition of plantsoften applied to the dying-offoflarge tracts

of similar species at the same timedimethylsulphide A volatile sulphurcompound in seawater produced by bacshyterial decay and planktonic algae It oxishydizes in the atmosphere to form a sulphateaerosoldischarge (rivers) The amount of waterthat flows in a riverDNA (deoxyribonucleic acid) The subshystance that is the carrier of genetic inforshymation found in the chromosomes of thenucleus of a celldomestication The taming and brecdshying of prcviously wild animals and plantsfor human usedrainage basin That part of the landsurface which is drained by a particularriver system and is defined by a divide orwatershed (British usage)drawdown The reduction in groundshywater level by pumping out water fasterthan it can be replenisheddwt storm A storm in a semi-arid areawhich carries dense clouds of dust someshytimes to a great height often obscuringvisibility to below 1000 metresecology The science which studies therelations between living organisms andtheir environmenteagtsystem A biological community ofany scale in which organisms interact withtheir physical environmentecotone A transition zone marking anoverlap rather than a distinct boundarybetween two plant communities It maybe a zone of tensionedaphic A term used to describe soilconditions which influence the growthof plants and other organisms Edaphicpoundactors include physical chemical andbiological properties of soils such as

Glossary 247

pH particle-size distribution and organiccontentEI Niiio events A term applied to theextensive intense and prolonged wanningof the eastern tropical Pacific Ocean whichoccurs every few years It is associated withmajor anomalies in the patterns of atmosshypheric circulation and rainfallendemic Normally found only among aparticular people or in a certain regionewtasy A worldwide change in sea levelindicating an acmal rise or fall of the seaeutrophication The process by which anaquatic eeosystem increases in productivityas a result of increased nutrient inputOften this is due to humanmiddotinduced addishytions of elements such as nitrogen andphosphorus However the process mayalso be a natural phenomenonevapotranspiration The combined lossof water by evaporation from the soil surmiddotface and transpiration from plantsex situ methods A term used to describemeans of conserving species outside theirnatural habitat (eg in zoos or botanicgardens)feral Term describing an animal or plantonce domtJticated that has gone wildfilling The deposition ofdredged matershyial to make new landfluvial Relating to a river or riversfood chain The transfer of energy fromgrecn plants through a sequence oforganshyisms in which each eats the one below itin the chain and is eaten by the one aboveforest decline The decline of forestvitality characterized by decreased andabnormal growth leading eventually todeath The causes are poor managementpractices climatic change fungal viral andpest attack nutrient deficiency and atmosshypheric pollutionfriable Easily crumbled (ofsoil rock orother material)gabion A wire-framed container full ofboulders or cobbles used to make wallsto stop erosion

248 Glossary

general circulation mood (GeM) Adynamic computer model which simulateslarge-scale features of atmospheric andoceanic circulationgenetic ~lating to genes which arcunits of heredity composed or DNA orRNA and fanning part of a chromosomethat determines thc particular characterisshytics of an individualgeomorphology Thc science of the orishygin and developmcnt of landformsglaciated Term used to dcscribe an areathat has becn at some point covcred ormoulded by glaciers or icc sheetsglobal warming Thc process by whichthe Earth may becomc warmcr because ofthe role of mcchanisms such as the greenshyhouse ejJeClgneiss A c03nC-grained metamorphicrock composed of feldspars quartz andferromagnesian mineralsgreenhouse effect A climatic cffcctcaused by permitting incoming solar 4shyriiation but inhibiting outgoing radiationIncoming short-wave radiation is absorbedby matcrials which thcn re-radiatc longerwavelengths Certain substances in theatmosphere eg carbon dioxide absorblong-wave radiation resulting in a warmshying effectgross primary production The totalamount of organic material synthesized ina given time period by living organismsfrom inorganic materialgroundwater Water occurring below thesoil surface that is held in the soil itself orin a deeper aquifergypsum A rock fonned ofnatural calciumsulphate caused by its crystallization as saltywater is concentrated by evaporationhabitat The place in which an organismlives characterized by its physical featuresor the dominant plant typesbalons Members of the halogenatedfluorocarbon (HF) group of ethane- ormethane-based compounds in which H+ions arc partially or completely replaced

by chloride fluoride andor bromideThey arc long-lived and nave been implishycated in ozone depletionha1ophytic Tolerant of high concentrashytions of saltsheathland An area of evergreen JwJeroshypbyOUJ shrubland where beath families(eg Ericaceae) are present though nOtnecessarily dominant Heathlands developon areas where soil is low in nutrient statusheavy metal Any metal or alloy of highspecific gravity especially one that has adensity higher than 5 g per cu cm eglead zinc copper mercuryherbicide Any agent organic or inorganicwed to destroy unwanted vegetationHolocene The most recent epoch of theQuaternary following the PleistoceneOften called the post-glacial it has exmiddottended from about 10000 years ago tothe present day It has been marked byvariow climatic 8uctuarionshumus The organic constituent ofa soilusually formed by the decomp05irion ofplants and leaveshydro-isostasy The reaction ofthe Eanh 5

crust to the application and removal of amass of water For example efMtlltic seashylevel changes have affected the depth ofwater over the continental shelvcs causingthe crust to be depressed at times of highsea level and elevated at times of low sealevelhydrocarbons Compounds of hydrogenand carbon some with minor or tracequantities ofoxygen suJphur nitrogcn andothcr elementshydrocompaetion The process by whichsediments arc compressed by an overlyingbody of waterhydrology The science concerned withthe study of the different fonns of wateras they exist in the natural environmentIts cenual focus is the circulation and disshytribution of wattChydrostatic uplift Uplift of land surfrcecaused by upward water pressure

hypoxia The condition experienced whenoxygen levels are low in blood and tissuesinbreeding Breeding from closely relatedanimals or personsinfiltration The movement ofwater intothe soil from the ground surfaceinterglacial A time period between twoglacial stages during which temperaturesare relatively highinterpluvial A time period between twopiuPiRI stages during which conditions arerelatively dryisopleth line on map connecting placeswhere a particular meteorological factoreg thunderstorms occurs with the samefrequencyisostasy A process that causes the Earthscrust to rise or sink according to whethera weight is removed or added to it Sucha weight could be for example an icecapkarst A limestone region with undershyground drainage and many cavities andpassages caused by the solution of the rocklandfill The disposal of waste by tippingit on land often in old mine workings orlow-lying landlaterite The residual deposits formed bythe chemical weathering of rock composedprimarily of hydrated iron and aluminiumoxides Extensively devcloped in the hushymid or subtropical regionsleachate The solution or soluble matershyial that results from a leRching processleaching The removal of dissolved mashyterial by the percolation of water througha soil or sedimentLessepsian migration An almost unishydirectional migration of biotR from one seaor lake to another Named after the manwho built the Suez Canal which allowedorganisms to pass from the Red Sea to theMediterraneanlevee A natural or man-made embankshyment along a riverlichenometry A method of time estimashytion (dating) on rock surfaces based on

Glossary 249

the rate of growth of lichens (eg Rhizoc4rpon geogrRphicum)lithosphere The solid earthloess A deposit of primarily silt-sizedmaterial that was originally dust transshyported by the windmacrobenthic Relating to large organshyisms that live on or near the bottom of abody of watermacropore A particularly large pore orvoid in the soilmammal A warm-blooded creature witha backbone which if female can nourishits youngmangrove Plant communities dominatedby mangrove trees RhizopherJl BruguieriRand ApicenniR which colonize tidalmudflats estuaries and other shelteredareas in tropical and subtropical areasmlllJuis Scrub vegetation of evergreenshrubs characteristic of the western Medishyterranean broadly equivalent to chJlparrRImarginal land Land that is difficult to

cultivate or unprofitablemariculture Farming of the seamarsupial A mammRI characterized bybeing born incompletely developed and sousually carried and suckled in a pouch onthe mothers belly for a timemeander The winding pattern of a sinushyous river channelMediterranean climate A climatic typecharacteristic of the western margins ofcontinents in the worlds warm temperatezones between latitudes 30 and 40 (egcentral Chile central California)megafauna The largest types of animalsin a communityMesolithic A cultural period foUowingthe Palaeolithic from 10000 BC to 4000BC characterized by the use of microlithicimplementsmetamorphie Term used to describerocks which have been altered by externalsowces of heat pressure or chemical subshystances rather than merely by burial underother rock

250 Glossary

metapedogenesis Human modificationof soilsmicroclimate The physical state of theatmosphere close to a very small area ofthe Earths surface often in relation toliving matter such as crops or insectsmonsoon A wind with seasonal reversalsof directionmorphology The form or shape of anobject or organismnanoplankton The smallest of the phytoshyplanktonnecrosis The localized death ofceUs tissueor an organ resulting from disease or injuryNeolithic A cultural period following theMesolithic from the fourth millennium Beuntil the onset of the Bronze Age It marksthe beginning of the domestication of anishymals and the cultivation of cropsnet biological primary production Seenet primary productionnet primary production The amount oforganic material produced by living organshyisms from inorganic sources in excess ofthat used in respirationnutrient sink A location in which nutrishyents accumulatenutrient source A location from whichnutrients are rcleasedoceanic conditions Climatic conditionsthat arc modified by the presence of ancarby sea or ocean in contrast to continshyental conditionsomnivore An animal which ears bothplant and animal matterorganochlorides Organic compoundswhich contain chlorine Often used asactive ingredients for pesticides they arevery persistent due to their chemical stabshyility and low solubility An example is theinsecticide DDTorographic A tenn used to describe climshyatic conditions or phenomena caused bythe presence ofhigh relief(eg mountains)osmosis The passage ofa solvent througha semi-permeable partition or membraneinto a more concentrated solution

oxidation A chemical reaction in whicha substance decreases its number of elecshytrons The most frequent oxidant is moshylecular oxygenpalaeolimnology The study of the envirshyonmemal history of a lake most imporshytantly from evidence preserved in itsbottom sedimentspastoralism A form of land use relatingto flocks and herds of animalspathogen An organism which causesdiseaseper capita For each personperennial Lasting through a year orseveral years Used to describe plants thatare not merely annuals and streams thatnormally flow through all seasons of theyearpermafrost The thermal conditions insoil and rock where temperatures ate bemiddotlow OC ror at least two consecutive yearspH The measure of the acidity or alkashylinity of a substance based on the numberof hydrogen ions present in a litre of thesubstance and expressed in terms of pH _logIO(lH) where H is the hydrogen ionconcentration The centre point on thescale is 7 representing neutrality Acidsubstances have a pH of less than 7 andalkaline substances have a pH of morethan 7photochemical reaction A chemical reshyaction which is speeded up by particularwavelengths ofelectromagnetic radiationphytoplankton Microscopic organismsespecially algae that live near the surfaceof the sea and form the basis of food formany other forms of aquatic lifepiezometric swface A subterranean surshyface marking the level to which water willrise within an lIiJuiftrPleistocene The first epoch of the Quashyternary including glacial and interglllcillstages between about 2 million and10000 years agopluvial A climatic phase with plentifulmoisture

podzol A soil characterized by the acidshyification of the A horizon the downwardle4ching ofcations metals and humic subshystances and their deposition in the B horishyzon often precipitating to form a panThe process is most prominent in cool andwet climatespollen analysis The analysis of plantpollen under the microscope to reconshysttuct the vegetation conditions underwhich the sediment in which it occurs wasdepositedprecipitate In chemistry the depositionin solid form from a solutionprecipitation Moisture that falls on theground including rain snow dew and fogpredator An animal which kills othersfor food by preying on them A secondaryconsumer in a food ch4inprofile An outline seen from one side(eg the cross profile of a river channel) ora vertical cross-section (eg of a soil andits various layers)radiation solar Electromagnetic wavesemitted by the sunradiation budget A term used in meshyteorology to describe the difference beshytween incoming and outgoing radi4honradiocarbon dating A method ofdetershymining the age ofan organic material (egwood charcoal peat) by measuring theproportion of the He isotope containedwithin its carbon contentrangeland Alarge area ofopen land usedfor grazing or huntingreclamation Bringing land into a newform This can involve either returningsomething to its original state (eg somedegraded land) or transforming it into anew state (eg by filling in a lake to makeland)redox potential A measurement of thewillingness of an electron carrier to act asa reducing or oxidizing agentrendzina A type of soil with dark surshyface layers or horizons that developes onsoft limestones

Glossary 251

rill A small channel in a soil or rocksurface often only a few centimetres longriparian Of or on a river bankrip~rap Large fragments of broken rockdumped along a shoreline to protect itagainst wave actionrunoff The water leaving a drainage areaIt is normally regarded as the rainfall mishynus the loss by evaporationsalinization The process whereby saltseg sulphates nitrates and chlorides beshycome concentrated in the soiLsanitization The process by which someshything is made more sanitary hygienic ordisinfected so that health conditions areimprovedsaturation excess overland flow Surfacerunoffthat is g~nerated wh~n rain falls onground that is already saturated withwatersavanna A grassland of the tropics andsubtropicsscarification The process by which seedsare cleaned by abrasion of the epidermisCan also refer to changes caused to sc~ds

by passing through th~ gut of an animalor by fireschist A met4morphic rock composed oflayers of different materials split into thinirregular platessderophyUous A term referring to speshycies ofevergreen trees and shrubs that haveadapted to lengthy seasonal droughtscrub A type of vegetation consistingmainly of brushwood or stunted forestgrowthsecondary forest Woodland which hasregenerated and colonized an area afterthe original forest has been removedsediment yield sediment load Sedimentyield is the mean sediment load carried bya stream giving some measure of the rateof erosion in a dr4in1JBt b4Sin The sedishyment yield is express~d as weight per unitareaseedbed An area of soil in which seedsare plant~d and take root

252 Glossary

seep An area moistened by the ~epage

of water from or into the ground$CIIlimiddotarid Dry with a shortage of moisshyture for much of the year but not so dryas an lind areashear strength The maximum resistanceof a material to the application of stressMajor sources of such resistance arc coheshysion and frictionsheet flow The flow ofwater in thin filmsover a low-angle surfaceshifting cultivation Cultivation of asmall area of land in which forest is clearedand the biomass removed or burned folmiddotlowed by the use of the site for the proshyduction of mixed agricultural crops forseveral years Eventually the area is abanshydoned as soil ~rtiliry decreases and thecultivators move on to a [(w area SJ4shshyut-bNrn is a type of shifting cultivationsink-hole A hole or depression in thelandscape into which water drains causedby concentration of solution of the bedshyrock usually limestone or chalkslash-and-burn A system of land useespecially prevalent in the tropics in whichland is cleared of forest by cutting andburning so that cultivation can take placeAJ fertility rapidly declines in the cultiv4

ated areas the farmer moves on to a newarea after a few yearssmectite A type of day often made upof montmorillonite that may have theproperty of swelling in watersmog A fog in which smoke or otherforms of atmospheric pollutants play animportant role in causing the fog to formand thicken It often has unpleasant ordangerous physiological effectssplash erosion Erosion produced by theimpact of raindrops splashing on theground surface particularly if it is notprotected by vegetationspontaneous combwtion Fire cawed bythe natural build-up ofheat within inflamshymable materialspp Abbreviation for specics (pluraJ)

steppe A generally dry grassy plainlandstratosphere The region of the aCDlOSshy

phert lying betwccn the tropopllllSe andabout 20 kIn in which there is lime changein temlXrature with heightsubstrates Material underlying thesurfacesuccession The sequence of changcs ina plant community as it devdops over timesupernatant Term describing liquidfloating on a surfacesustainable devdopment Dcvdopmentthat meets the needs of the prescnt withmiddotout compromising the ability of futuregenerations to meet their own needssymbiosis An interaction between twO

different organisms living in close contactand usually to the advantage of bothtalus A sloping mass of fragments simmiddotilar to scree at the foot of a clifftectonic A term describing the broadstructUreS of the Earths lithosphere andmovcments within the Earths crusttcrnperate A term used to describe aregion or climate characterized by mildtemlXraturestemperature inversion Normally airtemperature decreases as height increasesHowever under certain weather conditionsair temlXrature may increase with heightso that a layer of warmer air overlies acolder layer This is temperature inversionterracing The construction of banks orsteps on a hillside to give areas of lowgradient either to enable cultivation or toconserve soilthalweg Line where opposite slopes meetat the bottom of a valley river or lakethermokacst Topographical depressionsresulting from the thawing of ground icethreshold A condition which marks thetransition from one state of operation of asystem to another Rapid and irreversiblechange may occurtrace dementi Elements thl[ are requiredby living organisms to ensure normalgrowth development and maintenance

They occur at lower concentrations thanmajor elements and include iron mangashynese zinc copper iodine etctrau gases Gases which occur in verysmall amounts in the atmospheretrophic levels The positions that organshyisms occupy in a food chaintropopause The interface between thetroposphere and the stratospheretroposphere The lowest level of theatmosphere in which most of ourweather occurs It lies beneath the stratoshysphere and its thickness ranges from about7 km at the poles to about 28 km at theequatortundra The zone between the latitudishynal limits of tree growth and polar icecharacterized by severe winters and a shortgrowing seasonturbidity A measure of the lack of clearshyness in a liquid caused by the presence ofsuspended materialunderstory A layer ofvegetation beneaththe main tree canopyUV radiation Radiation from the sunwith shorter wavelengths than visiblelight It is classified into three rangesaccording to its effect on human skinUV-A is not normally harmful UV-Bproduces reddening and tanning uv-e(with the shortest wavelengths) is the mostdamagingvector-borne A term used to describe adisease that is passed on by an organism

Glossary 253

often an insect (eg as malaria is transmitshyted by the mosquito)volatilization Evaporation or the proshycess of turning from solid or liquid forminto a vapourwater table The level below which theground is saturated with waterwatershed (American usage) The areaoccupied by a drainage basin or streamcatchmentwatershed (British usage) A line ofseparation between waters flowing intodifferent rivers basins or seasweather front A sloping boundary surshyface separating two air masses that exhibitdifferent meteorological propertieswetlands The collective term for ecosysshytems whose formation has been dominatedby water and whose processes and characshyteristics are largely controlled by waterwilderness An area leA untouched andthus in a natural state with little or nohuman control or interferencewind reactivation The renewed moveshyment of sand and other material by thewind especially when vegetation cover isreducedwind throw The blowing over of treesby the windxerophilous A term describing plantswhich live in dry habitats and can endureprolonged drought Many such plantseg cactus have developed physiologicaladaptations to cope with these conditions

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Vogd C H and Drummond J H 1995Shades of green and brown environshymental issues in South Africa In A

Lemon (cd) Tht Geogrphy ofOJnalirl South AfrieR 85-98 ChichesterWl1ey

Wahren CmiddotH Papst W A and WilliamsR J 1994 Long-term vegetationchange in relation to canle grazing insubalpine grassland and heathland in theBugong High Plains an analysis ofvegshyetation records from 1945 to 1994 Autshytrlia lou_al of Botany 42 607-39

Walsh R P Hudson R N and HowellsK A 1982 Changa in the magnitudemiddotfrequency of800ding and heavy rainfallsin the Swansea valJey since 1875obri 9(2) 36-60

Waltham A C 1991 lAnd SubsUlenuGIOlSgOW Blackie

Ward R C 1978 Floods A GeogrRphicalPerspectivl London Macmillan

Warrick R A and Oerlemans ] 1990Sea level rise In J T Houghton G Jenkins and J J Ephraums CUmteChnge Thl IPCC Stientifie Autsmlt1lt257-81 Cambridge Cambridge Unishyversity Press

Watson R T Zinyowera M C andMoss R H 1996 Clite 01n811995 - IpiUts AApttictU ad Mitshyigtion Df Clite Chllge StientijiampshyTechnicl Antdyus Contribution ofWorking Group II to the Second Asshysessment Report of the Intergovernshymental Panel on Climate ChangeCambridge Cambridge University Press

Weber P 1993 Reviving coral reefs InL R Brown (ed) St of the WorU1993 42-60 London Earthscan

Wellbum A 1988 Air PolIMtimJ AcUlRAi The BiDloatd Imp HarlowLongman

Well S M 1988 c-aJ Ruft of thltWorld voL 2 [Iii Oct Rell Sellbullbull~ Golf Good SwitzerlandCammiddotbridge UNEPIIUeN (InternationalUnion for the Conservation of Nature)

White R 1994 Urb EnpjronmentlMn8ement Chichester WLley

Whitmore T M Turner B L JohnsonD L Kates R W and Gottschang TR 1990 Long term population changeIn B L Turner W C Clark R WKates J F Richards J T Matthewsand W B Meyer (cds) The Erth IJJ

Transformed by Human Action 26-39Cambridge Cambridge University Press

Wigley T M L and Raper S C B1992 Implications for climate and sealevel of revised IPCC emissions sceshynarios Nature 357 293-300

Wigley T M 1 and Raper S C B1993 Future changes in global meantemperatures and sea level In R AWarrick E M Barrow and T M LWigley (cds) Climate lInd Sell LevelChange 111-33 Cambridge Camshybridge University Press

WiJcove D S McLellan C H andDobson A P 1986 Habitat fragshymentation in the temperate wne InM E Soule (ed) Conservation BiologyThe Science of Scarcity and Diversity251-6 Sunderland Mass SinauerAssociates

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References 263

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INDEXNote Alphabetical arrangement ofheadings and subheadings is word by word ignoringand by in through etc Page numbers in italics refer to illustrations Rememberto consult the Glossary (pp 245-53) for definitions

Aberfan disaster 185 186accelerated landslides 185-8accelerated sedimentation 182accelerated soil erosion 165-74

180-2 201acid rain 116-20

and forest decline 45reduction in 118 120

Adriatic Sea eutrophication of 221aerosols atmospheric 83-9afforestation

hydrological effects 126 136-7144

ste also deforestationAfrica

fire use 20-1savanna ecosystem 4041see aso individual countries

Africanized honey bee 66 67Afromontane grassland 39-40agricultural empires 6agricultural revolutions 4-5agriculture

arid areas 27-8biotechnology in 76 77and dust storms 84 87 172energy use 10and global warming 97habitat destruction 69hydrological impact 126land drainage for 142-5machinery 46 168-9 170-1no regrets policies 243pollution from 145 151-2seasonally flooded wetlands 57soil conservation measures 169 174and soil erosion 166-7 168-9

172-4

technological developments 5 67-8 10

and tree damage 46air conditioning 100air pollution

and forest decline 44-6 47health effects 85 102 106 108-9increasing scale 83legislation controlling 44 85 104and stone decay 197-200urban areas 49 50 52 8599

102-9 197-200vehicle emissions 114115199Jee also acid rain

albedoland use changes affecting 90 92sulphate aerosol effects on 85urban areas 98

algal blooms 150 155 218alpine grasslands 43Amazon basin deforestation in 90

91America

Africanized honey bee spread 6667

Jtt aho USAanimals

channelization effects on 131domestication 4feral 66introduced species 66-7space requirements 70-1urban 48-9

Antarctic ozone hole 110 111 114anthropogeomorphology 165 167anticipatory adaptation 240 243-4apartheid 13 108-9aquaculture 232-4

aquif~rs

d~pletion and rccharg~ 159-61s~awat~r incursion 184

Aral Sea d~siccation of 155-8 184Arctic ozon~ depl~tion abov~ 114arid ar~as

agricultur~ 27-8 159d~forestation 28groundwat~r depletion 159urban groundwater recharge 142urban ston~ d~cay 197see IIlso d~sertification

arterial drainage systems 142asbestos 109ash trees di~back of 46Aswan Dam 125 128 129Atlantic industrial ~ra 6atmospheric carbon dioxide 22-3

9396atmospheric circulation

and global warming 94see tllso climate climate change

atolls 226Australia

alien plant species 68graring and grasslands 43groundwater abstraction 159introduced parasites 66savanna 41soil salinization 183 184

autumn-sown cereals 169 170

backscatter 84badlands 168Bahrain beach pollution in 219Baltic Sea dune managemem on 224Bangladesh coastal floods in 215barchans 176 177barrier islands 210 213beaches

nourishment 212 213pollution 219

biodiversity 58 -63preservation 60-3 78 242rain forests 35 36urban ar~as 48-9wetlands 55 232

Ind~x 265

bioeconomic analysis 60biological magnification 147218biomass burning 20-1 22-3

see also firebiotechnology 8 76-7bird habitat losses 69-70Biwa Lake eutrophication of 152153Black Sea eutrophication of 150Blackwater estuary sea-level rise in

208-9blowouts 222Blue Plan 221bogs 54Brazos River Texas channel changes

in 182Britain

acid rain 117air pollution 104 105dean air legislation 85 104coastal erosion 209 210 lll 212coastal flooding 215 216-17dunes and dune management 222

225field drainage 142fog 85 86 105forest decline 45-6global warming and agriculture 97groundwater recharge 160habitat loss and fragmentation

69-70heathland decline 42sea-level rise 208-9soil erosion 168-9 170-1 173waste and waste disposal 192wetland drainage 143wind erosion 173

buildingsrestoration 199 200weathering 118 197-200

butterfly habitat loss 69

Californiacliff erosion 210dust storms 172inter-basin water transfers 156subsidence 189see IIUO Los Angeles

266 Index

Cameroon rain forest management in36-7

canals animal migration along 67Canary Islands artificial channel in

179Cape Town air pollution in 109capitalism 13-14carbon dioxide atmospheric 22-3

9396see also greenhouse effect

carrying capacity 4centre-pivot irrigation 160CFCs 93 96 110 113channel straightening 178-80channelization 131chaparraJ 21Chicago

groundwater abstraction 159vegetation changes 51-2

Chinadesertification 30-1nature conservation 61 62-3

citiesair pollution 49 50 52 85 99

102-9 114 115 197-200ancient 5animals 48-9climate 98-101derelict land 49ecological footprint 48environmental improvement 50flood runoff 140 141groundwater depletion 159groundwater recharge 141-2

160-1less developed countries 7stone decay 118 197-200veget1ltion 48vehicle emissions 114115199wastes 192water pollution 49 148-9

clay soils drainage of 144clean air legislation 4485 104clear-felling

and debris ava1anches 188and runoff 136-8

clear-water erosion 128

cliff erosion 210climate

increasing human impact on 83urban 98-101

climate changeadaptation to 240-4aerosol effects 83-9deforestation causing 35 90 91

92and desertification 28-9inter-basin water transfers causing

155land use changes causing 90-2and megafauna extinctions 75-6and savanna development 40and sea-level rise 206-7see also global warming

cloud-condensation nuclei 84-5Clyde River pollution of 148-9coal waste tips 185 186coastal areas

aquaculture 232-4dune management 222-5erosion 208-9 210-14 223-4

225flooding 215-17managed retreat 209212management 235 241marshes 208-9pollution 218-21227red tides 150sea-level rise 206-9seawater incursion 184urban stone decay 197vulnerability 205 206 235

Colorado River regulation of133-5

communism 106see also Eastern Europe

conifer plantations 69conservation 14 58 60-1 62-3

242see also nature reserves

constructioncoral reefs damaged by 230soil erosion caused by 167

contributing factors 15

controlled burning 21coral

bleaching 227eutrophication effects 151

co~ reeamp 226-31crops drought resistant 243cumulative global change 10-11Czechoslovakia urban air pollution in

106

dams 125-31 133-5channel morphology effects 180ecological explosions caused by

65-6landslip caused by 185 186-7salinization caused by 183-4wetlands affected by 57

debris avalanches 188debt-for-nature swaps 34deflation see wind erosiondefoliants 13deforestation 32-7

arid areas 28climatic effects 909192and coral reef degradation 227and debris avalanches 188hydrological effects 136-8and soil erosion 165-7and soil salinization 184see aso afforestation forests

derelict land urban 49 50desertification 26-31

and dust storms 84deserts dune reactivation in 174-7desiccation

inter-basin water transfers causing155-8

and soil salinization 184developing countries

air pollution 104-5aspirations 239urbanization 7

diatoms 117dieback temperate forest 44-7dikes 142 143dimethylsulphide 84-5dinosaur extinction 73

Index 267

dischargeand deforestation 136-8and flood control works 180and land drainage 144regulation by dams 125 133and urbanization 140 180

diseaseand megafauna extinctions 75-6

diseases plantaccidental introduction 65

domestication 4 19dongas 168drainage 142-5

and subsidence 190drainage basin

planning 242stresses and responses to 14-15

drawdown 159-60dredging 132drought

crops resistant to 243planning for 242and soil erosion 172

dry deposition 116dunes

coastal 222-5reactivation and stabilization 30

174-7dung beedes 66dust atmospheric 84dust storms 84 87 155 172-3

earthquakes 190Eastern Europe

air pollution 47 106-7forest decline 45

ecological explosions 65-6ecological footprint 48ecological succession see successioneconomic development stages of 6ecotones wedands as 55ecotourism 12edaphic conditions see soilsE1 Niilo events 227dephants

in savanna ecosystem 41embankments river 131

268 Index

energy renewable 77energy conservation 96energy consumption 8-10environment

naturaJ changes 14systems approach to 14-15

environmental impact of humanactivity

complexity 239increasing scale 8 10-11 12 19trends 8-11uncertainties 1495 120

erodibility 174erosion

coastal 208-9210-14223-4225

dunes 223-4 225land use changes affecting 126

127river regulation affecting 128see also soil erosion

erosivity 174Essex marshes sea-level rise and

208-9estuaries red tides affecting 150Ethiopia river sediment load in 130Europe

forest decline 44see also individual countries

eustatic change 206eutrophication 146 150-3 221evaporation

from forest 136and salinization 183-4

evapotranspiration irrigation and 91-2evolution 58extinctions

global 73and habitat area 60through habitat fragmentation 70

71increasing rate 58 78Late Pleistocene 73-6

falls 187fens 54

drainage 143

feral animals 66fertilizers eutrophication caused by

151field drainage 142 152fire 20-5 77

early usc 3 4in heather management 42oil-well 85 88-9in savanna formation 40soil erosion following 167suppression 21 24systemic and cumulative effects

10-11vegetation adapted to 22 33 40see also smoke

fibacid rain affecting 118 119pollution affecting 148 150 154

fisheries coastal wetland 232-4fishing 205-6 228fishponds 232-4flood control

and channel morphology 180channel straightening for 17880

flood peakltand deforestation 136-7and land drainage 144and river regulation 133

flood protection schemes coastal215217

floodand afforestation 144coastal 215-17and deforestation 138and land use changes 126 127and soil erosion 171urbanization effects 140see aho flood peaks

floodwaters channelization effects on131

flows 187flue gas desulphurization 120fog 85 86 105food chain biological magnification

through 147 218food production 12

see also agriculture aquaculture

forest decline 44-7forest fires 21 22 23 24-5forestry

and surface water acidity lISforests

clearance lee deforestationecological roles 32economic uses 32 37evaporation 136expansion 33fire suppression 21 24fragmentation 69hot spots S9management and protection 37runoff from 136-7soils 165-6Ile alIo trees

fossil fuel combustionand acid rain 117and air pollution 104-8atmospheric carbon dioxide from

93reduction 118IU Iso vehicle emissions

frOSts urban 100fuel domestic poUution from 108-9fuelwood 28 37fungi accidentaJly inrroduced 65Pynbes heathland 64

game management controlled burningfor 21

gardens 52general circulation models 90genetic engineering 76Georgia (USA) land usc and channel

morphology in 180-2Germany forest decline in 44 47Glasgow watu pollution in 14S-9global environmental change 10-11global warming 93-7

adaptation to 240-4and coral reef degradation 227impact on resources 240no regrets policies on 95 96

241-4and sea-level rise 207

Index 269

Gobi Descn 30grassland 39-41

grazing effects 43mid-Iatimde 22origins and maintenance 22 39-41runoff on 136

grazing 43Great Barrier Reef 226 227 229greenhouse effect 83 92-7

III alIo global warminggreenhouse gases 83 92-3

policies for reducing 95 96groundwater

dam construction affecting 186-7groundwater abstraction 159-60

and salinization 183 184and subsidence 189

groundwater recharge 141-2 160-1Gulf War

and coastal pollution 219oil-well fires 85 88-9

gypsum crusts 197 200

habitatschanges in ecological explosions

caused by 65-6edge effects 71heterogeneity loss 71hot spots 59loss and frtgmentation 69-72size 60

halons 110health

air pollutants affecting 85 88 102106 108-9

coastal pollution affecting 220-1ozone concentrations affecting 114policies on 242wastes hazardous to 192 195water pollution affecting 146 147

heat island urban 98-101heathlands 41-2 64

hot spots 59hedgerow removal 169High Plains (USA)

groundwater abstraction 160irrigation effectS on rainfill 91-2

270 Index

Holme Fen Post 143Hoover Dam 133hot spots biodiversity 58 59human environmental impact see

environmental impacthuman life origins of 3humidity atmospheric land use

changes affecting 91hunter-gatherers 4 6 12hunting megafauna ntinctions

through 73-5Hurghada coral reefs in 230-1hydro-isostasy 190hydrocompaction 190hydrological systems suesses affecting

14hydrology

forests 136-8land use changes affecting 126-7river regulation effects 125-35urban 48 140-2

inbreeding 70incineration 194 196inciting factors 15India

plantations 137river regulation 131

Indonesia aquaculture in 232-3Indus River 131industrialization 5-7 12

air pollution 84 105 117coastal pollution 221greenhouse gases 93wastes 145 192water pollution 148221

infiltration capacityforests 136 137urban areas 140

insects introduced 66 67inter-basin water transfers 131-2

155-8and soil salinization 184

Intergovernmental Panel on ClimateChange 93

international agreementson coastal pollution 219

international environmentalconventions 56

introduced species 64-8urban 49 50 51

invasions biological 64-8irrigation

channel morphology effects 180climatic effects 9091-2early developments 5 6 7efficiency 243groundwater abstraction for 159

160inter-basin water transfers for 155-8river regulation for 131salinization effects 28 183-4

islandsbiogeography 70introduced species 65

isostatic change 206 208Israel groundwater recharge in 161

Japan eutrophication in 152 153Java fishponds in 233

Kakadu National Park alien plants in68

karst 189Kenya sustainable environmental

management in 29keystone species 41Kuwait oil-well fires in 88-9

Lagos harbour coastal erosion in213-14

lakesacidification 118artificial ecological explosions in

65-6desiccation 155-8 184sediment cores 117

Lancashire dune management in 225land degradation

through deforestation 138see Iso desertification

land drainage 142-5and nitrate pollution 152and subsidence 190

land-use changeschannel morphology effects 180-2climatic effects 90-2hydrological effects 126-7lee also particular ehangu eg

dc=forestation urbanizationland-use planning 241landfill 192 194 196landforms human impact on 165 167landslides 185-8legislation

dean air 44 85 104watc=r pollution control 148 153

Lesbos coastal pollution in 2211c=ss devdopc=d countries lee developing

countriesLessepsian migration 67Lesset Snow Goose 70 72lignite 106-7limestone

overpumping and ground subsidence189

weathering in buildings 199limestone pavements 8London

building stone decay 199groundwater levds 159 160precipitation 99smog 85

Los Angelesair pollution 104 lOS 106inter-basin water transfers 156subsidence 189vehicle emissions 114 115

Machacos District Kenya sustainableenvironmental management in 29

Malidust storms 87wetland management 57

mammoth 74managed retreat 209212mangrove swamps

aquaculture threats to 232 233234

in coastal flood protection 215Vieblam War effects 13

Index 271

malJuis 22 33marginal land 13marine parks 229 230-1marine pollution 218-21Marsh George Perlcins 83 136

138-9marshes 54

coastal 208-9mass movements hazardous 185-8Mauritania dust storms in 172-3meanders 178Mediterranean area deforestation in

32-3Mediterranean Sea pollution of

220-1megafauna extinctions 73-6metals water pollution from 146metapedogenesis 165 166methane increase in 93Mexico City subsidence in 189migration corridors 243mining

charmel morphology effects 182early developments 5open-cast 10and subsidence 189

Montreal Protocol noMorocco dune stabilization in 175municipal waste 145

Namibia dune stabilization in 176-7nature conservation 62-3 242nature reserves 14 61-3

alien plant species in 68coastal dunes 225marine 229 230-1size 70-1tropical forests 37

Nepal deforesration in 33-4net primary production

human domination and destruction12 13

Niger delta 56coastal erosion 210 213-14wetland management 57

Nile River regulation of 125 128129

272 Index

nitrate pollution 146 151 152nitrogen

in eutrophication process 150 153nitrous oxide emissions 93 1I 7no regrets policies 95 96 241-4non-point pollution sources 145North America debris avalanches in

188North Platte River 180nuclear winter 85nutrient enrichment

algal blooms caused by 218let also eutrophication

nutrientseffects of fire on 22losses under shifting cultivation 22let also nitrogen phosphorus

oceansimportance 205-6limited human impact on 235

oil abstraction subsidence due to189

oil pollution 218 220oil-well fires 85 88-9Olduvai Gorge 3open-cast mining 10osmotic pressure 182overcultivation 27-8overgrazing 28 84Oxford building stone decay in 199ozone layer

role 110thinning 110-14

ozone tropospheric 105 114

Pacific global era 6Pacific Ocean coral reefs in 227 228paired watersheds 136palaeolimnology 117pandas 61 62parasites introduced 66Paris urban heat island in 100 101particulate concentrations urban

102-4 105 106lee also PM 1Os

pastoralists 28

pasNres loss of 69peadands 54

drainage 143 144permafrost subsidence of 189-90Persian Gulf stawater incursion in

184pesticides water pollution by 147pests urban 49pH 116-17Philippines aquaculture in 234phosphate pollution 146phosphorus

in eutrophication process 150153

photochemical reactions 114phytoplankton 150 151piezometric surface 159planktonic algae 84-5plantations 137plants

acid rain damage 118domestication 4introduced 51 52 64-5 68salinization effects on 182-3

Pleistocene overkill 73-5ploughing 168PMI0s 85 88 106point sources of pollution 145Poland

acid rain damage 45dune management and coastal

erosion 224pollutants classification of 145-7pollution

coastal and marine 218-21coral reefs 227and forest decline 45urban areas 49 50Set abo air pollution waste water

pollutionpollution abatement

biotechnology in 77coastal 219 221

population growth 3-4 5arid areas 27 29coastal 205projections 7 60 220

136-8140-2

and sustainable environmentalmanagement 29

see also urbanizationpore-water pressure 186poverty 60power stations

emissions 85 108 118 120thermal pollution 154

prairies urbanization of 51precipitation

global warming effects on 94relationship with vegetation 40see also acid rain rainfall

predisposing factors 15prehistoric extinctions 73-6prescribed burning 21

rain forestsbiodiversity 35 36removal 34-5 90 91 92

rainfallarid areas 27~8 29irrigation affecting 91-2land-usc changes affecting 90

91-2in savanna development 40urban areas 98-9 100 101see also acid rain

Ramsar Convention 55-6reactive adaptation 240 243recreation erosion caused by 223

225Red Sea coral reef degradation in

230-1red tides 150reefS coral 226-31rendzinas 170renewable energy 77reservoirs

channel morphology effects 180evaporation from 183-4size 128thermal poUution effects 154

resource recovery biotechnology in76

respirable suspended particulates(PMIOs) 8588 106

Index 273

rice cultivation 72rills 167-8rivers

accelerated sedimentation 182channel changes 178-82inter~basin water transfers 131-2

155-8 184pollution 145-9 150 151regulation 125-35sediment load 125 128-31 133

178 180set also discharge floods runoff

roads tree dieback alongside 46runoff

deforestation affectingurbanization affecting

Sagan River sediment in 130Sahel dust storms in 87salinization 28 182-5 201

inter-basin water transfers causing155

salt marsh erosion of 208-9sand control of 175-7sand dunes see dunessanitary landfill 192 194 196sanitization 22Saudi Arabia groundwater depletion in

159savanna 20-139-41Scarborough cliff erosion in 210sea-level rise 206-9 235

and coral reef growth 228sea urchins 231seasonal flooding 56 57seawater incursion 184secondary forest uopical 38-9sediment load effect of dams on

125 128-31 133sediment movement coasta 211-12

213sediment transport

straightened channels 178 180sedimentation accelerated 182

following dam construction 129-31seed germination effects of fire on

21-2

274 Index

seedbeds effects of fire on 21-2sewage pollution

coastal 220 227coral reefs 227

sewers 140 141shear strength 186sheet flow 167shifting cultivation 22 38-9ships ocean-going 5

accidental species introductions 66silt

dredging effects on 132effect of dams on 125 128-31

Sinai-Negev region albedo differencesin 90

Sindcanals 131salinization 183

sink-holes 189slash and burn cultivation 22 38-9slides 187slope instability 185-8smog 85smoke

effects 84from oil-well fires 88 89trends lOS

socialist economies 13soil conservation 169174

channel morphology effects 180-2soil erosion middot8

grasslands 43prevention 169 174by water 165-71 180-2201by wind 172-4201see also dust storms

soil formation 165 166soils

acidification 118and deforestation 138drainage 142-5 190and fire 22forests 165-6salinization 182-5 201and savanna development 40tundra subsidence of 190see also soil erosion

South Africamarginal land 13urban air pollution 108-9

South Downs soil erosion on170-1

South Platte River 180Soviet Union

dust storms 172urban air pollution 107

Soweto air pollution in 50 108-9Sphagnum moss 144splash erosion 167squatter settlements 50 108-9steam engine 7Stone Age megafauna extinctions

during 73-5storm surges 216-17stratospheric ozone depletion

110-14stresses drainage basin 15subsidence 143-4 189-90succession

coastal dunes 222in response to fire 24 25in secondary forest formation 38

Suez Canal animal migration along67

sulphate aerosols 85sulphur dioxide emissions 103 104

105 108and acid rain 117and forest decline 45reduction 118 120and urban building decay 200

sunshine trends 105sustainable development 14 239-44

and biodiversity conservation 60cities 50rain forest 34

sustainable environmental managementand population growth 29

swamps 54channelization effects on 131see also mangrove swamps

Swaziland gully erosion in 173synthetic organic pollutants 146-7

218

systemic global change 10 11systems 14-15

tank landscape 131tannery wastes 221technology

agricultural 5 6 7-8 10early human 3

temperate forests decline of 44-7temperature

atmospheric aerosols affecting 8485

landmiddotusc changes affecting 9092

urban areas 98-101see bD global warming

Texas Gulf coast habitat changes on72

Thames River poUution of 151thermal pollution 154-5thermokarst 189-90thunderstorms urban 99Tokyo subsidence in 189tools see technologytourism

and coastal pollution 220 221230

coral reefs threatened by 230-1ecotourism 12

Towyn (Wales) flooding at 216-17trace clements toxic water polluted by

146tractors 10170-1ttaffilt

emissions from 114 115 199urban stone decay associated with

197 199transport 12Transvaal ground subsidence in

189trees

acid rain damage 119beneficial effects 96urban areas 51-2

tropical areasdeforestation 34-5fire usc 20-1

Index 275

savanna 39-41secondary forest 38-9

tropospheric ozone 105 114

ultraviolet radiation 110uncertainty

global warming predictions 95120

in understanding environmentalimpact 14

underdrainage 142United Nations Environment

Programmedesertification data 26pollution control measures 219

urban buildingsstone decay 197-200

urban heat island 98-101urbanization 567 1248

climatic effects 98-101ecological effects 48-52hydrological effects 48 140-2

160-1 180and pollution 49 SO 52 85 99

102-9 197-200and soil erosion 167thermal pollution 154see also cities

USAacid rain 116-17coastal erosion 210 211-12coastal population 205dust bowl 87 172groundwater abstraction 160irrigation effects on rainfall 91-2waste disposal 192

Vaiont Dam disaster 185 186-7vegetation

acid rain effects on 118 119burning 10-11 20-5coastal dunes 222 225destruction through dredging 132dune stabilization through 175fire adaptation 22 33 40human domination and destruction

12 13

276 Index

and precipitation 40river banks 182river regulation affecting 135urban areas 48see Iso forests plants etc

vegetation removalclimatic effects 90-2and dune reactivation 174-5and soil erosion 165-7 172

180-2and soil salinization 184and thermokarst subsidence 190see Iso deforestation

vehicle emissions 114 115 199Venice

building decay 198 200water pollution 221

Vietnam War 13

Walesafforestation and floods 144coastaJ flooding 216-17

Walvis Bay (Namibia) dunestabilization in 176-7

war 13Washington DC urban heat island in

100 101waste

channel morphology effects 182disposal and management 12-13

191-6 201water

importance 125inter-basin transfers 131-2

155-8misdirected efforts at controlling

125soil erosion by 165-71see also rivers

water consumption 125 132 159

water pollution 145-9coastal and marine 218-21control 148 153 219 241thermal 154-5urban 49see also eutrophication

water quality land use changesaffecting 126 127

water resources policies 241water table

falling 142 143 159-60 189rising 160-1 183 184

water-spreading 161watersheds

paired 136see also dC1inage basin

waterways animal migration along67

weatheringby acid rain 118buildings 197-200and slope instability 186

weeds 66West Bay (Dorset) erosion in 211wetlands 53-7

aquacultural usc 232-4conservation 55-6 241drainage 127 142-4ecological importance 53 55 232

wilderness 19 239wind erosion 172-7wind urban 99wood

as domestic fuel 28 37

Yellowstone Park fires 23 24-5

Zimbabwe gullies in 168

Index compiled by Ann Barham

Printed in the United Kingdom byLightning Source UK Ltd Milton Keynes137029UKOOOOI B123-132P

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enironmentby Andnw Goudie and Heather Vilesp em

Indudes bibliographical rderences and indexISBN 0-631-19464-9 -ISBN 0-631-19465-7 (pbk ~Jk p~pcr)

J Naturc-Effict of human beillgs 011 I ik~ Heather Ar1 TitleG75G677 199730428-DC20 96-26798

ellgt

CONTENTSPart I

Pan IIPan IIIPan IVPart VPart VIPart VII

Introduction to the DevelopingEnvironmentallrnpactThe BiosphereThe AtmosphereThe WatersThe Land SunaceOceans Seas and CoastsConclusion

11781

123163203237

GlossaryReferencesIndex

245254264

PART I

Introduction to theDevelopingEnvironmentalImpact

1 Early DY 32 Developing Populations 33 Agricultural Revolutions 44 Urban and Industrial Revolutions 55 The Modem Scene 76 Undersunding Environmental

Transfonruuions 14Key Tenns wd ConceplS 16Points for Review 16

1 EARLy DAYS

In this book we explore the many ways inwhich humans have transformed the faceof the Earth We stan by placing th~

mnsformations into an historical contextand ~dng how they have changed throughrime

Human life probably first appeared onEarth during the early part of the lee Agesome 3 million years ago The oldesthuman remains have been found in eastshyern and southern Mrica For a very longtime the numbers ofhumans on the planetwere small and even as recently as 10000years ago the global population was probshyably only about one-thousandth of its siutoday Also for much of that time hushymans had only modest technology andlimited capacity to harness energy Thesefactors combined to keep the impact of

Developing Populations 3

humans on the environment relativdysmall Nonetheless urly humans were nottorally powerless Their stone bone andwood tool technology developed throughtime improving their efficiency as humshyers They may have caused marked changesin the numbers ofsome species of animalsand in some cases even their extinction(see pan II section 13) No less imporshytam was the deliberate use of fire (see partII section 2) a technological developmentthat may have been acquired some 14million years ago Fire may have enabledeven smaU human groups to change thepattern of vegetation over large areas

2 DEVEWPING POPULATIONS

There Ire It least three interpretationsof global population trends over the llSt3 million years (Whitmore et aI 1990)

Plate 11 The OJduvai Gorge in Tanzania is one of a group of sites in the RiftValley of East Africa where some of the earliest remains of humans and their stonetools have been found ltA S Goudie

4 Introduction

Plate 12 A grass fire in the high grasslands of Swaziland southern Africa Firewas one of the first ways in which humans transfonned their environment andwas probably used deliberately in Africa over a million years ago (A S Goudie)

The first described as the arithmeticshyexponential view sees the history ofglobalpopuJation as a two-stage phenomenonthe first stage is one ofslow growth whilethe second stage related to the industrialrevolution (sec section 4 below) displaysa staggering acceleration in growth ratesThe second view described as ltIogarithmicshylogistic sees the last million or so yearsin terms of three revolutions - the toolagricultural and industrial revolutions Inthis view humans have increased thecarrying capacity of the Earth at leastthree times There is also a third viewdescribed as arithmetic-logistic whichsees the global population history over thelast 12000 years as a set of three cyclesthe primary cycle the medieval cycleand the modernization cycle These threealternative models are presented gnphishycally in figure 11

3 AGRICULTURAL REvOLUrIONS

Until the beginning of the Holoceneabout 10000 years ago humans wereprimarily hunters and gatherers After thattime in various parts of the world inshycreasing numbers of them started to keepanimals and grow plants Domesticationcaused genetic changes in plants and anishymals as people tried to breed more usefulbetter-tasting types Domestication alsomeant that human populations could proshyduce more reliable supplies of food froma much smaller area than hunter-gatherers(table 11) This in turn created a moresolid and secure foundation for culturaladvance and allowed a great increase inpopulation density This phase of developshyment is often called the first agriculturalrevolution

As the Holocene progressed many other

Urban and Indwtrial ~olutions 5

lOllllOk 5000

pastoralism (the use of land for keepinganimals) had a profound effect on manyenvironments in many parts of the world

A further significant ~eldopmcnr inhuman cultural and technological life wasthe mining of ores and the smelting ofmetals begun around 6000 years agoMetal artefacts gave humans greater powerto alter the environment The smeltingprocess required large quantities of woodwhich caused local deforestation

4 URBAN AND INDUSfRIAL

REVOLlTfIONS

The processes of urbanization and indusshytrialization are two Olher fundamentaldevelopments that have major environmenshytal implications Even in ancient timessome cities evolved with considerable popushylations Nineveh (the Assyrian capital)may have had a population of 700000Augustan Rome may have had a populashytion of around 1 million and Carthage(on the North African coast) at its ft11 in146 BC had 700000 inhabitants Suchcities would have exercised a considerableinOuence on their environs but this influshyence was never as extensive as that of citshyies in the last few centuries The modemera especially since the late seventeenthcentury has witnessed the transformationof culture and technology through the demiddotvelopment of major indwtries (table 12)This industrial revolution like the agrishycultural revolution has reduced the spacerequired to sustain each individual and hasseen resources utilized more intensively

Part of this indwtriaJ and economictnnsformation was the development ofsuccessful ocean-going ships in the sixshyteenth and seventeenth centuries As aresult during this time countries in verydifferent parts of the wond became inshycreasingly interconnected Among otherthings this gave humans the power to

fl iJ

i i I 0

sect

j

Figure 11 Three interpretations ofglobal population trends over themillennia (a) the arithmetic-exponential(b) the kgtgarithmic-Iogistic (c) thearithmetic-logisticSource Whitmore et aI (1990) figure 21

technological developments occurred withincreasing rapidity AU of them served toincrease the power of humans to modifythe surface of the Eanh One highJy imshyportant development with rapid and earlyeffects on environment was irrigation1bis was intrrouced in the Nile Valleyand Middle East over 5000 yevs agoAt around the same time the plough was~t used disturbing the soil as neverbefore ArUmals were used increasingly [0

pull ploughs and caru to lift water andto carry produce Altogether the introducshytion of intensive cultivation and intensive

6 Introduction

Table 11 Five stages of economic development

Economic stage Dates and characteristics

Hunting-gathering and early agriculture Domestication first fully established insouth-western Asia around 7500 BeE

hunter-gatherers persisted in diminishingnumbers until today Hunter-gatherersgenerally manipulate the environmentless than later cultures and adaptclosely to environmental conditions

Riverine civilizations Great irrigation-based economies lastingfrom c4000 Be to 1st century AD inplaces such as the Nile Valley andMesopotamia Technology developed toattempt to free civilizations from someof the constraints of a dry season

Agricultural empires From 500 BC to around 1800 AD anumber of city-dominated empiresexisted often affecting large areas ofthe globe Technology (eg terracingand selective breeding) developed tohelp overcome environmental barriers toincreased production

The Atlantic-industrial era From c1800 AD to today a belt of citiesfrom Chicago to Beirut and around theAsian shores to Tokyo form aneconomic core area based primarily onfossil fuel use Societies haveincreasingly divorced themselves fromthe natural environment through airconditioning for example Thesesocieties have also had major impactson the environment

The Pacific-global era Since the 1960s there has been ashifting emphasis to the Pacific Basin asthe primary focus of the globaleconomy accompanied by globalizationof communications and the growth ofmultinational corporations

Source Adapted from Simmons (1993) pp 2-3

The Modern Scenc 7

Plate 13 A simple irrigation system in use in the drier portions of Pakistan Suchirrigation was probably introduced in the Old World drylands around 5000-6000years ago (A S Goudie)

introducc planes and animals to puts ofthe world whert they had not previouslybeen Thc steam engine was invented inthe late eighteenth ccntury and the intershynal combustion engine in the late nineshyteenth century both these innovationsmassivdy increased human need for andaccess to energy and lessened dependenceon animals wind and water

5 THE MODERN SCENE

Modern science and modern medicine havecompounded the effects of me urban andindustrial revolutions leading to accelershyating popuJation incrtasc even in nonshyindustriaJ societies Urbanization has goneon speedily and it is now recognized thatlarge cities have their own environmentalproblems and produce a multitude of

environmental effects If present trendscontinue many citics in the less dcvdopcdcountries will become unimaginably largeand crowded For instance it is projcctedthat by the year 2000 Mexico City willhave more than 30 million people shyroughly three times the present populashytion of the New York metropolitan areaCalcutta Greater Bombay Greater CairoJakarta and Seoul are each expected to bein the 15-20 million range by that timeIn all around 400 cities will have passedthe million mark by the end of me twenshytieth century and UN estimatcs indicatethat b) then over 3000 million peoplewill live in cities compared with around1400 million people in 1970

Modern science technology and indusshytry have also been applied to agricultureIn recent decades some spectacular proshygress has been made Examples include

8 Introduction

Plate 14 A limestone pavement developed on the Carboniferous limestone ofnorth-west England Although they were formed in giadaI times by gladalabrasion they may be exposed at the surface today because of soil erosionproduced by forest dearance since the Mesolithic (A S Goudie)

the use of fertilizers and the selectivebreeding of plants and animals Biotechshynology has however immense potentialto cause environmental change (see partII section 14)

We can recognize cenain trends inhuman manipulation of the environmentduring the modem era First the numberof ways in which humans are affectingthe environment is growing rapidly Forexample nearly all the powerful pesticidespost-date the Second World War The sarJK

applies to the increasing construction ofnuclear reactors to the usc of jet aircraftand to many aspectS of biotechnologySecondly environmental issues that onceaffected only particular local arus havebecome regional or rven global problems

An instance of this is the appeanncc ofsubstances such as DDT (a major pestishycide) lead and sulphates at the North andSouth Poles far removed from the indusshytrial societies that produced them Thirdlythe complexity magnitude and frequencyof impacts are probably increasing Forinstance a massive modern dam like thuu Aswan in Egypt has a very diffcrentimpact from a small Roman darn Finallya general increase in per capita consumpshytion and environmental impact is comshypounding the effects of rapidly expandingpopulations Energy resources are beingdrveloped at an ever-increasing rate givinghumans enormous power to transform theenvironment One measure of this is worldcommercial energy consumption which

The Modem Scene 9

Table 12 Energy technology and environmental impact time line

Time Global Daily Energy Technological Environmentallone population energy source discoveries impacts

use perperson(kcals)

1 million lt 10 2000-5000 Food Tool local andto 5000 million human production short-termyears BC muscle fire animal kills

andvegetationchange

5000 BC 10 million 2ltXXl- Animals Cultivation Local andto AD -1 billion 26000 agricultural building longer-term1800 crops transport natural

wind irrigation vegetationwater coal removal soil

erosionurban airpollution

AD 1800 1 billion- 50000 Fossil fuels Industry Localto 1950 4 billion electricity regional and

steam permanentmajorlandscapechanges airand waterpollutioncommon

1950 to gt4 billion 300000 Internal Industry localpresent combustion cultural regional

engine globalization globalelectricity permanentnuclear and perhapsfossil fuels irreversible

add rainglobalwarming

10 Introduction

Plate 15 The power of humans to transform the lands surface in the modern erais illustrated by the size of the giant open-cast uranium mine at Rossing NamibiaModern technology allows humans to harness energy resources as never before(A S Goudie)

trebled in size bet1een the 1950s and1980

The importance of the harnessing ofenergy can be clearly seen in the contexrof world agriculture At the beginningof the twentieth century more or lessthroughout the world farmers relied upondomestic animals to provide both pullingpower and fertilizer They were largely selfshysutlicient in energy However in manyareas the situation has now changed Fosshysil fuels are eXhnsively used to carry outsuch tasks as pumping (or in many casesmining) water propelling tractors andmanufacturing synthetic fertilizers (whichin many cases cause pollution) The worldstractor fleet has quadrupled since 1950and as much as two-thirds of the worldscropland is being ploughed and compactedby increasingly large tractors

Above all as a result ofthe huge expansionof environmental transformation it is nowpossible to talk about global environmentalchange There are two aspectsofthis (TurnerKasperson et aI 1990) systemic globalchange and cumulative global changeSystemic global change refers to changesoperating at the global scale and includesfor example global changes in climatebrought about by atmospheric pollmioneg the greenhouse effect (see part III)Cumulative global change refers to thesnowballing effect of local changes whichadd up to produce change on a worldwidescale or change which affects a significantpart of a specific global resource eg acidrain or soil erosion (sec parts III and V)The two types ofchange are closely linkedFor example the burning of vegetationcan lead to systemic global change through

The Modem Scene II

Table 13 Systemic and cumulative global environmental changes

Type of change

Systemic

Cumulative

Charaderistic

Direct impact onglobally functioningsystem

Impact throughworldwide distributionof change

Impact throughmagnitude of change(share of globalresource)

Examples

(a) Industrial and land-use emissionsof greenhouse gases

(b) Industrial and consumer emissionsof ozone-depleting gases

(c) Land cover changes in albedo

(a) Groundwater pollution anddepletion

(b) Spelties depletiongenetic alteration(biodiversity)

(a) Deforestation(b) Industrial toxic pollutants(c) Soil depletion on prime agricultural

lands

Source Turner Clark et aL (1990) table 1

processes such as carbon dioxide releaseand albedo modification and to cumulashytive global change through its impact onsoil erosion and biodiversity (table 13)

Figure 12 shows how the human imshypact on six component indicators of thebiosphere has increased over time Thisgraph is based on work by Kates et aI(1990) For each component indicatorthey defined the total net change dearlyinduced by humans to be 0 per cent for10000 years ago (before the presentBI)and 100 per cem lor 1985 They thenestimated the dates by which each commiddotponent had reached successive quartiles(that is 25 50 and 75 per cent) of itstOtal change at 1985 They believe thatabout half of the components havechanged more in the single generationsince 1950 than in the whole of humanhistory before thar date

Human activities arc now atusing envirshyonmental transformation on the localregional continental and planetary scalesThe following examples both give an indishycarion of what is currently being achieved

and provide a sample of some of rhe issueswe cover in rhis book

Large areas of tcrnperate forest havcbeen c1eartd in the past few centuries Nowfarmers and foresters art removing forestsfrom the humid tropics at Idtes of aroundII million hectares (ha) per ycar This isexposing soils to intense and erosive rainshyfall and increasing Idtes of sediment yieldby an average of six times The worldsrivers are being dammed by around 800major new structures each year transformshying downstream sediment loads Hl1gereservoirs held behind dams as high as 300mctres are generating seismic hazardsand catastrophic slope failures Some ofthe worlds largest lakes most notably theAnI SCa in the fOrmer Soviet Union arcbecoming desiccated because the watcris being taken for irrigation usc and transshyferred to other water basirn at a nearmiddotcontinental scale Fluids both water andhydrocarbons (eg oil and gas) arc beingwithdrawn from beneath cities and farmmiddotlands leading to subsidence of up to 8-9metres Recreational vehicles and trampling

12 Introduction

1700~m~I~---Itmiddot-Imiddot50--2000YUI (0)

Figure 12 Percentage change (fromassumed zero human impact at 10000BP) of selected human impacts on theenvironment

feet are damaging many popular touristareas Development on tundra areas isdisturbing the thermal equilibrium ofpermafrost leading to more and moreinstances of thermokarst Coastlines arcbeing protected and reclaimed by theusc of large engineering structures oftenwithout due thought for the possible conshysequences We art pumping at least SOOmiUion tonnes of dissolved material intorivers and oceans around the world eachyear We arc acidifying precipitation tothe extent that some of it has the pHof vinegar or stomach fluid therebyaltering rates of mineral release and rockweathering

These human impacts are having greatdirect and indirect effects on vegetationtable 14 shows the amounts of vegetation(in terms of net primary production)ustd dominated or lost by humans

We shall return to these and other issuesin subsequent sections In this book wehave chosen to focus on specific environshymental issues as they affect the biosphere(part II) atmosphere (part III) surfacewaters (part IV) land surface (part V)and oceans seas and coasts (part VI)However you will notice through all of

these sections that a range of importanthuman activities play key roles and canhave a range of different impacts on manyst(tors of the environment

Even in the modern world economyhunting and gathering activities still havean important effect on the environmentlargely through the biological impacts offishing and the shaming of game Theseactivities arc becoming increasingly largeshyscale and mechanized Agricultureaquaculshyture and other forms of fOod productionnow occupy vasr areas of the Earthssurface and have a wide variety of eirmiddotonment1 efl~cts including soil erosionnutrient depiction changes in speciesdivesiry and genetic changes to crops 2ndanimals Forestry and quarrying as extracshytive industries are creating whole newbndscapes and releasing large amountsof sediment in parts of the globe rangingfrom the humid tropics to the ArcticHeavy industries (such as oil refining andchemical manufaetwC) power generationplants (from coal-fired to nuclear) andlight and high-technology industries havemany different environmental imp2cts andcontribute to pollution of land water 2ndair on the locaI and regional scales

Transport and urbanization have pershyhaps some of the most dr2matic localimpacts on the environment They createwhole new 12ndscapcs dominated by conshycrete add to pollution and affect plantand animal distributions and the circulashytion and distribution of w2ter Tourismwhich is now a booming global industryalso has considerable impacts on the envirshyonment In recent years there has beenmuch interest in the notion of ltccotourshyism or tourism which attempts to minishymize environmental damage

One of the consequences of all thesedifferent human interactions with the enshyvironment is the production of waste Thisitself hu had major environmental effectsThere arc problems of waste disposal and

------TorTlSlriII-brN oiotnily

--- COzmun------ 1lIpab--bull bull WaIftidaIl_- _ Nrdrun

100

The Modem Scene 13

Table 14 Terrestrial net primary production of vegetation used dominated or lostthrough human activities

Category

NPP usedconsumed by humansconsumed by domestic animalswood used by humans

Total

NPP dominatedcroplandsconverted pasturestree plantationshuman-occupied landsconsumed from little-managed areasland-clearing

Total

NPP lost to human activitiesdecreased NPP of croplanddesertificationhuman-occupied areas

Total

Total NPP dominated and lost

bull 1 Pg or Petagramme bull 1 x 10 gSource Vitousek (1994)

waste management Big issues like nuclearwaste disposal have potentially long-termenvironmental implications So do lesscontentious matters such as disposing ofdomestic and industrial waste on landfillsites

Human societies do not always runsmoothly War civil strife and smaller-scaledisruptions such as vandalism and crimehave their own environment1l conseshyquences Indeed some wars au pardymotivated by disputes over environmentalresources for example over water suppliesRecent conflicts in the Arabian GulfBosnia and Mglunistan have had bothshort-term and long-term environmentalconsequences induding pollution andsoil erosion In the 19605 and 19705 the

Amount (Pg per year)-

08222452 (4 of total global NPP)

151026043

1041 (31 of total global NPPl

104526

17 (8 of total global NPP)

58 (39 of total global NPPl

Vietnam War had widely publiciud effectson the mangrove vegetation of theMekong Delta The use of defoliantchemicals there has had long-term impacuon biodiversity from which the envirshyonment is only just recovering Evenwithout war political systems can imposeadditional stress on the environment Theapartheid system in pre-I994 South Africafor example forcibly distributed popushylation and wealth in a highly unhir wayleading to huge environmental pressureson marginal land The planned socialisteconomies of the fanner Soviet Union andmany East European states appear now tohave had particularly damaging environshymental impacts And capitalist enterprisewhich now dominates the global economy

14 Introduction

has often had a tendency to plunder anddespoil the environment

These many negative environmentalimpacts have generated in response a longshyterm and growing focus on conKrvationand improving human management of meenvironment Conservation and manageshyment themselvcs have environmental imshypacts as in the creation of nature reservesthere may also be less desirable impactswhere management schemes go wrongThe ideas of sustainable development arethe most recent attempt to combine remiddotsource exploitation with conservation anda concern for the environmental futureAs our scientific understanding of how theenvironment works has advanced we havegained a better view of how serious ourhuman impacts can be On the other handwe have also learnt that there is muchreason for hope The environmental fumiddotture is not all doom and gloom as westress in part VII of this book

6 UNDERSfANDING

ENVIRONMENTAL

TRANSFORMATIONS

We have already shown in this chapter thathuman impacts on environmental processeshave had a long and complex historyand now take on many complex and intershylinked forms The environment itself is alsonot a static simple entity but has a comshyplicated history of its own We now reashylize that the environment changes naturallyover a range of different time-scales as aresponse to a number of natural forcingfactors such as the varying position ofthe Earth Iithin its orbit around the sunOn shorter time-spans we know that theenvironment can work in abrupt and chalshylenging ways producing what are callednatural hazards such as volcanic erupshytions earthquakes floods and hurricanesSo putting together human and naturalfactors influencing the environment to

explain any single environmental transforshymation can be a hugely difficult usk It isimportant to realizc that there is still a lotof scientific uncertainty and debate overthe causes and consequences of many ofthe environmental issues we look at in thisbook

Understanding the role of human activmiddotities in environmental transformations isnot a completely hopeless task howeverThere arc several useful concepts whichwe can adopt to help us untangle whatis going on First it is useful to think ofthe environment (of which of course wearc a part) as being a series of interlockedsystems These systems arc affected by awhole series of stresses (which can behuman or natural in origin) The Stressesproduce some changes in the system orresponses these arc what we sec as environmiddotmenw transformations or environmentalissues Because the systems arc interlockedstresses on one system may produce linkedeffecu on other systems Some of the sysshytems arc more able to resist stresses thanothers and so some can be suessed greadybefore they show any response Others arcmore sensitive to stresses

As an example to clarify the ideas preshysented above we could look at a drainshyage basin (or watershed as it is knownin the USA) Drainage basins arc primashyrily hydrological systems with interlinkedvegetation communities Cutting downtrees (a stress) will produce a range ofresponses soil erosion increased floodingand changes in the way water is distributed(hydrological pathways) The severity ofthese outcomes will depend on the climateand topography of the area Normally amixture of natural and human-inducedstresses will affect the environment toshygether complicating the picture One wayof understanding such multi-causal situashytions is to identify different types ofstreSSeSor causal factors A uscful frameworkwhich has blaquon used in various ways inthe foUowing sections of this book is to

split causal faCtors into three typc=S that ispredisposing inciting and contributingfactors Pndisposing factors are those feashyturc=s of the natural or human environshyment which make a system vulnerable tosuess inciting factors are thosc= stressesthat trigger otT a change in the systemand conrributiJg factors are the whokrange of additional strc=sses which makethe rc=sponse more noticeable and acuteLct us apply this frtmc=work to the case ofa drainage basin The predisposing factorswhich may make it vulnerable to changefoUowing tree-cutting would lx the toshypography and climate and pcrhaps alsopast forest management pnctices Theinciting factor would lx the tete-euningitself The contributing factors could bethe health of the trees the sc=ason whenthe trees were felled the weather at thetime and over a longer time-span whatvegetation grows in place of the trees

FURTHER READING

Environmental Transformations IS

The concepts of stressc=s raponses anddifferent types of causal poundactors are veryuseful in trying to understand how humiddotmans are influencing thdr environmentSuch understanding is vital in any attemptsto solve or manage the resultant environshymental problems However to arrive atsolutions it is also necessary to have adeeper understanding of the human socishyeties involed in such environmental isshysuc=s as many of our subsequent examplesillustrate For example just knowing howtree-cutting can produce soil erosion andhydrological changes within a drainagebasin does not mean that we can solve theproblem We need also to know why peoshyple arc cutting down the trees Before wecan effect any great changes we need moreunderstanding of the economic conditionstechnological capability cultural organizashytion and political systems of the peopleinvolved

Freedman B 1995 Environmenral Ecowgy 2nd edn San Diego Academic Prc=ssAn enormously impressive and wide-ranging study with a strong ecological emphasis

Mannion A M 1995 Agriculture and Enpironmental Change London WikyA new and comprehensive study of the important rok that agriculture plays in landtransformation

Meyer W B 1996 Human Impact on the Earth Cambridge Cambridge UniversityPressA good point of entry to the literature that brims over with thought-provoking epigrams

Middleton N J 1995 The Gwbal Quino London EdWdrd ArnoldAn introductory text by a geographer which is wdl iIIustrated and clearly wrinen

Ponting c 1991 A Gnen History of the World London PenguinAn engaging and informative treatment of how humans have transformed the earththrough time

Simmons I G 1996 Changing the FRee of the EArth Cultl4re Environment andHistory 2nd edn Oxford BlackwellA characteristiCally amusing and perceptive review of many faceu of the tole ofhumansin transforming the earth from an essentially historical perspective

16 Introduction

KEy TERMS AND CONCEPTS

agricultural revolutionbiosphereglobal environmental changeHolocenehunter-gatherer

POINTS FOR REVIEW

industrial revolutionpredisposing inciting and contributing

factorsstresses and responsessystems

How much environmental change was achieved in prehistoric times and how much inthe last three centuries

To what extent are environmental changes the result of both natural and humanshyinduced stresses

What do you understand by the phrases global environmental change andsustainability

PART II

The Biosphere1 Introduction 19

2 Fire 20bull The YeDowsrone fires of 1988 24

3 Desertifiallion 26bull Desertification in north centr1l China 30

4 Oeforestuion 32bull Managing tropical rain forest in Cameroon 36

5 Tropical Secondary Forest Fonnacon 386 Grasslands and Heathlands The Human Role 39

bull Recent human impacts on subalpine grasslandand heathland in Victoria Australia 43

7 Temperate Forests under Stress 44bull Forest decline in Bavaria Germany 47

8 Urban Ecology 48bull Chicagos dunging vegetation 51

9 Wetlands The Kidneys ofme undsclpe 53bull Wetlands management in the Niger

Inland Delt 5710 Biodivmity and Extinctions 58

bull Pandas plants and parks conservingbiodiversity in China 62

The Biosphere11 Introductions Invasions and Explosions 64

bull Alien plant species invading KakaduNational Park Australia 68

12 Habitat Loss and Fragmentation 69bull Texas Gulfcoast habitat chages and the

Lesser Snow Goose 7213 Extinctions in the Past 7314 Biotechnology Genetic Engineering

and the Environment 7615 Conclusions 77

Key Tenns and Concepts 78Points for Review 79

1 INTRODUCTION

In this part of the book we look at someof the main ways in which humans havemodified the biosphere and the conseshyquenccs of these impacts

Humans have changed the biosphere invery many ways with wide-ranging andlong-lasting effects As soon as peoplediscovered how to use fire at a very earlystage in human development they obshytained tremendous power to modify thevegetalion cover of the Earths surfaceAlso during the Stone Age humans gradushyally developed the technology to enablethem to bccome ever more effecrive huntshyers Early people may have contributed tothe extinction ofsome of the worlds greatmammals Since the Mesolithic as passhytonlism and agriculture have becomewidespread modification of habitat hascontinued rapidly Humans also gainedthe ability to manipulate the genetic comshyposition of plants and animals - a majorpart of the process generally called domcs-

Introduction 19

ticarion This has been one of the mostdirect ways that humans have changed thebiosphere

As the human population of the Earthhas expanded in numbers and spread tomore and more parts of thc globe Ccrmore environments havc been modifiedThese include tundra anas deserts forshyests and wetlands The total area ofsurviving natural habitat has stcadil dimiddotminished and wilderness arcas are 110W

relatively few Figure 111 shows an attemptto mark out the areas of the planet thatcan still bc defined as wilderness Howshyever no part of the Earths surtacc call beconsidered entirely free from the imprintof human activities Air pollution and clishymatic changes causcd by human action arcevident even at the poles As it has beshycome easier for humans to move from oneplace to another so plants and animalshave been introduced to many new areasSometimcs the numbers ofthcsc= newcomerspecies have exploded damaging the comshymunity struetu~ of existing plants andanimals

bull

bullbulleJC1)-

~ )

Figure 111 Global wilderness remaining in the 1980sSource McCloskey and Spalding (1989)

20 The Biosphere

Table 111 Biomass burning in the tropical regions

Region Forest Savanna Fuel Agricultural Regional Regionalwood waste total total

(Tg dmlyr) (Tg dmlyr) (Tg dmlyr) (Tg dmlyr) (Tg dmlyr) (Tg Oyr)

America 590 770 170 200 1730 780Africa 390 2430 240 160 3210 1450Asia 280 70 850 990 2190 980Oceania - 420 8 17 450 200

Total tropics 1260 3690 1260 1360 7580 3410

Tg dmlyr = teragrammes of dry matter per yearTg elyr = teragrammes of carbon per yearSource Andreae (1991) table 13

2 FIRE

Fire is one of the earliest means that hushymans used to modifY the natural environshyment It is also one of the most powerfulFires do of course occur naturally andhave done so during the entire history ofme Earth For example they arc causedby volcanic eruptions by spontaneouscombustion oforganic materials by sparksfrom falling boulders and above all bylightning which on average strikes me landsurface of the globe 100000 times eachday However in some environments megreat majority of fires arc now caused byhumans either deliberately or accidentally

There arc many good reasons why hushymans from our early Stone Age ancestorsonwards have found fire useful

bull to clear forest for agriculturebull to improve the quality of grazing for

game or domestic animalsbull to deprive game of cover or to drive

them from coverbull to kHi or drive away predatory ani-

mals insects and other pestsbull to repcl or attack human enemiesbull to make travel quicker and easierbull to provide light and heatbull to enable them to cook

bull to transmit messages by smoke signsbull to break up stone for making tools or

pottery smelting ores and hardeningspears or arrowheads

bull to make charcoalbull to protect settlements or camps from

larger fires by controlled bumingbull to provide spectacle and comfort

Fire has been central to the life of manygroups ofhunter-gatherers pastoralists andfarmers (including shifting cultivators inthe tropics) It was much used by peoplesas different from one another as the Aborishyginals of Australia the cattle-keepers ofAfrica the original inhabitants of TIerradel Fuego (the land of fire) in the farsouth ofSouth America and the Polynesianinhabitants of New Zealand It is still muchused especially in the tropics and aboveall in Africa Biomass burning appears tobe especially significant in the tropicalenvironments of Africa in comparisonwith other tropical areas (table 111) Themain reason for this is the great extentof savanna which is subjected to regularburning As much as 75 per cent of Afrishycan savanna areas may be burned each year(Andreae 1991) This is probably an anshycient phenomenon in the African landscapewhich occurred long before people arrived

on the scene Nevenhelcss humans havegready increaKd the role of fire in thecontinent where they may have uKd it forover 14 million years (Gowlen et al 1981)

Naturally occurring fires break out withvarying frequency in different global en~

vironments Over a century may passbetween one firc and the next in tundraenvironments and ecosystems dominatedby thc spruce uec In areJs ofsavanna andMcditerranean shrubland on the otherhand the interval may be only five to

fifteen years and in semi-arid grasslandsless than five years

Fira can extend over huge areas In1963 in Parana Brazil no less than 2million hectares of forest were consumedin JUSt three weeks while the fire of 1987in China and the neighbouring SovietUnion destroyed around 5 million hecshytares over the same length of time

Fires can also cause some very highground surnce ttmperarures up to 800Cor higher The temperature reached deshypends very much on the size duration andintensity of the fire Some fires are relashytivdy quick and cool-burning and onlydestroy ground vegetation Other firessuch as crown fires affect whole forestsup to the Icvd of tree crowns and gcncrshyate very high temperatures In generalforest fires arc hotter than grassland firesIt is significant for forest management thatwhcre fires occur very often they do notattain the highest temperatures becausethcre is not enough flammable material tokeep them going However humans oftendeliberately prevent fires as part of normalpolicy in forest areas When this is donclargc quantities of flammable materialsaccumulate so that when a fire docs breuOut it is of the hot crown type that canbe ecologically disastrous There is nowmuch debate therefore about the wisdomof suppressing the fircs that in many forshyests would occur quite regularly under soshycalled natural conditions

fire 21

Recent studies have indicated that rigidpolicies of protecting habitats against firehave often had undesirable results Conseshyquendy many foresters now suess the needfor prescribed burning or environmenshytal restoration burning For example inthe coniferous forests of the middle andupper levds of the Sierra Nevada mounshytains of California protection from firesince 1890 has made the srands densershadier and less park-like and Slquoiaseedlings hae decreased in llumber as aresuh Ukeise at lower leels the charshyacter of [he semi-arid shrubland calledchaparrll has changed The lgetationhas bt-come denser the amount of flamshymable material has increased and fireshysensitive species have encroached Thevegetation has become less diverse witholder trees predominating instead of amosaic of trees at different stages ofgrowth In the Kruger National Park inSouth Africa fires have become less freshyqucnt since the game reserve was estabshylished when local hunters and farmerswere moved out AJ a rcsult bush hasencroached on areas that werc formerlygrassland and the carrying capacity forgrazing animals has declined Controlledburning has been reinstituted as a necesshysary element of game management

Fire has many positive ecological conseshyquences Fire may assist in seed germinashytion For example many investigatorshave reported the abundant germinationof dormant seeds on recently burnedchaparral in areas like California with aMediterranean climate and it Kerns thatsome Keds of chaparral species requirescarification by fire to germinate effecshytively Fire alters seedbeds and even thoseKeds not requiring scarification maygerminate better after a fire because fireremoves competing seeds litter and somesubstances in the soils which are toxic toplants If substantial amounts of litter andhumus arc removed large areas of rich

22 The Biosphere

ash bare soil or thin humus may becreated Some trees such as the Douglasfir and the giant sequoia benefit fromsuch seedbeds Fire sometimes triggers therelease of seeds from cones (as with Jackpine Pinus banlujana) and seems to stimushylate the vegetative reproduction of manywoody and herbaceous species Fire cancontrol forest insects parasites and fungi- a process termed sanitization - andseems to stimulate the flowering and fruitshying of many shrubs and herbs It alsoappears to modifY the physiochemical enshyvironment of plants with mineral elementsbeing released both as ash and throughfaster decomposition of organic layersAbove all areas subject [0 fire often showgreater species diversity which tends tofavour the Hability of the habitat over thelong term

Fire is also crucial to an unders[andingof some major biome types and manybiota have become adapted to it Forexample many savanna trees are fireshyresistant The same applies to the shrubvegetation (mafuis) of the Mediterraneanlands which contains certain species (egQuercus io and Quercus cocciera) whichthrive after burning by sending up a seriesof suckers from ground level Mid-latitudegrasslands (eg the prairies of NorthAmerica) were once thought to have deshyveloped in response to drought conditionsduring much of the year Now howeversome have argued that this is not necesshysarily the case and that in the absence offire trees could become dominant Thefollowing reasons are given to support thissuggestion

bull planted groves and protected trees seemable to flourish

bull some woodland species notably junishypers are remarkably drought-resistant

bull trees grow along escarpments and indeep valleys where moisture is conshycentrated at seeps and in shaded areas

and where fire is least effective theeffects of fire are greatest on flat plainswhere there are high wind speeds andno interruptions to the course of thefire

bull where fires have been restricted woodshyland has spread into grassland

Fire rapidly alters the amount formand distribution of plant nutrients in ecoshysystems and has been used deliberatelyto change the properties of the soil Boththe release of nutrients by fire and thevalue of ash have long been recognizednotably by those involved in shifting culshytivation based on slash-and-burn techshyniques However once land has beencultivated the loss of nutrients by lcachshying and erosion is very rapid This is whythe shifting cultivators have to move onto new plots after only a few years Firequickly releases some nutrients from thesoil in a form that plants can absorbThe normal biological decay of plant reshymains releases nutrients more slowly Theamounts of phosphorus (P) magnesium(Mg) potassium (K) and calcium (Ca)released by burning forest and scrubvegetation are high in relation to both thetotal and the available quantities of theseelements in soils

In forests burning often causes the pHvalue of the soil to rise by three units ormore creating alkaline conditions whereformerly there was acidity Burning alsoleads to some direct loss of nutrients fromthe soil by volatilization and by causingash to rise up into the air or by loss ofashto water erosion or wind deflation Wherefire removes trees soil temperatures inshycrease because of the absence of shade sothat humus is often lost at a faster ratethan it is formed

Concern is now being expressed aboutthe role of biomass burning in alteringatmospheric chemistry and contributingto the greenhouse effect by adding carbon

dioxid( (COl) to m( aunosph(r( (Levin(1991) About 40 per c(nt of m( worldsannual production ofCOJ may r(Sult from

FURTHER READING

Fire 23

th( destruction of biomass by fir( Firesalso produc( (missions ofsmok~ and nitricoxide

Crutzen P and Goldammer G 1993 Fire in the Environment Chicheu(rWileyThis book considers some of th( potential global dfects of fir~s including effects onatmospheric chemistry

Kozlowski T T and Ahlgren C C (eds) 1974 Fire 1 aosyrtems New YortAcademic PressAlthough relatively old this provides a very useful picture of the effects of fir~ on faunaand flora

Pyn~ S 1982 Fire in America A Cwlrural HiJrory of Wildnd and Rwral FinPrinceton Princ(ton Univ(rsity PressA massive and scholarly survey of how fires hav( been fundamental to und(rstandingmuch of the veg(tation of America

Plate 111 Forest burnt in the Yellowstone fires of 1988 (EPLRob Franklin)

u INO

I MONTANA OAKOTA

f-tN I

~i----IDAHO f r IIMWIJe1J SOVln

I OAKOTA-- I---- WYOMING ---___

L _ NtRIlASKAT-----___ LlJrAll I --I COLORAOO J

I 0 kl 2laquolI ~

24 The~iosphert

The Yellowstone fires of 1988

In the summer of 1988 wideshyspread fires ravaged the Yellowshystone National Park in theAmerican West Forest fires beshygan in June and did not die outcompletdy until the onset ofwinter in November Somcwherebetlcen 290000 alld 570000hectares burned in by tar theworst fire sinc Yellowstone wasestablished as the worlds firstnational park in the 1870s

Was this inferno the result of apolicy of fire suppression Without suh a policy the torest would burn at intershyvals of 10 or 20 years because of lightning strikes Could it be that the suppresshysion of fires over long periods of say 100 years or more allegedly to protect andpreserve the lorest led to the build-up of abnormal amounts of combustible fuelin the torm of trees and shrubs in the understory~ Should a programme ofprescribed burning be carried out to reduce the amount of available fueH

Fire suppression policies at Yellowstone did indeed lead to a critical build-upin flammable material However other factors must also be examined in explainingthe severity of the fire One of these was the fact that the last comparable firehad been in the 1700s so that the Yellowstone forests had had nearly 300 yearsin which to become increasingly flammable In other words because of the wayvegetation develops through time (a process called succession) very large firesmay occur every 200-300 years as part of the natural order of things (figureII2) Another crucial factor was that weather conditions in the summer of 1988were abnormally dry bringing a great danger of fire

Rommc and Despain (1989 p 28) remark in conclusion to their study of theYellowstone fires

It seems that unusually dry hot and windy weather conditions in July andAugust of 1988 coincided with multiple ignitions in a forest that was at itsmost flammable stage of succession Yet it is unlikely that past suppressionefforts were a major factor in exacerbating the Yellowstone fire If fires occurnaturally at intervals ranging from 200 (0 400 years then 30 or 40 years ofeffective suppression is simply not enough for excessive quantities of fuel tobuild up Major attempts at suppression in Yellowstone forests may have merelydelayed the inevi(able

Further reading

Remme W H and Despain D G 1989 The Yellowstone fires ScientifteAmerican 261 21-9

Fire 25

The old fomt

~i t~rfti (

---

Figure 112 EcotogicaJ succession in response to fire in Yellowstone NationalParle USASource After Romme and Despain (1989) pp 24-5

26 The Biosphere

3 DESERTIFICATION

The term desertification was first used bythe French forester Aubreville in 1949 buthe never formally defined it Since thenover 100 definitions have been publishedThe United Nations Environment Proshygramme (UNEP) has recently defineddesertification as land degradation in aridsemimiddotarid and dry sub-humid areas resultshying mainly from adverse human impacts(Tolba and EI-Kholy 1992 p 134) Othershowever suggest that climatic change mayalso play an important role

There are fundamental problems relatshying to how extensive the problem ofdesertification is how quickly it is takingplace and what the main causes are UNEP(Tolba and EI-Kholy 1992 p 134) hasno doubts about the significance of theproblem Desertification is the main envirshyonmental problem of arid lands whichoccupy more than 40 per cent of the totalglobal land area At present desertificationthreatens about 36 billion hectares shy70 of potentially productive drylands ornearly one-quarter of the total land areaof the world These figures exclude naturalhyper-arid deserts About one sixth of theworlds population is affected

UNEP recognizes the following seriesof symptoms of desertification that relateto a fall in the biological and economicproductivity and therefore value of a pieceof land

bull reductlon of crop yields (or completefailure of crops) in irrigated or rain-fedfarmland

bull reduction of biomass produced byrangeland and consequent depletionof feed material available to livestock

bull reduction of available wood biomassand consequent increase in the disshytances travelled to obtain fuelwood

bull reduction of available water due to

decreases in river flow or groundwaterresources

bull encroachment of sand bodies (dunessheets) that may overwhelm producshytive land settlements or infrastructures

bull social disruption due to deteriorationof life support systems and the associshyated need for outside help (relief aid)or for havens elsewhere producingenvironmental refugees

It is however by no means clear howextensive desertification is or how fast it isproceeding In a recent book called Desertshyification Exploding the Myth Thomas andMiddleton (1994) have discussed UNEPsviews on the amount of land that isdesertified They state

The bases for such data are at bestinaccurate and at worst centered onnothing better than guesswork Theadvancing desert concept may have beenuseful as a publicity tool but it is notone that represents the real nature ofdesertification processes (Thomas andMiddleton 1994 p 160)

There are indeed relatively few reliablestudies of the rate of desert advance orencroachment Lamprey (1975) attemptedto measure the shift of vegetation zonesin the Sudan and concluded that the Saharahad advanced by 90-100 km between1958 and 1975 an average rate of about55 km per year However on the basisof data amassed by remote sensors andground observation Helldcn (1984) foundlittle evidence that this had in fact hapshypened One problem is that biomass proshyduction may vary very substantially fromyear to year This has been revealed bysatellite observations of green biomassproduction levels on the southern side ofthe Sahara

The way in which desert-like conditionsspread is also [he subject of some controshyversy Contrary to popular rumour this

D~rtification 27

ADVANCE Of DtSmTflpoundATlOS OFDfS(RT-UKf CO~I)Jl1OIiS

lniptioa

Figure 113 The causes and development of desertificationSource Kemp (1994) figure 312

does not happen over a broad front likea wave overwhelming a beach Rather itis like a rash tending to appear in localpatches around settlements This distincshytion is important because it influences pershyceptions of how to tickle lhe problem

Another point made by Thomas andMiddleton (1994 p 160) is that drylandsmay be less fragile than is often thought

We should bear this controVersy in mindas we consider some of the undoubtedpressures that are being placed on aridenvironments (figure 113) It is gefKrallyagreed that the massive increase in humanpopulation numbers during the twentieth

century has been of fundamental imporshytance This demographic explosion has hadfour key consequences for dryland areasovercultivation overgrazing deforestationand salinization of irrigation systems

There arc two aspects ofovercuhivationmore intensive usc of land already undercultivation and the inuoduetion of agrishyculture into areas where conditions arc notsuitable to it primarily because of theiraridity or because their soils are fragile andinfertile Crops are now grown in areas ofthe Sahel of West Africa where annualrainhll is as low as 250 mm and in partsof the Near East and Nonh Africa which

28 The Biosph~re

SOUTIlERNKORDOFAN

bull 00~

Figure 114 The expanding wood andcharcoal exploitation zone south ofKhartoum SudanSource From Johnson and Lewis (1995)figure 62

have only 150 mm of rainfall a year Someof these areas hav~ friable soils d~vdopcdon lat~ Pleistocme dun~ fidds This makesth~m highly prone to water ~rosion andwind reactivation

Ov~rgrazing is rclat~d to ov~rcultivashy

tion for in many ar~as increasing numbersof humans r~quire incrusing numbers ofdomestic animals Larger tr~e-ralging stockherds r~duc~ th~ amount of pasturdandavailable and mean that the pastures thatremain have to support even mor~ animalsTh~ carrying capacity of the land may thenbe exceeded Thcr~ may also be conflictsbetw~~n pastoralists and cultivators Asthe fronti~r of cultivation is pushed outshywards into ever mor~ marginal ar~as itencroaches more and mort on th~ grazshying lands of the pastoralists In this waynomadic pastoralists many of whom haddeveloped sophisticated ways of keepingmarginal areas in productive use have oftenKen their traditional systems disintegrateThis has disrupted the equilibrium betweenpeople and land For nampie the nomads

Kasonal or annual migrations may havebc~n resuict~d by delibcrat~ policies ofscd~ntarization (making peopl~ setde inone place) imposed by central governshyments The same restrictive eff~ct resuJtsfrom th~ est2blishm~nt of national boundshyaries wh~re non~ previously existed

Another cause of overgrning has beenthe installation of boreholes and the digshyging out of wat~rholes These have mademor~ water available for domestic animalswhich thus rapidly increase in number Thisin turn leads to overgrazing Vegetationin ~fTect r~places water as the main factorlimiting stock numbers

The third human cause ofdesertificationis d~forestation and the removal of woodymaterial Many pwpl~ depend on woodfor domestic uses (cooking heating brickmanufacture ~tc) and th~ ccUection ofwood for charcoal and firewood is anespecially serious probl~m in the vicinityof urban c~ntres This is illustrated forKhartoum in Sudan in figure 114Th~ fourth prim~ cause ofdesertification

is salinization This kiUs plants destroysth~ soil struetur~ and reduces plant growthSalinization oft~n occurs where irrigationis introduc~d without making proper proshyvision for drainag~ It can howev~r alsobe an unwant~d consequ~nce of v~getamiddot

tion cl~arance Th~ r~moval of plantsr~duc~s the amount of moistur~ lost fromthe soil as a result of int~rccption of rainshyfall by leav~s and evapotranspiration Asa result groundwater levels rise and salin~

water is allowed to seep into lowmiddot lyingareas like valley bottoms This is a seriouscause of salinization both in the prairies ofNorth Am~rica and in the wheat belt ofW~st~rn Australia It is so important thatwe tr~at it in a separate section (part Ysection 5 below)

As we saw ~arli~r som~ obKrv~rs hav~

suggested that a naturaJ d~terioration inth~ climate may contribut~ to the damshyage don~ to drytand and the spread of

desen-like conditions When we examinerainfall data for recent deades we see thatfor some arid areas there is relatively clearevidence fur a downward trend while inother areas rainfall appears to be stable orto be increasing A downward trend hasbeen established for the Sudan and Sahelzones of Mrica This has had a range ofconsequences including a subslantial risein dust-storm activity and a severe reducshytion in thc area and watcr volumc of LakcChad By COntrast the latest analyscs ofsummer monsoon rainfall for the RajasthanDescrt in India show a modest upwardtrend between 1901 and 1982 Data fornorth-cast Brazil much of Australia andCalifornia and Arizona in the USA showno dear trend in either direction

Attempts to reduce damage to drylandcan be dividcd into twO types (1) technoshylogical methods and (2) fundamentalchanges in societies economies and polishytics For exampic a nnge of technologicalsolutions is available to control blowingsand and mobile dunes (see part V secshytion 3) It is much more difficult howshyever to make changes in the humanconditions that are the real rOOt causes ofthe problcm Population growth povertypolitical instability poor planning theattitudes of urban clites and the prevenshytion of traditional nomadic migration areamong the long-term basic issues thatneed to be addressed

FURTHER READING

Desertification 29

Land degradation is not however aninevitable result of rapidly growing humanpopulations Excellent proof of this isprovided by TifTen et als (1994) study ofthe semi-arid Machakos District in KenyaAround sixty years ago this area hadsevere fumine problems and was sufferingfrom sevcTe land degradation and soil eroshysion Photographs from the 1930s show agullied and impoverished landscape Sincethat time the population of the districthas increased more than fivefold but theenvironmcnt is now in a vcry much bcltcrcondition than it was then Slope terracshying has reduced the extent and rltc ofsoilerosion and gully formation A fuclwoodcrisis has been averted by planting a largenumba of farmed and protected trees Inaddition agricultural output has increasedTiffen e( al argue that high rates of popushylarion growth can be combined with susshytainable environmental management InMachakos District the local Akamba peoshyple have proved very adaptable Labouris plentiful and they have invested bothlabour and capital in land improvementand development They have added to theiragricultural incomes by doing much morenon-furm work and the huge growth inthe output of non-subsistence prodUCTS hasled to a development of jobs and skillsin marketing and processing In shorthumans can manage the landscape to goodeffect even when their numbers increase

Goudie A S (ed) 1990 Techniques for Desert Rulmarion Chichester WileyThis edited work looks at some of the solutions that arc available for dealing with theproblems of d~rt environments

Graingtt A) 1990 TJIt TbrtRuning DtJnt Controlling DesertifURtjon LondonEanhscanA very readable and wide-rIDging review of desertification

Middleton N J 1991 DeserrifitlltU1fl Oxford Oxford University PressA weU-illustrated simple introduction designed for usc in secondary eduation

30 The Bi06phere

Desertification in north central China

--

OIlNA

~

WuboII

Deserts and desertified lands coversome 149 million sq km of Chinaamounting to approximately 155per cent of the total land area of thecountry There are 12 named desertswithin China and it is estimated that 35W

various human and natural forces are ri-J------~

combining to produce desertificationof some 1560 sq km per yeararound these deserts (see table 112)Three main types of desertificationarc found in China the spread ofdesert-like conditions on sandy steppe reactivation of vegetated dunes (sandylands) and encroachment of mobile dunes on to settlements and farmland Studshyies within China suggest that such desertification is a blistering process ie thatit occurs in blister-like localized patches of rangeland away from the desert marginThese blisters then gradually grow and coalesce to produce large patches ofdescrtified land According to Fullen and Mitchell (1994) Chinese desertification

Plate 112 Encroaching sand dunes on the edge of the Gobi DesertDunghuang China The dunes are invading fields and many methods arebeing used to try to stabilize them (TripJ Batten)

Daertification 31

Table 112 Types causes and extent of desertlfted lands In China

Causes Area affected(sq km)

Overcultivation on steppe 44700Overgrazing on steppe 49900Overcollection of fuetwood 56000Misuse of water resources 14700Encroachment of dunes 9400

Source Adapted from Fullen and Mitchell (1994)

of totaldesertified land

252833188355

is mainly a result of land mismanagement encouraged by climatic factors whichproduce droughts and encourage sand movements

The severity of desertification and land degradation in China has prompted theInstitute of [kscrt Research of Academia Sinica (IDRAS) to set up research intocombating desertification IDRAS has nine research stations in desertified areasat which various reclamation techniques are practised At the Shapotou ResearchStation in Ningxia Autonomous ~gion established in 1957 to discover methodsof protecting a major railway line from sand movements the following techshyniques have been used

bull planting windbreaks of pines poplars and willows parallel to the railway linebull levelling dunes with bulldozersbull installing drip irrigation systems to aid topsoil development on levdled dune

sandsbull constructing straw checkerboards to stabilize surfaces and (ncourag( plants to

grow on shifting dunes to help stabilize them this produces an artificialecosystem on the dllOes increasing vegetltioll cover from less than 5 per cenl10 between 30 pc=r cent and 50 per cent and stopping dune movement

Irrigation land enclosure and chemical treatments arc also being lIs(d in this ar(ato help turn descrtified lands into productive rangdands According to r(c(ntstudies such reclamation efforts must be maintained and monitof(d over at kastsix y(ars b1=forc significant improv(ments can be seen

Further reading

Fullen M A and Mitchell D 1994 Desertification and reclamation in northcentrl1 China Ambjo 23 131-5

32 The Biosphere

4 DEFORESTATION

Clearing middotforests is probably the mostobvious way in which humans have transshyformed the face of the Earth It was theprime concern of George Perkins Marshwhen he wrote his pioneering book callshying for the conservation of nature Manatld Nature in 1864 (see part IV section3) Forests provide wood for construcshytion for shelter and for making toolsThey are also a source of fuel and whencleared provide land for fOCK productionFor all these reasons they have been usedby humans sometimes to the point ofdestruction

Forests however are more than aneconomic resource They play severnl keyecological roles They arc repositories ofbiodiversity (see section 10 below) theymay affect regional and local climates andair quality they playa major role in thehydrological cycle they influence soil qualshyity and rates of soil formation and preshyvent or slow down soil erosion

We do not have a dear view of how fastdeforestation is taking place This is partlybecause we have no record on a globalscale of how much woodland there is toshyday or how much there was in the pastIt is also because there are disagreementsabout the precise meaning of the worddeforestation For example shifting culshytivators and loggers in the tropics oftenleave a certain proportion of forest rnesstanding At what point does the proshyportion of trees left standing permit oneto say that deforestation has taken placdAlso in some coumries (eg India) scrubis included as forest while in others it isnot

What we do know is that deforestationhas been going on for a very long timePollen analysis shows that it started inprehistoric times in the Mesolithic (around9000 years ago) and Neolithic (around5000 years ago) urge traCts of Britain

had been deforested before the Romansarrived in the islands in the first centuryBC Classical writers refer to the effectsof fire cutting and the destructive nibbleof goats in Mediterranean lands ThePhoenicians were exporting cedars fromLebanon to the Pharoahs and to Mesopomiddottamia as early as 4600 years ago A greatwave of deforestation occurred in westernand central Europe in medieval times Asthe European empires established themshyselves from the sixteenth and seventeenthcenturies onwards the activities of tradersand colonists caused forests to contract inNorth America Australia New Zealandand South Africa especially in the nineshyteenth century Temperate North Americawhich was wooded from the Atlantic coastas far west as the Mississippi River whenthe first Europeans arrived lost morewoodland in the following 200 years thanEurope had in the previous 2000 At thepresent time the humid tropics arc undershygoing particularly rapid deforestationSome areas are under particularly seriousthreat including South-East Asia WestMrica Central America Madagascar andeastern Amazonia (figure II5)

The effects of deforestation can be seenespecially vividly in the Mediterraneanlands of the Old World As Ponting (1991p 75) puts it

Modern visitors regard the landscapeof olive trees vines low bushes andstrongly scented herbs as one of themain attractions of the region It ishowever the result of massive environshymental degradation brought about notby the creation of an artificial systemsuch as irrigation but by the relentlesspressure of longmiddotterm settlement andgrowing population The natural vegshyetation of the Mediterranean area wasa mixed evergreen and deciduous forshyest of oaks beech pines and cedarsThis forest was cleared bit by bit fora variety of reasons - to provide land

Deforestation 33

Figure 115 Estimated annual forest change rates 1981-1990Source World Resources Institute (1994) figure 71

for agriculture fuel for cooking andheating and construction materials forhouses and ships

Other processes linked to humans inshycluding grazing and fire have preventedforest from returning over wide areas Inplace of forcst a kind of vegetation calledmalfuis has become widesprcad This conshysists of a stand of xerophilous evergrecnbushes and shrubs whose foliage is thickand whose trunks arc normally obscuredby low-level branches It includes suchplants as holly oak (~ercu iJex) kermesoak (QuercllS coccim) tree heath (Ericaarbona) broom heath (Erica coparill) andstrawberry trees (Arbutus unedo) There isconsidenble evidence that malfuu vegetashytion is in part adapted to and in part aresponse to fire One efTeet of fire is toreduce the numbers of standard trees andto favour species which after burningsend up suckttS from ground level BothQJlercUI ita and Q1Iercus cocciera seemto respond to fire in this way A numberof species (for example Cistus albidllS

Erica arbona Pinu hlllepenJis) seem to

be encouraged by fire This may bc bccallS(it suppresses competing plants or perhapsbecause a short burst of heat encouragesgermination We have already noted thishappening in the chaparral of the southshywc=st USA an environment similar tomaluis (sce section 2 above)

Sinee premiddot agricultural times approxishymately one-fifth of the worlds forests havebeen lost The highest losses (about a thirdof the toul) have been in tcmperatc areasHowever deforestation is nO( an unstoppshyable or irreversible proceSS For examplea rebirth of forest has taken place in theUSA since the 19305 and 19405 Manyforests in developed countric=s are sJowlybut steadily expanding as marginal agrimiddotcultural land is abandoned This is hapshypening both ~causc of replanting schemesand because of fire suppression and conshytrol (see section 2 above) Also in somecases the extent and consequences ofdeforestation may have ~en exaggeratedA classic example of this is provided bythe mountains of parts of Nepal It was

34 The Biosphere

generally believed that rapid deforestationand changes in land use here had contrishybuted to higher flood runoffs floods soilerosion and increases in river sedimentloads The effects were thought to extendas far as the Ganges Delta in BangladeshA detailed study by Ives and Messerli(1989) however has cast doubt on thisargument by showing that little reductionin forest cover has taken place in theMiddle Mountains of Nepal since the1930

Many of the phenomena noted inNepal - flood runoffs soil erosion etc shymay be natural and inevitable consequencesof the presence of steep mountains rapiduplift by tectonic forces and monsoonalstorms Nonetheless the loss of moist rainforests in some of the worlds humid tropishycal regions is a very major concern Theconsequences are many and serious (tableII3) The causes are also diverse and inshyclude encroaching cultivation and pastorshyalism (including cattle ranching) miningand hydroelectric schemes as well as logshyging operations themselves

Views vary as to the present ratc of rainshyforest removal Recent FAO estimates(Lanly et aI 1991) put the total annualdeforestation in 1990 for 62 countries(representing some 78 per cem of thetropical forest area of the world) at 168million henares This figure is significandyhigher than the one obtained for thesesame countries for the period 1976-80(92 million hectares per year) Myers(1992) suggests that there has been an 89per cent increase in the tropical deforestashytion rate during the 1980s This contrastswith an FAQ estimate of a 59 per centincrease Myers believes that the annualrate of loss in 1991 amounted to about2 per cent of the total forest expanse

Plainly therefore rain forests whichMyers (1990) describes as these mostexuberant expressions of nature are underthreat A very significant proportion of

them will disappear in the next few decshyades unless some form of action is takento prevent this

Possible solutions to the tropical deforesshytation problem are as follows

bull research training and education to givepeople a better understanding of howforests work and why they arc imporshytant and to change public opinion sothat more people appreciate the usesand potential of forests

bull land reform to teduce the mountingpressures on landless peasants causedby inequalities in land ownership

bull conservation of natural ecosystems bysetting aside areas of rain forest asNational Parks or nature reserves

bull restoration and reforestation ofdamagedforests

bull sustainable development namely develshyopment which while protecting thehabitat allows a type and level of ecoshynomic activity that can be sustained intothe future with minimum damage topeople or forest (eg selective loggingrather than clear felling promotion ofnon-tree forest ptoducts small-scalefarming in plots within the forest)

bull control of the timber trade (eg by imshyposing heavy taxes on imported tropishycal forest products and outlawing thesale of tropical hardwoods from nooshysustainable sources)

bull rdebt-ormiddotnature swaps whereby debtshyridden tropical countries set a monshyetary value on their ecological capitalassets (in this case forests) and Iitetallytrade them for their internationalfinancial debt

bull involvement oflocal peoples in managingand developing the remaining rainforests

bull careful control of international aid anddevelopment funds to make sure theydo not inadvertently lead to forestdestruction

Deforestation 3S

Table 113 The consequences of tropical deforestation

Type of change

Reduced biological diversity

Changes in local andregiooal environments

Changes in global environments

Source Grainger (1992)

Examples

Species extinctionsReduced capacity to breed improved crop

varietiesInability to make some plants economic

cropsThreat to production of minor forest

products

More soil degradationChanges in water flows from catchmentsChanges in buffering of water flows by

wetland forestsIncreased sedimentation of rivers reservoirs

etcPossible changes in rainfall characteristics

Reduction in carbon stored in the terrestrialbiota

Increase in carbon dioxide content ofatmosphere

Changes in global temperature and rainfallpatterns through greenhouse effects

Other changes in global dimate due tochanges in land suriace processes

Thc situation is complex but it is alsourgcnt No simplc or singlc solution willbe adcquatc The time-bomb of ecologi-

FURTHBR READING

cal environmental climatic and humandamage caused by dcforestation continuesto tick (Park 1992 p 162)

Aiken S R and Leigh C R 1992 Vanishing Rainorens Their poundCologieRI Trlmsitionin Mallllysia Oxford Oxford University PressA case study from a threatened area

Gl2inger A 1992 Controlling Tropical DeforntatUm London EuthsanAn up-to-date introduction with a global perspective

Park C C 1992 Tropical Rainforuu London RoudedgeAnother relatively simple introduction to many aspccts of the rainmiddotforest environment

Williams M 1989 Americans anti their Fortm Cambridge Cmibridge UniversityPressA very fuU and scholarly discussion of the historical geography of American fomts

36 The Biosphere

n~anaging tropical rain forest In Cameroon

Cameroon in West Atiica is only 1ft

the 23rd largest country on the JhN

I continent but it contains the fitth r---------if---A---~I highest number of mammal md I p]lllt species as well as populations Loges

I of oer 40 globally thleUllled ani- ~I I 1 amp1 mals (Alpert 1993) It is pan of an f J ~+ (

illllJOrtant hlartland ofdiwrsit (on- -_ lllgt1 c~ II bull VIOImdP taining many endemic species III the

lowland forests of Clmeroon and - -somh-east Nigeria there aft oer8000 endemic plant spedcs as wdlas endemic animals such as theCameroon woolly bat (KfrivollfalUIscilla) Jnd pygmy squirrel(My(scillrtS pumifju) Lowland evergreen tropical loresr covers 34 per cenr ofrhecountry Sixty per cent of this total is classed as degraded and 4 per cent asprotected According to Stlfwys in the mid-1980s some 17 million hClrares havebeen ddorested out of an original area of neltlrly 38 million hectares In thedecade 1976-86 06 per cellt of the toral torest was lost each year

Plate 113 The landscape of Rumsiki Cameroon (Panos PicturesNictoriaKeblemiddotWilliams)

Deforestation 37

Figure 116 National parks and reselVes inCameroonSource After Kingdon (1990) pp 272-3

Exploitation of tropical forshyests in this part of Mrica hasgradually spread inland fromthe west coast Cameroonhas more forests left than anycoastal West Mrican countrybut less than any CentralAfrican country such as ZaireThe major cause of deforestashytion at me moment is fellingfOr fudwood and charcoal butmere are also increasing indusshytrial demands for timber andforest products Out ofa totalofover 14 million cu metres ofwood produced by Cameroonin 1989-91 more than 11million cu metres was roundshywood for fuel and charcoalHunting is also a major threatto animal life in the tropicalforests

Cameroon established lawsto manage and protect itstropical forests in 1981 Thislegislation decreed mat 20per cent of national territoryshould be designated as state forests Most of these are to be productive notprotected forests However several protected areas have been established withinthe forests an example is the Korup National Park which covers 1260 sq kmand has IS staff Maintenance is supported by the WFN (Worldwide Fund torNature)WWF (World Wildlife Fund) and other international bodies

Figure II6 illustrates the distribution of protected areas withill north-westCameroon many of which arc found in tropical forests At present forest reservesin Cameroon are poorly funded This may put their long-term protection at risk

Further reading

Alpert P 1993 Conserving biodiversity in Cameroon Ambia 22 44-8

Kingdon J 1990 bJRnd AfrieR The Evolution of Africa$ Rare AnimRu nndPlsmn London Collins

Williams M 1994 Forests and tree cover In W B Meyer and B L Turner(cds) O1aga in lAnd Use and LAnd CoP A Global Penpectipe 97-124Cambridge Cambridge University Press

38 The Biosphere

5 ThOPICAL SECONDARY

FOREST FORMATION

The clearance cultivation and subsequentabandonment of forests in the moist tropshyics has resulted in the development ofincreasing expanses of what is called secshyondary forest In a large and steadilyincreasing proportion of the tropics secshyondary forests make up most or all of theremaining forest

It is difficult to define precisely what wemean by secondary forest Some foresterswould define it as a type of forest thathas suffered some form of disturbance asa result of human actions This could beslight (eg hunting of animals or collecmiddottion of foodstuffs) or massive (eg clearfclling) Other forestcrs believe it is nowuseful and logical to restrict the use of theterm secondary forest to describe forestthat has regrown after clearance

Secondary forest development is oneconsequence of the practice ofshifting culshytivation Peasant farmers clear small plotsof just a few hectares cultivate them for afew years and then abandon them whensoil fertility and crop yields decline Theabandoned plots are then colonized byherbs shrubs and a canopy of pioneertrees This kind of tree grows rapidly needsa lot of light and has low-density woodand sparse branching These trees are typishycally short-lived with life-spans of one ortwO decades There are not many differshyent species As the process of successioncontinues the forest progressively apshyproaches its primary state However it maylake 500 years or even longer for the forshyest to recover its full diversity of species

Exactly how the forest recovers willdepend on the degree of initial disturbanceTraditional shifting cultivation employsonly small plots so that recolonization

Plate 114 Tropical secondary forest and slash-and-burn fields in the rainforestzone of Ghana (Rod Mcintosh)

from neighbouring primary forest is relashytively easy Whtn larger areas are clearedor when prolonged cultivation and freshyquent burning takes plate (leading tosevert soil degradation) the process willbe much slower However on sites whichhave not been seriously damaged thebiomass of leaves and fint roots (thoughnot total biomass) is restored to that ofprimary forest within as little as five to ten

FURTHER READING

Grasslands and Heathlands 39

years by which time net primary producmiddottion (NPP) is equal to or greatcr thanthat of primary forest Thus secondaryforest is probably highly effective at promiddotviding what are called laquoosystem Krvices- that is at preventing soil erosion andregulating runoff It also has some consershyvation value in that it provides a refugtfor some forest fauna and a habitat forsome Aora

Corlett R T 1995 TropicaJ secondary forests Progress in Physical Geography 19 159-72

Ellenberg H 1979 Mans influence on tropical mountain ecosystems in South AmericaJournal of ampoloDY 67 401-16

6 GRASSLANDS AND

HEATHLANDS

THE HUMAN ROLE

In the highlands of Africa there are largeareas of what are called AfTomontaneGrasslands Thty extend as a series ofismiddotlands from the mountains of Ethiopia tothose of the Cape area ofSouth Africa Arethey the result mainly of forest clearanceby humans in the recent past Or are theya long-standing and probably namral comshyponent of the pattern ofvegetation (Meadshyows and Linder 1993) Arc they causedby frost seasonal aridity excessively poorsoils or an intensive fire regimd This isone of the great controversies of Africanvegetation studies

Almost certainly a combination of facshytors has given riK to thesc grasslandsOn tht one hand currtnt land manageshyment pralaquoicts including tht usc of fireprevent forest from expanding Thtre hasundoubtedly been extensivt defortstationin recent centuries On the other handpollen analysis from various sites in southshytm Africa suggests that grassland waspresent in the area as long ago as 12000BP This would mean that much grassland

is not derived from forest through veryrtcent human activities

Similar argumtnts relate to many othtrof the worlds grtat areas of grasslandConsider for example the savannas oftropical rtgions which covtr about 18million sq km Grasses and sedges makeup most of the Vtgttation in savannaalthough woody plants arc present invarying proportions As with mOSI maorvegetation types a large number of intershyrelated factors are involved in causingsavanna It is important to distinguish clearlypredisposing causal resulting andmaintaining factors For instance aroundthe periphery of the Amazon Basin itappears that the climate predisposes the vegshyetation toward the development ofsavannarather than forest Tht geomor-phologicalevolution of the landscape and the formashytion of heavily leached old trosion surmiddotfaces may Ix a muml factor increaKdlaterite (iron crUSt) development a nIultshyinB factor and fire a maintaining factor

Originally savanna was belitved to bea predominandy natural vegetation typedevdoped to suit particular climatic conmiddotditiaRS (figure II7) It was thought thatsavanna is bentr adapted than other

40 The Biosphere

DtfOI~$tation

Dtsrrtifimion

Grudaflls

Aridshrubshygrlllslaoos

PrectpitatiOll

Figure 117 An idealized relationbetween the biomass density andproductivity of five major vegetationtypes (biomes) and precipitation Asprecipitation increases so doesproductivity and therefore biomasswith the two extremes being the lowsparsely shrubbed grasslands of thedeserts and the tall dosed forests bethey tropical temperate or borealSource Graetz (1994) pp 125-47

plant formations to cope with the greatfluctuations in rainfall during the year inthe seasonal tropics Rain torests could notresist the long wimer droughts while dryforests could not compete successfully withperennial grasscs during the lengthy periodof water surplus in the summer months

Other workers havc emphasized the imshyportance of edaphic (soil) conditions Theyargue that the development of savanna isencouraged by poor drainage soils witha low water-retention capacity in the dryseason soils with a shallow profile due tothe development of a lateritic crust andsoils with a low nutrient supply This lastcondition may arise because the soil hasdeveloped on a nutrient-poor parent rocksuch as quartzite or because the soil hasundergone an extended period of leachshying over millions ofyears on surfaces which

have been exposed to the elements for allthat time

A third group of researchers take theview that savannas are the product of drierconditions in former times such as thelate Pleistocene In spite of a moisteningclimate in the Holocene the savannas havebeen maintained by fire They point tothe fact that the patches of savanna insouthern Venezuela occur within areas offorest where the levels of humidity andsoil infertility are similar This suggests thatneither soil fertility nor drainage norclimate can be pinpointed as the cause ofsavanna Moreover the present islandsof savanna contain plant species which arcalso present elsewhere in tropical Amerishycan savannas This suggests that the isshylands were once part of a much largercontinuous expanse of savanna

The importance of fire in creating andmaintaining some savannas is suggested bythe fact that many kinds of tree that growin savanna are fire-resistant Controlledexperiments in Africa demonstrate thatsome tree species such as Burkea africanaand Lophira lanceoMa withstand repeatedburning better than others It has also beennotld that for example African herdsmenand agriculturalists frequently use fire overmuch of tropical Africa to maintain grassshyland Certainly the climate ofsavanna areasis conducive to fire

Some savannas are undoubtedly naturalPollen analysis in South America showsthat savanna vegetation was present beforethe arrival of human civilization Noneshytheless even natural savannas change theircharacteristics when subjected to humanpressures For example many studies fromwarm parts of the world have shown thatgrass cover cannot maintain itself underheavy grazing pressure Heavy grazingtends to remove the fuel (grass) from muchof the land surface This means that fireshappen much less often allowing trees andbushes to invade the savanna

Grasslands and Heathlands 4)

Plate 115 Savanna landscape in the west Kimberley region of northmiddotwesternAustralia The use of fire may be important in controlling both the nature and thedistribution of this extensive biome type (A S Goudie)

Whatever the fac[Ors that determine theorigin of savannas there arc others thathelp to determine some of their particularcharacteristics One example we can giveof this is the role of elephantS in Mricansavannas We do this partly because it isa good illustration of the interdependenceof vegetation and animals and partly bcshycause if elephant numbers arc reduced byhuman prcssures then the whole charaC[crof the savanna ecosystem may change Eleshyphants arc what is known as a keystonespecies because they cxert a strong influshyence on many aspects of the environmentin which they live They divcrsify the ecoshysystems which they occupy and create amosaic of habitats by browsing tramplingand knocking over bushes and trees Theyalso disperse seeds through their eatingand defecating habits and maintain orcreate water holes by wallowing All these

roles arc of benefit to other sptcies Conshyversely where human interference prcvcntsekphants from moving freely within theirhabitats and leads to their numbers exceedshying the carrying capacity of the slvannatheir etTen can be environmentally catamiddotstrophic Equally ifhumans redme dephuInumbers in a particular piece ofsavanna thesavanna may become less diverse and lessopen and its water holes may silt up Thiswill be to the detriment of other species

The mid-latitude grasslands (the prairiesof North America for example) are also thesubject of controversy as to their originsAs we discussed in section 2 above on firethere has been a debate as to whether theprairies arc ~ntially the result of lowprecipitation and high evapotranspirationlevels or whether they result from fires

Hcathland is another fascinating vegetashytion type It is characteristic of temperate

42 The Biosphere

oceanic conditions on acidic substratesIt is composed of cricoid (or heather-like)low shrubs which form a closed canopyat heights usually less than 2 metres Treesand tall shrubs are either absent altogetheror scattered Some heathlands are naturalThese include areas at altitudes abovethe forest limit on mountains and thoseon exposed coaSts There are also wellshydocumented examples of heathlands whichappear naturally in the course of plantsuccession This can happen for examplewhere Catuna vulgaris (heather) replacesgrasses like Ammophila arenana and CR-rexarenana on coastal dunes

However extensive areas of heathlandalso occur at low and medium altitudeson the western fringe of Europe betweenPortugal and Scandinavia The origin ofthese heathlands is strongly disputed Somewere once thought to have developedwhere there were appropriate edaphicconditions (for example well-drainedloess or very sandy nutrient-poor soils)but pollen analysis showed that mostheathlands occupy areas which were forshymerly tree-covered This evidence alone didnot settle the question whether the changefrom forest to heath was more likely tohave been caused by Holocene climaticchange or by human activity Howevertwo other factors suggest that humanactions established and then maintained

FURTHER READING

most of these heathland areas The first ofthese is the presence of human artefactsand buried charcoal the second is the fuctthat the replacement of forest by heathhas occurred at many different times beshytween the Neolithic and the late nineteenthcentury Fire is an important managementtool for heather in locations such as upshyland Britain since the value of CalJuna asa food for grazing animals increases if it isperiodically burned

The area covered by heathland in Westmiddotern Europe reached a peak around 1860Since then there has been a very rapiddecline Reductions in Britain averaged 40per cent between 1950 and 1984 and thiswas a continuation of a more long-termtrend In England the Dorset heathlandsthat were such a feature of Thomas Harshydys Wessex novels are now a fraction oftheir former size There are many reasonsfor this decline They include unsatisfacshytory burning practices the removal ofpeatdrainage fertilization replacement by immiddotproved grassland conversion to forest andthe quarrying of sand and gravel

Thus human activities over a very longtime can combine with natural changesboth to produce and to remove grasslandsand heathlands Many scientific debates arccontinuing on how such plant communshyities react to stress The box opposite givesan example from Australia

Gimingham C H and de Schmidt I T 1983 Heaths and natural and semi-naturalvegetation In W Holzner M J A Werger and I Ikusima (eds) Mtms Impact onVegetation 185-99 The Hague JunkThe best general review of the worlds heathlands

Harris D R (cd) 1980 Human Ecology in SRPanna Environments London Acashydemic PressA useful collection of papers on savannas in their human context

Grasslands and HeathJands 43

Recent human impacts on subalpine grassland andheathland in Victoria Australia

C]lndllYfflooornbullCattle grazing began in the 1850sin the Bugong High Plains alpinegrassland in what is now the Victoshyria Alpine National Park (created in1980) Eer since there have beendehates over the degradation ofgrassland and soil erosion In 1939there were disastrous hush fires heremd in the 19405 soil erosion beshycame very Knous u stock numbersincreascd Since the 1950$ there hasbeen an overall decline of about 60per cent in both stock numbers andthe area graud and by 1991 onlyabout 3100 cutle were grazing thearea benvc-en December and April

These changes in grazing densishyties have been echoed by an incretse in the area of shrub cover In 1945 pershymanent study plou were established by ecologists to monitor the changing vegshyetation cover on grazed and ungrazed land The rlaquoords produced from theseplots over five decades enab]( scientists today to test the relationship benveengrazing fire and the maintenance of grassland (Wahren et al 1994) It hu beensuggested that cattle grazing reduces shrub cover (therefore maintaining grassshyland) and also fire risk But the Bugong study docs not back this up as grazedplots have more bare patches than ungrazed (Ke table IlA) although by 1994old shrubs on some ungraud plots were beginning to die back In this areaalpine vegetation seems slow [0 recover after dislUrbance (such as fire) and evenslower where grazing is present

Table 114 Comparisons of percentage cover of different vegetation on grazed andungrazed grassland plots Bugong High Plains Victoria Australia 1982-1994

Cover 1982 1982 1989 1989 1994 1994dassmiddot Ungrazed Grazed Ungrazed Grazed Ungrazed Grazed

1 76 53 71 61 66 722 21 31 24 20 31 173 3 16 5 19 3 10

bull Cover class 1 = thick litter and dense vegetationCover class 2 thidc or thin litter sparse vegetationCover class 3 thin litter sparse to no vegetation

Source Adapted from Wahren et al (1994)

44 The Biosphere

7 TEMPERATE FORESTS UNDER

STRESS

Forest decline is an environmental issuethat came to the fore in the 1980s It hasmany symptoms including the discolorashytion and loss of needles and leaves reshyduced rates of grovlth abnormal growthforms and in extreme cases tree death

Germany is probably the Europeancountry most seriously affected by lorestdedine In 1985 55 per cent of the foreststands in West Germany were reponedto be damaged The decline is howeverwidespread in much of Europe (see tables115116) The process is now also undershymining the health of eastern NorthAmericas high coniferous forests In Gershymany it was the white fir Abies alba whichwas afflicted initially but since then the

symptoms have spread to at least ten otherspecies in Europe induding Norwayspruce (Picea abies) Scots pine (Pinussylvestris) European larch (Larix decidu)and seven broad-leaved species

In 1982-3 the German governmentadopted a comprehensive clean air legislashytion package However the data presentedin table II6 indicate that German forestsarc still suffering from decline In 1994at the Oslo international meeting Gershymany agreed to reduce sulphur emissionsby 83 per cent (from 1980 levels) by 2000In 1986 the Federal Environment Minisshytry concluded that there is no single typeof forest damage and no single cause Wearc dealing with a highly complex pheshyn0l111non which is difficult to untangle andin which air pollutants playa decisive rolc

Many suggested explanations for thisdieback have been put forward They

Table 115 Reported percentage of different tree species affected by forest declinein West European countries 1984

Species W Germany E France Switzerland Austria Italy (5 Tyrol)

Norway spruce 51 16 11 29 16Silver fir 87 26 13 28 35Scots pine 59 17 18 30 6Beech 50 3 8Oak 31 6 9Others 31 6 9

Source Goudie (1993)

Table 116 Results from German forest damage surveys 19B6-1993 percentage oftrees in classes 2-4 (ie defoliationgt 25) for all species

Area 1986 1987 1988 1989 1990 1991

EG 138 164 359WG 189 173 149 159 159G 252

bull EG = former East GermanyWG = former West GermanyG = Germany after reunification

Source Acid News 1995

1992 1993 1994

260 242 244

includ~ poor for~st manag~m~ntpracticesag~ing of strnds climatic chang~ sev~re

climatic events (such as the sev~re sumshym~r droughts in Britain during 1976 and1995) nutri~nt d~fici~ncy viruses fungalpathogens and pest infestations Howeverparticular attention is being paid to therol~ of pollution This may tak~ variousforms including gaseous pollutants suchas sulphur dioxid~ (SOl) nitrogen oxides(NOx) or ozone acid deposition on kav~s

and needles soil acidification and the assoshyciat~d probl~ms of aluminium toxicity and~xc~ss kaching of nutri~nl$ (for ~xampl~

magnesium) over-fertilization by d~posit~d

nitrog~n and the accumulation of trac~

metal or synth~tic organic compounds (~g

pesticides or herbicides) as a r~sult ofatmosph~ric d~position

In many cases forest d~clin~ may miuhfrom a combination of Strcsscs For ~X2m-

T~mpcrat~ For~sts und~r Str~ss 45

pk long-term climatic chang~ may cr~at~

a pmtisposing stTtSS (see pan I section 6)which ov~r a long period weakens a treesability to resist other forms of str~ss Thenth~r~ ar~ ineiling SlnJJeJ that operat~ overshort~r rime-spans for exampk droughtS(v~r~ frost or a short-li~d pollution ~pishy

sod~ These damage trees that are alr~ady

weaken~d by the predisposing str~sses

Thirdly w~ak~ned tr~~s ar~ then morepron~ to a scri~s of contributing SlrelJes(eg attack by insect pests or root fungi)

There may also be different causes indifferent ar~as Thus widespread for~st

death in Eastern Europe may r~sult fromhigh concentrations of sulphur dioxidecombined with extr~me winter stress Thisis a much less likely ~xplanation in Britainwh~r~ sulphur dioxide concentrationshav~ shown a mark~d d~cr~~ in r~c~nt

years Indeed Innes and Boswell (1990

Plate 116 Acid rain damage at Szkalrska Poreba south-west Poland Much ofthe pollution here comes from the burning of low-quality coals and lignites inGermany and the Czech Republic (Richard Baker Katz Pictures)

Figure 118 Estimates of total quantityof de-icing salt purchased annually inmainland Britain during the period1960-1991 Arrows represent yearswhen significant crown dieback ofLondon plane has occurred In the early1960s highway departments changedfrom using saltabrasive mixtures tousing pure rock salt This may accountfor some of the increase in salt usageSource Dobson (1991)

Ivgt with many environmental problemsinterpretation of forest decline is hamperedby a lack of long-term data and detailedsurveys Forest conditions vary fromyear to year in response to fluctuations inclimatic stress (eg drought frost windthrow) This means that it is dangerousto infer long-term trends from short-termdata (Innes and Boswell 1990) The probmiddotlem may well have been exaggerated inthe 1980s by some observers who fJiled to

recognize that stressed trees may be a morenormal phenomenon than they believed

46 The Biosphere

p 46) suggest that the direct effects ofgaseous pollutants in Britain appear to bevery limited

It is also important to recognize thatsome stresses may be especially significantfor a particular tree species In 1987 asurvey of ash trees (Fraxinus excelsior) inGreat Britain showed extensive diebackover large areas of the country Almostone-fifth of all ash trees sampled wereaffected Hull and Gibbs (1991) identifieda link between dieback and the way theland is managed around the tree Theynoted particularly high levels of damagein trees next to arable farmland They sugshygested this might be associated with unmiddotcontrolled stubble burning the effects ofdrifting herbicides and the consequencesof excessive nitrate fertilizer applicationsto adjacent fields However the primecause ofdieback was seen to be the disturshybance of tree roots and the compaction ofthe soil by large agricultural machineryAsh has shallow roots if these are damshyaged repeatedly the trees uptake of waterand nutrients might be seriously reducedBroken root surfJces would be prone toinfection by pathogenic fungi

Trees growing alongside roads which arcregularly salted to reduce ice problems incold winters may also become damagedThis may be a growing problem becausethe use of salt on roads has increased inrecent years (figure 118)

FURTHER READING

II I I II

Boehmer-Christiansen S and Skea ] 1991 Acid Politics Environment and EnergyPolicies in Britain and Germany London Belhaven

Innes ] 1 1992 Forest decline Progress in Physical Geography 16 1-64An impressive overview of the competing hypotheses that have been put forward toexplain forest decline

Schulze E-D Lange O L and Oren R 1989 Forest Decline and Air PollutionEcological Studies no 71 New York Springer-Verlag

Templ=rate FOrc5ts under Stress 47

Forest decline in Bavaria Germany

I AVARIA (--

--MwBdIbullhypotheses have been

to explain the apparent

Forest decline in Germany became amajor environmental issue during the1980s Many conifers and broadshyleaved trees showed signs of Stressranging from yellowing of needlesto death In the mountains of theFichtelgebirge in north-east Bavariamost forests at altitudes over 750metres currentlyshow signs ofdcdincBy 1986 30 per cent of Bavarianforests were cla~d as moderatelyor seriously damaged by unknownfactors

Severaladvanceddecline

bull natural climatic causes andepidemics

bull direct effects of air pollutionbull mineral deficiency and imbalances as a consequence of acid deposition and

soil acidificationbull a combination of some or all of the above factors

The forests in Bavaria grow on acid poor soils above granite and metamorphicgneiss and schist bedrocks In the sixteenth century beech was the major speciesBeech and sycamore together accoumed for 60 per cent of the canopy and firformed the remaining 40 per cent Over the following 400 years the forests weredepleted by mining smelting and agriculture During the ninetccnth centuryreforestation took place producing a difierent mix of trees Now there an~ 96 percent spruce 2 per cent beech and 1 per cent fir (Schulze et aI 1989)

During the twentieth century episodes of ozone sulphur dioxide and nitrogenoxide pollution have been very $Cvere It now appears that air pollution coupledwith a past history of polluted air and planting is a major problem lor these verysensitive forests Much of the pollution occurs in winter and comes trom steeland chemical industries and power plants in eastern Germany and the CzechRepublic The effects of air pollution are compounded by mble winter air conshyditions which encourage temperature inversions and the production of smogAmmonia produced by nearby cattlc and other Iarmed animals also adds to thenitrogen pollution

bull

bull

48 The Biosphere

8 URBAN ECOWGY

The world is becoming increasingly urshybanized In 1980 here were 35 cities withpopulations of over 4 million by 2025135 cities will probably have reached hissize Over the period 1950-90 the totalpopulation of the worlds cities has in~

creased tenfold and is now more than 2billion Cities thus contain around half theworlds population They also contributemost global pollution Funhermore urbanpopulations are concentrated into a rela~

tively small area for example only 34 percem of he Iand in the USA is urbanizedThis makes the urban impact upon theenvironment even more imense

The impacts ofurban areas on the envicshyonmem and ecology can be devastatingProblems have been felt for a long timein many countries where industrial citiesdeveloped early In many less developedcountries huge expansion in populationhas occurred relatively recently leading to

burgeoning environmental problemsWhat impacts do cities have 011 the

environment And how do these affectecology Cities do all of the following

bull produce a major dem3nu tor naturalresources in the surrounding arC3

bull obliterate the llatur3l hydrological sysshytem on the site of the dtyreduce biolll3SS and alter the speciescomposition 011 the site of thl cityproduce waste products which canalter the environment in and aroundthe city

bull create new land through reclamationand landfill

Together these impacts make up theecological footprint of a city that is thearea affected by pollution resource extracshytion devdopmem and transport causedby the city irsclf Cities demand raw matershyials such as tim bet coal and oil these must

be extracted from the surrounding areaor transported into the city They alsorequire agricultural products energy andlabour As the variow parts of the worldbecome increasingly interconnected theecological footprints of major cities beshycome bigger and bigger This means thata vast proportion of the Earths surface isbeing sucked intO the urban system oneway or another

On he site of cities the entire entershyprise of urbanization leads to dnsticchanges in geomorphology climate h)liroshylogy and ecology Urbanization is oftenseen as evidence of societys success intaming and overcoming nature Increasshying urban pollution problems howevetshow that this success has been limitedCities replace natural foteSts grasslandand other vegetation with vaSt swathes ofconcrete brick and nrmac as well as garshydens parks ponds and derelict land Thesechanges in vegetation rebound upon anishymal life they also affect the hydrologicalresponse Trees grassland and the soilsin which they grow act as butTers slowingdown the movement of water through adrainage basin As explained more fully inpart IV section 4 urbanization reducessuch butTers It acce1ciltes and streamlinesthe flows of water by reducing the diffuseflow below the land surface and replacingit by flows over the surtacc lnd throughpipc=s

Species diversity may be increased incities despite the great disruption causedby building work Gardens parks pondsand street plantings introduce a range ofexotic plants The urban climate also enshycourages growth and diversity favouringspecies which tolerate wanner 1css variableconditions than those found in neighbourshying rural areas The urban environmentalso produces behavioural changes in manyanimals For example animals which usushyally hibernate in winter in temperate counshytries can live normally throughout the year

Urban Ecology 49

Plate 117 A kestrel sitting on a street lamp in a British city These raptors andmany other organisms have proved their ability to adapt to the urbanenvironment (NHPNMichael leach)

in large cities where there is year-roundwarmth and food Street lighting confusesbirds and extends the hours of daylightfor them The vast amount of waste tOadfound in urban areas encourages scavenging animals such as racoons and foxesMany urban-dwelling species have nowcome to be regarded as pests Pigeons inmany British and American dty centres arean example their droppings arc a greatnuisance Many species arrie in cities alongrivers and canals Communications nctshyworks in general provide a major route formany animals and plants seeking to coloshynize new areas In Britain for examplemink which have escaped from fur farmsare now found on urban riverbanks inOxford

On the other hand the pollution anddereliction present in many citia depletethe ecology High levels ofsulphur dioxide

in the atmosphere for example kill offlichen species growing on trlaquo bark Manytrees themselves a~ threatened by air andsoil pollution Similarly urban and indusshytrial pollution of aterways depletes theaquatic ecology For example in Shangmiddothai China the Huangpu River is nowthought to be biologically dead as a resultof the 34 million cu metres of industrialand domestic waste dumped in it each daySome derelict land is highly contaminatedwith heavy metals and Other toxins thwmaking recolonization impossible Howshyever other derelict land areas provideopportunities for wildlife colonizationand conservation In Britain large areas ofurban allotments (small plots ofland rentedout for domestic food production) are nolonger cultivated and native and exoticspecies are colonizing the abandoned land

Increasingly city dwellers are becoming

50 The Biosphere

committed to improving the ecology ofcities A range of strategies is employed

bull reducing poUution to encourage desirshyable organisms to return

bull removing undesirable species throughcareful extermination programmes

bull reducing the use of lawn fertilizers andpesticides

bull planting trees in streetSbull cstablishing urban nature reserves city

forests and conservation areasbull undertaking backyard compostingbull developing urban farms thus bringing

food production back into cities

Such schemes are part ofa general trendtowards improving the urban environmentthrough managing pollution and immiddotproving stmdards of housing and healthSustainable development of cities is apopular phrase at prescnt However vastdisparities in wealth between inhabiuntsof different cities and between differentparts of anyone city make the goal ofsustainability hard to reach In manydeveloping countries squatter settlementson the outskirts oflarge cities are growingat an alarming rate as more and more poorinhabitants of outlying rural areas are atshytracted to the opportunities in cities These

FURTHER READING

settlements arc very destructive of theenvironment and also severely affected byenvironmental poUution and hazards Theyusually grow up on land which is dereUetbecause it is least suitable for developmentThey lack even basic services such as elecshytricity or running water Trees arc removedso that dwellings can be put up on steeptropical hillslopcs this can result in accelshyerated landslides (see part V section 6)Wastes produced in squatter settlementscannot be removed effectively because ofthe lack of sanitation and services Thiscauses pollution of land air and watermiddotcourses In South Africa for exampleSoweto (which has a population of around25 million according to some estimates)has horrendous air poUution from sulphurdioxide produced by coal burning becausethe electricity supply is completely inadshyequate The natural ecology has beenwiped out and human health is suffering

All round the world it is clear thatthe ecological impacts of cities are justone manifcstation of a deep problem withpresent-day urbanization A5 RichardRogers the architect put it in 1995 Inthe beginning we built cities to overcomeour environment In the future we mustbuild cities to nurture it

Bridgman H Warner H and Dodson J 1995 Urban Biophysical EnvironmentsMelbourne Oxford University PressA concise introduction with an Australian flavour

Hardoy J E Midin D and Satterthwaite D 1992 Environmental Problems inThird World Cities London u([hscanLike most Earthscan books this provides a clear introduction to the crucial issuesaccompanied by many short case studies

White R 1994 Urban EinmmentRI MRn4gement Chichester WdcyA modern general trcaonent of how city environments can be managed

Urban Ecology 51

Chicagos changing vegetation

CANADA

USA

In the 1840s ~fore urban development really began the flat gladated plainnext to Lake Michigan in the USA was dominated by natural forest and prairievegetation (figure 119) Low prairie grasslands occupied most of the area Deshydduow forests of oaks (such as the Bur oak Q4ercllS mlicroclirplI) ashes andcIms were common on sand ridges and the edges of streams By 1860 thepopulation of Chicago city had riscn to 50000 and by 1990 the metropolitanarea conDined over 8 million people

This urban explosion has been accompanied by an almost total loss of naturalvegetation apart from some large tracts designated as forest prescrves Severaldirect and indirect cawes of this loss of natural vegetation can be recognized Thefirst direct causc is the dearing of land for development Interestingly howeverindividual trees survived some trees identified in the 18305 by the original landsurveyors were still present in the 19705 (Schmid 1975) Studies of the forestvegetation in and around Chicago show that removing the dosed canopy bycreating clearings for building favours trees which cope well in the drier andlighter conditions (such as Bur oak) Other moisture-loving species such assugar maple and red oak suffer Indirectly construction has disturbed the soilsaffecting particularly trees such as red and white oaks Oil spills gas leaks thesalting of icy roads and digging to lay pipes have all had direct impacu on naturaland introduced vegetation in some parts of the dry

New kinds of trees and other vegetation have been introduced into ChicagoThcsc incorner species have had a key impact on the citys vegetation They havealso suffered from the urban environment Interestingly there has been an inshycrease in the proportion of Chiago covered by trees since urbanization This isbecause trees have been planted on upland sites which would naturally have beendominated by prairie

52 The BiosphereJ

~1lt1- N -

t laquo

-

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bull bull U U Range

Figure 119 The distribution of forest (black) and prairie (white) in theChicago region during the 1840s as recorded by the General land SurveySections formed by the townshiprange grid are 1 mile squareSource Schmid (1975) figure 3

Air pollution has had an indir~ct ~ff~ct on veg~tation In 1913 a study foundthat trees in Chicago near th~ railway stations w~re aff~ct~d by smoke and th~

vegetation around sted mills was reduc~d to a f~w w~~dy annuals Mor~ recentlythe mainly d~ciduous tr~~s in Chicago have shown much less damag~ from airpollution than th~ ev~rgreens in other North American cities A much moreserious ~vent for the urban vegetation of Chicago was the outbreak of Dmch elmdisease from the late 1950s Until 1950 American elm was the most commonlyplanted tree species her~ Dutch elm disease destroyed the great majority of them

Housing brings grass and shrubs planted for decorative purposes in gardensChicago residents especially in the wealthy suburbs have planted many exoticshrub and herb species but few native ones Of the native plants opportunisticherbs from flood plains have been the most successful These plants thrive onwasteland and abandoned plors The vegetation pattern of Chicago is now con-trolled by economic social and cultural factors The number and mix of speciesnow vary according to the age and social characteristics of different neighbour-hoods Natural ecological factors are no longer so important as they were

-

ltshyi

9 WETLANDS ThE KJDNEYS

OF THE LANDSCAPE

In th~ 19805 w~tlands becam~ a lOpic ofgr~al ~nvironm~nral conc~rn Th~y w~r~

pcrcdv~d to be vitally important ~cosysshy

t~ms as is mad~ dear in the followingintroductory remarks to Mitsch and Gosseshylinks pione~ring book WetlandJ

Wetlands are among the most imporshytant ecosystems on the Earth In thegreat scheme of things it was theswampy environment of the Carbonifshyerous P~riod that produced and preshyserved many of the fossil fuels on whichwe now d~pend On a much shortertime scale wetlands are valuable assources sinks and transformers of amultitude of ch~mical biological andg~netic materials Wetlands are someshyrimes described as the kidneys of thelmdsca~ for the functions they rtr-

Table 117 Threats to wetlands

W~dands 53

form in hydrologic md chemical cycl~s

and as the downstream rec~ivers ofwast~s from both natural and humansources Th~y have been found tod~anse pollut~d waters pr~middot~nt floodsprot~ct shor~lin~s and rechargegroundwat~r aquif~rs Furthermoreand most important to som~ w~tlands

play major roles in the landscape byproviding unique habitats for a widevariety of flora and fauna While thevalues of wetlands for fish and wildlifeprotection have be~n known for severaldecades some of the other benefitS havebeen id~ntified more rec~ndy (MitSchand Gossdink 1986 p 3)

W~t1ands arc also percdvcd to be underthreat mOSt notably from draining ditchshying dredging filling pollution and chanshyn~lization According to some sources theworld may have lost halfof all itS wetlandssince 1900 md the USA alone has lost54 rtr cent of its original w~t1and area

Human Indirect

Source Type

Human Direct

Examples

Drainage for crops timber mosquito control

Dredging and stream channelization

Filling for waste disposal and land claim

Construction of dykes dams and sea walls forflood control and storm protection

Discharge of materials (eg pesticides nutrientsfrom sewage sediments) into waters and wetlands

Mining of wetland soils for peat coal gravel andother minerals

Sediment diversion by dams and other structures

Hydrological alterations by canals roads etc

Subsidence from extraction of groundwater oiletc

Natural Direct and indirect Subsidence (including natural rise of sea leve)droughts hurricanes and other storms erosion andbiotic effects

Sourc~ Adapted from Maltby (1986) p 92

54 The Biosphere

Table 118 Wetland terms and types

Name Definition

Swamp Wetland dominated by trees or shrubs (US definition) InEurope a forested fen (see belowgt could easily be called aswamp In some areas wetlands dominated by reed grassare also called swamps

Marsh A frequently or continually inundated wetland characterizedby emergent herbaceous vegetation adapted to saturated soilconditions

Bog A peat-accumulating wetland that has no significant inflowsor outflows and supports acid-loving mosses particularlySphagnum

Fen A peat-accumulating wetland that receives some drainagefrom surrounding mineral soil and usually supports marshlikevegetation

Peatland A generic term for any wetland that accumulates partiallydecaying plant matter

Mire Synonymous with any peat-accumulating wetland (Europeandefinition)

Moor Synonymous with peatland (European definition) A highmoor is a raised bog while a low moor is a peatland in abasin of depression that is not elevated above its perimeter

Muskeg large expanses of peatland or bogs particularly used inCanada and Alaska

Bottomland

Wet prairie

Reed swamp

lowlands along streams and rivers usually on alluvialfloodplains that are periodically flooded

Similar to a marsh

Marsh dominated by Phragmites (common reed) term usedparticularly in Eastern Europe

Source Modified from Gleick (1993) table F1

primarily because of agricultural developshyments The pressures on wel1ands are listedin table 117

What precisely are wel1ands~ There isno single Wliversally recognized definitionbecause they take a variety of forms andoccur in a considerable range ofconditions(table IIB) However Maltbys (1986)definition is a useful one He defines wet-

lands as ecosystems whose formation hasbeen dominated by water and whose proshycesses and characteristics are largely conshytrolled by water A wetland is a place thathas been wet enough for a long time todevelop specially adapted vegetation andotherorganismsbull Wetlands therefore includeareas ofmarsh mire swamp fen peatlandor water whether natural or artificial per-

Wetlands 55

HlQIWATEl

Figure 1110 Diagram showing the hydrological and ecological characteristics ofwetlands which act as ecotones between dry terrestrial ecosystems andpermanently wet aquatic ecosystemsSource Mitsch and Gosselink (1986) figure 14

manent or temporary The water may lxstatic or flowing fresh brackish or saltyincluding marine water whose depth at lowtide does not exceed 6 meues

Wetlandscoversignificant areas In all theyaccount for about 6 per cent of the Earthsland surface This is not much less than theproportion orland under uopicaJ rain forestThey also account for as much as a quarterafthe Earths total net primary productionNotable wetlands include the Evergladesin Florida the Sudd and Okavango swampsof Mrica the Fens and Broads of EastAnglia in England and the mangroveswamps of South and South-East Asia

Wetlands are what are known as ccotonesthat is transitional zones They occupythe transitional space bt=tween largely dryterrestrial systems and deep-water aquaticsystems (figure 1110) This transitionalposition in the landscape allows them toplay valuable roles for example as nutrientsources or nutrient sinks It also causesthem to have high biodiversity for theyacquire and contain species from bochterrestrial and aquatic systems

Why are wetlands important and deservshying of careful management Because

bull they are fertile and highly productiveecosystems

bull they support fisheries of great valuebull they absorb and store carbon which has

implications for the greenhouse effectbull they sift dissolved and suspended mashy

terial from floodwaters thereby cncourshyaging plant growth and maintainingwater quality

bull they absorb and store floodwater(thereby mitigating flood peaks) andaCI as barriers against storm surgesetc

bull they are vital breeding and nurserygrounds for waterfowl animalsand plamsand provide refuges in times ofdrought

bull they provide staple food plams(eg rice)bull they provide fuel (eg peat)bull they provide building materials (eg

mangrove wood reeds for malch etc)bull they have recreational uses

Because of the great value of wetJands in 1971 many countries signed the Conshyvention on Wedands of International Imshyponance especially as Waterfowl HabitatAs this was signed at Ramsar in I~ it isotien more eonveniendy known as the

56 The Biosphere

Plate 118 The Niger River of West Africa creates a great wetland itsso-called inland delta This photograph shows an area flooded by the annualinundation near Jenne Mali (Rod Mcintosh)

Ramsar Convention Those states that havesigned the Convention which now amountto over 90 agree to designate at least oneof their national wetlands for inclusion ina List of Wetlands of International Imshyportance They also agree to formulateand implement their planning so as topromote the conservation of the wetlandsincluded in the List to establish wetlandnature reserves and to co-operate in themanagement ofshared wetlands and sharedwetland species

FURTHER READING

International collaboration is ofcourseessential It is no use conserving a wetlandin one country to provide a refuge forspecies that spend one particular season ofthe year at that wetland if another counshytry destroys the refuge which they use inanother season of the year Full details ofinternational environmental conventions ofthis type are listed each year in the GreenGlobe Yearbook which is prepared by theFridtjof Nansen Institute of Norway andpublished by Oxford University Press

Maltby E 1986 Waterlogged Wealth Why Waste the Worlds Wet Placet LondonEarthscanA very useful statement of why wetlands are important and the stresses they face

Williams M (ed) 1990 Wetlands A Threatened Landscape Oxford BlackwellA more advanced collection of papers that deals with many different types of wetlandsfrom an international perspective

Wt=tlands 57

Wetlands management in the Niger Inland Delta

Tht= Niger Inland Delta in MaliMrica is in the Sahel zone It formsan important seasonally flooded wetshyland environment in an area whereevaporation vastly exceeds precipitashytion It covers some 20000-30000sq km in me flood season and 4000sq km at low water and supportsa population of around 550000JKople (Adams 1993) Fishinggrazing and cultivation of rice andsorghum are all important activitiesSeventy-five JKr cent of me fishcaught along the entire River Nigerare caught hcre half the total rice area in Mali is found here Over 2 millionsheep and goats and around 1 million cattle graze on the delta in the dry seasonThcsc numbers make up around 20 per cent of all thcsc animals found in Mali

The key to the complex and abundant agricultural production of the delta isthe timing of the floods The high flow in the delta does not coincide with thelocal rainfall peak This means that there is frequent variation in environmentalconditions throughout the year The floodwaters JKak betwt=en September andNovember and recede between December and February rains ft11 between Juneand September and the delta is dry between April and June Different activitiesdominate the delta under these different hydrological conditions Rice is planttdas the waters rs( in July and August and harvested as they recede in Decemberto February Sorghum is planted on the fulling flood in January and the delta isextensively used for grazing from December to July

This wetland is also of international importance Migrating birds visit it and thedelta provides an important stop for them on the routes from the Arctic to otherparts of Africa

Failure of the rains and alterations to the flow of the Niger River may haveserious consequences for the rich natural and human ecology of the Niger InlandDelta Dams further up the Niger River are likely to remove about 12 JKr centof inflow to the delta in a dry year which could have impacts on fishing andagriculture Damming of rivers tends to affect both the quality and the quantityofwater and to detract from the significant economic uses ofdownstream wetlandsOne solution on regulatt=d rivers may be controlled flooding with artificial proshyduction of floodwaters from hydroelectric dams In this way the dams arc madeto work pith the natural river environment nther than replacing it

Further reading

Adams W M 1993 Indigenous usc of wetlands and sustainable developmentin West Africa Geographic1 jOJ4nuli 159 209-18

S8 The Biosphere

10 BIODIVERSITY AND

ExnNcrIONS

Wlut is biodiversity It has recently beendescribed as an enormous cornucopia ofwild and cultivated species dive~ in fonnand function with beauty and usefulnessbeyond the imagination (litis 1988 p98) Biodiversity has recently become amajor environmental issue With environshyments being degraded at an acceleratingrate much diversity is being irretrievablylost through the destruction of naturalhabitats At the same time science is disshycovering new uses for biological diversity

The fundamental concern is the finalityof the loss of biodiversity Once a specieshas gone it cannot be brought back Thedodo (a bird) is dead and gone and willnever be seen again

Biodiversity has five main aspects

bull the distribution of different kinds ofecosystems which comprise communshyities of plant and animal species andthe surrounding environment andwhich are valuable not only for thespecies they contain but also in theirown right

bull the total number of species in a regionor area

bull the number of endemic species (speshycies whose distribution is confined to

one particular location) in an areabull the genetic diversity of an individual

speciesbull the sub-populations of an individual

species that is the different groupswhich represent its genetic diversity

The Earths genes species and ecosysshytems have evolved over a period of 3000million years They form the basis forhuman survival on the planet Howeverhuman activities arc now leading to arapid loss of many of the components of

biodiversity Human self-interest arguesthat this process should be stemmed forecosystems playa major role in the globalclimate arc a source of useful productspreserve genetic strains which crop breedshyers use to improve cultivated varieties ofplants and conserve the soil

We have no clear idea of the totalnumber of species of organisms that exislon the face of the Earth Therefore it isdifficult to predict what numbers ofspeciesmay be lost in the coming decades Howshyever according to Myers (1979 p 31)during the last quarter of this century weshall witness an extinction spasm accountshying for one million species This is a conshysidenble proportion of the estimatednumber of species living in the world toshyday which Myers puts at between 3 and 9million He has calculated mat from AD

1600 to 1900 humans were causing thedemise of one species every four yearsthat from 1900 onwards the rate increasedto an average of around one per year matat present me C2te is about one per dayand that within a decade we could Ixlosing one every hour By the end of thecentury our planet could have lost anyshything between 20 per cent and 50 percent of its species (Lugo 1988) It isobvious from even this brief look at thequestion that the need to maintain bioshydiversity has become one of the crucialissues with which we must contend

Some environments are particularly imshyportant for their species diversity Suchbiodiversity hot spots (figure IIII) needto be made priorities for conservationThey include coral reefs (sec part VI secshytion 7) tropical forcst5 (which support weUover half the planets species on only about6 per cent of irs land area) and somt ofthe Mediterranean climate ecosystems (inshycluding the extraordinarily diverse Fynbosshrublands of me Cape region of SouthAfrica) Some environmtnts are crucial beshycause of their high levels ofspecies diversity

bull

i

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-Figure 1111 Forest and heathland hot spot areas Hot spots are habitats with many species found nowhere else and ingreatest danger of extinction from human activitySource Wilson (1992) pp 262-3

60 The Biosphere

or endemic species others are crucial beshycause their loss would have consequenceselsewhere This applies for example towetlands which provide habitats for mishygratory birds and produce the nutrientsfor many fisheries

Reduction in habitat area can lead to adecline in the population of each speciesas well as in the number of differentspecies that the habitat can hold Lowpopulations make species highly vulnerableto inbreeding disease habitat alterationand environmental stress If a species hasbeen reduced to one population in onesmall area a single fire a single diseasethe loss of a food source or any othersuch demographic accident can kad toextinction

Human demographic success has proshyduced the biodiversity crisis As E OWilson noted in his remarkable book TheDiversity of Life

Human beings - mammals of the 50shykilogram weight class and members ofa group the primates otherwise notedfor scarcity - have become a hundredtimes more numerous than any otherland animal of comparable size in thehistory of life By every conceivablemeasure humanity is ecologically abshynormal Our species appropriates beshytween 20 and 40 per cent of the solarenergy captured in organic material byland plants There is no way that wecan draw upon the resources of theplanet to such a degree without drastishycally reducing the state of most otherspecies (Wilson 1992 p 272)

With the human population expected todouble or treble by the middle of thetwenty-first century and the material andenergy demands of developing countrieslikely to accelerate at an even faster rateeven less habitat will be left for otherspecies

What needs to be done~ Wilson suggests

five enterprises that need to be undertakento save and use in perpetuity as much aspossible of the Earths diversity

1 Survey the worldJsfauna andflora Weknow very little about how many speshycies there are and even less about theirqualities or where they are Threatenedhabitats need to be paid particularattention

2 Create biological wealth As our reshycords of species expand they open theway to what is called bioeconomicanalysis - the broad assessment of theeconomic potential of entire ecosysshytems An aim will be to protect ecoshysystems by assigning to them a futurevalue We need for example to searchamong wild species (possibly using ethmiddotnographic sources) for useful medicalor chemical products

3 Promote sustainable development Aswith desertification (see section 3above) the root cause of the problemlies in society The solution lies thereas well As Wilson (1992 p 322) exshyplained it The rural poor of the thirdworld are locked into a downwardspiral of poverty and the destructionof diversity Lacking access to marshykets hammered by exploding popushylations they turn increasingly to thelast of the wild biological resourcesThey hunt out the animals withinwalking distance cut forests that canshynot be regrown put their herds onany land from which they cannot bedriven by force They use domesticcrops ill suited to their environmentfor too many years because they knowno alternative Their governmentslacking an adequate tax base andsaddled with huge foreign debtscollaborate in the devastation of theenvironment

4 Save what remains Seed banks boshytanical gardens zoos and the like (the

so-called ex sitw methods) may havesome limited scope to preserve geneticmaterial However the key issue is thepreservation of nantral ecosystems Weneed large areas of reserves to includeas many of the undisturbed habitats as

Biodiversity and Extinctions 61

possibk Priority shouJd be given tobiodiversity hot spots

S Restore tbe wild lAnds Existing ecoshysystems need to be salvaged and remiddotgenentcd

Plate 119 A giant panda Ailuropoda melanoleuca feeding on bamboo atWolong Sichuan China The panda has become a symbol of the worlds wildlifeconservation movement (Heather Angel)

FURTHER READING

Myers N 1979 Tht Si1lkilJg Ark A Ntw Look at thtlrobJem ofDif(Jpp((Jrin~q SpainOxford Pergamon PressOnt of [ht classic statements about txtinctions and biodivtrsity loss by one ofthc= mostpc=rsuasivt tnvironmental wriltrs

Wilson E 0 1992 nJt Dipersity of Lift London PtnguinA beautiful piece of science writing for the Ia)middot person by a kading biologist

62 The Biosphere

Pandas plants and parks conserving biodiversityin China

China is both the worlds most populous country and an important storehouseof global biodiversity The country is home to around 30000 species of plantsand around 400 species of mammals Exact statistics are hard to obtain but wedo know that there are many unique endemic species found in China such asthe well-known giant panda (Aiuropoda melanoleuca) In 1965 there were 19nature reserves covering 6500 sq km (007 per cent of the toral land area ofChina) In 1991 there were 708 reserves covering 560000 sq km or 583 percent of the total land aru

The history of nature conservation and the preservation of biodiversity inChina reflects the changing social economic and political conditions prevailingin the country Before 1944 China had a patchy history of nature conservationas rulers established parkland hunting grounds gardens and temple areas Manytemple lands and sacred sites acted as biodiversity reserves

The first modern nature reserve in China was established in 1956 in theDinghu Subtropical Mountain Forest in Guandong Province (Freedman 1995)The mountain was the sice of an ancient Buddhist temple and so had alreadyreceived much protection Two-thirds of the reserves 1200 hectares had beenplanted with pine or subjected to other land usc modifications In 1980 it wasincorporated into the International Biosphere Network It is now a major touristdestination with up to 700000 visitors a year

Table 119 shows that most nature reserves were not established until after1980 when Chinas nature conservation laws began to multiply By 1989 379vertebrate species and 389 plant species received official protection in China Bythe early 1990s 13 nature reserves were devoted to the conservation and protecshytion of the giant panda and even more are planned

Hunting poaching and traditional medicine are great threats to biodiversityconservation in China In 1990 the country was the worlds largest exporter ofcat and reptile skins and live orchids Immense indirect threats are also posedto biodiversity by the development of industry agriculture transport and urbanareas Although China has made great attempts to conserve biodiversity like allcountries its nature conStrvation programme faces many problems

bull The distribution of nature reserves is uneven (figure ILIl)bull Administration is of uneven qualitybull Many nature reserves arc too small to be ecologically effectivebull Nature conservation laws are not rigorously enforcedbull Environmental education in people living near nature reserves is low and

planners do not consider the economic concerns of these people sufficientlybull Tourism has placed an additional stress on many nature reserves

Biodiversity and Extinctions 63

Table 119 Nature reserves In the Peoples Republic of Chinbullbull 1965-1991

Year No of reserves

1965 191978 341980 721983 2621985 3101987 4811991 708

Total area of reserves(000 sq km)

6512616

156167237560

of totaf area ofcountry covered by reserves

007013017162174247583

Source Edmonds (1994) table 82

Figure 1112 The distribution of nature reserves in ChinaSource Edmonds (1994) figure 83

Further reading

Edmonds R L 1994 Parterns ofChjnas Lost Harmony A Survey of the Counshytrys Environmental Degradation and Protection London Routledge

64 Th~ Biospher~

11 INTRODUCfIONS

INVASIONS AND

EXPLOSIONS

Humans are gr~at transporters of otherorganisms whether deliberately or accidenshytally Thus many organisms hav~ arrivedin areas where they did not naturally occurThis applies both to plants and to animals

Di Castri (1989) has identified thr~e

main stages in the process of biologicalinvasions stimulated by human actions Thefirst stage covers several millennia lip toabout AD 1500 During this periodhuman historical events favoured invasionsItld migrations primarily within the OldWorld The second stage began aboutAD 1500 At this time the explorltion

discovery and colonization of new territorshyi~s began in earnest and the globalizationof ~xchang~s got under way During thisphase which lasted for about 350 y~ars

invasions occurred from to and withinth~ Old World The third stage whichonly covers the last 100 to 150 years hasseen a rapidly increasing rate of exchangesand an even more extensive multifocalglobalization with Europe taking a lesscentral place

Plants that have been deliberately introshyduced to a new location can be dividedinto two groups (I) an economic groupwhich consists of crops timber trees andcover plants for control of erosion~ and(2) an ornamental or amenity group whichconsists of plants introduced out of curishyosity or because of their decorative value

Plate 1110 The remarkable Fynbos heathland of the Cape Province of SouthAfrica is rich in species many of which are endemic A major threat to the Fynbosis posed by the spread of invasive plants introduced from Australia In thisexample it is being encroached upon from the rear by Acacia cyclops(A S Goudie)

Introductions Invasions Explosions 6S

Table 1110 Allen plant species on oceanic Islands

Island No of naUve No of alien of alienspecies spedes species in flora

New Zealand 1200 1700 586Campbell Island 128 81 390South Georgia 26 54 675Kerguelen 29 33 532Tristan da Cunha 70 97 586Falklands 160 89 357TIerra del Fuego 430 128 230

SOUfce From data In Moore (1983)

A major role in such deliberate introdshyuctions was played by botanic gardensboth th~ in Europe and those in thecolonial territories from thc sixteenthcentury onwards

Mants that have becn accidentally disshy~rsed have arrived in a variety of waysby adhercnce to individual people or theirmeans of transport among crop seedfodder or packing materials and as a comshyponcnt of transponed soil ballast roadmetal or minerals

Introduccd plants are capable of inshyvading areas to which they have beenintroduced cven to the extent of causingso-called ecological explosions Theyprove to be so successful in their newhabitat that they expand in range andnumbers to the detriment of the nativespecies The same applies to introducedplant pathogens In Britain for instancemany elm trees have died sincc the 1970sbecauS( of the accidental introduction ofthc Dutch elm disease fungus on timberimportcd through certain ports in southshycrn England In thc USA thc Americanchestnut was almost eliminated in less thanSO years following the introduction ofthe chestnut blight fungus from Asia latein the 1890$ In western Australia thegreat jarrah fOteSts have been invaded anddecimated by a root fungus which was

probably introduced on diseased nurserymaterial from eastern Australia

Occan islands have oncn been particUshylarly vulnerable to invasions The simplicshyity of their ecosystems inevitably Icads tolower stability Introduced species oltenfind that the relative lack of competitionenables them to spread into a wider rangeof habitats than they could on the continshyents Moreover because the naturl1 speshycies inhabiting remote islands have cometo be there primarily because of their abilshyity to disperse over large distances theyhave not necessarily been dominant or evcnhighly successful in their original continshyental setting Therefore introduced speshycies may be more vigorous and effectiveThere may also be a lack of indigenousspecies to adapt to conditions such as bareground caused by humans This enablesintroduced weeds to establish themselves

Table 1110 illustrates dearly how prominshyent alien specics have become among theflora of some islands The percentage ofintroduced plants varies between aboutone-quarter ilnd two-thirds of the tOtalnumber of species present

Another type of ecological explosioncan be cauS(d by human-induced habitatchange Some of the most striking examshyples are associated with the establishmentof artificial lakes behind dams in place of

66 The Biosphere

rivers Riverine species which cannot copewith the changed fluvial conditions tendto disappear Others that can exploit thenew sources of food and reproduce thcmmiddotselves under thl new conditions multiplyrapidly in the absence ofcompetition Vegshyetation on land flooded as the lake watersrise decomposes to providc a rich supplyof nutrients This allows explosive outshygrowth of organisms as the new lake fillsIn particular floating plants may formdense mats of vegetation which in turnsupport large populations of invertebrateanimals These may cause fish to die bydeoxygenating the water and can create aserious nuisance for turbines naviguorsand fishermen On Lake Kariba in CentralAfrica the communities of the SouthAmerican water fern (SAvinia molestll)bladder-wort (UtriJ4iAria) and the Afrishycan water lettuce (Pittill stratious) grewdramatically and on the Nile behind theJebel Aulia Dam there was a huge increasein the number of water hyacinths (Eihshyhornill musipes)

Various human activities including dearshying foresr cultivating depositing rubbishand many others have opened up a wholerange of environments which are favourshyable to colonization by a particular groupof plants Such plants which arc notintroduced intentionally arc generallythought of as weeds

Animals have been deliberately introshyduced to new areas for many reasons forfood for sport for revenue for sentimentfor control of other pests and for aesmiddotthetic purposes Such dclibcrare actionsprobably account for insunce for thewidespread distribution of trout

There have also been many accidenulintroductions especially since the develshyopment of ocean-going vessels These arcbecoming more frequent for whereas inthe eighteenth century there were fewocean-going vessels of more than 300tonnes today there arc thousands Because

of this in the words ofC S Elton (1958p_ 31) we arc seeing one of the greathistorical convulsions in the worlds faunaand flora Indeed many animals arc inshytroduced with vegetable products for justas trade followed the flag so animals havefollowed the plants

A recent example of the spread of anintroduced insect in the Americas is promiddotvided by the Mricanizcd honey bee Anumber of these were brought to Brazilfrom South Mrica in 1957 as an experishyment and some escaped Since thenthey have moved northwards to CentralAmerica and Texas (figure 1113) spreadshying at a rate of 300-500 kIn per year andcompeting with established populations ofEuropean honey bees

Some animals arrive accidenrally withother beasts that arc imported deliberatelyIn nonhern AusmIia for instance waterbuffilo were introduced They brought withthem their own bloodsucking fly a specieswhich bred in cattle dung and transmittedan organism sometimes fatal to caweAwtralias native dung beetles accustomedonly to the small sheep-like pellets of thegrazing marsupials could not tackle thelarge dung pats of the bufhlo Thw unmiddottouched pats abounded and the flies wereable to brecd undisturbed EventuallyMrican dung beetles were introduced tocompete with the flies

Domesticated plants have in most casesbeen unable to survive without humanhelp The same is not so true of domesshyticated animals There arc a great manyexamples of cattle hones donkeys andgoats which have effectively adapted to newenvironments and have become virtuallywild (feral) Frequently pigs and rabbitsthat have esublished themselves in this wayhave owted native animals Feral animalsmay also panicularly on ocean isJandscause dcscni6cation Fern goats for exmiddotample have degraded the Channel Islandsoff the California coast

Introductions Invasions Explosions 67

Figure 1113 The spread of the Africanized honey bee in the Americas between1957 (when it was introduced into Brazilgt and 1990Source Modified after Texas Agricultural Experiment Station in Christian Science MonitorSeptember 1991

Aquatic life can be spread accidentallythrough human alteration of waterwaysand by the construction of canals whichenables organisms to spread from onesea or one lake to another This processis called Lessepsian migration after thename of the man who built the Suez Canal

FURTHER READING

The construction of that great watershyway has enabled the exchange of animalsbetween the Red Sea and the easternMediterranean The migrants include amenacing jellyfish which has now inshyvaded beaches on the eastern shore of theMediterranean

Drake] A (ed) 1989 Biological Invasions A Global Perspective Chichester WileyAn advanced collection of edited papers

Elton C S 1958 The Ecology ofInvasions by PiRtI ad Animals London MethuenThe classic monograph on this theme

68 The Biosphere

Alien plant species invading Kakadu National ParkAustralia

N

tNORTHERN fERRlTORY

bull 10

The Kakadu National Park is a UNESCO World Heritage Site in the monsoonaltropical north of Australia containing most of the catchment of the South Alshyligator River The natural vegetation is mainly savanna woodland and open forestdominated by eucalyptus There are also extensive alluvial floodplains seasonshyally water-covered where herbaceous wetland vegetation grows Out of 1526plant species found here some 58 per cent (89 species) are considered to beinvasive (Corrie and Werner 1993) Most of these are weedy annuals from theNew World tropics Although this percentage of introduced species is low comshypared with the figure for the whole of Australia (10 per cent of all plant speciesare invasive) it is clearly a cause of worry for a nature reserve which is attractingan increasing number of visitors

Invasions have increased by an average of 16 species per year since 1948 astourism and mining have increased bringing in more habitat disturbance Mostalien species are found around camp-sites car parks roads and mines One of thebiggest problems is a fast-growing shrub (MimoJa pjgra) This plant was introshyduced deliberately into the Northern Territory from South America and was notrealized to be a serious nuisance until around 80 years later It has spread overthe alluvial floodplains changing herbaceous swamps into shrublands This inturn affects wildlife There has been a major effort to control the plant

There are also many other indirect ways in which alien plant species are spreadhere Feral water buffaloes for example make a major contribution to invasionsnear floodplains as they disturb the ground

Further reading

Kirkpatrick J 1994 A Continent Tramformed Melbourne Oxford University PressA concise discussion of human impacts on the natural vegetation of Australia

12 HABITAT Loss AND

FRAGMENTATION

One of the conscquences of human activshyitia is that many naturaJ habitats bc=comereducro in extent and also bc=come ampagshymented into isolated patches Figure 1114shows how both these processc=s haveoccurred in the forest cover of a part ofcentraJ England in the last 1500 yearsWhereas at the end of Romano- Britishtimes (AD 400) there were still large exshypanses of forest there are now only verysmall islands of forest in a sea of agriculshytural land

Certain types of habitat may be lostbecausc= of changes in agriculturaJ pracshytica In Britain for example the botanishycal diversity of much pastureland has been

Figure 1114 Forest fragmentation inWarwickshire England from AD 400 to1960 Forested areas are shown inbladeSource Wikove et aI (1986) figure 1

Habitat loss and Fragmentation 69

reduced as many old meadows have bunreplaced with fields planted solely withgrass (leys) or treated with selective hershybicides and fertiliurs This treatment cantake out of the habitat some of the basicrequirements essc=ntial for many speciesFor exampk the larva of the commonblue bunerfly (Polyommatus jcarus) feedsupon birds-foot trefoil (Lotus cornjeulshyaoo) This plant disappears when pastureis ploughed and converted into a grassfidd or when it is treated with a selectiveherbicide Once the plant has gone thebutterfly vanishes too because it is notadapted to feeding on the plants grown inleys of improved pasture Likewise numshybers of the large blue butterfly (Maculjneaarion) have decreased in Britain Its larvaelive solely on the wild thyme (Thymustiruul a plant which thrives on doseshycropped grassland Since the decimarionof the rabbit by myxomatosis conditionsfor the thyme have been less favourable50 that both the thyme and the large bluebutterfly have declined

Another major land-usc change of reshycent decades has been the replacement ofnatural oak-dominated woodlands in Britshyain and e1sewhere by conifer plantationsThis also has implications fOr wildlife Ithas been estimated that where this changehas totken place the numbc=r of species ofbirds found has been approximately halvedLikewisc the replacement of upland sheepwalks with conifer plantations in southern$corland and northern England has led toa sharp decline in numbers of ravens Theraven (Corvus eorax) feeds on carrionmuch ofwhich it obtains from open sheepcountry Other birds mat have sufferedfrom moorland areas being planted withforest trees are scera1 types of waderthe golden eagle peregrine falcons andbuzzards

Many species of birds in Britain havedeclined in numbers over the last twO deshycades because of habitat changes resulting

70 Thc Biosphere

from more intensive fuming methodsTheS( include no longer leaving fallowsless mixed farming ncw crops modernfarm management uS( of biocides andhedgerow removal

Reducing the areas of land covered byparticular habitats has a direct impact onthe fortunes of species It is usdul to secthe remaining fragments of habitat asislands We know from many of the classicstudies in true island biogeography thatthe number of species living al a particularlocation is related to its area Islands supshypurt fewer species than do similar areasof mainland and small islands have fewerspecies than do large ones Thus it maywell lollow that if humans destroy thegreuer part of a vaSI belt of natural forestleaving just a small reserve initially it willbe middotsupemnlrated with species containshying more than is appropriate to its areaunder nuural conditons Since there willbe tCwer individuals of each of the speciesliving in the forest now the extinction rat(will increase and the number of specieswill decline For this reason it is a soundprinciple to make rescrves as large as posshysible A large reserv( will support mor(species by allowing the existence of brgerpopulations and keeping extinction rateslower Size of course is not everythingand other factors such as the shape ofreserves and the existence of links betweenreserves arc also important

Reduction in area of habitat leads to

reduction in numbers of organisms Thisin turn can lead to genetic impoverishmiddotment through inbreeding with particuJarlymarked effect on reproductive performshyance [nbrttding degenention is howevernot the only effect of small populationsize In the longer term the depletion ofgenetic variety is more serious since itreduces the capacity for adaptive changeIt is therefore very important to provideenough space especially for th~ animalsthat require large expanses of territory For

example the population density of the wolfis arout one adult per 20 sq km and ithas been caJculaled thal for a viable popushylation to exist one mighr need 600 indishyviduals ranging over an area of 12000sq km The significance of this is apparentwhen onc realizes that most narure reshyserves art small 93 per cent of the worldsnational parks and reserves havc an arealess than 5000 sq km and 78 per centcover less than 1000 sq km

Habitat fragmentation has SOffiC othtrmajor clTects One of these is loss of habimiddottat heterogeneity In other words indiovidual fragments may lack the full rangeof ditlcrcnt habitats found in the originalblock For insnnce a small patch ofwoodmay not contain a reliable water supplyLikewise sollle species - certain amphibshyians for example - require two or morehabitat lypCs Habitat fragmtntation maymake it impossible for these animals tomove between habitats

A second effect of fragmentation is thatthe new landscape that replaces the orishyginal habitat such as human setdementsor agricultural land may act as a barrierpreventing colonization and interchangebetween groups Also the new landscapesmay enable populations to build up ofanimals that arc harmful to species withinthese fragments

A third consequence of fragmentationis what are called edge effects Some anishymals do well in edge habitats that is theboundary areas around the rim of theisland but others suffer For examplemany nest predators occur in higher denmiddotsities around forest edges

A fourth effect is secondary extinctionsFragmentation disrupts many of the imshyporum ecological interactions of a comshymunity For example small woodlandwands in the eastern USA contain few ifany of the large predators (eg mountainlions) that would nonnally regulate thenumber ofsmaUcr omnivorous species (eg

racoon) Th~ omnivores can thus preyunhindered upon the eggs and young of

FURTHER REAoING

Habitat Loss and Fragmentation 71

the forest songbirds and may wi~ themout

Wilcove D S McLellan C H and Dobson A P 1986 Habitat fngmemation inthe temperate zone In M E Soule (cd) OmserJl4tion Biology The Science ofSc4rcityand DiJlenity pp 251-6 Sunderland Massmiddot Sinauer AssociatesA short but useful chapter in an advanced book

Plate 1111 A flock of Lesser Snow Geese (NHPARobert Erwin)

_72 The Biosphere

Texas Gulf coast habitat changes and the LesserSnow GooseThe changing fortunes of the LesserSnow ~ (Chen caeruJescenscRerulmens) population in Tnasshow interesting links betweenhabitat changes and wildlife Presshyently around 600000-850000Lesser Snow Geese winter here everyyear (Robertson and Slack 1995)Until the 1920s the Lesser SnowGeese wintered mainly on coastalmarshes but now they arc found onthe inland prairie as well

During the twentieth century theTexas Gulf coast has secn the rise ofpetroleum rdining and oil extractionindustries coupled with the spreadof rice cultivation and a boom inpopulation Nearly 50 per cent ofthe entire USAs chemical producshytion is bascd in the Houston areaand 73 per cent of the US petroshyleum industry is there Rice cultivashytion peaked at 254800 hectares in1954 and now covers an a~a ofaround 141000 hectares These diverse changes to the landscape have causedsome areas to become more suitable for the Lesser Snow Goose while other areashave become less attractive in terms of availability of food and water

The wintering grounds of the Lesser Snow Goose spread to the prairies beshytween the 1920s and the 19505 following the spread of rice cultivation althoughthe movement of the birds lagged behind the expansion of the ricefields by someyears These changes may also have been encouraged by alterations to the coastalmarsh areas as urban and industrial development from the 1940s onwards led tomarsh drainage and pollution

The changes in wintering range were accompanied by a growth in populationnumbers the Lesser Snow Goose population peaked at around 813000 in theearly 1980$ Since then numbers have declined in association with declining riceproduction (the area sown with rice declined by a third from 1978 to 1991) Thisdecline in rice cultivation was in tum related to the lack of federal price supportSfor rice growers which made other crops more economicaUy viable

An airpon planned for construction on Katy Plains would afkct 1168 hecuresdirectly and 16)00 hectares indirectly This project will have further impacts onthe distribution and population numbers of the Texan Lesser Snow Geese

Extinctions in the Past 73

13 EXTINcrIONS IN THE PAST

Extinctions are nothing new They are apart of evolution and spasms of extincshytion have recurred through geologicaltime There have been five major massglobal extinctions over the last 600 milshylion years (figure IU5) The last of theseoccurred at the boundary between theCretaceous and Tertiary periods about66 million years ago This was when theextinction of the dinosaurs took placepossibly because of the environmentalimpact ofa massive meteorite crashing intothe Earth or perhaps because of somemajor volcanic eruptions The other massextinctions took place in earlier periodsthe Ordovician (440 million years ago)the Devonian (365 million years ago) thePermian (245 million years ago) and theTriassic (210 million years ago)

We arc now living in a sixth spasm ofmass global extinction This started toshywards the end of the Icc Age (round about11000 years ago) and is accelerating at

the present time Humans are implicatedin this sixth spasm though for prehistorictimes there is a major controversy as towhether the wave ofextinctions might havea natural (ie essentially climatic) cause

We have discussed present-day exshytinctions and their causes in section 10above on biodiversity In this section wewill explore the role of our prehistoricforebears in causing the decline and exshytinction of many species of animal

Over the last 30 years Paul Martin andco-workers have argued that Late Pleisshytocene extinctions closely followed thechronology of the spread of prehistorichuman cultures and the development ofbig-game hunting technology They wouldargue that there are no known continentsor islands in which accelerated extinctiondefinitely pre-dates the arrival of substanshytial numbers of humans They would alsoargue that the temporal pattern ofextinctions of large land mammals (themegafauna) follows in the footsteps ofStone Age humans They suggest that

~

Iz Iz z z

~~ ~ gt

~ lt I~

I~ ~

sect ~ ~ i ~~bull ii bull6 0 ~

I~pound ei~

~

B~ ]z

~ bull 500 bullMiI1iom of)laI1 ago

Figure 1115 Graph shOWing the five mass global extinctions of marine organisms(indicated by lightning flashes)Source Wilson (1992)

74 The Biosphere

Plate 1112 A reconstruction of mammoth being hunted in Europe at the end ofthe Ice Age Mammoths were one of the megafauna that became extinct at thetransition from the Pleistocene to the Holocene Was climatic change the cause orthe hunting activities of our ancestors (Natural History Museum london)

Mrica and parts ofsouthern Asia were firstaffected in this way with substantial lossesaround 200000 years ago North andSouth America were stripped of large hershybivores between 12000 and 10000 yearsago Extinctions extended into the Holoshycene (ie the last 10000 years or so) onocean islands where humans arrived lateon the scene (figure IIl6)

There were three main types of humanpressure involved in what is sometimescalled Pleistocene overkill

bull the blitzkrieg effect when humanpopulations with big-game huntingtechnology spread rapidly so that anishymal populations decline very quickly

bull the innovation effect when longshyestablished human population groupsadopt new hunting technologies andwipe out fauna that have already beenstressed by climatic changes

bull the attrition effect when extinctiontakes place relatively slowly after a longhistory of human activity because ofloss of habitat and competition forresources

What are the arguments that can bemarshalled in favour of this anthroposhygenic hypothesis First in areas like theHigh Plains of America the first massiveextinctions appear to coincide with thearrival of humans who were numerousenough and who had sufficient technoshylogical skills to be able to kill large numshybers ofanimals Secondly the vast numberof bones at some Late Pleistocene archaeoshylogical sites attests to the efficiency of themore advanced Stone Age hunters Thirdlymany animals unfamiliar with people areremarkably tame and naIve in their presshyence rendering them easy prey Fourthlyin addition to hunting animals to death

~~~~~lOllOOOO JOOOOO 10000 1000 100

YtlllUIO

Figure 1116 The percentage survival oflarge animals and flightless birds overthe last million years in four differentareas The extinction of these organismscoincided doseo with the arrival ofhumans in North America MadagascaIand New Zealand and less decisively inAustralia In Africa where humans andanimals evolved together for millions ofyears the damage was less severeSource Wilson (1992)

humans may also have competed withthem for particular food or water suppliesFifthly the supposed extinction of thelarger rather than the smaller mammalscould be related to thc= effc=cLS of humanprc=dation Large mammals havc= smallnumbers of offspring long gaution pc=rishyOOs and long periods before manlrity isreached This means that populations ofthese animals can survive only a very lowrate of slaughter ~en against primitivehunters

In addition cc=rtain objections havc= beenlc=velled against the climatic change model

Extinctions in the Past 75

which tend to support the anthropogenicmodel It has been suggested for instancethat changa in climatic zones arc gc=nershyally gradual enough to allow bcasLS to folshylow the shifting vegetation and climaticzones of their choice Similar environmentsarc available in North America today aswere present in different locations amiin different proportions during lIt(Pleistocene times Sccondl~ it can beargued that the climatic changes associmiddotated with the multiple glaciationsintugladals pluvials and interpluvialsearlier in the Icc Age do not seem [0 h3Ccaused the same striking degree of sjXcklgtelimination as the changes in the LattPleistoc~n~ A third difficulty with thec1imati cause theory is that animals likethe mammoth occupied a broad range ofhabitats from Arctic to tropical latitudesso that it is unlikely that all would perishas a result of a climatic chang~

However thc=re is some support for thealt~rnative climatic hypoth~sis namely thatrapid and substantial climatic change atthe end of the last Icc Age led to th~

extinction of the great mammals lik~ themammoth The migration of animals inresponse to the npid climatic change atthe cnd of the Pleistocene could bc haludby geographical barriers such as highmountain ranges or seas According to thispoint of view Africa is rclativc=ly rich inbig mammalian fauna because thc Africanbiota is not or was not greatly r~stricted

by any insupc=rable geographical barrierAnother way in which climatic chang~

could cause extinction is through its influshyence on the spread of disease It has beensuggested that during g1acials animalswould bc split intO sepal2te groups CUtoff from one another by ice sheets Theseisolated groups might lose immunity tocertain diseases to which they werc= nolonger exposed Then as the ice melted(before 1lOOO years ago in many areas)contacts bctwcen group5 would once again

76 The Biosphere

be made enabling any diseases to whichimmunity had been lost to spread rapidly

It has also been noted recently that insome areas it was not only the greatmegafauna that became extinct Some smallanimals and birds that would not have beenhunted by humans also died out Moreshyover as the radiocarbon dates for earlysocieties in some countries like Australiaand Brazil are pushed back it becomesincreasingly clear that humans and severalspecies of megafauna were living togethertor quite long periods This is underminshying the idea of rapid overkill Mso ifhumans were primarily responsible for thewaves of extinction how does one explainthe survival of many big game species in

FURTHER READING

North America well imo the nineteenthcemury~

The Late Pleistocene extinctions mayof course have been caused by bothclimatic and anthropogenic mechanismsor by a combination of the two types Forexample animal populations reduced andstressed by climatic change would be morevulnerable to increasing levels of humanpredation Nonetheless the rapidity withwhich extinctions took place in Madagasshycar New Zealand and the Pacific islandsafter they wete first settled in the Holoceneis striking evidence ofhow even quite smallnumbers of technologically not vetyadvanced people can cause major environshymental change

14 BIOTECHNOLOGY GENETIC

ENGINEERING AND THE

ENVIRONMENT

Biotechnology is the manipulation of livshying organisms and their components (eggenes or gene components) for specifictasks Genetic engineering is one form ofbimechnology involving the isolation ofgenes and gene components that conferdesired traits and their transfer betweenspecies It is also sometimes called recomshybinant DNA technology This branch ofscience has now reached a level where it ispossible to transfer genes between unnshylated species or types of organisms

There are many applications of biotechshynology that arc ofenvironmental relevancein agriculture resource recovery and re-

Ehrlich P R and Ehrlich A H 1982 Extinetiol London GollanczAn accessible treatment for the general reader

Martin P S and Klein R G 1984 Pleistocene Extinctions Tucson University ofArizona PressA massive advanced tome from two of the leading scientists involved in the study ofthe possible role of humans in causing extinctions in prehistory

cycling pollution abatement and the proshyduction of renewable energy resources

In agriculture biotechnology can helpto maximize energy and nutrient flowsfor example by increasing crop yield andby engineering resistance to disease inshysects and herbicides Nitrate levels can beenhanced by seeding the ground withnitrogen-fixing bacteria Stress tolerance(eg to frost) can be engineered

Biotechnology is also being developedto undertake the recovery of resourcesMineral orcs can be recovered through aprocess called biomining which exploitsthe ability of specific types of bacteria toobtain their energy supply by breakingdown certain types of ore-bearing deposmiddotits Certain micro-organisms can be emshyployed to scavenge metals from wastewaterso that the metals can be re-used

Biotechnology can also contribute topollution aba~ment Bioscnsors areorganisms that can be used to identifY critishycal levels of poUution Other organismscan be uscd to extract pollutants such asheavy metals from wastewater to neutralshyize hazardous substances in the environshyment (bioremediation) or to break downscwage

Another usc of biotechnology is to produce renewable energy resources For exshyample it is possible to extract alcohol fromsome plants this call be used as fuel forautomobiles Protein-rich animal feeds canbe obtained by using algae fungi (indudshying yeasts) and some bacteria to producecellular protein from energy and nutrientsources such as carbon dioxide methanolethanol sugars and carbohydrates

Biotechnology is potentially ofenormousvalue and it may have many environmenshytal benefits For example the environmenshytal advantages of using biotechnology inagriculture include

FURTHER READING

Conclusions 77

bull reduced need for fuelbull reduced usc of pesticidesbull reduced usc of artificial fertilizer thus

also lessening pollution by phosphatesand nitrates

bull increased food supply which could leadto less pressure on marginal lands andon remaining natural ecosystems

Similar types of advantages can apply tothe other uses of biotechnology which wehave described

On the other hand there are possibledisadvantages These include

bull the potential to create invasive organshyisms - as for instance when genesescape into the wild relative of an enshygineered crop creating potential pests

bull the potential to create organisms whichare toxic or contain toxic components

bull the potential to create organisms espeshycially bacteria that could profoundlyalter the nature of global biogeoshychemical cycles

Mannion A M 1991 Global Environmental Change Harlow LongmanA very general but useful treatment of all aspects of global change both natural andanthropogenic

Mannion A M) 1995 Agriculture and Enviroilmental Change Chichester WileyA more detailed treatment by the same author of biotechnology as one aspect of theagricultural impact on the environment

15 CONCLUSIONS

In this chapter we have demonstrated thathumans have had effects on the biospherefor a very long time For many good reamiddotsons our early ancestors developed the useof fire This powerful technological toolhas had many positive ecological conseshyquences It may also have had a majoreffect on some of the worlds biomes andvegetation types induding savannas andMediterranean shrublands The manage-

ment of fire is an important tool for themanagement ofsome major environmentsAs the Yellowstone study has shown firesuppression policies can have adverseeffects

Other major changes in the state of theworlds biomes include desertification anddeforestation Both phenomena are diffishycult to define and to quantifY There arcvarious ways in which desert margins andrain forests can be managed so that theseprocesses can be kept under control Even

78 The Biosphere

secondary forests which result from humanuse of tropical moist forests have positivevalue

With many such changes however wehave to recognize that very many proshycesses both anthropogenic and naturalmay have played an important role Thisis evident from a consideration of theorigin of tropical savannas heathlands andmid-latitude grasslands Indeed we haveseen recently how complex causes can bein the case of forest decline in Europe Aswe point out thete is no single type ofInrest damage and no single cause Equallywe should not necessarily equate urbanshyization with a reduction in biodiversity Thegrowth of dties as illustrated by Chicagohas major ecological consequences bur notall of them have negative impacts

Nonetheless there are some major habishytats and particular habitat types that deshyserve particular attention and protectionbecause of their importance for the preshyservation of biodiversity These indudewetlands and other crucial ecological hotspots such as the Fynbos heathlands ofsouthern Mrica or the forests inhabited

KEy TERMS AND CONCEPTS

biodiversiry biodiversity hot spotsbiomass burningbiotechnologydeforestationdesertificationecological explosionecosystem servicesecotonesedaphic conditionfufire suppressionforest decline and diebaekhabitatheathland

by the Giant Panda in China Many habishytats arc being considerably modified bythe spread of organisms introduced byhumans These organisms may then invadesusceptible habitats of which oceanicislands are a notable example Many otherhabitats are being greatly reduced in areaand continuity This creation of smallltislands of habitat increases the likelihoodof species extinctions Extinction is an irshyreversible process which results from bothnatural and anthropogenic causes It is oneof the great challenges we face in comingdecades

We are emering a new era in the humanmanipulation of the biosphere Biotechshynology and genetic engineering both offergreat opportunities and raise a great needlor prudence

The many case studies discussed in thispart of the book show how complex hushyman impacts on the biosphere are howscience cannot as yet answer all the quesshytions and how the many different presshysures on human societies affect the waysin which they use and abuse the resourcesof the biosphere

invasionskeystone speciesLessepsian migrationmegafaunaovercultivationovergrazingPleistocene overkillprescribed burningsalinizationsavannasecondary focestspecies diversityurban ecologywetlandswilderness

Points for Rl=view 79

POINTS FOR REVlEW

hat do you undefSlilnd by the term biosphete~

Why was fire one of humankinds first technological achievements~

ShouJd fires Ix suppresscd~

How would you identify if desertification was raking place~

How might you aim 10 reduce the effects of desertification~

In what ways might tropical deforestation rates be reduceJ~

gtltscss the role of predisposing causal resulting and maintaining tactors ill thedevelopment of grasslands savannas and heathlands

Discuss the many different factors that could account for lorest declinc

What characteristics of cities determine their impact on the environment

Why and how should wlt1ands be conserved

What do you understand by the term biodiversity~

What arguments would you use to support the view that biodiversity lgthOlild Illmaintained

Why should we be interested in ecological invasions and explosions~

What do you understand by the term habitat~

Did climatic change or human impact cause Pleistocene eXlinctions~

Consider the potential role of biotechnology in environmental prorCluon JnJdegradation

PART III

The Atmosphere1 Inrroduction 832 Amhropogenic Climate Change

bull The Role ofAerosols 83The dust bowl ifI

bull The GulfWar oil lites hype and reality 883 Anthropogenic Climate Change

bull The Role of Land Cover Changes 904 The Enhanced Greenhouse Effect

and Global Warming 92bull Global warming and UK agrigculture 97

5 Urban Climates 98bull The implications ofsome urban heat islands 100

6 Urban Air Pollution 102bull Air pollution in South African cities

the legacy ofapanheid 1087 Ozone Depletion and Ozone Pollution 1108 Acid Deposition 1169 Conclusion 120

Key Tenus and Concepts 121Points for Review 121

Aerosols 83

2 ANTHROPOGENIC CLIMATE

CHANGE ThE ROLE OF

AEROSOLS

Let us first consider the possible effects ofaerosols An aerosol is defined as an intimatemixture of two substances one of whichis in the liquid or solid state disperseduniformly within a gas_ The tcnn is normallyused to describe smokecondensation nuclei

and nitrous oxide (the greenhouse gases)play in global wurning There are howeverother mechanisms by which humans maycause global or regional climatic changeThey are not yet fully understood and inthe long term they may not have so greatan impact as the greenhouse gases Nevcrshytheless they may have a significant role toplay In some cases morcovn they couldscrve to counteract the greenhouse ctrect Incertain specific localities they may alreadybe producing a decipherable climatic trend

The mechanisms so far idenrificd thatmay be related to human innuenccs onglobal and regional climates and their maineffeclS can be summarized as follows

Greenhousegases

bull Gas emissionsCarbon dioxideMethaneChlorofluorocarbonsNitrous oxide

bull Aerosol BeneratwnDustSmokeSulphates

bull Therntal poUuti01lUrban heat generation

bull Albedo changeDust addition to icc capsDeforestation and afforestationOvergrazingExtension of irrigation

bull Altrltion of watr flow il rivers andoceansWater vapour changeDeforestationIrrigation

bull

When me gn~at American geographer andconservationist George Perkins Marshwrote Man and Natllr in 1864 (~e partIV section 3) in which he surveyed theways in which humankind had transformedthe Earths surface he scarcely consideredthe various ways in which humans mightaffect the quality of the atmosphere andthe nature of the Earths climate Howshyever just over 100 years later it is thisvery area that is the cause of greatest conshycern to many scientists and to others inshyterested in environmental matters To besure loatl air pollution was a major conshycern at the time Marsh wrote but for themost part broader-scale human impactson the atmosphere and climate were notgiven very much attention

Since the mid-nineteenth century whenMarsh wrote his book world industrialproduction and energy consumption haveaccelerated dramatically All sorts of newtechnologies including noably the intershynal combustion engine have been inuoshyduced As a consequence a cocktail ofgases that is growing in quantity and varishyety has been emitted into the atmosphereThis has created problems of poor airquality which can affect not only humanhealth but also the state of whole ecosysshytems (for example by acid rain) and alsoof global climatic conditions (for exampleby the greenhouse effect) It is also apparshyent that changes in land use (such as deforshyestation) of the type discussed in part IIarc causing changes at the Earths surfacewhich may have impacts on the climateGreat unceruinty still surrounds many ofthese issues but there is no denying thatmatters such as global wanning oronedepletion and acid rain have very greatimplications that deserve intensive study

Recent years have ~en a great concenshytration of interest in the so-called greenshyhou~ effect (section 4 below) and therole that gases like carbon dioxide methane

1 INTRODUcrlON

84 The Atmosphere

freezing nuclei or fog contained within theatmosphere or other pollutants such asdroplets containing sulphur dioxide ornitrogen dioxide (Encyclopaedic Dictionshyary of Physical Geography 1985 p 6)Many atmospheric aerosols (eg thosederived from volcanoes sea spray or naturalfires) were not placed there by humansHowever humans have become increasshyingly capable of adding various aerosolsinto the air For example one consequenceof the industrial revolution has been theemission of hugely increased quantities ofdust or smoke particles into the loweratmosphere from industrial sources Thesecould influence global or regional tempershyatures through their impact on the scanershying and absorption of solar radiation

The exact effects of aerosols in the atmoshysphere are still not dear however yenhemeradded aerosols cause heating or cooling ofthe Earth and atmosphere systems dependsnot only on their intrinsic absorption andbackscatter characteristics but also on theirlocation in the atmosphere with respect tosuch variables as cloud cover cloud reflecshytivity and underlying surface reflectivitySo for example over ice caps grey aerosolparticles would warm the atmosphere beshycause they would be less reflective than thewhite snow surfuces beneath Over a darkersurface on the other hand they wouldreflect a greater amount of radiation leadshying to cooling Thus it is difficult to assessprecisely the effects of increased aerosolcontent in the atmosphere

Uncertainty is heightened because of thetwo contrasting tendencies ofdust the backshyscattering effect producing cooling andthe thermalmiddot blanketingeffect causing warmshying In the second of these dust absorbssome of the Earths thermal radiation thatwould otherwise escape to space and thenre-radiales a portion of this back to theland surface raising surface temperaturesNatural dust from volcanic emissions tendsto enter the stratosphere (where backshyscattering and cooling are the main con-

sequences) while anthropogenic dust morefrequently occurs in the lower levels ofthe atmosphere where it could cause thershymal blanketing and warming

Industrialization is not the only source ofparticles in the atmosphere nor is a changein temperature the only possible conseshyquence Intensive agricultural exploitationof desert margins such as in RajasthanIndia can create a dust pall in the atmoshysphere by exposing larger areas of surfacematerials to deflation in dust storms Thisdust pall can change atmospheric tempershyature enough to cause a reduction in conshyvection and thus in rainfall Observationsof dust levels over the Atlantic during thedrought years of the late 1960s and early1970s in the Sahel suggest that the deshygradation of land surfaces there led to athreefold increase in atmospheric dust atthat time It is thus possible for humanshyinduced desertification to generate dustwhich in turn increases the degree ofdesertification by reducing rainfall levels

Dust storms generated by deflation fromland surfaces with limited vegetation coveroccur frequently in the worlds drylandsThey happen naturally when strong windsattack dry and unvegetated sandy and siltysurfaces Their frequency also varies fromyear to year in response to fluctuations inrainfall and wind conditions At presenthowever in some parts of the world thedust entering the atmosphere as a result ofdust storms is increasing because of theeffects of human activity In particular proshycesses such as overgrazing which are partof the phenomenon of desertification (seepart II section 3) strip the protective vegetashytion cover from the soils surface Elsewheresurfaces may be rendered more susceptibleto wind attack because of ploughing ordisturbance by wheeled vehicles

Atmospheric aerosols can be an imporshytant source of cloud-condensation nucleiOver the worlds oceans a major source ofsuch aerosols is dimethylsulphide (DMS)This compound is produced by planktonic

algae in seawater and then oxidizes inthe atmosphere to form sulphate aerosolsBecause the albedo of clouds (and thusthe Earths radiation budget) is sensitiveto the density ofcloud-condensation nucleiany factor that has an impact on planktonicalgae may also have an important impacton climate The production ofsuch planktoncould be affected by water pollution incoastal seas or by global warming Charlsonet al (1992) believe that anthropogenicallyderied sulphate aerosols could significantlyincrease plamtary albedo through theirJirect scattering of shon-wavelength solarradiation and their modification of theshort-wave reflective properties of cloudsThus the~ could eXtTt a (Ooling influenceon the planet Charlson et al maintainthat this eflect could be as great as thecurrent hllmanmiddotillduccJ global warmingbut acting of coursc in the opposite waya~ global cooling

A nuckar conflict could produce the mostcatastrophic dlects of anthropogenic leroshysols in the atmosphere Explosion tire andwind might generate a great pall of smokellld dust in the atmosphere which wouldmake the world dark and cold It has beenestimated that if the exchange reached alevd of several thousand megatons a nushyclear wimer would occur in which temshyperatures over much of the world wouldbe depressed ro well below freezing point

Fears were also expressed that the heavysmoke palls generated by oil-well fires inthe Gulf War of 1991 might have seriousclimatic impacts The actual ctlccts arc stillnotckar Howevt=r preliminary studies havesuggested that because most of the smokegenerated by the oil-well fires stayed in thelower troposphere and remaineJ in the airfor only a shon time the eflects (some coolshying) were local rather than global It alsoseems that the operation of the South Asianmonsoon was not significantly affected

Although some of this discussion of theeffects of aerosols in the atmosphere isspeculative at the global scale this is not

Aerosols 85

so at the more local scale where it is clearthat human actions can change levels ofvisibility This is especially true in urbanareas where the concentration of Iightshyscanering and light-absorbing aerosols inthe atmosphere is greatest For examplebefore the Clean Air Acts (most notablythose passed in 1956 and 1968) LondonsuHered some severe smogs that reductJvisibility to a few metres and killed thoushysands of people (eg in the winter of1952) Reduced burning of coal since theClean Air Acts has cut down smoke emisshysions improving visibility in many pans ofBritain Fogs have become much rarer overthe last three decades

Sulphate emissions ftom cOlI-fired powerstations have also btin riduced An analvshysis ofchanges in visibility at a largi numberof sites in the UK shows that oetwecn1962 and 1990 the median atmosphericisioility has improved ti-om 109 kill to

260 km (Lee 1994) Figure IIIl showsthe number of days per ~ear when tl)goccurred in Britain over the period 1950shy83 It is clear that although the ti-equellcyof fogs has not changed a great deal incoastal areas (where they arc largely anatural phenomenon) ill the inland inshydustrial heartland they have declined verysubstantially as a result of Clean Air legismiddotlation and changes in industrial technology

The total suspended particulates (TSP)is the total mass of aerosol particles pervolume of air (usually measured in Ilg perCll metre of air) or this TSr much recemconcern has IOclised on the respirable susshypended particulates (RSP) panicles withdiameters of less than 10 11m (also knownas PM10s) These small particles arc theonly ones which can be deposited in therespiratory system - lungs and bronchialtubes - as larger particles are filtered outby the nose mouth and throat In manyurban areas concentrations of RSP havebecome worryingly high The build-up ofparticles in lungs can contribute to branmiddotchitis and other respiratory diseases

86 The Atmosphere

bull

~[ -i ~o 19~~ 30 OI~0 lll96S-9c 2(1 bullJ97O-4C 10 ~ilm9

iTll93lgt-3o OJU(l~) -M~III00

fidays widfog (lhitk fos)1974-83

~ lJO(~6)

- Finningl~

bull 20HU)Widdingtl)Jl

_ ~1~ alnall2Q8(72)

llHU)

133(27)

1ltmiddotilL

H28)fjloo

~G18l(U)

bullRiIIgll)

Sllllwburybull

i 1lt

lU(~6)

bull Wick~J 100(20)

bull1 Tumhoo~

tu1h89(10)

11111U1h66(17)

SquimG~tt

Eslubllflluir L10HI7)

~H51 Mlwpn lLLU

us (1)

Figure 1111 The spatial variation of fog over Great Britain 1950-1983Source After Musk (1991) fig 66

Aerosols 87

The dust bowl

Tht= dust bowl of tht= 1930s in tht= Grt=at Plains of tht= USA is pt=rhaps tht= bestknown and most oftt=n quott=d t=umpk of largt=-sca1t= wind t=rosion and dU$[stonn activity anywht=rt= in tht= world Tht= most KVt=rt= storms (black blizzards)occurr~d in th~ dust bowl betw~~n 1933 and 1938 and wt=r~ most frc=qu~nt

during th~ spring of th~se y~an At Amarillo T~xas at th~ h~ight of the periodon~ month had 23 days with at I~ast 10 hours of airbocn~ dust and in on~ infiv~ storms visibility was z~ro For comparison th~ long-t~rm average for this partof T~xas is just six dU$[ storms a year

The reasons for this most dramatic of ~cological disast~rs have been widelydiscussed Blame has largely been laid at the feet of the pioneering farmers andsod busters who ploughed up the plains for cultivation For although duststorms are fr~quent in the area during dry years and the 1930s was a droughtperiocl the 5CaI~ and extent of the 1930s events wen unpr~cedented

Plate 1111 In the 19305 (the dirty thirties) the Great Plains of the USAexperienced many black blizzards (dust storms) caused by a combination ofa run of dry hot years and the ploughing up of large tracts of land forgrain production Similar phenomena occur at the present day in the Sahelzone of West Africa This example occurred in Mali in 1977 (Rod McIntosh)

Further reading

Goudie A S and Middleton N J 1992 Tht= changing fnqut=ncy of duststornu through time CJjti( Clmnge 20 197-225

88 The Atmosphere

The Gulf War oil fires hype and reality

I

I KUAlT

I---~----

I SAOOI ARABIA c-i-~)

Following the Iraqi invasion ofKuwaiton 2 August 1990 deliberate oil spillsand oil-well fires were used by the Iraqileader Saddam Hussein as a weaponof war In January 1991 Iraqi torcesdetonated over 800 oil wells (out ofatoal ofaround 1116 wells in Kuwait)ofwhkh 730 exploded Most of these(656) burned lor several monthsmd tht rtlllainder gushed om oilAround I billion barrels of cmde oilwere lost reprtsenting 15-2 per(ellt of the entire Kuwliti oil reserve

Immediately atter this cpisode scishycntists and environmental activistsspcculated that the fites kt alone the spilled oil would have serious local regional1Ild global climatic impacts Doomsday scenarios were slggested including dramati(global (ooJillg similar to thl nuclear winter hypothesis slIplr-acid rain diversionof the Asian summer monsoon and rapid SIlOW melt from talls of bla(k snow

Liter however scientific studies involving remote scnsing ground-level monimiddottoring and computer modelling studies showed that the global climatic impactshad heen exaggefltted The smoke was not injccted high enough to spread overlarge areas of the Northern Hemisphere most of it was confined to an altitudeof between I km and 3 km Reneath the plume of smoke daylight and daytimetemperatures were reduced Simulation modds suggested a decrease in surfacedaytime air temperaures of between 4middotC and 10C (Bakan et aI 1991 Browninget aI 1991) There has been no permanent winter no major diversion of themonsoon and no super-acid rain

Scientific studies have shown however that the months of burning producedemissions of sulphur dioxide carbon monoxide hydrogen sulphide carbon dioxshyide and nitrogen oxides (estimates are showll in table 1Il1) Particulates containshying partly burned hydrocarbons and metals such as vanadium and nickel were alsodischarged into the atmosphere These emissions may have severe local impactsFor exalllple monitoring of inhalable particulate matter (PM IOs) in the EasternProvince of Saudi Arabil during and after the Kuwaiti oil fires found high conshycentrations at various phlCes higher than the maximum permissible level of340 ~g pel- Cl1 metre (Husain and Amin 1994) Other studies in Kuwait itselfin tne April to early May 1991 showed high levels of total airborne particulatematter (soot organic carbon sulphate and chloride) but rather low levels ofsulphur dioxide nitrogen dioxide and carbon monoxide

The local health and ecological impacts of such elevated pollution levels arenow of major concern Some of the compounds released may Ix carcinogenicThe inhalable PMIOs may cause severe health problems Hospital studies inKuwait in 1991 showed a moderate rise (about 6 per cent) in lung and heartcomplaints (Hoffman 1991) Clearly long-term health issues need monitoring

Aerosols 89

Plate 1112 In the Gulf War of 1991 large quantities of oil were burnt ashere at the AI Burgan oil field Fears were expressed that this could have asevere climatic impact In the event these fears were to a large extentmisplaced (EPLJim Hodson)

Table 1111 Predicted annual production of kuwaltl 011 flres in 1991

Type of emission Amount Comparison with current(Tg per year) gfobal emissions

Fine particulate black smoke 5 Roughly onemiddotthird of carbonparticles produced by tropicalbiomass burning

Sulphur (as S oxides) 2 Slightly more than current UKannual S emissions

Nitrogen (as N oxides) 05

Carbon (ultimately as CO2) 60

Tg Teragramme I x 101lg

Source Browning et al (1991)

1988 UK emissions of nitrogenoxide were 075 Tg

About 1 of current globalannual CO2 emissions from Jfossil fuel combustion _

90 The Atmosphere

3 ANTHROPOGENIC CLIMATE

CHANGE ThE ROLE OF

LAND COVER CHANGES

Another major possible human-inducedcause of climate change is change in thereflectivity (albedo) of the ground surfaceand the proportion ofsolar radiation whichthe surface reflects Land-use changescreate differences in albedo which haveimportant effects on the energy balance ofan area Tall rain forest may have an albedoas low as 9 per cent while the albedo ofa desert may be as high as 37 per centThere has been growing interest recentlyin the possible consequences of deforestashytion on climate as a result of the associshyated change in albedo Ground deprivedof vegetation cover as a result of deforshyestation and overgrazing (as in parts ofthe Sahel) has a very much higher albedothan ground covered in plants This couldaffect temperature levels Satellite imageryof the Sinai-Negev region of the MiddleEast shows an enormous difference inimage between the relatively dark Negevand the very bright Sinai--Gaza Strip areaThis line coincides with the 1948-9armistice line between Israel and Egyptand results from different land-use andpopulation pressures on either side of thatboundary Otterman (1974) has suggestedthat the albedo affected by land use hasproduced temperature changes of the orderof SoC

Charney et al (1975) have argued thatthe increase in surface albedo resultingfrom a decrease in plant cover would leadto a reflection outwards of incoming radiashytion and an increase in the radiativ( coolmiddoting of the air Consequently they arguethe air would sink to maintain thermalequilibrium by adiabatic compressionand cumulus convection and its associatedrainfall would be suppressed A positivefeedback mechanism would appear at this

stage namely the lower rainfall would inturn adversely affect plants and lead to afurther decrease in planr cover

This view was disputed by Ripley(1976) He suggested that Charney andhis colleagues when considering the imshypact ofvegetation changes on albedo failedto consider the effect of vegetation onevapotranspiration He pointed out thatvegetated surfaces are usually cooler thanbare ground since much of the solar enshyergy absorbed is used to evaporate waterHe concluded from this that protectionfrom overgrazing and deforestation mightin contrast to Charneys views be expectedto lower surface temperatures and therebyreduce rather than increase convectionand precipitation

The models used by some scholars sugshygest that removal of the humid tropicalrain forests could also have direct climaticeffects Lean and Warrilow (1989) used ageneral circulation mood (GCM) whichsuggested that deforestation in the Annshyzon basin would lead to reductions in bothprecipitation and evaporation as a resultof the changes in surface roughness andalbedo The surface roughness effect occursbecause rain forest has quite a jaggedcanopy and this in turn affects wind flowlikewise a UK Meteorological OfficeGCM shows that the deforestation of bothAmazonia and Zaire would cause precipishytation levels to fall by changing surfacealbedo (Mylne and Rowntree 1992)

Budyko (1974) believes that the presentuse of irrigation over about 04 per centof the Earths surface (13 per cent of theland surface) is decreasing the albedo ofirrigated areas possibly on average by 10per cent The corresponding change in thealbedo of the entire Earth--atmosphere sysshytem would amount to about 003 per centenough according to Budyko to mainshytain the global mean temperature at a levelnearly OlC higher than it would othershywise be

Land Cover Changes 91

Figure 1112 Predictions of the change in climate following a conversion ofAmazonian rain forest to grassland (a) Temperature increase rC) (b) Evaporationdecrease (mm per year) (c) Rainfall decrease (mm per year) (d) Evapotranspirationdecrease (mm per year)Source After Shukla et al (1990)

A change in land use can also lead to achange in the moisture content of theatmosphere It is possible for example thatif humid tropical rain forests arc cut downthe amount of moisture transpired intothe atmosphere above them will be reshyduced This would reduce the potentialfor tain (figure m2(e)) The spread ofirrigation could have the opposite effectleading to increased atmospheric humiditylevels in the worlds drylands The HighPlains of the USA for example are normshyally covered with sparse grasses and havedry soils throughout the summer Evapo-

transpiration there is very low In thelast four decades however irrigation hasbeen developed throughout large partsof the area This has gready increasedsummer evapotranspiration levels Thereis strong statistical evidence that rainfall inthe warm season has been increased bythe use of irrigation in two parts of thisarea one extending through Kansas Nemiddotbraska and Colorado and a second in theTexas Panhandle The largest absolute inshycrease was in the latter area Significandyit occurred in June the wettest of the threeheavily irrigated months The effect appears

92 Thc= Armosphc=rc=

to bc= espc=cially important whc=n stationaryweathc=r fronts occur This is a situationwhich allows for maximum intc=racrionbc=twc=en the damp inigatc=d surface andthc= atmosphc=re Hail stonns and tornashydoes arc= also significantly morc= prc=valc=ntover irrigated dun ovc=r non-irrigated reshygions (Nicholson 1988)

Although wc= have discussc=d albc=doChUlgc= and atmospheric moisture changesas two separate dassc=s of processc=s thc=yneed to be seen as working togc=thc=r Uld

also in association with other mechanismsFor an example of why this is importantwe an look at tropical rain-forest removalThis causa albedo change reduction inmoisture loss by evapotranspiration and achange in surftce roughness The comshybinc=d effects may be considerable (figurem2) They include an increase in temshyIXrature a major dc=crease in loss of moisshyture into the atmosphere and a very majordecrease in rainfall

FURTHER REAoING

Kemp D D) 1994 GlobRl Environmental fuuu A Qimatological Approach 2nd ednLondon RoutledgeA well-iUustratc=d clnr and accessiblc= introduction to many areas of global climaticchange

Figure iII3 (a) The greenhouse effectin the atmosphere (b) A diagramshowing how a greenhouse acts as aradiation blanketSources (a) Houghton et aJ (1990)figure 1 (b) Houghton (1994) figure 22

s-fIl bull -w_IC~ lIt-r-bullbull__ rcc shy

ln6gt radWionis nnintd amp011I

tht eartl

MOll tgtdUIion bull~bytht

urthlltIIfxwi_it

b

4 ThE ENHANCED

GREENHOUSE EFFECT AND

GWBAL WARMING

Planet Earth rcccivcs warmth from thc= sunRadiation from the sun is pardy trappedby the atmosphc=re It passes through thc=atmosphere and heats the Earths surfacc=Thc= warmed surface radiates c=nergy butat a longer wavdength than sunshineSome of this cnc=rgy is absorbed by theatmosphere which as a result warms upThe rest of thc= c=nc=rgy c=scapes to spaceWe call this procc=ss of warming thc= greenshyhouse effc=ct because the atmosphere ispercdved to act rather like glass in a grec=nshyhouse (figure 1113) Although the atmosshyphere consists primarily of nitrogen andoxygen it is some of thc= so-called tracegases which absorb most of the heat inspite of the fact that they occur in verysmall concentrations These are called thegreenhouse gases

Various grc=cnhouse gases occur natushyrally - water vapour (HlO) carbon dioxshyide (COl) methane (CH) ozonc= (OJ)

and nitrous oxide (N20) In recent censhyturies and decades however the quantitiesof some of these greenbouse gases havestarted to increase because of humanactiviues In addition a new type ofgreenshyhouse gas the chloroflurocarbons (CFCs)has been introduced to the atmosphere inthe las[ fifty years

Since the start of the industrial revolushytion humans have been taking stored carshybon om of the earth in the form of fossilfuels (coal oil and natural gas) They burnthese fuels releasing CO2 in the processThe pre-industrial level of CO2 in the atshymosphere may have been as low as 260shy270 parts per million by volume (ppmv)The present level exceeds 350 ppmv andis still rising as is evidem in records ofatmospheric composition from variousparts of the world Fossil fuel burningand cement manufacture release over 6gigatonnes of carbon [Q the atmosphereas CO2 each year Burning of forests andchanges in the levels of organic carbon insoils subjected to deforestation and cultishyvation may also contribute substantially toCO2 levels in the atmosphere perhaps byaround 2 gigatonnes of carbon each year

Other gaslts as well as Calgt will probshyably contribute to the accelerated greenshyhouse effect The dTect ofeach on its ownmay be relatively small but the effects ofall of them combined may be considershyable Moreover molecule for moleculesome of these other gases may be moreeffective as greenhouse gaslts than CO2

This applies to methane (CH4 ) which is21 times more effective than COlgt tonitrous oxide (N20) which is 206 timesmore effective and [Q the CFCs whichare 12000-16000 times more effective

Where do these other gases come fromand why are amounts of them increasingConcentrations of methane are now over1600 parts per billion by volume (ppbv)compared to eighteenth-century backmiddotground levels of 600 ppbv Methane has

Global Warming 93

increased as a result of the spread of ricecultivation in waterlogged paddy fieldsenteric fermentation in the growing numshybers of belching and flatulent domesticcattle and the burning of oil and naturalgas Nitrous oxide levels have increasedbecause of the combustion of hydroshycarbon fuels the uslt of ammonia-basedsynthetic fertilizers deforestation andvegetation burning The increase in CFCsin the atmosphere (which is also associshyated with ozone depletion in the stratoshysphere - see section 7 below) results fromtheir use as refrigerants as foam makersas fire control agents and as propellantsin aerosol cans Use of CFCs is now beingrestricted by various international agreeshyments

The Earths climate has become genershyally warmer over the last century or soand the 1980s saw an unprecedentednumber ofwarm years This has promptedsome scientists to propose that globalwarming as a result of the acceleratedgreenhouse effect has already startedHowever the complexity of factors thatcan cause climatic fluctuations leads manyscientists to doubt that the case is yet fullyproven Most however believe that ifconcentrations of effective greenhousegases continue to rise and attain doubletheir natural levels by around the middleof the twenty-first century then temperashytures will rise by several degrees over thatperiod The Intergovernmental Panel onClimate Change (IPCC) which reportedin 1990 suggested that global mean temshyperature might increase during the nextcentury at a rate of 03degC per decade TheIPeC report of 1996 suggested a bestestimate of20degC increase in temperatureby 2100 (with a range of 1-3SdegC) Thisis somewhat lower than previous predicshytions because of improvements in inforshymation and modelling techniques Coolingeffects of aerosols are taken into accountin this prediction The rise in temperature

94 Thc= Atmosphere

I

Figure 1114 Change in global surface temperature following a doubling of CO2

(a) December January and February (b) June July and AugustSource Kemp (1994) figure 78 using data in Houghton et al (1990)

will not howevc=r bc= thc= samc= across thc=g1obc= In particular high latitudc=s (egnorthern Canada and Eurasia) will showeven morc= pronounced warming perhapstwo to three times the global average(figw-e III4)

Such increasc=s in tc=mperaturc= if thc=yoccur will undoubtedly causc= majorchanges in the general atmospheric circushylation These in turn will cause changc=sin precipitation patterns Overall levels ofprecipitation ovc=r the g1obc= will increasc=as morc= moistl1laquo is relc=ased by higher ratesofevaporation from the oceans However

some areas will get wetter while some willgc=t drier Thc=re is still considerable uncershytainty about what precise pattern precipishytation will take as a result of these changc=sThe very cold dry areas of high latitudesmay well become moister as a warmeratmosphw= will be able to hold moremoisture Some tropical areas may receivemore rain as the vigour of the monsoonalcirculation and of tropical cyclonc=s is inshycreasc=d Some mid-Iatitudc= areas like theHigh Plains of America may becomemarkedly drier

Therc= is however great uncertainty as

to how far the climate may change as aresult of me greenhouse effect The reashysons for this uncertainty include

bull doubts about how fast the global ecoshynomy will grow

bull doubts about what fuels will ~ usedin the future

bull doubts about the speed at which landshyuse changes are taking place

bull uncertainty regarding how much COlwill be absor~d by the oceans and bybiota

bull uncertainties about the role of omeranthropogenic and natural (eg volshycanic) causes of climatic change

bull the assumptions that are built intomany of our predictive general circulashytion models (eg about the role ofdouds)

bull the role of possible positive feedbacksand thresholds that may mean changesare more sudden than anticipated ordo not happen at all

The degree of global warming that IS

proposed for the coming decades does notat first sight appear enormous Howeverit may over a period that is very short ingeological terms produce warmer condishytions than have existed for several millionyears and set up a series of changes thathave important implications both for theenvironment and for humans Some ofthese implications may be benign (eg

Global Warming 95

warmer conditions will enable new cropsto be grown in Britain) but some of themwill be malign (eg more frequent andlonger droughts in the High Plains ofAmerica) Among the possibeenvironmenshytal consequences are

bull more intense widespread and frequenttropical cyclones

bull the melting of alpine glaciersbull the degradation of permafrost in tunshy

dra areasbull the wholesale displacement of major

vegetation belts such as the borealforests of the Northern Hemisphere

bull rising sea levels and associated floodshying of coral reefs deltas wetlands etcand accelerated rates of beach erosion

bull decreased flow of water in streams as aresult of increased loss of moisture byevapotranspiration

bull reduction in the extent of sea ice inpolar waters

bull shifts in the range of certain vectorshyborne diseases (eg malaria)

Many scientists and politicians believe thatthe case has now been made that globalwarming will occur and that the resultingchanges are likely to be so significant thataction needs to be taken In some countriesa policy of no regrets is being promotedThis is a policy under which the reductionof greenhouse emissions is also justifiableon other grounds (see table 1112)

Table 11I2 Examples of no regrets climate-warming policies

Policy

Tree planting

Energy conservation

Energy efficiency

CFC emission control

FURTHER READING

Effect on greenhouse gases

Increased biosphere sinkstrength to absorb CO2

Reduced CO2 emissions

Reduced CO2 emissions

Reduced CFC emissions

Other benefidal effects

Improved microdimate

Improved habitat for manyspedesReduced soil erosion

Reduced seasonal peak riverflows

Conservation of nonshyrenewable resources forcurrent and futuregenerations

Conservation of nonmiddotrenewable resources forcurrent and futuregenerations

Reduced stratospheric ozonemiddotlayer depletion (see section7)Reduced surface UV-S andassociated skin cancer andblindn~s

Houghton J T 1994 Global Warming The Camplere Briefing Oxford Lon BooksA useful clearly written introduction by a leading expcrt that summarizes the keyfindings of the worlds scientific community in this area

Houghton] T Jenkins G J and Ephraums]] (eds) 1990 Climate Change TheIPCC Scientific Assessment Cambridge Cambridge University PressHoughron J T Callander B A and Varney S K (eds) 1992 Climate Change 1992T1Jt Supplementary Report of the IPCC Scientific Mesrmet Cambridge CambridgeUniversity PressHoughton J T Meira Filho L G Callander B A Harris N Kaltenberg A andMaskell K (eds) 1996 Qimau OJtlnge 1995 The Stience of Climate OJange Camshybridge Cambridge University PressThree reports from the global bod) the Intergovernmental Panel on Climate Change(IPCq established to look at the causes and consequences of global warming

Kemp D D 1994 Global Enpironmental Imm A QimatoloBical Approach LondonRoutledge

- -

Figure 1115 The potential distributionof grain maize in the UK underdifferent warming scenariosSource After Parry in Jones (1993) fig 11

Global Warming 97

Global warming and UK agricultureA5 a result ofglobal warming the temshyperltu~ in Britain could rise by severaldegrees Celsius during the coune ofthe next 50-100 yean A change in theclimate of this magnitude would belikely to shift the thermal limits of agshyriculture by around 300 kin oflatitudeand 200 m of altitude per degree Celshysius Several crop species such as wheatmaize and sunflowers have their conshytemporary northern limits in the UKAn increase oftempcrltu~ could thereshyfore assuming that soil conditions ~resuitablelead to a substantial northwardshift of cropping zones This couldtransform the British agricultural landshyscape British 6dds and rural areas mightcome to resemble those currcndy foundfurther south in mainland Europe Foeexample the northern limit of grainmaize which currendy lies in the CIshy

treme south of England (see figureIlLS) could be shifted Kross centnlEngland by a OSmiddotC inclUSC in temshyperature across nocthern England bya lSmiddotC inclease and into the north ofScodand by an increase of 3C

A rise in temperatule apart fromtruufonning the range over which parshyticular CIOP types could be growncould be significant for the agriculshytural sector in other ways For example higher temperatures and more frequentsummer droughts migh[ Ieduce crop yiclds The occurrence of certain plant pestsand diseases could change for better 01 worse

Further reading

Jones D K C (ed) 1993 Earth surface resources management in a warmerBritain GeoIJr4phittd ]owNId 159 124-208

98 The Abnosphere

5 U RJlAN CLIMATES

Climate Stltistics for recent decades showthat many cities have become warmer thanthe countryside around them Climatoloshygists have long spoken of the urban heatisland in the cool rural sea The boundshyary between countryside and city forms asteep temperature gradient or difT to theurban heat island Much of the rest of theurban area appears as a plateau of warmair with a steady but shallower gradient ofincreasing warmth towards the city censhytre The urban core or central businessdistrict with its high-density buildings isa peak where the maximum temperatureis found The difference between this peakvalue and that in the rural sea defines theintensity of the urban heat island

There are various reasons why cities maybe relatively warmer than the fUJa1 areasthat surround them (figure 11I6) Firstcity surfaces absorb significantly moreradiation from the sun than rural surfacesThis is because a higher proportion of the

ttgtlto

Figure 1116 Mechanisms of urban climates

reflected radiation is retained by the highwaIls and dark-coloured roofs and roadsof the city environment These city surshyfaces have both great thermal capacity andhigh conductivity so that heat is storedduring the day and released by night Bycontrast vegetation cover gives plantshycovered rural areas an insulating blanketso that they experience rdatively lowertemperatures both by day and by nightThis effect is enhanced and compoundedby the evaporation and transpiration thatoccur from plant-covered surfaces Secshyondly cities are relatively warm becausethey generate a large amount of artificialheat Energy is produced and then usedby industrial commercial transport anddomestic usen

The heat island effect is nO the onlyway that towns and cities affcd theclimate HDWaCf the effects ofurban areason other aspects of climate are less easilymeasured and explained There is someevidence that rainfall induding that proshyduced by summer thundemorms can be

t t

bull

higher over urban than ruraJ areas Thereart various possible ccasons for this

bull the urbm hcat island generates conshyvection (ie thermally induced upwardmovement of air)

bull the presence of high-rise buildings anda mixture of building heights inducesair turbulence and promotes increasedvertical motion

bull cities may produce large amounts ofwater vapour from industrial sourcesand power stations and also variouspollutant aerosols that act as condenshysation nuclei

The London area provides an interestshying but by no means unique example ofthe effects of large chies on prccipitationlevels In this case it seems that the meshychanical dreer of the city was the maincause of local peak precipitation It hadthis effect by being a mechanical obstacleto air flow on the one hand and by causshying frictional convergence of flow on theother A long-term analysis of thundershystorm records for south-east Englandshows that thunderstorms arc mort freshyquent over the urban area than elsewherein the region (Atkinson 1968) The simshyilarity between the shape of the thundershystorm isopleth and that of the urbanarea is striking Moreover Brimblecombe(1977) found that thunderstorms havebecome steadily more frequent as the cityhas grown

Winds arc another aspect of the urban

Ft1IlTHBR READING

Urban Climates 99

climate There arc twO main aspects to theeffect that cities have on winds first therougher surface cities prescnt in comparishyson with rural areas and secondly thefrequently higher temperatures of the ciryBuildings especially those in cities with avery varied skyline exert a powerful mcshytional drag on air moving over and aroundthem This creates turbulence with rlpidand abrupt changes in both direction andspeed The average speed of the winds islower in built-up areas than over ruralareas However Chandler (1976) foundthat in London when winds arc lightspeeds arc greater in the inner city thanoutside whereas when winds arc strongspeeds arc greater outside the city centreand lower within it Overall annual windspeed in centraJ London is about 6 percent 10000er than outside but for the highershyvelocity winds (more than 15 metres persecond) the reduction is more than twicethat

Studies in two English cities Leicesterand London have shown that on calmdear nights when the urban heat islandeffect is at its greatest there is a surfaceinflow of cool air towards the warmestzones These so-called country breezesare low in velocity and arc quickly sloweddown further by intense surface friction inthe suburban areas One effect of thesebreezes is to transport pollution from theouter parts of an urban area into the citycentre accentuating the pollution probshylem during periods with photochemicalsmogs

Landsberg H E 1981 The Urba Ciuatt New York Academic PressThe classic study

OU T J 1987 amp LAyer Cliatu 2nd cdn London RoudedgeA thorough review of Iocalmiddotscale climates which includes an authoriativc study ofurban clinutes

100 The Atmosphere

Ghe implications of some urban heat islandsI ~ cities grow so does their heat island effect In Columbia Maryland USA for

example when the town had only 1000 inhabitants in 1968 the maximumtemperature difference between residential areas and the surrounding countrysidewas only ImiddotC By 1974 when it had grown to a town with a little over 20000inhabitants the maximum heat island effect had grown to rc

Thus the annual average temperatures over the hearts of great cities can besubstantially higher than those over the surrounding countryside This is dearfrom the temperature map of Paris (figure 1I17(araquo) The outlying weather stashytions have mean annual temperatures of 106-109middotC whereas in cennal Paristhe value is 123C about lSC higher These values have all been reduced toa uniform elevation of 50 metres above sea level to correct for possible orographiceffects

Urban climates are often characterized by different precipitation characteristicsfrom rural areas For example it is remarkable that there tends to be more rainin Paris during the week than at weekends (figure III7(b)) There is a gradualincrease in average rainfall from Monday to Friday (when factories art producingmore heat and aerosols) then a sharp drop for Saturdays and Sundays Theweekend average for May to October was 147 mm whereas the workday averagewas 193 mm - a decrease of 24 per cent for the weekend

In winter months the consequences of urban heat islands can be particularlysignificant in cold regions For example the average date of the last freezingtemperatures at the end of winter in Washington DC in the USA is about threeweeks earlier than in the surrounding rural areas (figure 1I17(c)) In aurumn thecity has on average the first freezing temperature on about 3 November whereasin the outlying suburbs OC will usually be observed about two weeks earlierThus in all the frost-free season will be about 35 days longer than it is in thecountryside Similar figures have been obtained for some other great cities Datafor Moscow Russia suggest an increase of around 30 days without freezingwhile those for Munich in Germany suggest an increase that can be as g~at as61 days

In summer months the urban heat island effect can lead to an increasingdemand for air conditioning and because the energy requirements of air conshyditioning are greater than those of heating the savings in winter heating bills aremore than offSet Moreover air conditioning can aggravate the heat island effectbecause air conditioning plant discharges heat to the outside air where it mixeswith air that has already been warmed up by the hot air forming adjacent to sunlitwalls and pavements

Further reading

Landsberg H E 1981 The Urban Climate New York Academic Press

Urban Climates 101

~ Ilourg~t 107bull

(b

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lS

bull $I rquCi 123 ~ll)bscwllolty 116

MontlOU 116 bull S M~ur IIS

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li]

I

Figure 1117 The impact of urban areas on climate (a) Annual isotherms inthe Paris region (b) Precipitation in Paris averaged by day of the week(c) Average date of last freezing temperature in spring in Washington DC(A = International Airport B =White House)Source Landsberg (1981) figures 55 86 525

102 The Atmosphere

6 URBAN AIR POLLUTION

The concentration of large numbers ofpeople factories power stations and carsmean that large amounts of pollutantsmay be emitted into urban atmospheresIf weather conditions permit the level ofpollution may build up The nature of thepollutants (table 1113) has changed astechnologies have changed For examplein the early phases of the industrial revoshylution in Britain the prime cause of airpollution in cities may have been the burnshying of coal whereas now it may be vehishycular emissions Different cities may havevery diffennt Icvels of pollution dependshying on factors such as the level of techshynology size wealth and anti-pollutionlegislation Differences may also arise beshycause of local topographic and climaticconditions Photochemical smogs for

Table 1113 Major urban pollutants

example are a more serious threat in areassubjected to intense sunlight

The variations in pollution Icvels beshytween different cities arc brought out infigure IIIB which shows data for twotypes of pollution for a large range of citytypes The data were prepared for the years1980--4 by the Global Environment Monishytoring System of the United NationsEnvironment Programme (UNEP) Figshyure IIIB(a) shows concentrations of totalparticulate matter Most of this comes fromthe burning of poor-quality fuels Theshaded horizontal bar indicates the rangeof concentrations that UNEP considers areasonable target for preserving humanhealth Note that the annual mean levelsrange from a low of about 35 lig percu metre to a high of about 800 ligper cu metre a range of about 25-foldThe higher values appear to be for rapidly

Type

Suspended particulate matter(characteristically 01-25 11m indiameter)

Sulphur dioxide (5deg2)

Photochemical oxidants ozoneand peroxyacetyl nitrate (PAN)

Oxides of nitrogen (NOx)

Carbon monoxide (CO)

Toxic metals lead

Toxic chemicals dioxins etc

Some consequences

Fog respiratory problems carcinogens soilingof buildings

Respiratory problems can cause asthmaattacks Damage to plants and lichenscorrosion of buildings and materials productionof haze and acid rain

Headaches eye irritation coughs chestdiscomfort damage to materials (eg rubber)damage to crops and natural vegetation smog

Photochemical reactions accelerated weatheringof bUildings respiratory problems production ofacid rain and haze

Heart problems headaches fatigue etc

Poisoning reduced educational attainments andincreased behavioural difficulties in children

Poisoning cancers etc

1

()

)

Urban Air Pollution 103

(For caption see overleaf)

104 The Atmosphere

growing cities in the developing countriesSome cities however such as Kuwait mayhave unusually high values because Qf theirsusceptibility to dust storms from deserthinterlands The lower values tend to comefrom cities in developed areas (eg Westshyern Europe Japan and North America)

Figure III8(b) shows concentrations forsulphur dioxide Much of this gas probshyably comes from the burning of highshysulphur coal Once again the horizontalshaded bar indicates the concentrationrange considered by UNEP to be a reashysonable target for preserving human healthThese data indicate that the concentrationsof sulphur dioxide can differ by as muchas three times among different sites withinthe same urban area and by as much as30 times between different urban areas

In some cities concentrations of polshylutants have tended to fall over recentdecades This can result from changes inindustrial technology or from legislative

changes (eg clean air legislation restricshytions on car use etc) In many Britishcities for example legislation since the1950s has reduced the burning ofcoal Asa consequence fogs have become lessfrequent and the amount of sunshine hasincreased Figure IlL9 shows the overalltrends for the United Kingdom and highshylights the decreasing fog frequency andincreasing sunshine levels The concentrashytions of various pollutants have also beenreduced in the Los Angeles area of C~lishy

fornia (figure 11110) Here carbon monshyoxide non-methane hydrocarbon nitrogenoxide and ozone concentrations have allfallen steadily over the period since thelate 1960s

However both of these examples ofimproving trends come from developedcoumries In many cities in poorer counshytries pollution is increasing at present Incertain countries heavy reliance on coaloil and even wood for domestic cooking

Figure 1118 (a) The range of annual averages of total particulate matterconcentrations measured at multiple sites within 41 cities 1980-1984 Eachnumbered bar represents a city as follows 1 Frankfurt 2 Copenhagen 3 Cali 4Osaka 5 Tokyo 6 New York 7 Vancouver 8 Montreal 9 Fairfield 10Chattanooga 11 Medellin 12 Melbourne 13 Toronto 14 Craiova 15 Houston16 Sydney 17 Hamilton 18 Helsinki 19 Birmingham 20 Caracas 21 Chicago22 Manila 23 lisbon 24 Accra 25 Bucharest 26 Rio de Janeiro 27 Zagreb28 Kuala lumpur 29 Bombay 30 Bangkok 31 Illigan City 32 Guangzhou 33Shanghai 34 Jakarta 35 Tehran 36 Calcutta 37 Beijing 38 New Delhi 39Xian 40 Shenyang 41 Kuwait City (b) The range of annual averages of sulphurdioxide concentrations measured at multiple sites within 54 cities 1980-1984Each numbered bar represents a city as follows 1 Craiova 2 Melbourne 3Auckland 4 Cali 5 Tel Aviv 6 Bucharest 7 Vancouver 8 Toronto 9 Bangkok10 Chicago 11 Houston 12 Kuala lumpur 13 Munich 14 Helsinki 15lisbon 16 Sydney 17 Christchurch 18 Bombay 19 Copenhagen 20Amsterdam 21 Hamilton 22 Osaka 23 Caracas 24 Tokyo 25 Wrodaw 26Athens 27 Warsaw 28 New Delhi 29 Montreal 30 Medellin 31 St louis 32Dublin 33 Hong Kong 34 Shanghai 35 New York 36 london 37 Calcutta38 Brussels 39 Santiago 40 Zagreb 41 Frankfurt 42 Glasgow 43Guangzhou 44 Manila 45 Madrid 46 Beijing 47 Paris 48 Xian 49 SioPaulo 50 Rio de Janeiro 51 Seoul 52 Tehran 53 Shenyang 54 MilanSource Graedel and Crutzen (1993)

and hating Imam that their levels ofsulphur dioxid~ and suspend~d particulatematter (SPM) ar~ high and climbing Inaddition rapid economic d~velopment is

Urban Air Pollution lOS

bringing increased emissions from indusshytry and motor vehicles which are g~nershy

ating progressively more serious air-qualityproblems

~ _ roaI COIlIbaIOooI

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1965-80

bull - Figure 11I9 Trends in atmospheric quality in the United Kingdom (a) Sulphurdioxide emissions from fuel combustion and average urban concentrations(b) Smoke emissions from coal combustion and average urban concentrations ofoil smoke (c) Increase in winter sunshine (10-year moving average) for londonand Edinburgh dty centres and for Kew outer london (d) Annual maximumhourly ozone concentrations at selected sites in the Los Angeles basin1958-1989 (e) Annual fog frequency at 0900 GMT in OxfOfd central England1926-1980Sources (a)-(c) Figures from Depa~nt of Environment (d) After Elsom (1992) figure211 (e) After Gomez and Smith (1984) figure 3

o lSU 70 72 74 Jf 11 ID a 14

in (ie smaller than 10 Jffi and so oftenknown as PMIOs) Also of great conc~min terms of human health ar~ elementalcarbon (for example from diesel vehicles)polynuclear aromatic hydrocarbons (PAHs)and toxic b~ metals (eg arsenic leadcadmium and mercury) in part becauseof their possible role as carcinogens

Urban air pollution V3S particularlysevere in the former Communist states ofEastern Europe Carter and Turnod(1993 p 63) described this problem andits political background in the comext ofCzechoslovakia (now the Czech ~public

and Slovakia)

Environmental quality has clearly detemiddotriorated as a result of human activitythe major cause is an excessive 3ndinconsiderate extraction of naturalresources extensive waste emissionsand failur( to observ( ecological andaadKtic laws These were compoundedby an inefficient economy which conshysumed inordinat( amounts of raw mashyterials and energy based on outmodedtechnology which produced manufacshytured goods with little respect for theccologicaJ consequences This ud situshyation was further aggravated by inadshyequate financial reoourcc allocation forenvironmental protection which was ofa rem~dial chancter rath~r than one ofdamage prevention Much of the blamefor this state of affairs must be laid uponthe Communist government over thepast fony years when legislative execushytive and political pow~r was concenshytlared in the hands ofa small controllinggroup (lIomenilRtJlrll) who did little tocorren adv~rse effects on the ~nvironshy

men( cauSoCd by their policies Addedto this dctrimentll domestic attitude wasthe significant contribution made bytrlrUboundary pollution from neighshybouring states particularly along thenorthern and western boundaries of thecountry

The problem was cncerbated by the uscof lignite (brown coal) in some of the East

Particular attention is being paid at thepreKnt time to the chemical compositionof SPMs and particularly to those partishycles that are snull enough to be bruthed

Figure 11110 Air quality trends in losAngeles and its environs have beenmeasured continuously and averagedover each hour The highest of thehourly averages is then selected fortrend analysis Part (a) shows thedownward trend in carbon monoxide(CO) concentrations this trend isconsistent with vehicular emissioncontrol measures part (b) shows thetrend for oxides of nitrogen (NOx) andozone (OJ Both are expressed in partsper billion by volume (ppbv)Source Modified from kun~ and Chang(19Sn copyright 1987 by Air PollutionControl Association

106 The Atmosphere

u (0)

1 bullAs I8

bull bull n bull ~ G ~ bully

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Urban Air Pollution 107

Plate 1113 Some of the worst urban air pollution occurred in the former SovietUnion A particularly gruesome pollution hot spot was the Magnitogorsk steeshymaking area (Katz Pictures)

European states Such col is of low qualshyity so disproportionatdy large quntiticshve to be burnt it can also have bull veryhigh sulphur content Cuter and Turnock(1993 p 189) refer to the dedly plI ofsulphurous smoke tht this fud source

FURTHER READING

has hdped to promote They point outthat even in the late 1980s over threeshyquarters of Polnds energy orne frombrown coal as did two-thirds of the enmiddotergy in Czechoslovakia and the fonner EastGermany

Brimblecombe P 1987 The Big Smoke London MethuenA diverting history of air pollution with particular reference to London

Carter F W and Turnock D (eds) 1993 Environmental Problems in Eastern EuropeLondon RoutledgeAn edited collection of papers on the kgacy of dtcadful air polJution problems inEastern Europe

Elsom D 1996 S418 Alert Mtma8in8 UrbAn Air ~AH London EanhscanA very readable and informative guide

108 The Atmosphere

Air pollution in South Mrican cities the legacy ofapartheidSouth Mrica produces the worldscheapest electricity but for manyyears it has only been available toaround 30 per cent of the populashytion This bald statement sums upthe major causes of South Africanurban air pollution Around 83 percent of South Africas electricity isgenerated by coal-fired power stashytions which burn coal with a sulshyphur content of around 12 per centSuch high sulphur content (relativeto many other types of coal) proshyduces high levels of polluting gasesMany of these plants are located inthe eastern Transvaal which suffersgreatly from air pollution and acid deposition Apartheid the system of governshyment which dominated South Africa from 1948 to 1994 and forced differentracial groups to live apart produced highly unequal distributions of access toenergy resources and of pollution conditions Apartheid forced black and Colshyoured populations into poor townships usually without electricity and withsevere pollution problems

The background air pollution in many parts of South Africa is increased inurban environments where coal paraffin and wood are burnt as important domesticenergy sources By 1985 about 57 per cent of the entire South African populashytion lived in cities many of them in squatter settlements and townships whereelectricity supply was limited Soweto for example some 15 Ion from Johannesshyburg covers nearly 60000 sq Ion and had a population in 1990 of around 25million according to some tstimates Electricity was brought into Soweto in1981 but coal is still widely used as it is cheaper and the supply more reliable

Sulphur dioxide pollution is now a critical health problem for Sowetan inhabshyitants In Soweto mean annual sulphur concentrations are up to 60 ~g percu metre whereas in the unpolluted north-west of Transvaal mean annual conshycentrations are on average only about 7 ~g per cu metre There are also highlevels of nitrogen oxides and carbon monoxide in Soweto

The air pollution problems of Soweto are exacerbated by climate andtopography North and north-westerly winds transport pollution here fromJohannesburg city centre and winter temperature inversions help trap the polshylution The South African Department of Health now believes coal smoke intownships to be the most serious national air pollution problem Air pollution isa problem indoors as well as outdoors especially in areas where open fires orinefficient stoves are used for cooking Suspended particulate matter carbon

Urban Air Pollution 109

Plate 1114 Air pollution in Cape Town South Africa Much of the pollutionis caused by the burning of low-quality fuel in the densely populatedtownships that surround the city At some times of year the pollutingsmoke and gases are trapped by climatic conditions called inversions(A S Goudie)

monoxide oxides of sulphur and nitrogen hydrocarbons and a range of otherpollutants are produced by stoves and fires The accumulation of indoor andoU[door pollution in Sowew and many other towns is leading to severe respirashytory problems especially in the poorest and most vulnerable members of societyAsbestos also poses an air pollution problem in South Africa where blue asbestosis mined in the northern Transvaal and northern Cape Asbestos can cause lungand other cancers and urbanized areas near mining operations are particularlyvulnerable to wind-blown asbestos

Further reading

Ramphele M 1991 Restoring the Land Environme1Jf and Change in PostshyApartheid South Africa London Panos

Vogel C H and Drummond J H 1995 Shades of green and brownenvironmental issues in South Africa In A Lemon (ed) The Geographyo[Changein South Africa 85-98 Chichester Wiley

110 The Atmosphere

7 OZONE DEPLETION AND

OZONE POLLUTION

Ozone (03) was discovered in 1840 It isa naturally occurring form ofoxygen whichconsists of three oxygen atoms rather thantwo It exists throughout the atmospherein very low concentrations never exceedshying around one molecule in every 100000present It is especially abundant in thestratosphere between 10 and 40 km abovethe ground This ozone layer containsabout 90 per cent of atmospheric ozoneand is important because it provides athin veil which absorbs ultraviolet (UV)radiation from the sun Indeed the ozonelayer prevents about 97 per cent of W-Blight from reaching the Earths surfaceToo much ultraviolet radiation can damshyage plants including the phytoplanktonthat live in the oceans In humans it cancause skin cancers it may also cause eyecataracts and damage the bodys immunesystem Thus it is clear that any reductionin the thickness and concentration ofozone in the ozone layer is worrying

In the 1980s satellite observationsground measurements and readings frominstruments on balloons and in aircraftbegan to suggest that the ozone layer wasbecoming thinner especially over theAntarctic More recent measurements haveindicated that the ozone layer is also thinshyning over America and northern Europe(see table III4) Here ozone decreasedon average by around 3 per cent in the1980s In the 1970s concern was expressedabout possible damage to the ozone layerby high-flying supersonic aircraft such asmilitary jets or Concorde However curshyrent concern among scientists is focusedon a range of manufactured gases ofrecent origin These include chloroflushyorocarbons (CFCs) and halODS Thesegases have been extremely useful in manyways - for example as refrigerants for

extinguishing fires for making foams andplastics and for use in aerosol spray cansThis is because they have some valuableproperties they are stable non-flammableand non-toxic Unfortunately their stabilshyity means that they can persist a long timein the atmosphere and can thus reach theozone layer witham being destroyed Oncethey are in the ozone layer UV radiationfrom the sun starts to break them downThis sets olf a chain of chemical reactionsin which reactive chlorine atoms arereleased These act as a catalyst causingozone (03) to be converted into oxygen(0) (figure IIUl)

Global production of CFC gases inshycreased gready during the I960s 1970sand 1980s from around 180 million kgper year in 1960 to nearly 1100 millionkg per year in 1990 However in responseto the thinning of the ozone layer manygovernments signed an international agreeshymenl called the Montreal Protocol in1987 This pledged them to a rapid phasshying out of CPCS and halons Productionhas since dropped substantially Howeverbecause of their stability these gases willpersist in the atmosphere for decades oreven centuries to come Even with themost stringent controls that are now beshying considered it will be the middle ofthe twenty-first century before the chloshyrine content of the stratosphere falls beshylow the level that triggered the formationof the Antarctic ozone hole (see below)in the first place

Some thinning of the ozone layer mayresult from time to time from naroralrather than anthropogenic processes Apossible factor may be the pollution of thestratosphere with particulate material (aeroshysols) emitted by volcanic eruptions suchas that of Mt Pinatubo in June 1991

The most drastic decline in stratoshyspheric ozone has been avec AntarcticaThis has led to the formation of theozone hole which expanded to an area

Ozone Depletion Ozone Pollution 11

()

Plate 1115 (a) The Antarctic Olone hole from space 8 October 1995 overleaf(b) the Northern Hemisphere ozone hole 12 March 1995 The colours representozone concentrations in Dobson units (NOAAScience Photo Library)

Table 1114 Trends in stratospheric Olone 1979-1991 ( per decade)

December-March May-August September-November

Satellite-derived data45degNEquator455

-56 35+03 plusmn 45-52 plusmn 15

-29 plusmn 21+01 plusmn 52-62 plusmn 30

-17 plusmn 19+03 plusmn 50-44 plusmn 32

Land-based data26middotN-64middotN -47 z 09 -33 z 12

Sour~ Tolba and E1middotKhoIy (eels) (1992) tabJe 2 p SO

-12 t 16

112 Th~ Atmosph~rc

(b)

Figure 11I11 opposite (a) The naturally occurring chemical processes leading tothe formation and decomposition of ozone in the atmosphere in the presence ofultraviolet radiation (b) The decomposition of ozone initiated by chlorine atomsreleased dUring the breakdown of a commonty occurring anthropogenicaUygenerated CFC believed to be harmful to the atmosphere (CFCll ) Not all thetwo-atom (diatomic) molecules of oxygen combine to form ozone and the freechlorine atoms that are liberated are potentially capable of initiating furtherreactions that lead to the breakdown of ozone (c) Schematic diagram to show theprindpaJ sources of atmospheric ozone and the main reactions that cause ozonedepletion in the stratosphereSource Pickering and Owen (1994)

Ozone Depletion Ozone Pollution 113

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114 The Atmosphere

of 24 million sq km during SeptembershyOctober 1992 and again in the same monthsof 1993 Record low ozone levels of lessthan 100 ozone units were registeredduring a few days in October 1993 Thesecompare with values from years before theozone hole (1957-78) of 330-350 units

The deS[ruction of ozone is grC=3[estover the Antandc because of the uniqueweather conditions during thc long darkwimer of the south polar regions Strongwinds circulate in a great vortex above theAntarctic essemially isolating the polarstratoshysphere from the rest of the atmosphereUnder the vcry cold conditions with ternmiddotperatures below -SOmiddotC icc clouds formcalled polar stratospheric clouds Theseprovide ideal conditions for the transforshymation ofchlorine (derived from the breakshydown of CFCs ampOd halons) into potentiallyreactive compounds When sunlight reshyturns in the spring months UV radiationfrom the sun triggers the reaction betweenthese chlorine compounds and ozonethereby leading to ozone destruction

No such clear ozone hole develops overthe Arctic becau$C the more complexarrangement of land and sc-a here leads toa less weU devel~d vortex system ofwinds In addition the winter stratosphereat the North Pole tends to be warmerthan its southern coumerpart This meansthat polar stratospheric clouds arc usuallyless abundant Nonetheless ozone depIcshytion docs seem to have occurred producshying an ozone crater rather than a hole

Paradoxically while ozone levels may be

FURTHER READING

dropping in the stntosphere at lowerlevels in the atmosphere they arc increasmiddoting This tropospheric ozone is producedb) the action of sunlight on the nitrogenoxides and hydrocarbons that are emittedin fossil fuel exhaust gases Such photoshychemical reactions as thcy arc caJlcd arcparticularly serious in some great citieslike Los Angeles where the high densityof chicles the frequent occurrcncc ofsunshyshine and the favourable topography leadto high concentrations ofa soup ofphotomiddotoxidant gases Rcscarch in both Americaand Europe has established that extensiveformation of tropospheric ozonc also freshyquently occurs in Northern Hcmispheremid-latitudes in thc summer in non-urbanareas most noticeably downwind of citksand major industrial regions The problemis fegional rather than mcrdy urban

High levels ofozone conccnrration havesc-vcral ~rious consequences Humanssuffef from eye irritation respiratory comshyplaints and headaches Ozone is also poshytcncally toxic to many species ofconiferoustrces herbaceous plants and crops at conmiddotccntrations nOt far above the natural backmiddotground le-d Rigorow controls on vehicleemissions can grcatly reduce thc problemSuch mcasures arc now being implementedin California Indeed as figure m12 showsin spite of a hefty increase in both popumiddotlation and the number of mOtOf vehicles inthc Los Angeles area since 1970 peak ozonclevels havc declincd vcry markedly and thearea subjected to high ozone concenmshytions has shrunk (Lents and Kdly 1993)

Gribbin J 1988 Tnt Hole in the sq MRns TbreRt to the Ozone lAyer London CorgiBooksAn introductory trcatment for the gencral public by a well-known scientific journalist

Minrur I M and Miller A S 1992 Stratospheric ozone depletion can wc savc thesky~ In Green GlDbe naboo 1992 83-91 Oxford Oxford Univcnity PressA morc rccent gcncra1 discussion of thc causes and consequences of the ozone hoIcand what can be done to deal with it

Ozone Depletion Ozone PoUution 115

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Figure 11112 AJr pollution in the Los Angeles area 1970s-1990sSource After Lents and Kelly (1993) p 22

116 The Atmosphere

pH

Figure 11113 The pH scale shOWingthe pH level of add rain in comparisonwith that of other common substancesSource Kemp (1994) figure 41

As a result ofair pollution precipitationin many parts of the world has pH valuesfar below 565 Snow and rain in thenorth-east USA have been known to havepH values as low as 21 In the eastern

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8 ACID DEPOSITION

Rain is slightly acid under natural conditionsbecause it contains some dissolved gasesincluding carbon dioxide (COl) sulphurdioxide (SOl) and nitrogen oxides (NOx)The~ gases are naturally pre-sent in theair Under natural conditions rain has apH of around 565 (figure 11113) Theterm acid rain was introduced as longago as the 1850s for rain which has a pHof less than 565 Such rain has becomemore than usually acid because of air polshylution Two of the chemical reactions inshyvolved are shown in figure IIIl4

Some scientists prefer the term aciddeposition to acid rain for not all envirshyonmental acidification is caused by acidrain in the narrow sense Acidity can reachthe ground surface without the assistanceof water droplets as particulate matter orgases This is termed dry deposition Furshythermore there are various different typesofwet deposition mist fog hail sleet andsnow as well as rain itself

(t) SuIplunlU$ Ind sulphuric acids

~ il tlDimd ampom lWurlllnd whropogtnic sourm Ind dissoIm in cloud _to pnld~ IUIphurous Kid

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NO alldN~ (rolIecliVlly known as Nih) art ptoduced by combuslion prornseI and lightnillshyNilric and nil10llS acids may b produced

Figure 11114 Chemical reactions producing acid depositionSource Modified after Mannion (1992) fig 112

Acid Deposition 117

Table 1115 Main sources of acid gases in the UK In 1990

Nitrogen oxidesRoad transportPower stationsIndustry

Sulphur dioxidePower stationsIndustry

Annual emissions(000 tonnes)

1400780270

2700710

of UK total

51289

7219

Source Department of Environment figures

USA as a whole the avcrage annual acidityvalues of precipitation tend to be aroundpH4 The pH scale is logarithmic so adecrease of one pH unit represents a tenshyfold increase in acidity Thus pH4 is tentimes more acidic than pHS The maingases responsible for this state of afhirsare the sulphur oxides and nitrogen oxshyides emined from fossil fuel combustion(see table ilLS) As a general rule sulshyphur oxides have the greatest effect andare responsible for about two-thirds of theproblem However in some regions suchas Japan and the west coast of the USAthe nitric acid contribution may well be ofrelatively greater importance

Whichever of these gases is most impormiddottant most acidification has occurred in theindustrialized lands of the Northern Hemishysphere It is here that emissions of sulphurand nitrogen oxides arc highest becauseof high rates of fossil fuel combustion bya range of sources notably industries carsand power stations However the polshylutants that cause acidification can berransponed over long distances by thewind The acidifiC2tion ofScaodinavia forexample has been attributed in part toemissions from Britain Similarly Canadareceives much of i[S acid deposition fromthe industrial heartland and tlK Ohio River

Valley region of the USA Recent estimatesof global emissions ofsulphur suggest thatanthropogenic sources now account for55-80 per cent of the combined total(anthropogenic and natural) and that over90 per cent of emissions from anthroshypogenic sources originate in the NorthernHemisphere

The effects of acid deposition arcgreatest in tho~ areas which have highlevels of precipitation (causing more acidshyity to be transferred to the ground) andthose which have base poor (acidic) rockswhich cannot neutralize the depositedacidity

Some of the most persuasive evidencefor long-term increases in acid deposishytion is provided by what is called thepalaeolimnological approach In this apshyproach past environmental information isobtained by looking at the changes in thefaunal and floral content of cores of sedishyment taken from the floors of lakes Therecord provided by diatoms is especiallyuseful for these algae are excellent indicashytors of water chemistry The compositionof fossil assemblages retrieved from datedcores can be used to reconstruct changesin water pH In Britain at sensitive sitespH values oflakc WlIters were close to 60before 1850 but since then pH declines

118 The Atmosphere

SipIilinlionrJaquotit

lnllIbilily1

Figure 11115 Pathways and effects ofacid precipitation through differentcomponents of the ecosystem showingsome of the adverse and beneficialconsequences

have varied between 05 and 15 unitsoverall

Acid precipitation has many ecologicalconsequences (figure IIUS) One harmfuleffect is a change in soil character Thehigh concentration of hydrogen ions inacid rain causes accelerated leaching ofessential nutrients making them less availshyable for plant usc Furthermore aluminiumand some heavy metal ions become moresoluble at low pH values and may havetoxic effects on plants and aquatic organshyisms Forest growth can also be affectedAcid rain can damage foliage increase susshyceptibility [0 disease affect germinationand reduce nutrient availability (figureIII16)

Particular fears have been expressedabout the possible effects of acid deposishytion on aquatic ecosystems especially on

fish populations Many fish are intoleranrof low pH values (table 1116) Fishlesslakes are now common in areas like theAdirondacks in the north-east USA Fishmay also be adversely affected by the inshycreasing amounts of toxic metal ions (egaluminium) in surface waters

Changes in land use can also make surmiddotface waters more acid Modern forestrypractices for example contribute to theproblem with drainage clear felling andthen the planting of monocultures of fastshygrowing species such as conifers In theseconditions acidic leaf litter builds up morespeedily than might be the case naturallyThis can add to the nutrient leachingeffects ofacid rain Tall trees are also moreeffective at scavenging airborne pollutshyants from douds than say upland grassshyland This serves to increase the amountof pollution deposited

Another adverse effect of acid rain isthe weathering of buildings particularlythose made from limestone marble andsandstone For example sulphate-richprecipitation reacts with limestone tobring about chemical changes (eg theformation ofcalcium sulphate or gypswn)which cause blistering while the low pHvalues encourage the dissolution of thelimestone Many of the great cathedrals ofEurope have been attacked in this way

Various methods are used to try to reducethe damaging effects ofadd deposition Oneof these is to add powdered limestone tolakes to increase their pH values Howshyever the only really effective and practicallong-term treatment is to curb the emisshysions of the offending gases This can beachieved in a variety of ways by reducingthe amount of fossil fuel combustion byusing less sulphur-rich fossil fuels byusing alternative energy sources that donot produce nitrate or sulphate gases (eghydropower or nuclear power) and byremoving the pollutants before they reachthe atmosphere For example after comshybustion at a power station sulphur can be

Acid Deposition 119

Figure 11I16 The impact of acid precipitation on the terrestrial environmentSource Various sources in Kemp (1994) figure 411

Table 11I6 Ecological effects of water pH on European freshwater fish

pH range

30-35

35-40

40-45

45-50

60-65

Effects

Unlikely that any fish can survive for more than a few hours

This range lethal to salmonids Tench roach pike and perch cansUlVive

likely to be harmful to salmonids tench bream roach goldfishand common carp Fish can become acclimatized to these levels

likely to be harmful to adults eggs and fry of salmonids Canharm common carp

Unlikely to harm fish unless free carbon dioxide concentrationgreater than 20 mgtl or water contains iron salts

Unlikely to harm fish unless free carbon dioxide in excess of 100mgI

Harmless to fish

100-105

90-95

95-100

likely to harm salmonids and perch if present for a long time

lethal to salmonids over prolonged periods

Can be withstood for only short periods by roach and salmonids

Rapidly lethal to salmonids Prolonged exposure lethal to carptench goldfish and pike

110-115 Rapidly lethal to all species of fish

Source Gleick (1993) table F2

120 The Atmosphere

removed (scrubbed) from flue gases by aprocess known as flue gas desulphurization(FGD) in which a mixture of limestoneand water is sprayed into the flue gas whichconverts the sulphur dioxide (502) intogypsum (calcium sulphate) NOx in flue

FURTHER READING

gas can be reduced by adding ammoniaand passing it over a catalyst to producenitrogen and water (a process called selecshytive catalytic reduction or SCR) NOxproduced by cars can be reduced by fittinga catalytic converter

Park C C 1987 Acid Rain Rhetoric and Reality London MethuenA general introduction that provides a useful overview

Wellburn A 1988 Air Pollution and Acid Rain The Biological Impact LondonLongmanA more advanced treatment with a strong biological emphasis

9 CoNCLUSION

Changes in the composition of the Earthsatmosphere as a result of human emissionsof trace gases and changes in the natureof land cover have caused great concernin recent years Global warming ozonedepletion and acid rain have become cenmiddottral issues in the study of environmentalchange Although most attention is oftenpaid to climatic change resulting fromgreenhouse gases there is a whole seriesofother mechanisms which have the potenshytial to cause climatic change Most notashybly we have pointed to the importance ofother changes in atmospheric compositionand properties whether these arc causedby aerosol generation or albedo change

However the greenhouse effect andglobal warming may prove to have greatsignificance for the environment and forhuman activities Huge uncertainties remainabout the speeddegree direction and spatialpatterning of potential change Nonetheshyless if the Earth warms up by a couple ofdegrees over the next hundred or so yearsthe impacts some negative and some posishytive are unlikely to ~ trivial The box inthis part on the effects of warming onagriculture in the UK indicates this clearly

For many people especially in citiesthe immediate climatic environment has

already been changed Urban climates aredifferent in many ways from those of theirrural surroundings The quality of the airin many cities has been transformed by arange of pollutants and we have pointedto the particularly serious levels of polshylution that developed in Eastern Europeand in South Africa Conversely we havepointed out that under certain circumshystances clean air legislation and othermeasures can cause rapid and often rcmiddotmarkable improvements in this area

The same is true of twO major pollutionissues - ozone depletion and acid deposishytion Both processes have serious environshymental consequences and their effects mayremain with us for many years but bothcan be slowed down or even reversed byregulating the production and output ofthe offending gases

The human impacts on the atmospherediscussed in this part of the book showclearly how different the impacts can beon different parts of the population andalso how impacts can spread widely oftenaffecting people a long way from thesource of the problem Furthermore imshypacts on the atmosphere show forcefullythe interlinked nature of environmentalsystems and the knock-on effects of manyatmospheric changes on the biospherefresh waters and land surface

Points for Rtview 121

KEy ThRMS AND CoNCEPTS

acid rainaerosolsalbedodust bowlglobal warminggreenhouse effect

POINTS FOR REVIEW

land coverozone holesUatospheric ozonethermal pollutiontropospheric ozoneurban heat island

What forces could (a) cause future climate to cool and (b) cause future climate tobecome wanner~

Can humans change regional and global precipitation patterns

Is global warming an important environmental issue and if so why~

Ozone concentrations are increasing in many cities but decreasing in the stratosphereWhy should this bd

Is acid rain an increasingly important or decreasingly important environmental issueDefend your answer

PART IV

The Waters1 Introduction 1252 River Regulation 125

bull Modification ofthe Colorado River USA 1333 Forests and River Row 136

bull George Perkins Marsh - pioneer investigatorofhuman impam on forests and hydrology 138

4 The Hydrological Response to Urbanization 1405 LutdDnimge 1426 Water Pollution 145

bull Past and present pollution ofthe River ClydeScotland 148

7 Eutrophication ISObull Controlling eutrophication Lake Bim Japan 153

8 Thennal pollution 1549 Inter-basin Water Transfers and the

Death ofthe Arll Sea 15510 Groundwater Depletion and

Groundwater Rise 15911 Conclusion 161

Key Terms and Concepts 162Points for Review 162

1 INTRODUCTION

In a recent review of the worlds freshshywater resources Gleick (1993 pl) summedup the importance of water in a few clearsentences

fresh water is a fundamental resourceintegral to all environmental and societalresponses Water is a critical componentofecological cycles Aquatic ecosystemsharbour diverse species and offer manyvaluable services Human beings requirewater to run industries to provide enshyergy and to grow food

Because water is so important to humanaffairs humans have sought to controlwater resources in a whole variety ofwaysAlso because water is such an importantpart of so many natural and human sysshytems its quantity and quality have undershygone major changes as a consequence ofhuman activities Again we can quoteGleick (1993 p 3)

As we approach the 21st century wemust now acknowledge that many ofour efforts to harness water have beeninadequate or misdirected Riverslakes and groundwater aquifers are inshycreasingly contaminated with biologishycal and chemical wastes Vast numbersof people lack clean drinking water andrudimentary sanitation services Millionsof people die every year from watershyrelated diseases such as malaria typhoidand cholera Massive water developshyments have destroyed many of theworlds most productive wetlands andother aquatic habitats

In this chapter we look at some of theways in which the quantity and quality ofwater have been modified in some ofthe worlds freshwater systems - riversgroundwater and lakes Table IVI sumshymarizes some of the hydrological effects

River Regulation 125

of land-usc change and demonstrates theirgreat number and diversity

2 RIvER REGULATION

In recent decades human demand for freshwater has increased rapidly Global wateruse has more than tripled since 1950 andnow stands at 4340 Cll km per year shyequivalent to eight times the annual flowof the Mississippi River Annual irretrievshyable water losses have increased aboutsevenfold this century

One major way of regulating rivers is tobuild dams Many new large dams havebeen built in the twentieth century espeshycially between 1945 and the early 1970sand there are now more than 36000 damsaround the world As table IV2 showslarge dams (ie more than 15 metres high)arc still being constructed in substantialnumbers especially in Asia In the late1980s some 45 very large dams (more than150 metres high) were being built Inshydeed one of the most striking features ofnewly constructed dams and reservoirs isthat they have ~come increasingly large(table IV3)

Most dams achieve their aim which isto regulate river discharge They arc alsohighly successful in meeting the needs ofsurrounding communities millions of peoshyple depend upon them for survival welmiddotfare and employment However dams havemany environmental consequences thatmayor may not have been anticipated(figure rvl) Some of these arc dealt within greater detail elsewhere (eg salinity inpart V section 5)

The River Nile before and after theconstruction of the great Aswan High Damin Egypt (table IVA) provides a goodexample of how dams retain sedimentUntil the dam was built concentrationsof silt were high in the late summer andautumn period of high flow on the NileSince the dam has been finished the silt

126 The Waters

Table IV1 Summary of the major hydrological effects of land-use changes

Land use change Hydrologicalcomponentaflected

Afforestation Annual flow(deforestation hasthe opposite Seasonal floweffects in general)

Floods

Water quality

Erosion

Climate

Agricultural Water quantityintensification

Water quality

Principal hydrological processes involved

Increased interception in wet periodsIncreased transpiration in dry periods

Increased interception and increased dryperiod transpiration reduce dry season flowDrainage improvements associated withplanting may increase dry season flowsCloud water (mist and fog) deposition ontrees will augment dry season flows

Interception reduces floods by removing aportion of the storm rainfall and allowingsoil moisture storage to increaseManagement activities such as drainageconstruction all increase floods

Leaching of nutrients reduced as surfacerunoff reduced and less application offertilizerDeposition of atmospheric pollutantsincreased because of larger exposed surfacearea of trees

High infiltration rates in natural mixedforests reduce surface runoff and erosionSlope stability enhanced by reduced soilpore water pressure and binding effect oftree rootsWind throw of trees reduces slope stabilityManagement activities (constructiondrainage) all increase erosion

Increased evaporation and reduced sensibleheat fluxes from forests affect climate

Alteration of transpiration rates affectsrunoffTiming of storm runoff altered through landdrainage

Application of inorganic fertilizers addsnutrientsPestidde application poses health risks tohumans and animalsFarm wastes pollute surface andgroundwater where inadequate disposal oforganic and inorganic wastes

Table continues opposite

River Regulation 127

Table IV1 Continued

Land use change Hydrologicalcomponentaffeded

Erosion

Principal hydrological processes involved

Cultivation without proper soil conservationmeasures and uncontrolled grazing increaseerosion

Draining wetlands Seasonal flow lowering of water table may induce soilmoisture stress reduce transpiration andincrease dry season flowsInitial dewatering on drainage will increasedry season flows

Annual flow Initial dewatering on drainage will increaseannual flowAfforestation after drainage will reduceannual flow

Floods Drainage method soil type and channelimprovement will all affect flood response

Water quality Redox potentials altered leading to peatdecomposition acidification and increasedorganic loads in runoffNew drainage systems intercepting mineralhorizons will reduce acidity

Carbon balance Accumulating peat bogs are sink foratmospheric CO2

Source Adapted from Calder (1992) table 1311

Table IV2 Number of large dams (over 15 metres high) 1950 and 1986

Continent 1950 1986 Under construction31 Dec 1986

Africa 133 885 58Asia 1562 23555 615

of which in China 8 18820 183AustralasiaOceania 151 497 25Europe 1323 4077 230North and Central America 2099 6663 39South America 885 69

TOTAL 5268 36562 1036

Source Data provided by UNEP

128 Th~ Waters

Table IV3 Worlds 20 largest reservoirs by reservoir volume

Namemiddot Country Capacity Year completed(million cu metres)

Owen Fallsb Uganda 204800 1954Bratsk FSUlt 169000 1964High Aswan Egypt 162000 1970Kariha Zimbabwe-Zambia 160368 1959Akosombo Ghana 147960 1965Daniel Johnson Canada 141851 1968Gun Venezuela 135000 1986Krasnoyarsk FSU 73300 1967W A C Bennett Canada 70309 1967Zeya FSU 68400 1978Cahara Bassa Mozambique 63000 1974La Grande 2

Barrage Canada 61715 1978La Grande 3

Barrage Canada 60020 1981Ustmiddotllim FSU 59300 1977Boguchany FSU 58200 under constructionKuibyshev FSU 58000 1955Serra da Mesa Brazil 54400 under constructionCaniapiscau

Barrage K A 3 Canada 53790 1980Bukhatarma FSU 49800 1960Ataturk Turkey 48700 1990

bull All these reservoirs have been constructed Since the Second World Warb Owen Falls capacity is not fully related to construction of a dam the major part of it is anatural lakelt Former Soviet Union

Source Modified from GJeick (1993) table G9

load is lower throughom the year and theseasonal peak is removed The Nile nowonly transports abom 8 per cent of itsnatural sediment load below the AswanHigh Dam This figure is exceptionally lowprobably because of the great length andsize of Lake Nasser the reservoir behindthe dam Other rivers for which data areavailable carry between 8 per cent and 50per cent of their natural suspended loadsbelow dams

The removal of sediment from the Nilehas various possible consequences These

include a reduction in flood-depositednutrients on fields less nutrients for fishin the south-cast Mediterranean Seaaccelerated erosion of the Nile Delta andaccelerated riverbed erosion since less sedishyment is available to cause bed aggradationThe last process is often called clearshywater erosion It may speed up the rate atwhich streams cut back into their banks inan upstream direction It may also causegroundwater tables to become lower andundermine bridge piers and other strucshytures downstream of the dam On the

River Regulation 129

WaIn chrmillry IIIImdS1mm Row ClIIIIIIllIrdIwponolicllllou IncmJtdGround _ aImecI(t bJ~)WJtor ltmptealurt ohanpI

diaurc_-shysalinity

Figure rV1 Generalized representation of the possible effects of dam constructionon human life and various components of the environment

Table IV4 Slit concentrations In the Nile at Gaafra before and after the construemiddottlon of the Aswan High Dam (ppm)

Jan Feb March April My June July Aug Sep Od Nov Dec

Before (averages for the period 1958-63)64 50 45 42 43 85 674 270 242 925 124 77

After44 47 45 50 51 49 48 45 41 43 48 47

Ratio of before to after15 11 10 08 08 17 140 600 591 215

Source AbumiddotAtia (1978) p 199

258 163

other hand in regions such as northernChina where modern dams trap silt thecutting-out of the river channel downshystream may alleviate the strain on leveesand so les~n the expense of strengthenshying or heightening the levees

However clear-water erosion does notalways follow from dam construction In

some rivers before a dam was built thesediment brought into the main streamby steep tributaries was carried away byfloods Once the dam is built these floodsno longer happen and so the sedimentaccumulates as large fans of sand or gravelbelow each tributary mouth The bed ofthe main stream is raised and any water

130 The Waters

Plate IV1 The Sagan River in southern Ethiopia The dark brown colour of thisriver is caused by its large load of sediment derived from accelerated erosionupstream This renders the river much less suitable as a source of drinking water(A S Goudie)

intakes towns or other structures thatlie alongside the river may be threatenedby flooding or channel shifting across theaccumulating wedge of sediment

Some landscapes are almost dominatedby dams canals and nservoirs Probablythe most striking example of this is thetank landscape of south-east India wheremyriads of linle streams and areas of overshyland flow have been dammed by smallearth structures to produce what Spate(Spate and Lcarmonth 1967 p 778) haslikened to a surface of vast overlappingfish-scales

In the northern part of the Indian subshycontinent in Sind the landscape changesbrought about by hydrology are no lessstriking Here the mighty snow-fed IndusRiver is controlled by large embankments(bunds) and interrupted by great damsIts waters are distributed over thousandsof square kilometres by a network ofcanals that has evolved over the past 4000years

Another direct means of river manishypulation is channelization This involvesconstructing embankments dikes lev~es

and floodwalls to confine floodwaters andimproving the ability of channels to transmiddotmit floods by enlarging their capacitythrough straightening widening deepenshying or smoothing

Some of the great rivers of the worldare now lined by extensive embankmentsystems such as those that run for morethan 1000 krn alongside the Nile 700km along the Hwang Ho in China 1400km by the Red River in Vietnam and over4500 km in the Mississippi Valley Likedarns embankments and other such strucshytures often fulfil their purpose but mayalso create environmental problems andhave some disadvantages For examplethey reduce natural storage for floodwatersboth by preventing water from spillingon to much of the floodplain and whereimpermeable f100dwalis are used by not

River Regulation 131

allowing water to be stored in the banksThe flow of water in tributaries may alsobe constrained Occasionally embankmentsmay exacerbate the flood problem theywere designed to reduce This can happenwhere the barriers downstream ofa breachprevent floodwater from draining back intothe channel once the peak has passed

Channel improvement designed to imshyprove water tlow may also have untoreshyseen or undesirable effects For examplethe more rapid movement of water alongimproved sections of a river channel canaggravate Rood peaks further downstreamand cause excessive erosion The loweringof water tables in the improved reachmay cause overdrainage of adjacent agrishycultural land In such cases sluices needto be constructed in the channel to mainshytain levels On the other hand channelslined with impermeable material mayobstruct soil water movement (interflow)and shallow groundwater flow therebycausing surface saturation

Channelization may also have variouseffects on fauna These may result fromfaster water flow reduced shelter in thechannel bed and reduced food suppliesdue to the destruction ofoverhanging bankvegetation If channelization of rivers werecarried out in large swamps like those ofthe Sudd in Sudan or the Okavango inBotswana where plans to do so exist itcould compktely transform the whole charshyacter of the swamp environment

Another type of channel modification isthe construction of bypass and diversionchannels either to carry excess floodwateror to enable irrigation to take place Thewe of such channels may be as old asirrigation itself They may contribute tothe salinity problems encountered in manyirrigated areas (see part V section 5)

Deliberate modification ofa river regimecan also be achieved by long-distance intershybasin water transfers (Shiklomanov1985and see section 9 below) Such transfers

132 The Waters

are necessitated by the unequal spatialdistribution of water resources and by theincreasing rates of water consumption Atpresent the world water consumption forall needs is 4340 cu km per year ninetimes what it was at the beginning of thetwentieth century By the year 2000 it isexpected to be 6000 sq km per year The[Ota volume of water in the various transshyfer systems in operation and under conmiddotstruction throughout the world at presentis about 300 sq km per year The greatestvolumes of transfers take place in Canadathe former USSR the USA and India

It is likely that many even greaterschemes will be constructed in future deshycades Route lengths of some hundreds ofkilometres will be common and the waterbalances of many rivers and lakes will betransformed (See section 9 below for whathas already happened to the Ami Sea)

A human activity that affects manycoastal portions of rivers or estuariesis dredging The effects of dredging canbe as complex as the effects of dams andreservoirs upstream (La Roe 1977) Dredshyging may be performed to create andmaintain canals navigation channels turn-

FURTHER READING

ing basins harbours and marinas to laypipelines and to obtain a source of matershyial for filling or construction The ecoshylogical effects of dredging are various Inthe first place filling directly disrupts habishytatS like salt marshes Second the largequantities of suspended silt generated canphysically smother plants and animals thatlive on river and estuary beds smotherfish by dogging their gills reduce photoshysynthesis through the effects of turbidityand lead to eutrophication by releasinglarge quantities of nutrients Ukewise thedestruction of marshes mangroves and seagrasses by dredging and filling can resultin the loss of these natural purifYing sysshytems (see part II section 9 on wetlands)The removal of vegetation may also causeerosion Moreover as silt deposits stirredup by dredging accumulate elsewhere inthe estuary they tend to create a falsebottom The dredged bonom with itsshifting unstable sediments is recolonizedby fauna and flora only slowly if at allFurthermore dredging tends to changethe configuration of currents and the rateof freshwater drainage and may provideavenues for salt-water intrusion

Brookes A 1985 River channelization traditional engineering methods physicalconsequences and alternative practices Progress in Physical Geography 9 44-73An advanced review by a leading authority

Gleick P H (ed) 1993 Water in Crisis A Guide to the World)s Freshwater ResourcesNew York Oxford University PressAn invaluable compendium of information on all aspects of water use and misuse Itcontains many useful tables of data

Gregory K J 1985 The impact of river channelization Geographjcal ]ournalI5153-74A useful overview in a relatively accessible journal

Petts G E 1985 Impounded Rjvers Perspeujves for Ecological Management Chichshyester WileyAn advanced textbook that looks at the large range ofconsequences ofdam construction

River Regulation J33

Modification of the Colorado River USA

Plate IV2 The Hoover Dam on the Colorado River Arizona USA The flowof the river and its sediment load are now almost totally controlled(TripM lee)

The Colorado River in the American WeSt (figure IY2(araquo which Aows throughthe Grand Canyon has been at several points dammed to control Aoods generateelectricity and provide water for irrigation Among the major dams are the Hooshyver and Glen Canyon dams both over 200 m high (figure JV2(b)) They havecaused radical adjustments in the hydrological regime Flood peaks are reducedas a flood control strategy and water is released at times of low Aow Dischargevaries rapidly in response to fluctuations in the need for hydropower during thecourse of a day The high dams trap most of the sediment carried by the riverSO that downstream discharges are largely sediment-free In the Colorado Riverthis combination of impacts has changed a natural river with very large springfloods lower summer flows and little daily variation ofsediment-laden waters intoa highly controlled system with only modest flood peaks in spring relatively highsummer flows and drastic daily variation of discharges of clear water Indeed atits seaward end the Colorado has been totally transformed Prior to 1930 beforethe dams were built it carried around 125-130 million tons of suspended sedishyment per year to irs delta at the head of the Gulf of California (figure IV2(c))Now the Colorado discharges neither sediment nor water to the sea Upstream

134- The Waters

(j

o ISO kmI

NEVADA

(AUFQRNlA

WYOMING

COlORADO

NEW MEXICO

----~IP~--~

1750

6000 g

]bull ]bull

3000 -g

River Regulation 135

PREmiddotDAM

~

f~~

-I ~-

rO$TmiddotDAM

bullwbull

bull bullr~1

--J-t-J

z-~hj~

~middot~oo-~11---~~lJ

(d)

w

1961l 197019lt40 1950

Walfrynr

Water discllarge (m~IiOllI ofam-ftetJyr)

()

1910 1920 1930 l~ 1950 116O 1910 1400 Suspmdeltktdiment dischargt (milliorui of lonlyr)

Figure IV2 (a) The Colorado River basin (b) Profiles of the Green andColorado Rivers showing locations of dams reservoirs and whitewatercanyons (c) Historical sediment and water discharge of the Colorado River(d) Pre- and post-dam riparian vegetation in the Grand Canyon downstreamfrom Glen Canyon dam Vegetation lones 1 stable desert vegetation2 stable woody vegetation 3 unstable lone 4 new riparian vegetationphreatophytesSources (a) After Schwarz et al (1990) (b) After various sources in Graf (1985)fig 13 (c) After Schwarz et al (1990) (d) After Graf (1985) from original byS W Carothers

in the vicinity of the Grand Canyon riparian vegetation communities have beencompletely changed since the construction of the Glen Canyon dam (figurelV2(d))

Further reading

Graf W L 1985 The Colorado Rifler Instability and Basi Management Washshyington DC Association of American Geognphers

136 The Waters

3 FORESTS AND RIvER FLOW

When George Perkins Marsh wrote hisremarkable book Man and Nature in1864 one of the main themes which conshycerned him was the consequences of forshyest removal In the early twentieth centuryscientists in America began to measurethe effects of forest removal on streamdischarges To do this they used what issometimes called the paired watershedtechnique First they compared the flowsOUt of two similar watersheds (catchments)over a period of years Then they c1earshyfelled one of the watersheds to see howthat basin responded in comparison withthe unchanged control valley The pioneershying study at Wagon Wheel Gap in ColoradoUSA in 1910 revealed that the clear-felledvalley yielded 17 per cent more waterflowthan would have been expected if it hadremained unchanged like the control valleySubsequent studies in the tropics haveindicated that dear-felling can lead to meanannual stream flow increases equivalent toabout 400-450 mm of rainfall

There are many reasons why the removalof a forest cover and its replacement withpasture crops or bare ground have suchimportant effects on stream flow A mashyture forest probably intercepts a higherproportion of rainfall tends to reduce fatesof overland flow and promotes soils witha higher infiltration capacity and bettergeneral structure All these factors ill tendto produce both a reduction in overallrunolT levels and less extreme flood peaksthough this is not invariably the case

Reforestation of abandoned farmlandsreverses the elTects of deforestation inshycreased interception of rainfall and higherlevels of evapotranspiration can cause adecline in water yield to rivers This cancause problems for human activities

Reviews ofcatchment experiments frommany parts of the world have pointed totwo conclusions

bull Pine and eucalypt forest types cause anaverage change of 40 mm in annualflow for a 10 per cent change in coverwith respect to grasslands that is a10 per cent increase in forest cover ongrassland will decrease annual flow by40 mm and a 10 per cent decrease incover will increase annual flow by thesame amount

bull The equivalent effect on annual flowof a 10 per cent change in cover ofdeciduous hardwood or scrub is 10shy25 mm that is if 10 per cem of agrassland catchment is converted tohardwood trees or scrub vegetation theannual runoff will decrease by 10-25mm

The increase in annual flow that resultsfrom tree or scrub removal tends to bemost marked in two particular environshyments those with very high rainfall andthose with very low rainfall In the formerevaporation from forest will tend to behigher than that from other land usesbecause of high levels of rainfall intercepshytion In the latter evaporation from forestis likely to be higher than that from otherland uses because forests composed oftrees that have deep root systems arebetter able to make use of soil andgroundwater reserves

Having discussed changes in annualflows now let us turn to a considerationof how forest removal influences low seashyson flows and flood peaks The higherlosses from forests in wet seasons fromrainfall interception and increased lossesin dry seasons from transpiration (becauseof trees deeper root systems) both tendto increase soil moisture deficits in dryseasons compared to those under otherland uses On the other hand in forests athigh altitudes whete there is a lot ofwaterdeposition on to trees from clouds thismay provide a significant component ofthe dry season flows in rivers and also

Forests and River Flow 137

Plate IV3 A well-managed tea and rubber plantation in the Nilgiri hills southernIndia (A S Goudie)

increase runoff The same applies in areaswith high-intensity storms where highshyintensity rainfall may lead to high 1Celsof surfolce runoff The higher infiltrationrates under indigenous forest comparedwith other land usa may help soils andtheir below-ground aquifers to rechargethemselves In steeply sloped areas forestsmay have the additional benefit of reducshying landslips (see part V section 6) andpreserving the soil aquifer which may bethe source of dry season flows Boththese effecLS of afforestation may there-

FURTHER READING

fore benefit stream flows in the lowseason

When it comes to flood peaks there isstill a great dcaJ of controversy as to howimportant forest cover is with respect tothe largest types of event Some authorssuggest that management practices assoshyciated with forestry (eg the building ofroads culverts and drainage ditches) orsubsequent activities (eg grazing) whichpromote the flood by causing compactionof the soil and reducing its infiltrationcapacity increase this type of hazard

1 R Calder 1992 Hydrologic e(fects ofland-usc change In D R Maidment (ed)HRndbool of Hydrology pp 131-1350 New York McGraw HillA Iengthy and detailed summary of the available Iiterature

138 The Waters

George Perkins Marsh pioneer investigator ofhuman impacts on forests and hydrology

George Perkins Marsh (1801-82) was born in Vermont USA and can be reshygarded as one of the most important pioneers of the conservation movcment In1864 he wrote Man and Nature This book was the product of two majorinfluences on him first his upbringing in New England and secondly his expeshyriences working for the US government in Turkey and elsewhere around theMediterranean basin In it he recognized how human occupation of the land hadtransformed it This brief extract from Man and NRture in which he deals withthe consequences of forest destruction gives a good indication of his clear anddirect style

With the disappearance of the forest all is changed At one season the earthparts with its warmth by radiation to an open sky - receives at another animmoderate heat from the unobstructed rays of the sun Henee the climatebecomes excessive and the soil is alternately parched by the fervors of summerand seared by the rigors of winter Bleak winds sweep unresisted over itssurface drift away the snow that sheltered it from the frost and dry up itsscanty moisture The precipitation becomes as regular as the temperature themelting snows and vernal rains no longer absorbed by a loose and bibulousvegetable mould rush over the frozen surface and pour down the valleysseaward instead of filling a retentive bed of absorbent earth and storing upa supply of moisture to feed perennial springs The soil is bared of its coveringof leaves broken and loosened by the plough deprived of the fibrous rootletswhich hold it together dried and pulverized by sun and wind and at lastexhausted by new combinations The face of the earth is no longer a spongebut a dust heap and the floods which the waters of the sky pour over it hurryswiftly along irs slopes carrying in suspension vast quantities of earthly partishycles which increase the abrading power and mechanical force of the currentand augmented by the sand and gravel of falling banks fill the beds of thestreams divert them into new channels and obstruct their outlets The rivushylets wanting their former regularity of supply and deprived of the protectingshade of the woods are heated evaporated and thus reduced in their summercurrents but swollen to raging torrents in autumn and spring From thesecauses there is a constant degradation of the uplands and a consequentelevation of the beds of the watercourses and of lakes by the deposition of themineral and vegetable matter carried down by the waters The channels ofgreat rivers become unnavigable their estuaries are choked up and harborswhich once sheltered large navies are shoaled by dangerous sandbars Theearth stripped of its vegetable glebe grows less and less productive andconsequently less able to protect itself by weaving a new carpet of turf toshield it from wind and sun and scouring rain Gradually it becomes altogetherbarren The washing of the soil from the mountains leaves bare ridges ofsterilerock and the rich organic mould which covered them now swept down intothe dank low grounds promotes a luxuriance of aquatic vegetation that breedsfever and more insidious forms of mortal disease by its decay and thus theearth is rendered no longer fit for the habitation of man

~t i

Forests and River Flow 139

MARSH 186r PHOTOGRAPH BY BRADY

Courtesy of Frederick H Meserve

Plate IV4 George Perkins Marsh author of Man and Nature (1864)and one of the major proponents of nature conservation

Further reading

Marsh G P18M Man and Nture (quoted from edition by D Lowenthal 1965Cambridge Mass Belknap Press of Harvard University Press pp 186-7)

140 The Waters

4 ThE HYDROLOGICAL

RESPONSE TO

URBANIZATION

The remarkable growth of the number andsize of cities in recent decades has createdmany new impacts on water resources anddistribution For example cities modify theprecipitation characterinics of their imshymediate environs (see par[ III section 5)They aso can cause changes in waterquality through thermal pollution (seesection 8 below) and chemical pollution(see section 6 below) Moreover the deshymand for water by city populations maybe so great that groundwater is mined fromcity aquifers (see section 10 below) andlarge amounts are brought in by inter-basinwater transfers Los Angeles for examplereceives water from distant parts of northshyern California In this section howeverwe will concentrate on the effect of urshybanization on river flow characteristics

Research in various countries has shownthat urbanization influences flood runoffFor example figure IV3 shows in a scheshymatic way the hydrological changes resultshying from urbanization in a part ofCanadaThese changes are caused mainly by theproduction of extended surfaces of tarmactiles and concrete Because these impershymeable surfaces have much lower infilshytration capacities than rural vegetatedsurfaces they generate a rapid response torainfall This response is further accelershyated by sewers storm drains and the likewhich are very efficient at catching andtransporting city rainfall In general thegreater the area that is sewered the greateris the discharge that will occur in any givenperiod of time In other words the intershyval between flood events becomes progresshysively shorter Moreover peak dischargesare higher and occur sooner after runoffstarts in basins that have been affectedby urbanization and sewer construction

Indpilllion

URBAN

Figure IV3 Hydrological changes inOntario Canada caused byurbanizationSource After OECD (1986) p 43

Table IV5 shows the impact of differentinfluences resulting from the urbanizationprocess

Some workers have found that urbanishyzation has a proportionately greater effecton smaller flood events than on larger oncsIn other words the effects of urbanizashytion appear less important as the size ofthe flood and the interval between floodsincrease A probable explanation for this isthat during a severe and prolonged rainmiddotstorm a rura catchment may become sosaturated over large areas and its channelnetwork so extended that it begins tobehave almost as if it were an imperviousurban catchment with a dense storm drainnetwork Under these conditions a ruralcatchment produces floods rather similarto those of its urban counterpart Alsoin very large floods subsurface drains indties may not be large enough to takethe volume ofwater resulting in less rapidand lower discharge

Urbanization 141

Table IVS Potential hydrological effects of urbanization

Urbanizing influence

Removal of trees andvegetation

Initial construction of housesstreets and culverts

Complete development ofresidential commercial andindustrial areas

Construction of storm drainsand channel improvements

Source KIbler (1982)

Potential hydrological response

Deltreased evapotranspiration and interceptionincreased stream sedimentation

Decreased infiltration and lowered groundwatertable increased storm flows and decreased baseflows during dry periods

Decreased porosity redUcing time of runoffconcentration thereby increasing peak dischargesand compressing the time distribution of the flowgreatly increased volume of runoff and flooddamage potential

Local relief from flooding concentration offloodwaters may aggravate flood problemsdownstream

I~middottPtKtfWIOO

ggt~i~f~~~

Lokinl waltlt mailgtl alwo)$

diJcha1 alrr II undu ~

Rrduetioniolrrfor e-apol1llUpirgttion

SfwI disltllgtrging 0--Stwm akiosn 8wllrr

I+---------III( in rn-------_ 11__ 0lt rrhllgr-----+-j

Figure IV4 Urban effects on groundwater rechargeSource After Lerner (1990) fig 2

Different dties different constructionmethods and other variable factors willall affect the response to rainfall inputsand we should avoid overgeneralizationUrban groundwater provides an exampleWe have suggested that surface runoff isincreased by the presence of impermeable

surfaces One consequence of this wouldbe that less water went to recharge groundshywater However there is an alternatiwpoint of view namely [hat groundwaterrecharge can be accelerated in urban areasbecause of leaking water mains sewersseptic tanks and soakaways (figure rv4)

142 The Waters

In cities in arid areas there is often noadequate provision for storm runoff andthe (rare) increased runoff from impermeshyable surfaces will infiltrate into the permeshyable surroundings In some cities rechargemay result from over-irrigation of parks

FURTHER READING

and gardens Indeed where the climate isdry or where large supplies of water areimported or where pipes and drains arepoorly maintained groundwater rechargein urban areas is likely to exceed that inrural areas

urner D 1990 Groundwater Rechatge in Urban Areas 59-65 IAHS Publicationno 198A cogent account of the role of groundwater in the urban environment

5 LAND DRAINAGE

The drainage of wet soils has been one ofthe most successful ways in which ruralcommunities have striven to increase agri~

cultural productivity It was for examplepractised centuries ago by the EtruscansGreeks and Romans

Large areas of marshland floodplain andother wetlands have been drained to hushyman advantage When water is led awaythe water table is lowered and stabilizedproviding greater soil depth for plant rootshying Moreover well-drained soils warm upearlier in the spring and thus permit cropsto be planted and to germinate earlierFarming is easier if the soil is not too wetsince the damage to crops by wimer freezshying may be reduced undesirable salts arecarried away from irrigated areas and thegeneral physical condition of the soil isimproved In addition drained land tendsto be flat and so is less prone to erosionand more amenable to mechanical cultivashytion It will also be less prone to droughtrisk than certain other types of land Byreducing the area of saturated grounddrainage can alleviate flood risk in somesituations by limiting the extent ofa drainshyage basin that generates saturation excessoverland flow but this is an issue we shallreturn to later

The most spectacular feats of drainageare the arterial drainage systems involv-

ing the construction of veritable rivers andnetworks of large dikes seen for examplein the Netherlands and the Fenlands ofeastern England These have received muchanention However more widespread thanarterial drainage and sometimes independshyent of it is the drainage of individual fieldsThis is done either by surface ditching orby underdrainage with tile pipes and thelike In Finland Denmark Great Britainthe Netherlands Hungary and the fertileMidwest of the USA the majority ofagricultural land is drained

In Britain underdrainage was promotedby government grants and in the 1970s inEngland and Wales reached a peak ofabout1 million hectares per year More recentlygovernment subsidies have been cut andthe uncertain economic future of farminghas led to a reduction in farm expenditureBoth tendencies have led to a reductionin the growth of field drainage which isnow being extended by only about 40000hectares per year (Robinson 1990)

Drainage is a widespread practice whichhas many advantages and benefits Howshyever it can also have environmental costsThe first of these is related to a reductionin the extent of highly important wetlandwildlife habitats (see part II section 9)Marshes fens and swamps are of majorecological significance for a wide range ofspecies

Secondly the drainage oforganically rich

Land Drainage 143

Plate IVS Drainage maintenance on agricultural land in the Fenlands of easternEngland at Spalding in lincolnshire (EPLRichard Teeuw)

Similar subsidence has taken place followshying drainage of portions of the Florida

Figure IVS The subsidence of theEnglish Fenlands peat in Holme FenPost from 1842 to 1960 followingdrainageSource After Goudie (1993) fig 68 fromdata in Fillenham (1963)

sa-kYt1 (OrdnanCf Datum)

bullbull0

-

soils (such as those that contain much peat)can lead to the degradation and eventualdisappearance of peaty materials which inthe early stages of post-drainage cultivashytion may be highly productive for agriculshyture The lowering of the water table makespeats susceptible to oxidation and deflashytion (removal by wind) so that their volshyume decreases One of the longest recordsof this process and one of the clearestdemonstrations of its efficacy has beenprovided by the measurements at HolmeFen Post in the English Fenlands Approximiddotmately 38 metres of subsidence occurredbetween 1848 and 1957 with the fastestrate occurring soon after drainage had beeninitiated (figure IVS) The present rateaverages about 14 em per year At itsmaximum natural extent before the Midshydle Ages the peat of the English Fernandcovered around 1750 sq Ion Now onlyabout one-quarter (430 sq km) remains

144 The Waters

Everglades there rates of subsidence of32 cm per year have been recorded

The moisture content of the soil canalso affect the degree to which soils aresubjected to expansion and contractioneffects which in turn may affect engineershying structures in areas with expansivesoils Particular problems are posed by soilscontaining smectite clays When drainedthey may dry Out and shrink and the soilmay crack damaging the foundations ofbuildings

In Britain there has been considerabledebate about the effects on river Oowsand in particular on flood peaks of drainshying upland peat areas for afforestationThere appear to be some cases where floodpeaks have increased after peat drainageand others where they have decreased Ithas been suggested that differences in peattype alone might account for the differenteffects Thus it is possible that the drainshyage of a catchment dominated by theSphagnum moss would lead to increasedflooding since drainage compacts Sphagshynum reducing both its storage volume andits permeability On the other hand in thecase of peat where Sphagnum moss didnot grow there would be relatively lesschange in structure but there would be areduction in moisture content and an inshycrease in storage capacity thereby tendingto reduce flood flows The nature of thepeat is however just one feature to beconsidered The intensity of the drainageworks (depth spacing etc) may also beimportant In any case there may be two(sometimes conflicting) processes operatshying as a result of peat drainage the inshycreased drainage network will encouragerapid runoff while the drier soil condishytions will provide greater storage for rainshyfall Which of these two tendencies isdominant will depend on local catchmentconditions

The impact of land drainage upon theincidence of floods downstream has alsolong been a source of controversy This

impact depends on the size of the areabeing considered the nature of land manshyagement and the character of the soil thathas been drained Robinson (1990) conshyducted a detailed review of experience inthe UK and found that the drainage ofheavy clay soils that are prone to prolongedsurface saturation in their undrained stategenerally led to a reduction of large andmedium flow peaks He attributed thisto the fact that their natural responsewith limited soil water storage availableis flashy whereas their drainage largelyeliminates surface saturation By contrastthe drainage of permeable soils which areless prone to such surface saturationimproves the speed of subsurface flowthereby tending to increase peak flowlevels

As with so many environmental issuesit is not always easy to determine whetheran increase in flood frequency or intensityis the result of land-use changes of thetype we have been discussing or whethersome natural changes in lOlinfall have playeda dominant role In central and southernWales for example there is some clearevidence of changes in the magnitude andfrequency of floods over recent decadesThis has sometimes been attributed to theincreasing amount of afforestation that hasbeen carried out by the Forestry Commis~

sian since the First World War and to thedrainage of upland areas that this has neshycessitated While in the Severn catchmentthis appears to be a partial explanation inother river basins the main cause of morefrequent and intense floods appears to havebeen a marked increase in the magnitudeand frequency of heavy daily rainfalls Forexample in the case of the Tawe Valleynear Swansea of 17 major floods since1875 14 occurred between 1929 and1981 and only 3 between 1875 and 1928Of 22 widespread heavy rainfalls in theTawe catchment since 1875 only 2 occurshyred during 1875-1928 but 20 bccween1929 and 1981 (Walsh et aI 1982)

Water Pollution 145

FURTHER REAoING

Robinson M 1990 Impact of Improved Land Drainage on River Flows Institute ofHydrology Wallingford UK Report no 113A state-of-the~art review produced by the UKs leading institute for the study ofhydrology

6 WATER POLLUTION

The activities of humans have begun todominate the quality of natural riverwaters both locally and increasingly at aregional scale The ever-increasing humanpopulation and its growing wasteload havebegun to overtax the recycling capabilitiesof rivers The water pollution challengesthat the world faces are enormous Theycan be categorized according to sourceinto three main groups

bull Municipal waste This is composedprimarily of human excreta While itcontains relatively few chemical conshytaminants it carries numerous pathoshygenic micro-organisms

bull InduseriRI wastes These are of veryvaried composition depending uponthe type of industry or processingactivity and they may contain a widevariety of both organic and inorganicsubstances

bull AgriculturRl wastes These are comshyposed of the excess phosphorus andnitrogen present in synthetic fertilmiddotizers and in animal wastes as well asresidues from a number of pesticidesand herbicides

It is also possible to categorize waterpollutants according to whether or notthey are derived from point or nonshypoint (also called diffuse) sources (figshyure N6) Municipal and industrial wastestend to full into the former category beshycause they are emitted from one specificand identifiable place (eg a sewage pipeor industrial outfill) Pollutants from nonmiddot

- ~--~~~~~~---

Figure IV6 Diffuse and point sourcesof pollution into river systemsSource After Newson (1992) fig 77

point sources include agricultural wastesmany of which enter rivers in a diffusemanner as chemicals percolate into groundshywater or are washed off into fields as wellas some mining pollmants uncollectedsewage and some urban stormwater runoff

Possibly the most useful way to categorshyize pollutants is on the basis of their chemishycal physical or biological composition andthis is the framework we shall use for therest of this section We will not cover thewhole range of waste pollutants but conshycentmte on three groups

bull nitrates and phosphatesbull metalsbull synthetic and industrial organic

pollutants

146 The Waters

Nitrates and phosphates are an importamcause of a process called eutrophication(see section 7 below) Nitrates normallyoccur in drainage waters and are derivedfrom soil nitrogen from nitrogen-richgeological deposits and from Mffiosphericdeposition Anthropogenic sources includesynthetic fertilizers sewagl and animalwastlS from feedlots Land-use changes(Ig logging) can also increasl nitrateinputs to streams Perhaps 3S much as oneshythird of the total dissolved nitrogen in riverwaters throughout the world is the resultof pollurion Indeed Peierls et ai (1991)have demonstrated that the quantity ofnitrates in rivers worldwide now appearsto be closely linked to the density ofhuman population nearby Using publisheddata for 42 major rivers they found ahighly significant correlation between nishytrate concentration and human populationdensity that explained 76 per cent of thevariation in nitrate concentration for the42 rivers They maintain that human acshytivity clearly dominates nitrate export fromland Nitrate levels in English rivers arenow clearly rising Current levels (1990s)are between 50 per cem and 400 per centhigher than a quarter of a century ago

Phosphate levels are also rising in someparts of the world Major sources includedetergents fertilizers and human wastes

MetalJ are another major class of pollutshyants Like nitrates and phosphates metalsoccur naturally in soil and water Howshyever as the human use of metals hasburgeoned so has the amount of waterpollution they cause Other factors alsocontribute to water pollution from metmiddotalso Some metal ions reach river watersbecause they become more quickly mobishylized as a result of acid rain (sec part IIIsection 8) Aluminium is a notable examshyple of this From a human point of viewthe metals of greatest concern arc probshyably lead mercury arsenic and cadmium

all of which have adverse health effectsOther metals can be toxic to aquatic lifeand these include copper silver seleniumzinc and chromium

The anthropogenic sources of metalpollution include the industrial processingof ores and minerals the use of metalsthe leaching of metals from garbage andsolid waste dumps and animal and hushyman excretions Nriagu and Pacyna (1988)estimated the global anthropogenic inputsof trace metals into aquatic systems (inshycluding the oceans) and concluded thatthe sources producing the greatest quanshytities were in descending order the folshylowing (the metals produced by eachsource are listed in parentheses)

bull domestic wastewater effluents (arsenicchromium copper manganese nickel)

bull coal-burning power stations (arsenicmercury selenium)

bull non-ferrous metal smelters (cadmiumnickel lead selenium)

bull iron and steel plants (chromium molybshydenum antimony zinc)

bull the dumping ofsewage sludge (arsenicmanganese lead)

However in some parts of the worldmetal pollution may be derived from othersources There is increasing evidence forexample that in the western USA waterderived from the drainage of irrigated landsmay contain high concentrations of toxicor potentially toxic trace elements suchas arsenic boron chromium molybdenumand selenium These can cause humanhealth problems and poison fish and wildshylife in desert wetlands (Lently 1994)

Synthetic and industrial ollInic polutllnnhave been manufactured and released invery large quantities since the 1960s Thedispersal of these substances into watershycourses has resulted in widespread envirshyonmental contamination There are manytens of thousands of synthetic organic

compounds currendy in use and many arethought [Q be hazardous [Q human healthand to aquatic life even at quite low conshycemratiolls - concentrations possibly lowerthan those that can routinclr be measuredby commonl~ available analytical methodsAmong thesl pollutants are syntheticorganic pesticides including chlorinatedhydrocarbon illst([icides (eg DDT) Someof these can rlach harmful concentrationsas a result of biological magnification inthe food chain Other important organicpollutams include PCBs which have beenused extensively in the electrical industry

FURTHER READING

Water Pollution 147

as di-electrics in large trl11stormers andcapacitors PAHs which result ti-om thlincompkte burning of I(lssil fuels variousorganic sohcnrs mcd in industrill anddomestic processes phth~IIltlmiddotS which Ireplasticizers used Illr exunpk in Ih proshyduction of polyvil1~1 chloride rlsills andDBPs which arl a mngc of JisinlcCliollby-products The long-term hlalth tttl-ctsof cumulativc exposure 10 such substancesare difficult to qlanti~ However somework suggests that rhey may be implicatcdin the development of birth detects andcertain types of cancer

Nash L 1993 Water quality and health In P H Gldck (ed) Water in Crisis AGuide to the WorJdJs Freshwater Resources 25-39 New York Oxford University PressAn excellent summary of pollution characteristics and effects

148 The Waters

Past and present pollution of the River ClydeScotlandThe River Clyde which runs woughGlasgow in Scotland has a mean disshycharge of 41 cu mecres per secondh is tidal in its lower sections up [Q

the Tidal Weir upstream of the AlbertBridge It has had a long hiswry ofpollution In 1872 the Royal RiverPollution Commission found theClyde to be the most pollU[ed riverin Scotland Parts were described asa foul and stinking flood Until thebeginning of the nineteenth centurythe river was probably quite deaneven in the heart of Glasgow Howshyever by 1845-50 fish populationshad been eliminated from the upperestuary Poor oxygen conditionsprevented them from returning until1972 (McLusky 1994) In 1872the Clyde through Glasgow was deshyscribed thus its water is loaded with sewage mud fould with sewage gas andpoisoned by sewage waste of every kind - from dye works chemical worksbleach works paraffin oil works tanyards distilleries privies and water closets(quoted in Hammerwn 1994)

This alarming pollution had come about because of the enormous boom inpopulation and industry in the area In summer many of the lower tributarieseg the Black Cart and White Cart were no more than open sewers conveyingsewage and industrial wastes to the main river By the 1930s over fifty years afterthe Commissions report the river was if anything in a worse condition Progressin cleaning it up was hindered by the two world wars and it was only in 1965that effective legislation began [Q improve things In 1968 when the first bioshylogical surveys of the Clyde were done (figure IV7(araquo no fish were foundwithin the boundary of Glasgow nor in the lower reaches of the North CalderSouth Calder Kelvin Black Cart and White Cart By autumn 1983 Atlanticsalmon (Salmo samar) had returned to the Clyde and some fish are now foundin all the river areas shown in figure IV7 Since 1972 dissolved oxygen levels inthe Clyde estuary have improved markedly The greatly improved pol1ution situ~

arion achieved by 1988 is shown in figure rv7(b) The number offish speciesin the upper estuary has steadily increased to 18 in 1978 34 in 1984 and 40in 1992 Thus even rivers with a long history of dire poUution can be cleanedup and their fauna and flora restored

Wat~r Polllltioll 149

Plate IV6 The River Clyde in Central Glasgow (Graham BurnsEnvironmental Picture library)

Figure IV7 The changing pollution of the River Clyde Scotland based onbiological classification of pollution (a) 1968 (b) 1988Source After Hammerton (1994) figs 201202

150 The Waters

7 EUTROPHICATION

The process ofeutrophication can be wellillustrated by the case of the Black Sea

The Black Sea is a very large body ofwater surrounded by land except for itsnarrow shallow connection to the Medishyterranean Sea called the Bosporus It reshyceives river discharge from a land area fivetimes greater than its own and coveringparts of nine different countries Two ofEuropes largest rivers the Danube andthe Dneiper flow into it Over 162 milshylion people live within the catchments ofthese rivers (Mee 1992) Therefore polshylution generated by all these people headsfor the Black Sea The Danube for examshyple currently introduces 60000 tons ofphosphorus per year and some 340000tons of total inorganic nitrogen into theSea

As a result and in spite of its size theBlack Sea shows many of the classic sympshytoms of a process caUed eutrophicationThe symptoms include

bull A gradual shallowing right across thebasin of the so-called euphotic zone(the surface layer ofwater in which thelight level is sufficient for net biologishycal primary production) In otherwords the lake is becoming more turshybid or cloudy thereby reducing theamount of light available to supportlife The decreased light penetration hasresulted in the massive loss oflarge shalshylowmiddotwater plants

bull Dense blooms of a single species ofnanoplankton have developed drashymatically modifying the base of themarine food chain

bull Widespread hypoxia (reduction ofoxygen levels) resulting from the enorshymollS increase in organic matter fallingto the shelf floor from blooming anddecaying organisms Thishas led to the

complete elimination of a large proshyportion of macrobenthie organismsand the demise of formerly rich comshymercial fisheries

What precisely is eutrophication Funshydamentally it is the enrichment of watersby nutrients Among these nutrientsphosphorus and nitrogen arc particularlyimportant as they regulate the growthof aquatic plants The process does occurnaturally - for example when lakes getolder - but it can be accelerated by hushyman activities both by runoff from fertilshyized and manured agricultural land andby the discharge of domestic sewage andindustrial effluents This amhropogenicallyaccelerated eutrophication - often calledcuJmraI eutrophication - commonly leadsas in the case of the Black Sea to excesmiddotsive growths of algae serious depletion ofdissolved oxygen as algae decay after deathand in extreme cases to an inability tosupport fish life It can affect all waterbodies from streams to lakes to estuariesand coastal seas Coastal and estuarywaters are sometimes affected by algal foamand scum often called red tides Someof these blooms arc so toxic that consumshyers of seafood that has been exposed to

them can be affected by diarrhoea someshytimes fatally

The nature of red tides has recently beendiscussed by Anderson (1994) who pointsout that these blooms produced bycertain types of phytoplankton (tiny pigshymented plana) can grow in such abundshyance that they change the colour of theseawater not only to red but also to brownor even green They may be sufficientlytoxic to kill marine animals such as fishand seals Long-term studies at the localand regional level in many parts of theworld suggest that these so-called red tidesare increasing in extent and frequency ascoastal pollution worsens and nutrientenrichment occurs more often

Eutrophication 151

Figure IV8 The natural process of lakeeutrophicationSource After Mannion (1991) fig 63

NIIIritnl input iaIioninm

with

L

Mlt- tnaltllI ftIlICn Iho mInml_ so t1u1 nulritnts IIoOlnodily Igtlibbk (intK) lG

oqwlic 1oninns

INCJWING Nl1T1UENT uvwbull HYDJOSW IJEVELOPS

~iIIP

bull LOW NUTlIOO IllPUTSmiddot1tlGlt DISSOLVW OXYGEN LpoundVpoundlS

bull HIGH NUTIIENT IlVpoundLSbull MAY HAVE lEDUCEDOXYQN UVFLS

Figure IV9 The major components ofthe drainage basin nutrient cycleleading to cultural eutrophicationSource After Newson (1992) fig 74

-

Initially coral productivity increases withrising nutrient supplies At the sametime however corals are losing their keyadvantage over other organisms theirsymbiotic self-sufficiency in nutrientshypoor seas As eutrophication progressesalgae start to win out over corals fornewly opened spaces on the reef beshycause they grow more rapidly than corshyals when fertilized The normally dearwaters cloud as phytoplankton begin tomultiply reducing the intensity of thesunlight reaching the corals furtherlowering their ability to compete At acertain point nutrients in the surroundshying waters begin to overfertilize thecorals own zooxanthdlae which multishyply to toxic levels inside the polypsEutrophication may also lead to blackband and white band disease twodeadly coral disorders thought to becaused by algal infections Throughthese stages of eutrophication thehealth and diversity of reefs declinespotentially leading to death

Eutrophication also has adverse effectson coral reefs This has been explained byWltbe (1993 p 49)

The natural process of eutrophication isshown in figure IVS using the exampleof how a lake ages What has happenedparticularly since the Second World Waris that various human actions have speededup the natural process (figure IV9) Thegrowth in fertilizer usage in the last fivedecades has been increasingly rapid Inspite of the increasing costs of energysupplies and hydrocarbons (from whichmany of the fertilizers are derived) in the1970s world fertilizer production hascontinued to rise inexorably and fertilizershyderived nitrates reach groundwater andrivers For example the mean annual nitrateconcentration of the River Thames whichprovides most of Londons water supplyincreased from around 11 mg per litre in1928 to 35 mg per litre in the 1980s

152 The Waters

Plate IV7 lake Tempe Sulawesi Indonesia (Frederic Pelras)

However it is necessary to point Olltthat the application of fertilizers is not theonly possible cause of rising nitrate levelsSome nitrate pollution may be derivedfrom organic wastes Intensive cultivationmay cause a decline in the amount oforganic matter present in the soil and thiscould limit a soils ability to assimilatenitrogen so that more is lost to waterThe pattern of tillage may also affect theliberation of nitrogen The increased areaand depth of modern ploughing accelershyates the decay of residues and may changethe pattern of water movement in thesoil Finally the area of England coveredby tile drainage has greatly expanded inrecent decades This has affected themovement of water through the soil

FURTHER REAnING

accelerating the flow of leached nitratesand other materials into streams

What can be done to control culturaleutrophicationl Preventive measures mayinclude the introduction oflaws to limit thetype and quantity of permitted dischargesfrom industrial sources Water companiesmay be forced to treat effluent to reduce itsnutrient content Bans can be introducedon detergents containing phosphates as hasalready been done in some areas The mostsevere problems however are posed bynutrients derived from agriculrural sourcesSteps may need to be taken to make agrishyculrure less intensive and to control the apshyplication offertilizers and sludge in locationsfrom which they can easily be washed intostreams and rivers such as floodplains

Mannion A M 1991 Global Environmental Change Harlow LongmanThis useful general review contains some perceptive information on eutrophication

Newson M 1992 Patterns of freshwater pollution In M Newson (cd) Man4gingthe Human Imp4t on the Natural Environment 130-49 London Belhaven PressA hydrological approach to understanding the pathways taken by pollutants

Eutrophication 153

Controlling eutrophication Lake Biwa JapanThe largest freshwater lake in Japancovering 674 sq lon is Lake Biwain Shiga Prefecture Honshu It isone of the oldest lakes in the worldand has a maximum depth of over100 metres The catchment area ofthe lake is less than five times thesurface area of the lake itself andthe lake is fed by high annual preshycipitation and in8ow Until around1950 Lake Biwa was oligotrophic(Le containing low nutrient loads)but since then has become eutrophic(ie containing high nutrient loads)with algaJ blooms first noticed ill1959 and red tides occurring everyyear since 1977

The causes of eutrophic conditionsare linked to the explosive economicdevelopment of the Shiga PrdectureLake Biwa today meets the waterneeds of 13 million people and all their industry The lake also provides animportant freshwater fishery and is of immense cultural and spiritual value Fiftyshytwo per cent of the catchment remains forested although Japanese red pines havereplaced the natural broadlcafforestj 173 per cent of the catchment area is nowurbanized The quality of the lakes water has declined as industry and agriculturehave expanded and domestic wastes have not been managed effectively (Petts1988) Eutrophication peaked in 1978 Since then the lake has shown signs ofimprovement as water quality has responded to a number ofmanagement strategies

A ten-year voluntary use soap campaign among local residents reduced drashymatically the 18 per cent of the toal phosphorus load that had been coming fromdomestic detergents In 1980 a Shiga Prefecture government ordinance regulatedindustrial domestic and agricultural discharges ofphosphorus and nitrogen Sincethen nitrogen and phosphorus concentrations in streams Howing into Lake Biwahave declined by 20 per cent even though population and industry have continshyued to grow Phosphorus levels in the southern part of the lake have also fallenby 30 per cent The Shiga Prefecture government has introduced conservationplans to ensure the monitoring of water quality conservation and environmentaleducation over the long term

Further reading

Petts G E 1988 Water management the case of Lake Biwa Japan Geo8aphishycRI Journal 154 367-76

154 The Waters

8 THERMAL POLLtTTlON

Thermal pollution is the pollution ofwater by increasing its temperJtun AsnlJllY orgJnisms arc SlnsitiC to tempershyature this lorm of pollution In haeconsiderable cologkal significane

Where docs the heat that produces thethermal pollution come from~ One of thelllJin sources in industrialized countries isthe condenser cooling water released frompower stations If there are large concenshytrations of big electricity generating plantsalong one stretch of river as for examplealong the River Trent in the midlands ofEngland the amount of water involvedcan be quite large River water dischargedalter it has been used for cooling may besome 6-9C warmer than it was beforebeing taken out of the river At times oflow flow this can raise river water temshypcntures downstream considenbly

The process of urbanization is anotherfactor that needs to be considered It has

a range of effects changes produced bythe urban heat island effect (see part IIIsection 5) changes in the temperature ofstreams brought about by the presence ofreservoirs changes in the volume of stormrunoff and changes in the nature of urshyban stream channds - how much they arecovered ou or shaded by egct3tion andhow their width and dcpth compare- withnatural channds

The-rmal pollution can also occur in ruralareas Large reservoirs will modify downshystream river temperatures Deforestationwhich removes shade cover may increasewater temperatures particularly in the sumshymer months

Thennal pollution has many ecologicaleffects Tempc=rilture increases can be harmshyful to temperature-sensitive fish such astrout and salmon and an disrupt spawnshying and migration patterns (figure IVIO)An increase in water tempentuce caU$C$a decr~ in the solubility of oxygenwhich is needed for the oxidation of

00~

l2~

29~

24~

Il~

~

O~

0-- WMnboib

j]1_ G_ _ 1 1_ G_ _ II j- GlllWlbrLpikt prrch WI1le)otsmaIlmoothbass 1tI1- SplIWllinl IIld II~IopmmtIicadbh buffalo shadI j __ Spawning Ind II lkoielopmmt oIlarzrmouth whik ytllow Ind lpotttd baniii i-- Egg dtvdoplllflli ofptrch Ind llIlal1mouth btu I1I__ Spawning~ II dMIopmmt of~ aDd mosllrout1-_ - _ tlJ_ w ~

FIgure JV10 Maximum temperatures for the spawning and growth of fishSouru After Giddings (1975) fig 13-2

biodegradable wastes At the same timethe tate of oxidation is accelerated deshymanding more and mote oxygen from thesmaller supply and thereby depleting theoxygen content of the water still furtherTemperature also affects the lower organshyisms such as plankton and crustaceans Ingeneral the higher the temperatun is theless desirable the types of algae in water

FURTHER READING

Inter-basin Water Transfers 155

In cooler waters diatoms are the predoshyminant phytoplankton in water that is notheavily eutrophic at higher temperatureswith the same nutrient levds green algaebegin to become dominant and diatomsdecline At the highest water temperaturesblue-green algae thrive and often developinto heavy blooms

Langford T E L 1990 Ecological Effects of Thermal Discha1lJes London ElsevierApplied ScienceThe most authoritative advanced treatment of thermal pollution

9 INTER-BASIN WATER

ThANSFERS AND THE

DEATH OF THE ARAL SEA

Increasing rates ofwater consumption andthe unequal distribution ofwater resourcesfrom one region to another mean tharin many parts of the world long-distancetransfers of water are made between riverbasins AJso in the worlds drylands largequantities of water are abstracted fromrivers to supply irrigation schemes One ofthe results of such large-scale modificashytions of river regimes is that the dischargesof some rivers have declined very substanshytially This in turn means that the extentand volume of any lakes into which theyempry have been reduced

Perhaps the most severe change to amajor inland sea or lake is that taking placeto the Aral Sea in the southern part of theformer Soviet Union (figure IVII) Untilvery recently this was the worlds fourthlargest lake with a high level of biologishycal activity and a rich and distinctive aquaticfauna and flora It had considerable comshymercial fisheries and was used for transshyport as weU as sporting and recreationalactivities It was also a refuge for hugeflocks of waterfowl and migratory birdsIt may also have exerted a favourable

climatic hydrological and hydrogeologicaleffect on the surrounding area

However since the 1960s a dramaticchange has taken place The inflow of waterinto the lake has decreased markedly (seefigure lV12) and it has now lost morethan 40 per cent of its area and about 60per ceO( of its water volume The lakeslevel has fallen by more than 14 rneuesIts saliniry has increased threefold Its faunaand flora have been desuoyed so that onlya small number of aquatic species hassurvived The climate around the lake mayalso have been affected The increasingareas ofexposed desiccating and salty lakebed provide an ideal environment for thegenesis of dust storms Such storms nowevacuate some tens of millions of tons ofsalt each year and dump them on agriculshytural land reducing crop yields The hushyman population also seems to be sufferingfrom poorer-quality water supply and fromrespiratory disorders caused by the blowshying salt and dust It is not surprising thereshyfore that the Aral Sea is now regarded asthe greatest ecological tragedy of theformer Soviet Union

Why has the inflow ofwater to the AralSea declined so extraordinarily The mainreason was that in the 1950s and early1960s a decision was taken to expand

156 The Waters

Plate IVS Inter-basin water transfers are vital for the survival of los AngelesThis large canal transports water from inland California (east of the Sierra Nevadamountains) to satisfy the needs of the sprawling conurbation hundreds ofkilometres away (A S Goudie)

MMn~ _

_ ~ Sibmo lDAni SaCWII

_ MIia itriplion tlllll

N

I

-- UZBEKISTAN

KmuwDuuf __

-

11JIIIMENISTAN

--IIi

-- r bull Nuhli _ rLJ-C

Figure IV11 Irrigation and the Aral Sea

Inter-basin Water Transfers 157

~C- ----1

19M 966I Ilnnow

c

11970

E -15

1~ 1965 197Q 1975 19amp1)40 ~I I I I

] ~-----~-=-~~

1985

=JMintrlJ~

~ -~IcI bull bull

I I I I I I

J965 JS7C 1m WIO J980 I JFigure IV12 (a) Changes in the Aral Sea 1960-1989 (b) The past and predictedcontraction of the Aral Sea as its level falls50urces (a) After Kotlyakov (1991) (b) Modified after Hollis (1978) p 63

irrigation in Central Asia and Kazakhstanso that crops like rice and conon whichconsume a great deal of water could becultivated in the middle of a desert Largevolumes of fertilizers and herbicides werealso used in growing these crops and thesehave contributed to the deterioration inwater quality In many cases too the irrishygation systems themselves were of poordesign construction and operation

Scientisrs economists and politicians arenow seeking solutions to the Aral tragedySome proposed ideas are

bull The local population should for healthreasons be provided with supplies ofsafe non-polluted piped water

bull The policy of growing cotton in thedeserts of Central Asia needs to bereconsidered

158 The Waters

Plate IV9 The rapid desiccation of the Arat Sea following the extraction of waterfrom the rivers that feed it to supply irrigation schemes has left these boats highdry and redundant (Marcus Rose Panos Pictures)

bull Agriculture needs to be made moreefficient by reducing the very subshystantial losses caused by inadequatestorage and transport infrastructure

bull A fundamental restructuring of theregions economy should be orientedtowards developing products thatdo not require the imensive usc ofwater

bull Irrigation systems need to be reconshystructed to reduce water losses and

FURTHER READING

application of water should be rationmiddotally controlled

bull A policy of expanding the arca of irrishygated agriculture should be replacedby more intensive use of existing irrimiddotgated tracts through better crop rotashytions technologies and the growth ofimproved varieties of crops

bull Attempts should be made to revegetatedesiccated areas to reduce dust stormactivity

MickJin P P 1988 Desiccation of the Aral Sca a water managellHnt disaster in theSoviet Union Science 241 1170-5One of the key papers that drew attention to the situation around the An Sea

Micklin P P 1992 The AnI crisis introduction to the special issue Pon-StnielGgraph] 33 (5) 269-82A coUection of papers on all aspects of tk AnI ampa problem

10 GROUNDWATER

DEPLETION AND

GROUNDWATER RISE

In some parts of the world groundwater isthe main source of water for industrialmunicipal and agricultural use Some rocksincluding sandstones and limestones havecharacteristics that enable them 10 holdand transmit large quantities of waterwhich (an be reached by installing pumpsand boreholes In some cases largeamounts of water can be abstracted withshyOut severe environmental effects This isparticularly true of areas where a combishynation of favourable climate topographygeological structure and rock compositionenables the water-bearing body - theaquifer - to recharge itself rapidly In suchcases the water is a renewable resourceHowever in other cases the rate ofexploishytation may greatly exceed the capacity ofthe aquifer to be recharged In these casesboth the quantity and the quality of thewater supply may deteriorate markedly overtime In such cases it is more appropriateto refer to the extraction ofwater as minshying of a largely non-renewable resource

Let us take m extreme example theexploitation of groundwater resources inthe oil-rich kingdom ofSaudi Arabia Mostof Saudi Arabia is desert so that climaticconditions are not favourable for rapidlarge-scale recharge of aquifers Also muchof the groundwater that lies beneath thedesert is a fossil resource created duringmore humid conditions - pluvials - thatexisted in the Late Pleistocene between15000 and 30000 years ago In spite ofthese inherently unfavourable circumshystances Saudi Arabias demand for wateris growing inexorably as its economy deshyvelops In 1980 the annual demand was24 billion cubic metres (bern) By 1990it had reached 12 bern (a fivefold increasein just a decade) and it is expected to

Changes in Groundwater 159

reach 20 bem by 2010 Only a very smallpart of the demand can be met fromdesalination plants or surface runoff overthree-quarters of the supply is obtainedfrom predominantly non-renewablegroundwater resources The drawdown onaquifers is thus enormous rt has been calshyculated that by 2010 the deep aquitcrswill contain 42 per cent less water than in1985 Much of the water is used ineffecshytively and inefficiently in the agriculturalsector (AI- Ibrahim 1991) to irrigate cropsthat could easily be grown in more humidregions and then imported

Saudi Arabia is not alone in its orashycious appetite for groundwater In manyparts of the world such problems havegrown with increasing population levelsand consumption demands together withthe adoption of new exploitation techshyniques (for example the replacement ofirrigation methods involving animal orhuman power by electric and dieselpumps)

Considerable reductions in groundshywater levels have been caused by abstrac~

tion in other areas The rapid increase inthe number of wells tapping groundwaterin the London area from 1850 until afterthe Second World War caused substantialchanges in groundwater conditions Thepiezometric surface in the confined chalkaquifer has fallen by more than 60 metresover hundreds of square kilometres Likeshywise beneath Chicago Illinois USApumping since the late nineteenth centuryhas lowered the piezometric head by some200 metres The drawdown that has takenplace in the Great Artesian Basin of Ausshytralia exceeds 80-100 metres in someplaces The environmental consequencesof excessive groundwater abstraction inshyclude salinization of coastal aquifers (seepart V section 5) and land subsidence (seepart V section 7)

Some of the most serious reductions inwater levels are taking place in the High

160 The Waters

Plate IV10 A major cause of groundwater depletion is the use of centre-pivotirrigation schemes The Ogallala aqUifer of the High Plains of Texas where thisphoto was taken is a major example of this phenomenon (A S Goudie)

Plains ofTexas threatening the long-termviability of irrigated agriculture in that areaBefore irrigation development started inthe 1930s the High Plains groundwatersystem was in a state of dynamic equilibshyrium with long-term recharge equal tolong-term discharge However the groundshywater is now being mined at a rapid rateto supply centre-pivot and other schemesIn a matter of only fifty years or less thewater level has declined by 30-50 metresin a large area to the north of LubbockTexas The aquifer has narrowed by morethan 50 per cent in large parts of certaincounties and the area irrigated by eachwell is contracting as well yields arc falling

In some industrial areas recent reducshytions in industrial activity have led to

less groundwater being taken out of theground As a consequence groundwaterlevels in such areas have begun to rise a

trend exacerbated by considerable leakagefrom ancient deteriorating pipe and sewersystems This is already happening in Britshyish cities including London Liverpool andBirmingham In London because of a 46per cent reduction in groundwater abstracshytion the water table in the Chalk andTertiary beds has risen by as much as 20metres Such a rise has numerous implicashytions both good and bad

bull increase in spring and river flowsbull re-emergence of flow from dry

springsbull surface water floodingbull pollution of surface waters and spread

of underground pollutionbull flooding of basementsbull increased leakage into tunnelsbull reduction in stability of slopes and

retaining walls

bull reduction in bearing capacity of founshydations and piles

bull increasedhydrostaticupliftandswelJingpressures on foundations and structures

bull swelling of clays as they absorb waterbull chemical attack on building foundations

There are various methods of rechargshying groundwater resources providing thatsufficient surface water is available Wherethe materials containing the aquifer arepermeable (as in some alluvial fans coastalsand dunes or glacial deposits) the techshynique of water-spreading is much usedIn relatively flat areas river water may bediverted to spread evenly over the groundso that infiltration takes place Alternativewater-spreading methods may involve reshyleasing water into basins which are formedby excavation or by the construction of

FURTHER READING

Conclusion 161

dikes or small dams On alluvial plainswater can also be encouraged to percolatedown to the water table by distributing itinto a series ofditches or furrows In somesituations natural channel infiltration canbe promoted by building small check damsdown a stream course In irrigated areassurplus water can be spread by irrigatingwith excess water during the dormant seashyson In sediments with impermeable layshyers such water-spreading techniques are noteffective and the appropriate method maythen be to pump water into deep pits orinto wells This last technique is used onthe heavily setded coastal plain of Israelboth to replenish the groundwater reshyservoirs when surplus irrigation water isavailable and to attempt to diminish theproblems associated with salt-water intrushysion from the Mediterranean

Downing R A and Wilkinson W B (eds) 1991 Applied Groundwater HydrologyA BririJh Pmpecrive Oxford Clarendon PressAn advanced textbook on all aspects of groundwater in the British context

11 CoNCLUSION

Freshwater resources are of vital imporshytance Their quality and quantity have unshydergone major changes as a consequenceof human activities Human demand forfreshwater has grown inexorably in reshycent decades As a result ever-increasingproportions of river flow are being conshytrolled or modified by deliberate humanmanipulation most notably by the conshystruction of dams the channelization ofstreams and by long-distance inter-basinwater transfers As our case study of theColorado River in the USA shows thedegree of control that can be achieved isradical

EquaUy important are changes in thehydrological cycle resulting unintentionshyally from changes in land use and land

cover The replacement of forests withfarms and of countryside with cities aretwo particularly important mechanisms inthis respect Also significant are the conshysequences - some anticipated some not shyof land drainage activities

Humans have modified not only thequantity of river flow but also its qualityMany water resources are polluted by arange of both point and non-pointsources River pollution can lead in turnto eutrophication of lakes and inland andmarginal seas However water pollutionand lake eutrophication as our case studiesof the River Clyde and Lake Biwa showare reversible if proper management stratshyegies are adopted Nonetheless as is shownin the case of the rapid desiccation ofthe AraI Sea the required solutions maybe extremely complex and technological

162 The Waters

change is seldom the only solution Wholeshysale changes in a regions economic andpolitical structure may be required

Finally we have pointed to the imporshytance of groundwater reserves and showedthat in some countries these resources arcbeing exploited at an unsustainable rateIn many areas the water table Ius beendrawn down too fur and too tast We havealso pointed out that in other parts of the

KEy TERMS AND CONCEPTS

aquiferbiological magnificationchannelizationdear-water erosioneutrophication

POINTS FOR REVIEW

world the reverse process is happening andthat groundwater levels are rising

The issues discussed in this part of thebook indicate how problems of humanimpacts on water are complicated by thelinks between bodies of water by themutual interaction of ditlcrent stressesand by the links between water and otheraspects of the environment such as theatmosphere biosphere and land surface

inter-basin water transterspoint and non-point sources of pollutionred tidesthermal pollution

Are dams a good or a bad thing

If you were in charge of providing large quantities of clean water in an area would youseek to increase or decrease the amount of forest in your catchments

How do humans increase the risk of river floods

What is the difference between point and non-point sources of water pollution

What do you understand by the term eutrophication

How do humans change the state of groundwater bodies

PART V

The Land Surface1 Introduction 1652 Soil Erosion by Water 165

bull Soil erosion on the South Downssouthern England 170

3 Wind Erosion and Dune Reactivation 172bull Controlling sand at Walvis Bay Namibia 186

4 River Channel Changes 1785 Salinization 1826 Accelerated Landslides 185

bull Slope erosion in the Pacific nolth-wcstof North America 188

7 Ground Subsidence 1898 Waste Disposal 1919 Stone Decay in Urban Buildings 197

bull Venices decaying treasures 20010 Conclusion 201

Key Terms and Concepts 202Points for Review 202

1 INTRODUCTION

This part of the book focuses on humanimpacts on the land surface - primarilysoils and landforms Humans havt modishyfied soils in many ways Most serious of allhas been the impact of land-use changeson the rates at which soils art eroded bywind and water The quality of soils hasalso been transformed At present fortxample many soils in irrigated regionsare being affected by salinization but atother times and in other places changtsin soil quality have included the formashytion of peat layers podzols and lateritehardpans Soil conditions are atfected bymodern farming practices heavy farmmachintry causes soil compaction andchemical changes are brought about bythe application ofsynthetic fertilizers Thtwhole impact of humans on soils is oftentermed metapedogenesis (table VI)

As well as soils the skin of the earth iscomposed of its landforms Here again thehuman impact can be considerable (tableY2) In particular humans can destabilizehillside slopes and cause wholesale groundsubsidence The range of human impactson landforms and landforming processesis considerable Some landforms may beproduced by dirtct anthropogenic processes Examples are landforms producedby constructional activity (eg tipping)excavation mining and farming (eg tershyracing) Landforms produced indirecdy byhuman activities while less easy to recogshynize are of particular importance Indeedthe indirect and unintentional modificashytion of processes by humans is the mostcrucial aspect of what is called anthropomiddotgeomorphology The geomorphologicaleffects of removing vegetation are anexample of this type of change Sometimeshumans deliberately try to change landshyforms and landforming processes but setin train a series of events which were notanticipated or desired As is noted in part

Soil Erosion by Water 165

VI section 3 for instance many attemptshave been made to rtduce coastal erosionby building impressive-looking and expenshysive engineering structures which have infact exacerbated the trosion rather thanhalting it

2 SOIL EROSION BY WATER

Soil erosion is a natural geomorphologicalprocess which takes place on many landsurfaces Under grassland or woodland ittakes place slowly and apptars to be moreor less balanced by soil formation Accelshyerated soil erosion takes place wherehumans have interfered with this balanceby modifYing or removing the natural vegshyetation cover Construction urbanizationwar mining and other such activities areonen significant in accelerating the probshylem However the main causes of soilerosion are deforestation and agriculture

Forests protect the underlying soil fromthe direct effects of rainfall generating anenvironment in which rates oferosion tendto be low The canopy plays an importantrole both by shortening the fall of rainshydrops and by decreasing the speed atwhich they hit the ground There art exshyamples of ctrtain types of trees (eg beech)in certain environments (eg maritimetemperate) creating large raindrops butin general most canopies reduce the eroshysive effects of rainfalls The prestl1ce ofhumus in forest soils may be even moreimportant than the canopy in reducingerosion rates in forest Humus in the soilboth absorbs the impact of raindrops andleads to soils with extremely high permeshyability Thus forest soils have high infiltrashytion capacities Another reason why forestsoils allow large quantities of water to passthrough them is that they have many largemacropores produced by roots and theirrich soil fauna Forest soils arc also wellaggregated making them resistant to boththe effects of wetting and water drop

166 The Land Surface

Table V1 Metapedogenesls human impacts on the main factors Involved in soilformation

Factor

Parent material

Topography

Climate

Organisms

Time

Human impacts

Beneficial adding mineral fertilizers accumulating shellsand bones accumulating ash removing excess amounts ofsubstances such as saltsDetrimental removing through harvest more plants andanimal nutrients than are replaced adding materials inamounts toxic to plants or animals altering soilconstituents in a way which depresses plant growth

Benehcia checking erosion through surface rougheningland forming and structure building raising land level byaccumulation of material land levellingDetrimental causing subsidence by draining wetlands andby mining accelerating erosion excavating

Beneficial adding water by irrigation rainmaking byseeding douds removing water by drainage diverting windsDetrimental subjecting soil to excessive insolation toextended frost action or to wind and rain

Beneficial introducing and controlling populations ofplants and animals adding organic matter loosening soilby ploughing to admit more oxygen fallowing removingpathogenic organisms eg by controlled burningDetrimental removing plants and animals reducingorganic content of soil through burning ploughingovergrazing harvesting adding or encouraging growth ofpathogenic organisms adding radioactive substances

Beneficial rejuvenating soil by adding fresh parentmaterial or through exposure of local parent material bysoil erosion reclaiming land from under waterDetrimental degrading soil by accelerated removal ofnutrients from soil and vegetation cover burying soilunder solid fill or water

Source Modified from Bidwell and Hole (15)

impact This high degree of aggregation isa result of the presence of considerablequantities of organic material which is animportant cementing agent in the formashytion of large water-stable aggregatesEarthworms also help to produce wellshyaggregated soil Finally deep-rooted treeshelp to stabilize steep slopes by increasingthe total shear strength of the soils

It is therefore to be expected that withthe removal of forest for agriculture orfor other reasons rates of soil loss will riseand mass movements (landslides debrisflows etc) will happen more often andon a larger scale Rates of erosion will beparticularly high if the deforested groundis left bare under crops the increase willbe less marked The method ofploughing

Soil Erosion by Water 167

Table V2 Major anthropogeomorphologlcal processes

Type of process

Dired anthropogenic processes

Constructional

Excavational

Hydrological interference

Indired anthropogenic processes

Acceleration of erosion andsedimentation

Subsidence

Slope failure

Earthquake generation

Source After Goudie (1993)

Examples

Tipping moulding ploughing terracing

Digging cutting mining blasting of cohesiveor non-cohesive materials cratering trampingand churning

Flooding damming canal constructiondredging channel modification drainingcoastal protection

Agricultural activity and vegetation clearanceengineering (especially road construction andurbanization)Incidental modifications of hydrological regime

Collapse and settling related to mininggroundwater pumping and permafrost melting(thermokarst)

landsliding flow and accelerated creep causedby loading undercutting shaking andlubrication

loading by reservoirs lubrication along faultplanes

the time of planting the nature of the cropand the size of the fields will all have aninfluence on the severity of erosion

Many fires are started by humanseither deliberately or accidentally Becausefires remove vegetation and expose theground they also tend to increase rates ofsoil erosion The burning of forests forexample can lead to high rates ofsoil lossespecially in the first years after the fireRates ofsoil loss in burnt forests are oftenup to ten times higher than those in proshytected areas

Soil erosion can also be caused by conshystruction and urbanization A number ofstudies have been done which illustrateclearly that urbanization can create signifishycant changes in erosion rates The highest

rates of erosion are produced in theconstruction phase when there is a largeamount of exposed ground and a lot ofdismrbance from vehicle movements andexcavations The equivalent of many decshyades of natural or even agricultural eroshysion may take place during a single year inareas cleared for construction Howeverconstruction does not go on for ever andeventually the building work is completedThen the disturbance ceases roads aresurfaced and gardens and lawns are culshytivated Rates of erosion fall dramaticallyperhaps to the levels prevailing under natshyural or pre-agriculrurai conditions

Soil erosion by water takes on a varietyof forms Splash erosion and sheet ftowmay occur in some areas Elsewhere rills

168 The Land Surface

Plate V1 Soil erosion at St Michaels Mission in central Zimbabwe A large donga(or erosional gully) has formed as a result of overgrazing and other land-usepressures (A S Goudie)

(small channels) may develop Under moreextreme conditions for example wheresoils are highly erodible large gullies mayform and these may coalesce to form abadlands topography Slopes can becomedestabilized so that mass movementsoccur

Concern about accelerated erosion foshycuses on two main categories of impactThe first of these relates to the threat itposes to our ability to grow crops and tofeed the worlds growing population Soilerosion reduces soil depth and often meansthat the most fertile humus- and nutrientshyrich portion of the soil profile is lost Thesecond category of impact is what aretermed off-farm impacts These include

bull accelerated siltation of reservoirs riversdrainage ditches etc

bull eutrophication of water bodies by the

transport of nutrients attached to soilparticles

bull damage to property by soil~laden waterand debris flows

There is some evidence that soil erosionis becoming a more serious problem inparts of Britain in spite of the fact thatthe countrys rainfall is much less intenseand so less erosive than in many parts ofthe world The following practices mayhave caused this state of affairs

bull Ploughing on steep slopes that wereformerly under grass in order to inshycrease the area of arable cultivation

bull Usc of larger and heavier agriculturalmachinery which tends to increase soilcompaction

bull Use ofmore powerful machinery whichpermits cultivation in the direction of

maximum slope rather than along thecontour Rills often develop along thewheel ruts (wheelings) left by tracshytors and farm implements and alongdrill lines

bull Use of powered harrows in seedbedpreparation and the rolling of fieldsafter drilling

bull Removal of hedgerows and the associshyated increase in field size Larger fieldscause an increase in slope length andthus a higher risk of erosion

bull Declining levels oforganic matter resultshying from intensive cultivation and relishyance on chemical fertilizers which inturn lead to reduced aggregate stability

bull Widespread introduction of autumnshysown cereals to replace spring-sowncereals Because of their longer growingseason autumn-sown cereals producegreater yields and are therefore moreprofitable The change means that seedshybeds with a fine tilth and little vegetashytion cover are exposed throughout theperiod of winter rainfall

Several measures can be used to reducethe rate at which soil is lost from agriculshyturalland In some parts of the world thesetechniques have been practised for sometime and have been quite successful Theyare

FURTHER READING

Soil Erosion by Water 169

bull Revegetation(a) deliberate planting(b) suppression of fire grazing etc

to allow regenerationbull Measures to stop stream bank erosion

(eg stone banks and rip-rap)bull Measures to stop gully enlargement

(a) planting of trailing plants etc(b) weirs dams gabions etc

bull Crop management(a) maintaining cover at critical times

of year(b) rotation of crops(c) growing cover crops(d) agroforestry

bull Slope runoff control(a) terracing(b) deep tillage and application of

humus(c) digging transverse hillside ditches

to interrupt runoff(d) contour ploughing(e) preservation ofvegetation strips (to

limit field width)bull Prevention of erosion from point

sources such as roads and feedlots(a) intelligent geomorphic location of

roads feedlots etc(b) channelling of drainage water to

non-susceptible areas(c) covering of banks cuttings etc

with vegetation

Boardman J Foster I D L and Dearing J A (cds) 1990 Soil Erosion on Agrishycultural Land Chichester WileyAn edited series of advanced reseatch papers providing some useful case studies

Hudson N 1971 Soil Conservation London BaufordA general introductory level textbook

Morgltln R P C 1995 Soil Erosion and Conservation 2nd edn Harlow LongmanA general introduction that is especially strong on methods of controlling erosion

Pimental D (cd) 1993 World Soil Erosion and Conservation Cambridge CambridgeUniversity PressA series of advanced edited papers that look at soil erosion in a regional context

170 The Land Surface

Soil erosion on the South Downs southernEnglandThe South Downs are a rAnge of L3chalk hills in south-east England ~~--J

which rise to an altitude of around todM200 metres They are deeply dis-sccted by a network of dry valleysIn the early Holocene the Downswere wooded and their soils weremuch thicker than they are now Soilsarc now typically shallow and stonyrendzinas with A horizons usuallyless than 25 cm thick Since thexcond World War the dominantland usc in the area has been farmshying of wheat and barley In the 1970s a major change of fuming practice ocmiddotculTed with the adoption of autumn-grown cereals (eg winter wheat) in prefshyerence to lower-yielding spring-sown varieties Farming has also become moreintensive fields have increased in size with the removal ofhedgcs and grass bankswhile larger and more powerful tractors have enabled farmers to cultivate slopesas steep as 25

Plite V2 Sotl erosion and flood runoff on the South Downs southmiddoteastEngland Uohn Boardman)

Soil Erosion by Water 171

figure V1 Typical location and form oferosion on agricultural land on the SouthDowns EnglandSource After Boardman (1992) fig 21

v

Angle ofslOjlf

525middot

CHALK

Valleyoonom riU and fan

As a result there has been anincrease in soil erosion by wateron the Downs especially betweenSeptember and December on landprepared for or drilledmiddot with wintercereals This is because large areasof smooth ground with minimalvegetation cover are exposed durshying the wettest months Rills developin hillsides (figure Vl) especiallyalong tractor wheel ruts (wheelshyings) and some gullies havedeveloped along valley bottomsSediment-laden runotT can causeserious problems for nearby housesLocalized erosion and flooding were recorded in 1958 and 1976 but there arefew records of such events earlier in the twentieth cenrnry Frequent and someshytimes serious erosion occurred in the 1980s especially during the wet autumnsand winters of 1982-3 1987-8 and 1990-1 John Boardman has monitoredabout 36 sq km of agricultural land in the area during this time (see table V3)and found that peak soil erosion in the 1987-8 winter season was accompaniedby serious flooding of roads and properties

Further reading

Boardman J 1995 Damage to property by runoff from agricultural land SouthDowns southern England 1976-1993 Geographieal Journal 161 177-91

Table V3 Rainfall and soil erosion on a monitored site in the eastern SouthDowns England 1982-1991

Year Total rainfall1 Sep-1 Mar (mm)

Total soilass(01 metres)

1982-31983-41984-51985-61986-71987-81988-91989-901990-11991-2

724560580453503739324621469298

181627

182541211

135292

9401527

112Source Modifled from Boardman (1995)

172 The Land Surface

3 WIND EROSION AND

DUNE REACTIVATION

In the drier parts of the world or onparticularly light soils wind erosion maybecome a major cause of accelerated soilloss As in the case of accelerated soilerosion by water the key factor is the reshymoval of vegetation cover

Possibly the most famous case of soilerosion by deflation was the dust bowl ofthe 1930s in the USA This was caused inpart by a series of hot dry years whichdepleted the vegetation cover and madethe soils dry enough to be susceptible towind erosion The effects of this droughtwere made very much worse by years ofovergrazing and unsatisfactory farmingtechniques However perhaps the primarycause of the dust bowl was the rapid exshypansion of wheat cultivation in the GreatPlains The number of cultivated hectaresdoubled during the First World War astractors (for the first time) rolled out onto the plains in their thousands In Kansasalone wheat cultivation increased fromunder 2 million hectares in 1910 to alshymost 5 million in 1919 After the warwheat cultivation continued apace helpedby the development of the combine harshyvester and government assistance Thefarmer busy sowing wheat and reapinggold could foresee no end to his land ofmilk and honey but the years of favourshyable climate were not to last and overlarge areas the tough sod which exaspershyated the earlier homesteaders had givenway to friable soils which were very susshyceptible to erosion Drought acting ondamaged soils created the black blizzardsthat carried dust as far as the Atlantic seashyboard (see box in part III section 2)

The dust bowl was not solely a featureof the 1930s and dust storms are still aserious problem in various parts of theUnited States For example in the San

Joaquin Valley area ofcentral California in1977 a dust storm caused extensive damshyage and erosion over an area of about2000 sq kIn More than 25 million tannesof soil were stripped from grazing landwithin a 24middothour period While the comshybination of drought and a very high wind(as much as 300 kIn per hour) providedthe predisposing conditions for the stripshyping to occur overgrazing and the genshyeral lack of windbreaks in the agriculturalland played a more significant role Inaddition broad areas of land had recentlybeen stripped of vegetation levelled orploughed up prior to planting Othercontributory factors albeit quantitltltivdyless important included the stripping ofvegetation for urban expansion extensivedenudation of land in the vicinity of oilshyfields and local denudation of land byrecreational use of vehicles One interestshying observation made in the months afterthe dust storm was that in subsequentrainstorms runoff occurred faster fromthose areas that had been stripped by thewind exacerbating problems of floodingand creating numerous gullies Elsewherein California dust yield has been considershyably increased by mining operations in drylake beds

A comparable acceleration ofdust stormactivity has also occurred in the formerSoviet Union After the Virgin Lands promiddotgramme of agricultural expansion in the1950s dust storms in the southern Omskregion became on average two and a halftimes more frequent and in some localareas five or six times more frequent

We can see how drought and humanpressures can combine to produce accelershyated wind erosion by considering themeteorological data for dust-storm freshyquency at Nouakchott in Mauritania westshyern Africa (figure V2) Since the 1960sthe number of dust storms has gone updramatically from just a few each year toover 80 a year This is partly caused by the

Wind Erosion 173

Plate V3 Gully erosion by water near luyengo central Swaziland southemAfrica (A $ Goudie)

]

l l )

bullo

Figure V2 Annual frequency of duststorm days and annual rainfall forNouakchott Mauritania Africa1960-1986Source After Goudie and Middleton (1992)fig 8

low rainfall of the Sahel drought that hasaftlicted the area bU[ also by human popushylation growth and increased disturbanceof the dcsert surface by vehicles

Wind erosion is also active in certainparts of Britain Dust storms have lxenrecorded in the Fen1ands the BrecklandsEast Yorkshire and Lincolnshire since the1920s and they seem to be happltningmore often in recent years The s[Qrmsresult from changing agricultural practicesincluding the usc of artificial fertilizc=rs inplace of farmyard manure a reduction inthe process of ltc1aying whereby day wasadded to the peat to stabilize it the reshymoval of hedgerows to facilitate the useof bigger farm machinery and perhapsmost importantly the increased cultivationof sugar beet This crop requires a finetilth and tends to leave the soil relativelybare in early summer compared with othercrops

174 The Land Surface

When and where wind erosion of soilstakes place is determined by two sets offactors wind erosivity and surfaceerodibility (table VA) Wind erosion willnormally be reduced if those variablesmarked in the table with a (+) are increasedand if those marked with a (-) are reshyduced (Those marked with a plusmn can haveeither effect) These are important pointsto be considered when selecting consershyvation methods which have to focus onimproving the stability of the soil and reshyducing wind velocities at the soil surface

Table V4 Key factors influencing winderosion of solismiddot

Erosivity Wind variablesVelocityFrequencyDurationMagnitudeShearTurbulence

Erodibility Debris variablesParticle size plusmnSoil clods andcohesive properties +AbradabilityTransportabilityOrganic matter +

Surface variablesVegetation residue +

height +orientation +density +fineness +cover +

Soil moisture +Surface roughness +Surface length(distance from shelter) shySurface slope plusmn

bull See text above for explanation

Source After Cooke and Doomkamp (1993)

Soil conservation measures can be dishyvided into three types

bull agronomic measures which manipulatevegetation to minimize erosion by proshytecting the soil

bull soil management methodJ which focuson ways of preparing the soil to proshymote good vegetative growth and imshyprove soil structure in order to increaseresistance to erosion

bull muhanicaJ methods which manipulatethe surface topography in order toreduce wind velocity and turbulence

Agronomic measures use living vegetationor the residues from harvested crops toprotect the soil Wind erosion problemsoccur on croplands only when the soil isexposed because the crop is not matureenough to provide adequate protectionHence stubble mulching which involvestilling but not to the extent whereby thefield is left dean has become a widelyused method of protection from erosionSoil management techniques are concernedwith different methods of soil tillage thefarmers methods of preparing a suitableseedbed for crop growth and of helpingto control weeds Mechanical methodsinclude the creation of protective barriersagainst the wind such as fences windshybreaks and shelter belts

Another aspect of wind erosion is dunereactivation This occurs on the marginsof the great subtropical and tropical deshyserts and is one facet of the process ofdesertification (see part II section 3)Dune reactivation arouses some of thestrongeS[ fears among those combatingdesertification The increasing populationlevels of both humans and their domesticanimals brought about by improvementsin health and by the provision of boreholeshas led to excessive pressure on the limitedvegetation resources As ground coverhas been reduced so dune instability has

Wind Erosion 175

Plate V4 The use of palm frond fences to reduce sand movement at Erfoudsouthern Morocco (A S Goudie)

increased The problem is not so muchthat dunes in the desert cores are relemmiddotIcssly marching on to moister areas morethat fossil dunes laid down during themore arid phase peaking around 18000years ago have been reactivated in litu bythe removal of stabilizing vegetation

Many methods are used in the attemptto control drifting sand and moving dunesIn practice most solutions to the problcmof dune instability and sand blowing haveinvolved establishing a vegetation coverThis is not always easy Plant species usedto control sand dunes must be able to

FURTHER READING

endure undermining of their roots buryshying abrasion and often severe deficienciesof soil moisture Thus the species selcctedneed to have the ability to recover afterpanial burying to have deep and spreadmiddoting roots to have rapid height growthin the seedling srages to promote rapidliner development and to add nitrogento the soil through root nodulcs Duringthe early stages of growth they may needto be protected by fences sand trapsand surface mulches Growth can also bestimulated by the addition of syntheticfertilizers

Goudie A S (ed) 1990 Techniques for Desert Reclamation Chichester WileyThis edited work contains several chapters on the control of dunes and dust hazards

176 The Land Surface

Controlling sand at Walvis Bay NamibiaThe movement of sand can be aserious problems for the inhabitantsof the worlds drylands Sand stormsreduce visibility on roads whileencroaching dunes can overwhelmhouses farms canals and transportlinks For this reason humans havedeveloped a range of techniques totry to control drifting sand andmoving dunes (table vS)

One location where moving sandhas proved to be a severe problemand where many of these controltechniques have been attempted isthe port town of Walvis Bay on thecoast of Namibia in southern Africa(figure V3) Here the annual rainshyfall is so low (around 2S mm) thatvegetation cover is minimal allowshying sand to move when windvelocities reach critical levels (as theyoften do) Many of the dunes nearWalvis Bay are individual crescentshyshaped dunes called barchans Theseare highly mobile travelling sometens of metres per year From timeto time they have blocked roadsthey have also caused the relocationof the main railway link with theinterior The local authority is tryshying to stabilize the sand by suchmeans as planting (and irrigating)shrubs and building sand fences (seeplates V4 V5)

PfiwI ~

- ir i WaMII Bay i

i Y - - - - - - - - - - - - - - - - - - 23S

ProbIelll$lronl dtiftirlJ wld dunA

it i t--AncicoldiltrigtIIwJolKuiKb iiu

~~ flood proIecion dun

N

I

~WIlI __

Figure V3 The coastal zone nearWalVis Bay Namibia The main coastroad is often blocked by sand whilethe main raHway line has had to berelocated inland

Tll

~

~

Wind Erosion 177

Plate V5 A road has been blocked by a migrating barchan dune nearWalvis Bay Namibia Sand fences have been constructed in an attempt toslow the process down (H A Viles)

Table VS Control technlque$ for drifting sand and mobile dunes

Problem

Drifting sand

Moving dunes

Control methods

Enhancement of deposition of sand through creatinglarge ditches vegetation belts and barriers and fencesEnhancement of sand transport by aerodynamicstreamlining of surface or changing surface materialsReduction of sand supply by surface treatmentimproved vegetation cover or erection of fencesDeflection of moving sand by fences barriers orvegetation belts

Removal by mechanical excavationDestruction by reshaping trenching through dune axis orsurface stabilization of barchan armsImmobilization by trimming surface treatment andfences

178 The Land Surface

4 RIvER CHANNEL CHANGES

River channels developed in alluvium(sediments deposited by the river itself)adjust their shape slope and velocity offlow in response to discharge sedimentload the calibre of the bed and bank sedishyment the banks vegetation and the slopeof the valley Humans have intervened innatural channel systems by building damsrealigning channel courses constructinglevees and embankments and in manyother ways (see part IV section 2) Howshyever they have also altered channel charshyacteristics unintentionally (table V6) forexample by modifYing the amounts ofdisshycharge the amount of sediment beingcarried and the nature of vegetation onthe river bank Sometimes too deliberatechanges have set in train a series of unshyintended changes

Let us consider channel straighteningFor purposes of navigation and flood conshytrol humans have deliberately straightenedmany river channels The elimination ofmeanders contributes to flood control intwo ways First it eliminates some floodsover banks on the outside ofcurves wherethe current is swiftest and where the water

Table V6 Accidental channel changes

surface rises highest Second and moreimportandy the shorter straightenedcourse increases both the gradient andthe velocity of the stream Floodwaterscan then erode and deepen the channelthereby increasing its flood capacity Deshyliberate channel-straightening causes varishyous types of adjustment in the channelboth within and downstream from straightshyened reaches The types ofadjustment varyaccording to such influences as stream grashydient and sediment characteristics (figureVA) Brookes (1988) has recognized fivetypes of change within the straightenedreaches (types WI to W5) and twO typesofchange downstream (types Dl and D2)

bull Type WI is degradation of the channelbed This happens because straightenshying shortens the channel path andtherefore increases the slope This inturn increases the efficiency ofsedimenttransport

bull Type W2 is the development of anarmoured layer on the channel bed bythe more efficient removal of finematerials as described under Type WI

bull Type W3 is the development of a sinushyous thalweg in streams which are not

Phenomenon

Channel incision

Channel aggradation

Channel enlargement

Channel diminution

Channel diminution

Cause

Clear-water erosion below dams caused by sedimentremoval

Reduction in peak flows below damsAddition of sediment to streams by mining agricultureetc

Increase in discharge level produced by urbanization

Discharge decrease following water abstraction or floodcontrol

Trapping and stabilizing of sediment by artificiallyintroduced plants

River Channel Changes 179

Plate V6 A completely artificial stream channel in Maspalomas Gran CanariaCanary Islands (A S Goudie)

Figure V4 Principal types of adjustment in straightened river channelsSource After Brookes (1987) fig 4

180 The Land Surface

only straightened but also widened beshyyond the width of the natural channel

bull Type W4 is the recovery of sinuosityas a result of bank erosion in channclswith high slope gradients

bull Type W5 is the development of a sinushyous course by deposition in streamswith a high sediment load and a rclashytivcly low valley gradient

bull Types 01 and 02 result from deposishytion downstream as the stream tries toeven out its gradient The depositionmay occur either as a general raisingof the levcl of the bed or as a series ofaccentuated point bar deposits

Another influence on channel form isthe growth ofsettlements It is now widclyrecognized that the urbanization of ariver basin results in an increase in thepeak flood flows in a river (see part Nsection 4) It is also recognized that themorphology of stream channels is relatedto their discharge characteristics and esshypecially to the discharge at which bankfull flow that is a complete filling of thechanncl occurs As a result of urbanizashytion the frequency ofdischarges which IiIlthe channcl will increase This will meanthat the beds and banks of channcls inerodible materials will be eroded so as toenlarge the channel This in turn will leadto bank caving possible undermining ofstructures and increases in turbidity

Similarly important changes in channelmorphology result from the lowering ofdischarge caused by flood-control worksand diversions for irrigation This can beshown for the North Platte and the SouthPlatte Rivers in America where both peakdischarge and mean annual discharge havedeclined to 10-30 per cent of their preshydam values The North Platte 762-1219metres wide in 1890 near the WyomingshyNebraska border has narrowed to about60 metres at present The South PlatteRiver 89 kIn above its junction with the

1m

Figure VS The configuration of thechannel of the South Platte River atBrule in Nebraska USA (a) in 1897and (b) in 1959 Such changes inchannel form result from dischargediminution caused by flood controlworks and diversions for irrigationSource After GoudIe (1993) fig 615(a)

North Platte was about 792 metres widein 1897 but had narrowed to about 60metres by 1959 The tendency of bothrivers has been to form one narrow wellshydefined channel in place of the previouslywide braided channels The new channclis also generally somewhat more sinuousthan the old (figure VS)

The building of dams can lead to chanshyncl aggradation upstream from the resershyvoir and channcl deepening downstreambecause of the changes brought about insediment loads The overall effect of th~

creation of a reservoir by the constructionof a dam is to lead to a reduction in downshystream channel capacity of about 30-70per cent

Equally far-reaching changes in channclform are produced by land-use changesand the introduction of soil conservationmeasures Figure V6 is an idealized repshyresentation of how the river basins ofGeorgia USA have been modified throughhuman agency between 1700 (the time ofEuropean settlement) and the presentClearing of the land for cultivation (figureV6(b)) caused massive slope erosion which

lbi

1lt1

Xvcdy erodeduplmds

Partial to cOOIpkttc~ndfilliJIg

~tlk lWmank ckposition

River Channel Changes 181

Trees lilJcd by thensing aler bd

Ltvm wIUky fillofmodern itdimenll

BloCm=p

Regrowth d lOmuprcdOOlinaody pine

Accumulation of~nt1y miggttiogsedirncnt ClwInol

Rill aggrading

Drained badslIolmpI I Suem iJlcised in modltrn lCdirncnt

Intensive coomaINm IcticQT- broad-based [(rrmspntUfC in Bermuda gr1Sl

Trees in bonomlands nor SoolI for darilf

SW oflm-kswoImp increasing

Figure V6 Changes in the evolution of the fluvial landscapes of the Piedmont ofGeorgia USA in response to land-use change between 1700 and 1970 (a) at thetime of European settlement c1700 (b) after the clearing and erosive cultivationof uplands (c) after the checking of erosion and the consequent incision of theheadwater streamSource After Trimble (1974) p 117

182 The Land Surface

resulted in large quantities of sedimentbeing moved into channels and floodplainsIntense erosive land use continued and wasparticularly strong during the nineteenthcentury and the first decades of the twenshytieth century Thereafter (figure V6(c))conservation measures reservoir construcshytion and a reduction in the intensity ofagricultural land use led to further chanshynel changes (Trimble 1974) Streamsceased to carry such a heavy sediment loadand became much less turbid As a resultthey cut down imo the floodplain sedishymems of modern alluvium lowering theirbeds by as much as 3-4 metres

Anmher causc of significant changes inchannels is the accelerated sedimentationassociated with changes in the vegetationgrowing alongside the channels In thesouthern USA the introduction of a bushytree the salt cedar has caused significant

FURTHER READING

floodplain aggradation In the case of theBrazos River in Texas for example theplants encouraged sedimentation by theirdamming and ponding effect Theyclogged channels by invading sand banksand sand bars and so increased the areasubject to flooding Between 1941 and1979 the channel width declined trom 157metres to 67 metres and the amount ofaggradation was as much as 55 metres(Blackburn et al 1983)

Finally mining can lead to very majorchanges in channel morphology The reashyson for this is that mining often requiresthe use of large quantities of water andproduces large quantities of waste Thewaste tends to lead to the aggradation ofthe channel bed and if the waste materialis coarse then there may be a tendency fora natural meandering pattern to be reshyplaced by a braiding one

Brookes A 1988 Channelized Rivers Chichester WileyAn advanced research monograph with broad scope

5 SALINIZATION

Salinity is a normal and natural feature ofsoils especially in dry areas Howevervarious human activities are increasing itsextent and severity

Salinity in soils has a range of undeshysirable consequences For example asirrigation water IS concentrated byevapotranspiration calcium and magneshysium components tend to precipitate ascarbonates leaving sodium ions dominantin the soil solution The sodium ions tendto be absorbed on to colloidal clay parshyticles deflocculating them and leavingthe soil structurdess almost impermeableto water and unfavourable to root develshyopment Poor soil structure and toxicitylead to the death of vegetation in areas ofsaline patches This creates bare ground

which is vulnerable to erosion by windand water

Probably the most serious result ofsalinization is its impact on plant growthThis takes place partly through its effecton soil structure but more significantlythrough its effects on osmotic pressuresand through direct toxicity When a watersolution containing large quantities ofdisshysolved salts comes into contact with a plantcell it causes the cells protoplasmic liningto shrink This is due to the osmoticmovement of me water which passes outfrom the cell towards the more concenshytrated soil solution The cell collapses andthe plant dies

This toxicity effect varies with differentplants and different salts Sodium carbonshyate by creating highly alkaline soil condishytions may damage plants by a direct caustic

effect high nitrate may promote undesirshyable vegetative growth in grapes or sugarbeets at the expense of sugar contentBoron is injurious to many crop plants atsolution concentrations of more than 1 or2 ppm

There are a variety of reasons why soilsalinity is spreading The most importantof these is the growth in the area ofirrigated land which has increased fromabout 8 million hectares in 1800 to 250million hectares in the 1990s (Thomasand Middkton 1993) The extension ofirrigation and the use of a wide range ofdifferent techniques for water abstractionand application can lead to a build-up ofsalt levels in the soil This happens beshycause water abstraction raises the groundshywater level so that it is near enough to theground surface for water to rise to thesurface by capillary action Evaporation

Salinization 183

then leaves the salts in the soil In the caseof the semi-arid northern plains of Victoshyria in Australia for instance the water tablehas been rising at around 15 metres peryear so that now in many areas it is linlemore than 1 metre below the surfaceWhen groundwater comes within 3 memiddottres of the surface in day soils - less forsilty and sandy soils - capillary forces bringmoisture to the surface where evaporationtakes place leaving salts behind

Second many irrigation schemes spreadlarge quantities of water over the soilsurface This is especially true for ricecultivation Such surface water is readilyevaporated so that again salinity levelsbuild up

Third the construction of large damsand barrages to control water flow and to

give a head ofwater creates large reservoirsfrom which further evaporation can take

Plate V7 A satanic mockery of snow Waterlogged and salinized land in SindPakistan The white surface is not snow but salt a major cause of decliningagricultural yields (A S Goudie)

Source Grelck (1993) table E5

Table V7 Salinization of irrigated cropshyland In selected countries

an increase in recharge rates of groundshywater and to an increase in the salinity ofstreams as salty groundwater seeps outfrom the ground and into stream flowReplanting has been shown to reverse theprocess (Bari and Schofield 1992)

Salinity can also be increased by salinematerials transferred from lake beds thathave dried up because of inter-basin watertransfers Around 30-40 million tonnesof salty soils are blown off the Aral Seaevery year (see part IV section 9) forexample and these add to the salt contentof soils downwind

It has been estimated (table V7) thatsalt-affected and waterlogged soils accountfor 50 per cent of the irrigated area in

184 The Land Surface

place The water gets saltier This saltywater is then used for irrigation with theeffects described in the previous paragraph

Fourth water seeps laterally from irrishygation canals especially in highly permeshyable soils so that further evaporation takesplace Many distribution channels in agravity irrigation scheme are located onthe elevated areas ofa floodplain or riverineplain to make maximum use of gravityThe elevated landforms selected are natushyral levees river-bordering dunes and tershyraces all of which arc composed of siltand sand which may be particularly proneto loss by seepage

In coastal areas salinity problems arccreated by seawater incursion broughtabout by overpumping of fresh groundshywater from aquifers If the aquifer is opento penetration from the sea salty watertends to replace the freshwater that hasbeen extracted This is a particularly sershyious problem along the shores of the Pershysian Gulf where bccallS( of the dry dimatethe freshwater can only slowly be replenshyished by rainfall However it can be aproblem for any coastal aquifer

Increases in soil salinity are nm restrictedto irrigated areas In some parts of theworld salinization has resulted fromvegetation clearance (Peck 1978) Theremoval of native forest vegetation allowsmore rainfall to ~netrate into deeper soillayers This causes groundwater levels torise creating seepage sometimes of salinewater in low-lying areas Through thismechanism an estimated 200000 hectaresof land in southern Australia which atthe start of European settlement in thelate eighteenth century supported goodcrops of pasture is now suitable only forhalophytic species Similar problems existalso in North America notably in Manishytoba Alberta Montana and North Dakota

The clearance of the native evergreenforest (predominantly Eucalyprusforest) insouth-western Australia has led both to

Country

AlgeriaAustraliaChinaColombiaCyprusEgyptGreeceIndiaIranIraqIsraelJordanPakistanPeruPortugalSenegalSri lankaSpainSudanSyriaUSA

of irrigated landsaffected by salinization

10-1515-2015202530-40

727lt30501316lt401210-1510-151310-152030-3520-25

Iraq up to 40 per cent of all Pakistan 50per cent in the Euphrates Valley of Syria30-40 per cent in Egypt and up to 30 percent in Iran In Africa however wherether~ are fewer great irrigation schemesless than 10 per cent of salt-affected soilsare so affected because of human action(Thomas and Middleton 1993) Lookingat the problem on a global basis the calshyculations of Rozanov et al (1990) makegrim reading They estimate (p 210) From1700 to 1984 the global areas of irrigatedland increased from 50000 to 22000001on2

while at the same time some 500000kIn2 were abandoned as a result ofsecondshyary salinization They believe that in thelast three centuries irrigation has resultedin I million sq km of land destroyed plus1 million sq kID of land with diminishedproductivity due to salinization

Given the seriousness of the problem arange of techniques for the eradicationconversion or control of salinity have beendeveloped These have been reviewed byRhoades (1990) and include the following

FURTHER READING

Accclerated Landslides 185

bull provision of adequate subsoil drainshyage to prevent waterlogging to keepthe water table low enough to reducethe effects of capillary rise and to reshymove water that is in excess of cropdemand

bull leaching of salts by applying water tothe soil surface and allowing it to passdownward through the root zone

bull treatment of the soil (with additions ofcalcium magnesium organic matteretc) to maintain soil permeability

bull planting of crops which do not needmuch water

bull planting of crops or crop varieties thatwill produce satisfactory yields undersaline conditions

bull reduction ofseepage losses from canalsand ditches by lining them (eg withconcrete)

bull reduction in the amounts of waterapplied by irrigation by using sprinkshylers and tricklers

bull storage of heavily salted waste waterfrom fields in evaporation ponds

Worthington E B (ed) 1977 Arid lAnd Irrigation in Dneloping Countries Envishyronmenttd ProblemJ and Effects Oxford PergamonA collection of papers that was among the first and most persuasive considerations ofthe problem caused by the rapid spread of irrigation schemes

6 ACCELERATED LANDSLIDES

In 19632600 people were killed in Italywhen a great landslide fell into a reservoirand caused a mass of water to spill overthe dam and cascade downstream Threeyears later at Aberfan in South Wales amassive debris flow killed over ISO peoplewhen it destroyed a school and houses asit rID down from a steep coal-waste tipThese are just two of the worst examplesof how human actions have created hazshyardous mass movements on slopes

Human capacity to change a hillside and

to make it more prone [Q failure has beentransformed by engineering developmentExcavations are going deeper buildingsand other structures are larger and manysites which are at best marginally suitablefor engineering projects are now beingused because of increasing pressure onland This applies especially to some ofthe expanding urban areas in the humidparts of low latitudes - Hong Kong KualaLumpur Rio de Janeiro and many othersMass movements are very seldom deshyliberately accelerated by human agencyMost are accidentally caused the exception

186 The Land Surface

possibly being the delibcrate triggering ofa threatening snow avalanche

The forces producing slope instabilityand landsliding can usefully be divided intodisturbing factors and resisting propertiesSome disturbing factors art natural othersmarked with an asterisk in the followinglist are caused by humans

bull Removal of lateral or ulld(rlyjn~q supshyportundercutting by wattr (tor exampleriver waves) or glacier icewcathering of weaker strata at the tOCof the slopewashing out of granular material byseepage erosionmiddothuman cuts and excavations drainmiddotage of lakes or reservoirs

bull Increased disturbing forcesnatural accumulations of water snowtalusmiddotpressure caused by human activity (forexample stockpiles of are tip-heapsrubbish dumps or buildings)

bull Transitory earth stressesearthquakesmiddotcontinual passing of heavy traffic

bull Increased internal pressurebuildmiddot up of pore-water pressures (forexample in joints and cracks especiallyin the tension crack zone at the rear ofthe slide)

Factors leading to a decrease in the reshysisting properties (shear strength) of thematerials making up a slope can also besummarized as follows Again those reshysulting from human activity are markedwith an asterisk

bull Materialsbeds which decrease in shear strengthif water content increases (clays shalemica schist talc scrpentine) for exshyample middotwhen local water table is artishyficially increased in height by reservoir

construction or as a result of stressrelease (vertical andor horizontal)following slope formationlow internal cohesion (tor example conshysolidated clays sands porous organicmatter)In bedrock faults bedding planesjoims foliation in schists ceaagebrecciated zones and pre-existingshears

bull Weathering changesweathering reduces effective cohesionand to a lesser extent the angle ofshearshying resistanceabsorption of watcr leads to changesin the fabric of days (for exampk lossof bonds bcrween particles or the forshymation of fissures)

bull Pore-JVater pressure jncreaseHigh groundwater table as a result ofincreased precipitation or middotas a resultof human interference (for example-dam construction) (see under Matershyials above)

Some mass movements are created byhumans piling up waste soil and rock intounstable accumulations that fail spontaneshyously The disaster at Aberfan in SouthWales referred to at the beginning of thissection occurred when a pile ofcoal waste180 metres high began to move as an earthflow The pile had been constructed notonly with steep slopes but also upon aspring line

In the case of the Vaionr Dam disasterin Italy (also referred to at the begilUlingof this section) heavy rainfall and the presshyence of young highly folded sedimentaryrocks provided the necessary predisposingconditions for a slip to take place Howshyever it was the construction of the VaiontDam itself which changed the localgroundwater conditions sufficiently toaffect the stability of a rock mass on themargins of the reservoir The result wasthat 240 million ell metres of ground

Accelerated Landslides 187

Table VS Examples of methods of controlling mass movements

Type of movement Method of control

Falls Flattening the slopeBenching the slopeDrainageReinforcement of rock walls by grouting with cementanchor boltsCovering of wall with steel mesh

Slides and flows Grading or benching to flatten the slopeDrainage of surface water with ditchesSealing surface cracks to prevent infiltrationSubsurface drainageRock or earth buttresses at footRetaining walls at footPilings through the potential slide mass

Source Dunne and leopold (1978) table 1516

slipped with enormous speed into thereservoir producing a sharp rise in waterlevel which spilled over the dam causingflooding and loss of life downstream

It is evident from what has been saidabout the predisposing causes of the slopefailure triJ8eretl by the Vaiont Dam thathuman agency was only able to have suchan impact because the natural conditionswere broadly filVourable to such an outshycome

Although the examples of acceleratedmass movements that have been givenhere are associated with the effects ofmodern construction projects more long-

FURTHER READING

established activities including deforeshystation and agriculture arc also highlyimportant For example Innes (1983) hasdemonstrated on the basis of the size oflichens developed on debris-flow depositsin the Scottish Highlands that most ofthe flows have developed in the last 250years He suggests that intensive burningand grazing may be responsible Presentshyday deforestation can generate spectacularmass movements

Because of the hazards presented bymass movements a whole series of techshyniques have been developed to attempt to

control them (table VB)

Cooke R U and Doornkamp J c 1993 Geomorphology in Environmental Manageshyment 2nd edn Oxford Oxford University PressThis general text contains useful material on slope problems and their control

Dikau R Brunsden D Schrott L and Ibsen M-L 1996 Landslide RecognjrionChichester WileyAn edited text rich in European examples which describes and classifies the main typesof landslides that pose hazards to human activities

188 The Land Surface

Slope erosion inNorth America

the Pacific north-west of

The mountainous regions of Oregon Washington British Columbia and Alaskaare areas with steep slopes high rainfall and active tectonics They are thus areasof high potential erosion rates Heavy forest vegetation and the high infiltrationcapacities of many forest soils protect the slopes however the removal of forestin the area and road-building to take the timber out have had a series ofprofoundeffects Studies by Swanston and Swanson (1976) have shown a dramatic increasein the occurrence of violent debris avalanches flows and slides (table V9) Theseshallow mass movements leave scars in the form of spoon-shaped depressionsfrom which up to 10000 cu metres of soil and organic material have moveddownslope They may move as fast as 20 metres per second Clear-cutting offorest results in an acceleration by two to four times of debris avalanche erosionwhile road construction could accelerate debris avalanche erosion by between 25and 340 times the rate under undisturbed forest

Table V9 Debris-avalanche erosion in forest c1eapcut and roaded areas

Site Period ofrecords(years)

Area(sq km)

No ofslides

Debris-avalancheerosion(cu metressq kmyr)

Rate of debrisshyavalancheerosion relativeto forested areas

Stequaleho Creek Olympic PeninsulaForest 84 193 25Clear-cut 6 44 0Road 6 07 83Total 244 108

Alder Creek western Cascade Range OregonForest 25 123 7Clear-cut 15 45 18Road 15 06 75Total 174 100

718o

11825

4531171

15565

x 10o

x165

x 10x 26x344

Selected drainages Coast Mountains south-west British ColumbiaForest 32 2461 29 112Clear-cut 32 264 18 245Road 32 42 11 2825Total 2767 58

H Andrews Experimental Forest western Cascade Range OregonForest 25 498 31 359Clear-cut 25 124 30 1322Road 25 20 69 1n2Total 642 130

x 10x 22x 252

x 10x 37x 49

7 GROUND SUBSIDENCE

Like many of the environmental issuesdiscussed in this book ground subsidencecan ~ an entirely natural phenomenonFor example climatic change may causepermanently frozen subsoil (permafrost) todecay in tundra areas this will produceswampy depressions called thermokarstLikewise in limestone areas true karsticphenomena such as swallow holes maydevelop when the ground surface collapsesinto a subterranean cavity produced by thesolution of limestone over a long period

Nevertheless humans are now causingground subsidence to occur at an accelermiddotating rate and with dramatic consequencesin certain sensitive areas The main mechshyamsms are

bull the transfer and removal of subterrashynean fluids such as oil gas and water

bull the removal of solids either throughunderground mining (eg coal andother minerals) or in solution (eg salt)

bull the disruption of permafrostbull the compaction or reduction of

sediments (especially organic-rich ones)by irrigation and land drainage

bull the construction of reservoirs

Ground subsidence is often a relativelygentle progress but sometimes it can besudden and catastrophic This is particushylarly the case in areas where the bedrockis limestone and where overpumping hasgreatly drawn down the level of the watertable A sensitive area of this kind is theFar West Rand of the Transvaal ill SouthAfrica when gold mining has requiredthat the local water table be lowcred bymore than 300 metres The tall of thewater table has caused clay-rich materialsfilling the roofs of large underground cavesto dry Out shrink and collapse This inturn has caused large depressions to deshyvelop at the ground surface In densely

Ground Subsidence 189

populated urban areas this is a considershyable hazard In another limestone areaAlabama in the southern USA groundshywater pumping has caused over 4000sink-holes or related features to formsince 1900 Fewer than 50 natural sinkshyholes developed in that area over the sameperiod

More gentle but in geological termsstill very rapid has been ground subsidshyence caused by oil abstraction The classiccase is the Los Angeles area where over 9metres of subsidence occurred as a resultof the development of the Wilmingtonoilfield between 1928 and 1971 Considerthat 9 metres is more than the averageheight of a two-storied house Even morewidespread is the subsidence caused bygroundwater abstraction for industrialagricultural and domestic purposes InMexico City subsidence of more than 75metres has occurred while in the CentralValley of California the figure exceeds 85metres In Tokyo Japan subsidence hasbrought some areas below sea level In1960 only 35 sq km of the Tokyo lowshyland was below sea level By 1974 thisfigure had almost doubled exposing atotal of 15 million people to major floodhazard Bangkok is suffering from a simshyilar problem

Perhaps the most familiar example ofground subsidence caused by humans isthat resulting from mining It causes damshyage to houses roads and other structuresas well as disrupting surface drainage 1l1dcausing flooding

In permafrost areas ground subsidenceis associated with thermokarst deeJopshymem Therl1lokant is the irregular humshymocky terrain produced by the melting ofground ice permafrost The developmentof thermokarst is due primarily to the disshyruption of the thermal equilibrium of thepermafrost and an increase in the depthof the active layer (the layer subjected toannual thawing) Consider an undistur~d

190 The Land Surface

tundra soil with an active layer of 4S emAssume also that the soil beneath 4S emis supersaturated permafrost and uponthawing yields (on a volume basis) SO percent water and 50 per cent saturated soilIf the top 15 em were removed the equishylibrium thickness of the active layer underthe bate ground conditions might increaseto 60 em As only 30 em of the originalactive layer remains 60 em of the permashyfrOSt must thaw before the active layercan thicken to 60 em since 30 em ofsupernatant water will be released Thusthe surface subsides 30 em because ofthermal melting associated with thc= deshygrading permafrost to produce an overalldc=pression of 4S em

Thus the kc=y factors involvc=d inthermokarst subsidence are the state of theactive layc=r and its thermal relationshipsWhen surface vegetation is cleared forpurposes of agriculture or construction forexample the dc=pth of thaw will tend to

increase as the ground will no longer beinsulated from the effects of dirc=et sunshylight The movement of uackc=d vehicleshas been particularly harmfuJ to surfacevegc=tation and deep channels may soonrc=sult from permafrost degradation wherethe$( have been used Similar c=ffects maybe producc=d by siting hc=atc=d buildings onpermafrost and by laying oil sewer andwater pipes in or on thc= active layer

Some subsidence is creatc=d by a processcalled hydrocompaction This occurs beshycause moisture-deficient unconsolidatedlow-density sediments tc=nd to have suffishycic=nt dry strength to support considenbleeffective stresses Vtithout compacting

FURTIIER READING

However when such sediments which mayinclude alluvial fan materials or loess art

thoroughly wetted for the first time (forexample by percolating irrigation water)the inter-granular strength of the depositsis diminished Rapid compaction resultsand subsidence of the ground surface folshylows Unequal subsidence can crate probshylems for irrigation schemes

Land drainage can promote subsidenceof a different type notably in soils rich inorganic matter The lowering of the watertable makes peat susceptible to oxidationand deflation (being blown away by thewind in dust storms) so that its volumedecreases We discuss this in the context ofthe English Fenlands in part IV section S

A further type of subsidence sometimesassociated with earthquake activity rcsultsfrom the effects on the earths crust oflarge masscs of water impounded behinddams Seismic effects can be generated inareas with susceptible fault systems Thismay account for eanhquakcs recorded at

Koyna (India) and elsewhere The processwhereby a mass of water causes crustaldepression is called hydro-isostasy

It is clear from this discunion thatground subsidence is a diverse but imporshytant facet of the geomorphological impactof human activity The damage caused ona worldwide basis can be measured in bilmiddotlions of dollars each year We have menshytioned some of the forms such damagetlkes in this section They include brokendams cracked buildings offset roads andrailways fractured well casings deformedcanals and impeded drainage among manyothers

Johnson A T (ed) 1991 LAnd SubJidmu IAHS Publication no 200A large collection of research-level papers

Waltham A C 1991 LAnd Subsithnu Glasgow BlackicA lower-level inuoductory study which is particularly strong on the effects of miningon subsidence

WaS[( Disposal 191

8 WASTE DISPOSAL

Waste can be loosely defined as all unshyused unwanted and discarded materialsincluding solids liquids and gases (Costaand Baker 1981 p 397) Alternatively itcan be defined as something for which

(Il tllUlllPJamptd WUQ

we have no further use and which we wishto get rid of However it is defined thereis no doubt that waste is generated in largequantities by humans that the amount ofwaste generated develops as societies bltshycome greater consumers of materials andthat the control and disposal of waste is a

tJ -A-

(~~

~-~

H ~-~aSlltS Rcoolltl of Runoff (fOOl urban lltiddquitioll TUJi spiJLampltllI fmnbnd ldltIiriva rmllJld tnJ other Ivtd rK khgcI

-8 ttltmM~ t B lilli ft- HolINtiIliun hydfQIrigttgtts gt011 W)

p(flriiti

~_-----Dmmilt nd 0001TlCrltial9

r8 PtMpwlIpoundIhpWttrgt

Demolition and llIUQuoon 8B Irbk rMJ fIa~iP

-- bull------------~

(tl DispouJ motIwllb for~ WUltl

(UKdl - toulfOO millioo ton)

~ -------UodIiU 57 -8 _Mew

-riIeI illIItgtUII W bullbullUI

--Ii I

SCi dlllllping 1~54_4yullllilriamps__IJIlliIIUIi

itWlIriM fMjiulJ

Figure V7 The main sources of and disposal strategies for wastes that canpollute land and water early 19905Source After Woodcock (1994) fig 161

192 The Land Surface

Table V10 Wastes arising In Englandand Wales late 19805

Source House of Commons EnvironmentCommittee Second Report Toxic Waste(19889)

major environmental issue Furthermorethe disposal of waste can substantiallymodify surface conditions and produce anarray of environmental impacts

Wastes can be divided into those thatare unmanaged and those that arc manshyaged (figure V7(a) and (braquo)

Table VIO shows the amounts of difshytcrcllt cangories of waste produced in Engshyland and Wales In terms of sheer wdghtliquid industrial etfhunt is the largest comshyponent but the production of emucntfrom the agricultural sector is also imporshytant Significant amounts of primarily solidwaste arise trom mining and quarryingindustrial sources the domestic seerorsewage sludge power station ash blast furshynace slag and the building ami cOllStrucshytion industries In the USA an average dtywith 250000 inhabitants has to collecttransport and dispose of 450 tonnes ofrefuse every day In general about 2-3 kgof municipal waste and 3-4 kg of industrialwaste are produced in the USA per person

Waste type

liquid industrial effluentAgriculturalMining and quarryingIndustrial

HazardousSpecial

Domestic and tradeSewage sludgePower station ashBlast furnace stagBuildingTotal

Quantity(mtlyr)

2000250130

503915

28241463

2505

per day In the UK about 137 million tonnesofcontrolled waste (waste which is eitherincinerated or disposed of to a landfill) areproduced every year Landfill takes 90-95per cent of the controlled waste

In this section we are mainly concernedwith solid waste a category which includesmaterials from a wide range of sources(table VII) There are a number of disshyposal options for solid waste (figure V7(c)) As we have already noted the mostimportant of these in the UK is so-calledsanitary landfill (table Vl2) The relashytive importance of different methods varshyies from country to country (table VI3)For example whereas most municipal solidwaste in the UK and Australia goes to

landfills in Switzerland nearly half is inshycinerated and in Japan about two-thirds isincinerated

The content of waste is also highly varishyable Some types contain contaminants thatcan pose a series of hazards to health andproperty (table VI4) For example inshydustrial waste may contain dangerous heavymetals building waste may contain asbesshytos and household food waste may genshyerate potentially explosive methane gasIf sites are not carefully controlled wastedraining from the site (leachate) may beheavily polilited Other problems are posedby the bct that landfill ma~ graduallycompact through time

Landfilling is a cheap means of disposalIn countrie~ where there are manr oldquarries and gravel pits it may be a conshyenient way not only to dispose of wastebut also to reclaim such land lor otheruses Such sites are not always availablehowever in cloS( proximity to sourcesAlso if the~ are badly managed they canproduce environmental problems of rhetypes just discussed

There may be advantages in reducingthe amount of landfill capacity that is reshyquired A range of methods is available

Waste Disposal 193

Table V11 Refuse materials (solid waste)

Type

Garbage

Rubbish

Ashes

Street refuse

Dead animals

Abandonedvehicles

industrial wastes

Demolition wastes

Constructionwastes

Special wastes

Sewage treatmentresidue

Composition

Wastes from preparation cookingand serving of food marketwastes wastes from handlingstorage and sale of produce

Combustible paper cartons boxesbarrels wood shavings treebranches yard trimmings woodfurniture bedding

Residue from fires used for cookingand heating and from onmiddotsiteincineration

Sweepings dirt leaves catch-basindirt contents of litter receptacles

Cats dogs horses cows

Unwanted cars and trucks left onpublic property

Food-processing wastes boilermiddothouse cinders lumber scraps metalscraps shavings

lumber pipes brick masonry andother construction materials fromrazed bUildings and other structures

Scrap lumber pipe otherconstruction materials

Hazardous solids and liqUidsexplosives pathological wastesradioactive materials

Solids from coarse screening andfrom grit chambers septic-tanksludge

Sources

Households restaurantsinstitutions storesmarkets

Same as garbage

Same as garbage

Streets Sidewalksalleys vacant lots

Same as street refuse

Same as street refuse

Factories power plants

Demolition sites to beused for new buildingsrenewal projectsexpressways

New constructionremodelling

Households hotelshospitals institutionsstores industry

Sewage treatmentplants septic tanks

Source Costa and Baker (1981) table 13-1 Data from Institute for Solid Wastes of theAmerican Public Works Association and Bureau of Solid Waste Management 1970

Incineration

Sanitary landfills

Method

Open dumps

194 The Land Surface

Table V12 Methods of solid waste disposal

Description

Practices vary from indiscriminate piles to periodic levellingand compacting

little effort taken to prevent rodents flies odours andother health hazards

Often located with little planning where land was available

Consists of alternating layers of compacted refuse and soiLEach day refuse is deposited compacted and covered withsoilDaily operation and a final cover of at least 70 em ofcompacted soil prevents many health problems

Requires planning for economical operation and for suppliesof topsoil for cover Operations vary depending ontopography and supplies

Reduces combustible waste by burning at 1700F to aninert residue Ash and noncombustibles dumped or placed inlandfills

Air pollution is a problem with poor management

Increasing in use and often combined with a sanitary landfilland salvage operation

Onmiddotsite disposal Small-scale incinerators and garbage disposals

Incinerators are expensive and require considerablemaintenance

Garbage disposals are increasing rapidly in use with wastetransferred directly to the sanitarymiddotsewer system

Swine feeding A decreasingly used method which involves collection ofgarbage for swine food (pig swill)

Composting Biochemical decomposition of organic materials to a humusshylike material usually carried out in mechanical digesters

Increasingly used method with a useful end product whichis often sold

Source Costa and Baker (1981) table 13-3 from Schneider (1970)

Waste Disposal 195

Tabe V13 Selected solid waste material statistics for various countries

Country Annual per capita disposed disposedprodudion (kg) by landfill by incineration

Australia 681 98 2Austria 216 57 19Canada 642 94 6Denmark 420 64 32France 289 33 32Germany (W) 447 83 9Italy 246 38 20Japan 342 28 67Netherlands 502 66 19Sweden 300 52 38Switzerland 336 13 49UK 332 80 6USA 744 nla nla

Source UNEP (1990)

Table V14 Some commonly encountered contaminants the sites on which theyare likely to occur and the principal hazards they produce

Underground fires

Principal hazards

Harmful to health ofhumans or animals ifingested directly orindirectly May restrictor prevent the growthof plants

Explosions within orbeneath buildings

Chemical attack onbuilding materials egconcrete foundations

Contamination of watersupplies by deteriorationof service mains

Dangerous jf inhaled

Likely to occur

Metal mines iron and steelworllts foundries smeltersElectroplating anodizing andgalvanizing works

Engineering works egshipbuilding Scrap yards andshipbreaking sites

Gasworks power stationsrailway land

landfill sites filled dockbasins

Made ground includingslags from blast furnaces

Other metals egcopper nickel zinc

Type of contaminant

Toxic metals egcadmium lead arsenicmercury

Combustiblesubstances eg coaland coke dust

Flammable gases egmethane

Aggressive substanceseg sulphateschlorides acids

Oily and tarrysubstances phenols

Chemical worllts refineriesby-products plants tardistilleries

Asbestos Industrial buildings Wastedisposal sites

Source Attewell (1993) table 41

196 The Land Surface

Plate VS Landfill is one way of disposing of waste but the choice of sites to usecan be a problem This site is filling in old gravel pits near Didcot central England

bull Incineration can greatly reduce thevolume ofwaste However incineratorsare expensive to construct and maycreate pollutant emissions to the auConcerns have been expressed forexample about dioxin emissions Onthe positive side incinerators can proshyduce usable energy

bull Compaction can also reduce wastevolume Powerful hydraulic rams canbe used to compress waste

bull Shredding and baling can also reducewaste volume

FURTHER READING

However it may be mort desirable toreduce the amount of waste produced inthe first place This can be achieved by

bull substituting durable goods for dispos-able ones

bull composting garden wastebull generating less wastebull reusing materials and extending their

lives (eg by using rechargeable batshyteries and refillable bottles)

bull recycling paper glass etcbull recovering materials from waste (eg

magnetic separation of ferrous metals)

Douglas T 1992 Patterns of land water and air pollution by wastes In M Newson(ed) Managing the Human Impact on the Natural Environment Patterns and Promiddotcesses 150-71 London Belhaven PressA very useful review chapter in an introductory textbook

9 STONE DECAY IN URBAN

BUILDINGS

The natural materials we use for buildingare just as prone to weathering and alterashytion as are natural rock outcrops Simishylarly manufactured building materials suchas bricks concrete and plastics also decayand change once in contact with theatmosphere Usually such decay processesare of no real concern as they act veryslowly and produce only slight changes tothe appearance of buildings monumentsand engineering structures and do notaffect their strength safety or economiclife-span However where decay processesbecome accelerated and altered usually asa result of air pollution they can oblitershyate priceless carvings prcxiuce unsightlydecay features and lead to structural weakshyness Many buildings and monuments areat risk from the historic basilica of StMarks in Venice to Lincoln Cathedral inEngland the Parthenon in Athens and theMerchants Exchange Building in Pniladelshyphia In many cities whole groups of buildshyings and monuments are under attackExamples are the historic university townof Oxford in England and the lxautifulcity of Prague in the Czech Republic

Buildings in the urban environment areparticularly vulnerable to decay because ofthe following factors

bull urban microclimatic changes such aswarming and increased local rainfall orhumidity

bull air pollution such as increased conshycentrations of sulphur dioxide andnitrogen oxides

bull increased urban traffic levels which conshytribute to air pollution lead to applishycation of de-icing salts in winter inmany temperate-zone cities and causevibrations affecting roadside buildings

Stone Decay in Urban Buildings 197

~ DStQIttff

3 C~~ ) cpm~~ r~lt ~ Lichtns

- ron surfacfWi

)

0) () (d) () if) disroloralKln

Figure VS Some common forms ofbUilding stone decay (a) sooty andgypsum encrustations on shelteredparts of a building (b) blistering andexfoliation of gypsum crusts from (a)(c) cracking (d) pitting blistering andexfoliation of porous stone which hasbeen affected by salts (e) lichengrowths on stone with biologicalweathering underneath (f) surfacelowering and roughening by add rain

bull increased human contan with buildshyings leading to abrasion graffiti etc

Cities on coasts and within the arid zonesuffer particularly from highly corrosiveenvironments because of high concenshytrations of salt in the atmosphere andgroundwater

These environmental conditions inurban areas produce the following effectson building and monument surfaces (seefigure VS)

bull gypsum crusts produced by directchemical reaction of sulphur dioxidewith calcium carbonate-rich stone

bull soiling of building materials by sootyparticulates commonly prcxiuced by coaland oil combustion and diesel engines

bull accelerated lowering of surfaces proshyduced by acidified rainfall hitting calshycium carbonate-rich stone

198 The Land Surface

Plate V9 Decaying bUildings in Venice The sheltered portion of the columnshows the development of a black crust which contrasts sharply with the lightcolour of the portion of the column that is washed by rain (Dr 8 Smith)

bull exfoliation and blistering produced bysalt crystallization and hydration inporous materials

bull cracking produced by vibration andother stresS(s

bull pitting and surface growths producedby organic colonization especially bymicro-organisms and lichens possiblyencouraged by nitrogen oxides actingas fertilizers

Vast changes in pollution and environshyment have occurred in many cities overrecent years These changes have had conshysequent impacts on the weathering anddecay of buildings and monuments Thusa rapid increase in urban traffic andphotochemical pollution in Athens seemsto have been reflected in increasing stonedamage on the many ancient marblemonuments in the city In other cities suchas those in Britain and the USA legislamiddottion to combat air pollution has resultedin sharp decreases in sulphur dioxide andsmoke pollution over the past 40 yearsbut not in nitrogen oxides Measurementsfrom St Pauls Cathedral in London howshyever indicate that the rate of decay inbuilding stone has not yet declined Inshydeed stone decay may worsen in someplaces as nitrogen oxides act as a fertilizerfor organic growths such as bacteria andlichens which are important agents ofstone decay

How serious a problem is urban stonedecay and what can we do about it Interms of cost stone decay can be a seriousproblem for the owners of buildingsespecially when it has turned into a longshyterm problem In Oxford England forexample by the middle of the twentiethcentury 200 years or so of air pollutionfrom domestic and industrial coal burninghad produced intense damage to buildshyings constructed from the rather vulshynerable Headington Freestone (a locallimestone which weathers badly in pollutedatmospheres) Restoration work costing

FURTHER READING

Stone Decay in Urban Buildings 199

over pound24 million was carried out in the1950s and 1960s More recently trafficand other sources ofair pollution arc damshyaging these restored buildings as well asnew ones and soiling paintwork withinthe city centre Stone decay is particularlyserious when it affects monuments ofgreatcultural and spiritual significance especiallythose which attract large numbers of tourshyists and their associated income Decaycan also be hazardous as when it affectsbridges or causes bits ofstone to fall fromhigh towers In most cities however buildshying stone decay is just one symptom ofincreasing urban pollution and environshymental despoliation The impacts of airpollution on human health and urbanecology in cities are also of great concern(as discussed in paC[ II section 8 and paC[III section 6)

Suategies for combating urban buildingstone decay include

bull removing the causes of accelerateddecay by reducing air pollution stopshyping the application ofddcing salts to

roads etcbull removing vaJuable and vulnerable sculpshy

tures and carvings from the aggressiveurban environment putting them inconuolled museum environments andreplacing them with copies

bull cleaning and repairing soiled and damshyaged buildings

bull preventing future -decay by applyingprotective treatments on new or newlycleaned and repaired stone

Winkler E M 1975 Stone Properties Durability in Mans Environment ViennaSpringer-VerlagContains much information about many aspects of stone weathering

Cooke R U and Gibbs G 1994 Crumbling Heritage Studies of Stone Weatheringin Polluted Atmospheres Report for National Power picA useful summary of the recent worries over stone decay in Britain and results fromresearch aimed at elucidating the problem

200 The Land Surface

Venices decaying treasures

Venice in Italy contains many imporshytant buildings and monuments whichform a key part of the European culshytural heritage and which are underthreat from decay accelerated by airpollution and rising u=a levels Thereare also over 2000 pieces ofoutdooran mainJy stone carvings and sculpshytures within the city Studies of oldphotographs have revealed that moSdeay has occurred since the SecondWorld War The cause seems to bethe high sulphur dioxide levels resultshying from rapid post-war industrialshyization of the surrounding area (DelMonte and Vittori 1985) Since1973 laws have banned the use ofoil within the city itself replacing itwith methane However pollutionstill drifts in from elu=where and much u=rious decay has already occurred Smokeand sulphur dioxide react with marble limestone and calarcous sandstones toproduce the blackened gypsum crusts vhich now coat many ampmoos buildings inVenice These crusts are not only unsightly they are also damaging the undershylying stone A local relative sea-level rise has been a problem over the past centuryin Venice This has been caused by a combination of natural subsidence andextraction of groundwau~r (which has now ceased) As well as creating floodingsuch higher u=a levels have had a less visible impact on Venices environmentthrough encouraging the penetration of water and salts into vulnerable buildingmaterials The humid environment also encourages the transformation ofcalciumcarbonate into gypsum in the presence of sulphur dioxide

Major research is currently under way into stone decay in Venice coupled withmany schemes to restore damaged buildings and outdoor art Estimates of thecosts of restoration suggest that all the sculptures and carvings in Venice couldbe restored at a cost of some $US9S million Grime accounts for IS per centof the damagt requiring conservation corrosion or decay accounts for 35 percent and structural problems for the remaining SO ~r ctnt (Carrera 1993)

Considerable care has to be taken in attempting to clean and restore valuableobjects and buildings It is essential first to diagnose the major causes of decaycorrectly Only then can the most appropriate solutions be proposed The Churchof Santa Maria dei Miracoli for example has marble decoration slabs which arcbadly damaged Surveys revealed that salts from rising damp were the major causeof decay and techniques to remove the salts were develop=d before any restotamiddottion began

10 CONCLUSION

In this part of the book we have considshyered the impact that humans have had onthe soil on geomorphic processes and onlandforms We have drawn attemion tothe unintended acceleration of rates ofsoilerosion by water caused by a range ofhuman actions including deforestation theuse of fire and urban growth Acceleratedsoil erosion threatens soil fertility andagricultural productivity It also has otheroffarm impacts which indude a lowershying of water quality While this has oftenbeen seen as a particular problem in dcmiddotveloping countries where it has been idenshytified as onc facet of desertification andland degradation we have also shown thatit is a problem demanding attemion inthe British context Likewise acceleratedsoil erosion by wind has been a majorproblem not only in the Sahel zone ofAfrica and China but also in the techshynologically advanced farmlands of theUSA and the lowlands of Britain Thereare however a wide range of soil conshyservation measures that can be adoptedto counter both water and wind eroshysion caused by land-use and land-coverchanges

Land-use and land-cover changes arealso responsible for many other geoshymorphological changes They affect theform of river channels and the nature ofmass movements (including landslides)on slopes As is the case with soil erosionnumerous methods arc available to try tostabilize slopes and so reduce the hazardsposed by slope failures

Soil erosion and accelerated landslidesare not the only serious ways in which theEarths surface materials are transformedIn particular the spread of irrigation andthe removal of trees can lead to one ofthe most pernicious forms of soil transshyformation or metapedogenesis acceler-

Conclusion 20 I

ated salinization This is a major problemfor agricultural production especially inthe drier parts of the world Again a rangeof techniques for the eradication conshyversion or control of salinity have beendeveloped

Another form of accelerated geoshymorphological change that we hac idenshytified for a range of environments fromthe tundra regions to the worlds greatdeserts is ground subsidence However inmany parts of the world it is not so muchthe subsidence of the ground that is theproblem but where to put the cvcrshyincreasing quantities of waste which weproduce Landfill is one solution but therearc other options including incinerationcompaction shredding and baling A morefundamental solution is to reduce theamount of waste produced in the firstplace

Finally we draw attention to the factthat humans alter the weathering environshyment particularly by subjecting rocks andother building materials to corrosive airStone decay whether in Venice or Oxshyford Prague or York Athens or Agra is aserious threat to our cultural heritage Eventhough the process is slow compared withthe accelerated soil erosion mentionedearlier in this part it can have a seriousimpact on buildings and monuments

Overall the human impacts on the landsurface discussed in this section are a rathermixed bag often spatially limited in exshytent and often inadvertently caused Theyare nevertheless serious and show linkshyages with human impacts on the bioshysphere and atmosphere Many technologishycal solutions have been developed to dealwith these problems Nevertheless asseveral of our case studies have shownthe success of such schemes depends onthe willingness and ability of the peopleinvolved at all levels to implement andmaintain them

202 The Land Surface

KEy ThRMS AND CONCEPTS

accelerated landslidesaccelerated soil erosiondune reactivationforest soilshydrocompactionlandfillmass movementspermafrost

POINTS FOR REVIEW

salinitysand controlseawater incursionsoil conservatonsubsidencethetmokarstwaste

Why shouJd we be concerned about soil erosion

How would you seek to control rates of soil erosion by (a) wind and (b) water

What are the main ways in which humans unintentionally cause river channel characshyteristics to change

Why is salinization such an important issue in the worlds drylands

What are the main geomorphological hazards that are being accelerated by humanactivities

How in your own life could you reduce the need for waste to be disposed of aslandfill

Is there are evidence in your own home area that buildings are suffering from severeweathering Why might this bd

PART VI

Oceans Seas andCoasts1 lncroduction 2052 Sea-level Rise 206

bull Sea level rise and the Essex coast marshesEngbnd 208

3 Coastal Erosion 210bull Erosion at Victoria Beach Nigeria 213

4 Coastal flooding 215bull flooding at Towyn North Wales

February 1990 2165 Coastal and Marine Pollution 218

bull Pollution in the Mediterranean Sea 2206 Coastal Dune Management 222

bull Muuging dunes on the lancashire coast

England 2257 Coral ReefDegradation 226

bull Threatened reefS ofthe Red Sea 2308 Aquaculnue and Coastal Wedands 232

bull Pond culture in the Philippines 2349 Conclusion 235

Key Tenns and Concepts 235Points for Review 236

1 INTRODUCTION

Today almost 3 billion people (about 60per cent of the worlds population) livenear coasts often in large cities Furthershymore coastal popuJations are rapidly increasshying In the USA for example populationdensity is growing faster in coastal statcsthan inland ones Nearly half of all buildshying in the USA between 1970 and 1989occurred in coastal regions which accountfor only 11 per cent of the countrys totalland area Similar trends are found in manyother countries

Human activity is contributing to arange of local and regional environmentalproblems in coastal areas The main envirshyonmental impacts along the worldscoastline involve disruption to coastal sedishymentation pathways through erosion andaccelerated deposition increased floodhazard through sea-level rise and encourshyagement of local subsidence disruption ofcoastal ecology through reclamation of

Introduction 205

land and changing land uses and coastalpollution Historically attempts to manmiddotage the coastal ecosystem have involvedtrying to make the coast more stable andfixed These have made many environmenshytal problems worse In recent years an extradimension has been added to concerns overcoastal environmental problems with thethreat of accelerated sea-level rise in thefuture as a result of global warming

The worlds oceans and seas cover over70 per cent of the Earths surface and playa vitaJ role in the biosphere These vastbodies of water are also being affectedby a range of human impacts Pollution isthe major worry Some pollutants comefrom ships and oil platforms but most arefrom onshore sources reaching the sea viathe atmosphere rivers or coastal outfallsFishing and harvesting of marine resourcesaJso have adverse consequences for the mashyrine environment leading to more pollushytion and also damaging ecosystems About53 million toones ofmarioe fish are caught

TropIc ofCIJm

Tropic ofCprirom

bull~

-- CltWIII KltgtIog ltiMply inJIutllCfd by pollution

Aniflri1 lt1115S (diktbullbull hubows lind ttbmgttion tic) ofloogtr atto

Figure VI1 World distribution of major coastal problemsSource After Kelletat (1989)

206 Oceans Seas and Coasts

worldwide for human consumption everyyear with an additional 22 million tonnescollected for processing into fish mealoil etc (Taiba and EI-Kholy 1992) Atpresent the most severe problems are reshystricted to enclosed seas such as the Medishyterranean and Baltic Seas surrounded bydense populations However the evershyincreasing load of pollution entering theworlds oceans is likely to cause wider proshyblems in the future

Coastal areas particularly vulnerable toenvironmental problems include estuariesdeltas and other low-lying coasts especiallyin highly populated areas Figure Vllshows the global distribution of suchareas Parts of the Mediterranean BalticNorth Sea and Bangladesh coasts arcparticularly vulnerable to a whole range of

FURTHER READING

problems Natural and human-inducedprocesses combine to create coastal proshyblems In most cases these do not occurin isolation but rather interact to producea complex web of stresses on the environmiddotment Thus salt-marsh erosion may beexacerbated by pollution which interfereswith the plant-sediment relationship vitalto marsh development where such eroshysion occurs it may encourage floodingStresses on one part of the coastline mayaffect other parts For example deforestashytion can cause mangrove swamp erosionwhich in turn leads to downdrift degradashytion of coral reefs as they become chokedby the extra sediment load The destrucshytion ofcoral reefs in turn encourages stormdamage to the coastal zone behind thereefs that once sheltered it

GESAMP 1990 The State of the Mnrine Environment Oxford Blackwell ScientificAn authoritative global survey of marine pollution

Bird E C F 1985 Coastline Changes Chichester WileyA counrry-by-country survey of the erosional state of the worlds coastline

Viles H A and Spencer T 1995 Coastal Problems London Edward ArnoldA textbook which surveys with many examples the range of ways in which humansinteract with the natural coastal processes

2 SEA-LEVEL RISE

Sea level is perhaps a misleading termfor the relative positions of land and oceansare continually changing on a variety oftime-scales These fluctuations range fromdaily tidal cycles to vast changes in oceanvolume related to glacial and interglacialcycles over periods of thousands and milshylions of years However a practical definishytion of mean sea level is the long-termaverage (usually over 19 yean at least) ofhigh and low tide levels at a particularplace This level is affected by changes inthe volume or mass of water (eustatic orglobal changes) and movements of land

(tectonic and isostatic changes) or a comshybination of the two Over the past 18000years since the peak of the last Ice Agethe rising volume of ocean water as theicc on land melted coupled with complexisostatic changes has produced a generallyincreasing mean sea level over the world

Individual areas however have experishyenced very different sea-level histories(Clark et al 1978) Over the past 1000or so years sea level has risen (accordingto a range of evidence) at 01-02 mm peryear During the last 100 years sea-level risehas accelerated to l0-25 mm per yearaccording to many estimates This accelershyation is mainly due to climatic factors such

S~a-l~v~1 Ris~ 207

as th~ thermal ~xpansion of oc~an watersand the melting of ice on land E

bullIt is predicted that over the next 50 to -100 years global warming will lead to a tfurther acceleration of the rat~ of sea-level lris~ through a combination of two effects

bull

bull increased volume as ocean warer warmsup (call~d the steric effect)

bull addition of water to the oceans fromth~ melting of small glaci~rs and largeic~ she~ts

Th~ direct impact of human actions on sealevel may also provide an additional accelshyeration These actions and their conseshyquences include the following

extraction of oil and groundwater mayencourage coastal subsidence

bull d~forestation may encourage incrtasedfreshwater runoff to oceans

bull groundwater extraction for irrigationand damming of rivers to produce resshyervoirs may encourage evaporation ofthis water which will eventually r~turn

to the oceans (Sahagian et aI 1994)bull w~dand drainage reduces the water holdshy

ing capacity ofw~dand soils and thereshyfore adds more wat~r to the oceans

It is very difficult to predict how suchinfluenc~s might combine to aff~ct seashylevel ris~ in the futur~ The b~haviour ofsom~ of th~ compartments of the system(eg ice sheets) is not well understoodand the magnitude of global warming in

High

Middlt

1-

Y - -- ---- 1-

----- -

00Yo

Figure VI2 Best estimate high middleand low projections of sea-level riseto the year 2100 under the IPCCemissions scenario IS92aSource After Wigley and Raper (1992)fig 4

the next few decades is itselfthe subject ofmuch debate Howewr the most recentestimates suggest an average sea level riseof about 5 mm per year over the nextcentury within a range of unc~rtainty of2-9 mOl per year This will produce a totalincrease ofabout 50 cm by 21 00 as shownin the middle curve in figure VI2 andm~ans that sea level will rise two to fivetimes fast~r than over th~ last 100 years(Watson ~t aI 1996) This rat~ althoughhigh is much lower than some ~arlier

estimates which predicted wid~spread

drowning of many coastal ar~as Whatev~r

its precise magnitude future s~amiddotlevel ris~

in association with a whol~ host of small~rhuman-induced and natural disturbancesis likely to provid~ a complex seri~s of~ffects on th~ coastal ~nvironment

208 Oceans Sus and Coasts

Sea-level rise and the Essex coast marshes England

bull

N

I

ESSEX

bull

FIgure VI3 The Blackwater estuaryEssex and its associated marshes andmudflatsSource After Pethick (1993) figs 1 2

=

Much of the eastern and southerncoasdine of England is already undershygoing rdative sea-Ievd rise Isostaticreadjustments to the removal of theicc cap over northern Britain at theend of the last lee Age (some 11000yurs ago) arc causing the north ofBritain to risc forcing the southernpart down as a consequence TheEssex coast has been experiencingrelative sea-level rise of 4-5 mm peryear over the past few decades as aresult of such a process The coast-line of Essex is dominated by lowshylying estuarine and open coastmarshes which play a valuable rolein coastal protection acting as bafflesto wave energy and protecting thesea walls on the landward side Reshycent sea-Ievd risc coupled with 10-eaI human activities has led toerosion ofmany of the marshes here

The Blackwater estuary (figureVI3) provides a good example ofthe problems faced by the Essexcoast It has 680 hectares of saltmarsh and 2640 hectares of inter- ~

tidal mudflats around it and isbacked by agricultural land TheBradwell nuclear power station islocated on its margins Much ofthe coastal marshland around theestuary has been reclaimed over thecenturies to increase the area offarmland Flood embankments nowline 95 per cent of the estuary Theselimit the ways in which the marshes can react to seamiddotkvel rise Studies show thatbetween 1973 and 1988 23 per cent of the total salt marsh area around theestuary was lost to erosion (Pethick 1993) Over the past 150 years sea-level risehere has lxen accompanied by an increase in width of the main estuary channeland a decrease in its depth John Pethick an eIpcrt on this particular area of thecoast thinks that accelerated sea-Icvd rise in the future will lead to erosion ofmarshes in the outer estuary and their replacement by sand and gravel habitltsFurther inland marshes will ~come less brackish as salt Wllter penetrates further

Sea-Icvel Rise 209

Plate VI1 The salt marshes at Tollesbury Essex Marshes such as these willbe modified by any future sea-level rise Marshes nearby are the site of ascheme to stimulate marsh development (H A Viles)

up the estuary The extensive coastal defences behind the Blackwater marshesmean that unless humans intervene sea-level rise will eventually lead to thedestruction of these marshes

As the marshes help to protect the sea walls tram coastal erosion there havebeen strenuous efforts [0 help save the marshes A pilot scheme on NortheyIsland (whose location is shown in figure VI3) for example has pioneered theuse of set-back techniques to stimulate new marsh growth by removing an oldbroken-down sea wall and allowing the sea to reclaim the land behind it AtTollesbury on the northern shore of the estuary similar experiments are takingplace Here 21 hectares of arable land bought by EngJish Nature specially for thepurpose is being flooded in a policy of managed retreat There is a danger thatsuch piecemeal schemes will make the problems worse for the rest of the estuaryunless they are carefully managed John Pethick suggests that a much biggeresmary-wide project is necessary to manage these vital coastal wetlands in the faceof future sea-level rise Such a scheme would involve allowing the outer estuarinechannel to widen coupled with a general retreat of flood embankments

Further reading

Pethick J 5 1993 Shoreline adjustments and coastal management physical andbiological processes under accelerated sea level rise GeographictJl Journal 159162-8

210 Oceans Seas and Coasts

3 COASTAL EROSION

Coastal erosion is a natural processpowered by wave energy and vital tothe maintenance of a dynamic coastlineHuman activity however has increasinglybeen responsible for accelerating coastalerosion Increasing human settlementnear the coast and use of the coastal zonehave also created a serious environmentalissue which requires sensitive long-termmanagement

Recent surveys have produced somestark statistics For example net erosionhas occurred on over 70 per cent of theworlds sandy coastline over the past fewdecades However such erosion does notonJy affect sandy coastlines There havebeen spectacularly high losses of land onthe Niger delta Here 487 hectares ofcoastal plain were lost as a result of subshysidence caused by oil and gas extractionfrom the delta and mangrove deforestamiddottion Where high rates of erosion howshyever localized they may be (see table VlIfor Britain) coincide with dense humansettlement and intensive coastal useserious problems result Along the midshyAtlantic coast of the USA for example

barrier islands have retreated at about 15metres per year as sediment from the oceanside is eroded and washed over the top asa response to locally rising sea level Manysuch barrier islands are now highly builtup for example places such as AtlanticCity and Ocean City arc built almost litershyally on the beach This restricts the naturalinland migration

Cliff erosion is often linked to beacherosion as removal of protective beachesexacerbates erosion of the cliffs Clifferosion is a serious problem along partsof the developed southern California coastwhere cliffmiddottop apartment buildings havehad to be demolished Here eliffi havefailed because of tectonic activity coupledwith groundwater seepage and waveundercutting of the cliffs In Britain therehave been many instances of buildingscollapsing as a result of cliff failure Arecent example was Holbeck Hall hotel inScarborough on the north-east coast ofEngland In most such cases naturally highrates of erosion on failure-prone e1iffi havebeen exacerbated by building which hasaltered the cliff hydrology

What causes coastal erosion Erosion isproduced by the interaction of natural and

Table VI1 Rapid rates of coastal retreat at sites In Britain

Area

North YorkshireHoldernessNoriolk (Cromer-Mundesley)Essex (The Naze)

Kent FolkestoneEast Sussex Seaford HeadEast Sussex Beachy HeadEast Sussex Cliff EndDorset Ballard DownDorset Kimmeridge Bay

Cliff geology

Glacial driftGlacial driftGlacial driftGlacial drift London Clay

and cragGault ClayChalkChalkSandstone (Hastings Beds)ChalkKimmeridge Clay

Average retreat rate(metres per 100 years)

2812096

11-88

281261061082339

Source After Goudie (1990 1995)

Coastal Erosion 211

Plate VI2 The jetty at West Bay Dorset southern England has plainly modifiedthe drift of sediment along the coastline In the foreground sediment hasaccumulated but in the background the beach is starved of sediment and erostenrs occurring neussrtating coastal protection engineering schemes (A S Goudie)

human hctotS both acting to increase waveenergy andor reduce sediment 2vail2bilshyity The rate of erosion depends upon theinterpl2Y between the erosive action of thewaves and other agents of erosion andthe etodibility of the rocks and sedimentsbeing affected Natural increases in thetendency of the coastal environment toerode arc caused by storms BI Ninoevents and longer-term increases in sealevd All these herotS increase wave enshyergy at the coast LocaJly human impactsmay be increasing the erodibility of coastsby the following means

bull reducing the availability ofsediment forprotection and accelenting erosion byaJtering the wave energy field and sedishyment stores with graynes breakwatersand cliff protection schemes

bull removing vegetation which stabilizes

coastal wetlands thus making the sedishyment more erodible

bull reducing the sediment supply by otTmiddotshore and onshore mining and by trapmiddotping sediment behind dams on riversthat enter the ocean

bull replacing the coastal plain over whichbarrier islands can migrate withbuilt-up areas which restrict sedimentmovements

bull reducing the stability of coastal cliffsthrough building and aJtering groundmiddotwater levels

The fact that sediment moves betweendifferent parts of the coast means thatattcrnpts to reduce erosion in one area canhave the opposite effect on areas downdriftIn New Jersey USA for example tenninalgroyncs at Sandy Hook at the southernend of Long Beach Island have encouraged

212 Oceans Seas and Coasts

Plate VI3 A sea wall and cliff stabilization measures at Weymouth Dorsetsouthern England Such engineering solutions are expensive and are not alwayssuccessful (A S Goudie)

accelerated erosion downdrift Beach nourshyishment that is feeding the beach bybringing in sediment has been utilized toovercome such problems with some success

It is clear then that managing coastalerosion can ~ a very difficuh task To besuccessful it requires understanding bothof what factors are causing erosion in aparticular area and of how remedial techshyniques will themselves affect the situationFor example a highly developed barrierisland where future sea-level rise inducedby global warming threatens to exacerbate

FURTHER READING

erosion on a naturally subsiding coast willrequire a very different management stratshyegy from a small beach where erosion canbe rdated to a specific episode of offshoresand mining Clearly the threat of afuture acceleration in sea-level rise becauseof global warming (see section 2 above) ismaking coastal erosion an increasinglyserious problem In many places managedretreat where coastal erosion is allowedto occur relatively naturally and settlementsmiddotmoved inland is perhaps the only feasiblelong-term solution

Nordstrom K F 1994 Developed coasts In R W G Carter and C D Woodroffe(eds) Coastal Evolution 477-509 Cambridge Cambridge University PressA wide-ranging review of the problems faced by coasts with large concentrations ofpeople in an edited collection of advanced papers

Bird E C E 1985 Coastline Changes A GJobfll Reliew Chichester WileyA survey of erosion and accretion on coasdines in various countries

Coast1l ElQ5ion 213

Erosion at Victoria Beach Nigeria

Around the port of Lagos is a 200kin long sttttch ofbarrier island coastcharaeteriud by a sandy barrierbacked by a mangrove-mnged lashygoon It appears to have grownseawards over the Holocene Nowhowever the coast is eroding atsometimes spectacular rates (Ibc1988) Wave energy is high in thisenvironment the coast is poundedby waves coming all the way acrossthe Adantic and there is a generaltrend from west to east in movementof material along the shore

The port and former capital cityof Lagos has a population of over 6million Much of its economic prosperity is based on the extraction of oil fromthe Niger Delta Lagos is situated where ~ere is a break in the coastal barrierand expanded rapidly in the nineteenth and early twentieth centuries on landreclaimed from mangrove swamps behind the barrier As the port developedimprovements were made to the harbour starting with dredging in 1907 Majorharbour works began in 1908 These involved the construction of two breakshywaters and a training wall or jetty to provide a safe deep-water entry for largeships These breakwaters interrupted the west-to-east longshore drift The conshysequence has been a long-term erosion problem on Victoria Beach (on the westside of the harbour) and accumulation of sand on Lighthou~ Beach to the eastVictoria Beach has eroded by up to 69 metres per year since then (by 2 km inall) and an estimated 25 sq km of beach has been lost (figure VIA)

Victoria Beach is an important recreational arca for Lagos Also its erosion wasstarting to threaten housing built on low-lying reclaimed land behind the beachwhich protects the coast under natural conditions Beach nourishment by bringshying in sediment has been used to try [Q solve the problem starting in 1976Although it was successful in the shott tetm dramatic erosion occurred in 1980necessitating further emergency nourishment using 21 million cu metres of sandbetween 1980 and 1981

The erosion problems of Victoria Beach are particularly hard to solve becausethe Lagos port must be kept open The sand accumulating on Lighthouse Beachis also proving to be a problem as eventually it will extend past the weslernbreakwater and be washed around into the harbour Long-term integrated manshyagement of the entire coast here is necessary This may involve pumping sandaround from wcst to east (mimicking the natural longshore drift) and preventingfurther development on vulnerable low-lying land

Erosion ofVictoria Beach must be set in the context of more general erosionaltrends along the Nigerian coast Altogether Nigeria has some 800 km ofcoasdineand there is much evidence of widesprcad erosion within the past few decades

214 Oceans Seas and Coasts

Figure VI4 Since breakwaters were built erosion and accretion haveresulted along the beaches around Lagos harbour NigeriaSource After Usoro (1985)

Along the Niger Delta coast which is situated to the east of the Lagos areaerosion - coupled with environmental problems related to the oil extractionindustry - is a serious problem and several schemes (usually involving beachnourishment like that at Victoria Beach) have been implemented with limitedsuccess Table VI2 below shows some recent typical erosion rates along barrierbeaches of the Niger Delta coast for comparison with those at Victoria Beach

Table VI2 Erosion on the Niser Delta cout

Location

OgboiodoEscravos(western part of the Niger Delta coast)Forcados(western part of the Niger Delta coast)Brass(central part of the Niger Delta coast)Kulama(central part of the Niser Delta coast)Bonny(eastern part of the Niger Delta coast)ImoOpobo(eastern part of the Niger Delta coast)

Erosion rate (metres per year)

18-24

20-22

16-19

15-20

20-24

10-14

4 COASTAL FWODlNG

Simply put coastal flooding is a result ofsubstantially increased water levels on thecoastal plain above high ride levd Floodsoccur therefore as the Ka level riKS orthe coast sinh or where a combination ofthe two happens The possibility of globalwarming raising sca levels worldwide ismaking coastal flooding an cver morcserious issue Currently flooding affectslow-lying coasts such as the MississippiNile and Ganges dehas the Thames estushyary Venice Bangkok and the NetherlandsIn many areas expensivc flood protectionstructures and schemes have been impleshymented usually after a serious flood Anexample is the Thames Barrier completedin 1982 In Bangladesh storm surges proshyduced by cyclones in the Bay of Ikngalhave produced particularly dcvasntingfloods such as that in April 1991 which isestimated to have killcd morc than100000 pltrople

The major causa of coastal floodingarc storm surges EJ Niio events hurrishycanes tidal waves (tsunamis) and subsidshyence through abrupt tectonic movementsThe size and severity of flooding are influshyenced by the tidal regime and the phaseof the tide when the flood event suikesIn esruanes peak river flows can also makematters worse

Factors which make places more proneto flooding by lowering the land include

bull natural compaction of delta sedimentswhich promotes subsidence

bull oil gas and groundwater extractionwhich promotes subsidence

bull removal of mangrove and marsh veg-

FURTHllR READING

Coastgtl Flooding 215

etation which reduces coast2l protecshytion for backshore areas

bull building on low-lying subsidingland

bull fli1ure of flood defences such asdikes

There are severa stages in managementof the coastal flood hazard The initialstages include understanding the majorcauses of flooding in the area buildingstructures and flood defence schemes andimproving prediction and disaster planningIn Bangladesh for example mangrovetrees have been planted on a large scale [0

encourage the stabilization and development of mangrove swamps These helpto provide a buffer and so to preventflooding inland Also the Coastal Embankmiddotment Project has been established to buildembankments and a series ofsluices to proshytect against flooding Flood hazard warnshying improvements and increased provisionofemergency shelters on high land are alsovital elements in flood management here

The management of coastal flooding inBritain is in the hands of the Ministry ofAgricuJrure Fisheries and Food (MAFF)Since 1985 MAFF has also managedcoastal protection works for example [0

control erosion The Environment Agencyformerly the National Rivers Authority alsohas an important role to play in floodwarning and flood defences The floodson the east coast in 1953 provided a majorstimulus to planning and defences in Britainin East Anglia most of the sea defencestructures date from the decade after 1953A national network of tide gauges and theStorm TIde Warning System (STWS) wasalso set up about this time

Perry A H 1981 EPiroflMnltlJl HtuImu i the British klu London Allen andUnwinWard R C 1978 FlHds A GeogrRphiuJ Perrpectipe London Macmillan

216 Oceans Seas and Coasts

Flooding at Towyn North Wales February 1990Towyn and the surrounding Clwyd coastal lowlands covering about 20 sq kmaltogether support a population of around 14000 people On 26 February 1990the sea wall at Towyn was breached as a result of a storm surge The floodwatersrose to over 5 metres above normal sea level or Ordnance Datum (00) in thecentre ofTowyn Over 64 sq km ofland was flooded including all ofTowyn andmuch of the adjacem settlement of Kinmel Bay (figure VIS) Many housesbungalows and caravans were destroyed Over 750 domestic and commercialproperties were ruined in Towyn alone The floodwaters reached up to 2 Ioninland covering much agricultural land

What caused these floods and why were the floodwaters so patchily distribshyuted Storm surges are a major cause of coastal flooding around the British coastTheir low barometric pressure and strong winds act to raise tide levels abovethose predicted When a strong depression occurs over the sea falling barometricpressure acts to suck up the water surface producing a rise of about 1 cm forevery 1 millibar (rob) drop in pressure

On 22 February 1990 there was a large anticyclone situated over central EUJopeand a strong depression over south-west Iceland Between 23 and 25 Februshyary this depression deepened and moved towards southern Scandinavia By 26February it was JUSt west of Denmark and a second related depression haddeveloped to the sourn-east of Iceland These depressions had low-pressure cores

Plate VI4 A flooded caravan and trailer park beind the sea wall at TowynNorth Wales in March 1990 (Richard SmithKatz)

~f ~

Coastal Flooding 217

bullo flood wmr in dilrhes C--

_ Roilwi) _ Majolt road

Figure VI5 (a) location of Clwyd lowlands (b) The extent of flooding westof the River Clwyd near Towyn North Wales in February 1990Source After Englefield et aJ (1990) fig 3

of between 950 and 960 mb and major storms with high winds occurred acrossthe UK between 2S and 26 February Rain hail gale-force winds and lowpressure occurred in the Clwyd lowlands coupled with exceptionally high sealevels (assisted by the storm surge conditions) This combination of circumstancesled to the floods

The Clwyd lowlands were particularly vulnerable to flooding as they are exshytremely low-lying situated on reclaimed land ranging from 35 metres 00 to 7metres 00 most of it below 5 metres Along much of the coast there is a naturalprotective shingle ridge this reaches a height of up to 7 metres at Kinmel Baybut dies out at Towyn

The history of land use and human intervention in the area also had a crucialrole to play in the flooding In 1847 the Chester to Holyhead railway wasopened running along the coast (figure VI5) This has interfered with coastalsediment movements ever since resulting in long-term coastal erosion problemsFor example between 1872 and 1899 along one section the coast eroded by 60metres in frOnt of the railway line During the nineteenth and early twentiethcentury sea defences were built to help overcome these problcms including a seawall and groynes at Towyn Very little sediment ever accumulated in front of thewall and on 26 February 1990 it faced the full force of the ocean breaking ataround 11 am

Studies carried out after the flood by Englefield et al (1990) showed theextent of the damage and explained that the pattern of flooding was controlledby microtopography and the road layout within settlements Roads and higherareas acted as flood barriers Interestingly the old bungalows nearest (0 the seaat Kinmel Bay escaped the worst 800ding as they were located on the shingleridge at 6-7 metres 00

218 Oceans Seas and Coasts

5 CoASlAL AND MARINEPOLLunON

A report in 1990 by the Group of ExpertSon the Scientific Aspects of Marine Pollumiddottion concluded that most of the worldscoasts are polluted while many parts ofthe open ocean arc still relatively cleanCoastal pollution is an important environshymental issue affecting human health andthe diversity of fisheries and coastal ecoshysystems Recent attention has focused onliner and sewage pollution on Britishbeaches red tides (algal blooms caused byan excess of nutrients sec part rv section7) in the Mediterranean and elsewhereand oil spills such as that resulting fromthe WTeck of the Braer tanker ofT the Shetshyland Islands in January 1993 and the SeaEmpress off West Wales in February 1996

Most marine and coastal pollution (over75 per cent) coma initially from landshybu4=d sources It is brought down to thesea by rivers dumped in sewage outfalls orarrives via the atmosphere The rest comafrom dumping by ships and from offsho~

mining and oil production To we oilpollution as an example a surprising 344per cent of a total of 32 million tonnaper year which reaches the sea coma fromland via urban runoff etc another 343per cent comes from marine tnnsport (oilshipment) the rcst comes from atmoshyspheric fail-out offshore oil production(only 16 per cent) and natunl sources

The major types and sources of coastalpollution are

bull nutrients from sewage agriculturalrunoff aquaculture

bull pathogenic organisms from sewagebull litter especially plastics from land and

shipsbull metals eg admium and lead from

mining and indwuybull sediments from deforestation soil

erosion mining and dredging which

may be contaminated with syntheticorganic compounds

bull orpnochJoride pesticides from agrimiddotcultural and industrial runoff

bull PCBs (polychlorinated biphenyls) fromindustry

bull oil from land and oil tanker dischargesbull radionuclides from discharges from

nuclear reactors and reprocessing plantsand naNral sources

The amounts involved can be hormiddotrifying In 1985 at least 450000 plasticcontainers were dumped by th~ worldsshipping fleet The impacts on humanscoastal ecosystems and coastal stability canbe devastating The effects can also belong-lasting Oil spilt from the Isla Payardioil refinery in Panama in 1986 for examshyple came ashore on to a mangrove coastand killed many shellfish as well as beshycoming absor~d in mangrove muds Fieyears later the oil was recycled as thesesediments eroded and started to threatennearby coral reefs

Other pollutants have more immediateand shortmiddotlived effects For examplenutrients whieh trigger algal blooms causedeoxygenation of the water killing otherspecies These algal blooms may also betoxic poisoning shellfish and affectinghuman health Many synthetic organiccompounds such as PCBs have a sinisterlong-term effect They tend to accumushylate in living organisms gradually gettingmore concentrated as they are passed upthe food chain and seriously affectingmarine mammals and sea birds

Some areas ofthe coastal and marine envirshyonment arc particularly prone to such polshylution Espccially vulnerable are areas wheretidal and wave acrion encourage the conshycenmrion of pollutants and where sedishyments can act as a sink Thus sheltued baysestuaries and coastallagoons are key areasaffected by pollution Enclosed seas such asthe Mediterranean and Baltic are now alsoseriouslyaffected by pollutionover vast areas

Coastal and Marine Pollution 219

Plate VI5 Beach pollution at Bahrain Arabian Gulf (A S Goudie)

What can we do to reduce coastal polshylution~ Great strides have already beenmade in limiting the influx of pollutantsthrough a number of international agreeshyments In 1987 for example eight counshytries bordering the North Sea agrccd tophase out the incineration of chemicalwastes at sea by 1994 Dumping of radioshyactive waste at sea was stopped worldwidein 1982 The United Nations EnvironmentProgramme (UNEP) has coordinatedmany attempts to tackle pollution in parshyticular areas such as the south-east Pacificand the Black Sea (which has already sufshyfered serious ecological damage from toxic

FURTHER READING

chemicals pathogens and eutrophication- see part IV section 7) Agriculture inshydustry urbanization maricu1turc marinetransport dumping oil extraction miningand war are all important polluters Allmust be addressed if the problem is goingto be tackled successfully In many areasit is still difficult to get accurate infonnationon coastal pollution and its effects Duringand after the Gulf War for example disshyagreements raged about how much the warhad increased coastal pollution (throughdeliberate sabotage of oil fields) or deshycreased it (through preventing oil shipshyments and their associated pollution)

GESAMP 1990 The State of the Marine Enronment Oxford Blackwell ScientificA general report by an authoritative international group on pollution of the oceans andthe coastal seas

Clark R B 1989 Mllrine Pollution 2nd edn Oxford Clarendon PressA very good overview

220 Oceans Seas and ~ts

Pollution in the Mediterranean Sea

It is estimated that the population ofcountries around the Mediterranean will riseto 430 million by 2000 CB These countries and especially their coastal zonesalso attract large numbers oftounsts 100 million visited the area in 1984 Thereare huge disparities between the economies of countries on the northern andsouthern sides of the Mediterranean but pollution is getting worse everywhere

The major types of pollution are

bull oilbull domestic wastebull industrial and urban wastewaterbull organochlorine pesticidesbull heavy metalsbull PCBs

All these harm wildlife affect human health and may lead to long-tenn damageto the entire Mediterranean ecosystem Oil pollution is now a chronic problemover most of the Mediterranean as a result of tankers discharging ballast and bilgewaters in the network of shipping lanes which criss-cross the sea carrying some250 million tonnes of oil per year Sewage is a severe problem especially aroundthe Italian Spanish and French coasts (see figure VI6) The costs of reducingsuch sewage pollution may be very high In 1990 GESAMP suggested it wouldcost USS150 per person to construct sewage treatment and disposal facilities forall the 132 million inhabitants of the coastal settlements around the Mediterrashynean That would amount to US$lS billion overall at 1990 prices Sewage polshylution can make swimmers ill and can also contaminate seafood In 1973 acholera epidemic broke out in Naples Italy because of contaminated molluscsand hepatitis can also be transmitted by seafood Organochlorine pesticides PCBsand heavy metals are a problem in particular areas such as the Venice lagoonwhere lack of flushing allows them to accumulate in bottom sediments Sewageleads to algal blooms and red tides under extreme circumstances which firstposed a problem in the Gulf of Venice in 1972 Eutrophication is a seriousproblem in the western Adriatic Sea where rivers coming from Italy bring around29000 cu metres of phosphates and over 120000 cu metres of nitrates everyyear Like acid rain this results in a transnational problem beaches along thecoast of Croatia are affected as seriously as Italian beaches

i

CoOStal and Marine Popution 221

shyFigure VI6 Sewage and industrial waste discharges into the MediterraneanSea (BOD = biological oxygen demand)Source After Clark (1989) fig 93

Some pollution problems affect only small areas and arc easily solved Anexample is the discharge of tannery wastes contaminated with chromium into theGulf of Geras on the Isle of Lesbos The impact of this was lessened in 1983when an effluent treatment plant was installed (Papathanassiou and Zenclos1993) Some pollution problems however are less easily solved and some areassuch as the Vcnice lagoon appear to be polluted beyond acceptable limits

In 1979 as a response to concerns about many oftheslt issues the Blue Planset up with the help of UNEP was adopted by the Mediterranean countries Thisplan aimed to help both economic development and environmental protectionand to limit pollution from land-based sources As always however dealing withinternational environmental problems is a difficult task and implementing susshytainable development and tourism has so far proved very hard amp tourism is oneof the major industries of the Mediterranean and is affected by pollution as wellas contributing to it perhaps the initiation of ecotourism would make a starttowards solving the poUution problems here

222 Oceans Seas and Coasts

6 COASTAL DUNE

MANAGEMENT

Coastal dunes provide an important bufferbetween land and sea and act as a storefor sediment They arc dosdly linked withbeaches as there is a regular interchangeof sediment nutrients and organismsbetween beach and dune systems Coastaldunes arc a common component of mostcoasdines and arc often of very impresshysive height and extent Notable examplesarc found on the west coast of Americawhere the Coos Bay dunes arc 72 kID longand reach heights of 50 metres In Eurshyope high dunes occur along the CocoDonana in southern Spain where theyreach 90 metres Coastal dunes unlikemany descrr dunes tend to be vegetatedHardy salt-tolennt plants grow on themnearest the sea as dune environments getmore sheltered and better soils occur furshyther inland and over time other plantsfollow

Coastal dunes provide many attractionsfor human society Because of this as wellas their natural dynamism and role asagents of coastal protection their successshyful management has become an irnporuntissue especially as most sandy coastlinesarc undergoing erosion As cliffs areprevented from eroding so the supply oferoded material going to beaches anddunes is reduced In Britain for exampledunes on the East Anglian coast probablynow have a diminished supply of sandbecause of coastal protection works covershying about 60 per cent of the coast hereDunes themselves are eroded by both windand waves

Sand dunes provide a harsh environshyment colonized at first by hardy plantsthat can tolerate salt and sand such as searocket (CiJtie mllritimll) and salt won(SIIsoJ4 W) whose seeds can tolente longperiods soaked in seawatec As these plants

grow they trap sand and help the dunesto grow Grasses such as A1fJmophili4llrettllrill (marram grass) and sand couchshygrass (Aaropyrtm jmuitmfIU) are themajor sand-accumulating species Gradushyally plant succession creates a diverse ecoshysystem which is attractive to birds insectsreptiles and small mammals For examplehalf the flowering plants of Britain can befound in coastal dune areas around thecountry

Important human uses ofdunes include

bull golf coursesbull sand and water extractionbull afforestation and grazingbull recreation such as horse-riding walkmiddot

ing biking and off-road vehiclesbull military training and exercisesbull housing camping and caravan parksbull transport such as coods and airfieldsbull pipelines

Most of these uses however inoledisrurbing the narura ecosystem Suchdisrurbance often encourages dune mobilmiddotiution and destabiliution and the develmiddotopment ofblowouts This can lad to sandmigrating inland ovec valuable agriculturalland or housing it also removes the coastalprotection afforded by the dunes Otherimpacts affect the groundwater level ofdunes which in turn affects the ecologyIn the Netherlands for example coastaldunes provide an important source ofdrinking watec Other human uses ofdunescan fossilize them removing any chanceof natunl dynamism through such thingsas planting grass and trecs for golf courscsFinally some human impacts affect dunesindirectly removing sand from beachesdamming rivers offshore sand mining andpoUution can aU tip the balance betweensedimentation and erosion

Because of the many and vuloW usesand abuses of coastal dunes considenblemoney and time have been invested in

trying to conserve and protect dunes inorder to save them and the wildlife theysupport Dune management schemes usushyally involve all or some of the following

bull aiding deposition of sand on beachesthrough groynes sea walls and beachnourishment

bull shaping dunes using bulldozers tomove sand

bull planting and watering dunesbull using biofabrics mulches etc to help

stabilize fragile dune surfacesbull fencing to restrict accessbull providing walkways to channel people

away from sensitive areas and preventdamage to the underlying dune

Coastal Dune Management 223

bull providing signs information displaysand education to involve the public indune conservation

However overmanagement can also be aserious problem Most coastal dunes unshyder natural circumstances are not fixedand movement ofdunes and blowouts areperfectly natural occurrences Some eleshyment of disturbance needs to be includedin successful dune management schemesFigure Vl7 shows how dune managementis also affected by natural coastal erosionon the Baltic coast of Poland a catastrophicstorm in January 1983 led to severe eroshysion of beach and foredunes which thenthreatened the stabilized dunes behind(Piotrowska 1989)

Plate VI6 Footpaths causing erosion patterns across coastal sand dunes atWinterton Norfolk eastern England This is a dear example of the effects ofrecreational pressures on the landscape (University of Cambridge Air Photographcollectlon)

224 Oceans Seas and Coasts

18th Ctntury Browndulll m

SI 8mh Fortmlll Yellow dun~ Grt)dune S v 0

EIymo-Ammophiletum HeUehryraquo-jasionetum Em~ro-Pinetum

IS

19th20th Century 10

S

0Bnch JgtuJtrd gmsn He~dllp(l-Jasionum Pine lIlQIlocult=

2nd halfof2Oth Century

After 1983 rommon slate

lkach Young pinrmonocullUn

After 198310cat slates

I Btach

IS

10

S

0Old pine monocultun

IS

10

S

0Old pi~ llJOIlocuhun

Figure VI7 The history of dune management and coastal erosion on the Balticcoast of PolandSource After Piotrowska (1989) fig 5

FURTHER RBAoING

Ranwell D S and Boar R 1986 Coast Dune Management Guide HuntingdonInstitute of Terrestrial EcologyA useful practical guide to management techniques with plenty of C~ studies

Goasral Dune Management 225

Managing dunes on the Lancashire coast EnglandThe Ainsdale-Forrnby dunes cover 800 hectares of which 490 hectares is aNational Nature Reserve The coast here faces north-west and the dunes form asuite of more or less parallel ridges with low-lying areas called dune slacks inbetween Behind these are more irregular dunes Erosion has dominated at thesouth end of the area since the beginning of the twentieth century The coast isprotected in the north towards Stockport by wide sand flats The sand here is richin calcium carbonate so dune soils are not very acidified The area is rich in plantspecies with marram dune scrub and woodland including Anm and BetultlHippophae rhamnoides (sea buckthorn) was introduced here and has spread conshysiderably over the dunes (Boorman 1993) In 1959 myxamatosis arrived decishymating the rabbit population and aiding the spread ofscrub (by preventing rabbitgrazing which maintains grass) Now the Formby dunes to the south of thenature reserve are threatened by both public pressure and coastal erosion

Detailed studies by the geomorphologist Ken Pye have revealed the long-termimportance of human activities to the dunes here (Pye 1990) Marram grass wasintroduced into the area at the start of the eighteenth century when strict lawswere introduced to encourage planting indeed planting was obligatory until1866 Marram favours the development of hummocky sand hills as found tomiddotwards the back of todays dune system In the late nineteenth and early twentiethcentury brushwood fencing and backshore planting were wed to encouragedune development resulting in the parallel dune ridges found over most of thedune system

By the late 1920s recreational pressure was causing severe erosion and producmiddoting much blown sand Other activities which have affected these dunes include

bull excavation of flat-floored depressions for asparagus cultivationbull sand miningbull waste dumpingbull development of caravan and car parksbull road-buildingbull development of golf courses

These pressures have led to dune management and restoration schemes such asthe Sefton Coast Management Scheme established in 1978 This scheme beganto restore the dunes using brushwood fencing marram planting and woodenfencing and restricting access by vehicles and pedestrians Covering some 17 kmof coast the Sefton Coast Management Scheme provides a framework for natureconservation projects within an area which includes several different landownersA Coast Management Officer has been appointed who promotes co-operationbetween the different landowners and ensures integrated management of thissensitive coastal environment

226 Oceans Seas and Coasts

7 CORAL REEF DEGRADATION

ConJ reefs arc some of the worlds mostdiverse ecosystems containing a bewildershying array ofcorUs fish and other organismsAlthough mey cover only 017 per cent ofthe ocean floor (an area roughly the sizeofTexas) they are home to perhaps 25 percent of all marine species One hundredand nine countries have bctween them over100000 km of reefs and many of theseare threatened by a series of natural andhuman-induced stresses (figure VI8)

Coral reefs require very specific envirshyonmental conditions Reef-forming coralsonly grow in waters with temperatures of2S-29degC where there is a suitable relashytively shallow platform less than 100 meshytres below sca level to grow on and wheresediment and pollution do nOt kill themof[ Thus meir growth is restricted to suitshyable tropical and subtropical shores Onesuch is the north-eastern coast ofAustraliawhere the Great Barrier Reef forms thelargest agglomeration of reefS in the worldstretching for over 2000 km and comshyprising ova 2500 individual reefs Othermajor reefs are found along the Gulf coastof Belize and around many South Pacificislands

As Charles Darwin explained in the nineshyteenth century there arc three main typesof reefS related in a genetic sequence First

there are fringing reefS which connectdirectly with the shore Then there arcbarrier reefs which arc separated from theshore by a lagoon Finally when such reefSarc growing around a gently subidingoceanic island atoUs arc produced Anaroll is a ring of coral reefs around a lashygoon in the centre ofwhich was once theisland Sand and gravel islands accumulatshying on the margins of such atolls providea precarious home for flora fauna andhumans as in the Maldives

Reefs arc remarkable in that their entiregeological structure is formed from bioshylogical growths now dead covered by athin veneer of living corals Despite thename coral reefs most reefs arc in factcomposed of a number of important reefmiddotbuilding species including coralline algaeas well as a range of corals

Stresses affecting coral reefs in todaysworld include

bull storms and hurricanesbull EJ Nino eventsbull scamiddotlevel rise and other effects ofglobal

warmingbull outbreaks of disease and preduors

(such as the Crown ofThoms starfish)bull increased sedimentation produced by

deforcstation on landbull eutrOphication produced by sewage and

other pollutants

Figure VI8 A generalized map of threatened coral reefs around the worldSource After C R Wilkinson personal communicationUnivmity of Guam

bull onshore and offshore mining producshying scdimcntenrichcd with heavy metals

bull trampling and physical damage fromboats and divers

bull overfishing and the usc of damagingfishing techniques such as dynamiting

bull direct quarrying and removal of coralsfor building or curios

bull oil pollution from land and shippingbull nuclear weapons testing and other

military activitybull pollution and damage from landfill

(used for example to create new landfor airports and sometimes constructedwith toxic waste)

Natural disturbances such as hurricanescan damage fragile corals and fling themup on to the reef flat However the imshypact of such events is probably short-livedand may in fact be good for the overallhealth of reefs providing a disturbancewhich may increase species diversity andgrowth in the long term El Nino eventswhich occur every two to ten years andinvolve widespread changes in ocean curshyrents and temperature have a potentiallymore scrious effect They temporarily warmthe water around reefs this can causecoral bleaching when the corals expel thezooxanthellae the tiny algae that livesymbiotically with them In severe casesbleaching can cause mass death of coralsGlobal warming may mue such bleachingepisodes more frequent and more seriousas it will heat the oceans and may providefurther stresses by accelerating the rate ofsea-level rise forcing corals to grow fasterin order to keep up with sea level Locallysome corals have been badly affected byoutbreaks of pests and diseases Crownof Thorns starfish for example eat coralsthese predators spread rapidly across manySouth Pacific reefs in the 19605 In 1993South Pacific reefs were first observed tobe suffering from another biological probshylem CLOD (coralline lethal orange dis-

Coral Reef Degradation 227

ease) which affects coralline algae anotherimportant part of reef frameworks (Littlerand Uttler 1995) The causes of suchbiological disturbances arc unknown andmuch-debated but they may be at leastpartly due to environmental pollution

Other stresses on coral reefs can dearlybe blamed on human impacts both dishyrectly on the reefs themselves (from divshying and fishing for example) or indirectlyfrom activities on land or offshore Inshycreased sediment load pollution fromsewage agriculture and industry and deshystructive fishing techniques all damage thereef ecosystem by upsetting the balance ofspecies At the Green Island resort on theGreat Barrier Reef sewage has led to anincrease in the area of seagrasses largelyat the expenS( of corals Thcsc seagrassestrap sediments which usually circulate freelyaround the beaches of the island Thuspollution here is damaging both reef andbeach environments Deforestation inThailand and conversion of forest to rubshyber and cocoa plantations has had severeimpacts on the reefs on southern PhuketIsland producing excessive sedimentationand killing corals

Many of these stresses on reefs are nowacting together and many reefs are goinginto the twenty-first century in an increasshyingly unhealthy state (table VI3) If gloshybal warming continues some reefs may beunable to cope How serious is the proshyblem and what can we do about it~

Reefs have many uses and roles for society

bull they are agents of coastal protectionproviding a natural sponge absorbingwave energy

bull they are major tourist attractionsbull they arc an important focus for bioshy

diversity and conservation of marinespecies

bull they contain living and nonmiddotliving reshysources ofgreat elaquogtnomic value such asfish crustaceans coral rockand sediment

228 Oceans Seas and Coasts

Plate VI7 The destruction of a coral reef by draglines used to build a new porton the island of Taketoni off Okinawa Japan (Panos PicturesJim Holmes)

Most counrries cannm afford to lose theirreefs In terms of fishing alone Pacificislanders get up ro 90 per cent of theirprotein requirements from reef fish andworldwide reefs are home ro a toral fishcatch of 4-8 million ronnes per year (Weshyber 1993)

Furure sea-level rise will affecr reefs asreef-building corals and algae only growwithin relatively shallow water Three majorreef strategies have been identified (figureVI9) Keep-up Catch-up or Give-updepending on he balance between therelative rate of sea-level rise and the growthrate of the corals involved Ifsea levels risevery fast most reefs will be unable ro keepup Given the receor predictions of 4-5mm per year mean sea-level rise over thenext 50-100 years (see section 2 above)most reefs will keep up or catch up Unshyhealthy reefs however are less able to keeptheir growth rates up and are more likelyto give up

- ---_ _-$fa~ ___~ _ - bull r

~ Z4 -- _~ampJt)

RftfswflKe

~lnb_~--~Rftfiuface (tl

--$fIlM rise -Rffi growth

Figure VI9 Coral reef growthscenarios (a) keep-up reef growthproceeds at roughly the same rate assea-level rise (b) catch-Up sea levelinitially rises faster than reef growththen reef growth catches up (c) giveshyup sea level rises too fast for slowshygrowing or unhealthy coral reefs

Area

Coral Reef Degradation 229

Table VI3 Summary of the health of coral reefs In various parts of the world

worlds reefs Reef healthfound in the area

South-east Asia 30 60-70 reefs sick Deforestation miningand fishing problems

Pacific Ocean 25 Mainly good condition because of lowpopulations

Indian Ocean 24 20 reefs lost Mining fishing and coastalpollution problems

Caribbean Sea 8 Deforestation and tourism problems

Atlantic Ocean 6 Coastal development and tourism problemsBermuda has good reef reserves

Middle East 6 low runoff low population and littletourism aid reef health oil spills a problem

Source Adapted from Weber (1993) table 3-2

Currently many reefs are protected tovarying degrees in an attempt to reducethe suesses on them The Great BarrierReef Marine Park in Australia was createdin the 19705 It contains five sectionswith different reef uses allowed in eachOil drilling and mining are prohibitedthroughout the park and in some secshytions only scientific research and traditionalfishing are permitted Where relatively poorcountries have vulnerable reefs which arealso major touriSt attractions there can bemany conflicts involved in successful reefmanagement and marine parks can be hardto monitor and control If reef manage-

FURTHER READING

ment and protection is to be successful itis necessary to understand how reefs workmanage the various human uses of themand plan onshore land use (0 reduce damshyage from external sources The problemhas many dimensions as Weber (1993p 53) explains Ultimately the forcesbehind reef dedine are hard to untangleOverexploitation and coastal pollutionstem from business interests wealthy conshysumers the growing numbers of coastalpoor and governments trying to balanceconflicting development goals No singlegroup is the cause of reefs precipitousdecline yet all contribute to the tragedy

Guilcher A 1988 Coral Reef GeomorphokJgy Chichester WileyA general clearly written study of coral reefs with a useful section on human pressureson reefs

230 Oceans Seas and Coasts

Threatened reefs of the Red Sea

The Red Sea which extends from 13 N to 30 N has fringing reefs along almostall of its coastline Reefs are especially well developed along the north and centralcoasts Conditions arc particularly suitable for reef growth here There are nopermanent rivers flowing into the Red Sea from its arid hinterland andphytoplankton productivity is low both of which encourage clear water Thereare few storms and no tropical cyclones Reefs along the northernmost part of theRed Sea however are affected by occasional extremely low tides and sea temshyperatures here are near the minimum level acceptable for reef-building coralsMost countries bordering on the Red Sea are arid and sparsely populated andthere have therefore been few onshore threats to the reefs Pollution from thebusy Red Sea shipping lanes is a problem and oil pollution from oil explorationin the Gulf of Suez is especially serious

Tourism is a growth industry here most concentrated in the northern counshytries of Israel Egypt and Jordan Studies estimate that 19 per cent of Egyptsreefs are now affected by tourism and this figure is expected to rise to 73 percent by the year 2000 The Egyptian resort of Hurghada provides a good examshyple of the actual and potential impacts of tourism on Red Sea reefs The townof Hurghada was founded in 1909 to supply the oil industry It did not start toamact many tourists until the late 1970s Now it has huge tourist complexesstretching some 20 km along the coast and many more are planned (figureVIlO) Diving is a major attraction for tourists here What damage does tourismcause to these reefs~

First construction creates dust which in the dry Red Sea climate gets blownon to reefs creating a sediment nuisance Secondly construction often involvescreation of new coastal land from landfill This can cause major damage to reefsAlso enhancement of tourist beaches through beach nourishment etc can upsetregional sediment dynamics Thirdly sewage disposal desalination irrigation andrubbish disposal all pose problems At Hurghada sewage is treated before itenters the sea but observations of high algal growth on reefs nearest the shoresuggest that high nutrient inputs may still be a problem (Hawkins and Roberts1994) Fourthly tourism may encourage overfishing and the collection of coralsand shells for sale Fifthly diving and boat anchoring have been shown to damagereefs over small areas Finally it should be noted that tourism has positive benefitsfor neighbouring reefs as it reduces the industrial development in the area andbrings an added awareness of the value of natural reef habitats

A Marine Station was established at Hurghada in 1931 which has providedinvaluable data on marine biology A national park has been proposed to helpprotect the reefs Oil pollution remains a serious problem For example in 1982fresh oil was found over a wide area affecting turdes white shark spoonbill andosprey (Wells 1988)

Further north around the tourist resort of Sharm-el-Sheikh the Ras Mohamshymed Marine Park was set up in 1983 to aid reef conservation Here there is a

Coral lkef Dt=gradarion 231

WI e-J

DpIo

N

j -----

EGYPT

Figure Vl10 Present and planned coastal tourist development aroundHurghada EgyptSource After Hawkins et al (1993)

high density and diversity of corals as well as sharks giant clams green turtlesand many interesting bird species

According to a recent scudy tourism is causing worrying rather than alarmingdamage to Red Sea ~efs However the situation could easily worsen as touristnumbers grow and global warming and natural stresses compound the problemsNatural stresses include outbreaks of sea urchins and other grazing organismsSea urchins can reach high population densities on the coral reefs here Theygraze on coral and can inflict damage on the reefs Several areas of reefs alongthe Ikd Sea coast have shown signs of urchin damage in the past and similarproblems may recur in the future

Further reading

Hawkins] P and Roberts C M 1994 The growth of coastal tourism in theRJd Sea present and future effects on coral reefs Ambio 23 503-8

232 Oceans Seas and Coasu

Io 0

19t5 1986 1917 1911 1919 1990

8 AQUACULTURE AND

COASTAL WETLANDS

Figure VI11 Global aquacultureproduction 1985-1990Source After UNEP (1993) fig 310

ments where wave energy is low andwhere tidal processes dominate such asestuaries deltas and bays In the upperintertidal zone and above salHolerant vegshyetation may grow In the temperate zonesalt marsh communities such as SpRrtin4grasses dominate grading into mangrovetrees (eg speeies of Rbiuphora andApUnR) in the tropics At lower tidallevels there are mudflat surfaces which lookbare but actually support large numbersof algae and mud-dwelling animals

Coastal wetlands have often been seenas wastelands but 1ikc other wetlands (seepart II section 9) they play some veryuseful roles These include acting as anatural agent of coastal protection buffshyering the land behind them from the seaand acting as a purifying agent by removshying roxic wastes from the water enteringthem They are also invaluable in preservshying biodiversity for example they provideimportant stopping-off points for numershyous migrating birds In mangrove swampsthe mangrove trees themselves are a useshyful source of timber and firewood for manylocal communities

There arc many large areas of coastalwetlands such as nearly 600000 hectaresof salt marsh on the Atlantic coast ofthe USA and an estimated 22 millionhectares of mangrove swamps worldwideMany coastal wetlands are threatened bydevelopment Agriculture industry andurban expansions can all lead to landreclamation and the removal of naturalmangrove ecosystems Aquaculture alsoleads to disruption of the natural coastalwetland as trees and other natural vegetashytion are cleared ponds dug and filled withwater and nutrients and waste productsdischarged into the water Eutrophicationcan become a problem as a result of theinflux of nutrients The species mix maybe affected and total biodiversity reduced

In Indonesia for eumple brackish waterfishponds (locaUy known u tRmbu) nowoccupy over 269000 hectares or 65 per

Aquaculture is the water-based version ofagriculture where plants and animals aregrown and harvested for food and otherproducts Since the 1970s aquaculture hasdeveloped enormously and now accountsfor about IS million tonnes or 17 per centof world fisheries production (figureVIll) Aquaculture can take place inlandon freshwater lakes and ponds but a largeproportion of aquaculture takes place inbrackish water or seawater ponds in coastalwetlands Along tropical coasts for examshyple it is estimated that about 765000hecrares of land are currently in usc forshrimp production Shrimps oysters catshyfish tilapia salmon rainbow trout andtiger prawns among a wide range ofotherspecies are regularly farmed throughaquacultural techniques

Why are coastal wetlands commonlyconverted to aquacultural use~ And whydoes it matter Coastal wetlands whichinclude salt marshes mangrove swampsand mud flats arc found along low~lying

sheltered coastlines with a large sedimentsupply In general they form in environ-

ED] Ra1I olWoridlMOllr Dlnltil

olloulfuh (Itch

IlJ~f

I~ uoo-

-Aquaculture and Coastal Wetlands 233

---~--

Plate VI8 Aquaculture is expanding rapidly in South-East Asia These fish pondsare located on Java Indonesia The creation of fish ponds can destroy importantnatural coastal vegetation and contribute to coastal pollution (Panos PicturesJeremy Hartley)

cent of the total former mangrove areaConversion to tambak is often unsuccessshyful as erosion and pollution can becomeserious problems if the sites are not choshysen correctly As with agriculture on landaquaculture will only succeed in the longterm without causing ecological damageif there is a good understanding ofhow the natural environment works andaquacultural techniques are developed thatavoid disturbing these environmental sysshytems too much In the Far East whereaquaculture has been practised for thoushysands ofyears technological improvements

FURTHER READING

and more sensitive management techniquesare helping to reduce environmental probshylems associated with aquaculture Technoshylogical improvements include better diseasecontrol and nutrition and genetic enhanceshyment Technological advances also enablemangroves to be planted on dikes aroundponds The mangroves provide useful fuelshywood and fertilizer (from decaying leaves)and protect the ponds from erosion Moresensitive management techniques involveensuring that aquaculture ponds andmangrove forests are not seen as mutuallyexclusive

Beveridge M C M Ross L G and Kelly L A 1994 Aquaculture and biodiversityAmfri 23 497-503An introductory review in a journal that is full of important case studies on many topicscovered in this book

234 Oceans Seas and Coasts

Pond culture in the PhilippinesThe Philippines consist ofsome 7100islands in all Between 1920 and 1990the area of mangroves around theseislands shrank from 450000 hectaresto 132500 hectares Over the sameperiod the area covered by ponds in~

creased to 223000 hectares Around50 per cent of mangrove loss in thePhilippines can be ascribed [Q theconstruction ofbrackish water pondsBy 1991 27 ~r cent of the totalPhilippines fish production (some26 million tonnes) came from suchaquaculture

Brackish water pond aquaculturein south-east Asia started in Java Inshydonesia in the fifteenth century andspread to the Philippines whereponds were first constructed on theshores around Manila Bay (Primavera 1995) There have been several phases ofbrackish water aquaculture in the Philippines and several effects

bull In the 1950s and 1960s the government sponsored fishpond developmentespecially for milkfish production for local consumption

bull The 1970s was declared a conservation decade andbull The 1980s saw shrimp fever with a boom in production of shrimps and

especially tiger prawns mainly for export and the urban macket

The notable effects of brackish water pond aquaculture in the Philippines havebeen mangrove loss pollution of coastal waters and decline in production ofdomestic food crops

The loss of mangroves affects coastal stability removes protection against the20 or so typhoons which affect the Philippines each year and removes some veryversatile plants There ace 26 mangrove tree species found here many of whichhave a wide range of traditional meso The most seriously affected areas arewestern Visayas and central Luzon

The ecological damage inflicted by pond aquaculture has prompted the Philipshypines government and others to take action Rtforestation has been carried outfor example in 1984 when 650 hectares in central Visayas were replanted As of1990 8705 hectares of mangroves have been successfully planted

9 CoNCLUSION

The worlds coastlines and their immedishyate hinterlands are the focus of a greatdeal ofhuman activity They are thus undersevere pressure from humankind By conshytrast the worlds oceans which are enorshymous have so far been much less affectedby anthropogenic changes Their sheer sizeoffers them some protection from theeffects of pollution and waste disposalHowever the depletion ofworld fish stocksis an increasingly serious issue Halfwaybetween coastlines and the great oceansare the marginal seas - water bodies likethe Mediterranean the Baltic and theNorth Sea These do show the dear imshypacts of a wide range of human activities

The worlds coastlines are experiencingslowly rising sea levels (There arc someexceptions such as those areas undergoshying rapid uplift because of isostatic responseor tectonic activity) If the enhanced greenshyhouse effect causes global warming to takeplace the nHe ofsea-level rise will increaseover the coming decades Many of theworlds coastlines are also being subjectedto accelerated fates of erosion or retreatbecause of a range of human impactsSome are also being flooded more oftenpartly because of sea-level rise but alsobecause of a combination of local humanand natural stresses

Many types of coastal terrain are bothdynamic and fragile Dunes deltasbeaches reefS swamps and marshes comeinto this category They all offer many

KEy ThRMS AND CoNCEPTS

aquaculturecoral blachingcoral reefsEl Ninoeustatic changeisostatic change

Conclusion 235

ecological services to humankind Forexample they act as agents of coastal deshyfence or as highly productive ecosystemsThus we need to treat them with particushylar care and respect

Overall the issues covered in this partof the book illustrate that there are a wholerange of immediate environmental probshylems affecting many parts of the worldscoastline resulting from a combination ofhuman and natural stresses Future seashylevel rises if they do occur will be affectshying coastlines which are already stressedand therefore unlikely to be able to reshyspond as they would naturally to suchchanges Furthermore as we have showncoasts arc naturally dynamic over a rangeof time-scales and any attempts at coastalmanagement must take this into aCCOUD[We cannot fossilize the coast Because ofthe many attractions of coastal environshyments a multitude of people are involvedina wide range of activities within thecoastal zone Effective coastal zone manshyagement must involve and consider thesepeople Finally several of the examplcs wehave used show the many links betweencoastal environments and those on landand in the oceans There are also manylinks between different segments of thecoastline and between the different comshyponents of the coastal enviroment (ecolshyogy sediments water) In orGa to copesuccessfully with all these componentsand interlinkages coastal zone manageshyment schemes must be truly integratedprogrammes

salt marshessea levelsediment circulation celissurgestectonics

236 Oceans Seas and Coasts

POINTS FOR REVIEW

Why arc coastal areas being placed under increasing pressure

Why might sea levels rise in some areas in coming decades

Why are so many stretches of the worlds coastlines showing signs of erosion

How would you aim to reduce the impacts of coastal flooding

What marine environments are especially prone to [he effects of pollution

Which coastal types do you think are especially fragile and dynamic

Why should we aim to conserve coastal wetlands and coral reefs

PART VII

Conclusion1 Introduction 2392 The Complexity ofthe Human Impact 2393 Towards a Sustainable FUlUre 239

Key Tenns and Concepts 244Points for Review 244

1 INTRODUCTION

The human transformation of nature hasbeen going on for a very long time andhas been very pervasive The Earths surshyface still has areas ofsome size which showlittle obvious manifestation of the impactof humans (c=g the deep oceans pans ofthe polar regions some of the tropical rainforests) and we talk of wilderness areasin which very little human activity occursHowever there is no place on the face ofthe Earth which is not to some extentaffected by the changes in the chemicalcomposition of the atmosphere and assoshyciated changes in climate and levels ofpollution

2 THE COMPLEXITY OF THE

HUMAN IMPACT

We have demonstrated in this book thatdifferent types of human activity causedifferent types of land transformation Forexample at the one extreme we have disshycussed some of the changes in the envirshyonment that have been caused in andaround cities by the process of urbanizashytion At the other we have demonstratedhow even hunters and gatherers livingin scattered groups have contributed tosuch processes as deforestation anddesertification We have selected our casestudies to illustrate this theme We haveshown how some changes in the environshyment are made deliberately by humans butalso how many others are accidental byshyproducts of human activity Often it takessome time for the environments responsesto such impacts to become apparentOften too their exact causes are hard toidentify In many cases human impactsarc increasingly becoming interlinked andaccompanied by natural fluctuations toproduce massive and often unpredictablechanges in the environment We have idenshytified a whole spectrUm of different types

A Sustainable Future 239

of environmental response to stress Theserange from short-term fluctuations whichcan be easily reversed to long-term poshytentially irreversible changes which poseintractable problems for environmentalmanagement Our case studies have alsoillustrated the wide variety of types of atmiddottempted solutions to environmental probshylems These range from technologicalquick-fix solutions such as engineeringstructures to control coastal erosion tosofter and more ecologically friendlyinterventions such as replanting riparianbuffer zones to lessen the amount ofnitrate pollution that enters rivers fromagricultural slopes Increasingly any suchschemes need to be integrated That isenvironmental problems should nO[ beconsidered in isolation but should beviewed as linked parts of the same seriesof problems Inevitably any such schemeswill work only if the additional complexshyities of human society economy cultureand politics arc also taken into account

3 TOWARDS A SUSTAINABLE

FUTURE

It is likely that in coming decades many ofthe transformations we have described anddiscussed will become even more imporshytant and the need for effective environshymental management even more pressingHuman population levels arc increasingnew technologies are emerging and evershyincreasing quantities of energy and reshysources are being produced and consumedespecially in countries that aspire to thelevels of development achieved by someof the worlds richest nations There mustbe severe doubts as to whether these trendsarc sustainable Will the world be transshyformed by global warming Will we cutdown all our rain forests1 Will a large proshyportion of the worlds flora and faunabecome extinct Will many of the worldsdryIands tum into dust bowls Will urban

240 Conclusion

Table VII1 Some potential adverse Impacts of global warming on resources

Resource Possible effects

Agriculture Lower crop yieldsSpread of pestsSoil erosion

Forests

Conservation areas and naturereserves

Coastal areas

Fisheries

Water resources

Human health

Energy demand and production

Change in rate of growthChange in species compositionShifts in geographical distribution

Disruption or loss of habitatInvasion of new species

Inundation of land and accelerated erosion byrising sea levels

Changes in composition of stocks and theirlocation

Droughts floods changes in amount of supply

Heat stressShifts in prevalence of infectious diseases

Increases in need for summer aiHonditionlng

atmospheres continue to become morepoUuted and more health-threatening Willour water supplies dwindle in quantity anddeteriorate in quality~ These are some ofthe many questions that we can ask aboutthe future They form the basis of muchof the environmental concern that is deshyveloping throughout the world

Arc such massive and unwelcometransformations of the face of the Earthinevitabld Is human life sustainable Canhuman energies be harnessed over thecoming decades to improve rather than to

degrade the environment We arc notwithout hope We have indicated in manyof our cast studies that there are waysmeans and opportunities to overcomesome of the undesirable processes that wehave identified Each and everyone of usin our daily life has the power to makesure that the generations to come have asustaUnable future

There is now very great interest in howwe might adapt to global warming shouldit occur Such adaptations would be necshyessary if we could not limit emissions ofgreenhouse gases sufficiently to rule outthe possibility ofsignificant warming Theywould also be necessary because of thevery great range of environments activshyities and resources that might be modifiedas a result of global warming (table VIIl)It is onen said that there are two types ofadaptation that may be necessary The firstof these is reactive adaptation wherebywe respond to climatic change aner itoccurs The second is anticipatory adapshytation in which we take steps in advanceofclimatic change to minimize any potenshytially negative effects or to increase ourability to adapt to changes rapidly andinexpensively

Reactive adaptation may well be feasibleand effective In many parts of the world

A Sustainable Future 241

Table VII2 Examples of no-regrets policies In response to possible global warming

Policy area and measures

Coastal zone management

Wetland preservation andmigrations

Integrated development ofcoastal datasets

Improved development ofcoastal models

land-use planning

Water resources

Conservation

Market allocation

Pollution control

Benefits

Maintains healthy wetlands which are morelikely to have higher value than artificiallycreated replacements Maintains existing coastalfisheries that are difficult to relocate

Integrated data allow formation ofcomprehensive planning and identification ofregions most likely to be affected by physicalor social changes Allows effects of changes tobe examined beyond the local or regional scale

Improved modelling allows more accurateevaluation of how coastal systems respond toclimate change and also to other shocks

Sensible land-use planning such as the use ofland setbacks to control shoreline developmentbetter preserves the landscape and alsominimizes the concerns of beach erosion fromany cause

Reducing demand can increase excess supplygiving more safety margin for future droughtsUsing efficient technologies such as dripirrigation reduces demand to some extentPreserving some flexibility of demand is usefulas less valuable uses allow reduced demandduring droughts

Market-based allocation allows water to bediverted to its most efficient uses in contrastwith non-market mechanisms that can result inwasteful uses Market allocations are able torespond more rapidly to changing supplyconditions and also tend to lower demandconserving water

Improving water quality by improving thequality of incoming emissions prOVides greaterwater quality safety margins dUring droughtsand makes water supply systems lessvulnerable to declines in quality because ofclimate change

Table continues overleaf

242 Conclusion

Table VII2 Continued

Policy area and measures

River basin planning

Drought contingency planning

Human health

Weatherhealth watch warningsystems

Improved public health andpest management procedures

Improved surveillance systems

Ecosystems

Protect biodiversity and nature

Benefits

Comprehensive planning across a river basincan allow for imposition of cost-effectivesolutions to water quality and water supplyproblems Planning can also help cope withpopulation growth and changes in supply anddemand from many causes induding climatechange

Plans for short-term measures to adapt todroughts These measures would help offsetdroughts of known or greater intensity andduration

Warning systems to notify people of heatstress conditions or other dangerous weathersituations will allow people to take necessaryprecautions This can reduce heat stress andother types of fatalities both now and if heatwaves become more severe

Many diseases which will spread if climatechanges are curable or controllable and effortsin these areas will raise the quality of humanlife both now and if climate change occurs

More and better data on the incidence andspread of diseases are necessary to betterdetermine the future patems of infection anddisease spread This information is helpfulunder any scenario

Biodiversity protection maintains ecologicaldiversity and richness preserves variety ingenotypes for medical and other research Amore diverse gene pool proVides morecandidates for successful adaption to climatechange One possibility is to preserveendangered species outside of their naturalhabitat such as in zoos

Table continues opposite

A Sustainable Future 243

Table VII2 Continued

Policy area and measures

Protect and enhance migrationcorridors

Watershed protection

Benefits

Such policies help maintain an ecosystem andanimal and tree species diversity Corridors andbuffer zones around current reserve areas thatinclude different altitudes and ecosystems aremore likely to withstand climate change byincreasing the likelihood of successful animaland tree migration

Forest cover provides watershed protectionincluding protection from bank erosionsiltation and soil losss All of these functionsare extremely valuable whether climatechanges occur or not

Agriculture

Irrigation effiCiency Many improvements are possible and efficientfrom a cost-benefit standpoint Improvementsallow greater flexibility to future change byreducing water consumption without reducingcrop yields

Development of new crop types Development of more and better heat- anddrought-resistant crops will help alleviatecurrent and future world food demand byenabling production in marginal areas toexpand Improvements will be critical as worldpopulation continues to increase with orwithout climate change

Source After Smith et al (1995) table 3

we may well be able to adapt to the mostlikely ways in which the climate maychange For example we could substituteheat- and drought-resistant crops for thosewhose yields are reduced Infrastructure isgenerally replaced on a much faster timeshyscale than climatic change so it could beadapted to changes in climate It can alsobe argued in favour of reactive adaptashytion that it does not involve prematurelyspending money in advance of uncertainchanges

On the other hand one can argue thatrapid climate change or significant in-

creases in the intensity and frequency ofextreme events such as floods storms ordroughts could make reactive adaptationsdifficult and could pose immediate probshylems for large numbers ofpeople Equallysome policies would have significant beneshyfits even under current environmentalconditions and would be valuable from acost-benefit perspective even if no climaticchange toolc place These types of anticishypatory policies are often called no regretspolicies because they will succeed whetheror not climatic change takes place meaningthat policy-makers should never have to

244 Conclusion

regret their adoption No regrets policiesmay none the less be expensive TableVII2 illustrates a selection of these policies

One can argue that the central challengefor policy-makers in coming decades willbe to find ways of allowing the globaleconomy to grow at a moderate rate whileat the same time maintaining or enhancingthe protection of wilderness the prevenshytion of pollution and the sustenance ofecological resources We cannot be sure

KEy TERMS AND CoNCEPTS

anticipatory adaptationno-regrets policiesreactive adaptation

POINTS FOR REVIEW

that we will find policies that enable thisto happen Governments and society willinevitably need to make difficult trade-ofTsbetween economic growth and environshymental protection We cannot envisage asituation where there is indefinite growthin the human population and indefinitegrowth in the consumption of resourcesWe need to ensure to use Sir CrispinTickells phrase (Tickdl 1993) that hushymans are nOt a suicidal success

Which environmental issues wiU become increasingly important in coming decades

Can human energies be harnessed over the coming decades to improve rather than todegrade the environment

How might we adapt to global warming should it occur

GLOSSARYIn each definition any words that themselves ap~ar in the glossary are printed in iudieltyplt

adiabatic compression The process bywhich as a parcel of air falls the internalenergy is increased and its temperature israisedacid rain Rain which because of the preshysence ofdissolved substances derived fromair pollution has a pH of less than 565aerosol (atmospheric) An aggregation ofminute particles (solid or liquid) suspendedin the atmosphere The term is often usedto describe smoke condensation nucleifreezing nuclei or fog or pollutants suchas droplets containing sulphur dioxide ornitrogen dioxideaggradation The building upwards oroutwards of the land surface by the deposhysition of sedimentalbedo A measure for the reflectivity ofabody or surface defined as the total radiashytion reflected by the body divided by thetotal radiation falling on it Values are exshypressed on a scale ofeither 0-1 or 1-100alluvial floodplain A flat-lying area comshyposed ofsedim~nts (sands silts clays gravshyels etc) deposited by riversamphibian A creature that can live onland or in wat~r

anthropogenic Caused by human activshyitiesanthropogeomorphology The study ofthe human impact on landforms and landshyforming processesaquaculture The cultivation or rearingof plants or animals that grow or live in ornear wateraquifer An underground water-bearinglayer of porous rock through which watercan Row

arid Dry with limited vegetation rainshyfall less than about 250 mm and a greatexcess of evaporation over precipitationarterial drainage A system of majordrainage channels into which numeroussmall channels feedatoll An irregular annular (ring-shaped)coral algal reef enclosing or almost enclosmiddoting a central lagoon The reefS are oftenbreached by channelsbackscatter To send back rather thanlet through incoming radiation from thesunbadlands Areas that have been erodedby deep systems of ravines or gulliesbarrier island An elongated mainlysandy ridge feature running parallel to thecoast and separated from it by a lagoonbase levd The lower limit down to whicherosion on land may operate usually deshyfined with reference to the role of runshyning water For example sea level acts asa general base level though there can bea wide range of local base levels above andbelow sea levelbasin The area that drains into a partishycular river It has the same general meaningas catchment (British usage) or watershed(American usage)biodegradable A term used to describea substance that can be rendered harmlessor be broken down by natural processesbiodiversity A term used to describe thevariety of species both floral and faunalcontained within an ecosyrtembiofabrica Fabrics made of organicmaterialbiological magnification The increased

246 Glossary

concentration of toxic material at consecushytive higher trophic levels in an ecosystemToxins such as heavy metals and persistentpesticides become incorporated into livshying tissue from the environmentbiomass The total mass of biologicalmaterial contained in a given area of theEarths surface (expressed as dry weightper unit area)biorne A major ecological community orcomplex ofcommunities that extends overa large geographical area and is charactershyized by a dominant type ofvegetation (egtundra desert rain forest)bioremediation The use of microshyorganisms to restore the qualities of enshyvironments contaminated by hazardoussubstancesbiosphere The interlinked communitiesofanimals plants and micro-organisms thatlive on the land and sea of the Earthbiota The animal and plant life of aregionbiotechnology The manipulation ofliving organisms and their components(eg genes or gene components) for speshycific tasksbloom A scum produced by algae on thesurface of standing waterblowout An area of dune that has beenbreached by wind excavationboreal Of northern regions A termapplied both to a climatic zone charactershyized by cold snowy winters and shortsummers and to the coniferous forests ofthe high mid-latitudes in the NorthernHemisphere also known as taigabrecciate Break lip into angular fragmentscarbon budget The balance between theamount of carbon which accumulates in asystem and the amount that is releasedcarcinogen Any substance that producescancercarrying capacity The maximum popushylation of a given organism which a parshyticular environment can sustain without atendency to decrease or increase

catalyst A substance that without itselfundergoing any permanent change setsoff a change or increases the rate at whicha change occurscatchment The area that drains into ariver It is bounded by a drainage divideor watershed (British usage)centre-pivot irrigation The artificialdistribution of water to land for agriculshytural use in which Broundwater is pumpedand from a central point is dispersed in acirclechannelization The modification of riverchannds for the purpose of flood controlland drainage navigation and the reducshytion or prevention of erosionchaparral A type of stunted (scrub)woodland found in temperate regions withdry summers It is dominared by droughtshyresistant evergreen shrubschlorofluorocarbons A range of synshyrhetically manufactured chemically inertcompounds containing atoms of carbonfluorine and chlorine They have beendeveloped and widely used as solventsrefrigerants and aerosol propellanrs and inrhe manufacture of foam plasticscolloidal Composed of ultramicroscopicpaniclesconvection The transfer of heat in theatmosphere by the upward flow of hot airor the downward flow of cold airdeflation The removal of dry unconshysolidated material eg dust or sand froma surface by winddeflocculate To disperse or break up anaggregate so that particles become susshypended in a solution This may be achievedby the presence of sodium cationsdefolianr An agent tha[ removes foliage(eg leaves) from a plantdeforestation The permanent removal ofuees from an area of forest or woodlanddesertification The spread of desenmiddotlikeconditions in arid or semi-arid areas dueto human interference or climatic changeor both

desiccation Drying up of the environshymentdiatom A microscopic single-celled algawith a siliceous cell walLdieback A diseased condition of plantsoften applied to the dying-offoflarge tracts

of similar species at the same timedimethylsulphide A volatile sulphurcompound in seawater produced by bacshyterial decay and planktonic algae It oxishydizes in the atmosphere to form a sulphateaerosoldischarge (rivers) The amount of waterthat flows in a riverDNA (deoxyribonucleic acid) The subshystance that is the carrier of genetic inforshymation found in the chromosomes of thenucleus of a celldomestication The taming and brecdshying of prcviously wild animals and plantsfor human usedrainage basin That part of the landsurface which is drained by a particularriver system and is defined by a divide orwatershed (British usage)drawdown The reduction in groundshywater level by pumping out water fasterthan it can be replenisheddwt storm A storm in a semi-arid areawhich carries dense clouds of dust someshytimes to a great height often obscuringvisibility to below 1000 metresecology The science which studies therelations between living organisms andtheir environmenteagtsystem A biological community ofany scale in which organisms interact withtheir physical environmentecotone A transition zone marking anoverlap rather than a distinct boundarybetween two plant communities It maybe a zone of tensionedaphic A term used to describe soilconditions which influence the growthof plants and other organisms Edaphicpoundactors include physical chemical andbiological properties of soils such as

Glossary 247

pH particle-size distribution and organiccontentEI Niiio events A term applied to theextensive intense and prolonged wanningof the eastern tropical Pacific Ocean whichoccurs every few years It is associated withmajor anomalies in the patterns of atmosshypheric circulation and rainfallendemic Normally found only among aparticular people or in a certain regionewtasy A worldwide change in sea levelindicating an acmal rise or fall of the seaeutrophication The process by which anaquatic eeosystem increases in productivityas a result of increased nutrient inputOften this is due to humanmiddotinduced addishytions of elements such as nitrogen andphosphorus However the process mayalso be a natural phenomenonevapotranspiration The combined lossof water by evaporation from the soil surmiddotface and transpiration from plantsex situ methods A term used to describemeans of conserving species outside theirnatural habitat (eg in zoos or botanicgardens)feral Term describing an animal or plantonce domtJticated that has gone wildfilling The deposition ofdredged matershyial to make new landfluvial Relating to a river or riversfood chain The transfer of energy fromgrecn plants through a sequence oforganshyisms in which each eats the one below itin the chain and is eaten by the one aboveforest decline The decline of forestvitality characterized by decreased andabnormal growth leading eventually todeath The causes are poor managementpractices climatic change fungal viral andpest attack nutrient deficiency and atmosshypheric pollutionfriable Easily crumbled (ofsoil rock orother material)gabion A wire-framed container full ofboulders or cobbles used to make wallsto stop erosion

248 Glossary

general circulation mood (GeM) Adynamic computer model which simulateslarge-scale features of atmospheric andoceanic circulationgenetic ~lating to genes which arcunits of heredity composed or DNA orRNA and fanning part of a chromosomethat determines thc particular characterisshytics of an individualgeomorphology Thc science of the orishygin and developmcnt of landformsglaciated Term used to dcscribe an areathat has becn at some point covcred ormoulded by glaciers or icc sheetsglobal warming Thc process by whichthe Earth may becomc warmcr because ofthe role of mcchanisms such as the greenshyhouse ejJeClgneiss A c03nC-grained metamorphicrock composed of feldspars quartz andferromagnesian mineralsgreenhouse effect A climatic cffcctcaused by permitting incoming solar 4shyriiation but inhibiting outgoing radiationIncoming short-wave radiation is absorbedby matcrials which thcn re-radiatc longerwavelengths Certain substances in theatmosphere eg carbon dioxide absorblong-wave radiation resulting in a warmshying effectgross primary production The totalamount of organic material synthesized ina given time period by living organismsfrom inorganic materialgroundwater Water occurring below thesoil surface that is held in the soil itself orin a deeper aquifergypsum A rock fonned ofnatural calciumsulphate caused by its crystallization as saltywater is concentrated by evaporationhabitat The place in which an organismlives characterized by its physical featuresor the dominant plant typesbalons Members of the halogenatedfluorocarbon (HF) group of ethane- ormethane-based compounds in which H+ions arc partially or completely replaced

by chloride fluoride andor bromideThey arc long-lived and nave been implishycated in ozone depletionha1ophytic Tolerant of high concentrashytions of saltsheathland An area of evergreen JwJeroshypbyOUJ shrubland where beath families(eg Ericaceae) are present though nOtnecessarily dominant Heathlands developon areas where soil is low in nutrient statusheavy metal Any metal or alloy of highspecific gravity especially one that has adensity higher than 5 g per cu cm eglead zinc copper mercuryherbicide Any agent organic or inorganicwed to destroy unwanted vegetationHolocene The most recent epoch of theQuaternary following the PleistoceneOften called the post-glacial it has exmiddottended from about 10000 years ago tothe present day It has been marked byvariow climatic 8uctuarionshumus The organic constituent ofa soilusually formed by the decomp05irion ofplants and leaveshydro-isostasy The reaction ofthe Eanh 5

crust to the application and removal of amass of water For example efMtlltic seashylevel changes have affected the depth ofwater over the continental shelvcs causingthe crust to be depressed at times of highsea level and elevated at times of low sealevelhydrocarbons Compounds of hydrogenand carbon some with minor or tracequantities ofoxygen suJphur nitrogcn andothcr elementshydrocompaetion The process by whichsediments arc compressed by an overlyingbody of waterhydrology The science concerned withthe study of the different fonns of wateras they exist in the natural environmentIts cenual focus is the circulation and disshytribution of wattChydrostatic uplift Uplift of land surfrcecaused by upward water pressure

hypoxia The condition experienced whenoxygen levels are low in blood and tissuesinbreeding Breeding from closely relatedanimals or personsinfiltration The movement ofwater intothe soil from the ground surfaceinterglacial A time period between twoglacial stages during which temperaturesare relatively highinterpluvial A time period between twopiuPiRI stages during which conditions arerelatively dryisopleth line on map connecting placeswhere a particular meteorological factoreg thunderstorms occurs with the samefrequencyisostasy A process that causes the Earthscrust to rise or sink according to whethera weight is removed or added to it Sucha weight could be for example an icecapkarst A limestone region with undershyground drainage and many cavities andpassages caused by the solution of the rocklandfill The disposal of waste by tippingit on land often in old mine workings orlow-lying landlaterite The residual deposits formed bythe chemical weathering of rock composedprimarily of hydrated iron and aluminiumoxides Extensively devcloped in the hushymid or subtropical regionsleachate The solution or soluble matershyial that results from a leRching processleaching The removal of dissolved mashyterial by the percolation of water througha soil or sedimentLessepsian migration An almost unishydirectional migration of biotR from one seaor lake to another Named after the manwho built the Suez Canal which allowedorganisms to pass from the Red Sea to theMediterraneanlevee A natural or man-made embankshyment along a riverlichenometry A method of time estimashytion (dating) on rock surfaces based on

Glossary 249

the rate of growth of lichens (eg Rhizoc4rpon geogrRphicum)lithosphere The solid earthloess A deposit of primarily silt-sizedmaterial that was originally dust transshyported by the windmacrobenthic Relating to large organshyisms that live on or near the bottom of abody of watermacropore A particularly large pore orvoid in the soilmammal A warm-blooded creature witha backbone which if female can nourishits youngmangrove Plant communities dominatedby mangrove trees RhizopherJl BruguieriRand ApicenniR which colonize tidalmudflats estuaries and other shelteredareas in tropical and subtropical areasmlllJuis Scrub vegetation of evergreenshrubs characteristic of the western Medishyterranean broadly equivalent to chJlparrRImarginal land Land that is difficult to

cultivate or unprofitablemariculture Farming of the seamarsupial A mammRI characterized bybeing born incompletely developed and sousually carried and suckled in a pouch onthe mothers belly for a timemeander The winding pattern of a sinushyous river channelMediterranean climate A climatic typecharacteristic of the western margins ofcontinents in the worlds warm temperatezones between latitudes 30 and 40 (egcentral Chile central California)megafauna The largest types of animalsin a communityMesolithic A cultural period foUowingthe Palaeolithic from 10000 BC to 4000BC characterized by the use of microlithicimplementsmetamorphie Term used to describerocks which have been altered by externalsowces of heat pressure or chemical subshystances rather than merely by burial underother rock

250 Glossary

metapedogenesis Human modificationof soilsmicroclimate The physical state of theatmosphere close to a very small area ofthe Earths surface often in relation toliving matter such as crops or insectsmonsoon A wind with seasonal reversalsof directionmorphology The form or shape of anobject or organismnanoplankton The smallest of the phytoshyplanktonnecrosis The localized death ofceUs tissueor an organ resulting from disease or injuryNeolithic A cultural period following theMesolithic from the fourth millennium Beuntil the onset of the Bronze Age It marksthe beginning of the domestication of anishymals and the cultivation of cropsnet biological primary production Seenet primary productionnet primary production The amount oforganic material produced by living organshyisms from inorganic sources in excess ofthat used in respirationnutrient sink A location in which nutrishyents accumulatenutrient source A location from whichnutrients are rcleasedoceanic conditions Climatic conditionsthat arc modified by the presence of ancarby sea or ocean in contrast to continshyental conditionsomnivore An animal which ears bothplant and animal matterorganochlorides Organic compoundswhich contain chlorine Often used asactive ingredients for pesticides they arevery persistent due to their chemical stabshyility and low solubility An example is theinsecticide DDTorographic A tenn used to describe climshyatic conditions or phenomena caused bythe presence ofhigh relief(eg mountains)osmosis The passage ofa solvent througha semi-permeable partition or membraneinto a more concentrated solution

oxidation A chemical reaction in whicha substance decreases its number of elecshytrons The most frequent oxidant is moshylecular oxygenpalaeolimnology The study of the envirshyonmemal history of a lake most imporshytantly from evidence preserved in itsbottom sedimentspastoralism A form of land use relatingto flocks and herds of animalspathogen An organism which causesdiseaseper capita For each personperennial Lasting through a year orseveral years Used to describe plants thatare not merely annuals and streams thatnormally flow through all seasons of theyearpermafrost The thermal conditions insoil and rock where temperatures ate bemiddotlow OC ror at least two consecutive yearspH The measure of the acidity or alkashylinity of a substance based on the numberof hydrogen ions present in a litre of thesubstance and expressed in terms of pH _logIO(lH) where H is the hydrogen ionconcentration The centre point on thescale is 7 representing neutrality Acidsubstances have a pH of less than 7 andalkaline substances have a pH of morethan 7photochemical reaction A chemical reshyaction which is speeded up by particularwavelengths ofelectromagnetic radiationphytoplankton Microscopic organismsespecially algae that live near the surfaceof the sea and form the basis of food formany other forms of aquatic lifepiezometric swface A subterranean surshyface marking the level to which water willrise within an lIiJuiftrPleistocene The first epoch of the Quashyternary including glacial and interglllcillstages between about 2 million and10000 years agopluvial A climatic phase with plentifulmoisture

podzol A soil characterized by the acidshyification of the A horizon the downwardle4ching ofcations metals and humic subshystances and their deposition in the B horishyzon often precipitating to form a panThe process is most prominent in cool andwet climatespollen analysis The analysis of plantpollen under the microscope to reconshysttuct the vegetation conditions underwhich the sediment in which it occurs wasdepositedprecipitate In chemistry the depositionin solid form from a solutionprecipitation Moisture that falls on theground including rain snow dew and fogpredator An animal which kills othersfor food by preying on them A secondaryconsumer in a food ch4inprofile An outline seen from one side(eg the cross profile of a river channel) ora vertical cross-section (eg of a soil andits various layers)radiation solar Electromagnetic wavesemitted by the sunradiation budget A term used in meshyteorology to describe the difference beshytween incoming and outgoing radi4honradiocarbon dating A method ofdetershymining the age ofan organic material (egwood charcoal peat) by measuring theproportion of the He isotope containedwithin its carbon contentrangeland Alarge area ofopen land usedfor grazing or huntingreclamation Bringing land into a newform This can involve either returningsomething to its original state (eg somedegraded land) or transforming it into anew state (eg by filling in a lake to makeland)redox potential A measurement of thewillingness of an electron carrier to act asa reducing or oxidizing agentrendzina A type of soil with dark surshyface layers or horizons that developes onsoft limestones

Glossary 251

rill A small channel in a soil or rocksurface often only a few centimetres longriparian Of or on a river bankrip~rap Large fragments of broken rockdumped along a shoreline to protect itagainst wave actionrunoff The water leaving a drainage areaIt is normally regarded as the rainfall mishynus the loss by evaporationsalinization The process whereby saltseg sulphates nitrates and chlorides beshycome concentrated in the soiLsanitization The process by which someshything is made more sanitary hygienic ordisinfected so that health conditions areimprovedsaturation excess overland flow Surfacerunoffthat is g~nerated wh~n rain falls onground that is already saturated withwatersavanna A grassland of the tropics andsubtropicsscarification The process by which seedsare cleaned by abrasion of the epidermisCan also refer to changes caused to sc~ds

by passing through th~ gut of an animalor by fireschist A met4morphic rock composed oflayers of different materials split into thinirregular platessderophyUous A term referring to speshycies ofevergreen trees and shrubs that haveadapted to lengthy seasonal droughtscrub A type of vegetation consistingmainly of brushwood or stunted forestgrowthsecondary forest Woodland which hasregenerated and colonized an area afterthe original forest has been removedsediment yield sediment load Sedimentyield is the mean sediment load carried bya stream giving some measure of the rateof erosion in a dr4in1JBt b4Sin The sedishyment yield is express~d as weight per unitareaseedbed An area of soil in which seedsare plant~d and take root

252 Glossary

seep An area moistened by the ~epage

of water from or into the ground$CIIlimiddotarid Dry with a shortage of moisshyture for much of the year but not so dryas an lind areashear strength The maximum resistanceof a material to the application of stressMajor sources of such resistance arc coheshysion and frictionsheet flow The flow ofwater in thin filmsover a low-angle surfaceshifting cultivation Cultivation of asmall area of land in which forest is clearedand the biomass removed or burned folmiddotlowed by the use of the site for the proshyduction of mixed agricultural crops forseveral years Eventually the area is abanshydoned as soil ~rtiliry decreases and thecultivators move on to a [(w area SJ4shshyut-bNrn is a type of shifting cultivationsink-hole A hole or depression in thelandscape into which water drains causedby concentration of solution of the bedshyrock usually limestone or chalkslash-and-burn A system of land useespecially prevalent in the tropics in whichland is cleared of forest by cutting andburning so that cultivation can take placeAJ fertility rapidly declines in the cultiv4

ated areas the farmer moves on to a newarea after a few yearssmectite A type of day often made upof montmorillonite that may have theproperty of swelling in watersmog A fog in which smoke or otherforms of atmospheric pollutants play animportant role in causing the fog to formand thicken It often has unpleasant ordangerous physiological effectssplash erosion Erosion produced by theimpact of raindrops splashing on theground surface particularly if it is notprotected by vegetationspontaneous combwtion Fire cawed bythe natural build-up ofheat within inflamshymable materialspp Abbreviation for specics (pluraJ)

steppe A generally dry grassy plainlandstratosphere The region of the aCDlOSshy

phert lying betwccn the tropopllllSe andabout 20 kIn in which there is lime changein temlXrature with heightsubstrates Material underlying thesurfacesuccession The sequence of changcs ina plant community as it devdops over timesupernatant Term describing liquidfloating on a surfacesustainable devdopment Dcvdopmentthat meets the needs of the prescnt withmiddotout compromising the ability of futuregenerations to meet their own needssymbiosis An interaction between twO

different organisms living in close contactand usually to the advantage of bothtalus A sloping mass of fragments simmiddotilar to scree at the foot of a clifftectonic A term describing the broadstructUreS of the Earths lithosphere andmovcments within the Earths crusttcrnperate A term used to describe aregion or climate characterized by mildtemlXraturestemperature inversion Normally airtemperature decreases as height increasesHowever under certain weather conditionsair temlXrature may increase with heightso that a layer of warmer air overlies acolder layer This is temperature inversionterracing The construction of banks orsteps on a hillside to give areas of lowgradient either to enable cultivation or toconserve soilthalweg Line where opposite slopes meetat the bottom of a valley river or lakethermokacst Topographical depressionsresulting from the thawing of ground icethreshold A condition which marks thetransition from one state of operation of asystem to another Rapid and irreversiblechange may occurtrace dementi Elements thl[ are requiredby living organisms to ensure normalgrowth development and maintenance

They occur at lower concentrations thanmajor elements and include iron mangashynese zinc copper iodine etctrau gases Gases which occur in verysmall amounts in the atmospheretrophic levels The positions that organshyisms occupy in a food chaintropopause The interface between thetroposphere and the stratospheretroposphere The lowest level of theatmosphere in which most of ourweather occurs It lies beneath the stratoshysphere and its thickness ranges from about7 km at the poles to about 28 km at theequatortundra The zone between the latitudishynal limits of tree growth and polar icecharacterized by severe winters and a shortgrowing seasonturbidity A measure of the lack of clearshyness in a liquid caused by the presence ofsuspended materialunderstory A layer ofvegetation beneaththe main tree canopyUV radiation Radiation from the sunwith shorter wavelengths than visiblelight It is classified into three rangesaccording to its effect on human skinUV-A is not normally harmful UV-Bproduces reddening and tanning uv-e(with the shortest wavelengths) is the mostdamagingvector-borne A term used to describe adisease that is passed on by an organism

Glossary 253

often an insect (eg as malaria is transmitshyted by the mosquito)volatilization Evaporation or the proshycess of turning from solid or liquid forminto a vapourwater table The level below which theground is saturated with waterwatershed (American usage) The areaoccupied by a drainage basin or streamcatchmentwatershed (British usage) A line ofseparation between waters flowing intodifferent rivers basins or seasweather front A sloping boundary surshyface separating two air masses that exhibitdifferent meteorological propertieswetlands The collective term for ecosysshytems whose formation has been dominatedby water and whose processes and characshyteristics are largely controlled by waterwilderness An area leA untouched andthus in a natural state with little or nohuman control or interferencewind reactivation The renewed moveshyment of sand and other material by thewind especially when vegetation cover isreducedwind throw The blowing over of treesby the windxerophilous A term describing plantswhich live in dry habitats and can endureprolonged drought Many such plantseg cactus have developed physiologicaladaptations to cope with these conditions

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Wigley T M 1 and Raper S C B1993 Future changes in global meantemperatures and sea level In R AWarrick E M Barrow and T M LWigley (cds) Climate lInd Sell LevelChange 111-33 Cambridge Camshybridge University Press

WiJcove D S McLellan C H andDobson A P 1986 Habitat fragshymentation in the temperate wne InM E Soule (ed) Conservation BiologyThe Science of Scarcity and Diversity251-6 Sunderland Mass SinauerAssociates

Williams M 1989 Americans and theirForests Cambridge Cambridge Univershysity Press

References 263

Wlliiams M 1994 Forests and tree coverIn W B Meyer and B 1 Turner (cds)Changes in LAnd Use and umd CoverA Global Perspective 97-124 Camshybridge Cambridge University Press

Williams M (ed) 1990 Wetlands AThreatened Landscape Oxford Blackshywell

Wilson E 0 1992 The Dipersity ofLifeLondon Penguin

Winkler E M 1975 Stone PropertiesDurability in Man)s EnvironmentVienna Springer-Verlag

Woodcock N 1994 Geology and Envirshyonment in Britain and Ireland LondonUniversity College London Press

World Resources Institute 1994 WorldResources 19945 New York OxfordUniversity Press

Worthington E B (cd) 1977 Arid umdIrrigation in Developing CountriesEnvironmentll1 Problems and EffectsOxford Pergamon

Vim W W-S 1993 Future sea level risein Hong Kong and possible environshymental effects In R A Warrick E MBarrow and T M L Wigley (eds) Clishymate and Sea Level Change 349-76Cambridge Cambridge University Press

INDEXNote Alphabetical arrangement ofheadings and subheadings is word by word ignoringand by in through etc Page numbers in italics refer to illustrations Rememberto consult the Glossary (pp 245-53) for definitions

Aberfan disaster 185 186accelerated landslides 185-8accelerated sedimentation 182accelerated soil erosion 165-74

180-2 201acid rain 116-20

and forest decline 45reduction in 118 120

Adriatic Sea eutrophication of 221aerosols atmospheric 83-9afforestation

hydrological effects 126 136-7144

ste also deforestationAfrica

fire use 20-1savanna ecosystem 4041see aso individual countries

Africanized honey bee 66 67Afromontane grassland 39-40agricultural empires 6agricultural revolutions 4-5agriculture

arid areas 27-8biotechnology in 76 77and dust storms 84 87 172energy use 10and global warming 97habitat destruction 69hydrological impact 126land drainage for 142-5machinery 46 168-9 170-1no regrets policies 243pollution from 145 151-2seasonally flooded wetlands 57soil conservation measures 169 174and soil erosion 166-7 168-9

172-4

technological developments 5 67-8 10

and tree damage 46air conditioning 100air pollution

and forest decline 44-6 47health effects 85 102 106 108-9increasing scale 83legislation controlling 44 85 104and stone decay 197-200urban areas 49 50 52 8599

102-9 197-200vehicle emissions 114115199Jee also acid rain

albedoland use changes affecting 90 92sulphate aerosol effects on 85urban areas 98

algal blooms 150 155 218alpine grasslands 43Amazon basin deforestation in 90

91America

Africanized honey bee spread 6667

Jtt aho USAanimals

channelization effects on 131domestication 4feral 66introduced species 66-7space requirements 70-1urban 48-9

Antarctic ozone hole 110 111 114anthropogeomorphology 165 167anticipatory adaptation 240 243-4apartheid 13 108-9aquaculture 232-4

aquif~rs

d~pletion and rccharg~ 159-61s~awat~r incursion 184

Aral Sea d~siccation of 155-8 184Arctic ozon~ depl~tion abov~ 114arid ar~as

agricultur~ 27-8 159d~forestation 28groundwat~r depletion 159urban groundwater recharge 142urban ston~ d~cay 197see IIlso d~sertification

arterial drainage systems 142asbestos 109ash trees di~back of 46Aswan Dam 125 128 129Atlantic industrial ~ra 6atmospheric carbon dioxide 22-3

9396atmospheric circulation

and global warming 94see tllso climate climate change

atolls 226Australia

alien plant species 68graring and grasslands 43groundwater abstraction 159introduced parasites 66savanna 41soil salinization 183 184

autumn-sown cereals 169 170

backscatter 84badlands 168Bahrain beach pollution in 219Baltic Sea dune managemem on 224Bangladesh coastal floods in 215barchans 176 177barrier islands 210 213beaches

nourishment 212 213pollution 219

biodiversity 58 -63preservation 60-3 78 242rain forests 35 36urban ar~as 48-9wetlands 55 232

Ind~x 265

bioeconomic analysis 60biological magnification 147218biomass burning 20-1 22-3

see also firebiotechnology 8 76-7bird habitat losses 69-70Biwa Lake eutrophication of 152153Black Sea eutrophication of 150Blackwater estuary sea-level rise in

208-9blowouts 222Blue Plan 221bogs 54Brazos River Texas channel changes

in 182Britain

acid rain 117air pollution 104 105dean air legislation 85 104coastal erosion 209 210 lll 212coastal flooding 215 216-17dunes and dune management 222

225field drainage 142fog 85 86 105forest decline 45-6global warming and agriculture 97groundwater recharge 160habitat loss and fragmentation

69-70heathland decline 42sea-level rise 208-9soil erosion 168-9 170-1 173waste and waste disposal 192wetland drainage 143wind erosion 173

buildingsrestoration 199 200weathering 118 197-200

butterfly habitat loss 69

Californiacliff erosion 210dust storms 172inter-basin water transfers 156subsidence 189see IIUO Los Angeles

266 Index

Cameroon rain forest management in36-7

canals animal migration along 67Canary Islands artificial channel in

179Cape Town air pollution in 109capitalism 13-14carbon dioxide atmospheric 22-3

9396see also greenhouse effect

carrying capacity 4centre-pivot irrigation 160CFCs 93 96 110 113channel straightening 178-80channelization 131chaparraJ 21Chicago

groundwater abstraction 159vegetation changes 51-2

Chinadesertification 30-1nature conservation 61 62-3

citiesair pollution 49 50 52 85 99

102-9 114 115 197-200ancient 5animals 48-9climate 98-101derelict land 49ecological footprint 48environmental improvement 50flood runoff 140 141groundwater depletion 159groundwater recharge 141-2

160-1less developed countries 7stone decay 118 197-200veget1ltion 48vehicle emissions 114115199wastes 192water pollution 49 148-9

clay soils drainage of 144clean air legislation 4485 104clear-felling

and debris ava1anches 188and runoff 136-8

clear-water erosion 128

cliff erosion 210climate

increasing human impact on 83urban 98-101

climate changeadaptation to 240-4aerosol effects 83-9deforestation causing 35 90 91

92and desertification 28-9inter-basin water transfers causing

155land use changes causing 90-2and megafauna extinctions 75-6and savanna development 40and sea-level rise 206-7see also global warming

cloud-condensation nuclei 84-5Clyde River pollution of 148-9coal waste tips 185 186coastal areas

aquaculture 232-4dune management 222-5erosion 208-9 210-14 223-4

225flooding 215-17managed retreat 209212management 235 241marshes 208-9pollution 218-21227red tides 150sea-level rise 206-9seawater incursion 184urban stone decay 197vulnerability 205 206 235

Colorado River regulation of133-5

communism 106see also Eastern Europe

conifer plantations 69conservation 14 58 60-1 62-3

242see also nature reserves

constructioncoral reefs damaged by 230soil erosion caused by 167

contributing factors 15

controlled burning 21coral

bleaching 227eutrophication effects 151

co~ reeamp 226-31crops drought resistant 243cumulative global change 10-11Czechoslovakia urban air pollution in

106

dams 125-31 133-5channel morphology effects 180ecological explosions caused by

65-6landslip caused by 185 186-7salinization caused by 183-4wetlands affected by 57

debris avalanches 188debt-for-nature swaps 34deflation see wind erosiondefoliants 13deforestation 32-7

arid areas 28climatic effects 909192and coral reef degradation 227and debris avalanches 188hydrological effects 136-8and soil erosion 165-7and soil salinization 184see aso afforestation forests

derelict land urban 49 50desertification 26-31

and dust storms 84deserts dune reactivation in 174-7desiccation

inter-basin water transfers causing155-8

and soil salinization 184developing countries

air pollution 104-5aspirations 239urbanization 7

diatoms 117dieback temperate forest 44-7dikes 142 143dimethylsulphide 84-5dinosaur extinction 73

Index 267

dischargeand deforestation 136-8and flood control works 180and land drainage 144regulation by dams 125 133and urbanization 140 180

diseaseand megafauna extinctions 75-6

diseases plantaccidental introduction 65

domestication 4 19dongas 168drainage 142-5

and subsidence 190drainage basin

planning 242stresses and responses to 14-15

drawdown 159-60dredging 132drought

crops resistant to 243planning for 242and soil erosion 172

dry deposition 116dunes

coastal 222-5reactivation and stabilization 30

174-7dung beedes 66dust atmospheric 84dust storms 84 87 155 172-3

earthquakes 190Eastern Europe

air pollution 47 106-7forest decline 45

ecological explosions 65-6ecological footprint 48ecological succession see successioneconomic development stages of 6ecotones wedands as 55ecotourism 12edaphic conditions see soilsE1 Niilo events 227dephants

in savanna ecosystem 41embankments river 131

268 Index

energy renewable 77energy conservation 96energy consumption 8-10environment

naturaJ changes 14systems approach to 14-15

environmental impact of humanactivity

complexity 239increasing scale 8 10-11 12 19trends 8-11uncertainties 1495 120

erodibility 174erosion

coastal 208-9210-14223-4225

dunes 223-4 225land use changes affecting 126

127river regulation affecting 128see also soil erosion

erosivity 174Essex marshes sea-level rise and

208-9estuaries red tides affecting 150Ethiopia river sediment load in 130Europe

forest decline 44see also individual countries

eustatic change 206eutrophication 146 150-3 221evaporation

from forest 136and salinization 183-4

evapotranspiration irrigation and 91-2evolution 58extinctions

global 73and habitat area 60through habitat fragmentation 70

71increasing rate 58 78Late Pleistocene 73-6

falls 187fens 54

drainage 143

feral animals 66fertilizers eutrophication caused by

151field drainage 142 152fire 20-5 77

early usc 3 4in heather management 42oil-well 85 88-9in savanna formation 40soil erosion following 167suppression 21 24systemic and cumulative effects

10-11vegetation adapted to 22 33 40see also smoke

fibacid rain affecting 118 119pollution affecting 148 150 154

fisheries coastal wetland 232-4fishing 205-6 228fishponds 232-4flood control

and channel morphology 180channel straightening for 17880

flood peakltand deforestation 136-7and land drainage 144and river regulation 133

flood protection schemes coastal215217

floodand afforestation 144coastal 215-17and deforestation 138and land use changes 126 127and soil erosion 171urbanization effects 140see aho flood peaks

floodwaters channelization effects on131

flows 187flue gas desulphurization 120fog 85 86 105food chain biological magnification

through 147 218food production 12

see also agriculture aquaculture

forest decline 44-7forest fires 21 22 23 24-5forestry

and surface water acidity lISforests

clearance lee deforestationecological roles 32economic uses 32 37evaporation 136expansion 33fire suppression 21 24fragmentation 69hot spots S9management and protection 37runoff from 136-7soils 165-6Ile alIo trees

fossil fuel combustionand acid rain 117and air pollution 104-8atmospheric carbon dioxide from

93reduction 118IU Iso vehicle emissions

frOSts urban 100fuel domestic poUution from 108-9fuelwood 28 37fungi accidentaJly inrroduced 65Pynbes heathland 64

game management controlled burningfor 21

gardens 52general circulation models 90genetic engineering 76Georgia (USA) land usc and channel

morphology in 180-2Germany forest decline in 44 47Glasgow watu pollution in 14S-9global environmental change 10-11global warming 93-7

adaptation to 240-4and coral reef degradation 227impact on resources 240no regrets policies on 95 96

241-4and sea-level rise 207

Index 269

Gobi Descn 30grassland 39-41

grazing effects 43mid-Iatimde 22origins and maintenance 22 39-41runoff on 136

grazing 43Great Barrier Reef 226 227 229greenhouse effect 83 92-7

III alIo global warminggreenhouse gases 83 92-3

policies for reducing 95 96groundwater

dam construction affecting 186-7groundwater abstraction 159-60

and salinization 183 184and subsidence 189

groundwater recharge 141-2 160-1Gulf War

and coastal pollution 219oil-well fires 85 88-9

gypsum crusts 197 200

habitatschanges in ecological explosions

caused by 65-6edge effects 71heterogeneity loss 71hot spots 59loss and frtgmentation 69-72size 60

halons 110health

air pollutants affecting 85 88 102106 108-9

coastal pollution affecting 220-1ozone concentrations affecting 114policies on 242wastes hazardous to 192 195water pollution affecting 146 147

heat island urban 98-101heathlands 41-2 64

hot spots 59hedgerow removal 169High Plains (USA)

groundwater abstraction 160irrigation effectS on rainfill 91-2

270 Index

Holme Fen Post 143Hoover Dam 133hot spots biodiversity 58 59human environmental impact see

environmental impacthuman life origins of 3humidity atmospheric land use

changes affecting 91hunter-gatherers 4 6 12hunting megafauna ntinctions

through 73-5Hurghada coral reefs in 230-1hydro-isostasy 190hydrocompaction 190hydrological systems suesses affecting

14hydrology

forests 136-8land use changes affecting 126-7river regulation effects 125-35urban 48 140-2

inbreeding 70incineration 194 196inciting factors 15India

plantations 137river regulation 131

Indonesia aquaculture in 232-3Indus River 131industrialization 5-7 12

air pollution 84 105 117coastal pollution 221greenhouse gases 93wastes 145 192water pollution 148221

infiltration capacityforests 136 137urban areas 140

insects introduced 66 67inter-basin water transfers 131-2

155-8and soil salinization 184

Intergovernmental Panel on ClimateChange 93

international agreementson coastal pollution 219

international environmentalconventions 56

introduced species 64-8urban 49 50 51

invasions biological 64-8irrigation

channel morphology effects 180climatic effects 9091-2early developments 5 6 7efficiency 243groundwater abstraction for 159

160inter-basin water transfers for 155-8river regulation for 131salinization effects 28 183-4

islandsbiogeography 70introduced species 65

isostatic change 206 208Israel groundwater recharge in 161

Japan eutrophication in 152 153Java fishponds in 233

Kakadu National Park alien plants in68

karst 189Kenya sustainable environmental

management in 29keystone species 41Kuwait oil-well fires in 88-9

Lagos harbour coastal erosion in213-14

lakesacidification 118artificial ecological explosions in

65-6desiccation 155-8 184sediment cores 117

Lancashire dune management in 225land degradation

through deforestation 138see Iso desertification

land drainage 142-5and nitrate pollution 152and subsidence 190

land-use changeschannel morphology effects 180-2climatic effects 90-2hydrological effects 126-7lee also particular ehangu eg

dc=forestation urbanizationland-use planning 241landfill 192 194 196landforms human impact on 165 167landslides 185-8legislation

dean air 44 85 104watc=r pollution control 148 153

Lesbos coastal pollution in 2211c=ss devdopc=d countries lee developing

countriesLessepsian migration 67Lesset Snow Goose 70 72lignite 106-7limestone

overpumping and ground subsidence189

weathering in buildings 199limestone pavements 8London

building stone decay 199groundwater levds 159 160precipitation 99smog 85

Los Angelesair pollution 104 lOS 106inter-basin water transfers 156subsidence 189vehicle emissions 114 115

Machacos District Kenya sustainableenvironmental management in 29

Malidust storms 87wetland management 57

mammoth 74managed retreat 209212mangrove swamps

aquaculture threats to 232 233234

in coastal flood protection 215Vieblam War effects 13

Index 271

malJuis 22 33marginal land 13marine parks 229 230-1marine pollution 218-21Marsh George Perlcins 83 136

138-9marshes 54

coastal 208-9mass movements hazardous 185-8Mauritania dust storms in 172-3meanders 178Mediterranean area deforestation in

32-3Mediterranean Sea pollution of

220-1megafauna extinctions 73-6metals water pollution from 146metapedogenesis 165 166methane increase in 93Mexico City subsidence in 189migration corridors 243mining

charmel morphology effects 182early developments 5open-cast 10and subsidence 189

Montreal Protocol noMorocco dune stabilization in 175municipal waste 145

Namibia dune stabilization in 176-7nature conservation 62-3 242nature reserves 14 61-3

alien plant species in 68coastal dunes 225marine 229 230-1size 70-1tropical forests 37

Nepal deforesration in 33-4net primary production

human domination and destruction12 13

Niger delta 56coastal erosion 210 213-14wetland management 57

Nile River regulation of 125 128129

272 Index

nitrate pollution 146 151 152nitrogen

in eutrophication process 150 153nitrous oxide emissions 93 1I 7no regrets policies 95 96 241-4non-point pollution sources 145North America debris avalanches in

188North Platte River 180nuclear winter 85nutrient enrichment

algal blooms caused by 218let also eutrophication

nutrientseffects of fire on 22losses under shifting cultivation 22let also nitrogen phosphorus

oceansimportance 205-6limited human impact on 235

oil abstraction subsidence due to189

oil pollution 218 220oil-well fires 85 88-9Olduvai Gorge 3open-cast mining 10osmotic pressure 182overcultivation 27-8overgrazing 28 84Oxford building stone decay in 199ozone layer

role 110thinning 110-14

ozone tropospheric 105 114

Pacific global era 6Pacific Ocean coral reefs in 227 228paired watersheds 136palaeolimnology 117pandas 61 62parasites introduced 66Paris urban heat island in 100 101particulate concentrations urban

102-4 105 106lee also PM 1Os

pastoralists 28

pasNres loss of 69peadands 54

drainage 143 144permafrost subsidence of 189-90Persian Gulf stawater incursion in

184pesticides water pollution by 147pests urban 49pH 116-17Philippines aquaculture in 234phosphate pollution 146phosphorus

in eutrophication process 150153

photochemical reactions 114phytoplankton 150 151piezometric surface 159planktonic algae 84-5plantations 137plants

acid rain damage 118domestication 4introduced 51 52 64-5 68salinization effects on 182-3

Pleistocene overkill 73-5ploughing 168PMI0s 85 88 106point sources of pollution 145Poland

acid rain damage 45dune management and coastal

erosion 224pollutants classification of 145-7pollution

coastal and marine 218-21coral reefs 227and forest decline 45urban areas 49 50Set abo air pollution waste water

pollutionpollution abatement

biotechnology in 77coastal 219 221

population growth 3-4 5arid areas 27 29coastal 205projections 7 60 220

136-8140-2

and sustainable environmentalmanagement 29

see also urbanizationpore-water pressure 186poverty 60power stations

emissions 85 108 118 120thermal pollution 154

prairies urbanization of 51precipitation

global warming effects on 94relationship with vegetation 40see also acid rain rainfall

predisposing factors 15prehistoric extinctions 73-6prescribed burning 21

rain forestsbiodiversity 35 36removal 34-5 90 91 92

rainfallarid areas 27~8 29irrigation affecting 91-2land-usc changes affecting 90

91-2in savanna development 40urban areas 98-9 100 101see also acid rain

Ramsar Convention 55-6reactive adaptation 240 243recreation erosion caused by 223

225Red Sea coral reef degradation in

230-1red tides 150reefS coral 226-31rendzinas 170renewable energy 77reservoirs

channel morphology effects 180evaporation from 183-4size 128thermal poUution effects 154

resource recovery biotechnology in76

respirable suspended particulates(PMIOs) 8588 106

Index 273

rice cultivation 72rills 167-8rivers

accelerated sedimentation 182channel changes 178-82inter~basin water transfers 131-2

155-8 184pollution 145-9 150 151regulation 125-35sediment load 125 128-31 133

178 180set also discharge floods runoff

roads tree dieback alongside 46runoff

deforestation affectingurbanization affecting

Sagan River sediment in 130Sahel dust storms in 87salinization 28 182-5 201

inter-basin water transfers causing155

salt marsh erosion of 208-9sand control of 175-7sand dunes see dunessanitary landfill 192 194 196sanitization 22Saudi Arabia groundwater depletion in

159savanna 20-139-41Scarborough cliff erosion in 210sea-level rise 206-9 235

and coral reef growth 228sea urchins 231seasonal flooding 56 57seawater incursion 184secondary forest uopical 38-9sediment load effect of dams on

125 128-31 133sediment movement coasta 211-12

213sediment transport

straightened channels 178 180sedimentation accelerated 182

following dam construction 129-31seed germination effects of fire on

21-2

274 Index

seedbeds effects of fire on 21-2sewage pollution

coastal 220 227coral reefs 227

sewers 140 141shear strength 186sheet flow 167shifting cultivation 22 38-9ships ocean-going 5

accidental species introductions 66silt

dredging effects on 132effect of dams on 125 128-31

Sinai-Negev region albedo differencesin 90

Sindcanals 131salinization 183

sink-holes 189slash and burn cultivation 22 38-9slides 187slope instability 185-8smog 85smoke

effects 84from oil-well fires 88 89trends lOS

socialist economies 13soil conservation 169174

channel morphology effects 180-2soil erosion middot8

grasslands 43prevention 169 174by water 165-71 180-2201by wind 172-4201see also dust storms

soil formation 165 166soils

acidification 118and deforestation 138drainage 142-5 190and fire 22forests 165-6salinization 182-5 201and savanna development 40tundra subsidence of 190see also soil erosion

South Africamarginal land 13urban air pollution 108-9

South Downs soil erosion on170-1

South Platte River 180Soviet Union

dust storms 172urban air pollution 107

Soweto air pollution in 50 108-9Sphagnum moss 144splash erosion 167squatter settlements 50 108-9steam engine 7Stone Age megafauna extinctions

during 73-5storm surges 216-17stratospheric ozone depletion

110-14stresses drainage basin 15subsidence 143-4 189-90succession

coastal dunes 222in response to fire 24 25in secondary forest formation 38

Suez Canal animal migration along67

sulphate aerosols 85sulphur dioxide emissions 103 104

105 108and acid rain 117and forest decline 45reduction 118 120and urban building decay 200

sunshine trends 105sustainable development 14 239-44

and biodiversity conservation 60cities 50rain forest 34

sustainable environmental managementand population growth 29

swamps 54channelization effects on 131see also mangrove swamps

Swaziland gully erosion in 173synthetic organic pollutants 146-7

218

systemic global change 10 11systems 14-15

tank landscape 131tannery wastes 221technology

agricultural 5 6 7-8 10early human 3

temperate forests decline of 44-7temperature

atmospheric aerosols affecting 8485

landmiddotusc changes affecting 9092

urban areas 98-101see bD global warming

Texas Gulf coast habitat changes on72

Thames River poUution of 151thermal pollution 154-5thermokarst 189-90thunderstorms urban 99Tokyo subsidence in 189tools see technologytourism

and coastal pollution 220 221230

coral reefs threatened by 230-1ecotourism 12

Towyn (Wales) flooding at 216-17trace clements toxic water polluted by

146tractors 10170-1ttaffilt

emissions from 114 115 199urban stone decay associated with

197 199transport 12Transvaal ground subsidence in

189trees

acid rain damage 119beneficial effects 96urban areas 51-2

tropical areasdeforestation 34-5fire usc 20-1

Index 275

savanna 39-41secondary forest 38-9

tropospheric ozone 105 114

ultraviolet radiation 110uncertainty

global warming predictions 95120

in understanding environmentalimpact 14

underdrainage 142United Nations Environment

Programmedesertification data 26pollution control measures 219

urban buildingsstone decay 197-200

urban heat island 98-101urbanization 567 1248

climatic effects 98-101ecological effects 48-52hydrological effects 48 140-2

160-1 180and pollution 49 SO 52 85 99

102-9 197-200and soil erosion 167thermal pollution 154see also cities

USAacid rain 116-17coastal erosion 210 211-12coastal population 205dust bowl 87 172groundwater abstraction 160irrigation effects on rainfall 91-2waste disposal 192

Vaiont Dam disaster 185 186-7vegetation

acid rain effects on 118 119burning 10-11 20-5coastal dunes 222 225destruction through dredging 132dune stabilization through 175fire adaptation 22 33 40human domination and destruction

12 13

276 Index

and precipitation 40river banks 182river regulation affecting 135urban areas 48see Iso forests plants etc

vegetation removalclimatic effects 90-2and dune reactivation 174-5and soil erosion 165-7 172

180-2and soil salinization 184and thermokarst subsidence 190see Iso deforestation

vehicle emissions 114 115 199Venice

building decay 198 200water pollution 221

Vietnam War 13

Walesafforestation and floods 144coastaJ flooding 216-17

Walvis Bay (Namibia) dunestabilization in 176-7

war 13Washington DC urban heat island in

100 101waste

channel morphology effects 182disposal and management 12-13

191-6 201water

importance 125inter-basin transfers 131-2

155-8misdirected efforts at controlling

125soil erosion by 165-71see also rivers

water consumption 125 132 159

water pollution 145-9coastal and marine 218-21control 148 153 219 241thermal 154-5urban 49see also eutrophication

water quality land use changesaffecting 126 127

water resources policies 241water table

falling 142 143 159-60 189rising 160-1 183 184

water-spreading 161watersheds

paired 136see also dC1inage basin

waterways animal migration along67

weatheringby acid rain 118buildings 197-200and slope instability 186

weeds 66West Bay (Dorset) erosion in 211wetlands 53-7

aquacultural usc 232-4conservation 55-6 241drainage 127 142-4ecological importance 53 55 232

wilderness 19 239wind erosion 172-7wind urban 99wood

as domestic fuel 28 37

Yellowstone Park fires 23 24-5

Zimbabwe gullies in 168

Index compiled by Ann Barham

Printed in the United Kingdom byLightning Source UK Ltd Milton Keynes137029UKOOOOI B123-132P

CONTENTSPart I

Pan IIPan IIIPan IVPart VPart VIPart VII

Introduction to the DevelopingEnvironmentallrnpactThe BiosphereThe AtmosphereThe WatersThe Land SunaceOceans Seas and CoastsConclusion

11781

123163203237

GlossaryReferencesIndex

245254264

PART I

Introduction to theDevelopingEnvironmentalImpact

1 Early DY 32 Developing Populations 33 Agricultural Revolutions 44 Urban and Industrial Revolutions 55 The Modem Scene 76 Undersunding Environmental

Transfonruuions 14Key Tenns wd ConceplS 16Points for Review 16

1 EARLy DAYS

In this book we explore the many ways inwhich humans have transformed the faceof the Earth We stan by placing th~

mnsformations into an historical contextand ~dng how they have changed throughrime

Human life probably first appeared onEarth during the early part of the lee Agesome 3 million years ago The oldesthuman remains have been found in eastshyern and southern Mrica For a very longtime the numbers ofhumans on the planetwere small and even as recently as 10000years ago the global population was probshyably only about one-thousandth of its siutoday Also for much of that time hushymans had only modest technology andlimited capacity to harness energy Thesefactors combined to keep the impact of

Developing Populations 3

humans on the environment relativdysmall Nonetheless urly humans were nottorally powerless Their stone bone andwood tool technology developed throughtime improving their efficiency as humshyers They may have caused marked changesin the numbers ofsome species of animalsand in some cases even their extinction(see pan II section 13) No less imporshytam was the deliberate use of fire (see partII section 2) a technological developmentthat may have been acquired some 14million years ago Fire may have enabledeven smaU human groups to change thepattern of vegetation over large areas

2 DEVEWPING POPULATIONS

There Ire It least three interpretationsof global population trends over the llSt3 million years (Whitmore et aI 1990)

Plate 11 The OJduvai Gorge in Tanzania is one of a group of sites in the RiftValley of East Africa where some of the earliest remains of humans and their stonetools have been found ltA S Goudie

4 Introduction

Plate 12 A grass fire in the high grasslands of Swaziland southern Africa Firewas one of the first ways in which humans transfonned their environment andwas probably used deliberately in Africa over a million years ago (A S Goudie)

The first described as the arithmeticshyexponential view sees the history ofglobalpopuJation as a two-stage phenomenonthe first stage is one ofslow growth whilethe second stage related to the industrialrevolution (sec section 4 below) displaysa staggering acceleration in growth ratesThe second view described as ltIogarithmicshylogistic sees the last million or so yearsin terms of three revolutions - the toolagricultural and industrial revolutions Inthis view humans have increased thecarrying capacity of the Earth at leastthree times There is also a third viewdescribed as arithmetic-logistic whichsees the global population history over thelast 12000 years as a set of three cyclesthe primary cycle the medieval cycleand the modernization cycle These threealternative models are presented gnphishycally in figure 11

3 AGRICULTURAL REvOLUrIONS

Until the beginning of the Holoceneabout 10000 years ago humans wereprimarily hunters and gatherers After thattime in various parts of the world inshycreasing numbers of them started to keepanimals and grow plants Domesticationcaused genetic changes in plants and anishymals as people tried to breed more usefulbetter-tasting types Domestication alsomeant that human populations could proshyduce more reliable supplies of food froma much smaller area than hunter-gatherers(table 11) This in turn created a moresolid and secure foundation for culturaladvance and allowed a great increase inpopulation density This phase of developshyment is often called the first agriculturalrevolution

As the Holocene progressed many other

Urban and Indwtrial ~olutions 5

lOllllOk 5000

pastoralism (the use of land for keepinganimals) had a profound effect on manyenvironments in many parts of the world

A further significant ~eldopmcnr inhuman cultural and technological life wasthe mining of ores and the smelting ofmetals begun around 6000 years agoMetal artefacts gave humans greater powerto alter the environment The smeltingprocess required large quantities of woodwhich caused local deforestation

4 URBAN AND INDUSfRIAL

REVOLlTfIONS

The processes of urbanization and indusshytrialization are two Olher fundamentaldevelopments that have major environmenshytal implications Even in ancient timessome cities evolved with considerable popushylations Nineveh (the Assyrian capital)may have had a population of 700000Augustan Rome may have had a populashytion of around 1 million and Carthage(on the North African coast) at its ft11 in146 BC had 700000 inhabitants Suchcities would have exercised a considerableinOuence on their environs but this influshyence was never as extensive as that of citshyies in the last few centuries The modemera especially since the late seventeenthcentury has witnessed the transformationof culture and technology through the demiddotvelopment of major indwtries (table 12)This industrial revolution like the agrishycultural revolution has reduced the spacerequired to sustain each individual and hasseen resources utilized more intensively

Part of this indwtriaJ and economictnnsformation was the development ofsuccessful ocean-going ships in the sixshyteenth and seventeenth centuries As aresult during this time countries in verydifferent parts of the wond became inshycreasingly interconnected Among otherthings this gave humans the power to

fl iJ

i i I 0

sect

j

Figure 11 Three interpretations ofglobal population trends over themillennia (a) the arithmetic-exponential(b) the kgtgarithmic-Iogistic (c) thearithmetic-logisticSource Whitmore et aI (1990) figure 21

technological developments occurred withincreasing rapidity AU of them served toincrease the power of humans to modifythe surface of the Eanh One highJy imshyportant development with rapid and earlyeffects on environment was irrigation1bis was intrrouced in the Nile Valleyand Middle East over 5000 yevs agoAt around the same time the plough was~t used disturbing the soil as neverbefore ArUmals were used increasingly [0

pull ploughs and caru to lift water andto carry produce Altogether the introducshytion of intensive cultivation and intensive

6 Introduction

Table 11 Five stages of economic development

Economic stage Dates and characteristics

Hunting-gathering and early agriculture Domestication first fully established insouth-western Asia around 7500 BeE

hunter-gatherers persisted in diminishingnumbers until today Hunter-gatherersgenerally manipulate the environmentless than later cultures and adaptclosely to environmental conditions

Riverine civilizations Great irrigation-based economies lastingfrom c4000 Be to 1st century AD inplaces such as the Nile Valley andMesopotamia Technology developed toattempt to free civilizations from someof the constraints of a dry season

Agricultural empires From 500 BC to around 1800 AD anumber of city-dominated empiresexisted often affecting large areas ofthe globe Technology (eg terracingand selective breeding) developed tohelp overcome environmental barriers toincreased production

The Atlantic-industrial era From c1800 AD to today a belt of citiesfrom Chicago to Beirut and around theAsian shores to Tokyo form aneconomic core area based primarily onfossil fuel use Societies haveincreasingly divorced themselves fromthe natural environment through airconditioning for example Thesesocieties have also had major impactson the environment

The Pacific-global era Since the 1960s there has been ashifting emphasis to the Pacific Basin asthe primary focus of the globaleconomy accompanied by globalizationof communications and the growth ofmultinational corporations

Source Adapted from Simmons (1993) pp 2-3

The Modern Scenc 7

Plate 13 A simple irrigation system in use in the drier portions of Pakistan Suchirrigation was probably introduced in the Old World drylands around 5000-6000years ago (A S Goudie)

introducc planes and animals to puts ofthe world whert they had not previouslybeen Thc steam engine was invented inthe late eighteenth ccntury and the intershynal combustion engine in the late nineshyteenth century both these innovationsmassivdy increased human need for andaccess to energy and lessened dependenceon animals wind and water

5 THE MODERN SCENE

Modern science and modern medicine havecompounded the effects of me urban andindustrial revolutions leading to accelershyating popuJation incrtasc even in nonshyindustriaJ societies Urbanization has goneon speedily and it is now recognized thatlarge cities have their own environmentalproblems and produce a multitude of

environmental effects If present trendscontinue many citics in the less dcvdopcdcountries will become unimaginably largeand crowded For instance it is projcctedthat by the year 2000 Mexico City willhave more than 30 million people shyroughly three times the present populashytion of the New York metropolitan areaCalcutta Greater Bombay Greater CairoJakarta and Seoul are each expected to bein the 15-20 million range by that timeIn all around 400 cities will have passedthe million mark by the end of me twenshytieth century and UN estimatcs indicatethat b) then over 3000 million peoplewill live in cities compared with around1400 million people in 1970

Modern science technology and indusshytry have also been applied to agricultureIn recent decades some spectacular proshygress has been made Examples include

8 Introduction

Plate 14 A limestone pavement developed on the Carboniferous limestone ofnorth-west England Although they were formed in giadaI times by gladalabrasion they may be exposed at the surface today because of soil erosionproduced by forest dearance since the Mesolithic (A S Goudie)

the use of fertilizers and the selectivebreeding of plants and animals Biotechshynology has however immense potentialto cause environmental change (see partII section 14)

We can recognize cenain trends inhuman manipulation of the environmentduring the modem era First the numberof ways in which humans are affectingthe environment is growing rapidly Forexample nearly all the powerful pesticidespost-date the Second World War The sarJK

applies to the increasing construction ofnuclear reactors to the usc of jet aircraftand to many aspectS of biotechnologySecondly environmental issues that onceaffected only particular local arus havebecome regional or rven global problems

An instance of this is the appeanncc ofsubstances such as DDT (a major pestishycide) lead and sulphates at the North andSouth Poles far removed from the indusshytrial societies that produced them Thirdlythe complexity magnitude and frequencyof impacts are probably increasing Forinstance a massive modern dam like thuu Aswan in Egypt has a very diffcrentimpact from a small Roman darn Finallya general increase in per capita consumpshytion and environmental impact is comshypounding the effects of rapidly expandingpopulations Energy resources are beingdrveloped at an ever-increasing rate givinghumans enormous power to transform theenvironment One measure of this is worldcommercial energy consumption which

The Modem Scene 9

Table 12 Energy technology and environmental impact time line

Time Global Daily Energy Technological Environmentallone population energy source discoveries impacts

use perperson(kcals)

1 million lt 10 2000-5000 Food Tool local andto 5000 million human production short-termyears BC muscle fire animal kills

andvegetationchange

5000 BC 10 million 2ltXXl- Animals Cultivation Local andto AD -1 billion 26000 agricultural building longer-term1800 crops transport natural

wind irrigation vegetationwater coal removal soil

erosionurban airpollution

AD 1800 1 billion- 50000 Fossil fuels Industry Localto 1950 4 billion electricity regional and

steam permanentmajorlandscapechanges airand waterpollutioncommon

1950 to gt4 billion 300000 Internal Industry localpresent combustion cultural regional

engine globalization globalelectricity permanentnuclear and perhapsfossil fuels irreversible

add rainglobalwarming

10 Introduction

Plate 15 The power of humans to transform the lands surface in the modern erais illustrated by the size of the giant open-cast uranium mine at Rossing NamibiaModern technology allows humans to harness energy resources as never before(A S Goudie)

trebled in size bet1een the 1950s and1980

The importance of the harnessing ofenergy can be clearly seen in the contexrof world agriculture At the beginningof the twentieth century more or lessthroughout the world farmers relied upondomestic animals to provide both pullingpower and fertilizer They were largely selfshysutlicient in energy However in manyareas the situation has now changed Fosshysil fuels are eXhnsively used to carry outsuch tasks as pumping (or in many casesmining) water propelling tractors andmanufacturing synthetic fertilizers (whichin many cases cause pollution) The worldstractor fleet has quadrupled since 1950and as much as two-thirds of the worldscropland is being ploughed and compactedby increasingly large tractors

Above all as a result ofthe huge expansionof environmental transformation it is nowpossible to talk about global environmentalchange There are two aspectsofthis (TurnerKasperson et aI 1990) systemic globalchange and cumulative global changeSystemic global change refers to changesoperating at the global scale and includesfor example global changes in climatebrought about by atmospheric pollmioneg the greenhouse effect (see part III)Cumulative global change refers to thesnowballing effect of local changes whichadd up to produce change on a worldwidescale or change which affects a significantpart of a specific global resource eg acidrain or soil erosion (sec parts III and V)The two types ofchange are closely linkedFor example the burning of vegetationcan lead to systemic global change through

The Modem Scene II

Table 13 Systemic and cumulative global environmental changes

Type of change

Systemic

Cumulative

Charaderistic

Direct impact onglobally functioningsystem

Impact throughworldwide distributionof change

Impact throughmagnitude of change(share of globalresource)

Examples

(a) Industrial and land-use emissionsof greenhouse gases

(b) Industrial and consumer emissionsof ozone-depleting gases

(c) Land cover changes in albedo

(a) Groundwater pollution anddepletion

(b) Spelties depletiongenetic alteration(biodiversity)

(a) Deforestation(b) Industrial toxic pollutants(c) Soil depletion on prime agricultural

lands

Source Turner Clark et aL (1990) table 1

processes such as carbon dioxide releaseand albedo modification and to cumulashytive global change through its impact onsoil erosion and biodiversity (table 13)

Figure 12 shows how the human imshypact on six component indicators of thebiosphere has increased over time Thisgraph is based on work by Kates et aI(1990) For each component indicatorthey defined the total net change dearlyinduced by humans to be 0 per cent for10000 years ago (before the presentBI)and 100 per cem lor 1985 They thenestimated the dates by which each commiddotponent had reached successive quartiles(that is 25 50 and 75 per cent) of itstOtal change at 1985 They believe thatabout half of the components havechanged more in the single generationsince 1950 than in the whole of humanhistory before thar date

Human activities arc now atusing envirshyonmental transformation on the localregional continental and planetary scalesThe following examples both give an indishycarion of what is currently being achieved

and provide a sample of some of rhe issueswe cover in rhis book

Large areas of tcrnperate forest havcbeen c1eartd in the past few centuries Nowfarmers and foresters art removing forestsfrom the humid tropics at Idtes of aroundII million hectares (ha) per ycar This isexposing soils to intense and erosive rainshyfall and increasing Idtes of sediment yieldby an average of six times The worldsrivers are being dammed by around 800major new structures each year transformshying downstream sediment loads Hl1gereservoirs held behind dams as high as 300mctres are generating seismic hazardsand catastrophic slope failures Some ofthe worlds largest lakes most notably theAnI SCa in the fOrmer Soviet Union arcbecoming desiccated because the watcris being taken for irrigation usc and transshyferred to other water basirn at a nearmiddotcontinental scale Fluids both water andhydrocarbons (eg oil and gas) arc beingwithdrawn from beneath cities and farmmiddotlands leading to subsidence of up to 8-9metres Recreational vehicles and trampling

12 Introduction

1700~m~I~---Itmiddot-Imiddot50--2000YUI (0)

Figure 12 Percentage change (fromassumed zero human impact at 10000BP) of selected human impacts on theenvironment

feet are damaging many popular touristareas Development on tundra areas isdisturbing the thermal equilibrium ofpermafrost leading to more and moreinstances of thermokarst Coastlines arcbeing protected and reclaimed by theusc of large engineering structures oftenwithout due thought for the possible conshysequences We art pumping at least SOOmiUion tonnes of dissolved material intorivers and oceans around the world eachyear We arc acidifying precipitation tothe extent that some of it has the pHof vinegar or stomach fluid therebyaltering rates of mineral release and rockweathering

These human impacts are having greatdirect and indirect effects on vegetationtable 14 shows the amounts of vegetation(in terms of net primary production)ustd dominated or lost by humans

We shall return to these and other issuesin subsequent sections In this book wehave chosen to focus on specific environshymental issues as they affect the biosphere(part II) atmosphere (part III) surfacewaters (part IV) land surface (part V)and oceans seas and coasts (part VI)However you will notice through all of

these sections that a range of importanthuman activities play key roles and canhave a range of different impacts on manyst(tors of the environment

Even in the modern world economyhunting and gathering activities still havean important effect on the environmentlargely through the biological impacts offishing and the shaming of game Theseactivities arc becoming increasingly largeshyscale and mechanized Agricultureaquaculshyture and other forms of fOod productionnow occupy vasr areas of the Earthssurface and have a wide variety of eirmiddotonment1 efl~cts including soil erosionnutrient depiction changes in speciesdivesiry and genetic changes to crops 2ndanimals Forestry and quarrying as extracshytive industries are creating whole newbndscapes and releasing large amountsof sediment in parts of the globe rangingfrom the humid tropics to the ArcticHeavy industries (such as oil refining andchemical manufaetwC) power generationplants (from coal-fired to nuclear) andlight and high-technology industries havemany different environmental imp2cts andcontribute to pollution of land water 2ndair on the locaI and regional scales

Transport and urbanization have pershyhaps some of the most dr2matic localimpacts on the environment They createwhole new 12ndscapcs dominated by conshycrete add to pollution and affect plantand animal distributions and the circulashytion and distribution of w2ter Tourismwhich is now a booming global industryalso has considerable impacts on the envirshyonment In recent years there has beenmuch interest in the notion of ltccotourshyism or tourism which attempts to minishymize environmental damage

One of the consequences of all thesedifferent human interactions with the enshyvironment is the production of waste Thisitself hu had major environmental effectsThere arc problems of waste disposal and

------TorTlSlriII-brN oiotnily

--- COzmun------ 1lIpab--bull bull WaIftidaIl_- _ Nrdrun

100

The Modem Scene 13

Table 14 Terrestrial net primary production of vegetation used dominated or lostthrough human activities

Category

NPP usedconsumed by humansconsumed by domestic animalswood used by humans

Total

NPP dominatedcroplandsconverted pasturestree plantationshuman-occupied landsconsumed from little-managed areasland-clearing

Total

NPP lost to human activitiesdecreased NPP of croplanddesertificationhuman-occupied areas

Total

Total NPP dominated and lost

bull 1 Pg or Petagramme bull 1 x 10 gSource Vitousek (1994)

waste management Big issues like nuclearwaste disposal have potentially long-termenvironmental implications So do lesscontentious matters such as disposing ofdomestic and industrial waste on landfillsites

Human societies do not always runsmoothly War civil strife and smaller-scaledisruptions such as vandalism and crimehave their own environment1l conseshyquences Indeed some wars au pardymotivated by disputes over environmentalresources for example over water suppliesRecent conflicts in the Arabian GulfBosnia and Mglunistan have had bothshort-term and long-term environmentalconsequences induding pollution andsoil erosion In the 19605 and 19705 the

Amount (Pg per year)-

08222452 (4 of total global NPP)

151026043

1041 (31 of total global NPPl

104526

17 (8 of total global NPP)

58 (39 of total global NPPl

Vietnam War had widely publiciud effectson the mangrove vegetation of theMekong Delta The use of defoliantchemicals there has had long-term impacuon biodiversity from which the envirshyonment is only just recovering Evenwithout war political systems can imposeadditional stress on the environment Theapartheid system in pre-I994 South Africafor example forcibly distributed popushylation and wealth in a highly unhir wayleading to huge environmental pressureson marginal land The planned socialisteconomies of the fanner Soviet Union andmany East European states appear now tohave had particularly damaging environshymental impacts And capitalist enterprisewhich now dominates the global economy

14 Introduction

has often had a tendency to plunder anddespoil the environment

These many negative environmentalimpacts have generated in response a longshyterm and growing focus on conKrvationand improving human management of meenvironment Conservation and manageshyment themselvcs have environmental imshypacts as in the creation of nature reservesthere may also be less desirable impactswhere management schemes go wrongThe ideas of sustainable development arethe most recent attempt to combine remiddotsource exploitation with conservation anda concern for the environmental futureAs our scientific understanding of how theenvironment works has advanced we havegained a better view of how serious ourhuman impacts can be On the other handwe have also learnt that there is muchreason for hope The environmental fumiddotture is not all doom and gloom as westress in part VII of this book

6 UNDERSfANDING

ENVIRONMENTAL

TRANSFORMATIONS

We have already shown in this chapter thathuman impacts on environmental processeshave had a long and complex historyand now take on many complex and intershylinked forms The environment itself is alsonot a static simple entity but has a comshyplicated history of its own We now reashylize that the environment changes naturallyover a range of different time-scales as aresponse to a number of natural forcingfactors such as the varying position ofthe Earth Iithin its orbit around the sunOn shorter time-spans we know that theenvironment can work in abrupt and chalshylenging ways producing what are callednatural hazards such as volcanic erupshytions earthquakes floods and hurricanesSo putting together human and naturalfactors influencing the environment to

explain any single environmental transforshymation can be a hugely difficult usk It isimportant to realizc that there is still a lotof scientific uncertainty and debate overthe causes and consequences of many ofthe environmental issues we look at in thisbook

Understanding the role of human activmiddotities in environmental transformations isnot a completely hopeless task howeverThere arc several useful concepts whichwe can adopt to help us untangle whatis going on First it is useful to think ofthe environment (of which of course wearc a part) as being a series of interlockedsystems These systems arc affected by awhole series of stresses (which can behuman or natural in origin) The Stressesproduce some changes in the system orresponses these arc what we sec as environmiddotmenw transformations or environmentalissues Because the systems arc interlockedstresses on one system may produce linkedeffecu on other systems Some of the sysshytems arc more able to resist stresses thanothers and so some can be suessed greadybefore they show any response Others arcmore sensitive to stresses

As an example to clarify the ideas preshysented above we could look at a drainshyage basin (or watershed as it is knownin the USA) Drainage basins arc primashyrily hydrological systems with interlinkedvegetation communities Cutting downtrees (a stress) will produce a range ofresponses soil erosion increased floodingand changes in the way water is distributed(hydrological pathways) The severity ofthese outcomes will depend on the climateand topography of the area Normally amixture of natural and human-inducedstresses will affect the environment toshygether complicating the picture One wayof understanding such multi-causal situashytions is to identify different types ofstreSSeSor causal factors A uscful frameworkwhich has blaquon used in various ways inthe foUowing sections of this book is to

split causal faCtors into three typc=S that ispredisposing inciting and contributingfactors Pndisposing factors are those feashyturc=s of the natural or human environshyment which make a system vulnerable tosuess inciting factors are thosc= stressesthat trigger otT a change in the systemand conrributiJg factors are the whokrange of additional strc=sses which makethe rc=sponse more noticeable and acuteLct us apply this frtmc=work to the case ofa drainage basin The predisposing factorswhich may make it vulnerable to changefoUowing tree-cutting would lx the toshypography and climate and pcrhaps alsopast forest management pnctices Theinciting factor would lx the tete-euningitself The contributing factors could bethe health of the trees the sc=ason whenthe trees were felled the weather at thetime and over a longer time-span whatvegetation grows in place of the trees

FURTHER READING

Environmental Transformations IS

The concepts of stressc=s raponses anddifferent types of causal poundactors are veryuseful in trying to understand how humiddotmans are influencing thdr environmentSuch understanding is vital in any attemptsto solve or manage the resultant environshymental problems However to arrive atsolutions it is also necessary to have adeeper understanding of the human socishyeties involed in such environmental isshysuc=s as many of our subsequent examplesillustrate For example just knowing howtree-cutting can produce soil erosion andhydrological changes within a drainagebasin does not mean that we can solve theproblem We need also to know why peoshyple arc cutting down the trees Before wecan effect any great changes we need moreunderstanding of the economic conditionstechnological capability cultural organizashytion and political systems of the peopleinvolved

Freedman B 1995 Environmenral Ecowgy 2nd edn San Diego Academic Prc=ssAn enormously impressive and wide-ranging study with a strong ecological emphasis

Mannion A M 1995 Agriculture and Enpironmental Change London WikyA new and comprehensive study of the important rok that agriculture plays in landtransformation

Meyer W B 1996 Human Impact on the Earth Cambridge Cambridge UniversityPressA good point of entry to the literature that brims over with thought-provoking epigrams

Middleton N J 1995 The Gwbal Quino London EdWdrd ArnoldAn introductory text by a geographer which is wdl iIIustrated and clearly wrinen

Ponting c 1991 A Gnen History of the World London PenguinAn engaging and informative treatment of how humans have transformed the earththrough time

Simmons I G 1996 Changing the FRee of the EArth Cultl4re Environment andHistory 2nd edn Oxford BlackwellA characteristiCally amusing and perceptive review of many faceu of the tole ofhumansin transforming the earth from an essentially historical perspective

16 Introduction

KEy TERMS AND CONCEPTS

agricultural revolutionbiosphereglobal environmental changeHolocenehunter-gatherer

POINTS FOR REVIEW

industrial revolutionpredisposing inciting and contributing

factorsstresses and responsessystems

How much environmental change was achieved in prehistoric times and how much inthe last three centuries

To what extent are environmental changes the result of both natural and humanshyinduced stresses

What do you understand by the phrases global environmental change andsustainability

PART II

The Biosphere1 Introduction 19

2 Fire 20bull The YeDowsrone fires of 1988 24

3 Desertifiallion 26bull Desertification in north centr1l China 30

4 Oeforestuion 32bull Managing tropical rain forest in Cameroon 36

5 Tropical Secondary Forest Fonnacon 386 Grasslands and Heathlands The Human Role 39

bull Recent human impacts on subalpine grasslandand heathland in Victoria Australia 43

7 Temperate Forests under Stress 44bull Forest decline in Bavaria Germany 47

8 Urban Ecology 48bull Chicagos dunging vegetation 51

9 Wetlands The Kidneys ofme undsclpe 53bull Wetlands management in the Niger

Inland Delt 5710 Biodivmity and Extinctions 58

bull Pandas plants and parks conservingbiodiversity in China 62

The Biosphere11 Introductions Invasions and Explosions 64

bull Alien plant species invading KakaduNational Park Australia 68

12 Habitat Loss and Fragmentation 69bull Texas Gulfcoast habitat chages and the

Lesser Snow Goose 7213 Extinctions in the Past 7314 Biotechnology Genetic Engineering

and the Environment 7615 Conclusions 77

Key Tenns and Concepts 78Points for Review 79

1 INTRODUCTION

In this part of the book we look at someof the main ways in which humans havemodified the biosphere and the conseshyquenccs of these impacts

Humans have changed the biosphere invery many ways with wide-ranging andlong-lasting effects As soon as peoplediscovered how to use fire at a very earlystage in human development they obshytained tremendous power to modify thevegetalion cover of the Earths surfaceAlso during the Stone Age humans gradushyally developed the technology to enablethem to bccome ever more effecrive huntshyers Early people may have contributed tothe extinction ofsome of the worlds greatmammals Since the Mesolithic as passhytonlism and agriculture have becomewidespread modification of habitat hascontinued rapidly Humans also gainedthe ability to manipulate the genetic comshyposition of plants and animals - a majorpart of the process generally called domcs-

Introduction 19

ticarion This has been one of the mostdirect ways that humans have changed thebiosphere

As the human population of the Earthhas expanded in numbers and spread tomore and more parts of thc globe Ccrmore environments havc been modifiedThese include tundra anas deserts forshyests and wetlands The total area ofsurviving natural habitat has stcadil dimiddotminished and wilderness arcas are 110W

relatively few Figure 111 shows an attemptto mark out the areas of the planet thatcan still bc defined as wilderness Howshyever no part of the Earths surtacc call beconsidered entirely free from the imprintof human activities Air pollution and clishymatic changes causcd by human action arcevident even at the poles As it has beshycome easier for humans to move from oneplace to another so plants and animalshave been introduced to many new areasSometimcs the numbers ofthcsc= newcomerspecies have exploded damaging the comshymunity struetu~ of existing plants andanimals

bull

bullbulleJC1)-

~ )

Figure 111 Global wilderness remaining in the 1980sSource McCloskey and Spalding (1989)

20 The Biosphere

Table 111 Biomass burning in the tropical regions

Region Forest Savanna Fuel Agricultural Regional Regionalwood waste total total

(Tg dmlyr) (Tg dmlyr) (Tg dmlyr) (Tg dmlyr) (Tg dmlyr) (Tg Oyr)

America 590 770 170 200 1730 780Africa 390 2430 240 160 3210 1450Asia 280 70 850 990 2190 980Oceania - 420 8 17 450 200

Total tropics 1260 3690 1260 1360 7580 3410

Tg dmlyr = teragrammes of dry matter per yearTg elyr = teragrammes of carbon per yearSource Andreae (1991) table 13

2 FIRE

Fire is one of the earliest means that hushymans used to modifY the natural environshyment It is also one of the most powerfulFires do of course occur naturally andhave done so during the entire history ofme Earth For example they arc causedby volcanic eruptions by spontaneouscombustion oforganic materials by sparksfrom falling boulders and above all bylightning which on average strikes me landsurface of the globe 100000 times eachday However in some environments megreat majority of fires arc now caused byhumans either deliberately or accidentally

There arc many good reasons why hushymans from our early Stone Age ancestorsonwards have found fire useful

bull to clear forest for agriculturebull to improve the quality of grazing for

game or domestic animalsbull to deprive game of cover or to drive

them from coverbull to kHi or drive away predatory ani-

mals insects and other pestsbull to repcl or attack human enemiesbull to make travel quicker and easierbull to provide light and heatbull to enable them to cook

bull to transmit messages by smoke signsbull to break up stone for making tools or

pottery smelting ores and hardeningspears or arrowheads

bull to make charcoalbull to protect settlements or camps from

larger fires by controlled bumingbull to provide spectacle and comfort

Fire has been central to the life of manygroups ofhunter-gatherers pastoralists andfarmers (including shifting cultivators inthe tropics) It was much used by peoplesas different from one another as the Aborishyginals of Australia the cattle-keepers ofAfrica the original inhabitants of TIerradel Fuego (the land of fire) in the farsouth ofSouth America and the Polynesianinhabitants of New Zealand It is still muchused especially in the tropics and aboveall in Africa Biomass burning appears tobe especially significant in the tropicalenvironments of Africa in comparisonwith other tropical areas (table 111) Themain reason for this is the great extentof savanna which is subjected to regularburning As much as 75 per cent of Afrishycan savanna areas may be burned each year(Andreae 1991) This is probably an anshycient phenomenon in the African landscapewhich occurred long before people arrived

on the scene Nevenhelcss humans havegready increaKd the role of fire in thecontinent where they may have uKd it forover 14 million years (Gowlen et al 1981)

Naturally occurring fires break out withvarying frequency in different global en~

vironments Over a century may passbetween one firc and the next in tundraenvironments and ecosystems dominatedby thc spruce uec In areJs ofsavanna andMcditerranean shrubland on the otherhand the interval may be only five to

fifteen years and in semi-arid grasslandsless than five years

Fira can extend over huge areas In1963 in Parana Brazil no less than 2million hectares of forest were consumedin JUSt three weeks while the fire of 1987in China and the neighbouring SovietUnion destroyed around 5 million hecshytares over the same length of time

Fires can also cause some very highground surnce ttmperarures up to 800Cor higher The temperature reached deshypends very much on the size duration andintensity of the fire Some fires are relashytivdy quick and cool-burning and onlydestroy ground vegetation Other firessuch as crown fires affect whole forestsup to the Icvd of tree crowns and gcncrshyate very high temperatures In generalforest fires arc hotter than grassland firesIt is significant for forest management thatwhcre fires occur very often they do notattain the highest temperatures becausethcre is not enough flammable material tokeep them going However humans oftendeliberately prevent fires as part of normalpolicy in forest areas When this is donclargc quantities of flammable materialsaccumulate so that when a fire docs breuOut it is of the hot crown type that canbe ecologically disastrous There is nowmuch debate therefore about the wisdomof suppressing the fircs that in many forshyests would occur quite regularly under soshycalled natural conditions

fire 21

Recent studies have indicated that rigidpolicies of protecting habitats against firehave often had undesirable results Conseshyquendy many foresters now suess the needfor prescribed burning or environmenshytal restoration burning For example inthe coniferous forests of the middle andupper levds of the Sierra Nevada mounshytains of California protection from firesince 1890 has made the srands densershadier and less park-like and Slquoiaseedlings hae decreased in llumber as aresuh Ukeise at lower leels the charshyacter of [he semi-arid shrubland calledchaparrll has changed The lgetationhas bt-come denser the amount of flamshymable material has increased and fireshysensitive species have encroached Thevegetation has become less diverse witholder trees predominating instead of amosaic of trees at different stages ofgrowth In the Kruger National Park inSouth Africa fires have become less freshyqucnt since the game reserve was estabshylished when local hunters and farmerswere moved out AJ a rcsult bush hasencroached on areas that werc formerlygrassland and the carrying capacity forgrazing animals has declined Controlledburning has been reinstituted as a necesshysary element of game management

Fire has many positive ecological conseshyquences Fire may assist in seed germinashytion For example many investigatorshave reported the abundant germinationof dormant seeds on recently burnedchaparral in areas like California with aMediterranean climate and it Kerns thatsome Keds of chaparral species requirescarification by fire to germinate effecshytively Fire alters seedbeds and even thoseKeds not requiring scarification maygerminate better after a fire because fireremoves competing seeds litter and somesubstances in the soils which are toxic toplants If substantial amounts of litter andhumus arc removed large areas of rich

22 The Biosphere

ash bare soil or thin humus may becreated Some trees such as the Douglasfir and the giant sequoia benefit fromsuch seedbeds Fire sometimes triggers therelease of seeds from cones (as with Jackpine Pinus banlujana) and seems to stimushylate the vegetative reproduction of manywoody and herbaceous species Fire cancontrol forest insects parasites and fungi- a process termed sanitization - andseems to stimulate the flowering and fruitshying of many shrubs and herbs It alsoappears to modifY the physiochemical enshyvironment of plants with mineral elementsbeing released both as ash and throughfaster decomposition of organic layersAbove all areas subject [0 fire often showgreater species diversity which tends tofavour the Hability of the habitat over thelong term

Fire is also crucial to an unders[andingof some major biome types and manybiota have become adapted to it Forexample many savanna trees are fireshyresistant The same applies to the shrubvegetation (mafuis) of the Mediterraneanlands which contains certain species (egQuercus io and Quercus cocciera) whichthrive after burning by sending up a seriesof suckers from ground level Mid-latitudegrasslands (eg the prairies of NorthAmerica) were once thought to have deshyveloped in response to drought conditionsduring much of the year Now howeversome have argued that this is not necesshysarily the case and that in the absence offire trees could become dominant Thefollowing reasons are given to support thissuggestion

bull planted groves and protected trees seemable to flourish

bull some woodland species notably junishypers are remarkably drought-resistant

bull trees grow along escarpments and indeep valleys where moisture is conshycentrated at seeps and in shaded areas

and where fire is least effective theeffects of fire are greatest on flat plainswhere there are high wind speeds andno interruptions to the course of thefire

bull where fires have been restricted woodshyland has spread into grassland

Fire rapidly alters the amount formand distribution of plant nutrients in ecoshysystems and has been used deliberatelyto change the properties of the soil Boththe release of nutrients by fire and thevalue of ash have long been recognizednotably by those involved in shifting culshytivation based on slash-and-burn techshyniques However once land has beencultivated the loss of nutrients by lcachshying and erosion is very rapid This is whythe shifting cultivators have to move onto new plots after only a few years Firequickly releases some nutrients from thesoil in a form that plants can absorbThe normal biological decay of plant reshymains releases nutrients more slowly Theamounts of phosphorus (P) magnesium(Mg) potassium (K) and calcium (Ca)released by burning forest and scrubvegetation are high in relation to both thetotal and the available quantities of theseelements in soils

In forests burning often causes the pHvalue of the soil to rise by three units ormore creating alkaline conditions whereformerly there was acidity Burning alsoleads to some direct loss of nutrients fromthe soil by volatilization and by causingash to rise up into the air or by loss ofashto water erosion or wind deflation Wherefire removes trees soil temperatures inshycrease because of the absence of shade sothat humus is often lost at a faster ratethan it is formed

Concern is now being expressed aboutthe role of biomass burning in alteringatmospheric chemistry and contributingto the greenhouse effect by adding carbon

dioxid( (COl) to m( aunosph(r( (Levin(1991) About 40 per c(nt of m( worldsannual production ofCOJ may r(Sult from

FURTHER READING

Fire 23

th( destruction of biomass by fir( Firesalso produc( (missions ofsmok~ and nitricoxide

Crutzen P and Goldammer G 1993 Fire in the Environment Chicheu(rWileyThis book considers some of th( potential global dfects of fir~s including effects onatmospheric chemistry

Kozlowski T T and Ahlgren C C (eds) 1974 Fire 1 aosyrtems New YortAcademic PressAlthough relatively old this provides a very useful picture of the effects of fir~ on faunaand flora

Pyn~ S 1982 Fire in America A Cwlrural HiJrory of Wildnd and Rwral FinPrinceton Princ(ton Univ(rsity PressA massive and scholarly survey of how fires hav( been fundamental to und(rstandingmuch of the veg(tation of America

Plate 111 Forest burnt in the Yellowstone fires of 1988 (EPLRob Franklin)

u INO

I MONTANA OAKOTA

f-tN I

~i----IDAHO f r IIMWIJe1J SOVln

I OAKOTA-- I---- WYOMING ---___

L _ NtRIlASKAT-----___ LlJrAll I --I COLORAOO J

I 0 kl 2laquolI ~

24 The~iosphert

The Yellowstone fires of 1988

In the summer of 1988 wideshyspread fires ravaged the Yellowshystone National Park in theAmerican West Forest fires beshygan in June and did not die outcompletdy until the onset ofwinter in November Somcwherebetlcen 290000 alld 570000hectares burned in by tar theworst fire sinc Yellowstone wasestablished as the worlds firstnational park in the 1870s

Was this inferno the result of apolicy of fire suppression Without suh a policy the torest would burn at intershyvals of 10 or 20 years because of lightning strikes Could it be that the suppresshysion of fires over long periods of say 100 years or more allegedly to protect andpreserve the lorest led to the build-up of abnormal amounts of combustible fuelin the torm of trees and shrubs in the understory~ Should a programme ofprescribed burning be carried out to reduce the amount of available fueH

Fire suppression policies at Yellowstone did indeed lead to a critical build-upin flammable material However other factors must also be examined in explainingthe severity of the fire One of these was the fact that the last comparable firehad been in the 1700s so that the Yellowstone forests had had nearly 300 yearsin which to become increasingly flammable In other words because of the wayvegetation develops through time (a process called succession) very large firesmay occur every 200-300 years as part of the natural order of things (figureII2) Another crucial factor was that weather conditions in the summer of 1988were abnormally dry bringing a great danger of fire

Rommc and Despain (1989 p 28) remark in conclusion to their study of theYellowstone fires

It seems that unusually dry hot and windy weather conditions in July andAugust of 1988 coincided with multiple ignitions in a forest that was at itsmost flammable stage of succession Yet it is unlikely that past suppressionefforts were a major factor in exacerbating the Yellowstone fire If fires occurnaturally at intervals ranging from 200 (0 400 years then 30 or 40 years ofeffective suppression is simply not enough for excessive quantities of fuel tobuild up Major attempts at suppression in Yellowstone forests may have merelydelayed the inevi(able

Further reading

Remme W H and Despain D G 1989 The Yellowstone fires ScientifteAmerican 261 21-9

Fire 25

The old fomt

~i t~rfti (

---

Figure 112 EcotogicaJ succession in response to fire in Yellowstone NationalParle USASource After Romme and Despain (1989) pp 24-5

26 The Biosphere

3 DESERTIFICATION

The term desertification was first used bythe French forester Aubreville in 1949 buthe never formally defined it Since thenover 100 definitions have been publishedThe United Nations Environment Proshygramme (UNEP) has recently defineddesertification as land degradation in aridsemimiddotarid and dry sub-humid areas resultshying mainly from adverse human impacts(Tolba and EI-Kholy 1992 p 134) Othershowever suggest that climatic change mayalso play an important role

There are fundamental problems relatshying to how extensive the problem ofdesertification is how quickly it is takingplace and what the main causes are UNEP(Tolba and EI-Kholy 1992 p 134) hasno doubts about the significance of theproblem Desertification is the main envirshyonmental problem of arid lands whichoccupy more than 40 per cent of the totalglobal land area At present desertificationthreatens about 36 billion hectares shy70 of potentially productive drylands ornearly one-quarter of the total land areaof the world These figures exclude naturalhyper-arid deserts About one sixth of theworlds population is affected

UNEP recognizes the following seriesof symptoms of desertification that relateto a fall in the biological and economicproductivity and therefore value of a pieceof land

bull reductlon of crop yields (or completefailure of crops) in irrigated or rain-fedfarmland

bull reduction of biomass produced byrangeland and consequent depletionof feed material available to livestock

bull reduction of available wood biomassand consequent increase in the disshytances travelled to obtain fuelwood

bull reduction of available water due to

decreases in river flow or groundwaterresources

bull encroachment of sand bodies (dunessheets) that may overwhelm producshytive land settlements or infrastructures

bull social disruption due to deteriorationof life support systems and the associshyated need for outside help (relief aid)or for havens elsewhere producingenvironmental refugees

It is however by no means clear howextensive desertification is or how fast it isproceeding In a recent book called Desertshyification Exploding the Myth Thomas andMiddleton (1994) have discussed UNEPsviews on the amount of land that isdesertified They state

The bases for such data are at bestinaccurate and at worst centered onnothing better than guesswork Theadvancing desert concept may have beenuseful as a publicity tool but it is notone that represents the real nature ofdesertification processes (Thomas andMiddleton 1994 p 160)

There are indeed relatively few reliablestudies of the rate of desert advance orencroachment Lamprey (1975) attemptedto measure the shift of vegetation zonesin the Sudan and concluded that the Saharahad advanced by 90-100 km between1958 and 1975 an average rate of about55 km per year However on the basisof data amassed by remote sensors andground observation Helldcn (1984) foundlittle evidence that this had in fact hapshypened One problem is that biomass proshyduction may vary very substantially fromyear to year This has been revealed bysatellite observations of green biomassproduction levels on the southern side ofthe Sahara

The way in which desert-like conditionsspread is also [he subject of some controshyversy Contrary to popular rumour this

D~rtification 27

ADVANCE Of DtSmTflpoundATlOS OFDfS(RT-UKf CO~I)Jl1OIiS

lniptioa

Figure 113 The causes and development of desertificationSource Kemp (1994) figure 312

does not happen over a broad front likea wave overwhelming a beach Rather itis like a rash tending to appear in localpatches around settlements This distincshytion is important because it influences pershyceptions of how to tickle lhe problem

Another point made by Thomas andMiddleton (1994 p 160) is that drylandsmay be less fragile than is often thought

We should bear this controVersy in mindas we consider some of the undoubtedpressures that are being placed on aridenvironments (figure 113) It is gefKrallyagreed that the massive increase in humanpopulation numbers during the twentieth

century has been of fundamental imporshytance This demographic explosion has hadfour key consequences for dryland areasovercultivation overgrazing deforestationand salinization of irrigation systems

There arc two aspects ofovercuhivationmore intensive usc of land already undercultivation and the inuoduetion of agrishyculture into areas where conditions arc notsuitable to it primarily because of theiraridity or because their soils are fragile andinfertile Crops are now grown in areas ofthe Sahel of West Africa where annualrainhll is as low as 250 mm and in partsof the Near East and Nonh Africa which

28 The Biosph~re

SOUTIlERNKORDOFAN

bull 00~

Figure 114 The expanding wood andcharcoal exploitation zone south ofKhartoum SudanSource From Johnson and Lewis (1995)figure 62

have only 150 mm of rainfall a year Someof these areas hav~ friable soils d~vdopcdon lat~ Pleistocme dun~ fidds This makesth~m highly prone to water ~rosion andwind reactivation

Ov~rgrazing is rclat~d to ov~rcultivashy

tion for in many ar~as increasing numbersof humans r~quire incrusing numbers ofdomestic animals Larger tr~e-ralging stockherds r~duc~ th~ amount of pasturdandavailable and mean that the pastures thatremain have to support even mor~ animalsTh~ carrying capacity of the land may thenbe exceeded Thcr~ may also be conflictsbetw~~n pastoralists and cultivators Asthe fronti~r of cultivation is pushed outshywards into ever mor~ marginal ar~as itencroaches more and mort on th~ grazshying lands of the pastoralists In this waynomadic pastoralists many of whom haddeveloped sophisticated ways of keepingmarginal areas in productive use have oftenKen their traditional systems disintegrateThis has disrupted the equilibrium betweenpeople and land For nampie the nomads

Kasonal or annual migrations may havebc~n resuict~d by delibcrat~ policies ofscd~ntarization (making peopl~ setde inone place) imposed by central governshyments The same restrictive eff~ct resuJtsfrom th~ est2blishm~nt of national boundshyaries wh~re non~ previously existed

Another cause of overgrning has beenthe installation of boreholes and the digshyging out of wat~rholes These have mademor~ water available for domestic animalswhich thus rapidly increase in number Thisin turn leads to overgrazing Vegetationin ~fTect r~places water as the main factorlimiting stock numbers

The third human cause ofdesertificationis d~forestation and the removal of woodymaterial Many pwpl~ depend on woodfor domestic uses (cooking heating brickmanufacture ~tc) and th~ ccUection ofwood for charcoal and firewood is anespecially serious probl~m in the vicinityof urban c~ntres This is illustrated forKhartoum in Sudan in figure 114Th~ fourth prim~ cause ofdesertification

is salinization This kiUs plants destroysth~ soil struetur~ and reduces plant growthSalinization oft~n occurs where irrigationis introduc~d without making proper proshyvision for drainag~ It can howev~r alsobe an unwant~d consequ~nce of v~getamiddot

tion cl~arance Th~ r~moval of plantsr~duc~s the amount of moistur~ lost fromthe soil as a result of int~rccption of rainshyfall by leav~s and evapotranspiration Asa result groundwater levels rise and salin~

water is allowed to seep into lowmiddot lyingareas like valley bottoms This is a seriouscause of salinization both in the prairies ofNorth Am~rica and in the wheat belt ofW~st~rn Australia It is so important thatwe tr~at it in a separate section (part Ysection 5 below)

As we saw ~arli~r som~ obKrv~rs hav~

suggested that a naturaJ d~terioration inth~ climate may contribut~ to the damshyage don~ to drytand and the spread of

desen-like conditions When we examinerainfall data for recent deades we see thatfor some arid areas there is relatively clearevidence fur a downward trend while inother areas rainfall appears to be stable orto be increasing A downward trend hasbeen established for the Sudan and Sahelzones of Mrica This has had a range ofconsequences including a subslantial risein dust-storm activity and a severe reducshytion in thc area and watcr volumc of LakcChad By COntrast the latest analyscs ofsummer monsoon rainfall for the RajasthanDescrt in India show a modest upwardtrend between 1901 and 1982 Data fornorth-cast Brazil much of Australia andCalifornia and Arizona in the USA showno dear trend in either direction

Attempts to reduce damage to drylandcan be dividcd into twO types (1) technoshylogical methods and (2) fundamentalchanges in societies economies and polishytics For exampic a nnge of technologicalsolutions is available to control blowingsand and mobile dunes (see part V secshytion 3) It is much more difficult howshyever to make changes in the humanconditions that are the real rOOt causes ofthe problcm Population growth povertypolitical instability poor planning theattitudes of urban clites and the prevenshytion of traditional nomadic migration areamong the long-term basic issues thatneed to be addressed

FURTHER READING

Desertification 29

Land degradation is not however aninevitable result of rapidly growing humanpopulations Excellent proof of this isprovided by TifTen et als (1994) study ofthe semi-arid Machakos District in KenyaAround sixty years ago this area hadsevere fumine problems and was sufferingfrom sevcTe land degradation and soil eroshysion Photographs from the 1930s show agullied and impoverished landscape Sincethat time the population of the districthas increased more than fivefold but theenvironmcnt is now in a vcry much bcltcrcondition than it was then Slope terracshying has reduced the extent and rltc ofsoilerosion and gully formation A fuclwoodcrisis has been averted by planting a largenumba of farmed and protected trees Inaddition agricultural output has increasedTiffen e( al argue that high rates of popushylarion growth can be combined with susshytainable environmental management InMachakos District the local Akamba peoshyple have proved very adaptable Labouris plentiful and they have invested bothlabour and capital in land improvementand development They have added to theiragricultural incomes by doing much morenon-furm work and the huge growth inthe output of non-subsistence prodUCTS hasled to a development of jobs and skillsin marketing and processing In shorthumans can manage the landscape to goodeffect even when their numbers increase

Goudie A S (ed) 1990 Techniques for Desert Rulmarion Chichester WileyThis edited work looks at some of the solutions that arc available for dealing with theproblems of d~rt environments

Graingtt A) 1990 TJIt TbrtRuning DtJnt Controlling DesertifURtjon LondonEanhscanA very readable and wide-rIDging review of desertification

Middleton N J 1991 DeserrifitlltU1fl Oxford Oxford University PressA weU-illustrated simple introduction designed for usc in secondary eduation

30 The Bi06phere

Desertification in north central China

--

OIlNA

~

WuboII

Deserts and desertified lands coversome 149 million sq km of Chinaamounting to approximately 155per cent of the total land area of thecountry There are 12 named desertswithin China and it is estimated that 35W

various human and natural forces are ri-J------~

combining to produce desertificationof some 1560 sq km per yeararound these deserts (see table 112)Three main types of desertificationarc found in China the spread ofdesert-like conditions on sandy steppe reactivation of vegetated dunes (sandylands) and encroachment of mobile dunes on to settlements and farmland Studshyies within China suggest that such desertification is a blistering process ie thatit occurs in blister-like localized patches of rangeland away from the desert marginThese blisters then gradually grow and coalesce to produce large patches ofdescrtified land According to Fullen and Mitchell (1994) Chinese desertification

Plate 112 Encroaching sand dunes on the edge of the Gobi DesertDunghuang China The dunes are invading fields and many methods arebeing used to try to stabilize them (TripJ Batten)

Daertification 31

Table 112 Types causes and extent of desertlfted lands In China

Causes Area affected(sq km)

Overcultivation on steppe 44700Overgrazing on steppe 49900Overcollection of fuetwood 56000Misuse of water resources 14700Encroachment of dunes 9400

Source Adapted from Fullen and Mitchell (1994)

of totaldesertified land

252833188355

is mainly a result of land mismanagement encouraged by climatic factors whichproduce droughts and encourage sand movements

The severity of desertification and land degradation in China has prompted theInstitute of [kscrt Research of Academia Sinica (IDRAS) to set up research intocombating desertification IDRAS has nine research stations in desertified areasat which various reclamation techniques are practised At the Shapotou ResearchStation in Ningxia Autonomous ~gion established in 1957 to discover methodsof protecting a major railway line from sand movements the following techshyniques have been used

bull planting windbreaks of pines poplars and willows parallel to the railway linebull levelling dunes with bulldozersbull installing drip irrigation systems to aid topsoil development on levdled dune

sandsbull constructing straw checkerboards to stabilize surfaces and (ncourag( plants to

grow on shifting dunes to help stabilize them this produces an artificialecosystem on the dllOes increasing vegetltioll cover from less than 5 per cenl10 between 30 pc=r cent and 50 per cent and stopping dune movement

Irrigation land enclosure and chemical treatments arc also being lIs(d in this ar(ato help turn descrtified lands into productive rangdands According to r(c(ntstudies such reclamation efforts must be maintained and monitof(d over at kastsix y(ars b1=forc significant improv(ments can be seen

Further reading

Fullen M A and Mitchell D 1994 Desertification and reclamation in northcentrl1 China Ambjo 23 131-5

32 The Biosphere

4 DEFORESTATION

Clearing middotforests is probably the mostobvious way in which humans have transshyformed the face of the Earth It was theprime concern of George Perkins Marshwhen he wrote his pioneering book callshying for the conservation of nature Manatld Nature in 1864 (see part IV section3) Forests provide wood for construcshytion for shelter and for making toolsThey are also a source of fuel and whencleared provide land for fOCK productionFor all these reasons they have been usedby humans sometimes to the point ofdestruction

Forests however are more than aneconomic resource They play severnl keyecological roles They arc repositories ofbiodiversity (see section 10 below) theymay affect regional and local climates andair quality they playa major role in thehydrological cycle they influence soil qualshyity and rates of soil formation and preshyvent or slow down soil erosion

We do not have a dear view of how fastdeforestation is taking place This is partlybecause we have no record on a globalscale of how much woodland there is toshyday or how much there was in the pastIt is also because there are disagreementsabout the precise meaning of the worddeforestation For example shifting culshytivators and loggers in the tropics oftenleave a certain proportion of forest rnesstanding At what point does the proshyportion of trees left standing permit oneto say that deforestation has taken placdAlso in some coumries (eg India) scrubis included as forest while in others it isnot

What we do know is that deforestationhas been going on for a very long timePollen analysis shows that it started inprehistoric times in the Mesolithic (around9000 years ago) and Neolithic (around5000 years ago) urge traCts of Britain

had been deforested before the Romansarrived in the islands in the first centuryBC Classical writers refer to the effectsof fire cutting and the destructive nibbleof goats in Mediterranean lands ThePhoenicians were exporting cedars fromLebanon to the Pharoahs and to Mesopomiddottamia as early as 4600 years ago A greatwave of deforestation occurred in westernand central Europe in medieval times Asthe European empires established themshyselves from the sixteenth and seventeenthcenturies onwards the activities of tradersand colonists caused forests to contract inNorth America Australia New Zealandand South Africa especially in the nineshyteenth century Temperate North Americawhich was wooded from the Atlantic coastas far west as the Mississippi River whenthe first Europeans arrived lost morewoodland in the following 200 years thanEurope had in the previous 2000 At thepresent time the humid tropics arc undershygoing particularly rapid deforestationSome areas are under particularly seriousthreat including South-East Asia WestMrica Central America Madagascar andeastern Amazonia (figure II5)

The effects of deforestation can be seenespecially vividly in the Mediterraneanlands of the Old World As Ponting (1991p 75) puts it

Modern visitors regard the landscapeof olive trees vines low bushes andstrongly scented herbs as one of themain attractions of the region It ishowever the result of massive environshymental degradation brought about notby the creation of an artificial systemsuch as irrigation but by the relentlesspressure of longmiddotterm settlement andgrowing population The natural vegshyetation of the Mediterranean area wasa mixed evergreen and deciduous forshyest of oaks beech pines and cedarsThis forest was cleared bit by bit fora variety of reasons - to provide land

Deforestation 33

Figure 115 Estimated annual forest change rates 1981-1990Source World Resources Institute (1994) figure 71

for agriculture fuel for cooking andheating and construction materials forhouses and ships

Other processes linked to humans inshycluding grazing and fire have preventedforest from returning over wide areas Inplace of forcst a kind of vegetation calledmalfuis has become widesprcad This conshysists of a stand of xerophilous evergrecnbushes and shrubs whose foliage is thickand whose trunks arc normally obscuredby low-level branches It includes suchplants as holly oak (~ercu iJex) kermesoak (QuercllS coccim) tree heath (Ericaarbona) broom heath (Erica coparill) andstrawberry trees (Arbutus unedo) There isconsidenble evidence that malfuu vegetashytion is in part adapted to and in part aresponse to fire One efTeet of fire is toreduce the numbers of standard trees andto favour species which after burningsend up suckttS from ground level BothQJlercUI ita and Q1Iercus cocciera seemto respond to fire in this way A numberof species (for example Cistus albidllS

Erica arbona Pinu hlllepenJis) seem to

be encouraged by fire This may bc bccallS(it suppresses competing plants or perhapsbecause a short burst of heat encouragesgermination We have already noted thishappening in the chaparral of the southshywc=st USA an environment similar tomaluis (sce section 2 above)

Sinee premiddot agricultural times approxishymately one-fifth of the worlds forests havebeen lost The highest losses (about a thirdof the toul) have been in tcmperatc areasHowever deforestation is nO( an unstoppshyable or irreversible proceSS For examplea rebirth of forest has taken place in theUSA since the 19305 and 19405 Manyforests in developed countric=s are sJowlybut steadily expanding as marginal agrimiddotcultural land is abandoned This is hapshypening both ~causc of replanting schemesand because of fire suppression and conshytrol (see section 2 above) Also in somecases the extent and consequences ofdeforestation may have ~en exaggeratedA classic example of this is provided bythe mountains of parts of Nepal It was

34 The Biosphere

generally believed that rapid deforestationand changes in land use here had contrishybuted to higher flood runoffs floods soilerosion and increases in river sedimentloads The effects were thought to extendas far as the Ganges Delta in BangladeshA detailed study by Ives and Messerli(1989) however has cast doubt on thisargument by showing that little reductionin forest cover has taken place in theMiddle Mountains of Nepal since the1930

Many of the phenomena noted inNepal - flood runoffs soil erosion etc shymay be natural and inevitable consequencesof the presence of steep mountains rapiduplift by tectonic forces and monsoonalstorms Nonetheless the loss of moist rainforests in some of the worlds humid tropishycal regions is a very major concern Theconsequences are many and serious (tableII3) The causes are also diverse and inshyclude encroaching cultivation and pastorshyalism (including cattle ranching) miningand hydroelectric schemes as well as logshyging operations themselves

Views vary as to the present ratc of rainshyforest removal Recent FAO estimates(Lanly et aI 1991) put the total annualdeforestation in 1990 for 62 countries(representing some 78 per cem of thetropical forest area of the world) at 168million henares This figure is significandyhigher than the one obtained for thesesame countries for the period 1976-80(92 million hectares per year) Myers(1992) suggests that there has been an 89per cent increase in the tropical deforestashytion rate during the 1980s This contrastswith an FAQ estimate of a 59 per centincrease Myers believes that the annualrate of loss in 1991 amounted to about2 per cent of the total forest expanse

Plainly therefore rain forests whichMyers (1990) describes as these mostexuberant expressions of nature are underthreat A very significant proportion of

them will disappear in the next few decshyades unless some form of action is takento prevent this

Possible solutions to the tropical deforesshytation problem are as follows

bull research training and education to givepeople a better understanding of howforests work and why they arc imporshytant and to change public opinion sothat more people appreciate the usesand potential of forests

bull land reform to teduce the mountingpressures on landless peasants causedby inequalities in land ownership

bull conservation of natural ecosystems bysetting aside areas of rain forest asNational Parks or nature reserves

bull restoration and reforestation ofdamagedforests

bull sustainable development namely develshyopment which while protecting thehabitat allows a type and level of ecoshynomic activity that can be sustained intothe future with minimum damage topeople or forest (eg selective loggingrather than clear felling promotion ofnon-tree forest ptoducts small-scalefarming in plots within the forest)

bull control of the timber trade (eg by imshyposing heavy taxes on imported tropishycal forest products and outlawing thesale of tropical hardwoods from nooshysustainable sources)

bull rdebt-ormiddotnature swaps whereby debtshyridden tropical countries set a monshyetary value on their ecological capitalassets (in this case forests) and Iitetallytrade them for their internationalfinancial debt

bull involvement oflocal peoples in managingand developing the remaining rainforests

bull careful control of international aid anddevelopment funds to make sure theydo not inadvertently lead to forestdestruction

Deforestation 3S

Table 113 The consequences of tropical deforestation

Type of change

Reduced biological diversity

Changes in local andregiooal environments

Changes in global environments

Source Grainger (1992)

Examples

Species extinctionsReduced capacity to breed improved crop

varietiesInability to make some plants economic

cropsThreat to production of minor forest

products

More soil degradationChanges in water flows from catchmentsChanges in buffering of water flows by

wetland forestsIncreased sedimentation of rivers reservoirs

etcPossible changes in rainfall characteristics

Reduction in carbon stored in the terrestrialbiota

Increase in carbon dioxide content ofatmosphere

Changes in global temperature and rainfallpatterns through greenhouse effects

Other changes in global dimate due tochanges in land suriace processes

Thc situation is complex but it is alsourgcnt No simplc or singlc solution willbe adcquatc The time-bomb of ecologi-

FURTHBR READING

cal environmental climatic and humandamage caused by dcforestation continuesto tick (Park 1992 p 162)

Aiken S R and Leigh C R 1992 Vanishing Rainorens Their poundCologieRI Trlmsitionin Mallllysia Oxford Oxford University PressA case study from a threatened area

Gl2inger A 1992 Controlling Tropical DeforntatUm London EuthsanAn up-to-date introduction with a global perspective

Park C C 1992 Tropical Rainforuu London RoudedgeAnother relatively simple introduction to many aspccts of the rainmiddotforest environment

Williams M 1989 Americans anti their Fortm Cambridge Cmibridge UniversityPressA very fuU and scholarly discussion of the historical geography of American fomts

36 The Biosphere

n~anaging tropical rain forest In Cameroon

Cameroon in West Atiica is only 1ft

the 23rd largest country on the JhN

I continent but it contains the fitth r---------if---A---~I highest number of mammal md I p]lllt species as well as populations Loges

I of oer 40 globally thleUllled ani- ~I I 1 amp1 mals (Alpert 1993) It is pan of an f J ~+ (

illllJOrtant hlartland ofdiwrsit (on- -_ lllgt1 c~ II bull VIOImdP taining many endemic species III the

lowland forests of Clmeroon and - -somh-east Nigeria there aft oer8000 endemic plant spedcs as wdlas endemic animals such as theCameroon woolly bat (KfrivollfalUIscilla) Jnd pygmy squirrel(My(scillrtS pumifju) Lowland evergreen tropical loresr covers 34 per cenr ofrhecountry Sixty per cent of this total is classed as degraded and 4 per cent asprotected According to Stlfwys in the mid-1980s some 17 million hClrares havebeen ddorested out of an original area of neltlrly 38 million hectares In thedecade 1976-86 06 per cellt of the toral torest was lost each year

Plate 113 The landscape of Rumsiki Cameroon (Panos PicturesNictoriaKeblemiddotWilliams)

Deforestation 37

Figure 116 National parks and reselVes inCameroonSource After Kingdon (1990) pp 272-3

Exploitation of tropical forshyests in this part of Mrica hasgradually spread inland fromthe west coast Cameroonhas more forests left than anycoastal West Mrican countrybut less than any CentralAfrican country such as ZaireThe major cause of deforestashytion at me moment is fellingfOr fudwood and charcoal butmere are also increasing indusshytrial demands for timber andforest products Out ofa totalofover 14 million cu metres ofwood produced by Cameroonin 1989-91 more than 11million cu metres was roundshywood for fuel and charcoalHunting is also a major threatto animal life in the tropicalforests

Cameroon established lawsto manage and protect itstropical forests in 1981 Thislegislation decreed mat 20per cent of national territoryshould be designated as state forests Most of these are to be productive notprotected forests However several protected areas have been established withinthe forests an example is the Korup National Park which covers 1260 sq kmand has IS staff Maintenance is supported by the WFN (Worldwide Fund torNature)WWF (World Wildlife Fund) and other international bodies

Figure II6 illustrates the distribution of protected areas withill north-westCameroon many of which arc found in tropical forests At present forest reservesin Cameroon are poorly funded This may put their long-term protection at risk

Further reading

Alpert P 1993 Conserving biodiversity in Cameroon Ambia 22 44-8

Kingdon J 1990 bJRnd AfrieR The Evolution of Africa$ Rare AnimRu nndPlsmn London Collins

Williams M 1994 Forests and tree cover In W B Meyer and B L Turner(cds) O1aga in lAnd Use and LAnd CoP A Global Penpectipe 97-124Cambridge Cambridge University Press

38 The Biosphere

5 ThOPICAL SECONDARY

FOREST FORMATION

The clearance cultivation and subsequentabandonment of forests in the moist tropshyics has resulted in the development ofincreasing expanses of what is called secshyondary forest In a large and steadilyincreasing proportion of the tropics secshyondary forests make up most or all of theremaining forest

It is difficult to define precisely what wemean by secondary forest Some foresterswould define it as a type of forest thathas suffered some form of disturbance asa result of human actions This could beslight (eg hunting of animals or collecmiddottion of foodstuffs) or massive (eg clearfclling) Other forestcrs believe it is nowuseful and logical to restrict the use of theterm secondary forest to describe forestthat has regrown after clearance

Secondary forest development is oneconsequence of the practice ofshifting culshytivation Peasant farmers clear small plotsof just a few hectares cultivate them for afew years and then abandon them whensoil fertility and crop yields decline Theabandoned plots are then colonized byherbs shrubs and a canopy of pioneertrees This kind of tree grows rapidly needsa lot of light and has low-density woodand sparse branching These trees are typishycally short-lived with life-spans of one ortwO decades There are not many differshyent species As the process of successioncontinues the forest progressively apshyproaches its primary state However it maylake 500 years or even longer for the forshyest to recover its full diversity of species

Exactly how the forest recovers willdepend on the degree of initial disturbanceTraditional shifting cultivation employsonly small plots so that recolonization

Plate 114 Tropical secondary forest and slash-and-burn fields in the rainforestzone of Ghana (Rod Mcintosh)

from neighbouring primary forest is relashytively easy Whtn larger areas are clearedor when prolonged cultivation and freshyquent burning takes plate (leading tosevert soil degradation) the process willbe much slower However on sites whichhave not been seriously damaged thebiomass of leaves and fint roots (thoughnot total biomass) is restored to that ofprimary forest within as little as five to ten

FURTHER READING

Grasslands and Heathlands 39

years by which time net primary producmiddottion (NPP) is equal to or greatcr thanthat of primary forest Thus secondaryforest is probably highly effective at promiddotviding what are called laquoosystem Krvices- that is at preventing soil erosion andregulating runoff It also has some consershyvation value in that it provides a refugtfor some forest fauna and a habitat forsome Aora

Corlett R T 1995 TropicaJ secondary forests Progress in Physical Geography 19 159-72

Ellenberg H 1979 Mans influence on tropical mountain ecosystems in South AmericaJournal of ampoloDY 67 401-16

6 GRASSLANDS AND

HEATHLANDS

THE HUMAN ROLE

In the highlands of Africa there are largeareas of what are called AfTomontaneGrasslands Thty extend as a series ofismiddotlands from the mountains of Ethiopia tothose of the Cape area ofSouth Africa Arethey the result mainly of forest clearanceby humans in the recent past Or are theya long-standing and probably namral comshyponent of the pattern ofvegetation (Meadshyows and Linder 1993) Arc they causedby frost seasonal aridity excessively poorsoils or an intensive fire regimd This isone of the great controversies of Africanvegetation studies

Almost certainly a combination of facshytors has given riK to thesc grasslandsOn tht one hand currtnt land manageshyment pralaquoicts including tht usc of fireprevent forest from expanding Thtre hasundoubtedly been extensivt defortstationin recent centuries On the other handpollen analysis from various sites in southshytm Africa suggests that grassland waspresent in the area as long ago as 12000BP This would mean that much grassland

is not derived from forest through veryrtcent human activities

Similar argumtnts relate to many othtrof the worlds grtat areas of grasslandConsider for example the savannas oftropical rtgions which covtr about 18million sq km Grasses and sedges makeup most of the Vtgttation in savannaalthough woody plants arc present invarying proportions As with mOSI maorvegetation types a large number of intershyrelated factors are involved in causingsavanna It is important to distinguish clearlypredisposing causal resulting andmaintaining factors For instance aroundthe periphery of the Amazon Basin itappears that the climate predisposes the vegshyetation toward the development ofsavannarather than forest Tht geomor-phologicalevolution of the landscape and the formashytion of heavily leached old trosion surmiddotfaces may Ix a muml factor increaKdlaterite (iron crUSt) development a nIultshyinB factor and fire a maintaining factor

Originally savanna was belitved to bea predominandy natural vegetation typedevdoped to suit particular climatic conmiddotditiaRS (figure II7) It was thought thatsavanna is bentr adapted than other

40 The Biosphere

DtfOI~$tation

Dtsrrtifimion

Grudaflls

Aridshrubshygrlllslaoos

PrectpitatiOll

Figure 117 An idealized relationbetween the biomass density andproductivity of five major vegetationtypes (biomes) and precipitation Asprecipitation increases so doesproductivity and therefore biomasswith the two extremes being the lowsparsely shrubbed grasslands of thedeserts and the tall dosed forests bethey tropical temperate or borealSource Graetz (1994) pp 125-47

plant formations to cope with the greatfluctuations in rainfall during the year inthe seasonal tropics Rain torests could notresist the long wimer droughts while dryforests could not compete successfully withperennial grasscs during the lengthy periodof water surplus in the summer months

Other workers havc emphasized the imshyportance of edaphic (soil) conditions Theyargue that the development of savanna isencouraged by poor drainage soils witha low water-retention capacity in the dryseason soils with a shallow profile due tothe development of a lateritic crust andsoils with a low nutrient supply This lastcondition may arise because the soil hasdeveloped on a nutrient-poor parent rocksuch as quartzite or because the soil hasundergone an extended period of leachshying over millions ofyears on surfaces which

have been exposed to the elements for allthat time

A third group of researchers take theview that savannas are the product of drierconditions in former times such as thelate Pleistocene In spite of a moisteningclimate in the Holocene the savannas havebeen maintained by fire They point tothe fact that the patches of savanna insouthern Venezuela occur within areas offorest where the levels of humidity andsoil infertility are similar This suggests thatneither soil fertility nor drainage norclimate can be pinpointed as the cause ofsavanna Moreover the present islandsof savanna contain plant species which arcalso present elsewhere in tropical Amerishycan savannas This suggests that the isshylands were once part of a much largercontinuous expanse of savanna

The importance of fire in creating andmaintaining some savannas is suggested bythe fact that many kinds of tree that growin savanna are fire-resistant Controlledexperiments in Africa demonstrate thatsome tree species such as Burkea africanaand Lophira lanceoMa withstand repeatedburning better than others It has also beennotld that for example African herdsmenand agriculturalists frequently use fire overmuch of tropical Africa to maintain grassshyland Certainly the climate ofsavanna areasis conducive to fire

Some savannas are undoubtedly naturalPollen analysis in South America showsthat savanna vegetation was present beforethe arrival of human civilization Noneshytheless even natural savannas change theircharacteristics when subjected to humanpressures For example many studies fromwarm parts of the world have shown thatgrass cover cannot maintain itself underheavy grazing pressure Heavy grazingtends to remove the fuel (grass) from muchof the land surface This means that fireshappen much less often allowing trees andbushes to invade the savanna

Grasslands and Heathlands 4)

Plate 115 Savanna landscape in the west Kimberley region of northmiddotwesternAustralia The use of fire may be important in controlling both the nature and thedistribution of this extensive biome type (A S Goudie)

Whatever the fac[Ors that determine theorigin of savannas there arc others thathelp to determine some of their particularcharacteristics One example we can giveof this is the role of elephantS in Mricansavannas We do this partly because it isa good illustration of the interdependenceof vegetation and animals and partly bcshycause if elephant numbers arc reduced byhuman prcssures then the whole charaC[crof the savanna ecosystem may change Eleshyphants arc what is known as a keystonespecies because they cxert a strong influshyence on many aspects of the environmentin which they live They divcrsify the ecoshysystems which they occupy and create amosaic of habitats by browsing tramplingand knocking over bushes and trees Theyalso disperse seeds through their eatingand defecating habits and maintain orcreate water holes by wallowing All these

roles arc of benefit to other sptcies Conshyversely where human interference prcvcntsekphants from moving freely within theirhabitats and leads to their numbers exceedshying the carrying capacity of the slvannatheir etTen can be environmentally catamiddotstrophic Equally ifhumans redme dephuInumbers in a particular piece ofsavanna thesavanna may become less diverse and lessopen and its water holes may silt up Thiswill be to the detriment of other species

The mid-latitude grasslands (the prairiesof North America for example) are also thesubject of controversy as to their originsAs we discussed in section 2 above on firethere has been a debate as to whether theprairies arc ~ntially the result of lowprecipitation and high evapotranspirationlevels or whether they result from fires

Hcathland is another fascinating vegetashytion type It is characteristic of temperate

42 The Biosphere

oceanic conditions on acidic substratesIt is composed of cricoid (or heather-like)low shrubs which form a closed canopyat heights usually less than 2 metres Treesand tall shrubs are either absent altogetheror scattered Some heathlands are naturalThese include areas at altitudes abovethe forest limit on mountains and thoseon exposed coaSts There are also wellshydocumented examples of heathlands whichappear naturally in the course of plantsuccession This can happen for examplewhere Catuna vulgaris (heather) replacesgrasses like Ammophila arenana and CR-rexarenana on coastal dunes

However extensive areas of heathlandalso occur at low and medium altitudeson the western fringe of Europe betweenPortugal and Scandinavia The origin ofthese heathlands is strongly disputed Somewere once thought to have developedwhere there were appropriate edaphicconditions (for example well-drainedloess or very sandy nutrient-poor soils)but pollen analysis showed that mostheathlands occupy areas which were forshymerly tree-covered This evidence alone didnot settle the question whether the changefrom forest to heath was more likely tohave been caused by Holocene climaticchange or by human activity Howevertwo other factors suggest that humanactions established and then maintained

FURTHER READING

most of these heathland areas The first ofthese is the presence of human artefactsand buried charcoal the second is the fuctthat the replacement of forest by heathhas occurred at many different times beshytween the Neolithic and the late nineteenthcentury Fire is an important managementtool for heather in locations such as upshyland Britain since the value of CalJuna asa food for grazing animals increases if it isperiodically burned

The area covered by heathland in Westmiddotern Europe reached a peak around 1860Since then there has been a very rapiddecline Reductions in Britain averaged 40per cent between 1950 and 1984 and thiswas a continuation of a more long-termtrend In England the Dorset heathlandsthat were such a feature of Thomas Harshydys Wessex novels are now a fraction oftheir former size There are many reasonsfor this decline They include unsatisfacshytory burning practices the removal ofpeatdrainage fertilization replacement by immiddotproved grassland conversion to forest andthe quarrying of sand and gravel

Thus human activities over a very longtime can combine with natural changesboth to produce and to remove grasslandsand heathlands Many scientific debates arccontinuing on how such plant communshyities react to stress The box opposite givesan example from Australia

Gimingham C H and de Schmidt I T 1983 Heaths and natural and semi-naturalvegetation In W Holzner M J A Werger and I Ikusima (eds) Mtms Impact onVegetation 185-99 The Hague JunkThe best general review of the worlds heathlands

Harris D R (cd) 1980 Human Ecology in SRPanna Environments London Acashydemic PressA useful collection of papers on savannas in their human context

Grasslands and HeathJands 43

Recent human impacts on subalpine grassland andheathland in Victoria Australia

C]lndllYfflooornbullCattle grazing began in the 1850sin the Bugong High Plains alpinegrassland in what is now the Victoshyria Alpine National Park (created in1980) Eer since there have beendehates over the degradation ofgrassland and soil erosion In 1939there were disastrous hush fires heremd in the 19405 soil erosion beshycame very Knous u stock numbersincreascd Since the 1950$ there hasbeen an overall decline of about 60per cent in both stock numbers andthe area graud and by 1991 onlyabout 3100 cutle were grazing thearea benvc-en December and April

These changes in grazing densishyties have been echoed by an incretse in the area of shrub cover In 1945 pershymanent study plou were established by ecologists to monitor the changing vegshyetation cover on grazed and ungrazed land The rlaquoords produced from theseplots over five decades enab]( scientists today to test the relationship benveengrazing fire and the maintenance of grassland (Wahren et al 1994) It hu beensuggested that cattle grazing reduces shrub cover (therefore maintaining grassshyland) and also fire risk But the Bugong study docs not back this up as grazedplots have more bare patches than ungrazed (Ke table IlA) although by 1994old shrubs on some ungraud plots were beginning to die back In this areaalpine vegetation seems slow [0 recover after dislUrbance (such as fire) and evenslower where grazing is present

Table 114 Comparisons of percentage cover of different vegetation on grazed andungrazed grassland plots Bugong High Plains Victoria Australia 1982-1994

Cover 1982 1982 1989 1989 1994 1994dassmiddot Ungrazed Grazed Ungrazed Grazed Ungrazed Grazed

1 76 53 71 61 66 722 21 31 24 20 31 173 3 16 5 19 3 10

bull Cover class 1 = thick litter and dense vegetationCover class 2 thidc or thin litter sparse vegetationCover class 3 thin litter sparse to no vegetation

Source Adapted from Wahren et al (1994)

44 The Biosphere

7 TEMPERATE FORESTS UNDER

STRESS

Forest decline is an environmental issuethat came to the fore in the 1980s It hasmany symptoms including the discolorashytion and loss of needles and leaves reshyduced rates of grovlth abnormal growthforms and in extreme cases tree death

Germany is probably the Europeancountry most seriously affected by lorestdedine In 1985 55 per cent of the foreststands in West Germany were reponedto be damaged The decline is howeverwidespread in much of Europe (see tables115116) The process is now also undershymining the health of eastern NorthAmericas high coniferous forests In Gershymany it was the white fir Abies alba whichwas afflicted initially but since then the

symptoms have spread to at least ten otherspecies in Europe induding Norwayspruce (Picea abies) Scots pine (Pinussylvestris) European larch (Larix decidu)and seven broad-leaved species

In 1982-3 the German governmentadopted a comprehensive clean air legislashytion package However the data presentedin table II6 indicate that German forestsarc still suffering from decline In 1994at the Oslo international meeting Gershymany agreed to reduce sulphur emissionsby 83 per cent (from 1980 levels) by 2000In 1986 the Federal Environment Minisshytry concluded that there is no single typeof forest damage and no single cause Wearc dealing with a highly complex pheshyn0l111non which is difficult to untangle andin which air pollutants playa decisive rolc

Many suggested explanations for thisdieback have been put forward They

Table 115 Reported percentage of different tree species affected by forest declinein West European countries 1984

Species W Germany E France Switzerland Austria Italy (5 Tyrol)

Norway spruce 51 16 11 29 16Silver fir 87 26 13 28 35Scots pine 59 17 18 30 6Beech 50 3 8Oak 31 6 9Others 31 6 9

Source Goudie (1993)

Table 116 Results from German forest damage surveys 19B6-1993 percentage oftrees in classes 2-4 (ie defoliationgt 25) for all species

Area 1986 1987 1988 1989 1990 1991

EG 138 164 359WG 189 173 149 159 159G 252

bull EG = former East GermanyWG = former West GermanyG = Germany after reunification

Source Acid News 1995

1992 1993 1994

260 242 244

includ~ poor for~st manag~m~ntpracticesag~ing of strnds climatic chang~ sev~re

climatic events (such as the sev~re sumshym~r droughts in Britain during 1976 and1995) nutri~nt d~fici~ncy viruses fungalpathogens and pest infestations Howeverparticular attention is being paid to therol~ of pollution This may tak~ variousforms including gaseous pollutants suchas sulphur dioxid~ (SOl) nitrogen oxides(NOx) or ozone acid deposition on kav~s

and needles soil acidification and the assoshyciat~d probl~ms of aluminium toxicity and~xc~ss kaching of nutri~nl$ (for ~xampl~

magnesium) over-fertilization by d~posit~d

nitrog~n and the accumulation of trac~

metal or synth~tic organic compounds (~g

pesticides or herbicides) as a r~sult ofatmosph~ric d~position

In many cases forest d~clin~ may miuhfrom a combination of Strcsscs For ~X2m-

T~mpcrat~ For~sts und~r Str~ss 45

pk long-term climatic chang~ may cr~at~

a pmtisposing stTtSS (see pan I section 6)which ov~r a long period weakens a treesability to resist other forms of str~ss Thenth~r~ ar~ ineiling SlnJJeJ that operat~ overshort~r rime-spans for exampk droughtS(v~r~ frost or a short-li~d pollution ~pishy

sod~ These damage trees that are alr~ady

weaken~d by the predisposing str~sses

Thirdly w~ak~ned tr~~s ar~ then morepron~ to a scri~s of contributing SlrelJes(eg attack by insect pests or root fungi)

There may also be different causes indifferent ar~as Thus widespread for~st

death in Eastern Europe may r~sult fromhigh concentrations of sulphur dioxidecombined with extr~me winter stress Thisis a much less likely ~xplanation in Britainwh~r~ sulphur dioxide concentrationshav~ shown a mark~d d~cr~~ in r~c~nt

years Indeed Innes and Boswell (1990

Plate 116 Acid rain damage at Szkalrska Poreba south-west Poland Much ofthe pollution here comes from the burning of low-quality coals and lignites inGermany and the Czech Republic (Richard Baker Katz Pictures)

Figure 118 Estimates of total quantityof de-icing salt purchased annually inmainland Britain during the period1960-1991 Arrows represent yearswhen significant crown dieback ofLondon plane has occurred In the early1960s highway departments changedfrom using saltabrasive mixtures tousing pure rock salt This may accountfor some of the increase in salt usageSource Dobson (1991)

Ivgt with many environmental problemsinterpretation of forest decline is hamperedby a lack of long-term data and detailedsurveys Forest conditions vary fromyear to year in response to fluctuations inclimatic stress (eg drought frost windthrow) This means that it is dangerousto infer long-term trends from short-termdata (Innes and Boswell 1990) The probmiddotlem may well have been exaggerated inthe 1980s by some observers who fJiled to

recognize that stressed trees may be a morenormal phenomenon than they believed

46 The Biosphere

p 46) suggest that the direct effects ofgaseous pollutants in Britain appear to bevery limited

It is also important to recognize thatsome stresses may be especially significantfor a particular tree species In 1987 asurvey of ash trees (Fraxinus excelsior) inGreat Britain showed extensive diebackover large areas of the country Almostone-fifth of all ash trees sampled wereaffected Hull and Gibbs (1991) identifieda link between dieback and the way theland is managed around the tree Theynoted particularly high levels of damagein trees next to arable farmland They sugshygested this might be associated with unmiddotcontrolled stubble burning the effects ofdrifting herbicides and the consequencesof excessive nitrate fertilizer applicationsto adjacent fields However the primecause ofdieback was seen to be the disturshybance of tree roots and the compaction ofthe soil by large agricultural machineryAsh has shallow roots if these are damshyaged repeatedly the trees uptake of waterand nutrients might be seriously reducedBroken root surfJces would be prone toinfection by pathogenic fungi

Trees growing alongside roads which arcregularly salted to reduce ice problems incold winters may also become damagedThis may be a growing problem becausethe use of salt on roads has increased inrecent years (figure 118)

FURTHER READING

II I I II

Boehmer-Christiansen S and Skea ] 1991 Acid Politics Environment and EnergyPolicies in Britain and Germany London Belhaven

Innes ] 1 1992 Forest decline Progress in Physical Geography 16 1-64An impressive overview of the competing hypotheses that have been put forward toexplain forest decline

Schulze E-D Lange O L and Oren R 1989 Forest Decline and Air PollutionEcological Studies no 71 New York Springer-Verlag

Templ=rate FOrc5ts under Stress 47

Forest decline in Bavaria Germany

I AVARIA (--

--MwBdIbullhypotheses have been

to explain the apparent

Forest decline in Germany became amajor environmental issue during the1980s Many conifers and broadshyleaved trees showed signs of Stressranging from yellowing of needlesto death In the mountains of theFichtelgebirge in north-east Bavariamost forests at altitudes over 750metres currentlyshow signs ofdcdincBy 1986 30 per cent of Bavarianforests were cla~d as moderatelyor seriously damaged by unknownfactors

Severaladvanceddecline

bull natural climatic causes andepidemics

bull direct effects of air pollutionbull mineral deficiency and imbalances as a consequence of acid deposition and

soil acidificationbull a combination of some or all of the above factors

The forests in Bavaria grow on acid poor soils above granite and metamorphicgneiss and schist bedrocks In the sixteenth century beech was the major speciesBeech and sycamore together accoumed for 60 per cent of the canopy and firformed the remaining 40 per cent Over the following 400 years the forests weredepleted by mining smelting and agriculture During the ninetccnth centuryreforestation took place producing a difierent mix of trees Now there an~ 96 percent spruce 2 per cent beech and 1 per cent fir (Schulze et aI 1989)

During the twentieth century episodes of ozone sulphur dioxide and nitrogenoxide pollution have been very $Cvere It now appears that air pollution coupledwith a past history of polluted air and planting is a major problem lor these verysensitive forests Much of the pollution occurs in winter and comes trom steeland chemical industries and power plants in eastern Germany and the CzechRepublic The effects of air pollution are compounded by mble winter air conshyditions which encourage temperature inversions and the production of smogAmmonia produced by nearby cattlc and other Iarmed animals also adds to thenitrogen pollution

bull

bull

48 The Biosphere

8 URBAN ECOWGY

The world is becoming increasingly urshybanized In 1980 here were 35 cities withpopulations of over 4 million by 2025135 cities will probably have reached hissize Over the period 1950-90 the totalpopulation of the worlds cities has in~

creased tenfold and is now more than 2billion Cities thus contain around half theworlds population They also contributemost global pollution Funhermore urbanpopulations are concentrated into a rela~

tively small area for example only 34 percem of he Iand in the USA is urbanizedThis makes the urban impact upon theenvironment even more imense

The impacts ofurban areas on the envicshyonmem and ecology can be devastatingProblems have been felt for a long timein many countries where industrial citiesdeveloped early In many less developedcountries huge expansion in populationhas occurred relatively recently leading to

burgeoning environmental problemsWhat impacts do cities have 011 the

environment And how do these affectecology Cities do all of the following

bull produce a major dem3nu tor naturalresources in the surrounding arC3

bull obliterate the llatur3l hydrological sysshytem on the site of the dtyreduce biolll3SS and alter the speciescomposition 011 the site of thl cityproduce waste products which canalter the environment in and aroundthe city

bull create new land through reclamationand landfill

Together these impacts make up theecological footprint of a city that is thearea affected by pollution resource extracshytion devdopmem and transport causedby the city irsclf Cities demand raw matershyials such as tim bet coal and oil these must

be extracted from the surrounding areaor transported into the city They alsorequire agricultural products energy andlabour As the variow parts of the worldbecome increasingly interconnected theecological footprints of major cities beshycome bigger and bigger This means thata vast proportion of the Earths surface isbeing sucked intO the urban system oneway or another

On he site of cities the entire entershyprise of urbanization leads to dnsticchanges in geomorphology climate h)liroshylogy and ecology Urbanization is oftenseen as evidence of societys success intaming and overcoming nature Increasshying urban pollution problems howevetshow that this success has been limitedCities replace natural foteSts grasslandand other vegetation with vaSt swathes ofconcrete brick and nrmac as well as garshydens parks ponds and derelict land Thesechanges in vegetation rebound upon anishymal life they also affect the hydrologicalresponse Trees grassland and the soilsin which they grow act as butTers slowingdown the movement of water through adrainage basin As explained more fully inpart IV section 4 urbanization reducessuch butTers It acce1ciltes and streamlinesthe flows of water by reducing the diffuseflow below the land surface and replacingit by flows over the surtacc lnd throughpipc=s

Species diversity may be increased incities despite the great disruption causedby building work Gardens parks pondsand street plantings introduce a range ofexotic plants The urban climate also enshycourages growth and diversity favouringspecies which tolerate wanner 1css variableconditions than those found in neighbourshying rural areas The urban environmentalso produces behavioural changes in manyanimals For example animals which usushyally hibernate in winter in temperate counshytries can live normally throughout the year

Urban Ecology 49

Plate 117 A kestrel sitting on a street lamp in a British city These raptors andmany other organisms have proved their ability to adapt to the urbanenvironment (NHPNMichael leach)

in large cities where there is year-roundwarmth and food Street lighting confusesbirds and extends the hours of daylightfor them The vast amount of waste tOadfound in urban areas encourages scavenging animals such as racoons and foxesMany urban-dwelling species have nowcome to be regarded as pests Pigeons inmany British and American dty centres arean example their droppings arc a greatnuisance Many species arrie in cities alongrivers and canals Communications nctshyworks in general provide a major route formany animals and plants seeking to coloshynize new areas In Britain for examplemink which have escaped from fur farmsare now found on urban riverbanks inOxford

On the other hand the pollution anddereliction present in many citia depletethe ecology High levels ofsulphur dioxide

in the atmosphere for example kill offlichen species growing on trlaquo bark Manytrees themselves a~ threatened by air andsoil pollution Similarly urban and indusshytrial pollution of aterways depletes theaquatic ecology For example in Shangmiddothai China the Huangpu River is nowthought to be biologically dead as a resultof the 34 million cu metres of industrialand domestic waste dumped in it each daySome derelict land is highly contaminatedwith heavy metals and Other toxins thwmaking recolonization impossible Howshyever other derelict land areas provideopportunities for wildlife colonizationand conservation In Britain large areas ofurban allotments (small plots ofland rentedout for domestic food production) are nolonger cultivated and native and exoticspecies are colonizing the abandoned land

Increasingly city dwellers are becoming

50 The Biosphere

committed to improving the ecology ofcities A range of strategies is employed

bull reducing poUution to encourage desirshyable organisms to return

bull removing undesirable species throughcareful extermination programmes

bull reducing the use of lawn fertilizers andpesticides

bull planting trees in streetSbull cstablishing urban nature reserves city

forests and conservation areasbull undertaking backyard compostingbull developing urban farms thus bringing

food production back into cities

Such schemes are part ofa general trendtowards improving the urban environmentthrough managing pollution and immiddotproving stmdards of housing and healthSustainable development of cities is apopular phrase at prescnt However vastdisparities in wealth between inhabiuntsof different cities and between differentparts of anyone city make the goal ofsustainability hard to reach In manydeveloping countries squatter settlementson the outskirts oflarge cities are growingat an alarming rate as more and more poorinhabitants of outlying rural areas are atshytracted to the opportunities in cities These

FURTHER READING

settlements arc very destructive of theenvironment and also severely affected byenvironmental poUution and hazards Theyusually grow up on land which is dereUetbecause it is least suitable for developmentThey lack even basic services such as elecshytricity or running water Trees arc removedso that dwellings can be put up on steeptropical hillslopcs this can result in accelshyerated landslides (see part V section 6)Wastes produced in squatter settlementscannot be removed effectively because ofthe lack of sanitation and services Thiscauses pollution of land air and watermiddotcourses In South Africa for exampleSoweto (which has a population of around25 million according to some estimates)has horrendous air poUution from sulphurdioxide produced by coal burning becausethe electricity supply is completely inadshyequate The natural ecology has beenwiped out and human health is suffering

All round the world it is clear thatthe ecological impacts of cities are justone manifcstation of a deep problem withpresent-day urbanization A5 RichardRogers the architect put it in 1995 Inthe beginning we built cities to overcomeour environment In the future we mustbuild cities to nurture it

Bridgman H Warner H and Dodson J 1995 Urban Biophysical EnvironmentsMelbourne Oxford University PressA concise introduction with an Australian flavour

Hardoy J E Midin D and Satterthwaite D 1992 Environmental Problems inThird World Cities London u([hscanLike most Earthscan books this provides a clear introduction to the crucial issuesaccompanied by many short case studies

White R 1994 Urban EinmmentRI MRn4gement Chichester WdcyA modern general trcaonent of how city environments can be managed

Urban Ecology 51

Chicagos changing vegetation

CANADA

USA

In the 1840s ~fore urban development really began the flat gladated plainnext to Lake Michigan in the USA was dominated by natural forest and prairievegetation (figure 119) Low prairie grasslands occupied most of the area Deshydduow forests of oaks (such as the Bur oak Q4ercllS mlicroclirplI) ashes andcIms were common on sand ridges and the edges of streams By 1860 thepopulation of Chicago city had riscn to 50000 and by 1990 the metropolitanarea conDined over 8 million people

This urban explosion has been accompanied by an almost total loss of naturalvegetation apart from some large tracts designated as forest prescrves Severaldirect and indirect cawes of this loss of natural vegetation can be recognized Thefirst direct causc is the dearing of land for development Interestingly howeverindividual trees survived some trees identified in the 18305 by the original landsurveyors were still present in the 19705 (Schmid 1975) Studies of the forestvegetation in and around Chicago show that removing the dosed canopy bycreating clearings for building favours trees which cope well in the drier andlighter conditions (such as Bur oak) Other moisture-loving species such assugar maple and red oak suffer Indirectly construction has disturbed the soilsaffecting particularly trees such as red and white oaks Oil spills gas leaks thesalting of icy roads and digging to lay pipes have all had direct impacu on naturaland introduced vegetation in some parts of the dry

New kinds of trees and other vegetation have been introduced into ChicagoThcsc incorner species have had a key impact on the citys vegetation They havealso suffered from the urban environment Interestingly there has been an inshycrease in the proportion of Chiago covered by trees since urbanization This isbecause trees have been planted on upland sites which would naturally have beendominated by prairie

52 The BiosphereJ

~1lt1- N -

t laquo

-

-

WISCONSIN W

Midip~ _MOUIhoflht-------------

f~ ChialBo Riou

ILUNOlS ~ ------ rr ~tI

Chicago ~

INDIANA -

1l- - -~~

~

bull bull U U Range

Figure 119 The distribution of forest (black) and prairie (white) in theChicago region during the 1840s as recorded by the General land SurveySections formed by the townshiprange grid are 1 mile squareSource Schmid (1975) figure 3

Air pollution has had an indir~ct ~ff~ct on veg~tation In 1913 a study foundthat trees in Chicago near th~ railway stations w~re aff~ct~d by smoke and th~

vegetation around sted mills was reduc~d to a f~w w~~dy annuals Mor~ recentlythe mainly d~ciduous tr~~s in Chicago have shown much less damag~ from airpollution than th~ ev~rgreens in other North American cities A much moreserious ~vent for the urban vegetation of Chicago was the outbreak of Dmch elmdisease from the late 1950s Until 1950 American elm was the most commonlyplanted tree species her~ Dutch elm disease destroyed the great majority of them

Housing brings grass and shrubs planted for decorative purposes in gardensChicago residents especially in the wealthy suburbs have planted many exoticshrub and herb species but few native ones Of the native plants opportunisticherbs from flood plains have been the most successful These plants thrive onwasteland and abandoned plors The vegetation pattern of Chicago is now con-trolled by economic social and cultural factors The number and mix of speciesnow vary according to the age and social characteristics of different neighbour-hoods Natural ecological factors are no longer so important as they were

-

ltshyi

9 WETLANDS ThE KJDNEYS

OF THE LANDSCAPE

In th~ 19805 w~tlands becam~ a lOpic ofgr~al ~nvironm~nral conc~rn Th~y w~r~

pcrcdv~d to be vitally important ~cosysshy

t~ms as is mad~ dear in the followingintroductory remarks to Mitsch and Gosseshylinks pione~ring book WetlandJ

Wetlands are among the most imporshytant ecosystems on the Earth In thegreat scheme of things it was theswampy environment of the Carbonifshyerous P~riod that produced and preshyserved many of the fossil fuels on whichwe now d~pend On a much shortertime scale wetlands are valuable assources sinks and transformers of amultitude of ch~mical biological andg~netic materials Wetlands are someshyrimes described as the kidneys of thelmdsca~ for the functions they rtr-

Table 117 Threats to wetlands

W~dands 53

form in hydrologic md chemical cycl~s

and as the downstream rec~ivers ofwast~s from both natural and humansources Th~y have been found tod~anse pollut~d waters pr~middot~nt floodsprot~ct shor~lin~s and rechargegroundwat~r aquif~rs Furthermoreand most important to som~ w~tlands

play major roles in the landscape byproviding unique habitats for a widevariety of flora and fauna While thevalues of wetlands for fish and wildlifeprotection have be~n known for severaldecades some of the other benefitS havebeen id~ntified more rec~ndy (MitSchand Gossdink 1986 p 3)

W~t1ands arc also percdvcd to be underthreat mOSt notably from draining ditchshying dredging filling pollution and chanshyn~lization According to some sources theworld may have lost halfof all itS wetlandssince 1900 md the USA alone has lost54 rtr cent of its original w~t1and area

Human Indirect

Source Type

Human Direct

Examples

Drainage for crops timber mosquito control

Dredging and stream channelization

Filling for waste disposal and land claim

Construction of dykes dams and sea walls forflood control and storm protection

Discharge of materials (eg pesticides nutrientsfrom sewage sediments) into waters and wetlands

Mining of wetland soils for peat coal gravel andother minerals

Sediment diversion by dams and other structures

Hydrological alterations by canals roads etc

Subsidence from extraction of groundwater oiletc

Natural Direct and indirect Subsidence (including natural rise of sea leve)droughts hurricanes and other storms erosion andbiotic effects

Sourc~ Adapted from Maltby (1986) p 92

54 The Biosphere

Table 118 Wetland terms and types

Name Definition

Swamp Wetland dominated by trees or shrubs (US definition) InEurope a forested fen (see belowgt could easily be called aswamp In some areas wetlands dominated by reed grassare also called swamps

Marsh A frequently or continually inundated wetland characterizedby emergent herbaceous vegetation adapted to saturated soilconditions

Bog A peat-accumulating wetland that has no significant inflowsor outflows and supports acid-loving mosses particularlySphagnum

Fen A peat-accumulating wetland that receives some drainagefrom surrounding mineral soil and usually supports marshlikevegetation

Peatland A generic term for any wetland that accumulates partiallydecaying plant matter

Mire Synonymous with any peat-accumulating wetland (Europeandefinition)

Moor Synonymous with peatland (European definition) A highmoor is a raised bog while a low moor is a peatland in abasin of depression that is not elevated above its perimeter

Muskeg large expanses of peatland or bogs particularly used inCanada and Alaska

Bottomland

Wet prairie

Reed swamp

lowlands along streams and rivers usually on alluvialfloodplains that are periodically flooded

Similar to a marsh

Marsh dominated by Phragmites (common reed) term usedparticularly in Eastern Europe

Source Modified from Gleick (1993) table F1

primarily because of agricultural developshyments The pressures on wel1ands are listedin table 117

What precisely are wel1ands~ There isno single Wliversally recognized definitionbecause they take a variety of forms andoccur in a considerable range ofconditions(table IIB) However Maltbys (1986)definition is a useful one He defines wet-

lands as ecosystems whose formation hasbeen dominated by water and whose proshycesses and characteristics are largely conshytrolled by water A wetland is a place thathas been wet enough for a long time todevelop specially adapted vegetation andotherorganismsbull Wetlands therefore includeareas ofmarsh mire swamp fen peatlandor water whether natural or artificial per-

Wetlands 55

HlQIWATEl

Figure 1110 Diagram showing the hydrological and ecological characteristics ofwetlands which act as ecotones between dry terrestrial ecosystems andpermanently wet aquatic ecosystemsSource Mitsch and Gosselink (1986) figure 14

manent or temporary The water may lxstatic or flowing fresh brackish or saltyincluding marine water whose depth at lowtide does not exceed 6 meues

Wetlandscoversignificant areas In all theyaccount for about 6 per cent of the Earthsland surface This is not much less than theproportion orland under uopicaJ rain forestThey also account for as much as a quarterafthe Earths total net primary productionNotable wetlands include the Evergladesin Florida the Sudd and Okavango swampsof Mrica the Fens and Broads of EastAnglia in England and the mangroveswamps of South and South-East Asia

Wetlands are what are known as ccotonesthat is transitional zones They occupythe transitional space bt=tween largely dryterrestrial systems and deep-water aquaticsystems (figure 1110) This transitionalposition in the landscape allows them toplay valuable roles for example as nutrientsources or nutrient sinks It also causesthem to have high biodiversity for theyacquire and contain species from bochterrestrial and aquatic systems

Why are wetlands important and deservshying of careful management Because

bull they are fertile and highly productiveecosystems

bull they support fisheries of great valuebull they absorb and store carbon which has

implications for the greenhouse effectbull they sift dissolved and suspended mashy

terial from floodwaters thereby cncourshyaging plant growth and maintainingwater quality

bull they absorb and store floodwater(thereby mitigating flood peaks) andaCI as barriers against storm surgesetc

bull they are vital breeding and nurserygrounds for waterfowl animalsand plamsand provide refuges in times ofdrought

bull they provide staple food plams(eg rice)bull they provide fuel (eg peat)bull they provide building materials (eg

mangrove wood reeds for malch etc)bull they have recreational uses

Because of the great value of wetJands in 1971 many countries signed the Conshyvention on Wedands of International Imshyponance especially as Waterfowl HabitatAs this was signed at Ramsar in I~ it isotien more eonveniendy known as the

56 The Biosphere

Plate 118 The Niger River of West Africa creates a great wetland itsso-called inland delta This photograph shows an area flooded by the annualinundation near Jenne Mali (Rod Mcintosh)

Ramsar Convention Those states that havesigned the Convention which now amountto over 90 agree to designate at least oneof their national wetlands for inclusion ina List of Wetlands of International Imshyportance They also agree to formulateand implement their planning so as topromote the conservation of the wetlandsincluded in the List to establish wetlandnature reserves and to co-operate in themanagement ofshared wetlands and sharedwetland species

FURTHER READING

International collaboration is ofcourseessential It is no use conserving a wetlandin one country to provide a refuge forspecies that spend one particular season ofthe year at that wetland if another counshytry destroys the refuge which they use inanother season of the year Full details ofinternational environmental conventions ofthis type are listed each year in the GreenGlobe Yearbook which is prepared by theFridtjof Nansen Institute of Norway andpublished by Oxford University Press

Maltby E 1986 Waterlogged Wealth Why Waste the Worlds Wet Placet LondonEarthscanA very useful statement of why wetlands are important and the stresses they face

Williams M (ed) 1990 Wetlands A Threatened Landscape Oxford BlackwellA more advanced collection of papers that deals with many different types of wetlandsfrom an international perspective

Wt=tlands 57

Wetlands management in the Niger Inland Delta

Tht= Niger Inland Delta in MaliMrica is in the Sahel zone It formsan important seasonally flooded wetshyland environment in an area whereevaporation vastly exceeds precipitashytion It covers some 20000-30000sq km in me flood season and 4000sq km at low water and supportsa population of around 550000JKople (Adams 1993) Fishinggrazing and cultivation of rice andsorghum are all important activitiesSeventy-five JKr cent of me fishcaught along the entire River Nigerare caught hcre half the total rice area in Mali is found here Over 2 millionsheep and goats and around 1 million cattle graze on the delta in the dry seasonThcsc numbers make up around 20 per cent of all thcsc animals found in Mali

The key to the complex and abundant agricultural production of the delta isthe timing of the floods The high flow in the delta does not coincide with thelocal rainfall peak This means that there is frequent variation in environmentalconditions throughout the year The floodwaters JKak betwt=en September andNovember and recede between December and February rains ft11 between Juneand September and the delta is dry between April and June Different activitiesdominate the delta under these different hydrological conditions Rice is planttdas the waters rs( in July and August and harvested as they recede in Decemberto February Sorghum is planted on the fulling flood in January and the delta isextensively used for grazing from December to July

This wetland is also of international importance Migrating birds visit it and thedelta provides an important stop for them on the routes from the Arctic to otherparts of Africa

Failure of the rains and alterations to the flow of the Niger River may haveserious consequences for the rich natural and human ecology of the Niger InlandDelta Dams further up the Niger River are likely to remove about 12 JKr centof inflow to the delta in a dry year which could have impacts on fishing andagriculture Damming of rivers tends to affect both the quality and the quantityofwater and to detract from the significant economic uses ofdownstream wetlandsOne solution on regulatt=d rivers may be controlled flooding with artificial proshyduction of floodwaters from hydroelectric dams In this way the dams arc madeto work pith the natural river environment nther than replacing it

Further reading

Adams W M 1993 Indigenous usc of wetlands and sustainable developmentin West Africa Geographic1 jOJ4nuli 159 209-18

S8 The Biosphere

10 BIODIVERSITY AND

ExnNcrIONS

Wlut is biodiversity It has recently beendescribed as an enormous cornucopia ofwild and cultivated species dive~ in fonnand function with beauty and usefulnessbeyond the imagination (litis 1988 p98) Biodiversity has recently become amajor environmental issue With environshyments being degraded at an acceleratingrate much diversity is being irretrievablylost through the destruction of naturalhabitats At the same time science is disshycovering new uses for biological diversity

The fundamental concern is the finalityof the loss of biodiversity Once a specieshas gone it cannot be brought back Thedodo (a bird) is dead and gone and willnever be seen again

Biodiversity has five main aspects

bull the distribution of different kinds ofecosystems which comprise communshyities of plant and animal species andthe surrounding environment andwhich are valuable not only for thespecies they contain but also in theirown right

bull the total number of species in a regionor area

bull the number of endemic species (speshycies whose distribution is confined to

one particular location) in an areabull the genetic diversity of an individual

speciesbull the sub-populations of an individual

species that is the different groupswhich represent its genetic diversity

The Earths genes species and ecosysshytems have evolved over a period of 3000million years They form the basis forhuman survival on the planet Howeverhuman activities arc now leading to arapid loss of many of the components of

biodiversity Human self-interest arguesthat this process should be stemmed forecosystems playa major role in the globalclimate arc a source of useful productspreserve genetic strains which crop breedshyers use to improve cultivated varieties ofplants and conserve the soil

We have no clear idea of the totalnumber of species of organisms that exislon the face of the Earth Therefore it isdifficult to predict what numbers ofspeciesmay be lost in the coming decades Howshyever according to Myers (1979 p 31)during the last quarter of this century weshall witness an extinction spasm accountshying for one million species This is a conshysidenble proportion of the estimatednumber of species living in the world toshyday which Myers puts at between 3 and 9million He has calculated mat from AD

1600 to 1900 humans were causing thedemise of one species every four yearsthat from 1900 onwards the rate increasedto an average of around one per year matat present me C2te is about one per dayand that within a decade we could Ixlosing one every hour By the end of thecentury our planet could have lost anyshything between 20 per cent and 50 percent of its species (Lugo 1988) It isobvious from even this brief look at thequestion that the need to maintain bioshydiversity has become one of the crucialissues with which we must contend

Some environments are particularly imshyportant for their species diversity Suchbiodiversity hot spots (figure IIII) needto be made priorities for conservationThey include coral reefs (sec part VI secshytion 7) tropical forcst5 (which support weUover half the planets species on only about6 per cent of irs land area) and somt ofthe Mediterranean climate ecosystems (inshycluding the extraordinarily diverse Fynbosshrublands of me Cape region of SouthAfrica) Some environmtnts are crucial beshycause of their high levels ofspecies diversity

bull

i

-N

Caltdon~

AIllnli

- --

~dk~~~Mrn I( -~_=C)Soulh~llfm V

~A-

- ~

Eamm Hirnaayls

rJtbrh~r

~

TanunilJJ

-

CpePIOIi(mIni(Me

CoIllmbUn

Wnlern

dlt

N

t

(aliformFlorinkPf()yeninu

~

~

Hawaii

-Figure 1111 Forest and heathland hot spot areas Hot spots are habitats with many species found nowhere else and ingreatest danger of extinction from human activitySource Wilson (1992) pp 262-3

60 The Biosphere

or endemic species others are crucial beshycause their loss would have consequenceselsewhere This applies for example towetlands which provide habitats for mishygratory birds and produce the nutrientsfor many fisheries

Reduction in habitat area can lead to adecline in the population of each speciesas well as in the number of differentspecies that the habitat can hold Lowpopulations make species highly vulnerableto inbreeding disease habitat alterationand environmental stress If a species hasbeen reduced to one population in onesmall area a single fire a single diseasethe loss of a food source or any othersuch demographic accident can kad toextinction

Human demographic success has proshyduced the biodiversity crisis As E OWilson noted in his remarkable book TheDiversity of Life

Human beings - mammals of the 50shykilogram weight class and members ofa group the primates otherwise notedfor scarcity - have become a hundredtimes more numerous than any otherland animal of comparable size in thehistory of life By every conceivablemeasure humanity is ecologically abshynormal Our species appropriates beshytween 20 and 40 per cent of the solarenergy captured in organic material byland plants There is no way that wecan draw upon the resources of theplanet to such a degree without drastishycally reducing the state of most otherspecies (Wilson 1992 p 272)

With the human population expected todouble or treble by the middle of thetwenty-first century and the material andenergy demands of developing countrieslikely to accelerate at an even faster rateeven less habitat will be left for otherspecies

What needs to be done~ Wilson suggests

five enterprises that need to be undertakento save and use in perpetuity as much aspossible of the Earths diversity

1 Survey the worldJsfauna andflora Weknow very little about how many speshycies there are and even less about theirqualities or where they are Threatenedhabitats need to be paid particularattention

2 Create biological wealth As our reshycords of species expand they open theway to what is called bioeconomicanalysis - the broad assessment of theeconomic potential of entire ecosysshytems An aim will be to protect ecoshysystems by assigning to them a futurevalue We need for example to searchamong wild species (possibly using ethmiddotnographic sources) for useful medicalor chemical products

3 Promote sustainable development Aswith desertification (see section 3above) the root cause of the problemlies in society The solution lies thereas well As Wilson (1992 p 322) exshyplained it The rural poor of the thirdworld are locked into a downwardspiral of poverty and the destructionof diversity Lacking access to marshykets hammered by exploding popushylations they turn increasingly to thelast of the wild biological resourcesThey hunt out the animals withinwalking distance cut forests that canshynot be regrown put their herds onany land from which they cannot bedriven by force They use domesticcrops ill suited to their environmentfor too many years because they knowno alternative Their governmentslacking an adequate tax base andsaddled with huge foreign debtscollaborate in the devastation of theenvironment

4 Save what remains Seed banks boshytanical gardens zoos and the like (the

so-called ex sitw methods) may havesome limited scope to preserve geneticmaterial However the key issue is thepreservation of nantral ecosystems Weneed large areas of reserves to includeas many of the undisturbed habitats as

Biodiversity and Extinctions 61

possibk Priority shouJd be given tobiodiversity hot spots

S Restore tbe wild lAnds Existing ecoshysystems need to be salvaged and remiddotgenentcd

Plate 119 A giant panda Ailuropoda melanoleuca feeding on bamboo atWolong Sichuan China The panda has become a symbol of the worlds wildlifeconservation movement (Heather Angel)

FURTHER READING

Myers N 1979 Tht Si1lkilJg Ark A Ntw Look at thtlrobJem ofDif(Jpp((Jrin~q SpainOxford Pergamon PressOnt of [ht classic statements about txtinctions and biodivtrsity loss by one ofthc= mostpc=rsuasivt tnvironmental wriltrs

Wilson E 0 1992 nJt Dipersity of Lift London PtnguinA beautiful piece of science writing for the Ia)middot person by a kading biologist

62 The Biosphere

Pandas plants and parks conserving biodiversityin China

China is both the worlds most populous country and an important storehouseof global biodiversity The country is home to around 30000 species of plantsand around 400 species of mammals Exact statistics are hard to obtain but wedo know that there are many unique endemic species found in China such asthe well-known giant panda (Aiuropoda melanoleuca) In 1965 there were 19nature reserves covering 6500 sq km (007 per cent of the toral land area ofChina) In 1991 there were 708 reserves covering 560000 sq km or 583 percent of the total land aru

The history of nature conservation and the preservation of biodiversity inChina reflects the changing social economic and political conditions prevailingin the country Before 1944 China had a patchy history of nature conservationas rulers established parkland hunting grounds gardens and temple areas Manytemple lands and sacred sites acted as biodiversity reserves

The first modern nature reserve in China was established in 1956 in theDinghu Subtropical Mountain Forest in Guandong Province (Freedman 1995)The mountain was the sice of an ancient Buddhist temple and so had alreadyreceived much protection Two-thirds of the reserves 1200 hectares had beenplanted with pine or subjected to other land usc modifications In 1980 it wasincorporated into the International Biosphere Network It is now a major touristdestination with up to 700000 visitors a year

Table 119 shows that most nature reserves were not established until after1980 when Chinas nature conservation laws began to multiply By 1989 379vertebrate species and 389 plant species received official protection in China Bythe early 1990s 13 nature reserves were devoted to the conservation and protecshytion of the giant panda and even more are planned

Hunting poaching and traditional medicine are great threats to biodiversityconservation in China In 1990 the country was the worlds largest exporter ofcat and reptile skins and live orchids Immense indirect threats are also posedto biodiversity by the development of industry agriculture transport and urbanareas Although China has made great attempts to conserve biodiversity like allcountries its nature conStrvation programme faces many problems

bull The distribution of nature reserves is uneven (figure ILIl)bull Administration is of uneven qualitybull Many nature reserves arc too small to be ecologically effectivebull Nature conservation laws are not rigorously enforcedbull Environmental education in people living near nature reserves is low and

planners do not consider the economic concerns of these people sufficientlybull Tourism has placed an additional stress on many nature reserves

Biodiversity and Extinctions 63

Table 119 Nature reserves In the Peoples Republic of Chinbullbull 1965-1991

Year No of reserves

1965 191978 341980 721983 2621985 3101987 4811991 708

Total area of reserves(000 sq km)

6512616

156167237560

of totaf area ofcountry covered by reserves

007013017162174247583

Source Edmonds (1994) table 82

Figure 1112 The distribution of nature reserves in ChinaSource Edmonds (1994) figure 83

Further reading

Edmonds R L 1994 Parterns ofChjnas Lost Harmony A Survey of the Counshytrys Environmental Degradation and Protection London Routledge

64 Th~ Biospher~

11 INTRODUCfIONS

INVASIONS AND

EXPLOSIONS

Humans are gr~at transporters of otherorganisms whether deliberately or accidenshytally Thus many organisms hav~ arrivedin areas where they did not naturally occurThis applies both to plants and to animals

Di Castri (1989) has identified thr~e

main stages in the process of biologicalinvasions stimulated by human actions Thefirst stage covers several millennia lip toabout AD 1500 During this periodhuman historical events favoured invasionsItld migrations primarily within the OldWorld The second stage began aboutAD 1500 At this time the explorltion

discovery and colonization of new territorshyi~s began in earnest and the globalizationof ~xchang~s got under way During thisphase which lasted for about 350 y~ars

invasions occurred from to and withinth~ Old World The third stage whichonly covers the last 100 to 150 years hasseen a rapidly increasing rate of exchangesand an even more extensive multifocalglobalization with Europe taking a lesscentral place

Plants that have been deliberately introshyduced to a new location can be dividedinto two groups (I) an economic groupwhich consists of crops timber trees andcover plants for control of erosion~ and(2) an ornamental or amenity group whichconsists of plants introduced out of curishyosity or because of their decorative value

Plate 1110 The remarkable Fynbos heathland of the Cape Province of SouthAfrica is rich in species many of which are endemic A major threat to the Fynbosis posed by the spread of invasive plants introduced from Australia In thisexample it is being encroached upon from the rear by Acacia cyclops(A S Goudie)

Introductions Invasions Explosions 6S

Table 1110 Allen plant species on oceanic Islands

Island No of naUve No of alien of alienspecies spedes species in flora

New Zealand 1200 1700 586Campbell Island 128 81 390South Georgia 26 54 675Kerguelen 29 33 532Tristan da Cunha 70 97 586Falklands 160 89 357TIerra del Fuego 430 128 230

SOUfce From data In Moore (1983)

A major role in such deliberate introdshyuctions was played by botanic gardensboth th~ in Europe and those in thecolonial territories from thc sixteenthcentury onwards

Mants that have becn accidentally disshy~rsed have arrived in a variety of waysby adhercnce to individual people or theirmeans of transport among crop seedfodder or packing materials and as a comshyponcnt of transponed soil ballast roadmetal or minerals

Introduccd plants are capable of inshyvading areas to which they have beenintroduced cven to the extent of causingso-called ecological explosions Theyprove to be so successful in their newhabitat that they expand in range andnumbers to the detriment of the nativespecies The same applies to introducedplant pathogens In Britain for instancemany elm trees have died sincc the 1970sbecauS( of the accidental introduction ofthc Dutch elm disease fungus on timberimportcd through certain ports in southshycrn England In thc USA thc Americanchestnut was almost eliminated in less thanSO years following the introduction ofthe chestnut blight fungus from Asia latein the 1890$ In western Australia thegreat jarrah fOteSts have been invaded anddecimated by a root fungus which was

probably introduced on diseased nurserymaterial from eastern Australia

Occan islands have oncn been particUshylarly vulnerable to invasions The simplicshyity of their ecosystems inevitably Icads tolower stability Introduced species oltenfind that the relative lack of competitionenables them to spread into a wider rangeof habitats than they could on the continshyents Moreover because the naturl1 speshycies inhabiting remote islands have cometo be there primarily because of their abilshyity to disperse over large distances theyhave not necessarily been dominant or evcnhighly successful in their original continshyental setting Therefore introduced speshycies may be more vigorous and effectiveThere may also be a lack of indigenousspecies to adapt to conditions such as bareground caused by humans This enablesintroduced weeds to establish themselves

Table 1110 illustrates dearly how prominshyent alien specics have become among theflora of some islands The percentage ofintroduced plants varies between aboutone-quarter ilnd two-thirds of the tOtalnumber of species present

Another type of ecological explosioncan be cauS(d by human-induced habitatchange Some of the most striking examshyples are associated with the establishmentof artificial lakes behind dams in place of

66 The Biosphere

rivers Riverine species which cannot copewith the changed fluvial conditions tendto disappear Others that can exploit thenew sources of food and reproduce thcmmiddotselves under thl new conditions multiplyrapidly in the absence ofcompetition Vegshyetation on land flooded as the lake watersrise decomposes to providc a rich supplyof nutrients This allows explosive outshygrowth of organisms as the new lake fillsIn particular floating plants may formdense mats of vegetation which in turnsupport large populations of invertebrateanimals These may cause fish to die bydeoxygenating the water and can create aserious nuisance for turbines naviguorsand fishermen On Lake Kariba in CentralAfrica the communities of the SouthAmerican water fern (SAvinia molestll)bladder-wort (UtriJ4iAria) and the Afrishycan water lettuce (Pittill stratious) grewdramatically and on the Nile behind theJebel Aulia Dam there was a huge increasein the number of water hyacinths (Eihshyhornill musipes)

Various human activities including dearshying foresr cultivating depositing rubbishand many others have opened up a wholerange of environments which are favourshyable to colonization by a particular groupof plants Such plants which arc notintroduced intentionally arc generallythought of as weeds

Animals have been deliberately introshyduced to new areas for many reasons forfood for sport for revenue for sentimentfor control of other pests and for aesmiddotthetic purposes Such dclibcrare actionsprobably account for insunce for thewidespread distribution of trout

There have also been many accidenulintroductions especially since the develshyopment of ocean-going vessels These arcbecoming more frequent for whereas inthe eighteenth century there were fewocean-going vessels of more than 300tonnes today there arc thousands Because

of this in the words ofC S Elton (1958p_ 31) we arc seeing one of the greathistorical convulsions in the worlds faunaand flora Indeed many animals arc inshytroduced with vegetable products for justas trade followed the flag so animals havefollowed the plants

A recent example of the spread of anintroduced insect in the Americas is promiddotvided by the Mricanizcd honey bee Anumber of these were brought to Brazilfrom South Mrica in 1957 as an experishyment and some escaped Since thenthey have moved northwards to CentralAmerica and Texas (figure 1113) spreadshying at a rate of 300-500 kIn per year andcompeting with established populations ofEuropean honey bees

Some animals arrive accidenrally withother beasts that arc imported deliberatelyIn nonhern AusmIia for instance waterbuffilo were introduced They brought withthem their own bloodsucking fly a specieswhich bred in cattle dung and transmittedan organism sometimes fatal to caweAwtralias native dung beetles accustomedonly to the small sheep-like pellets of thegrazing marsupials could not tackle thelarge dung pats of the bufhlo Thw unmiddottouched pats abounded and the flies wereable to brecd undisturbed EventuallyMrican dung beetles were introduced tocompete with the flies

Domesticated plants have in most casesbeen unable to survive without humanhelp The same is not so true of domesshyticated animals There arc a great manyexamples of cattle hones donkeys andgoats which have effectively adapted to newenvironments and have become virtuallywild (feral) Frequently pigs and rabbitsthat have esublished themselves in this wayhave owted native animals Feral animalsmay also panicularly on ocean isJandscause dcscni6cation Fern goats for exmiddotample have degraded the Channel Islandsoff the California coast

Introductions Invasions Explosions 67

Figure 1113 The spread of the Africanized honey bee in the Americas between1957 (when it was introduced into Brazilgt and 1990Source Modified after Texas Agricultural Experiment Station in Christian Science MonitorSeptember 1991

Aquatic life can be spread accidentallythrough human alteration of waterwaysand by the construction of canals whichenables organisms to spread from onesea or one lake to another This processis called Lessepsian migration after thename of the man who built the Suez Canal

FURTHER READING

The construction of that great watershyway has enabled the exchange of animalsbetween the Red Sea and the easternMediterranean The migrants include amenacing jellyfish which has now inshyvaded beaches on the eastern shore of theMediterranean

Drake] A (ed) 1989 Biological Invasions A Global Perspective Chichester WileyAn advanced collection of edited papers

Elton C S 1958 The Ecology ofInvasions by PiRtI ad Animals London MethuenThe classic monograph on this theme

68 The Biosphere

Alien plant species invading Kakadu National ParkAustralia

N

tNORTHERN fERRlTORY

bull 10

The Kakadu National Park is a UNESCO World Heritage Site in the monsoonaltropical north of Australia containing most of the catchment of the South Alshyligator River The natural vegetation is mainly savanna woodland and open forestdominated by eucalyptus There are also extensive alluvial floodplains seasonshyally water-covered where herbaceous wetland vegetation grows Out of 1526plant species found here some 58 per cent (89 species) are considered to beinvasive (Corrie and Werner 1993) Most of these are weedy annuals from theNew World tropics Although this percentage of introduced species is low comshypared with the figure for the whole of Australia (10 per cent of all plant speciesare invasive) it is clearly a cause of worry for a nature reserve which is attractingan increasing number of visitors

Invasions have increased by an average of 16 species per year since 1948 astourism and mining have increased bringing in more habitat disturbance Mostalien species are found around camp-sites car parks roads and mines One of thebiggest problems is a fast-growing shrub (MimoJa pjgra) This plant was introshyduced deliberately into the Northern Territory from South America and was notrealized to be a serious nuisance until around 80 years later It has spread overthe alluvial floodplains changing herbaceous swamps into shrublands This inturn affects wildlife There has been a major effort to control the plant

There are also many other indirect ways in which alien plant species are spreadhere Feral water buffaloes for example make a major contribution to invasionsnear floodplains as they disturb the ground

Further reading

Kirkpatrick J 1994 A Continent Tramformed Melbourne Oxford University PressA concise discussion of human impacts on the natural vegetation of Australia

12 HABITAT Loss AND

FRAGMENTATION

One of the conscquences of human activshyitia is that many naturaJ habitats bc=comereducro in extent and also bc=come ampagshymented into isolated patches Figure 1114shows how both these processc=s haveoccurred in the forest cover of a part ofcentraJ England in the last 1500 yearsWhereas at the end of Romano- Britishtimes (AD 400) there were still large exshypanses of forest there are now only verysmall islands of forest in a sea of agriculshytural land

Certain types of habitat may be lostbecausc= of changes in agriculturaJ pracshytica In Britain for example the botanishycal diversity of much pastureland has been

Figure 1114 Forest fragmentation inWarwickshire England from AD 400 to1960 Forested areas are shown inbladeSource Wikove et aI (1986) figure 1

Habitat loss and Fragmentation 69

reduced as many old meadows have bunreplaced with fields planted solely withgrass (leys) or treated with selective hershybicides and fertiliurs This treatment cantake out of the habitat some of the basicrequirements essc=ntial for many speciesFor exampk the larva of the commonblue bunerfly (Polyommatus jcarus) feedsupon birds-foot trefoil (Lotus cornjeulshyaoo) This plant disappears when pastureis ploughed and converted into a grassfidd or when it is treated with a selectiveherbicide Once the plant has gone thebutterfly vanishes too because it is notadapted to feeding on the plants grown inleys of improved pasture Likewise numshybers of the large blue butterfly (Maculjneaarion) have decreased in Britain Its larvaelive solely on the wild thyme (Thymustiruul a plant which thrives on doseshycropped grassland Since the decimarionof the rabbit by myxomatosis conditionsfor the thyme have been less favourable50 that both the thyme and the large bluebutterfly have declined

Another major land-usc change of reshycent decades has been the replacement ofnatural oak-dominated woodlands in Britshyain and e1sewhere by conifer plantationsThis also has implications fOr wildlife Ithas been estimated that where this changehas totken place the numbc=r of species ofbirds found has been approximately halvedLikewisc the replacement of upland sheepwalks with conifer plantations in southern$corland and northern England has led toa sharp decline in numbers of ravens Theraven (Corvus eorax) feeds on carrionmuch ofwhich it obtains from open sheepcountry Other birds mat have sufferedfrom moorland areas being planted withforest trees are scera1 types of waderthe golden eagle peregrine falcons andbuzzards

Many species of birds in Britain havedeclined in numbers over the last twO deshycades because of habitat changes resulting

70 Thc Biosphere

from more intensive fuming methodsTheS( include no longer leaving fallowsless mixed farming ncw crops modernfarm management uS( of biocides andhedgerow removal

Reducing the areas of land covered byparticular habitats has a direct impact onthe fortunes of species It is usdul to secthe remaining fragments of habitat asislands We know from many of the classicstudies in true island biogeography thatthe number of species living al a particularlocation is related to its area Islands supshypurt fewer species than do similar areasof mainland and small islands have fewerspecies than do large ones Thus it maywell lollow that if humans destroy thegreuer part of a vaSI belt of natural forestleaving just a small reserve initially it willbe middotsupemnlrated with species containshying more than is appropriate to its areaunder nuural conditons Since there willbe tCwer individuals of each of the speciesliving in the forest now the extinction rat(will increase and the number of specieswill decline For this reason it is a soundprinciple to make rescrves as large as posshysible A large reserv( will support mor(species by allowing the existence of brgerpopulations and keeping extinction rateslower Size of course is not everythingand other factors such as the shape ofreserves and the existence of links betweenreserves arc also important

Reduction in area of habitat leads to

reduction in numbers of organisms Thisin turn can lead to genetic impoverishmiddotment through inbreeding with particuJarlymarked effect on reproductive performshyance [nbrttding degenention is howevernot the only effect of small populationsize In the longer term the depletion ofgenetic variety is more serious since itreduces the capacity for adaptive changeIt is therefore very important to provideenough space especially for th~ animalsthat require large expanses of territory For

example the population density of the wolfis arout one adult per 20 sq km and ithas been caJculaled thal for a viable popushylation to exist one mighr need 600 indishyviduals ranging over an area of 12000sq km The significance of this is apparentwhen onc realizes that most narure reshyserves art small 93 per cent of the worldsnational parks and reserves havc an arealess than 5000 sq km and 78 per centcover less than 1000 sq km

Habitat fragmentation has SOffiC othtrmajor clTects One of these is loss of habimiddottat heterogeneity In other words indiovidual fragments may lack the full rangeof ditlcrcnt habitats found in the originalblock For insnnce a small patch ofwoodmay not contain a reliable water supplyLikewise sollle species - certain amphibshyians for example - require two or morehabitat lypCs Habitat fragmtntation maymake it impossible for these animals tomove between habitats

A second effect of fragmentation is thatthe new landscape that replaces the orishyginal habitat such as human setdementsor agricultural land may act as a barrierpreventing colonization and interchangebetween groups Also the new landscapesmay enable populations to build up ofanimals that arc harmful to species withinthese fragments

A third consequence of fragmentationis what are called edge effects Some anishymals do well in edge habitats that is theboundary areas around the rim of theisland but others suffer For examplemany nest predators occur in higher denmiddotsities around forest edges

A fourth effect is secondary extinctionsFragmentation disrupts many of the imshyporum ecological interactions of a comshymunity For example small woodlandwands in the eastern USA contain few ifany of the large predators (eg mountainlions) that would nonnally regulate thenumber ofsmaUcr omnivorous species (eg

racoon) Th~ omnivores can thus preyunhindered upon the eggs and young of

FURTHER REAoING

Habitat Loss and Fragmentation 71

the forest songbirds and may wi~ themout

Wilcove D S McLellan C H and Dobson A P 1986 Habitat fngmemation inthe temperate zone In M E Soule (cd) OmserJl4tion Biology The Science ofSc4rcityand DiJlenity pp 251-6 Sunderland Massmiddot Sinauer AssociatesA short but useful chapter in an advanced book

Plate 1111 A flock of Lesser Snow Geese (NHPARobert Erwin)

_72 The Biosphere

Texas Gulf coast habitat changes and the LesserSnow GooseThe changing fortunes of the LesserSnow ~ (Chen caeruJescenscRerulmens) population in Tnasshow interesting links betweenhabitat changes and wildlife Presshyently around 600000-850000Lesser Snow Geese winter here everyyear (Robertson and Slack 1995)Until the 1920s the Lesser SnowGeese wintered mainly on coastalmarshes but now they arc found onthe inland prairie as well

During the twentieth century theTexas Gulf coast has secn the rise ofpetroleum rdining and oil extractionindustries coupled with the spreadof rice cultivation and a boom inpopulation Nearly 50 per cent ofthe entire USAs chemical producshytion is bascd in the Houston areaand 73 per cent of the US petroshyleum industry is there Rice cultivashytion peaked at 254800 hectares in1954 and now covers an a~a ofaround 141000 hectares These diverse changes to the landscape have causedsome areas to become more suitable for the Lesser Snow Goose while other areashave become less attractive in terms of availability of food and water

The wintering grounds of the Lesser Snow Goose spread to the prairies beshytween the 1920s and the 19505 following the spread of rice cultivation althoughthe movement of the birds lagged behind the expansion of the ricefields by someyears These changes may also have been encouraged by alterations to the coastalmarsh areas as urban and industrial development from the 1940s onwards led tomarsh drainage and pollution

The changes in wintering range were accompanied by a growth in populationnumbers the Lesser Snow Goose population peaked at around 813000 in theearly 1980$ Since then numbers have declined in association with declining riceproduction (the area sown with rice declined by a third from 1978 to 1991) Thisdecline in rice cultivation was in tum related to the lack of federal price supportSfor rice growers which made other crops more economicaUy viable

An airpon planned for construction on Katy Plains would afkct 1168 hecuresdirectly and 16)00 hectares indirectly This project will have further impacts onthe distribution and population numbers of the Texan Lesser Snow Geese

Extinctions in the Past 73

13 EXTINcrIONS IN THE PAST

Extinctions are nothing new They are apart of evolution and spasms of extincshytion have recurred through geologicaltime There have been five major massglobal extinctions over the last 600 milshylion years (figure IU5) The last of theseoccurred at the boundary between theCretaceous and Tertiary periods about66 million years ago This was when theextinction of the dinosaurs took placepossibly because of the environmentalimpact ofa massive meteorite crashing intothe Earth or perhaps because of somemajor volcanic eruptions The other massextinctions took place in earlier periodsthe Ordovician (440 million years ago)the Devonian (365 million years ago) thePermian (245 million years ago) and theTriassic (210 million years ago)

We arc now living in a sixth spasm ofmass global extinction This started toshywards the end of the Icc Age (round about11000 years ago) and is accelerating at

the present time Humans are implicatedin this sixth spasm though for prehistorictimes there is a major controversy as towhether the wave ofextinctions might havea natural (ie essentially climatic) cause

We have discussed present-day exshytinctions and their causes in section 10above on biodiversity In this section wewill explore the role of our prehistoricforebears in causing the decline and exshytinction of many species of animal

Over the last 30 years Paul Martin andco-workers have argued that Late Pleisshytocene extinctions closely followed thechronology of the spread of prehistorichuman cultures and the development ofbig-game hunting technology They wouldargue that there are no known continentsor islands in which accelerated extinctiondefinitely pre-dates the arrival of substanshytial numbers of humans They would alsoargue that the temporal pattern ofextinctions of large land mammals (themegafauna) follows in the footsteps ofStone Age humans They suggest that

~

Iz Iz z z

~~ ~ gt

~ lt I~

I~ ~

sect ~ ~ i ~~bull ii bull6 0 ~

I~pound ei~

~

B~ ]z

~ bull 500 bullMiI1iom of)laI1 ago

Figure 1115 Graph shOWing the five mass global extinctions of marine organisms(indicated by lightning flashes)Source Wilson (1992)

74 The Biosphere

Plate 1112 A reconstruction of mammoth being hunted in Europe at the end ofthe Ice Age Mammoths were one of the megafauna that became extinct at thetransition from the Pleistocene to the Holocene Was climatic change the cause orthe hunting activities of our ancestors (Natural History Museum london)

Mrica and parts ofsouthern Asia were firstaffected in this way with substantial lossesaround 200000 years ago North andSouth America were stripped of large hershybivores between 12000 and 10000 yearsago Extinctions extended into the Holoshycene (ie the last 10000 years or so) onocean islands where humans arrived lateon the scene (figure IIl6)

There were three main types of humanpressure involved in what is sometimescalled Pleistocene overkill

bull the blitzkrieg effect when humanpopulations with big-game huntingtechnology spread rapidly so that anishymal populations decline very quickly

bull the innovation effect when longshyestablished human population groupsadopt new hunting technologies andwipe out fauna that have already beenstressed by climatic changes

bull the attrition effect when extinctiontakes place relatively slowly after a longhistory of human activity because ofloss of habitat and competition forresources

What are the arguments that can bemarshalled in favour of this anthroposhygenic hypothesis First in areas like theHigh Plains of America the first massiveextinctions appear to coincide with thearrival of humans who were numerousenough and who had sufficient technoshylogical skills to be able to kill large numshybers ofanimals Secondly the vast numberof bones at some Late Pleistocene archaeoshylogical sites attests to the efficiency of themore advanced Stone Age hunters Thirdlymany animals unfamiliar with people areremarkably tame and naIve in their presshyence rendering them easy prey Fourthlyin addition to hunting animals to death

~~~~~lOllOOOO JOOOOO 10000 1000 100

YtlllUIO

Figure 1116 The percentage survival oflarge animals and flightless birds overthe last million years in four differentareas The extinction of these organismscoincided doseo with the arrival ofhumans in North America MadagascaIand New Zealand and less decisively inAustralia In Africa where humans andanimals evolved together for millions ofyears the damage was less severeSource Wilson (1992)

humans may also have competed withthem for particular food or water suppliesFifthly the supposed extinction of thelarger rather than the smaller mammalscould be related to thc= effc=cLS of humanprc=dation Large mammals havc= smallnumbers of offspring long gaution pc=rishyOOs and long periods before manlrity isreached This means that populations ofthese animals can survive only a very lowrate of slaughter ~en against primitivehunters

In addition cc=rtain objections havc= beenlc=velled against the climatic change model

Extinctions in the Past 75

which tend to support the anthropogenicmodel It has been suggested for instancethat changa in climatic zones arc gc=nershyally gradual enough to allow bcasLS to folshylow the shifting vegetation and climaticzones of their choice Similar environmentsarc available in North America today aswere present in different locations amiin different proportions during lIt(Pleistocene times Sccondl~ it can beargued that the climatic changes associmiddotated with the multiple glaciationsintugladals pluvials and interpluvialsearlier in the Icc Age do not seem [0 h3Ccaused the same striking degree of sjXcklgtelimination as the changes in the LattPleistoc~n~ A third difficulty with thec1imati cause theory is that animals likethe mammoth occupied a broad range ofhabitats from Arctic to tropical latitudesso that it is unlikely that all would perishas a result of a climatic chang~

However thc=re is some support for thealt~rnative climatic hypoth~sis namely thatrapid and substantial climatic change atthe end of the last Icc Age led to th~

extinction of the great mammals lik~ themammoth The migration of animals inresponse to the npid climatic change atthe cnd of the Pleistocene could bc haludby geographical barriers such as highmountain ranges or seas According to thispoint of view Africa is rclativc=ly rich inbig mammalian fauna because thc Africanbiota is not or was not greatly r~stricted

by any insupc=rable geographical barrierAnother way in which climatic chang~

could cause extinction is through its influshyence on the spread of disease It has beensuggested that during g1acials animalswould bc split intO sepal2te groups CUtoff from one another by ice sheets Theseisolated groups might lose immunity tocertain diseases to which they werc= nolonger exposed Then as the ice melted(before 1lOOO years ago in many areas)contacts bctwcen group5 would once again

76 The Biosphere

be made enabling any diseases to whichimmunity had been lost to spread rapidly

It has also been noted recently that insome areas it was not only the greatmegafauna that became extinct Some smallanimals and birds that would not have beenhunted by humans also died out Moreshyover as the radiocarbon dates for earlysocieties in some countries like Australiaand Brazil are pushed back it becomesincreasingly clear that humans and severalspecies of megafauna were living togethertor quite long periods This is underminshying the idea of rapid overkill Mso ifhumans were primarily responsible for thewaves of extinction how does one explainthe survival of many big game species in

FURTHER READING

North America well imo the nineteenthcemury~

The Late Pleistocene extinctions mayof course have been caused by bothclimatic and anthropogenic mechanismsor by a combination of the two types Forexample animal populations reduced andstressed by climatic change would be morevulnerable to increasing levels of humanpredation Nonetheless the rapidity withwhich extinctions took place in Madagasshycar New Zealand and the Pacific islandsafter they wete first settled in the Holoceneis striking evidence ofhow even quite smallnumbers of technologically not vetyadvanced people can cause major environshymental change

14 BIOTECHNOLOGY GENETIC

ENGINEERING AND THE

ENVIRONMENT

Biotechnology is the manipulation of livshying organisms and their components (eggenes or gene components) for specifictasks Genetic engineering is one form ofbimechnology involving the isolation ofgenes and gene components that conferdesired traits and their transfer betweenspecies It is also sometimes called recomshybinant DNA technology This branch ofscience has now reached a level where it ispossible to transfer genes between unnshylated species or types of organisms

There are many applications of biotechshynology that arc ofenvironmental relevancein agriculture resource recovery and re-

Ehrlich P R and Ehrlich A H 1982 Extinetiol London GollanczAn accessible treatment for the general reader

Martin P S and Klein R G 1984 Pleistocene Extinctions Tucson University ofArizona PressA massive advanced tome from two of the leading scientists involved in the study ofthe possible role of humans in causing extinctions in prehistory

cycling pollution abatement and the proshyduction of renewable energy resources

In agriculture biotechnology can helpto maximize energy and nutrient flowsfor example by increasing crop yield andby engineering resistance to disease inshysects and herbicides Nitrate levels can beenhanced by seeding the ground withnitrogen-fixing bacteria Stress tolerance(eg to frost) can be engineered

Biotechnology is also being developedto undertake the recovery of resourcesMineral orcs can be recovered through aprocess called biomining which exploitsthe ability of specific types of bacteria toobtain their energy supply by breakingdown certain types of ore-bearing deposmiddotits Certain micro-organisms can be emshyployed to scavenge metals from wastewaterso that the metals can be re-used

Biotechnology can also contribute topollution aba~ment Bioscnsors areorganisms that can be used to identifY critishycal levels of poUution Other organismscan be uscd to extract pollutants such asheavy metals from wastewater to neutralshyize hazardous substances in the environshyment (bioremediation) or to break downscwage

Another usc of biotechnology is to produce renewable energy resources For exshyample it is possible to extract alcohol fromsome plants this call be used as fuel forautomobiles Protein-rich animal feeds canbe obtained by using algae fungi (indudshying yeasts) and some bacteria to producecellular protein from energy and nutrientsources such as carbon dioxide methanolethanol sugars and carbohydrates

Biotechnology is potentially ofenormousvalue and it may have many environmenshytal benefits For example the environmenshytal advantages of using biotechnology inagriculture include

FURTHER READING

Conclusions 77

bull reduced need for fuelbull reduced usc of pesticidesbull reduced usc of artificial fertilizer thus

also lessening pollution by phosphatesand nitrates

bull increased food supply which could leadto less pressure on marginal lands andon remaining natural ecosystems

Similar types of advantages can apply tothe other uses of biotechnology which wehave described

On the other hand there are possibledisadvantages These include

bull the potential to create invasive organshyisms - as for instance when genesescape into the wild relative of an enshygineered crop creating potential pests

bull the potential to create organisms whichare toxic or contain toxic components

bull the potential to create organisms espeshycially bacteria that could profoundlyalter the nature of global biogeoshychemical cycles

Mannion A M 1991 Global Environmental Change Harlow LongmanA very general but useful treatment of all aspects of global change both natural andanthropogenic

Mannion A M) 1995 Agriculture and Enviroilmental Change Chichester WileyA more detailed treatment by the same author of biotechnology as one aspect of theagricultural impact on the environment

15 CONCLUSIONS

In this chapter we have demonstrated thathumans have had effects on the biospherefor a very long time For many good reamiddotsons our early ancestors developed the useof fire This powerful technological toolhas had many positive ecological conseshyquences It may also have had a majoreffect on some of the worlds biomes andvegetation types induding savannas andMediterranean shrublands The manage-

ment of fire is an important tool for themanagement ofsome major environmentsAs the Yellowstone study has shown firesuppression policies can have adverseeffects

Other major changes in the state of theworlds biomes include desertification anddeforestation Both phenomena are diffishycult to define and to quantifY There arcvarious ways in which desert margins andrain forests can be managed so that theseprocesses can be kept under control Even

78 The Biosphere

secondary forests which result from humanuse of tropical moist forests have positivevalue

With many such changes however wehave to recognize that very many proshycesses both anthropogenic and naturalmay have played an important role Thisis evident from a consideration of theorigin of tropical savannas heathlands andmid-latitude grasslands Indeed we haveseen recently how complex causes can bein the case of forest decline in Europe Aswe point out thete is no single type ofInrest damage and no single cause Equallywe should not necessarily equate urbanshyization with a reduction in biodiversity Thegrowth of dties as illustrated by Chicagohas major ecological consequences bur notall of them have negative impacts

Nonetheless there are some major habishytats and particular habitat types that deshyserve particular attention and protectionbecause of their importance for the preshyservation of biodiversity These indudewetlands and other crucial ecological hotspots such as the Fynbos heathlands ofsouthern Mrica or the forests inhabited

KEy TERMS AND CONCEPTS

biodiversiry biodiversity hot spotsbiomass burningbiotechnologydeforestationdesertificationecological explosionecosystem servicesecotonesedaphic conditionfufire suppressionforest decline and diebaekhabitatheathland

by the Giant Panda in China Many habishytats arc being considerably modified bythe spread of organisms introduced byhumans These organisms may then invadesusceptible habitats of which oceanicislands are a notable example Many otherhabitats are being greatly reduced in areaand continuity This creation of smallltislands of habitat increases the likelihoodof species extinctions Extinction is an irshyreversible process which results from bothnatural and anthropogenic causes It is oneof the great challenges we face in comingdecades

We are emering a new era in the humanmanipulation of the biosphere Biotechshynology and genetic engineering both offergreat opportunities and raise a great needlor prudence

The many case studies discussed in thispart of the book show how complex hushyman impacts on the biosphere are howscience cannot as yet answer all the quesshytions and how the many different presshysures on human societies affect the waysin which they use and abuse the resourcesof the biosphere

invasionskeystone speciesLessepsian migrationmegafaunaovercultivationovergrazingPleistocene overkillprescribed burningsalinizationsavannasecondary focestspecies diversityurban ecologywetlandswilderness

Points for Rl=view 79

POINTS FOR REVlEW

hat do you undefSlilnd by the term biosphete~

Why was fire one of humankinds first technological achievements~

ShouJd fires Ix suppresscd~

How would you identify if desertification was raking place~

How might you aim 10 reduce the effects of desertification~

In what ways might tropical deforestation rates be reduceJ~

gtltscss the role of predisposing causal resulting and maintaining tactors ill thedevelopment of grasslands savannas and heathlands

Discuss the many different factors that could account for lorest declinc

What characteristics of cities determine their impact on the environment

Why and how should wlt1ands be conserved

What do you understand by the term biodiversity~

What arguments would you use to support the view that biodiversity lgthOlild Illmaintained

Why should we be interested in ecological invasions and explosions~

What do you understand by the term habitat~

Did climatic change or human impact cause Pleistocene eXlinctions~

Consider the potential role of biotechnology in environmental prorCluon JnJdegradation

PART III

The Atmosphere1 Inrroduction 832 Amhropogenic Climate Change

bull The Role ofAerosols 83The dust bowl ifI

bull The GulfWar oil lites hype and reality 883 Anthropogenic Climate Change

bull The Role of Land Cover Changes 904 The Enhanced Greenhouse Effect

and Global Warming 92bull Global warming and UK agrigculture 97

5 Urban Climates 98bull The implications ofsome urban heat islands 100

6 Urban Air Pollution 102bull Air pollution in South African cities

the legacy ofapanheid 1087 Ozone Depletion and Ozone Pollution 1108 Acid Deposition 1169 Conclusion 120

Key Tenus and Concepts 121Points for Review 121

Aerosols 83

2 ANTHROPOGENIC CLIMATE

CHANGE ThE ROLE OF

AEROSOLS

Let us first consider the possible effects ofaerosols An aerosol is defined as an intimatemixture of two substances one of whichis in the liquid or solid state disperseduniformly within a gas_ The tcnn is normallyused to describe smokecondensation nuclei

and nitrous oxide (the greenhouse gases)play in global wurning There are howeverother mechanisms by which humans maycause global or regional climatic changeThey are not yet fully understood and inthe long term they may not have so greatan impact as the greenhouse gases Nevcrshytheless they may have a significant role toplay In some cases morcovn they couldscrve to counteract the greenhouse ctrect Incertain specific localities they may alreadybe producing a decipherable climatic trend

The mechanisms so far idenrificd thatmay be related to human innuenccs onglobal and regional climates and their maineffeclS can be summarized as follows

Greenhousegases

bull Gas emissionsCarbon dioxideMethaneChlorofluorocarbonsNitrous oxide

bull Aerosol BeneratwnDustSmokeSulphates

bull Therntal poUuti01lUrban heat generation

bull Albedo changeDust addition to icc capsDeforestation and afforestationOvergrazingExtension of irrigation

bull Altrltion of watr flow il rivers andoceansWater vapour changeDeforestationIrrigation

bull

When me gn~at American geographer andconservationist George Perkins Marshwrote Man and Natllr in 1864 (~e partIV section 3) in which he surveyed theways in which humankind had transformedthe Earths surface he scarcely consideredthe various ways in which humans mightaffect the quality of the atmosphere andthe nature of the Earths climate Howshyever just over 100 years later it is thisvery area that is the cause of greatest conshycern to many scientists and to others inshyterested in environmental matters To besure loatl air pollution was a major conshycern at the time Marsh wrote but for themost part broader-scale human impactson the atmosphere and climate were notgiven very much attention

Since the mid-nineteenth century whenMarsh wrote his book world industrialproduction and energy consumption haveaccelerated dramatically All sorts of newtechnologies including noably the intershynal combustion engine have been inuoshyduced As a consequence a cocktail ofgases that is growing in quantity and varishyety has been emitted into the atmosphereThis has created problems of poor airquality which can affect not only humanhealth but also the state of whole ecosysshytems (for example by acid rain) and alsoof global climatic conditions (for exampleby the greenhouse effect) It is also apparshyent that changes in land use (such as deforshyestation) of the type discussed in part IIarc causing changes at the Earths surfacewhich may have impacts on the climateGreat unceruinty still surrounds many ofthese issues but there is no denying thatmatters such as global wanning oronedepletion and acid rain have very greatimplications that deserve intensive study

Recent years have ~en a great concenshytration of interest in the so-called greenshyhou~ effect (section 4 below) and therole that gases like carbon dioxide methane

1 INTRODUcrlON

84 The Atmosphere

freezing nuclei or fog contained within theatmosphere or other pollutants such asdroplets containing sulphur dioxide ornitrogen dioxide (Encyclopaedic Dictionshyary of Physical Geography 1985 p 6)Many atmospheric aerosols (eg thosederived from volcanoes sea spray or naturalfires) were not placed there by humansHowever humans have become increasshyingly capable of adding various aerosolsinto the air For example one consequenceof the industrial revolution has been theemission of hugely increased quantities ofdust or smoke particles into the loweratmosphere from industrial sources Thesecould influence global or regional tempershyatures through their impact on the scanershying and absorption of solar radiation

The exact effects of aerosols in the atmoshysphere are still not dear however yenhemeradded aerosols cause heating or cooling ofthe Earth and atmosphere systems dependsnot only on their intrinsic absorption andbackscatter characteristics but also on theirlocation in the atmosphere with respect tosuch variables as cloud cover cloud reflecshytivity and underlying surface reflectivitySo for example over ice caps grey aerosolparticles would warm the atmosphere beshycause they would be less reflective than thewhite snow surfuces beneath Over a darkersurface on the other hand they wouldreflect a greater amount of radiation leadshying to cooling Thus it is difficult to assessprecisely the effects of increased aerosolcontent in the atmosphere

Uncertainty is heightened because of thetwo contrasting tendencies ofdust the backshyscattering effect producing cooling andthe thermalmiddot blanketingeffect causing warmshying In the second of these dust absorbssome of the Earths thermal radiation thatwould otherwise escape to space and thenre-radiales a portion of this back to theland surface raising surface temperaturesNatural dust from volcanic emissions tendsto enter the stratosphere (where backshyscattering and cooling are the main con-

sequences) while anthropogenic dust morefrequently occurs in the lower levels ofthe atmosphere where it could cause thershymal blanketing and warming

Industrialization is not the only source ofparticles in the atmosphere nor is a changein temperature the only possible conseshyquence Intensive agricultural exploitationof desert margins such as in RajasthanIndia can create a dust pall in the atmoshysphere by exposing larger areas of surfacematerials to deflation in dust storms Thisdust pall can change atmospheric tempershyature enough to cause a reduction in conshyvection and thus in rainfall Observationsof dust levels over the Atlantic during thedrought years of the late 1960s and early1970s in the Sahel suggest that the deshygradation of land surfaces there led to athreefold increase in atmospheric dust atthat time It is thus possible for humanshyinduced desertification to generate dustwhich in turn increases the degree ofdesertification by reducing rainfall levels

Dust storms generated by deflation fromland surfaces with limited vegetation coveroccur frequently in the worlds drylandsThey happen naturally when strong windsattack dry and unvegetated sandy and siltysurfaces Their frequency also varies fromyear to year in response to fluctuations inrainfall and wind conditions At presenthowever in some parts of the world thedust entering the atmosphere as a result ofdust storms is increasing because of theeffects of human activity In particular proshycesses such as overgrazing which are partof the phenomenon of desertification (seepart II section 3) strip the protective vegetashytion cover from the soils surface Elsewheresurfaces may be rendered more susceptibleto wind attack because of ploughing ordisturbance by wheeled vehicles

Atmospheric aerosols can be an imporshytant source of cloud-condensation nucleiOver the worlds oceans a major source ofsuch aerosols is dimethylsulphide (DMS)This compound is produced by planktonic

algae in seawater and then oxidizes inthe atmosphere to form sulphate aerosolsBecause the albedo of clouds (and thusthe Earths radiation budget) is sensitiveto the density ofcloud-condensation nucleiany factor that has an impact on planktonicalgae may also have an important impacton climate The production ofsuch planktoncould be affected by water pollution incoastal seas or by global warming Charlsonet al (1992) believe that anthropogenicallyderied sulphate aerosols could significantlyincrease plamtary albedo through theirJirect scattering of shon-wavelength solarradiation and their modification of theshort-wave reflective properties of cloudsThus the~ could eXtTt a (Ooling influenceon the planet Charlson et al maintainthat this eflect could be as great as thecurrent hllmanmiddotillduccJ global warmingbut acting of coursc in the opposite waya~ global cooling

A nuckar conflict could produce the mostcatastrophic dlects of anthropogenic leroshysols in the atmosphere Explosion tire andwind might generate a great pall of smokellld dust in the atmosphere which wouldmake the world dark and cold It has beenestimated that if the exchange reached alevd of several thousand megatons a nushyclear wimer would occur in which temshyperatures over much of the world wouldbe depressed ro well below freezing point

Fears were also expressed that the heavysmoke palls generated by oil-well fires inthe Gulf War of 1991 might have seriousclimatic impacts The actual ctlccts arc stillnotckar Howevt=r preliminary studies havesuggested that because most of the smokegenerated by the oil-well fires stayed in thelower troposphere and remaineJ in the airfor only a shon time the eflects (some coolshying) were local rather than global It alsoseems that the operation of the South Asianmonsoon was not significantly affected

Although some of this discussion of theeffects of aerosols in the atmosphere isspeculative at the global scale this is not

Aerosols 85

so at the more local scale where it is clearthat human actions can change levels ofvisibility This is especially true in urbanareas where the concentration of Iightshyscanering and light-absorbing aerosols inthe atmosphere is greatest For examplebefore the Clean Air Acts (most notablythose passed in 1956 and 1968) LondonsuHered some severe smogs that reductJvisibility to a few metres and killed thoushysands of people (eg in the winter of1952) Reduced burning of coal since theClean Air Acts has cut down smoke emisshysions improving visibility in many pans ofBritain Fogs have become much rarer overthe last three decades

Sulphate emissions ftom cOlI-fired powerstations have also btin riduced An analvshysis ofchanges in visibility at a largi numberof sites in the UK shows that oetwecn1962 and 1990 the median atmosphericisioility has improved ti-om 109 kill to

260 km (Lee 1994) Figure IIIl showsthe number of days per ~ear when tl)goccurred in Britain over the period 1950shy83 It is clear that although the ti-equellcyof fogs has not changed a great deal incoastal areas (where they arc largely anatural phenomenon) ill the inland inshydustrial heartland they have declined verysubstantially as a result of Clean Air legismiddotlation and changes in industrial technology

The total suspended particulates (TSP)is the total mass of aerosol particles pervolume of air (usually measured in Ilg perCll metre of air) or this TSr much recemconcern has IOclised on the respirable susshypended particulates (RSP) panicles withdiameters of less than 10 11m (also knownas PM10s) These small particles arc theonly ones which can be deposited in therespiratory system - lungs and bronchialtubes - as larger particles are filtered outby the nose mouth and throat In manyurban areas concentrations of RSP havebecome worryingly high The build-up ofparticles in lungs can contribute to branmiddotchitis and other respiratory diseases

86 The Atmosphere

bull

~[ -i ~o 19~~ 30 OI~0 lll96S-9c 2(1 bullJ97O-4C 10 ~ilm9

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Figure 1111 The spatial variation of fog over Great Britain 1950-1983Source After Musk (1991) fig 66

Aerosols 87

The dust bowl

Tht= dust bowl of tht= 1930s in tht= Grt=at Plains of tht= USA is pt=rhaps tht= bestknown and most oftt=n quott=d t=umpk of largt=-sca1t= wind t=rosion and dU$[stonn activity anywht=rt= in tht= world Tht= most KVt=rt= storms (black blizzards)occurr~d in th~ dust bowl betw~~n 1933 and 1938 and wt=r~ most frc=qu~nt

during th~ spring of th~se y~an At Amarillo T~xas at th~ h~ight of the periodon~ month had 23 days with at I~ast 10 hours of airbocn~ dust and in on~ infiv~ storms visibility was z~ro For comparison th~ long-t~rm average for this partof T~xas is just six dU$[ storms a year

The reasons for this most dramatic of ~cological disast~rs have been widelydiscussed Blame has largely been laid at the feet of the pioneering farmers andsod busters who ploughed up the plains for cultivation For although duststorms are fr~quent in the area during dry years and the 1930s was a droughtperiocl the 5CaI~ and extent of the 1930s events wen unpr~cedented

Plate 1111 In the 19305 (the dirty thirties) the Great Plains of the USAexperienced many black blizzards (dust storms) caused by a combination ofa run of dry hot years and the ploughing up of large tracts of land forgrain production Similar phenomena occur at the present day in the Sahelzone of West Africa This example occurred in Mali in 1977 (Rod McIntosh)

Further reading

Goudie A S and Middleton N J 1992 Tht= changing fnqut=ncy of duststornu through time CJjti( Clmnge 20 197-225

88 The Atmosphere

The Gulf War oil fires hype and reality

I

I KUAlT

I---~----

I SAOOI ARABIA c-i-~)

Following the Iraqi invasion ofKuwaiton 2 August 1990 deliberate oil spillsand oil-well fires were used by the Iraqileader Saddam Hussein as a weaponof war In January 1991 Iraqi torcesdetonated over 800 oil wells (out ofatoal ofaround 1116 wells in Kuwait)ofwhkh 730 exploded Most of these(656) burned lor several monthsmd tht rtlllainder gushed om oilAround I billion barrels of cmde oilwere lost reprtsenting 15-2 per(ellt of the entire Kuwliti oil reserve

Immediately atter this cpisode scishycntists and environmental activistsspcculated that the fites kt alone the spilled oil would have serious local regional1Ild global climatic impacts Doomsday scenarios were slggested including dramati(global (ooJillg similar to thl nuclear winter hypothesis slIplr-acid rain diversionof the Asian summer monsoon and rapid SIlOW melt from talls of bla(k snow

Liter however scientific studies involving remote scnsing ground-level monimiddottoring and computer modelling studies showed that the global climatic impactshad heen exaggefltted The smoke was not injccted high enough to spread overlarge areas of the Northern Hemisphere most of it was confined to an altitudeof between I km and 3 km Reneath the plume of smoke daylight and daytimetemperatures were reduced Simulation modds suggested a decrease in surfacedaytime air temperaures of between 4middotC and 10C (Bakan et aI 1991 Browninget aI 1991) There has been no permanent winter no major diversion of themonsoon and no super-acid rain

Scientific studies have shown however that the months of burning producedemissions of sulphur dioxide carbon monoxide hydrogen sulphide carbon dioxshyide and nitrogen oxides (estimates are showll in table 1Il1) Particulates containshying partly burned hydrocarbons and metals such as vanadium and nickel were alsodischarged into the atmosphere These emissions may have severe local impactsFor exalllple monitoring of inhalable particulate matter (PM IOs) in the EasternProvince of Saudi Arabil during and after the Kuwaiti oil fires found high conshycentrations at various phlCes higher than the maximum permissible level of340 ~g pel- Cl1 metre (Husain and Amin 1994) Other studies in Kuwait itselfin tne April to early May 1991 showed high levels of total airborne particulatematter (soot organic carbon sulphate and chloride) but rather low levels ofsulphur dioxide nitrogen dioxide and carbon monoxide

The local health and ecological impacts of such elevated pollution levels arenow of major concern Some of the compounds released may Ix carcinogenicThe inhalable PMIOs may cause severe health problems Hospital studies inKuwait in 1991 showed a moderate rise (about 6 per cent) in lung and heartcomplaints (Hoffman 1991) Clearly long-term health issues need monitoring

Aerosols 89

Plate 1112 In the Gulf War of 1991 large quantities of oil were burnt ashere at the AI Burgan oil field Fears were expressed that this could have asevere climatic impact In the event these fears were to a large extentmisplaced (EPLJim Hodson)

Table 1111 Predicted annual production of kuwaltl 011 flres in 1991

Type of emission Amount Comparison with current(Tg per year) gfobal emissions

Fine particulate black smoke 5 Roughly onemiddotthird of carbonparticles produced by tropicalbiomass burning

Sulphur (as S oxides) 2 Slightly more than current UKannual S emissions

Nitrogen (as N oxides) 05

Carbon (ultimately as CO2) 60

Tg Teragramme I x 101lg

Source Browning et al (1991)

1988 UK emissions of nitrogenoxide were 075 Tg

About 1 of current globalannual CO2 emissions from Jfossil fuel combustion _

90 The Atmosphere

3 ANTHROPOGENIC CLIMATE

CHANGE ThE ROLE OF

LAND COVER CHANGES

Another major possible human-inducedcause of climate change is change in thereflectivity (albedo) of the ground surfaceand the proportion ofsolar radiation whichthe surface reflects Land-use changescreate differences in albedo which haveimportant effects on the energy balance ofan area Tall rain forest may have an albedoas low as 9 per cent while the albedo ofa desert may be as high as 37 per centThere has been growing interest recentlyin the possible consequences of deforestashytion on climate as a result of the associshyated change in albedo Ground deprivedof vegetation cover as a result of deforshyestation and overgrazing (as in parts ofthe Sahel) has a very much higher albedothan ground covered in plants This couldaffect temperature levels Satellite imageryof the Sinai-Negev region of the MiddleEast shows an enormous difference inimage between the relatively dark Negevand the very bright Sinai--Gaza Strip areaThis line coincides with the 1948-9armistice line between Israel and Egyptand results from different land-use andpopulation pressures on either side of thatboundary Otterman (1974) has suggestedthat the albedo affected by land use hasproduced temperature changes of the orderof SoC

Charney et al (1975) have argued thatthe increase in surface albedo resultingfrom a decrease in plant cover would leadto a reflection outwards of incoming radiashytion and an increase in the radiativ( coolmiddoting of the air Consequently they arguethe air would sink to maintain thermalequilibrium by adiabatic compressionand cumulus convection and its associatedrainfall would be suppressed A positivefeedback mechanism would appear at this

stage namely the lower rainfall would inturn adversely affect plants and lead to afurther decrease in planr cover

This view was disputed by Ripley(1976) He suggested that Charney andhis colleagues when considering the imshypact ofvegetation changes on albedo failedto consider the effect of vegetation onevapotranspiration He pointed out thatvegetated surfaces are usually cooler thanbare ground since much of the solar enshyergy absorbed is used to evaporate waterHe concluded from this that protectionfrom overgrazing and deforestation mightin contrast to Charneys views be expectedto lower surface temperatures and therebyreduce rather than increase convectionand precipitation

The models used by some scholars sugshygest that removal of the humid tropicalrain forests could also have direct climaticeffects Lean and Warrilow (1989) used ageneral circulation mood (GCM) whichsuggested that deforestation in the Annshyzon basin would lead to reductions in bothprecipitation and evaporation as a resultof the changes in surface roughness andalbedo The surface roughness effect occursbecause rain forest has quite a jaggedcanopy and this in turn affects wind flowlikewise a UK Meteorological OfficeGCM shows that the deforestation of bothAmazonia and Zaire would cause precipishytation levels to fall by changing surfacealbedo (Mylne and Rowntree 1992)

Budyko (1974) believes that the presentuse of irrigation over about 04 per centof the Earths surface (13 per cent of theland surface) is decreasing the albedo ofirrigated areas possibly on average by 10per cent The corresponding change in thealbedo of the entire Earth--atmosphere sysshytem would amount to about 003 per centenough according to Budyko to mainshytain the global mean temperature at a levelnearly OlC higher than it would othershywise be

Land Cover Changes 91

Figure 1112 Predictions of the change in climate following a conversion ofAmazonian rain forest to grassland (a) Temperature increase rC) (b) Evaporationdecrease (mm per year) (c) Rainfall decrease (mm per year) (d) Evapotranspirationdecrease (mm per year)Source After Shukla et al (1990)

A change in land use can also lead to achange in the moisture content of theatmosphere It is possible for example thatif humid tropical rain forests arc cut downthe amount of moisture transpired intothe atmosphere above them will be reshyduced This would reduce the potentialfor tain (figure m2(e)) The spread ofirrigation could have the opposite effectleading to increased atmospheric humiditylevels in the worlds drylands The HighPlains of the USA for example are normshyally covered with sparse grasses and havedry soils throughout the summer Evapo-

transpiration there is very low In thelast four decades however irrigation hasbeen developed throughout large partsof the area This has gready increasedsummer evapotranspiration levels Thereis strong statistical evidence that rainfall inthe warm season has been increased bythe use of irrigation in two parts of thisarea one extending through Kansas Nemiddotbraska and Colorado and a second in theTexas Panhandle The largest absolute inshycrease was in the latter area Significandyit occurred in June the wettest of the threeheavily irrigated months The effect appears

92 Thc= Armosphc=rc=

to bc= espc=cially important whc=n stationaryweathc=r fronts occur This is a situationwhich allows for maximum intc=racrionbc=twc=en the damp inigatc=d surface andthc= atmosphc=re Hail stonns and tornashydoes arc= also significantly morc= prc=valc=ntover irrigated dun ovc=r non-irrigated reshygions (Nicholson 1988)

Although wc= have discussc=d albc=doChUlgc= and atmospheric moisture changesas two separate dassc=s of processc=s thc=yneed to be seen as working togc=thc=r Uld

also in association with other mechanismsFor an example of why this is importantwe an look at tropical rain-forest removalThis causa albedo change reduction inmoisture loss by evapotranspiration and achange in surftce roughness The comshybinc=d effects may be considerable (figurem2) They include an increase in temshyIXrature a major dc=crease in loss of moisshyture into the atmosphere and a very majordecrease in rainfall

FURTHER REAoING

Kemp D D) 1994 GlobRl Environmental fuuu A Qimatological Approach 2nd ednLondon RoutledgeA well-iUustratc=d clnr and accessiblc= introduction to many areas of global climaticchange

Figure iII3 (a) The greenhouse effectin the atmosphere (b) A diagramshowing how a greenhouse acts as aradiation blanketSources (a) Houghton et aJ (1990)figure 1 (b) Houghton (1994) figure 22

s-fIl bull -w_IC~ lIt-r-bullbull__ rcc shy

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4 ThE ENHANCED

GREENHOUSE EFFECT AND

GWBAL WARMING

Planet Earth rcccivcs warmth from thc= sunRadiation from the sun is pardy trappedby the atmosphc=re It passes through thc=atmosphere and heats the Earths surfacc=Thc= warmed surface radiates c=nergy butat a longer wavdength than sunshineSome of this cnc=rgy is absorbed by theatmosphere which as a result warms upThe rest of thc= c=nc=rgy c=scapes to spaceWe call this procc=ss of warming thc= greenshyhouse effc=ct because the atmosphere ispercdved to act rather like glass in a grec=nshyhouse (figure 1113) Although the atmosshyphere consists primarily of nitrogen andoxygen it is some of thc= so-called tracegases which absorb most of the heat inspite of the fact that they occur in verysmall concentrations These are called thegreenhouse gases

Various grc=cnhouse gases occur natushyrally - water vapour (HlO) carbon dioxshyide (COl) methane (CH) ozonc= (OJ)

and nitrous oxide (N20) In recent censhyturies and decades however the quantitiesof some of these greenbouse gases havestarted to increase because of humanactiviues In addition a new type ofgreenshyhouse gas the chloroflurocarbons (CFCs)has been introduced to the atmosphere inthe las[ fifty years

Since the start of the industrial revolushytion humans have been taking stored carshybon om of the earth in the form of fossilfuels (coal oil and natural gas) They burnthese fuels releasing CO2 in the processThe pre-industrial level of CO2 in the atshymosphere may have been as low as 260shy270 parts per million by volume (ppmv)The present level exceeds 350 ppmv andis still rising as is evidem in records ofatmospheric composition from variousparts of the world Fossil fuel burningand cement manufacture release over 6gigatonnes of carbon [Q the atmosphereas CO2 each year Burning of forests andchanges in the levels of organic carbon insoils subjected to deforestation and cultishyvation may also contribute substantially toCO2 levels in the atmosphere perhaps byaround 2 gigatonnes of carbon each year

Other gaslts as well as Calgt will probshyably contribute to the accelerated greenshyhouse effect The dTect ofeach on its ownmay be relatively small but the effects ofall of them combined may be considershyable Moreover molecule for moleculesome of these other gases may be moreeffective as greenhouse gaslts than CO2

This applies to methane (CH4 ) which is21 times more effective than COlgt tonitrous oxide (N20) which is 206 timesmore effective and [Q the CFCs whichare 12000-16000 times more effective

Where do these other gases come fromand why are amounts of them increasingConcentrations of methane are now over1600 parts per billion by volume (ppbv)compared to eighteenth-century backmiddotground levels of 600 ppbv Methane has

Global Warming 93

increased as a result of the spread of ricecultivation in waterlogged paddy fieldsenteric fermentation in the growing numshybers of belching and flatulent domesticcattle and the burning of oil and naturalgas Nitrous oxide levels have increasedbecause of the combustion of hydroshycarbon fuels the uslt of ammonia-basedsynthetic fertilizers deforestation andvegetation burning The increase in CFCsin the atmosphere (which is also associshyated with ozone depletion in the stratoshysphere - see section 7 below) results fromtheir use as refrigerants as foam makersas fire control agents and as propellantsin aerosol cans Use of CFCs is now beingrestricted by various international agreeshyments

The Earths climate has become genershyally warmer over the last century or soand the 1980s saw an unprecedentednumber ofwarm years This has promptedsome scientists to propose that globalwarming as a result of the acceleratedgreenhouse effect has already startedHowever the complexity of factors thatcan cause climatic fluctuations leads manyscientists to doubt that the case is yet fullyproven Most however believe that ifconcentrations of effective greenhousegases continue to rise and attain doubletheir natural levels by around the middleof the twenty-first century then temperashytures will rise by several degrees over thatperiod The Intergovernmental Panel onClimate Change (IPCC) which reportedin 1990 suggested that global mean temshyperature might increase during the nextcentury at a rate of 03degC per decade TheIPeC report of 1996 suggested a bestestimate of20degC increase in temperatureby 2100 (with a range of 1-3SdegC) Thisis somewhat lower than previous predicshytions because of improvements in inforshymation and modelling techniques Coolingeffects of aerosols are taken into accountin this prediction The rise in temperature

94 Thc= Atmosphere

I

Figure 1114 Change in global surface temperature following a doubling of CO2

(a) December January and February (b) June July and AugustSource Kemp (1994) figure 78 using data in Houghton et al (1990)

will not howevc=r bc= thc= samc= across thc=g1obc= In particular high latitudc=s (egnorthern Canada and Eurasia) will showeven morc= pronounced warming perhapstwo to three times the global average(figw-e III4)

Such increasc=s in tc=mperaturc= if thc=yoccur will undoubtedly causc= majorchanges in the general atmospheric circushylation These in turn will cause changc=sin precipitation patterns Overall levels ofprecipitation ovc=r the g1obc= will increasc=as morc= moistl1laquo is relc=ased by higher ratesofevaporation from the oceans However

some areas will get wetter while some willgc=t drier Thc=re is still considerable uncershytainty about what precise pattern precipishytation will take as a result of these changc=sThe very cold dry areas of high latitudesmay well become moister as a warmeratmosphw= will be able to hold moremoisture Some tropical areas may receivemore rain as the vigour of the monsoonalcirculation and of tropical cyclonc=s is inshycreasc=d Some mid-Iatitudc= areas like theHigh Plains of America may becomemarkedly drier

Therc= is however great uncertainty as

to how far the climate may change as aresult of me greenhouse effect The reashysons for this uncertainty include

bull doubts about how fast the global ecoshynomy will grow

bull doubts about what fuels will ~ usedin the future

bull doubts about the speed at which landshyuse changes are taking place

bull uncertainty regarding how much COlwill be absor~d by the oceans and bybiota

bull uncertainties about the role of omeranthropogenic and natural (eg volshycanic) causes of climatic change

bull the assumptions that are built intomany of our predictive general circulashytion models (eg about the role ofdouds)

bull the role of possible positive feedbacksand thresholds that may mean changesare more sudden than anticipated ordo not happen at all

The degree of global warming that IS

proposed for the coming decades does notat first sight appear enormous Howeverit may over a period that is very short ingeological terms produce warmer condishytions than have existed for several millionyears and set up a series of changes thathave important implications both for theenvironment and for humans Some ofthese implications may be benign (eg

Global Warming 95

warmer conditions will enable new cropsto be grown in Britain) but some of themwill be malign (eg more frequent andlonger droughts in the High Plains ofAmerica) Among the possibeenvironmenshytal consequences are

bull more intense widespread and frequenttropical cyclones

bull the melting of alpine glaciersbull the degradation of permafrost in tunshy

dra areasbull the wholesale displacement of major

vegetation belts such as the borealforests of the Northern Hemisphere

bull rising sea levels and associated floodshying of coral reefs deltas wetlands etcand accelerated rates of beach erosion

bull decreased flow of water in streams as aresult of increased loss of moisture byevapotranspiration

bull reduction in the extent of sea ice inpolar waters

bull shifts in the range of certain vectorshyborne diseases (eg malaria)

Many scientists and politicians believe thatthe case has now been made that globalwarming will occur and that the resultingchanges are likely to be so significant thataction needs to be taken In some countriesa policy of no regrets is being promotedThis is a policy under which the reductionof greenhouse emissions is also justifiableon other grounds (see table 1112)

Table 11I2 Examples of no regrets climate-warming policies

Policy

Tree planting

Energy conservation

Energy efficiency

CFC emission control

FURTHER READING

Effect on greenhouse gases

Increased biosphere sinkstrength to absorb CO2

Reduced CO2 emissions

Reduced CO2 emissions

Reduced CFC emissions

Other benefidal effects

Improved microdimate

Improved habitat for manyspedesReduced soil erosion

Reduced seasonal peak riverflows

Conservation of nonshyrenewable resources forcurrent and futuregenerations

Conservation of nonmiddotrenewable resources forcurrent and futuregenerations

Reduced stratospheric ozonemiddotlayer depletion (see section7)Reduced surface UV-S andassociated skin cancer andblindn~s

Houghton J T 1994 Global Warming The Camplere Briefing Oxford Lon BooksA useful clearly written introduction by a leading expcrt that summarizes the keyfindings of the worlds scientific community in this area

Houghton] T Jenkins G J and Ephraums]] (eds) 1990 Climate Change TheIPCC Scientific Assessment Cambridge Cambridge University PressHoughron J T Callander B A and Varney S K (eds) 1992 Climate Change 1992T1Jt Supplementary Report of the IPCC Scientific Mesrmet Cambridge CambridgeUniversity PressHoughton J T Meira Filho L G Callander B A Harris N Kaltenberg A andMaskell K (eds) 1996 Qimau OJtlnge 1995 The Stience of Climate OJange Camshybridge Cambridge University PressThree reports from the global bod) the Intergovernmental Panel on Climate Change(IPCq established to look at the causes and consequences of global warming

Kemp D D 1994 Global Enpironmental Imm A QimatoloBical Approach LondonRoutledge

- -

Figure 1115 The potential distributionof grain maize in the UK underdifferent warming scenariosSource After Parry in Jones (1993) fig 11

Global Warming 97

Global warming and UK agricultureA5 a result ofglobal warming the temshyperltu~ in Britain could rise by severaldegrees Celsius during the coune ofthe next 50-100 yean A change in theclimate of this magnitude would belikely to shift the thermal limits of agshyriculture by around 300 kin oflatitudeand 200 m of altitude per degree Celshysius Several crop species such as wheatmaize and sunflowers have their conshytemporary northern limits in the UKAn increase oftempcrltu~ could thereshyfore assuming that soil conditions ~resuitablelead to a substantial northwardshift of cropping zones This couldtransform the British agricultural landshyscape British 6dds and rural areas mightcome to resemble those currcndy foundfurther south in mainland Europe Foeexample the northern limit of grainmaize which currendy lies in the CIshy

treme south of England (see figureIlLS) could be shifted Kross centnlEngland by a OSmiddotC inclUSC in temshyperature across nocthern England bya lSmiddotC inclease and into the north ofScodand by an increase of 3C

A rise in temperatule apart fromtruufonning the range over which parshyticular CIOP types could be growncould be significant for the agriculshytural sector in other ways For example higher temperatures and more frequentsummer droughts migh[ Ieduce crop yiclds The occurrence of certain plant pestsand diseases could change for better 01 worse

Further reading

Jones D K C (ed) 1993 Earth surface resources management in a warmerBritain GeoIJr4phittd ]owNId 159 124-208

98 The Abnosphere

5 U RJlAN CLIMATES

Climate Stltistics for recent decades showthat many cities have become warmer thanthe countryside around them Climatoloshygists have long spoken of the urban heatisland in the cool rural sea The boundshyary between countryside and city forms asteep temperature gradient or difT to theurban heat island Much of the rest of theurban area appears as a plateau of warmair with a steady but shallower gradient ofincreasing warmth towards the city censhytre The urban core or central businessdistrict with its high-density buildings isa peak where the maximum temperatureis found The difference between this peakvalue and that in the rural sea defines theintensity of the urban heat island

There are various reasons why cities maybe relatively warmer than the fUJa1 areasthat surround them (figure 11I6) Firstcity surfaces absorb significantly moreradiation from the sun than rural surfacesThis is because a higher proportion of the

ttgtlto

Figure 1116 Mechanisms of urban climates

reflected radiation is retained by the highwaIls and dark-coloured roofs and roadsof the city environment These city surshyfaces have both great thermal capacity andhigh conductivity so that heat is storedduring the day and released by night Bycontrast vegetation cover gives plantshycovered rural areas an insulating blanketso that they experience rdatively lowertemperatures both by day and by nightThis effect is enhanced and compoundedby the evaporation and transpiration thatoccur from plant-covered surfaces Secshyondly cities are relatively warm becausethey generate a large amount of artificialheat Energy is produced and then usedby industrial commercial transport anddomestic usen

The heat island effect is nO the onlyway that towns and cities affcd theclimate HDWaCf the effects ofurban areason other aspects of climate are less easilymeasured and explained There is someevidence that rainfall induding that proshyduced by summer thundemorms can be

t t

bull

higher over urban than ruraJ areas Thereart various possible ccasons for this

bull the urbm hcat island generates conshyvection (ie thermally induced upwardmovement of air)

bull the presence of high-rise buildings anda mixture of building heights inducesair turbulence and promotes increasedvertical motion

bull cities may produce large amounts ofwater vapour from industrial sourcesand power stations and also variouspollutant aerosols that act as condenshysation nuclei

The London area provides an interestshying but by no means unique example ofthe effects of large chies on prccipitationlevels In this case it seems that the meshychanical dreer of the city was the maincause of local peak precipitation It hadthis effect by being a mechanical obstacleto air flow on the one hand and by causshying frictional convergence of flow on theother A long-term analysis of thundershystorm records for south-east Englandshows that thunderstorms arc mort freshyquent over the urban area than elsewherein the region (Atkinson 1968) The simshyilarity between the shape of the thundershystorm isopleth and that of the urbanarea is striking Moreover Brimblecombe(1977) found that thunderstorms havebecome steadily more frequent as the cityhas grown

Winds arc another aspect of the urban

Ft1IlTHBR READING

Urban Climates 99

climate There arc twO main aspects to theeffect that cities have on winds first therougher surface cities prescnt in comparishyson with rural areas and secondly thefrequently higher temperatures of the ciryBuildings especially those in cities with avery varied skyline exert a powerful mcshytional drag on air moving over and aroundthem This creates turbulence with rlpidand abrupt changes in both direction andspeed The average speed of the winds islower in built-up areas than over ruralareas However Chandler (1976) foundthat in London when winds arc lightspeeds arc greater in the inner city thanoutside whereas when winds arc strongspeeds arc greater outside the city centreand lower within it Overall annual windspeed in centraJ London is about 6 percent 10000er than outside but for the highershyvelocity winds (more than 15 metres persecond) the reduction is more than twicethat

Studies in two English cities Leicesterand London have shown that on calmdear nights when the urban heat islandeffect is at its greatest there is a surfaceinflow of cool air towards the warmestzones These so-called country breezesare low in velocity and arc quickly sloweddown further by intense surface friction inthe suburban areas One effect of thesebreezes is to transport pollution from theouter parts of an urban area into the citycentre accentuating the pollution probshylem during periods with photochemicalsmogs

Landsberg H E 1981 The Urba Ciuatt New York Academic PressThe classic study

OU T J 1987 amp LAyer Cliatu 2nd cdn London RoudedgeA thorough review of Iocalmiddotscale climates which includes an authoriativc study ofurban clinutes

100 The Atmosphere

Ghe implications of some urban heat islandsI ~ cities grow so does their heat island effect In Columbia Maryland USA for

example when the town had only 1000 inhabitants in 1968 the maximumtemperature difference between residential areas and the surrounding countrysidewas only ImiddotC By 1974 when it had grown to a town with a little over 20000inhabitants the maximum heat island effect had grown to rc

Thus the annual average temperatures over the hearts of great cities can besubstantially higher than those over the surrounding countryside This is dearfrom the temperature map of Paris (figure 1I17(araquo) The outlying weather stashytions have mean annual temperatures of 106-109middotC whereas in cennal Paristhe value is 123C about lSC higher These values have all been reduced toa uniform elevation of 50 metres above sea level to correct for possible orographiceffects

Urban climates are often characterized by different precipitation characteristicsfrom rural areas For example it is remarkable that there tends to be more rainin Paris during the week than at weekends (figure III7(b)) There is a gradualincrease in average rainfall from Monday to Friday (when factories art producingmore heat and aerosols) then a sharp drop for Saturdays and Sundays Theweekend average for May to October was 147 mm whereas the workday averagewas 193 mm - a decrease of 24 per cent for the weekend

In winter months the consequences of urban heat islands can be particularlysignificant in cold regions For example the average date of the last freezingtemperatures at the end of winter in Washington DC in the USA is about threeweeks earlier than in the surrounding rural areas (figure 1I17(c)) In aurumn thecity has on average the first freezing temperature on about 3 November whereasin the outlying suburbs OC will usually be observed about two weeks earlierThus in all the frost-free season will be about 35 days longer than it is in thecountryside Similar figures have been obtained for some other great cities Datafor Moscow Russia suggest an increase of around 30 days without freezingwhile those for Munich in Germany suggest an increase that can be as g~at as61 days

In summer months the urban heat island effect can lead to an increasingdemand for air conditioning and because the energy requirements of air conshyditioning are greater than those of heating the savings in winter heating bills aremore than offSet Moreover air conditioning can aggravate the heat island effectbecause air conditioning plant discharges heat to the outside air where it mixeswith air that has already been warmed up by the hot air forming adjacent to sunlitwalls and pavements

Further reading

Landsberg H E 1981 The Urban Climate New York Academic Press

Urban Climates 101

~ Ilourg~t 107bull

(b

~

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bull $I rquCi 123 ~ll)bscwllolty 116

MontlOU 116 bull S M~ur IIS

0 109Mrm 0 Cmtul P-risMoo-Fri

li]

I

Figure 1117 The impact of urban areas on climate (a) Annual isotherms inthe Paris region (b) Precipitation in Paris averaged by day of the week(c) Average date of last freezing temperature in spring in Washington DC(A = International Airport B =White House)Source Landsberg (1981) figures 55 86 525

102 The Atmosphere

6 URBAN AIR POLLUTION

The concentration of large numbers ofpeople factories power stations and carsmean that large amounts of pollutantsmay be emitted into urban atmospheresIf weather conditions permit the level ofpollution may build up The nature of thepollutants (table 1113) has changed astechnologies have changed For examplein the early phases of the industrial revoshylution in Britain the prime cause of airpollution in cities may have been the burnshying of coal whereas now it may be vehishycular emissions Different cities may havevery diffennt Icvels of pollution dependshying on factors such as the level of techshynology size wealth and anti-pollutionlegislation Differences may also arise beshycause of local topographic and climaticconditions Photochemical smogs for

Table 1113 Major urban pollutants

example are a more serious threat in areassubjected to intense sunlight

The variations in pollution Icvels beshytween different cities arc brought out infigure IIIB which shows data for twotypes of pollution for a large range of citytypes The data were prepared for the years1980--4 by the Global Environment Monishytoring System of the United NationsEnvironment Programme (UNEP) Figshyure IIIB(a) shows concentrations of totalparticulate matter Most of this comes fromthe burning of poor-quality fuels Theshaded horizontal bar indicates the rangeof concentrations that UNEP considers areasonable target for preserving humanhealth Note that the annual mean levelsrange from a low of about 35 lig percu metre to a high of about 800 ligper cu metre a range of about 25-foldThe higher values appear to be for rapidly

Type

Suspended particulate matter(characteristically 01-25 11m indiameter)

Sulphur dioxide (5deg2)

Photochemical oxidants ozoneand peroxyacetyl nitrate (PAN)

Oxides of nitrogen (NOx)

Carbon monoxide (CO)

Toxic metals lead

Toxic chemicals dioxins etc

Some consequences

Fog respiratory problems carcinogens soilingof buildings

Respiratory problems can cause asthmaattacks Damage to plants and lichenscorrosion of buildings and materials productionof haze and acid rain

Headaches eye irritation coughs chestdiscomfort damage to materials (eg rubber)damage to crops and natural vegetation smog

Photochemical reactions accelerated weatheringof bUildings respiratory problems production ofacid rain and haze

Heart problems headaches fatigue etc

Poisoning reduced educational attainments andincreased behavioural difficulties in children

Poisoning cancers etc

1

()

)

Urban Air Pollution 103

(For caption see overleaf)

104 The Atmosphere

growing cities in the developing countriesSome cities however such as Kuwait mayhave unusually high values because Qf theirsusceptibility to dust storms from deserthinterlands The lower values tend to comefrom cities in developed areas (eg Westshyern Europe Japan and North America)

Figure III8(b) shows concentrations forsulphur dioxide Much of this gas probshyably comes from the burning of highshysulphur coal Once again the horizontalshaded bar indicates the concentrationrange considered by UNEP to be a reashysonable target for preserving human healthThese data indicate that the concentrationsof sulphur dioxide can differ by as muchas three times among different sites withinthe same urban area and by as much as30 times between different urban areas

In some cities concentrations of polshylutants have tended to fall over recentdecades This can result from changes inindustrial technology or from legislative

changes (eg clean air legislation restricshytions on car use etc) In many Britishcities for example legislation since the1950s has reduced the burning ofcoal Asa consequence fogs have become lessfrequent and the amount of sunshine hasincreased Figure IlL9 shows the overalltrends for the United Kingdom and highshylights the decreasing fog frequency andincreasing sunshine levels The concentrashytions of various pollutants have also beenreduced in the Los Angeles area of C~lishy

fornia (figure 11110) Here carbon monshyoxide non-methane hydrocarbon nitrogenoxide and ozone concentrations have allfallen steadily over the period since thelate 1960s

However both of these examples ofimproving trends come from developedcoumries In many cities in poorer counshytries pollution is increasing at present Incertain countries heavy reliance on coaloil and even wood for domestic cooking

Figure 1118 (a) The range of annual averages of total particulate matterconcentrations measured at multiple sites within 41 cities 1980-1984 Eachnumbered bar represents a city as follows 1 Frankfurt 2 Copenhagen 3 Cali 4Osaka 5 Tokyo 6 New York 7 Vancouver 8 Montreal 9 Fairfield 10Chattanooga 11 Medellin 12 Melbourne 13 Toronto 14 Craiova 15 Houston16 Sydney 17 Hamilton 18 Helsinki 19 Birmingham 20 Caracas 21 Chicago22 Manila 23 lisbon 24 Accra 25 Bucharest 26 Rio de Janeiro 27 Zagreb28 Kuala lumpur 29 Bombay 30 Bangkok 31 Illigan City 32 Guangzhou 33Shanghai 34 Jakarta 35 Tehran 36 Calcutta 37 Beijing 38 New Delhi 39Xian 40 Shenyang 41 Kuwait City (b) The range of annual averages of sulphurdioxide concentrations measured at multiple sites within 54 cities 1980-1984Each numbered bar represents a city as follows 1 Craiova 2 Melbourne 3Auckland 4 Cali 5 Tel Aviv 6 Bucharest 7 Vancouver 8 Toronto 9 Bangkok10 Chicago 11 Houston 12 Kuala lumpur 13 Munich 14 Helsinki 15lisbon 16 Sydney 17 Christchurch 18 Bombay 19 Copenhagen 20Amsterdam 21 Hamilton 22 Osaka 23 Caracas 24 Tokyo 25 Wrodaw 26Athens 27 Warsaw 28 New Delhi 29 Montreal 30 Medellin 31 St louis 32Dublin 33 Hong Kong 34 Shanghai 35 New York 36 london 37 Calcutta38 Brussels 39 Santiago 40 Zagreb 41 Frankfurt 42 Glasgow 43Guangzhou 44 Manila 45 Madrid 46 Beijing 47 Paris 48 Xian 49 SioPaulo 50 Rio de Janeiro 51 Seoul 52 Tehran 53 Shenyang 54 MilanSource Graedel and Crutzen (1993)

and hating Imam that their levels ofsulphur dioxid~ and suspend~d particulatematter (SPM) ar~ high and climbing Inaddition rapid economic d~velopment is

Urban Air Pollution lOS

bringing increased emissions from indusshytry and motor vehicles which are g~nershy

ating progressively more serious air-qualityproblems

~ _ roaI COIlIbaIOooI

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00bull J1

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1965-80

bull - Figure 11I9 Trends in atmospheric quality in the United Kingdom (a) Sulphurdioxide emissions from fuel combustion and average urban concentrations(b) Smoke emissions from coal combustion and average urban concentrations ofoil smoke (c) Increase in winter sunshine (10-year moving average) for londonand Edinburgh dty centres and for Kew outer london (d) Annual maximumhourly ozone concentrations at selected sites in the Los Angeles basin1958-1989 (e) Annual fog frequency at 0900 GMT in OxfOfd central England1926-1980Sources (a)-(c) Figures from Depa~nt of Environment (d) After Elsom (1992) figure211 (e) After Gomez and Smith (1984) figure 3

o lSU 70 72 74 Jf 11 ID a 14

in (ie smaller than 10 Jffi and so oftenknown as PMIOs) Also of great conc~min terms of human health ar~ elementalcarbon (for example from diesel vehicles)polynuclear aromatic hydrocarbons (PAHs)and toxic b~ metals (eg arsenic leadcadmium and mercury) in part becauseof their possible role as carcinogens

Urban air pollution V3S particularlysevere in the former Communist states ofEastern Europe Carter and Turnod(1993 p 63) described this problem andits political background in the comext ofCzechoslovakia (now the Czech ~public

and Slovakia)

Environmental quality has clearly detemiddotriorated as a result of human activitythe major cause is an excessive 3ndinconsiderate extraction of naturalresources extensive waste emissionsand failur( to observ( ecological andaadKtic laws These were compoundedby an inefficient economy which conshysumed inordinat( amounts of raw mashyterials and energy based on outmodedtechnology which produced manufacshytured goods with little respect for theccologicaJ consequences This ud situshyation was further aggravated by inadshyequate financial reoourcc allocation forenvironmental protection which was ofa rem~dial chancter rath~r than one ofdamage prevention Much of the blamefor this state of affairs must be laid uponthe Communist government over thepast fony years when legislative execushytive and political pow~r was concenshytlared in the hands ofa small controllinggroup (lIomenilRtJlrll) who did little tocorren adv~rse effects on the ~nvironshy

men( cauSoCd by their policies Addedto this dctrimentll domestic attitude wasthe significant contribution made bytrlrUboundary pollution from neighshybouring states particularly along thenorthern and western boundaries of thecountry

The problem was cncerbated by the uscof lignite (brown coal) in some of the East

Particular attention is being paid at thepreKnt time to the chemical compositionof SPMs and particularly to those partishycles that are snull enough to be bruthed

Figure 11110 Air quality trends in losAngeles and its environs have beenmeasured continuously and averagedover each hour The highest of thehourly averages is then selected fortrend analysis Part (a) shows thedownward trend in carbon monoxide(CO) concentrations this trend isconsistent with vehicular emissioncontrol measures part (b) shows thetrend for oxides of nitrogen (NOx) andozone (OJ Both are expressed in partsper billion by volume (ppbv)Source Modified from kun~ and Chang(19Sn copyright 1987 by Air PollutionControl Association

106 The Atmosphere

u (0)

1 bullAs I8

bull bull n bull ~ G ~ bully

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00

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--0

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Urban Air Pollution 107

Plate 1113 Some of the worst urban air pollution occurred in the former SovietUnion A particularly gruesome pollution hot spot was the Magnitogorsk steeshymaking area (Katz Pictures)

European states Such col is of low qualshyity so disproportionatdy large quntiticshve to be burnt it can also have bull veryhigh sulphur content Cuter and Turnock(1993 p 189) refer to the dedly plI ofsulphurous smoke tht this fud source

FURTHER READING

has hdped to promote They point outthat even in the late 1980s over threeshyquarters of Polnds energy orne frombrown coal as did two-thirds of the enmiddotergy in Czechoslovakia and the fonner EastGermany

Brimblecombe P 1987 The Big Smoke London MethuenA diverting history of air pollution with particular reference to London

Carter F W and Turnock D (eds) 1993 Environmental Problems in Eastern EuropeLondon RoutledgeAn edited collection of papers on the kgacy of dtcadful air polJution problems inEastern Europe

Elsom D 1996 S418 Alert Mtma8in8 UrbAn Air ~AH London EanhscanA very readable and informative guide

108 The Atmosphere

Air pollution in South Mrican cities the legacy ofapartheidSouth Mrica produces the worldscheapest electricity but for manyyears it has only been available toaround 30 per cent of the populashytion This bald statement sums upthe major causes of South Africanurban air pollution Around 83 percent of South Africas electricity isgenerated by coal-fired power stashytions which burn coal with a sulshyphur content of around 12 per centSuch high sulphur content (relativeto many other types of coal) proshyduces high levels of polluting gasesMany of these plants are located inthe eastern Transvaal which suffersgreatly from air pollution and acid deposition Apartheid the system of governshyment which dominated South Africa from 1948 to 1994 and forced differentracial groups to live apart produced highly unequal distributions of access toenergy resources and of pollution conditions Apartheid forced black and Colshyoured populations into poor townships usually without electricity and withsevere pollution problems

The background air pollution in many parts of South Africa is increased inurban environments where coal paraffin and wood are burnt as important domesticenergy sources By 1985 about 57 per cent of the entire South African populashytion lived in cities many of them in squatter settlements and townships whereelectricity supply was limited Soweto for example some 15 Ion from Johannesshyburg covers nearly 60000 sq Ion and had a population in 1990 of around 25million according to some tstimates Electricity was brought into Soweto in1981 but coal is still widely used as it is cheaper and the supply more reliable

Sulphur dioxide pollution is now a critical health problem for Sowetan inhabshyitants In Soweto mean annual sulphur concentrations are up to 60 ~g percu metre whereas in the unpolluted north-west of Transvaal mean annual conshycentrations are on average only about 7 ~g per cu metre There are also highlevels of nitrogen oxides and carbon monoxide in Soweto

The air pollution problems of Soweto are exacerbated by climate andtopography North and north-westerly winds transport pollution here fromJohannesburg city centre and winter temperature inversions help trap the polshylution The South African Department of Health now believes coal smoke intownships to be the most serious national air pollution problem Air pollution isa problem indoors as well as outdoors especially in areas where open fires orinefficient stoves are used for cooking Suspended particulate matter carbon

Urban Air Pollution 109

Plate 1114 Air pollution in Cape Town South Africa Much of the pollutionis caused by the burning of low-quality fuel in the densely populatedtownships that surround the city At some times of year the pollutingsmoke and gases are trapped by climatic conditions called inversions(A S Goudie)

monoxide oxides of sulphur and nitrogen hydrocarbons and a range of otherpollutants are produced by stoves and fires The accumulation of indoor andoU[door pollution in Sowew and many other towns is leading to severe respirashytory problems especially in the poorest and most vulnerable members of societyAsbestos also poses an air pollution problem in South Africa where blue asbestosis mined in the northern Transvaal and northern Cape Asbestos can cause lungand other cancers and urbanized areas near mining operations are particularlyvulnerable to wind-blown asbestos

Further reading

Ramphele M 1991 Restoring the Land Environme1Jf and Change in PostshyApartheid South Africa London Panos

Vogel C H and Drummond J H 1995 Shades of green and brownenvironmental issues in South Africa In A Lemon (ed) The Geographyo[Changein South Africa 85-98 Chichester Wiley

110 The Atmosphere

7 OZONE DEPLETION AND

OZONE POLLUTION

Ozone (03) was discovered in 1840 It isa naturally occurring form ofoxygen whichconsists of three oxygen atoms rather thantwo It exists throughout the atmospherein very low concentrations never exceedshying around one molecule in every 100000present It is especially abundant in thestratosphere between 10 and 40 km abovethe ground This ozone layer containsabout 90 per cent of atmospheric ozoneand is important because it provides athin veil which absorbs ultraviolet (UV)radiation from the sun Indeed the ozonelayer prevents about 97 per cent of W-Blight from reaching the Earths surfaceToo much ultraviolet radiation can damshyage plants including the phytoplanktonthat live in the oceans In humans it cancause skin cancers it may also cause eyecataracts and damage the bodys immunesystem Thus it is clear that any reductionin the thickness and concentration ofozone in the ozone layer is worrying

In the 1980s satellite observationsground measurements and readings frominstruments on balloons and in aircraftbegan to suggest that the ozone layer wasbecoming thinner especially over theAntarctic More recent measurements haveindicated that the ozone layer is also thinshyning over America and northern Europe(see table III4) Here ozone decreasedon average by around 3 per cent in the1980s In the 1970s concern was expressedabout possible damage to the ozone layerby high-flying supersonic aircraft such asmilitary jets or Concorde However curshyrent concern among scientists is focusedon a range of manufactured gases ofrecent origin These include chloroflushyorocarbons (CFCs) and halODS Thesegases have been extremely useful in manyways - for example as refrigerants for

extinguishing fires for making foams andplastics and for use in aerosol spray cansThis is because they have some valuableproperties they are stable non-flammableand non-toxic Unfortunately their stabilshyity means that they can persist a long timein the atmosphere and can thus reach theozone layer witham being destroyed Oncethey are in the ozone layer UV radiationfrom the sun starts to break them downThis sets olf a chain of chemical reactionsin which reactive chlorine atoms arereleased These act as a catalyst causingozone (03) to be converted into oxygen(0) (figure IIUl)

Global production of CFC gases inshycreased gready during the I960s 1970sand 1980s from around 180 million kgper year in 1960 to nearly 1100 millionkg per year in 1990 However in responseto the thinning of the ozone layer manygovernments signed an international agreeshymenl called the Montreal Protocol in1987 This pledged them to a rapid phasshying out of CPCS and halons Productionhas since dropped substantially Howeverbecause of their stability these gases willpersist in the atmosphere for decades oreven centuries to come Even with themost stringent controls that are now beshying considered it will be the middle ofthe twenty-first century before the chloshyrine content of the stratosphere falls beshylow the level that triggered the formationof the Antarctic ozone hole (see below)in the first place

Some thinning of the ozone layer mayresult from time to time from naroralrather than anthropogenic processes Apossible factor may be the pollution of thestratosphere with particulate material (aeroshysols) emitted by volcanic eruptions suchas that of Mt Pinatubo in June 1991

The most drastic decline in stratoshyspheric ozone has been avec AntarcticaThis has led to the formation of theozone hole which expanded to an area

Ozone Depletion Ozone Pollution 11

()

Plate 1115 (a) The Antarctic Olone hole from space 8 October 1995 overleaf(b) the Northern Hemisphere ozone hole 12 March 1995 The colours representozone concentrations in Dobson units (NOAAScience Photo Library)

Table 1114 Trends in stratospheric Olone 1979-1991 ( per decade)

December-March May-August September-November

Satellite-derived data45degNEquator455

-56 35+03 plusmn 45-52 plusmn 15

-29 plusmn 21+01 plusmn 52-62 plusmn 30

-17 plusmn 19+03 plusmn 50-44 plusmn 32

Land-based data26middotN-64middotN -47 z 09 -33 z 12

Sour~ Tolba and E1middotKhoIy (eels) (1992) tabJe 2 p SO

-12 t 16

112 Th~ Atmosph~rc

(b)

Figure 11I11 opposite (a) The naturally occurring chemical processes leading tothe formation and decomposition of ozone in the atmosphere in the presence ofultraviolet radiation (b) The decomposition of ozone initiated by chlorine atomsreleased dUring the breakdown of a commonty occurring anthropogenicaUygenerated CFC believed to be harmful to the atmosphere (CFCll ) Not all thetwo-atom (diatomic) molecules of oxygen combine to form ozone and the freechlorine atoms that are liberated are potentially capable of initiating furtherreactions that lead to the breakdown of ozone (c) Schematic diagram to show theprindpaJ sources of atmospheric ozone and the main reactions that cause ozonedepletion in the stratosphereSource Pickering and Owen (1994)

Ozone Depletion Ozone Pollution 113

(-

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114 The Atmosphere

of 24 million sq km during SeptembershyOctober 1992 and again in the same monthsof 1993 Record low ozone levels of lessthan 100 ozone units were registeredduring a few days in October 1993 Thesecompare with values from years before theozone hole (1957-78) of 330-350 units

The deS[ruction of ozone is grC=3[estover the Antandc because of the uniqueweather conditions during thc long darkwimer of the south polar regions Strongwinds circulate in a great vortex above theAntarctic essemially isolating the polarstratoshysphere from the rest of the atmosphereUnder the vcry cold conditions with ternmiddotperatures below -SOmiddotC icc clouds formcalled polar stratospheric clouds Theseprovide ideal conditions for the transforshymation ofchlorine (derived from the breakshydown of CFCs ampOd halons) into potentiallyreactive compounds When sunlight reshyturns in the spring months UV radiationfrom the sun triggers the reaction betweenthese chlorine compounds and ozonethereby leading to ozone destruction

No such clear ozone hole develops overthe Arctic becau$C the more complexarrangement of land and sc-a here leads toa less weU devel~d vortex system ofwinds In addition the winter stratosphereat the North Pole tends to be warmerthan its southern coumerpart This meansthat polar stratospheric clouds arc usuallyless abundant Nonetheless ozone depIcshytion docs seem to have occurred producshying an ozone crater rather than a hole

Paradoxically while ozone levels may be

FURTHER READING

dropping in the stntosphere at lowerlevels in the atmosphere they arc increasmiddoting This tropospheric ozone is producedb) the action of sunlight on the nitrogenoxides and hydrocarbons that are emittedin fossil fuel exhaust gases Such photoshychemical reactions as thcy arc caJlcd arcparticularly serious in some great citieslike Los Angeles where the high densityof chicles the frequent occurrcncc ofsunshyshine and the favourable topography leadto high concentrations ofa soup ofphotomiddotoxidant gases Rcscarch in both Americaand Europe has established that extensiveformation of tropospheric ozonc also freshyquently occurs in Northern Hcmispheremid-latitudes in thc summer in non-urbanareas most noticeably downwind of citksand major industrial regions The problemis fegional rather than mcrdy urban

High levels ofozone conccnrration havesc-vcral ~rious consequences Humanssuffef from eye irritation respiratory comshyplaints and headaches Ozone is also poshytcncally toxic to many species ofconiferoustrces herbaceous plants and crops at conmiddotccntrations nOt far above the natural backmiddotground le-d Rigorow controls on vehicleemissions can grcatly reduce thc problemSuch mcasures arc now being implementedin California Indeed as figure m12 showsin spite of a hefty increase in both popumiddotlation and the number of mOtOf vehicles inthc Los Angeles area since 1970 peak ozonclevels havc declincd vcry markedly and thearea subjected to high ozone concenmshytions has shrunk (Lents and Kdly 1993)

Gribbin J 1988 Tnt Hole in the sq MRns TbreRt to the Ozone lAyer London CorgiBooksAn introductory trcatment for the gencral public by a well-known scientific journalist

Minrur I M and Miller A S 1992 Stratospheric ozone depletion can wc savc thesky~ In Green GlDbe naboo 1992 83-91 Oxford Oxford Univcnity PressA morc rccent gcncra1 discussion of thc causes and consequences of the ozone hoIcand what can be done to deal with it

Ozone Depletion Ozone PoUution 115

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Figure 11112 AJr pollution in the Los Angeles area 1970s-1990sSource After Lents and Kelly (1993) p 22

116 The Atmosphere

pH

Figure 11113 The pH scale shOWingthe pH level of add rain in comparisonwith that of other common substancesSource Kemp (1994) figure 41

As a result ofair pollution precipitationin many parts of the world has pH valuesfar below 565 Snow and rain in thenorth-east USA have been known to havepH values as low as 21 In the eastern

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8 ACID DEPOSITION

Rain is slightly acid under natural conditionsbecause it contains some dissolved gasesincluding carbon dioxide (COl) sulphurdioxide (SOl) and nitrogen oxides (NOx)The~ gases are naturally pre-sent in theair Under natural conditions rain has apH of around 565 (figure 11113) Theterm acid rain was introduced as longago as the 1850s for rain which has a pHof less than 565 Such rain has becomemore than usually acid because of air polshylution Two of the chemical reactions inshyvolved are shown in figure IIIl4

Some scientists prefer the term aciddeposition to acid rain for not all envirshyonmental acidification is caused by acidrain in the narrow sense Acidity can reachthe ground surface without the assistanceof water droplets as particulate matter orgases This is termed dry deposition Furshythermore there are various different typesofwet deposition mist fog hail sleet andsnow as well as rain itself

(t) SuIplunlU$ Ind sulphuric acids

~ il tlDimd ampom lWurlllnd whropogtnic sourm Ind dissoIm in cloud _to pnld~ IUIphurous Kid

SuJphlllOU$lcid Cln b oxidimi in the pi or ~ueouI plwe by IlIrious oxidants

~ amp ~

AqUtltlll$ sulphur lrioxidt fonm IlIIpburil acid

(2) Nilrow lind nilric arids

NO alldN~ (rolIecliVlly known as Nih) art ptoduced by combuslion prornseI and lightnillshyNilric and nil10llS acids may b produced

Figure 11114 Chemical reactions producing acid depositionSource Modified after Mannion (1992) fig 112

Acid Deposition 117

Table 1115 Main sources of acid gases in the UK In 1990

Nitrogen oxidesRoad transportPower stationsIndustry

Sulphur dioxidePower stationsIndustry

Annual emissions(000 tonnes)

1400780270

2700710

of UK total

51289

7219

Source Department of Environment figures

USA as a whole the avcrage annual acidityvalues of precipitation tend to be aroundpH4 The pH scale is logarithmic so adecrease of one pH unit represents a tenshyfold increase in acidity Thus pH4 is tentimes more acidic than pHS The maingases responsible for this state of afhirsare the sulphur oxides and nitrogen oxshyides emined from fossil fuel combustion(see table ilLS) As a general rule sulshyphur oxides have the greatest effect andare responsible for about two-thirds of theproblem However in some regions suchas Japan and the west coast of the USAthe nitric acid contribution may well be ofrelatively greater importance

Whichever of these gases is most impormiddottant most acidification has occurred in theindustrialized lands of the Northern Hemishysphere It is here that emissions of sulphurand nitrogen oxides arc highest becauseof high rates of fossil fuel combustion bya range of sources notably industries carsand power stations However the polshylutants that cause acidification can berransponed over long distances by thewind The acidifiC2tion ofScaodinavia forexample has been attributed in part toemissions from Britain Similarly Canadareceives much of i[S acid deposition fromthe industrial heartland and tlK Ohio River

Valley region of the USA Recent estimatesof global emissions ofsulphur suggest thatanthropogenic sources now account for55-80 per cent of the combined total(anthropogenic and natural) and that over90 per cent of emissions from anthroshypogenic sources originate in the NorthernHemisphere

The effects of acid deposition arcgreatest in tho~ areas which have highlevels of precipitation (causing more acidshyity to be transferred to the ground) andthose which have base poor (acidic) rockswhich cannot neutralize the depositedacidity

Some of the most persuasive evidencefor long-term increases in acid deposishytion is provided by what is called thepalaeolimnological approach In this apshyproach past environmental information isobtained by looking at the changes in thefaunal and floral content of cores of sedishyment taken from the floors of lakes Therecord provided by diatoms is especiallyuseful for these algae are excellent indicashytors of water chemistry The compositionof fossil assemblages retrieved from datedcores can be used to reconstruct changesin water pH In Britain at sensitive sitespH values oflakc WlIters were close to 60before 1850 but since then pH declines

118 The Atmosphere

SipIilinlionrJaquotit

lnllIbilily1

Figure 11115 Pathways and effects ofacid precipitation through differentcomponents of the ecosystem showingsome of the adverse and beneficialconsequences

have varied between 05 and 15 unitsoverall

Acid precipitation has many ecologicalconsequences (figure IIUS) One harmfuleffect is a change in soil character Thehigh concentration of hydrogen ions inacid rain causes accelerated leaching ofessential nutrients making them less availshyable for plant usc Furthermore aluminiumand some heavy metal ions become moresoluble at low pH values and may havetoxic effects on plants and aquatic organshyisms Forest growth can also be affectedAcid rain can damage foliage increase susshyceptibility [0 disease affect germinationand reduce nutrient availability (figureIII16)

Particular fears have been expressedabout the possible effects of acid deposishytion on aquatic ecosystems especially on

fish populations Many fish are intoleranrof low pH values (table 1116) Fishlesslakes are now common in areas like theAdirondacks in the north-east USA Fishmay also be adversely affected by the inshycreasing amounts of toxic metal ions (egaluminium) in surface waters

Changes in land use can also make surmiddotface waters more acid Modern forestrypractices for example contribute to theproblem with drainage clear felling andthen the planting of monocultures of fastshygrowing species such as conifers In theseconditions acidic leaf litter builds up morespeedily than might be the case naturallyThis can add to the nutrient leachingeffects ofacid rain Tall trees are also moreeffective at scavenging airborne pollutshyants from douds than say upland grassshyland This serves to increase the amountof pollution deposited

Another adverse effect of acid rain isthe weathering of buildings particularlythose made from limestone marble andsandstone For example sulphate-richprecipitation reacts with limestone tobring about chemical changes (eg theformation ofcalcium sulphate or gypswn)which cause blistering while the low pHvalues encourage the dissolution of thelimestone Many of the great cathedrals ofEurope have been attacked in this way

Various methods are used to try to reducethe damaging effects ofadd deposition Oneof these is to add powdered limestone tolakes to increase their pH values Howshyever the only really effective and practicallong-term treatment is to curb the emisshysions of the offending gases This can beachieved in a variety of ways by reducingthe amount of fossil fuel combustion byusing less sulphur-rich fossil fuels byusing alternative energy sources that donot produce nitrate or sulphate gases (eghydropower or nuclear power) and byremoving the pollutants before they reachthe atmosphere For example after comshybustion at a power station sulphur can be

Acid Deposition 119

Figure 11I16 The impact of acid precipitation on the terrestrial environmentSource Various sources in Kemp (1994) figure 411

Table 11I6 Ecological effects of water pH on European freshwater fish

pH range

30-35

35-40

40-45

45-50

60-65

Effects

Unlikely that any fish can survive for more than a few hours

This range lethal to salmonids Tench roach pike and perch cansUlVive

likely to be harmful to salmonids tench bream roach goldfishand common carp Fish can become acclimatized to these levels

likely to be harmful to adults eggs and fry of salmonids Canharm common carp

Unlikely to harm fish unless free carbon dioxide concentrationgreater than 20 mgtl or water contains iron salts

Unlikely to harm fish unless free carbon dioxide in excess of 100mgI

Harmless to fish

100-105

90-95

95-100

likely to harm salmonids and perch if present for a long time

lethal to salmonids over prolonged periods

Can be withstood for only short periods by roach and salmonids

Rapidly lethal to salmonids Prolonged exposure lethal to carptench goldfish and pike

110-115 Rapidly lethal to all species of fish

Source Gleick (1993) table F2

120 The Atmosphere

removed (scrubbed) from flue gases by aprocess known as flue gas desulphurization(FGD) in which a mixture of limestoneand water is sprayed into the flue gas whichconverts the sulphur dioxide (502) intogypsum (calcium sulphate) NOx in flue

FURTHER READING

gas can be reduced by adding ammoniaand passing it over a catalyst to producenitrogen and water (a process called selecshytive catalytic reduction or SCR) NOxproduced by cars can be reduced by fittinga catalytic converter

Park C C 1987 Acid Rain Rhetoric and Reality London MethuenA general introduction that provides a useful overview

Wellburn A 1988 Air Pollution and Acid Rain The Biological Impact LondonLongmanA more advanced treatment with a strong biological emphasis

9 CoNCLUSION

Changes in the composition of the Earthsatmosphere as a result of human emissionsof trace gases and changes in the natureof land cover have caused great concernin recent years Global warming ozonedepletion and acid rain have become cenmiddottral issues in the study of environmentalchange Although most attention is oftenpaid to climatic change resulting fromgreenhouse gases there is a whole seriesofother mechanisms which have the potenshytial to cause climatic change Most notashybly we have pointed to the importance ofother changes in atmospheric compositionand properties whether these arc causedby aerosol generation or albedo change

However the greenhouse effect andglobal warming may prove to have greatsignificance for the environment and forhuman activities Huge uncertainties remainabout the speeddegree direction and spatialpatterning of potential change Nonetheshyless if the Earth warms up by a couple ofdegrees over the next hundred or so yearsthe impacts some negative and some posishytive are unlikely to ~ trivial The box inthis part on the effects of warming onagriculture in the UK indicates this clearly

For many people especially in citiesthe immediate climatic environment has

already been changed Urban climates aredifferent in many ways from those of theirrural surroundings The quality of the airin many cities has been transformed by arange of pollutants and we have pointedto the particularly serious levels of polshylution that developed in Eastern Europeand in South Africa Conversely we havepointed out that under certain circumshystances clean air legislation and othermeasures can cause rapid and often rcmiddotmarkable improvements in this area

The same is true of twO major pollutionissues - ozone depletion and acid deposishytion Both processes have serious environshymental consequences and their effects mayremain with us for many years but bothcan be slowed down or even reversed byregulating the production and output ofthe offending gases

The human impacts on the atmospherediscussed in this part of the book showclearly how different the impacts can beon different parts of the population andalso how impacts can spread widely oftenaffecting people a long way from thesource of the problem Furthermore imshypacts on the atmosphere show forcefullythe interlinked nature of environmentalsystems and the knock-on effects of manyatmospheric changes on the biospherefresh waters and land surface

Points for Rtview 121

KEy ThRMS AND CoNCEPTS

acid rainaerosolsalbedodust bowlglobal warminggreenhouse effect

POINTS FOR REVIEW

land coverozone holesUatospheric ozonethermal pollutiontropospheric ozoneurban heat island

What forces could (a) cause future climate to cool and (b) cause future climate tobecome wanner~

Can humans change regional and global precipitation patterns

Is global warming an important environmental issue and if so why~

Ozone concentrations are increasing in many cities but decreasing in the stratosphereWhy should this bd

Is acid rain an increasingly important or decreasingly important environmental issueDefend your answer

PART IV

The Waters1 Introduction 1252 River Regulation 125

bull Modification ofthe Colorado River USA 1333 Forests and River Row 136

bull George Perkins Marsh - pioneer investigatorofhuman impam on forests and hydrology 138

4 The Hydrological Response to Urbanization 1405 LutdDnimge 1426 Water Pollution 145

bull Past and present pollution ofthe River ClydeScotland 148

7 Eutrophication ISObull Controlling eutrophication Lake Bim Japan 153

8 Thennal pollution 1549 Inter-basin Water Transfers and the

Death ofthe Arll Sea 15510 Groundwater Depletion and

Groundwater Rise 15911 Conclusion 161

Key Terms and Concepts 162Points for Review 162

1 INTRODUCTION

In a recent review of the worlds freshshywater resources Gleick (1993 pl) summedup the importance of water in a few clearsentences

fresh water is a fundamental resourceintegral to all environmental and societalresponses Water is a critical componentofecological cycles Aquatic ecosystemsharbour diverse species and offer manyvaluable services Human beings requirewater to run industries to provide enshyergy and to grow food

Because water is so important to humanaffairs humans have sought to controlwater resources in a whole variety ofwaysAlso because water is such an importantpart of so many natural and human sysshytems its quantity and quality have undershygone major changes as a consequence ofhuman activities Again we can quoteGleick (1993 p 3)

As we approach the 21st century wemust now acknowledge that many ofour efforts to harness water have beeninadequate or misdirected Riverslakes and groundwater aquifers are inshycreasingly contaminated with biologishycal and chemical wastes Vast numbersof people lack clean drinking water andrudimentary sanitation services Millionsof people die every year from watershyrelated diseases such as malaria typhoidand cholera Massive water developshyments have destroyed many of theworlds most productive wetlands andother aquatic habitats

In this chapter we look at some of theways in which the quantity and quality ofwater have been modified in some ofthe worlds freshwater systems - riversgroundwater and lakes Table IVI sumshymarizes some of the hydrological effects

River Regulation 125

of land-usc change and demonstrates theirgreat number and diversity

2 RIvER REGULATION

In recent decades human demand for freshwater has increased rapidly Global wateruse has more than tripled since 1950 andnow stands at 4340 Cll km per year shyequivalent to eight times the annual flowof the Mississippi River Annual irretrievshyable water losses have increased aboutsevenfold this century

One major way of regulating rivers is tobuild dams Many new large dams havebeen built in the twentieth century espeshycially between 1945 and the early 1970sand there are now more than 36000 damsaround the world As table IV2 showslarge dams (ie more than 15 metres high)arc still being constructed in substantialnumbers especially in Asia In the late1980s some 45 very large dams (more than150 metres high) were being built Inshydeed one of the most striking features ofnewly constructed dams and reservoirs isthat they have ~come increasingly large(table IV3)

Most dams achieve their aim which isto regulate river discharge They arc alsohighly successful in meeting the needs ofsurrounding communities millions of peoshyple depend upon them for survival welmiddotfare and employment However dams havemany environmental consequences thatmayor may not have been anticipated(figure rvl) Some of these arc dealt within greater detail elsewhere (eg salinity inpart V section 5)

The River Nile before and after theconstruction of the great Aswan High Damin Egypt (table IVA) provides a goodexample of how dams retain sedimentUntil the dam was built concentrationsof silt were high in the late summer andautumn period of high flow on the NileSince the dam has been finished the silt

126 The Waters

Table IV1 Summary of the major hydrological effects of land-use changes

Land use change Hydrologicalcomponentaflected

Afforestation Annual flow(deforestation hasthe opposite Seasonal floweffects in general)

Floods

Water quality

Erosion

Climate

Agricultural Water quantityintensification

Water quality

Principal hydrological processes involved

Increased interception in wet periodsIncreased transpiration in dry periods

Increased interception and increased dryperiod transpiration reduce dry season flowDrainage improvements associated withplanting may increase dry season flowsCloud water (mist and fog) deposition ontrees will augment dry season flows

Interception reduces floods by removing aportion of the storm rainfall and allowingsoil moisture storage to increaseManagement activities such as drainageconstruction all increase floods

Leaching of nutrients reduced as surfacerunoff reduced and less application offertilizerDeposition of atmospheric pollutantsincreased because of larger exposed surfacearea of trees

High infiltration rates in natural mixedforests reduce surface runoff and erosionSlope stability enhanced by reduced soilpore water pressure and binding effect oftree rootsWind throw of trees reduces slope stabilityManagement activities (constructiondrainage) all increase erosion

Increased evaporation and reduced sensibleheat fluxes from forests affect climate

Alteration of transpiration rates affectsrunoffTiming of storm runoff altered through landdrainage

Application of inorganic fertilizers addsnutrientsPestidde application poses health risks tohumans and animalsFarm wastes pollute surface andgroundwater where inadequate disposal oforganic and inorganic wastes

Table continues opposite

River Regulation 127

Table IV1 Continued

Land use change Hydrologicalcomponentaffeded

Erosion

Principal hydrological processes involved

Cultivation without proper soil conservationmeasures and uncontrolled grazing increaseerosion

Draining wetlands Seasonal flow lowering of water table may induce soilmoisture stress reduce transpiration andincrease dry season flowsInitial dewatering on drainage will increasedry season flows

Annual flow Initial dewatering on drainage will increaseannual flowAfforestation after drainage will reduceannual flow

Floods Drainage method soil type and channelimprovement will all affect flood response

Water quality Redox potentials altered leading to peatdecomposition acidification and increasedorganic loads in runoffNew drainage systems intercepting mineralhorizons will reduce acidity

Carbon balance Accumulating peat bogs are sink foratmospheric CO2

Source Adapted from Calder (1992) table 1311

Table IV2 Number of large dams (over 15 metres high) 1950 and 1986

Continent 1950 1986 Under construction31 Dec 1986

Africa 133 885 58Asia 1562 23555 615

of which in China 8 18820 183AustralasiaOceania 151 497 25Europe 1323 4077 230North and Central America 2099 6663 39South America 885 69

TOTAL 5268 36562 1036

Source Data provided by UNEP

128 Th~ Waters

Table IV3 Worlds 20 largest reservoirs by reservoir volume

Namemiddot Country Capacity Year completed(million cu metres)

Owen Fallsb Uganda 204800 1954Bratsk FSUlt 169000 1964High Aswan Egypt 162000 1970Kariha Zimbabwe-Zambia 160368 1959Akosombo Ghana 147960 1965Daniel Johnson Canada 141851 1968Gun Venezuela 135000 1986Krasnoyarsk FSU 73300 1967W A C Bennett Canada 70309 1967Zeya FSU 68400 1978Cahara Bassa Mozambique 63000 1974La Grande 2

Barrage Canada 61715 1978La Grande 3

Barrage Canada 60020 1981Ustmiddotllim FSU 59300 1977Boguchany FSU 58200 under constructionKuibyshev FSU 58000 1955Serra da Mesa Brazil 54400 under constructionCaniapiscau

Barrage K A 3 Canada 53790 1980Bukhatarma FSU 49800 1960Ataturk Turkey 48700 1990

bull All these reservoirs have been constructed Since the Second World Warb Owen Falls capacity is not fully related to construction of a dam the major part of it is anatural lakelt Former Soviet Union

Source Modified from GJeick (1993) table G9

load is lower throughom the year and theseasonal peak is removed The Nile nowonly transports abom 8 per cent of itsnatural sediment load below the AswanHigh Dam This figure is exceptionally lowprobably because of the great length andsize of Lake Nasser the reservoir behindthe dam Other rivers for which data areavailable carry between 8 per cent and 50per cent of their natural suspended loadsbelow dams

The removal of sediment from the Nilehas various possible consequences These

include a reduction in flood-depositednutrients on fields less nutrients for fishin the south-cast Mediterranean Seaaccelerated erosion of the Nile Delta andaccelerated riverbed erosion since less sedishyment is available to cause bed aggradationThe last process is often called clearshywater erosion It may speed up the rate atwhich streams cut back into their banks inan upstream direction It may also causegroundwater tables to become lower andundermine bridge piers and other strucshytures downstream of the dam On the

River Regulation 129

WaIn chrmillry IIIImdS1mm Row ClIIIIIIllIrdIwponolicllllou IncmJtdGround _ aImecI(t bJ~)WJtor ltmptealurt ohanpI

diaurc_-shysalinity

Figure rV1 Generalized representation of the possible effects of dam constructionon human life and various components of the environment

Table IV4 Slit concentrations In the Nile at Gaafra before and after the construemiddottlon of the Aswan High Dam (ppm)

Jan Feb March April My June July Aug Sep Od Nov Dec

Before (averages for the period 1958-63)64 50 45 42 43 85 674 270 242 925 124 77

After44 47 45 50 51 49 48 45 41 43 48 47

Ratio of before to after15 11 10 08 08 17 140 600 591 215

Source AbumiddotAtia (1978) p 199

258 163

other hand in regions such as northernChina where modern dams trap silt thecutting-out of the river channel downshystream may alleviate the strain on leveesand so les~n the expense of strengthenshying or heightening the levees

However clear-water erosion does notalways follow from dam construction In

some rivers before a dam was built thesediment brought into the main streamby steep tributaries was carried away byfloods Once the dam is built these floodsno longer happen and so the sedimentaccumulates as large fans of sand or gravelbelow each tributary mouth The bed ofthe main stream is raised and any water

130 The Waters

Plate IV1 The Sagan River in southern Ethiopia The dark brown colour of thisriver is caused by its large load of sediment derived from accelerated erosionupstream This renders the river much less suitable as a source of drinking water(A S Goudie)

intakes towns or other structures thatlie alongside the river may be threatenedby flooding or channel shifting across theaccumulating wedge of sediment

Some landscapes are almost dominatedby dams canals and nservoirs Probablythe most striking example of this is thetank landscape of south-east India wheremyriads of linle streams and areas of overshyland flow have been dammed by smallearth structures to produce what Spate(Spate and Lcarmonth 1967 p 778) haslikened to a surface of vast overlappingfish-scales

In the northern part of the Indian subshycontinent in Sind the landscape changesbrought about by hydrology are no lessstriking Here the mighty snow-fed IndusRiver is controlled by large embankments(bunds) and interrupted by great damsIts waters are distributed over thousandsof square kilometres by a network ofcanals that has evolved over the past 4000years

Another direct means of river manishypulation is channelization This involvesconstructing embankments dikes lev~es

and floodwalls to confine floodwaters andimproving the ability of channels to transmiddotmit floods by enlarging their capacitythrough straightening widening deepenshying or smoothing

Some of the great rivers of the worldare now lined by extensive embankmentsystems such as those that run for morethan 1000 krn alongside the Nile 700km along the Hwang Ho in China 1400km by the Red River in Vietnam and over4500 km in the Mississippi Valley Likedarns embankments and other such strucshytures often fulfil their purpose but mayalso create environmental problems andhave some disadvantages For examplethey reduce natural storage for floodwatersboth by preventing water from spillingon to much of the floodplain and whereimpermeable f100dwalis are used by not

River Regulation 131

allowing water to be stored in the banksThe flow of water in tributaries may alsobe constrained Occasionally embankmentsmay exacerbate the flood problem theywere designed to reduce This can happenwhere the barriers downstream ofa breachprevent floodwater from draining back intothe channel once the peak has passed

Channel improvement designed to imshyprove water tlow may also have untoreshyseen or undesirable effects For examplethe more rapid movement of water alongimproved sections of a river channel canaggravate Rood peaks further downstreamand cause excessive erosion The loweringof water tables in the improved reachmay cause overdrainage of adjacent agrishycultural land In such cases sluices needto be constructed in the channel to mainshytain levels On the other hand channelslined with impermeable material mayobstruct soil water movement (interflow)and shallow groundwater flow therebycausing surface saturation

Channelization may also have variouseffects on fauna These may result fromfaster water flow reduced shelter in thechannel bed and reduced food suppliesdue to the destruction ofoverhanging bankvegetation If channelization of rivers werecarried out in large swamps like those ofthe Sudd in Sudan or the Okavango inBotswana where plans to do so exist itcould compktely transform the whole charshyacter of the swamp environment

Another type of channel modification isthe construction of bypass and diversionchannels either to carry excess floodwateror to enable irrigation to take place Thewe of such channels may be as old asirrigation itself They may contribute tothe salinity problems encountered in manyirrigated areas (see part V section 5)

Deliberate modification ofa river regimecan also be achieved by long-distance intershybasin water transfers (Shiklomanov1985and see section 9 below) Such transfers

132 The Waters

are necessitated by the unequal spatialdistribution of water resources and by theincreasing rates of water consumption Atpresent the world water consumption forall needs is 4340 cu km per year ninetimes what it was at the beginning of thetwentieth century By the year 2000 it isexpected to be 6000 sq km per year The[Ota volume of water in the various transshyfer systems in operation and under conmiddotstruction throughout the world at presentis about 300 sq km per year The greatestvolumes of transfers take place in Canadathe former USSR the USA and India

It is likely that many even greaterschemes will be constructed in future deshycades Route lengths of some hundreds ofkilometres will be common and the waterbalances of many rivers and lakes will betransformed (See section 9 below for whathas already happened to the Ami Sea)

A human activity that affects manycoastal portions of rivers or estuariesis dredging The effects of dredging canbe as complex as the effects of dams andreservoirs upstream (La Roe 1977) Dredshyging may be performed to create andmaintain canals navigation channels turn-

FURTHER READING

ing basins harbours and marinas to laypipelines and to obtain a source of matershyial for filling or construction The ecoshylogical effects of dredging are various Inthe first place filling directly disrupts habishytatS like salt marshes Second the largequantities of suspended silt generated canphysically smother plants and animals thatlive on river and estuary beds smotherfish by dogging their gills reduce photoshysynthesis through the effects of turbidityand lead to eutrophication by releasinglarge quantities of nutrients Ukewise thedestruction of marshes mangroves and seagrasses by dredging and filling can resultin the loss of these natural purifYing sysshytems (see part II section 9 on wetlands)The removal of vegetation may also causeerosion Moreover as silt deposits stirredup by dredging accumulate elsewhere inthe estuary they tend to create a falsebottom The dredged bonom with itsshifting unstable sediments is recolonizedby fauna and flora only slowly if at allFurthermore dredging tends to changethe configuration of currents and the rateof freshwater drainage and may provideavenues for salt-water intrusion

Brookes A 1985 River channelization traditional engineering methods physicalconsequences and alternative practices Progress in Physical Geography 9 44-73An advanced review by a leading authority

Gleick P H (ed) 1993 Water in Crisis A Guide to the World)s Freshwater ResourcesNew York Oxford University PressAn invaluable compendium of information on all aspects of water use and misuse Itcontains many useful tables of data

Gregory K J 1985 The impact of river channelization Geographjcal ]ournalI5153-74A useful overview in a relatively accessible journal

Petts G E 1985 Impounded Rjvers Perspeujves for Ecological Management Chichshyester WileyAn advanced textbook that looks at the large range ofconsequences ofdam construction

River Regulation J33

Modification of the Colorado River USA

Plate IV2 The Hoover Dam on the Colorado River Arizona USA The flowof the river and its sediment load are now almost totally controlled(TripM lee)

The Colorado River in the American WeSt (figure IY2(araquo which Aows throughthe Grand Canyon has been at several points dammed to control Aoods generateelectricity and provide water for irrigation Among the major dams are the Hooshyver and Glen Canyon dams both over 200 m high (figure JV2(b)) They havecaused radical adjustments in the hydrological regime Flood peaks are reducedas a flood control strategy and water is released at times of low Aow Dischargevaries rapidly in response to fluctuations in the need for hydropower during thecourse of a day The high dams trap most of the sediment carried by the riverSO that downstream discharges are largely sediment-free In the Colorado Riverthis combination of impacts has changed a natural river with very large springfloods lower summer flows and little daily variation ofsediment-laden waters intoa highly controlled system with only modest flood peaks in spring relatively highsummer flows and drastic daily variation of discharges of clear water Indeed atits seaward end the Colorado has been totally transformed Prior to 1930 beforethe dams were built it carried around 125-130 million tons of suspended sedishyment per year to irs delta at the head of the Gulf of California (figure IV2(c))Now the Colorado discharges neither sediment nor water to the sea Upstream

134- The Waters

(j

o ISO kmI

NEVADA

(AUFQRNlA

WYOMING

COlORADO

NEW MEXICO

----~IP~--~

1750

6000 g

]bull ]bull

3000 -g

River Regulation 135

PREmiddotDAM

~

f~~

-I ~-

rO$TmiddotDAM

bullwbull

bull bullr~1

--J-t-J

z-~hj~

~middot~oo-~11---~~lJ

(d)

w

1961l 197019lt40 1950

Walfrynr

Water discllarge (m~IiOllI ofam-ftetJyr)

()

1910 1920 1930 l~ 1950 116O 1910 1400 Suspmdeltktdiment dischargt (milliorui of lonlyr)

Figure IV2 (a) The Colorado River basin (b) Profiles of the Green andColorado Rivers showing locations of dams reservoirs and whitewatercanyons (c) Historical sediment and water discharge of the Colorado River(d) Pre- and post-dam riparian vegetation in the Grand Canyon downstreamfrom Glen Canyon dam Vegetation lones 1 stable desert vegetation2 stable woody vegetation 3 unstable lone 4 new riparian vegetationphreatophytesSources (a) After Schwarz et al (1990) (b) After various sources in Graf (1985)fig 13 (c) After Schwarz et al (1990) (d) After Graf (1985) from original byS W Carothers

in the vicinity of the Grand Canyon riparian vegetation communities have beencompletely changed since the construction of the Glen Canyon dam (figurelV2(d))

Further reading

Graf W L 1985 The Colorado Rifler Instability and Basi Management Washshyington DC Association of American Geognphers

136 The Waters

3 FORESTS AND RIvER FLOW

When George Perkins Marsh wrote hisremarkable book Man and Nature in1864 one of the main themes which conshycerned him was the consequences of forshyest removal In the early twentieth centuryscientists in America began to measurethe effects of forest removal on streamdischarges To do this they used what issometimes called the paired watershedtechnique First they compared the flowsOUt of two similar watersheds (catchments)over a period of years Then they c1earshyfelled one of the watersheds to see howthat basin responded in comparison withthe unchanged control valley The pioneershying study at Wagon Wheel Gap in ColoradoUSA in 1910 revealed that the clear-felledvalley yielded 17 per cent more waterflowthan would have been expected if it hadremained unchanged like the control valleySubsequent studies in the tropics haveindicated that dear-felling can lead to meanannual stream flow increases equivalent toabout 400-450 mm of rainfall

There are many reasons why the removalof a forest cover and its replacement withpasture crops or bare ground have suchimportant effects on stream flow A mashyture forest probably intercepts a higherproportion of rainfall tends to reduce fatesof overland flow and promotes soils witha higher infiltration capacity and bettergeneral structure All these factors ill tendto produce both a reduction in overallrunolT levels and less extreme flood peaksthough this is not invariably the case

Reforestation of abandoned farmlandsreverses the elTects of deforestation inshycreased interception of rainfall and higherlevels of evapotranspiration can cause adecline in water yield to rivers This cancause problems for human activities

Reviews ofcatchment experiments frommany parts of the world have pointed totwo conclusions

bull Pine and eucalypt forest types cause anaverage change of 40 mm in annualflow for a 10 per cent change in coverwith respect to grasslands that is a10 per cent increase in forest cover ongrassland will decrease annual flow by40 mm and a 10 per cent decrease incover will increase annual flow by thesame amount

bull The equivalent effect on annual flowof a 10 per cent change in cover ofdeciduous hardwood or scrub is 10shy25 mm that is if 10 per cem of agrassland catchment is converted tohardwood trees or scrub vegetation theannual runoff will decrease by 10-25mm

The increase in annual flow that resultsfrom tree or scrub removal tends to bemost marked in two particular environshyments those with very high rainfall andthose with very low rainfall In the formerevaporation from forest will tend to behigher than that from other land usesbecause of high levels of rainfall intercepshytion In the latter evaporation from forestis likely to be higher than that from otherland uses because forests composed oftrees that have deep root systems arebetter able to make use of soil andgroundwater reserves

Having discussed changes in annualflows now let us turn to a considerationof how forest removal influences low seashyson flows and flood peaks The higherlosses from forests in wet seasons fromrainfall interception and increased lossesin dry seasons from transpiration (becauseof trees deeper root systems) both tendto increase soil moisture deficits in dryseasons compared to those under otherland uses On the other hand in forests athigh altitudes whete there is a lot ofwaterdeposition on to trees from clouds thismay provide a significant component ofthe dry season flows in rivers and also

Forests and River Flow 137

Plate IV3 A well-managed tea and rubber plantation in the Nilgiri hills southernIndia (A S Goudie)

increase runoff The same applies in areaswith high-intensity storms where highshyintensity rainfall may lead to high 1Celsof surfolce runoff The higher infiltrationrates under indigenous forest comparedwith other land usa may help soils andtheir below-ground aquifers to rechargethemselves In steeply sloped areas forestsmay have the additional benefit of reducshying landslips (see part V section 6) andpreserving the soil aquifer which may bethe source of dry season flows Boththese effecLS of afforestation may there-

FURTHER READING

fore benefit stream flows in the lowseason

When it comes to flood peaks there isstill a great dcaJ of controversy as to howimportant forest cover is with respect tothe largest types of event Some authorssuggest that management practices assoshyciated with forestry (eg the building ofroads culverts and drainage ditches) orsubsequent activities (eg grazing) whichpromote the flood by causing compactionof the soil and reducing its infiltrationcapacity increase this type of hazard

1 R Calder 1992 Hydrologic e(fects ofland-usc change In D R Maidment (ed)HRndbool of Hydrology pp 131-1350 New York McGraw HillA Iengthy and detailed summary of the available Iiterature

138 The Waters

George Perkins Marsh pioneer investigator ofhuman impacts on forests and hydrology

George Perkins Marsh (1801-82) was born in Vermont USA and can be reshygarded as one of the most important pioneers of the conservation movcment In1864 he wrote Man and Nature This book was the product of two majorinfluences on him first his upbringing in New England and secondly his expeshyriences working for the US government in Turkey and elsewhere around theMediterranean basin In it he recognized how human occupation of the land hadtransformed it This brief extract from Man and NRture in which he deals withthe consequences of forest destruction gives a good indication of his clear anddirect style

With the disappearance of the forest all is changed At one season the earthparts with its warmth by radiation to an open sky - receives at another animmoderate heat from the unobstructed rays of the sun Henee the climatebecomes excessive and the soil is alternately parched by the fervors of summerand seared by the rigors of winter Bleak winds sweep unresisted over itssurface drift away the snow that sheltered it from the frost and dry up itsscanty moisture The precipitation becomes as regular as the temperature themelting snows and vernal rains no longer absorbed by a loose and bibulousvegetable mould rush over the frozen surface and pour down the valleysseaward instead of filling a retentive bed of absorbent earth and storing upa supply of moisture to feed perennial springs The soil is bared of its coveringof leaves broken and loosened by the plough deprived of the fibrous rootletswhich hold it together dried and pulverized by sun and wind and at lastexhausted by new combinations The face of the earth is no longer a spongebut a dust heap and the floods which the waters of the sky pour over it hurryswiftly along irs slopes carrying in suspension vast quantities of earthly partishycles which increase the abrading power and mechanical force of the currentand augmented by the sand and gravel of falling banks fill the beds of thestreams divert them into new channels and obstruct their outlets The rivushylets wanting their former regularity of supply and deprived of the protectingshade of the woods are heated evaporated and thus reduced in their summercurrents but swollen to raging torrents in autumn and spring From thesecauses there is a constant degradation of the uplands and a consequentelevation of the beds of the watercourses and of lakes by the deposition of themineral and vegetable matter carried down by the waters The channels ofgreat rivers become unnavigable their estuaries are choked up and harborswhich once sheltered large navies are shoaled by dangerous sandbars Theearth stripped of its vegetable glebe grows less and less productive andconsequently less able to protect itself by weaving a new carpet of turf toshield it from wind and sun and scouring rain Gradually it becomes altogetherbarren The washing of the soil from the mountains leaves bare ridges ofsterilerock and the rich organic mould which covered them now swept down intothe dank low grounds promotes a luxuriance of aquatic vegetation that breedsfever and more insidious forms of mortal disease by its decay and thus theearth is rendered no longer fit for the habitation of man

~t i

Forests and River Flow 139

MARSH 186r PHOTOGRAPH BY BRADY

Courtesy of Frederick H Meserve

Plate IV4 George Perkins Marsh author of Man and Nature (1864)and one of the major proponents of nature conservation

Further reading

Marsh G P18M Man and Nture (quoted from edition by D Lowenthal 1965Cambridge Mass Belknap Press of Harvard University Press pp 186-7)

140 The Waters

4 ThE HYDROLOGICAL

RESPONSE TO

URBANIZATION

The remarkable growth of the number andsize of cities in recent decades has createdmany new impacts on water resources anddistribution For example cities modify theprecipitation characterinics of their imshymediate environs (see par[ III section 5)They aso can cause changes in waterquality through thermal pollution (seesection 8 below) and chemical pollution(see section 6 below) Moreover the deshymand for water by city populations maybe so great that groundwater is mined fromcity aquifers (see section 10 below) andlarge amounts are brought in by inter-basinwater transfers Los Angeles for examplereceives water from distant parts of northshyern California In this section howeverwe will concentrate on the effect of urshybanization on river flow characteristics

Research in various countries has shownthat urbanization influences flood runoffFor example figure IV3 shows in a scheshymatic way the hydrological changes resultshying from urbanization in a part ofCanadaThese changes are caused mainly by theproduction of extended surfaces of tarmactiles and concrete Because these impershymeable surfaces have much lower infilshytration capacities than rural vegetatedsurfaces they generate a rapid response torainfall This response is further accelershyated by sewers storm drains and the likewhich are very efficient at catching andtransporting city rainfall In general thegreater the area that is sewered the greateris the discharge that will occur in any givenperiod of time In other words the intershyval between flood events becomes progresshysively shorter Moreover peak dischargesare higher and occur sooner after runoffstarts in basins that have been affectedby urbanization and sewer construction

Indpilllion

URBAN

Figure IV3 Hydrological changes inOntario Canada caused byurbanizationSource After OECD (1986) p 43

Table IV5 shows the impact of differentinfluences resulting from the urbanizationprocess

Some workers have found that urbanishyzation has a proportionately greater effecton smaller flood events than on larger oncsIn other words the effects of urbanizashytion appear less important as the size ofthe flood and the interval between floodsincrease A probable explanation for this isthat during a severe and prolonged rainmiddotstorm a rura catchment may become sosaturated over large areas and its channelnetwork so extended that it begins tobehave almost as if it were an imperviousurban catchment with a dense storm drainnetwork Under these conditions a ruralcatchment produces floods rather similarto those of its urban counterpart Alsoin very large floods subsurface drains indties may not be large enough to takethe volume ofwater resulting in less rapidand lower discharge

Urbanization 141

Table IVS Potential hydrological effects of urbanization

Urbanizing influence

Removal of trees andvegetation

Initial construction of housesstreets and culverts

Complete development ofresidential commercial andindustrial areas

Construction of storm drainsand channel improvements

Source KIbler (1982)

Potential hydrological response

Deltreased evapotranspiration and interceptionincreased stream sedimentation

Decreased infiltration and lowered groundwatertable increased storm flows and decreased baseflows during dry periods

Decreased porosity redUcing time of runoffconcentration thereby increasing peak dischargesand compressing the time distribution of the flowgreatly increased volume of runoff and flooddamage potential

Local relief from flooding concentration offloodwaters may aggravate flood problemsdownstream

I~middottPtKtfWIOO

ggt~i~f~~~

Lokinl waltlt mailgtl alwo)$

diJcha1 alrr II undu ~

Rrduetioniolrrfor e-apol1llUpirgttion

SfwI disltllgtrging 0--Stwm akiosn 8wllrr

I+---------III( in rn-------_ 11__ 0lt rrhllgr-----+-j

Figure IV4 Urban effects on groundwater rechargeSource After Lerner (1990) fig 2

Different dties different constructionmethods and other variable factors willall affect the response to rainfall inputsand we should avoid overgeneralizationUrban groundwater provides an exampleWe have suggested that surface runoff isincreased by the presence of impermeable

surfaces One consequence of this wouldbe that less water went to recharge groundshywater However there is an alternatiwpoint of view namely [hat groundwaterrecharge can be accelerated in urban areasbecause of leaking water mains sewersseptic tanks and soakaways (figure rv4)

142 The Waters

In cities in arid areas there is often noadequate provision for storm runoff andthe (rare) increased runoff from impermeshyable surfaces will infiltrate into the permeshyable surroundings In some cities rechargemay result from over-irrigation of parks

FURTHER READING

and gardens Indeed where the climate isdry or where large supplies of water areimported or where pipes and drains arepoorly maintained groundwater rechargein urban areas is likely to exceed that inrural areas

urner D 1990 Groundwater Rechatge in Urban Areas 59-65 IAHS Publicationno 198A cogent account of the role of groundwater in the urban environment

5 LAND DRAINAGE

The drainage of wet soils has been one ofthe most successful ways in which ruralcommunities have striven to increase agri~

cultural productivity It was for examplepractised centuries ago by the EtruscansGreeks and Romans

Large areas of marshland floodplain andother wetlands have been drained to hushyman advantage When water is led awaythe water table is lowered and stabilizedproviding greater soil depth for plant rootshying Moreover well-drained soils warm upearlier in the spring and thus permit cropsto be planted and to germinate earlierFarming is easier if the soil is not too wetsince the damage to crops by wimer freezshying may be reduced undesirable salts arecarried away from irrigated areas and thegeneral physical condition of the soil isimproved In addition drained land tendsto be flat and so is less prone to erosionand more amenable to mechanical cultivashytion It will also be less prone to droughtrisk than certain other types of land Byreducing the area of saturated grounddrainage can alleviate flood risk in somesituations by limiting the extent ofa drainshyage basin that generates saturation excessoverland flow but this is an issue we shallreturn to later

The most spectacular feats of drainageare the arterial drainage systems involv-

ing the construction of veritable rivers andnetworks of large dikes seen for examplein the Netherlands and the Fenlands ofeastern England These have received muchanention However more widespread thanarterial drainage and sometimes independshyent of it is the drainage of individual fieldsThis is done either by surface ditching orby underdrainage with tile pipes and thelike In Finland Denmark Great Britainthe Netherlands Hungary and the fertileMidwest of the USA the majority ofagricultural land is drained

In Britain underdrainage was promotedby government grants and in the 1970s inEngland and Wales reached a peak ofabout1 million hectares per year More recentlygovernment subsidies have been cut andthe uncertain economic future of farminghas led to a reduction in farm expenditureBoth tendencies have led to a reductionin the growth of field drainage which isnow being extended by only about 40000hectares per year (Robinson 1990)

Drainage is a widespread practice whichhas many advantages and benefits Howshyever it can also have environmental costsThe first of these is related to a reductionin the extent of highly important wetlandwildlife habitats (see part II section 9)Marshes fens and swamps are of majorecological significance for a wide range ofspecies

Secondly the drainage oforganically rich

Land Drainage 143

Plate IVS Drainage maintenance on agricultural land in the Fenlands of easternEngland at Spalding in lincolnshire (EPLRichard Teeuw)

Similar subsidence has taken place followshying drainage of portions of the Florida

Figure IVS The subsidence of theEnglish Fenlands peat in Holme FenPost from 1842 to 1960 followingdrainageSource After Goudie (1993) fig 68 fromdata in Fillenham (1963)

sa-kYt1 (OrdnanCf Datum)

bullbull0

-

soils (such as those that contain much peat)can lead to the degradation and eventualdisappearance of peaty materials which inthe early stages of post-drainage cultivashytion may be highly productive for agriculshyture The lowering of the water table makespeats susceptible to oxidation and deflashytion (removal by wind) so that their volshyume decreases One of the longest recordsof this process and one of the clearestdemonstrations of its efficacy has beenprovided by the measurements at HolmeFen Post in the English Fenlands Approximiddotmately 38 metres of subsidence occurredbetween 1848 and 1957 with the fastestrate occurring soon after drainage had beeninitiated (figure IVS) The present rateaverages about 14 em per year At itsmaximum natural extent before the Midshydle Ages the peat of the English Fernandcovered around 1750 sq Ion Now onlyabout one-quarter (430 sq km) remains

144 The Waters

Everglades there rates of subsidence of32 cm per year have been recorded

The moisture content of the soil canalso affect the degree to which soils aresubjected to expansion and contractioneffects which in turn may affect engineershying structures in areas with expansivesoils Particular problems are posed by soilscontaining smectite clays When drainedthey may dry Out and shrink and the soilmay crack damaging the foundations ofbuildings

In Britain there has been considerabledebate about the effects on river Oowsand in particular on flood peaks of drainshying upland peat areas for afforestationThere appear to be some cases where floodpeaks have increased after peat drainageand others where they have decreased Ithas been suggested that differences in peattype alone might account for the differenteffects Thus it is possible that the drainshyage of a catchment dominated by theSphagnum moss would lead to increasedflooding since drainage compacts Sphagshynum reducing both its storage volume andits permeability On the other hand in thecase of peat where Sphagnum moss didnot grow there would be relatively lesschange in structure but there would be areduction in moisture content and an inshycrease in storage capacity thereby tendingto reduce flood flows The nature of thepeat is however just one feature to beconsidered The intensity of the drainageworks (depth spacing etc) may also beimportant In any case there may be two(sometimes conflicting) processes operatshying as a result of peat drainage the inshycreased drainage network will encouragerapid runoff while the drier soil condishytions will provide greater storage for rainshyfall Which of these two tendencies isdominant will depend on local catchmentconditions

The impact of land drainage upon theincidence of floods downstream has alsolong been a source of controversy This

impact depends on the size of the areabeing considered the nature of land manshyagement and the character of the soil thathas been drained Robinson (1990) conshyducted a detailed review of experience inthe UK and found that the drainage ofheavy clay soils that are prone to prolongedsurface saturation in their undrained stategenerally led to a reduction of large andmedium flow peaks He attributed thisto the fact that their natural responsewith limited soil water storage availableis flashy whereas their drainage largelyeliminates surface saturation By contrastthe drainage of permeable soils which areless prone to such surface saturationimproves the speed of subsurface flowthereby tending to increase peak flowlevels

As with so many environmental issuesit is not always easy to determine whetheran increase in flood frequency or intensityis the result of land-use changes of thetype we have been discussing or whethersome natural changes in lOlinfall have playeda dominant role In central and southernWales for example there is some clearevidence of changes in the magnitude andfrequency of floods over recent decadesThis has sometimes been attributed to theincreasing amount of afforestation that hasbeen carried out by the Forestry Commis~

sian since the First World War and to thedrainage of upland areas that this has neshycessitated While in the Severn catchmentthis appears to be a partial explanation inother river basins the main cause of morefrequent and intense floods appears to havebeen a marked increase in the magnitudeand frequency of heavy daily rainfalls Forexample in the case of the Tawe Valleynear Swansea of 17 major floods since1875 14 occurred between 1929 and1981 and only 3 between 1875 and 1928Of 22 widespread heavy rainfalls in theTawe catchment since 1875 only 2 occurshyred during 1875-1928 but 20 bccween1929 and 1981 (Walsh et aI 1982)

Water Pollution 145

FURTHER REAoING

Robinson M 1990 Impact of Improved Land Drainage on River Flows Institute ofHydrology Wallingford UK Report no 113A state-of-the~art review produced by the UKs leading institute for the study ofhydrology

6 WATER POLLUTION

The activities of humans have begun todominate the quality of natural riverwaters both locally and increasingly at aregional scale The ever-increasing humanpopulation and its growing wasteload havebegun to overtax the recycling capabilitiesof rivers The water pollution challengesthat the world faces are enormous Theycan be categorized according to sourceinto three main groups

bull Municipal waste This is composedprimarily of human excreta While itcontains relatively few chemical conshytaminants it carries numerous pathoshygenic micro-organisms

bull InduseriRI wastes These are of veryvaried composition depending uponthe type of industry or processingactivity and they may contain a widevariety of both organic and inorganicsubstances

bull AgriculturRl wastes These are comshyposed of the excess phosphorus andnitrogen present in synthetic fertilmiddotizers and in animal wastes as well asresidues from a number of pesticidesand herbicides

It is also possible to categorize waterpollutants according to whether or notthey are derived from point or nonshypoint (also called diffuse) sources (figshyure N6) Municipal and industrial wastestend to full into the former category beshycause they are emitted from one specificand identifiable place (eg a sewage pipeor industrial outfill) Pollutants from nonmiddot

- ~--~~~~~~---

Figure IV6 Diffuse and point sourcesof pollution into river systemsSource After Newson (1992) fig 77

point sources include agricultural wastesmany of which enter rivers in a diffusemanner as chemicals percolate into groundshywater or are washed off into fields as wellas some mining pollmants uncollectedsewage and some urban stormwater runoff

Possibly the most useful way to categorshyize pollutants is on the basis of their chemishycal physical or biological composition andthis is the framework we shall use for therest of this section We will not cover thewhole range of waste pollutants but conshycentmte on three groups

bull nitrates and phosphatesbull metalsbull synthetic and industrial organic

pollutants

146 The Waters

Nitrates and phosphates are an importamcause of a process called eutrophication(see section 7 below) Nitrates normallyoccur in drainage waters and are derivedfrom soil nitrogen from nitrogen-richgeological deposits and from Mffiosphericdeposition Anthropogenic sources includesynthetic fertilizers sewagl and animalwastlS from feedlots Land-use changes(Ig logging) can also increasl nitrateinputs to streams Perhaps 3S much as oneshythird of the total dissolved nitrogen in riverwaters throughout the world is the resultof pollurion Indeed Peierls et ai (1991)have demonstrated that the quantity ofnitrates in rivers worldwide now appearsto be closely linked to the density ofhuman population nearby Using publisheddata for 42 major rivers they found ahighly significant correlation between nishytrate concentration and human populationdensity that explained 76 per cent of thevariation in nitrate concentration for the42 rivers They maintain that human acshytivity clearly dominates nitrate export fromland Nitrate levels in English rivers arenow clearly rising Current levels (1990s)are between 50 per cem and 400 per centhigher than a quarter of a century ago

Phosphate levels are also rising in someparts of the world Major sources includedetergents fertilizers and human wastes

MetalJ are another major class of pollutshyants Like nitrates and phosphates metalsoccur naturally in soil and water Howshyever as the human use of metals hasburgeoned so has the amount of waterpollution they cause Other factors alsocontribute to water pollution from metmiddotalso Some metal ions reach river watersbecause they become more quickly mobishylized as a result of acid rain (sec part IIIsection 8) Aluminium is a notable examshyple of this From a human point of viewthe metals of greatest concern arc probshyably lead mercury arsenic and cadmium

all of which have adverse health effectsOther metals can be toxic to aquatic lifeand these include copper silver seleniumzinc and chromium

The anthropogenic sources of metalpollution include the industrial processingof ores and minerals the use of metalsthe leaching of metals from garbage andsolid waste dumps and animal and hushyman excretions Nriagu and Pacyna (1988)estimated the global anthropogenic inputsof trace metals into aquatic systems (inshycluding the oceans) and concluded thatthe sources producing the greatest quanshytities were in descending order the folshylowing (the metals produced by eachsource are listed in parentheses)

bull domestic wastewater effluents (arsenicchromium copper manganese nickel)

bull coal-burning power stations (arsenicmercury selenium)

bull non-ferrous metal smelters (cadmiumnickel lead selenium)

bull iron and steel plants (chromium molybshydenum antimony zinc)

bull the dumping ofsewage sludge (arsenicmanganese lead)

However in some parts of the worldmetal pollution may be derived from othersources There is increasing evidence forexample that in the western USA waterderived from the drainage of irrigated landsmay contain high concentrations of toxicor potentially toxic trace elements suchas arsenic boron chromium molybdenumand selenium These can cause humanhealth problems and poison fish and wildshylife in desert wetlands (Lently 1994)

Synthetic and industrial ollInic polutllnnhave been manufactured and released invery large quantities since the 1960s Thedispersal of these substances into watershycourses has resulted in widespread envirshyonmental contamination There are manytens of thousands of synthetic organic

compounds currendy in use and many arethought [Q be hazardous [Q human healthand to aquatic life even at quite low conshycemratiolls - concentrations possibly lowerthan those that can routinclr be measuredby commonl~ available analytical methodsAmong thesl pollutants are syntheticorganic pesticides including chlorinatedhydrocarbon illst([icides (eg DDT) Someof these can rlach harmful concentrationsas a result of biological magnification inthe food chain Other important organicpollutams include PCBs which have beenused extensively in the electrical industry

FURTHER READING

Water Pollution 147

as di-electrics in large trl11stormers andcapacitors PAHs which result ti-om thlincompkte burning of I(lssil fuels variousorganic sohcnrs mcd in industrill anddomestic processes phth~IIltlmiddotS which Ireplasticizers used Illr exunpk in Ih proshyduction of polyvil1~1 chloride rlsills andDBPs which arl a mngc of JisinlcCliollby-products The long-term hlalth tttl-ctsof cumulativc exposure 10 such substancesare difficult to qlanti~ However somework suggests that rhey may be implicatcdin the development of birth detects andcertain types of cancer

Nash L 1993 Water quality and health In P H Gldck (ed) Water in Crisis AGuide to the WorJdJs Freshwater Resources 25-39 New York Oxford University PressAn excellent summary of pollution characteristics and effects

148 The Waters

Past and present pollution of the River ClydeScotlandThe River Clyde which runs woughGlasgow in Scotland has a mean disshycharge of 41 cu mecres per secondh is tidal in its lower sections up [Q

the Tidal Weir upstream of the AlbertBridge It has had a long hiswry ofpollution In 1872 the Royal RiverPollution Commission found theClyde to be the most pollU[ed riverin Scotland Parts were described asa foul and stinking flood Until thebeginning of the nineteenth centurythe river was probably quite deaneven in the heart of Glasgow Howshyever by 1845-50 fish populationshad been eliminated from the upperestuary Poor oxygen conditionsprevented them from returning until1972 (McLusky 1994) In 1872the Clyde through Glasgow was deshyscribed thus its water is loaded with sewage mud fould with sewage gas andpoisoned by sewage waste of every kind - from dye works chemical worksbleach works paraffin oil works tanyards distilleries privies and water closets(quoted in Hammerwn 1994)

This alarming pollution had come about because of the enormous boom inpopulation and industry in the area In summer many of the lower tributarieseg the Black Cart and White Cart were no more than open sewers conveyingsewage and industrial wastes to the main river By the 1930s over fifty years afterthe Commissions report the river was if anything in a worse condition Progressin cleaning it up was hindered by the two world wars and it was only in 1965that effective legislation began [Q improve things In 1968 when the first bioshylogical surveys of the Clyde were done (figure IV7(araquo no fish were foundwithin the boundary of Glasgow nor in the lower reaches of the North CalderSouth Calder Kelvin Black Cart and White Cart By autumn 1983 Atlanticsalmon (Salmo samar) had returned to the Clyde and some fish are now foundin all the river areas shown in figure IV7 Since 1972 dissolved oxygen levels inthe Clyde estuary have improved markedly The greatly improved pol1ution situ~

arion achieved by 1988 is shown in figure rv7(b) The number offish speciesin the upper estuary has steadily increased to 18 in 1978 34 in 1984 and 40in 1992 Thus even rivers with a long history of dire poUution can be cleanedup and their fauna and flora restored

Wat~r Polllltioll 149

Plate IV6 The River Clyde in Central Glasgow (Graham BurnsEnvironmental Picture library)

Figure IV7 The changing pollution of the River Clyde Scotland based onbiological classification of pollution (a) 1968 (b) 1988Source After Hammerton (1994) figs 201202

150 The Waters

7 EUTROPHICATION

The process ofeutrophication can be wellillustrated by the case of the Black Sea

The Black Sea is a very large body ofwater surrounded by land except for itsnarrow shallow connection to the Medishyterranean Sea called the Bosporus It reshyceives river discharge from a land area fivetimes greater than its own and coveringparts of nine different countries Two ofEuropes largest rivers the Danube andthe Dneiper flow into it Over 162 milshylion people live within the catchments ofthese rivers (Mee 1992) Therefore polshylution generated by all these people headsfor the Black Sea The Danube for examshyple currently introduces 60000 tons ofphosphorus per year and some 340000tons of total inorganic nitrogen into theSea

As a result and in spite of its size theBlack Sea shows many of the classic sympshytoms of a process caUed eutrophicationThe symptoms include

bull A gradual shallowing right across thebasin of the so-called euphotic zone(the surface layer ofwater in which thelight level is sufficient for net biologishycal primary production) In otherwords the lake is becoming more turshybid or cloudy thereby reducing theamount of light available to supportlife The decreased light penetration hasresulted in the massive loss oflarge shalshylowmiddotwater plants

bull Dense blooms of a single species ofnanoplankton have developed drashymatically modifying the base of themarine food chain

bull Widespread hypoxia (reduction ofoxygen levels) resulting from the enorshymollS increase in organic matter fallingto the shelf floor from blooming anddecaying organisms Thishas led to the

complete elimination of a large proshyportion of macrobenthie organismsand the demise of formerly rich comshymercial fisheries

What precisely is eutrophication Funshydamentally it is the enrichment of watersby nutrients Among these nutrientsphosphorus and nitrogen arc particularlyimportant as they regulate the growthof aquatic plants The process does occurnaturally - for example when lakes getolder - but it can be accelerated by hushyman activities both by runoff from fertilshyized and manured agricultural land andby the discharge of domestic sewage andindustrial effluents This amhropogenicallyaccelerated eutrophication - often calledcuJmraI eutrophication - commonly leadsas in the case of the Black Sea to excesmiddotsive growths of algae serious depletion ofdissolved oxygen as algae decay after deathand in extreme cases to an inability tosupport fish life It can affect all waterbodies from streams to lakes to estuariesand coastal seas Coastal and estuarywaters are sometimes affected by algal foamand scum often called red tides Someof these blooms arc so toxic that consumshyers of seafood that has been exposed to

them can be affected by diarrhoea someshytimes fatally

The nature of red tides has recently beendiscussed by Anderson (1994) who pointsout that these blooms produced bycertain types of phytoplankton (tiny pigshymented plana) can grow in such abundshyance that they change the colour of theseawater not only to red but also to brownor even green They may be sufficientlytoxic to kill marine animals such as fishand seals Long-term studies at the localand regional level in many parts of theworld suggest that these so-called red tidesare increasing in extent and frequency ascoastal pollution worsens and nutrientenrichment occurs more often

Eutrophication 151

Figure IV8 The natural process of lakeeutrophicationSource After Mannion (1991) fig 63

NIIIritnl input iaIioninm

with

L

Mlt- tnaltllI ftIlICn Iho mInml_ so t1u1 nulritnts IIoOlnodily Igtlibbk (intK) lG

oqwlic 1oninns

INCJWING Nl1T1UENT uvwbull HYDJOSW IJEVELOPS

~iIIP

bull LOW NUTlIOO IllPUTSmiddot1tlGlt DISSOLVW OXYGEN LpoundVpoundlS

bull HIGH NUTIIENT IlVpoundLSbull MAY HAVE lEDUCEDOXYQN UVFLS

Figure IV9 The major components ofthe drainage basin nutrient cycleleading to cultural eutrophicationSource After Newson (1992) fig 74

-

Initially coral productivity increases withrising nutrient supplies At the sametime however corals are losing their keyadvantage over other organisms theirsymbiotic self-sufficiency in nutrientshypoor seas As eutrophication progressesalgae start to win out over corals fornewly opened spaces on the reef beshycause they grow more rapidly than corshyals when fertilized The normally dearwaters cloud as phytoplankton begin tomultiply reducing the intensity of thesunlight reaching the corals furtherlowering their ability to compete At acertain point nutrients in the surroundshying waters begin to overfertilize thecorals own zooxanthdlae which multishyply to toxic levels inside the polypsEutrophication may also lead to blackband and white band disease twodeadly coral disorders thought to becaused by algal infections Throughthese stages of eutrophication thehealth and diversity of reefs declinespotentially leading to death

Eutrophication also has adverse effectson coral reefs This has been explained byWltbe (1993 p 49)

The natural process of eutrophication isshown in figure IVS using the exampleof how a lake ages What has happenedparticularly since the Second World Waris that various human actions have speededup the natural process (figure IV9) Thegrowth in fertilizer usage in the last fivedecades has been increasingly rapid Inspite of the increasing costs of energysupplies and hydrocarbons (from whichmany of the fertilizers are derived) in the1970s world fertilizer production hascontinued to rise inexorably and fertilizershyderived nitrates reach groundwater andrivers For example the mean annual nitrateconcentration of the River Thames whichprovides most of Londons water supplyincreased from around 11 mg per litre in1928 to 35 mg per litre in the 1980s

152 The Waters

Plate IV7 lake Tempe Sulawesi Indonesia (Frederic Pelras)

However it is necessary to point Olltthat the application of fertilizers is not theonly possible cause of rising nitrate levelsSome nitrate pollution may be derivedfrom organic wastes Intensive cultivationmay cause a decline in the amount oforganic matter present in the soil and thiscould limit a soils ability to assimilatenitrogen so that more is lost to waterThe pattern of tillage may also affect theliberation of nitrogen The increased areaand depth of modern ploughing accelershyates the decay of residues and may changethe pattern of water movement in thesoil Finally the area of England coveredby tile drainage has greatly expanded inrecent decades This has affected themovement of water through the soil

FURTHER REAnING

accelerating the flow of leached nitratesand other materials into streams

What can be done to control culturaleutrophicationl Preventive measures mayinclude the introduction oflaws to limit thetype and quantity of permitted dischargesfrom industrial sources Water companiesmay be forced to treat effluent to reduce itsnutrient content Bans can be introducedon detergents containing phosphates as hasalready been done in some areas The mostsevere problems however are posed bynutrients derived from agriculrural sourcesSteps may need to be taken to make agrishyculrure less intensive and to control the apshyplication offertilizers and sludge in locationsfrom which they can easily be washed intostreams and rivers such as floodplains

Mannion A M 1991 Global Environmental Change Harlow LongmanThis useful general review contains some perceptive information on eutrophication

Newson M 1992 Patterns of freshwater pollution In M Newson (cd) Man4gingthe Human Imp4t on the Natural Environment 130-49 London Belhaven PressA hydrological approach to understanding the pathways taken by pollutants

Eutrophication 153

Controlling eutrophication Lake Biwa JapanThe largest freshwater lake in Japancovering 674 sq lon is Lake Biwain Shiga Prefecture Honshu It isone of the oldest lakes in the worldand has a maximum depth of over100 metres The catchment area ofthe lake is less than five times thesurface area of the lake itself andthe lake is fed by high annual preshycipitation and in8ow Until around1950 Lake Biwa was oligotrophic(Le containing low nutrient loads)but since then has become eutrophic(ie containing high nutrient loads)with algaJ blooms first noticed ill1959 and red tides occurring everyyear since 1977

The causes of eutrophic conditionsare linked to the explosive economicdevelopment of the Shiga PrdectureLake Biwa today meets the waterneeds of 13 million people and all their industry The lake also provides animportant freshwater fishery and is of immense cultural and spiritual value Fiftyshytwo per cent of the catchment remains forested although Japanese red pines havereplaced the natural broadlcafforestj 173 per cent of the catchment area is nowurbanized The quality of the lakes water has declined as industry and agriculturehave expanded and domestic wastes have not been managed effectively (Petts1988) Eutrophication peaked in 1978 Since then the lake has shown signs ofimprovement as water quality has responded to a number ofmanagement strategies

A ten-year voluntary use soap campaign among local residents reduced drashymatically the 18 per cent of the toal phosphorus load that had been coming fromdomestic detergents In 1980 a Shiga Prefecture government ordinance regulatedindustrial domestic and agricultural discharges ofphosphorus and nitrogen Sincethen nitrogen and phosphorus concentrations in streams Howing into Lake Biwahave declined by 20 per cent even though population and industry have continshyued to grow Phosphorus levels in the southern part of the lake have also fallenby 30 per cent The Shiga Prefecture government has introduced conservationplans to ensure the monitoring of water quality conservation and environmentaleducation over the long term

Further reading

Petts G E 1988 Water management the case of Lake Biwa Japan Geo8aphishycRI Journal 154 367-76

154 The Waters

8 THERMAL POLLtTTlON

Thermal pollution is the pollution ofwater by increasing its temperJtun AsnlJllY orgJnisms arc SlnsitiC to tempershyature this lorm of pollution In haeconsiderable cologkal significane

Where docs the heat that produces thethermal pollution come from~ One of thelllJin sources in industrialized countries isthe condenser cooling water released frompower stations If there are large concenshytrations of big electricity generating plantsalong one stretch of river as for examplealong the River Trent in the midlands ofEngland the amount of water involvedcan be quite large River water dischargedalter it has been used for cooling may besome 6-9C warmer than it was beforebeing taken out of the river At times oflow flow this can raise river water temshypcntures downstream considenbly

The process of urbanization is anotherfactor that needs to be considered It has

a range of effects changes produced bythe urban heat island effect (see part IIIsection 5) changes in the temperature ofstreams brought about by the presence ofreservoirs changes in the volume of stormrunoff and changes in the nature of urshyban stream channds - how much they arecovered ou or shaded by egct3tion andhow their width and dcpth compare- withnatural channds

The-rmal pollution can also occur in ruralareas Large reservoirs will modify downshystream river temperatures Deforestationwhich removes shade cover may increasewater temperatures particularly in the sumshymer months

Thennal pollution has many ecologicaleffects Tempc=rilture increases can be harmshyful to temperature-sensitive fish such astrout and salmon and an disrupt spawnshying and migration patterns (figure IVIO)An increase in water tempentuce caU$C$a decr~ in the solubility of oxygenwhich is needed for the oxidation of

00~

l2~

29~

24~

Il~

~

O~

0-- WMnboib

j]1_ G_ _ 1 1_ G_ _ II j- GlllWlbrLpikt prrch WI1le)otsmaIlmoothbass 1tI1- SplIWllinl IIld II~IopmmtIicadbh buffalo shadI j __ Spawning Ind II lkoielopmmt oIlarzrmouth whik ytllow Ind lpotttd baniii i-- Egg dtvdoplllflli ofptrch Ind llIlal1mouth btu I1I__ Spawning~ II dMIopmmt of~ aDd mosllrout1-_ - _ tlJ_ w ~

FIgure JV10 Maximum temperatures for the spawning and growth of fishSouru After Giddings (1975) fig 13-2

biodegradable wastes At the same timethe tate of oxidation is accelerated deshymanding more and mote oxygen from thesmaller supply and thereby depleting theoxygen content of the water still furtherTemperature also affects the lower organshyisms such as plankton and crustaceans Ingeneral the higher the temperatun is theless desirable the types of algae in water

FURTHER READING

Inter-basin Water Transfers 155

In cooler waters diatoms are the predoshyminant phytoplankton in water that is notheavily eutrophic at higher temperatureswith the same nutrient levds green algaebegin to become dominant and diatomsdecline At the highest water temperaturesblue-green algae thrive and often developinto heavy blooms

Langford T E L 1990 Ecological Effects of Thermal Discha1lJes London ElsevierApplied ScienceThe most authoritative advanced treatment of thermal pollution

9 INTER-BASIN WATER

ThANSFERS AND THE

DEATH OF THE ARAL SEA

Increasing rates ofwater consumption andthe unequal distribution ofwater resourcesfrom one region to another mean tharin many parts of the world long-distancetransfers of water are made between riverbasins AJso in the worlds drylands largequantities of water are abstracted fromrivers to supply irrigation schemes One ofthe results of such large-scale modificashytions of river regimes is that the dischargesof some rivers have declined very substanshytially This in turn means that the extentand volume of any lakes into which theyempry have been reduced

Perhaps the most severe change to amajor inland sea or lake is that taking placeto the Aral Sea in the southern part of theformer Soviet Union (figure IVII) Untilvery recently this was the worlds fourthlargest lake with a high level of biologishycal activity and a rich and distinctive aquaticfauna and flora It had considerable comshymercial fisheries and was used for transshyport as weU as sporting and recreationalactivities It was also a refuge for hugeflocks of waterfowl and migratory birdsIt may also have exerted a favourable

climatic hydrological and hydrogeologicaleffect on the surrounding area

However since the 1960s a dramaticchange has taken place The inflow of waterinto the lake has decreased markedly (seefigure lV12) and it has now lost morethan 40 per cent of its area and about 60per ceO( of its water volume The lakeslevel has fallen by more than 14 rneuesIts saliniry has increased threefold Its faunaand flora have been desuoyed so that onlya small number of aquatic species hassurvived The climate around the lake mayalso have been affected The increasingareas ofexposed desiccating and salty lakebed provide an ideal environment for thegenesis of dust storms Such storms nowevacuate some tens of millions of tons ofsalt each year and dump them on agriculshytural land reducing crop yields The hushyman population also seems to be sufferingfrom poorer-quality water supply and fromrespiratory disorders caused by the blowshying salt and dust It is not surprising thereshyfore that the Aral Sea is now regarded asthe greatest ecological tragedy of theformer Soviet Union

Why has the inflow ofwater to the AralSea declined so extraordinarily The mainreason was that in the 1950s and early1960s a decision was taken to expand

156 The Waters

Plate IVS Inter-basin water transfers are vital for the survival of los AngelesThis large canal transports water from inland California (east of the Sierra Nevadamountains) to satisfy the needs of the sprawling conurbation hundreds ofkilometres away (A S Goudie)

MMn~ _

_ ~ Sibmo lDAni SaCWII

_ MIia itriplion tlllll

N

I

-- UZBEKISTAN

KmuwDuuf __

-

11JIIIMENISTAN

--IIi

-- r bull Nuhli _ rLJ-C

Figure IV11 Irrigation and the Aral Sea

Inter-basin Water Transfers 157

~C- ----1

19M 966I Ilnnow

c

11970

E -15

1~ 1965 197Q 1975 19amp1)40 ~I I I I

] ~-----~-=-~~

1985

=JMintrlJ~

~ -~IcI bull bull

I I I I I I

J965 JS7C 1m WIO J980 I JFigure IV12 (a) Changes in the Aral Sea 1960-1989 (b) The past and predictedcontraction of the Aral Sea as its level falls50urces (a) After Kotlyakov (1991) (b) Modified after Hollis (1978) p 63

irrigation in Central Asia and Kazakhstanso that crops like rice and conon whichconsume a great deal of water could becultivated in the middle of a desert Largevolumes of fertilizers and herbicides werealso used in growing these crops and thesehave contributed to the deterioration inwater quality In many cases too the irrishygation systems themselves were of poordesign construction and operation

Scientisrs economists and politicians arenow seeking solutions to the Aral tragedySome proposed ideas are

bull The local population should for healthreasons be provided with supplies ofsafe non-polluted piped water

bull The policy of growing cotton in thedeserts of Central Asia needs to bereconsidered

158 The Waters

Plate IV9 The rapid desiccation of the Arat Sea following the extraction of waterfrom the rivers that feed it to supply irrigation schemes has left these boats highdry and redundant (Marcus Rose Panos Pictures)

bull Agriculture needs to be made moreefficient by reducing the very subshystantial losses caused by inadequatestorage and transport infrastructure

bull A fundamental restructuring of theregions economy should be orientedtowards developing products thatdo not require the imensive usc ofwater

bull Irrigation systems need to be reconshystructed to reduce water losses and

FURTHER READING

application of water should be rationmiddotally controlled

bull A policy of expanding the arca of irrishygated agriculture should be replacedby more intensive use of existing irrimiddotgated tracts through better crop rotashytions technologies and the growth ofimproved varieties of crops

bull Attempts should be made to revegetatedesiccated areas to reduce dust stormactivity

MickJin P P 1988 Desiccation of the Aral Sca a water managellHnt disaster in theSoviet Union Science 241 1170-5One of the key papers that drew attention to the situation around the An Sea

Micklin P P 1992 The AnI crisis introduction to the special issue Pon-StnielGgraph] 33 (5) 269-82A coUection of papers on all aspects of tk AnI ampa problem

10 GROUNDWATER

DEPLETION AND

GROUNDWATER RISE

In some parts of the world groundwater isthe main source of water for industrialmunicipal and agricultural use Some rocksincluding sandstones and limestones havecharacteristics that enable them 10 holdand transmit large quantities of waterwhich (an be reached by installing pumpsand boreholes In some cases largeamounts of water can be abstracted withshyOut severe environmental effects This isparticularly true of areas where a combishynation of favourable climate topographygeological structure and rock compositionenables the water-bearing body - theaquifer - to recharge itself rapidly In suchcases the water is a renewable resourceHowever in other cases the rate ofexploishytation may greatly exceed the capacity ofthe aquifer to be recharged In these casesboth the quantity and the quality of thewater supply may deteriorate markedly overtime In such cases it is more appropriateto refer to the extraction ofwater as minshying of a largely non-renewable resource

Let us take m extreme example theexploitation of groundwater resources inthe oil-rich kingdom ofSaudi Arabia Mostof Saudi Arabia is desert so that climaticconditions are not favourable for rapidlarge-scale recharge of aquifers Also muchof the groundwater that lies beneath thedesert is a fossil resource created duringmore humid conditions - pluvials - thatexisted in the Late Pleistocene between15000 and 30000 years ago In spite ofthese inherently unfavourable circumshystances Saudi Arabias demand for wateris growing inexorably as its economy deshyvelops In 1980 the annual demand was24 billion cubic metres (bern) By 1990it had reached 12 bern (a fivefold increasein just a decade) and it is expected to

Changes in Groundwater 159

reach 20 bem by 2010 Only a very smallpart of the demand can be met fromdesalination plants or surface runoff overthree-quarters of the supply is obtainedfrom predominantly non-renewablegroundwater resources The drawdown onaquifers is thus enormous rt has been calshyculated that by 2010 the deep aquitcrswill contain 42 per cent less water than in1985 Much of the water is used ineffecshytively and inefficiently in the agriculturalsector (AI- Ibrahim 1991) to irrigate cropsthat could easily be grown in more humidregions and then imported

Saudi Arabia is not alone in its orashycious appetite for groundwater In manyparts of the world such problems havegrown with increasing population levelsand consumption demands together withthe adoption of new exploitation techshyniques (for example the replacement ofirrigation methods involving animal orhuman power by electric and dieselpumps)

Considerable reductions in groundshywater levels have been caused by abstrac~

tion in other areas The rapid increase inthe number of wells tapping groundwaterin the London area from 1850 until afterthe Second World War caused substantialchanges in groundwater conditions Thepiezometric surface in the confined chalkaquifer has fallen by more than 60 metresover hundreds of square kilometres Likeshywise beneath Chicago Illinois USApumping since the late nineteenth centuryhas lowered the piezometric head by some200 metres The drawdown that has takenplace in the Great Artesian Basin of Ausshytralia exceeds 80-100 metres in someplaces The environmental consequencesof excessive groundwater abstraction inshyclude salinization of coastal aquifers (seepart V section 5) and land subsidence (seepart V section 7)

Some of the most serious reductions inwater levels are taking place in the High

160 The Waters

Plate IV10 A major cause of groundwater depletion is the use of centre-pivotirrigation schemes The Ogallala aqUifer of the High Plains of Texas where thisphoto was taken is a major example of this phenomenon (A S Goudie)

Plains ofTexas threatening the long-termviability of irrigated agriculture in that areaBefore irrigation development started inthe 1930s the High Plains groundwatersystem was in a state of dynamic equilibshyrium with long-term recharge equal tolong-term discharge However the groundshywater is now being mined at a rapid rateto supply centre-pivot and other schemesIn a matter of only fifty years or less thewater level has declined by 30-50 metresin a large area to the north of LubbockTexas The aquifer has narrowed by morethan 50 per cent in large parts of certaincounties and the area irrigated by eachwell is contracting as well yields arc falling

In some industrial areas recent reducshytions in industrial activity have led to

less groundwater being taken out of theground As a consequence groundwaterlevels in such areas have begun to rise a

trend exacerbated by considerable leakagefrom ancient deteriorating pipe and sewersystems This is already happening in Britshyish cities including London Liverpool andBirmingham In London because of a 46per cent reduction in groundwater abstracshytion the water table in the Chalk andTertiary beds has risen by as much as 20metres Such a rise has numerous implicashytions both good and bad

bull increase in spring and river flowsbull re-emergence of flow from dry

springsbull surface water floodingbull pollution of surface waters and spread

of underground pollutionbull flooding of basementsbull increased leakage into tunnelsbull reduction in stability of slopes and

retaining walls

bull reduction in bearing capacity of founshydations and piles

bull increasedhydrostaticupliftandswelJingpressures on foundations and structures

bull swelling of clays as they absorb waterbull chemical attack on building foundations

There are various methods of rechargshying groundwater resources providing thatsufficient surface water is available Wherethe materials containing the aquifer arepermeable (as in some alluvial fans coastalsand dunes or glacial deposits) the techshynique of water-spreading is much usedIn relatively flat areas river water may bediverted to spread evenly over the groundso that infiltration takes place Alternativewater-spreading methods may involve reshyleasing water into basins which are formedby excavation or by the construction of

FURTHER READING

Conclusion 161

dikes or small dams On alluvial plainswater can also be encouraged to percolatedown to the water table by distributing itinto a series ofditches or furrows In somesituations natural channel infiltration canbe promoted by building small check damsdown a stream course In irrigated areassurplus water can be spread by irrigatingwith excess water during the dormant seashyson In sediments with impermeable layshyers such water-spreading techniques are noteffective and the appropriate method maythen be to pump water into deep pits orinto wells This last technique is used onthe heavily setded coastal plain of Israelboth to replenish the groundwater reshyservoirs when surplus irrigation water isavailable and to attempt to diminish theproblems associated with salt-water intrushysion from the Mediterranean

Downing R A and Wilkinson W B (eds) 1991 Applied Groundwater HydrologyA BririJh Pmpecrive Oxford Clarendon PressAn advanced textbook on all aspects of groundwater in the British context

11 CoNCLUSION

Freshwater resources are of vital imporshytance Their quality and quantity have unshydergone major changes as a consequenceof human activities Human demand forfreshwater has grown inexorably in reshycent decades As a result ever-increasingproportions of river flow are being conshytrolled or modified by deliberate humanmanipulation most notably by the conshystruction of dams the channelization ofstreams and by long-distance inter-basinwater transfers As our case study of theColorado River in the USA shows thedegree of control that can be achieved isradical

EquaUy important are changes in thehydrological cycle resulting unintentionshyally from changes in land use and land

cover The replacement of forests withfarms and of countryside with cities aretwo particularly important mechanisms inthis respect Also significant are the conshysequences - some anticipated some not shyof land drainage activities

Humans have modified not only thequantity of river flow but also its qualityMany water resources are polluted by arange of both point and non-pointsources River pollution can lead in turnto eutrophication of lakes and inland andmarginal seas However water pollutionand lake eutrophication as our case studiesof the River Clyde and Lake Biwa showare reversible if proper management stratshyegies are adopted Nonetheless as is shownin the case of the rapid desiccation ofthe AraI Sea the required solutions maybe extremely complex and technological

162 The Waters

change is seldom the only solution Wholeshysale changes in a regions economic andpolitical structure may be required

Finally we have pointed to the imporshytance of groundwater reserves and showedthat in some countries these resources arcbeing exploited at an unsustainable rateIn many areas the water table Ius beendrawn down too fur and too tast We havealso pointed out that in other parts of the

KEy TERMS AND CONCEPTS

aquiferbiological magnificationchannelizationdear-water erosioneutrophication

POINTS FOR REVIEW

world the reverse process is happening andthat groundwater levels are rising

The issues discussed in this part of thebook indicate how problems of humanimpacts on water are complicated by thelinks between bodies of water by themutual interaction of ditlcrent stressesand by the links between water and otheraspects of the environment such as theatmosphere biosphere and land surface

inter-basin water transterspoint and non-point sources of pollutionred tidesthermal pollution

Are dams a good or a bad thing

If you were in charge of providing large quantities of clean water in an area would youseek to increase or decrease the amount of forest in your catchments

How do humans increase the risk of river floods

What is the difference between point and non-point sources of water pollution

What do you understand by the term eutrophication

How do humans change the state of groundwater bodies

PART V

The Land Surface1 Introduction 1652 Soil Erosion by Water 165

bull Soil erosion on the South Downssouthern England 170

3 Wind Erosion and Dune Reactivation 172bull Controlling sand at Walvis Bay Namibia 186

4 River Channel Changes 1785 Salinization 1826 Accelerated Landslides 185

bull Slope erosion in the Pacific nolth-wcstof North America 188

7 Ground Subsidence 1898 Waste Disposal 1919 Stone Decay in Urban Buildings 197

bull Venices decaying treasures 20010 Conclusion 201

Key Terms and Concepts 202Points for Review 202

1 INTRODUCTION

This part of the book focuses on humanimpacts on the land surface - primarilysoils and landforms Humans havt modishyfied soils in many ways Most serious of allhas been the impact of land-use changeson the rates at which soils art eroded bywind and water The quality of soils hasalso been transformed At present fortxample many soils in irrigated regionsare being affected by salinization but atother times and in other places changtsin soil quality have included the formashytion of peat layers podzols and lateritehardpans Soil conditions are atfected bymodern farming practices heavy farmmachintry causes soil compaction andchemical changes are brought about bythe application ofsynthetic fertilizers Thtwhole impact of humans on soils is oftentermed metapedogenesis (table VI)

As well as soils the skin of the earth iscomposed of its landforms Here again thehuman impact can be considerable (tableY2) In particular humans can destabilizehillside slopes and cause wholesale groundsubsidence The range of human impactson landforms and landforming processesis considerable Some landforms may beproduced by dirtct anthropogenic processes Examples are landforms producedby constructional activity (eg tipping)excavation mining and farming (eg tershyracing) Landforms produced indirecdy byhuman activities while less easy to recogshynize are of particular importance Indeedthe indirect and unintentional modificashytion of processes by humans is the mostcrucial aspect of what is called anthropomiddotgeomorphology The geomorphologicaleffects of removing vegetation are anexample of this type of change Sometimeshumans deliberately try to change landshyforms and landforming processes but setin train a series of events which were notanticipated or desired As is noted in part

Soil Erosion by Water 165

VI section 3 for instance many attemptshave been made to rtduce coastal erosionby building impressive-looking and expenshysive engineering structures which have infact exacerbated the trosion rather thanhalting it

2 SOIL EROSION BY WATER

Soil erosion is a natural geomorphologicalprocess which takes place on many landsurfaces Under grassland or woodland ittakes place slowly and apptars to be moreor less balanced by soil formation Accelshyerated soil erosion takes place wherehumans have interfered with this balanceby modifYing or removing the natural vegshyetation cover Construction urbanizationwar mining and other such activities areonen significant in accelerating the probshylem However the main causes of soilerosion are deforestation and agriculture

Forests protect the underlying soil fromthe direct effects of rainfall generating anenvironment in which rates oferosion tendto be low The canopy plays an importantrole both by shortening the fall of rainshydrops and by decreasing the speed atwhich they hit the ground There art exshyamples of ctrtain types of trees (eg beech)in certain environments (eg maritimetemperate) creating large raindrops butin general most canopies reduce the eroshysive effects of rainfalls The prestl1ce ofhumus in forest soils may be even moreimportant than the canopy in reducingerosion rates in forest Humus in the soilboth absorbs the impact of raindrops andleads to soils with extremely high permeshyability Thus forest soils have high infiltrashytion capacities Another reason why forestsoils allow large quantities of water to passthrough them is that they have many largemacropores produced by roots and theirrich soil fauna Forest soils arc also wellaggregated making them resistant to boththe effects of wetting and water drop

166 The Land Surface

Table V1 Metapedogenesls human impacts on the main factors Involved in soilformation

Factor

Parent material

Topography

Climate

Organisms

Time

Human impacts

Beneficial adding mineral fertilizers accumulating shellsand bones accumulating ash removing excess amounts ofsubstances such as saltsDetrimental removing through harvest more plants andanimal nutrients than are replaced adding materials inamounts toxic to plants or animals altering soilconstituents in a way which depresses plant growth

Benehcia checking erosion through surface rougheningland forming and structure building raising land level byaccumulation of material land levellingDetrimental causing subsidence by draining wetlands andby mining accelerating erosion excavating

Beneficial adding water by irrigation rainmaking byseeding douds removing water by drainage diverting windsDetrimental subjecting soil to excessive insolation toextended frost action or to wind and rain

Beneficial introducing and controlling populations ofplants and animals adding organic matter loosening soilby ploughing to admit more oxygen fallowing removingpathogenic organisms eg by controlled burningDetrimental removing plants and animals reducingorganic content of soil through burning ploughingovergrazing harvesting adding or encouraging growth ofpathogenic organisms adding radioactive substances

Beneficial rejuvenating soil by adding fresh parentmaterial or through exposure of local parent material bysoil erosion reclaiming land from under waterDetrimental degrading soil by accelerated removal ofnutrients from soil and vegetation cover burying soilunder solid fill or water

Source Modified from Bidwell and Hole (15)

impact This high degree of aggregation isa result of the presence of considerablequantities of organic material which is animportant cementing agent in the formashytion of large water-stable aggregatesEarthworms also help to produce wellshyaggregated soil Finally deep-rooted treeshelp to stabilize steep slopes by increasingthe total shear strength of the soils

It is therefore to be expected that withthe removal of forest for agriculture orfor other reasons rates of soil loss will riseand mass movements (landslides debrisflows etc) will happen more often andon a larger scale Rates of erosion will beparticularly high if the deforested groundis left bare under crops the increase willbe less marked The method ofploughing

Soil Erosion by Water 167

Table V2 Major anthropogeomorphologlcal processes

Type of process

Dired anthropogenic processes

Constructional

Excavational

Hydrological interference

Indired anthropogenic processes

Acceleration of erosion andsedimentation

Subsidence

Slope failure

Earthquake generation

Source After Goudie (1993)

Examples

Tipping moulding ploughing terracing

Digging cutting mining blasting of cohesiveor non-cohesive materials cratering trampingand churning

Flooding damming canal constructiondredging channel modification drainingcoastal protection

Agricultural activity and vegetation clearanceengineering (especially road construction andurbanization)Incidental modifications of hydrological regime

Collapse and settling related to mininggroundwater pumping and permafrost melting(thermokarst)

landsliding flow and accelerated creep causedby loading undercutting shaking andlubrication

loading by reservoirs lubrication along faultplanes

the time of planting the nature of the cropand the size of the fields will all have aninfluence on the severity of erosion

Many fires are started by humanseither deliberately or accidentally Becausefires remove vegetation and expose theground they also tend to increase rates ofsoil erosion The burning of forests forexample can lead to high rates ofsoil lossespecially in the first years after the fireRates ofsoil loss in burnt forests are oftenup to ten times higher than those in proshytected areas

Soil erosion can also be caused by conshystruction and urbanization A number ofstudies have been done which illustrateclearly that urbanization can create signifishycant changes in erosion rates The highest

rates of erosion are produced in theconstruction phase when there is a largeamount of exposed ground and a lot ofdismrbance from vehicle movements andexcavations The equivalent of many decshyades of natural or even agricultural eroshysion may take place during a single year inareas cleared for construction Howeverconstruction does not go on for ever andeventually the building work is completedThen the disturbance ceases roads aresurfaced and gardens and lawns are culshytivated Rates of erosion fall dramaticallyperhaps to the levels prevailing under natshyural or pre-agriculrurai conditions

Soil erosion by water takes on a varietyof forms Splash erosion and sheet ftowmay occur in some areas Elsewhere rills

168 The Land Surface

Plate V1 Soil erosion at St Michaels Mission in central Zimbabwe A large donga(or erosional gully) has formed as a result of overgrazing and other land-usepressures (A S Goudie)

(small channels) may develop Under moreextreme conditions for example wheresoils are highly erodible large gullies mayform and these may coalesce to form abadlands topography Slopes can becomedestabilized so that mass movementsoccur

Concern about accelerated erosion foshycuses on two main categories of impactThe first of these relates to the threat itposes to our ability to grow crops and tofeed the worlds growing population Soilerosion reduces soil depth and often meansthat the most fertile humus- and nutrientshyrich portion of the soil profile is lost Thesecond category of impact is what aretermed off-farm impacts These include

bull accelerated siltation of reservoirs riversdrainage ditches etc

bull eutrophication of water bodies by the

transport of nutrients attached to soilparticles

bull damage to property by soil~laden waterand debris flows

There is some evidence that soil erosionis becoming a more serious problem inparts of Britain in spite of the fact thatthe countrys rainfall is much less intenseand so less erosive than in many parts ofthe world The following practices mayhave caused this state of affairs

bull Ploughing on steep slopes that wereformerly under grass in order to inshycrease the area of arable cultivation

bull Usc of larger and heavier agriculturalmachinery which tends to increase soilcompaction

bull Use ofmore powerful machinery whichpermits cultivation in the direction of

maximum slope rather than along thecontour Rills often develop along thewheel ruts (wheelings) left by tracshytors and farm implements and alongdrill lines

bull Use of powered harrows in seedbedpreparation and the rolling of fieldsafter drilling

bull Removal of hedgerows and the associshyated increase in field size Larger fieldscause an increase in slope length andthus a higher risk of erosion

bull Declining levels oforganic matter resultshying from intensive cultivation and relishyance on chemical fertilizers which inturn lead to reduced aggregate stability

bull Widespread introduction of autumnshysown cereals to replace spring-sowncereals Because of their longer growingseason autumn-sown cereals producegreater yields and are therefore moreprofitable The change means that seedshybeds with a fine tilth and little vegetashytion cover are exposed throughout theperiod of winter rainfall

Several measures can be used to reducethe rate at which soil is lost from agriculshyturalland In some parts of the world thesetechniques have been practised for sometime and have been quite successful Theyare

FURTHER READING

Soil Erosion by Water 169

bull Revegetation(a) deliberate planting(b) suppression of fire grazing etc

to allow regenerationbull Measures to stop stream bank erosion

(eg stone banks and rip-rap)bull Measures to stop gully enlargement

(a) planting of trailing plants etc(b) weirs dams gabions etc

bull Crop management(a) maintaining cover at critical times

of year(b) rotation of crops(c) growing cover crops(d) agroforestry

bull Slope runoff control(a) terracing(b) deep tillage and application of

humus(c) digging transverse hillside ditches

to interrupt runoff(d) contour ploughing(e) preservation ofvegetation strips (to

limit field width)bull Prevention of erosion from point

sources such as roads and feedlots(a) intelligent geomorphic location of

roads feedlots etc(b) channelling of drainage water to

non-susceptible areas(c) covering of banks cuttings etc

with vegetation

Boardman J Foster I D L and Dearing J A (cds) 1990 Soil Erosion on Agrishycultural Land Chichester WileyAn edited series of advanced reseatch papers providing some useful case studies

Hudson N 1971 Soil Conservation London BaufordA general introductory level textbook

Morgltln R P C 1995 Soil Erosion and Conservation 2nd edn Harlow LongmanA general introduction that is especially strong on methods of controlling erosion

Pimental D (cd) 1993 World Soil Erosion and Conservation Cambridge CambridgeUniversity PressA series of advanced edited papers that look at soil erosion in a regional context

170 The Land Surface

Soil erosion on the South Downs southernEnglandThe South Downs are a rAnge of L3chalk hills in south-east England ~~--J

which rise to an altitude of around todM200 metres They are deeply dis-sccted by a network of dry valleysIn the early Holocene the Downswere wooded and their soils weremuch thicker than they are now Soilsarc now typically shallow and stonyrendzinas with A horizons usuallyless than 25 cm thick Since thexcond World War the dominantland usc in the area has been farmshying of wheat and barley In the 1970s a major change of fuming practice ocmiddotculTed with the adoption of autumn-grown cereals (eg winter wheat) in prefshyerence to lower-yielding spring-sown varieties Farming has also become moreintensive fields have increased in size with the removal ofhedgcs and grass bankswhile larger and more powerful tractors have enabled farmers to cultivate slopesas steep as 25

Plite V2 Sotl erosion and flood runoff on the South Downs southmiddoteastEngland Uohn Boardman)

Soil Erosion by Water 171

figure V1 Typical location and form oferosion on agricultural land on the SouthDowns EnglandSource After Boardman (1992) fig 21

v

Angle ofslOjlf

525middot

CHALK

Valleyoonom riU and fan

As a result there has been anincrease in soil erosion by wateron the Downs especially betweenSeptember and December on landprepared for or drilledmiddot with wintercereals This is because large areasof smooth ground with minimalvegetation cover are exposed durshying the wettest months Rills developin hillsides (figure Vl) especiallyalong tractor wheel ruts (wheelshyings) and some gullies havedeveloped along valley bottomsSediment-laden runotT can causeserious problems for nearby housesLocalized erosion and flooding were recorded in 1958 and 1976 but there arefew records of such events earlier in the twentieth cenrnry Frequent and someshytimes serious erosion occurred in the 1980s especially during the wet autumnsand winters of 1982-3 1987-8 and 1990-1 John Boardman has monitoredabout 36 sq km of agricultural land in the area during this time (see table V3)and found that peak soil erosion in the 1987-8 winter season was accompaniedby serious flooding of roads and properties

Further reading

Boardman J 1995 Damage to property by runoff from agricultural land SouthDowns southern England 1976-1993 Geographieal Journal 161 177-91

Table V3 Rainfall and soil erosion on a monitored site in the eastern SouthDowns England 1982-1991

Year Total rainfall1 Sep-1 Mar (mm)

Total soilass(01 metres)

1982-31983-41984-51985-61986-71987-81988-91989-901990-11991-2

724560580453503739324621469298

181627

182541211

135292

9401527

112Source Modifled from Boardman (1995)

172 The Land Surface

3 WIND EROSION AND

DUNE REACTIVATION

In the drier parts of the world or onparticularly light soils wind erosion maybecome a major cause of accelerated soilloss As in the case of accelerated soilerosion by water the key factor is the reshymoval of vegetation cover

Possibly the most famous case of soilerosion by deflation was the dust bowl ofthe 1930s in the USA This was caused inpart by a series of hot dry years whichdepleted the vegetation cover and madethe soils dry enough to be susceptible towind erosion The effects of this droughtwere made very much worse by years ofovergrazing and unsatisfactory farmingtechniques However perhaps the primarycause of the dust bowl was the rapid exshypansion of wheat cultivation in the GreatPlains The number of cultivated hectaresdoubled during the First World War astractors (for the first time) rolled out onto the plains in their thousands In Kansasalone wheat cultivation increased fromunder 2 million hectares in 1910 to alshymost 5 million in 1919 After the warwheat cultivation continued apace helpedby the development of the combine harshyvester and government assistance Thefarmer busy sowing wheat and reapinggold could foresee no end to his land ofmilk and honey but the years of favourshyable climate were not to last and overlarge areas the tough sod which exaspershyated the earlier homesteaders had givenway to friable soils which were very susshyceptible to erosion Drought acting ondamaged soils created the black blizzardsthat carried dust as far as the Atlantic seashyboard (see box in part III section 2)

The dust bowl was not solely a featureof the 1930s and dust storms are still aserious problem in various parts of theUnited States For example in the San

Joaquin Valley area ofcentral California in1977 a dust storm caused extensive damshyage and erosion over an area of about2000 sq kIn More than 25 million tannesof soil were stripped from grazing landwithin a 24middothour period While the comshybination of drought and a very high wind(as much as 300 kIn per hour) providedthe predisposing conditions for the stripshyping to occur overgrazing and the genshyeral lack of windbreaks in the agriculturalland played a more significant role Inaddition broad areas of land had recentlybeen stripped of vegetation levelled orploughed up prior to planting Othercontributory factors albeit quantitltltivdyless important included the stripping ofvegetation for urban expansion extensivedenudation of land in the vicinity of oilshyfields and local denudation of land byrecreational use of vehicles One interestshying observation made in the months afterthe dust storm was that in subsequentrainstorms runoff occurred faster fromthose areas that had been stripped by thewind exacerbating problems of floodingand creating numerous gullies Elsewherein California dust yield has been considershyably increased by mining operations in drylake beds

A comparable acceleration ofdust stormactivity has also occurred in the formerSoviet Union After the Virgin Lands promiddotgramme of agricultural expansion in the1950s dust storms in the southern Omskregion became on average two and a halftimes more frequent and in some localareas five or six times more frequent

We can see how drought and humanpressures can combine to produce accelershyated wind erosion by considering themeteorological data for dust-storm freshyquency at Nouakchott in Mauritania westshyern Africa (figure V2) Since the 1960sthe number of dust storms has gone updramatically from just a few each year toover 80 a year This is partly caused by the

Wind Erosion 173

Plate V3 Gully erosion by water near luyengo central Swaziland southemAfrica (A $ Goudie)

]

l l )

bullo

Figure V2 Annual frequency of duststorm days and annual rainfall forNouakchott Mauritania Africa1960-1986Source After Goudie and Middleton (1992)fig 8

low rainfall of the Sahel drought that hasaftlicted the area bU[ also by human popushylation growth and increased disturbanceof the dcsert surface by vehicles

Wind erosion is also active in certainparts of Britain Dust storms have lxenrecorded in the Fen1ands the BrecklandsEast Yorkshire and Lincolnshire since the1920s and they seem to be happltningmore often in recent years The s[Qrmsresult from changing agricultural practicesincluding the usc of artificial fertilizc=rs inplace of farmyard manure a reduction inthe process of ltc1aying whereby day wasadded to the peat to stabilize it the reshymoval of hedgerows to facilitate the useof bigger farm machinery and perhapsmost importantly the increased cultivationof sugar beet This crop requires a finetilth and tends to leave the soil relativelybare in early summer compared with othercrops

174 The Land Surface

When and where wind erosion of soilstakes place is determined by two sets offactors wind erosivity and surfaceerodibility (table VA) Wind erosion willnormally be reduced if those variablesmarked in the table with a (+) are increasedand if those marked with a (-) are reshyduced (Those marked with a plusmn can haveeither effect) These are important pointsto be considered when selecting consershyvation methods which have to focus onimproving the stability of the soil and reshyducing wind velocities at the soil surface

Table V4 Key factors influencing winderosion of solismiddot

Erosivity Wind variablesVelocityFrequencyDurationMagnitudeShearTurbulence

Erodibility Debris variablesParticle size plusmnSoil clods andcohesive properties +AbradabilityTransportabilityOrganic matter +

Surface variablesVegetation residue +

height +orientation +density +fineness +cover +

Soil moisture +Surface roughness +Surface length(distance from shelter) shySurface slope plusmn

bull See text above for explanation

Source After Cooke and Doomkamp (1993)

Soil conservation measures can be dishyvided into three types

bull agronomic measures which manipulatevegetation to minimize erosion by proshytecting the soil

bull soil management methodJ which focuson ways of preparing the soil to proshymote good vegetative growth and imshyprove soil structure in order to increaseresistance to erosion

bull muhanicaJ methods which manipulatethe surface topography in order toreduce wind velocity and turbulence

Agronomic measures use living vegetationor the residues from harvested crops toprotect the soil Wind erosion problemsoccur on croplands only when the soil isexposed because the crop is not matureenough to provide adequate protectionHence stubble mulching which involvestilling but not to the extent whereby thefield is left dean has become a widelyused method of protection from erosionSoil management techniques are concernedwith different methods of soil tillage thefarmers methods of preparing a suitableseedbed for crop growth and of helpingto control weeds Mechanical methodsinclude the creation of protective barriersagainst the wind such as fences windshybreaks and shelter belts

Another aspect of wind erosion is dunereactivation This occurs on the marginsof the great subtropical and tropical deshyserts and is one facet of the process ofdesertification (see part II section 3)Dune reactivation arouses some of thestrongeS[ fears among those combatingdesertification The increasing populationlevels of both humans and their domesticanimals brought about by improvementsin health and by the provision of boreholeshas led to excessive pressure on the limitedvegetation resources As ground coverhas been reduced so dune instability has

Wind Erosion 175

Plate V4 The use of palm frond fences to reduce sand movement at Erfoudsouthern Morocco (A S Goudie)

increased The problem is not so muchthat dunes in the desert cores are relemmiddotIcssly marching on to moister areas morethat fossil dunes laid down during themore arid phase peaking around 18000years ago have been reactivated in litu bythe removal of stabilizing vegetation

Many methods are used in the attemptto control drifting sand and moving dunesIn practice most solutions to the problcmof dune instability and sand blowing haveinvolved establishing a vegetation coverThis is not always easy Plant species usedto control sand dunes must be able to

FURTHER READING

endure undermining of their roots buryshying abrasion and often severe deficienciesof soil moisture Thus the species selcctedneed to have the ability to recover afterpanial burying to have deep and spreadmiddoting roots to have rapid height growthin the seedling srages to promote rapidliner development and to add nitrogento the soil through root nodulcs Duringthe early stages of growth they may needto be protected by fences sand trapsand surface mulches Growth can also bestimulated by the addition of syntheticfertilizers

Goudie A S (ed) 1990 Techniques for Desert Reclamation Chichester WileyThis edited work contains several chapters on the control of dunes and dust hazards

176 The Land Surface

Controlling sand at Walvis Bay NamibiaThe movement of sand can be aserious problems for the inhabitantsof the worlds drylands Sand stormsreduce visibility on roads whileencroaching dunes can overwhelmhouses farms canals and transportlinks For this reason humans havedeveloped a range of techniques totry to control drifting sand andmoving dunes (table vS)

One location where moving sandhas proved to be a severe problemand where many of these controltechniques have been attempted isthe port town of Walvis Bay on thecoast of Namibia in southern Africa(figure V3) Here the annual rainshyfall is so low (around 2S mm) thatvegetation cover is minimal allowshying sand to move when windvelocities reach critical levels (as theyoften do) Many of the dunes nearWalvis Bay are individual crescentshyshaped dunes called barchans Theseare highly mobile travelling sometens of metres per year From timeto time they have blocked roadsthey have also caused the relocationof the main railway link with theinterior The local authority is tryshying to stabilize the sand by suchmeans as planting (and irrigating)shrubs and building sand fences (seeplates V4 V5)

PfiwI ~

- ir i WaMII Bay i

i Y - - - - - - - - - - - - - - - - - - 23S

ProbIelll$lronl dtiftirlJ wld dunA

it i t--AncicoldiltrigtIIwJolKuiKb iiu

~~ flood proIecion dun

N

I

~WIlI __

Figure V3 The coastal zone nearWalVis Bay Namibia The main coastroad is often blocked by sand whilethe main raHway line has had to berelocated inland

Tll

~

~

Wind Erosion 177

Plate V5 A road has been blocked by a migrating barchan dune nearWalvis Bay Namibia Sand fences have been constructed in an attempt toslow the process down (H A Viles)

Table VS Control technlque$ for drifting sand and mobile dunes

Problem

Drifting sand

Moving dunes

Control methods

Enhancement of deposition of sand through creatinglarge ditches vegetation belts and barriers and fencesEnhancement of sand transport by aerodynamicstreamlining of surface or changing surface materialsReduction of sand supply by surface treatmentimproved vegetation cover or erection of fencesDeflection of moving sand by fences barriers orvegetation belts

Removal by mechanical excavationDestruction by reshaping trenching through dune axis orsurface stabilization of barchan armsImmobilization by trimming surface treatment andfences

178 The Land Surface

4 RIvER CHANNEL CHANGES

River channels developed in alluvium(sediments deposited by the river itself)adjust their shape slope and velocity offlow in response to discharge sedimentload the calibre of the bed and bank sedishyment the banks vegetation and the slopeof the valley Humans have intervened innatural channel systems by building damsrealigning channel courses constructinglevees and embankments and in manyother ways (see part IV section 2) Howshyever they have also altered channel charshyacteristics unintentionally (table V6) forexample by modifYing the amounts ofdisshycharge the amount of sediment beingcarried and the nature of vegetation onthe river bank Sometimes too deliberatechanges have set in train a series of unshyintended changes

Let us consider channel straighteningFor purposes of navigation and flood conshytrol humans have deliberately straightenedmany river channels The elimination ofmeanders contributes to flood control intwo ways First it eliminates some floodsover banks on the outside ofcurves wherethe current is swiftest and where the water

Table V6 Accidental channel changes

surface rises highest Second and moreimportandy the shorter straightenedcourse increases both the gradient andthe velocity of the stream Floodwaterscan then erode and deepen the channelthereby increasing its flood capacity Deshyliberate channel-straightening causes varishyous types of adjustment in the channelboth within and downstream from straightshyened reaches The types ofadjustment varyaccording to such influences as stream grashydient and sediment characteristics (figureVA) Brookes (1988) has recognized fivetypes of change within the straightenedreaches (types WI to W5) and twO typesofchange downstream (types Dl and D2)

bull Type WI is degradation of the channelbed This happens because straightenshying shortens the channel path andtherefore increases the slope This inturn increases the efficiency ofsedimenttransport

bull Type W2 is the development of anarmoured layer on the channel bed bythe more efficient removal of finematerials as described under Type WI

bull Type W3 is the development of a sinushyous thalweg in streams which are not

Phenomenon

Channel incision

Channel aggradation

Channel enlargement

Channel diminution

Channel diminution

Cause

Clear-water erosion below dams caused by sedimentremoval

Reduction in peak flows below damsAddition of sediment to streams by mining agricultureetc

Increase in discharge level produced by urbanization

Discharge decrease following water abstraction or floodcontrol

Trapping and stabilizing of sediment by artificiallyintroduced plants

River Channel Changes 179

Plate V6 A completely artificial stream channel in Maspalomas Gran CanariaCanary Islands (A S Goudie)

Figure V4 Principal types of adjustment in straightened river channelsSource After Brookes (1987) fig 4

180 The Land Surface

only straightened but also widened beshyyond the width of the natural channel

bull Type W4 is the recovery of sinuosityas a result of bank erosion in channclswith high slope gradients

bull Type W5 is the development of a sinushyous course by deposition in streamswith a high sediment load and a rclashytivcly low valley gradient

bull Types 01 and 02 result from deposishytion downstream as the stream tries toeven out its gradient The depositionmay occur either as a general raisingof the levcl of the bed or as a series ofaccentuated point bar deposits

Another influence on channel form isthe growth ofsettlements It is now widclyrecognized that the urbanization of ariver basin results in an increase in thepeak flood flows in a river (see part Nsection 4) It is also recognized that themorphology of stream channels is relatedto their discharge characteristics and esshypecially to the discharge at which bankfull flow that is a complete filling of thechanncl occurs As a result of urbanizashytion the frequency ofdischarges which IiIlthe channcl will increase This will meanthat the beds and banks of channcls inerodible materials will be eroded so as toenlarge the channel This in turn will leadto bank caving possible undermining ofstructures and increases in turbidity

Similarly important changes in channelmorphology result from the lowering ofdischarge caused by flood-control worksand diversions for irrigation This can beshown for the North Platte and the SouthPlatte Rivers in America where both peakdischarge and mean annual discharge havedeclined to 10-30 per cent of their preshydam values The North Platte 762-1219metres wide in 1890 near the WyomingshyNebraska border has narrowed to about60 metres at present The South PlatteRiver 89 kIn above its junction with the

1m

Figure VS The configuration of thechannel of the South Platte River atBrule in Nebraska USA (a) in 1897and (b) in 1959 Such changes inchannel form result from dischargediminution caused by flood controlworks and diversions for irrigationSource After GoudIe (1993) fig 615(a)

North Platte was about 792 metres widein 1897 but had narrowed to about 60metres by 1959 The tendency of bothrivers has been to form one narrow wellshydefined channel in place of the previouslywide braided channels The new channclis also generally somewhat more sinuousthan the old (figure VS)

The building of dams can lead to chanshyncl aggradation upstream from the resershyvoir and channcl deepening downstreambecause of the changes brought about insediment loads The overall effect of th~

creation of a reservoir by the constructionof a dam is to lead to a reduction in downshystream channel capacity of about 30-70per cent

Equally far-reaching changes in channclform are produced by land-use changesand the introduction of soil conservationmeasures Figure V6 is an idealized repshyresentation of how the river basins ofGeorgia USA have been modified throughhuman agency between 1700 (the time ofEuropean settlement) and the presentClearing of the land for cultivation (figureV6(b)) caused massive slope erosion which

lbi

1lt1

Xvcdy erodeduplmds

Partial to cOOIpkttc~ndfilliJIg

~tlk lWmank ckposition

River Channel Changes 181

Trees lilJcd by thensing aler bd

Ltvm wIUky fillofmodern itdimenll

BloCm=p

Regrowth d lOmuprcdOOlinaody pine

Accumulation of~nt1y miggttiogsedirncnt ClwInol

Rill aggrading

Drained badslIolmpI I Suem iJlcised in modltrn lCdirncnt

Intensive coomaINm IcticQT- broad-based [(rrmspntUfC in Bermuda gr1Sl

Trees in bonomlands nor SoolI for darilf

SW oflm-kswoImp increasing

Figure V6 Changes in the evolution of the fluvial landscapes of the Piedmont ofGeorgia USA in response to land-use change between 1700 and 1970 (a) at thetime of European settlement c1700 (b) after the clearing and erosive cultivationof uplands (c) after the checking of erosion and the consequent incision of theheadwater streamSource After Trimble (1974) p 117

182 The Land Surface

resulted in large quantities of sedimentbeing moved into channels and floodplainsIntense erosive land use continued and wasparticularly strong during the nineteenthcentury and the first decades of the twenshytieth century Thereafter (figure V6(c))conservation measures reservoir construcshytion and a reduction in the intensity ofagricultural land use led to further chanshynel changes (Trimble 1974) Streamsceased to carry such a heavy sediment loadand became much less turbid As a resultthey cut down imo the floodplain sedishymems of modern alluvium lowering theirbeds by as much as 3-4 metres

Anmher causc of significant changes inchannels is the accelerated sedimentationassociated with changes in the vegetationgrowing alongside the channels In thesouthern USA the introduction of a bushytree the salt cedar has caused significant

FURTHER READING

floodplain aggradation In the case of theBrazos River in Texas for example theplants encouraged sedimentation by theirdamming and ponding effect Theyclogged channels by invading sand banksand sand bars and so increased the areasubject to flooding Between 1941 and1979 the channel width declined trom 157metres to 67 metres and the amount ofaggradation was as much as 55 metres(Blackburn et al 1983)

Finally mining can lead to very majorchanges in channel morphology The reashyson for this is that mining often requiresthe use of large quantities of water andproduces large quantities of waste Thewaste tends to lead to the aggradation ofthe channel bed and if the waste materialis coarse then there may be a tendency fora natural meandering pattern to be reshyplaced by a braiding one

Brookes A 1988 Channelized Rivers Chichester WileyAn advanced research monograph with broad scope

5 SALINIZATION

Salinity is a normal and natural feature ofsoils especially in dry areas Howevervarious human activities are increasing itsextent and severity

Salinity in soils has a range of undeshysirable consequences For example asirrigation water IS concentrated byevapotranspiration calcium and magneshysium components tend to precipitate ascarbonates leaving sodium ions dominantin the soil solution The sodium ions tendto be absorbed on to colloidal clay parshyticles deflocculating them and leavingthe soil structurdess almost impermeableto water and unfavourable to root develshyopment Poor soil structure and toxicitylead to the death of vegetation in areas ofsaline patches This creates bare ground

which is vulnerable to erosion by windand water

Probably the most serious result ofsalinization is its impact on plant growthThis takes place partly through its effecton soil structure but more significantlythrough its effects on osmotic pressuresand through direct toxicity When a watersolution containing large quantities ofdisshysolved salts comes into contact with a plantcell it causes the cells protoplasmic liningto shrink This is due to the osmoticmovement of me water which passes outfrom the cell towards the more concenshytrated soil solution The cell collapses andthe plant dies

This toxicity effect varies with differentplants and different salts Sodium carbonshyate by creating highly alkaline soil condishytions may damage plants by a direct caustic

effect high nitrate may promote undesirshyable vegetative growth in grapes or sugarbeets at the expense of sugar contentBoron is injurious to many crop plants atsolution concentrations of more than 1 or2 ppm

There are a variety of reasons why soilsalinity is spreading The most importantof these is the growth in the area ofirrigated land which has increased fromabout 8 million hectares in 1800 to 250million hectares in the 1990s (Thomasand Middkton 1993) The extension ofirrigation and the use of a wide range ofdifferent techniques for water abstractionand application can lead to a build-up ofsalt levels in the soil This happens beshycause water abstraction raises the groundshywater level so that it is near enough to theground surface for water to rise to thesurface by capillary action Evaporation

Salinization 183

then leaves the salts in the soil In the caseof the semi-arid northern plains of Victoshyria in Australia for instance the water tablehas been rising at around 15 metres peryear so that now in many areas it is linlemore than 1 metre below the surfaceWhen groundwater comes within 3 memiddottres of the surface in day soils - less forsilty and sandy soils - capillary forces bringmoisture to the surface where evaporationtakes place leaving salts behind

Second many irrigation schemes spreadlarge quantities of water over the soilsurface This is especially true for ricecultivation Such surface water is readilyevaporated so that again salinity levelsbuild up

Third the construction of large damsand barrages to control water flow and to

give a head ofwater creates large reservoirsfrom which further evaporation can take

Plate V7 A satanic mockery of snow Waterlogged and salinized land in SindPakistan The white surface is not snow but salt a major cause of decliningagricultural yields (A S Goudie)

Source Grelck (1993) table E5

Table V7 Salinization of irrigated cropshyland In selected countries

an increase in recharge rates of groundshywater and to an increase in the salinity ofstreams as salty groundwater seeps outfrom the ground and into stream flowReplanting has been shown to reverse theprocess (Bari and Schofield 1992)

Salinity can also be increased by salinematerials transferred from lake beds thathave dried up because of inter-basin watertransfers Around 30-40 million tonnesof salty soils are blown off the Aral Seaevery year (see part IV section 9) forexample and these add to the salt contentof soils downwind

It has been estimated (table V7) thatsalt-affected and waterlogged soils accountfor 50 per cent of the irrigated area in

184 The Land Surface

place The water gets saltier This saltywater is then used for irrigation with theeffects described in the previous paragraph

Fourth water seeps laterally from irrishygation canals especially in highly permeshyable soils so that further evaporation takesplace Many distribution channels in agravity irrigation scheme are located onthe elevated areas ofa floodplain or riverineplain to make maximum use of gravityThe elevated landforms selected are natushyral levees river-bordering dunes and tershyraces all of which arc composed of siltand sand which may be particularly proneto loss by seepage

In coastal areas salinity problems arccreated by seawater incursion broughtabout by overpumping of fresh groundshywater from aquifers If the aquifer is opento penetration from the sea salty watertends to replace the freshwater that hasbeen extracted This is a particularly sershyious problem along the shores of the Pershysian Gulf where bccallS( of the dry dimatethe freshwater can only slowly be replenshyished by rainfall However it can be aproblem for any coastal aquifer

Increases in soil salinity are nm restrictedto irrigated areas In some parts of theworld salinization has resulted fromvegetation clearance (Peck 1978) Theremoval of native forest vegetation allowsmore rainfall to ~netrate into deeper soillayers This causes groundwater levels torise creating seepage sometimes of salinewater in low-lying areas Through thismechanism an estimated 200000 hectaresof land in southern Australia which atthe start of European settlement in thelate eighteenth century supported goodcrops of pasture is now suitable only forhalophytic species Similar problems existalso in North America notably in Manishytoba Alberta Montana and North Dakota

The clearance of the native evergreenforest (predominantly Eucalyprusforest) insouth-western Australia has led both to

Country

AlgeriaAustraliaChinaColombiaCyprusEgyptGreeceIndiaIranIraqIsraelJordanPakistanPeruPortugalSenegalSri lankaSpainSudanSyriaUSA

of irrigated landsaffected by salinization

10-1515-2015202530-40

727lt30501316lt401210-1510-151310-152030-3520-25

Iraq up to 40 per cent of all Pakistan 50per cent in the Euphrates Valley of Syria30-40 per cent in Egypt and up to 30 percent in Iran In Africa however wherether~ are fewer great irrigation schemesless than 10 per cent of salt-affected soilsare so affected because of human action(Thomas and Middleton 1993) Lookingat the problem on a global basis the calshyculations of Rozanov et al (1990) makegrim reading They estimate (p 210) From1700 to 1984 the global areas of irrigatedland increased from 50000 to 22000001on2

while at the same time some 500000kIn2 were abandoned as a result ofsecondshyary salinization They believe that in thelast three centuries irrigation has resultedin I million sq km of land destroyed plus1 million sq kID of land with diminishedproductivity due to salinization

Given the seriousness of the problem arange of techniques for the eradicationconversion or control of salinity have beendeveloped These have been reviewed byRhoades (1990) and include the following

FURTHER READING

Accclerated Landslides 185

bull provision of adequate subsoil drainshyage to prevent waterlogging to keepthe water table low enough to reducethe effects of capillary rise and to reshymove water that is in excess of cropdemand

bull leaching of salts by applying water tothe soil surface and allowing it to passdownward through the root zone

bull treatment of the soil (with additions ofcalcium magnesium organic matteretc) to maintain soil permeability

bull planting of crops which do not needmuch water

bull planting of crops or crop varieties thatwill produce satisfactory yields undersaline conditions

bull reduction ofseepage losses from canalsand ditches by lining them (eg withconcrete)

bull reduction in the amounts of waterapplied by irrigation by using sprinkshylers and tricklers

bull storage of heavily salted waste waterfrom fields in evaporation ponds

Worthington E B (ed) 1977 Arid lAnd Irrigation in Dneloping Countries Envishyronmenttd ProblemJ and Effects Oxford PergamonA collection of papers that was among the first and most persuasive considerations ofthe problem caused by the rapid spread of irrigation schemes

6 ACCELERATED LANDSLIDES

In 19632600 people were killed in Italywhen a great landslide fell into a reservoirand caused a mass of water to spill overthe dam and cascade downstream Threeyears later at Aberfan in South Wales amassive debris flow killed over ISO peoplewhen it destroyed a school and houses asit rID down from a steep coal-waste tipThese are just two of the worst examplesof how human actions have created hazshyardous mass movements on slopes

Human capacity to change a hillside and

to make it more prone [Q failure has beentransformed by engineering developmentExcavations are going deeper buildingsand other structures are larger and manysites which are at best marginally suitablefor engineering projects are now beingused because of increasing pressure onland This applies especially to some ofthe expanding urban areas in the humidparts of low latitudes - Hong Kong KualaLumpur Rio de Janeiro and many othersMass movements are very seldom deshyliberately accelerated by human agencyMost are accidentally caused the exception

186 The Land Surface

possibly being the delibcrate triggering ofa threatening snow avalanche

The forces producing slope instabilityand landsliding can usefully be divided intodisturbing factors and resisting propertiesSome disturbing factors art natural othersmarked with an asterisk in the followinglist are caused by humans

bull Removal of lateral or ulld(rlyjn~q supshyportundercutting by wattr (tor exampleriver waves) or glacier icewcathering of weaker strata at the tOCof the slopewashing out of granular material byseepage erosionmiddothuman cuts and excavations drainmiddotage of lakes or reservoirs

bull Increased disturbing forcesnatural accumulations of water snowtalusmiddotpressure caused by human activity (forexample stockpiles of are tip-heapsrubbish dumps or buildings)

bull Transitory earth stressesearthquakesmiddotcontinual passing of heavy traffic

bull Increased internal pressurebuildmiddot up of pore-water pressures (forexample in joints and cracks especiallyin the tension crack zone at the rear ofthe slide)

Factors leading to a decrease in the reshysisting properties (shear strength) of thematerials making up a slope can also besummarized as follows Again those reshysulting from human activity are markedwith an asterisk

bull Materialsbeds which decrease in shear strengthif water content increases (clays shalemica schist talc scrpentine) for exshyample middotwhen local water table is artishyficially increased in height by reservoir

construction or as a result of stressrelease (vertical andor horizontal)following slope formationlow internal cohesion (tor example conshysolidated clays sands porous organicmatter)In bedrock faults bedding planesjoims foliation in schists ceaagebrecciated zones and pre-existingshears

bull Weathering changesweathering reduces effective cohesionand to a lesser extent the angle ofshearshying resistanceabsorption of watcr leads to changesin the fabric of days (for exampk lossof bonds bcrween particles or the forshymation of fissures)

bull Pore-JVater pressure jncreaseHigh groundwater table as a result ofincreased precipitation or middotas a resultof human interference (for example-dam construction) (see under Matershyials above)

Some mass movements are created byhumans piling up waste soil and rock intounstable accumulations that fail spontaneshyously The disaster at Aberfan in SouthWales referred to at the beginning of thissection occurred when a pile ofcoal waste180 metres high began to move as an earthflow The pile had been constructed notonly with steep slopes but also upon aspring line

In the case of the Vaionr Dam disasterin Italy (also referred to at the begilUlingof this section) heavy rainfall and the presshyence of young highly folded sedimentaryrocks provided the necessary predisposingconditions for a slip to take place Howshyever it was the construction of the VaiontDam itself which changed the localgroundwater conditions sufficiently toaffect the stability of a rock mass on themargins of the reservoir The result wasthat 240 million ell metres of ground

Accelerated Landslides 187

Table VS Examples of methods of controlling mass movements

Type of movement Method of control

Falls Flattening the slopeBenching the slopeDrainageReinforcement of rock walls by grouting with cementanchor boltsCovering of wall with steel mesh

Slides and flows Grading or benching to flatten the slopeDrainage of surface water with ditchesSealing surface cracks to prevent infiltrationSubsurface drainageRock or earth buttresses at footRetaining walls at footPilings through the potential slide mass

Source Dunne and leopold (1978) table 1516

slipped with enormous speed into thereservoir producing a sharp rise in waterlevel which spilled over the dam causingflooding and loss of life downstream

It is evident from what has been saidabout the predisposing causes of the slopefailure triJ8eretl by the Vaiont Dam thathuman agency was only able to have suchan impact because the natural conditionswere broadly filVourable to such an outshycome

Although the examples of acceleratedmass movements that have been givenhere are associated with the effects ofmodern construction projects more long-

FURTHER READING

established activities including deforeshystation and agriculture arc also highlyimportant For example Innes (1983) hasdemonstrated on the basis of the size oflichens developed on debris-flow depositsin the Scottish Highlands that most ofthe flows have developed in the last 250years He suggests that intensive burningand grazing may be responsible Presentshyday deforestation can generate spectacularmass movements

Because of the hazards presented bymass movements a whole series of techshyniques have been developed to attempt to

control them (table VB)

Cooke R U and Doornkamp J c 1993 Geomorphology in Environmental Manageshyment 2nd edn Oxford Oxford University PressThis general text contains useful material on slope problems and their control

Dikau R Brunsden D Schrott L and Ibsen M-L 1996 Landslide RecognjrionChichester WileyAn edited text rich in European examples which describes and classifies the main typesof landslides that pose hazards to human activities

188 The Land Surface

Slope erosion inNorth America

the Pacific north-west of

The mountainous regions of Oregon Washington British Columbia and Alaskaare areas with steep slopes high rainfall and active tectonics They are thus areasof high potential erosion rates Heavy forest vegetation and the high infiltrationcapacities of many forest soils protect the slopes however the removal of forestin the area and road-building to take the timber out have had a series ofprofoundeffects Studies by Swanston and Swanson (1976) have shown a dramatic increasein the occurrence of violent debris avalanches flows and slides (table V9) Theseshallow mass movements leave scars in the form of spoon-shaped depressionsfrom which up to 10000 cu metres of soil and organic material have moveddownslope They may move as fast as 20 metres per second Clear-cutting offorest results in an acceleration by two to four times of debris avalanche erosionwhile road construction could accelerate debris avalanche erosion by between 25and 340 times the rate under undisturbed forest

Table V9 Debris-avalanche erosion in forest c1eapcut and roaded areas

Site Period ofrecords(years)

Area(sq km)

No ofslides

Debris-avalancheerosion(cu metressq kmyr)

Rate of debrisshyavalancheerosion relativeto forested areas

Stequaleho Creek Olympic PeninsulaForest 84 193 25Clear-cut 6 44 0Road 6 07 83Total 244 108

Alder Creek western Cascade Range OregonForest 25 123 7Clear-cut 15 45 18Road 15 06 75Total 174 100

718o

11825

4531171

15565

x 10o

x165

x 10x 26x344

Selected drainages Coast Mountains south-west British ColumbiaForest 32 2461 29 112Clear-cut 32 264 18 245Road 32 42 11 2825Total 2767 58

H Andrews Experimental Forest western Cascade Range OregonForest 25 498 31 359Clear-cut 25 124 30 1322Road 25 20 69 1n2Total 642 130

x 10x 22x 252

x 10x 37x 49

7 GROUND SUBSIDENCE

Like many of the environmental issuesdiscussed in this book ground subsidencecan ~ an entirely natural phenomenonFor example climatic change may causepermanently frozen subsoil (permafrost) todecay in tundra areas this will produceswampy depressions called thermokarstLikewise in limestone areas true karsticphenomena such as swallow holes maydevelop when the ground surface collapsesinto a subterranean cavity produced by thesolution of limestone over a long period

Nevertheless humans are now causingground subsidence to occur at an accelermiddotating rate and with dramatic consequencesin certain sensitive areas The main mechshyamsms are

bull the transfer and removal of subterrashynean fluids such as oil gas and water

bull the removal of solids either throughunderground mining (eg coal andother minerals) or in solution (eg salt)

bull the disruption of permafrostbull the compaction or reduction of

sediments (especially organic-rich ones)by irrigation and land drainage

bull the construction of reservoirs

Ground subsidence is often a relativelygentle progress but sometimes it can besudden and catastrophic This is particushylarly the case in areas where the bedrockis limestone and where overpumping hasgreatly drawn down the level of the watertable A sensitive area of this kind is theFar West Rand of the Transvaal ill SouthAfrica when gold mining has requiredthat the local water table be lowcred bymore than 300 metres The tall of thewater table has caused clay-rich materialsfilling the roofs of large underground cavesto dry Out shrink and collapse This inturn has caused large depressions to deshyvelop at the ground surface In densely

Ground Subsidence 189

populated urban areas this is a considershyable hazard In another limestone areaAlabama in the southern USA groundshywater pumping has caused over 4000sink-holes or related features to formsince 1900 Fewer than 50 natural sinkshyholes developed in that area over the sameperiod

More gentle but in geological termsstill very rapid has been ground subsidshyence caused by oil abstraction The classiccase is the Los Angeles area where over 9metres of subsidence occurred as a resultof the development of the Wilmingtonoilfield between 1928 and 1971 Considerthat 9 metres is more than the averageheight of a two-storied house Even morewidespread is the subsidence caused bygroundwater abstraction for industrialagricultural and domestic purposes InMexico City subsidence of more than 75metres has occurred while in the CentralValley of California the figure exceeds 85metres In Tokyo Japan subsidence hasbrought some areas below sea level In1960 only 35 sq km of the Tokyo lowshyland was below sea level By 1974 thisfigure had almost doubled exposing atotal of 15 million people to major floodhazard Bangkok is suffering from a simshyilar problem

Perhaps the most familiar example ofground subsidence caused by humans isthat resulting from mining It causes damshyage to houses roads and other structuresas well as disrupting surface drainage 1l1dcausing flooding

In permafrost areas ground subsidenceis associated with thermokarst deeJopshymem Therl1lokant is the irregular humshymocky terrain produced by the melting ofground ice permafrost The developmentof thermokarst is due primarily to the disshyruption of the thermal equilibrium of thepermafrost and an increase in the depthof the active layer (the layer subjected toannual thawing) Consider an undistur~d

190 The Land Surface

tundra soil with an active layer of 4S emAssume also that the soil beneath 4S emis supersaturated permafrost and uponthawing yields (on a volume basis) SO percent water and 50 per cent saturated soilIf the top 15 em were removed the equishylibrium thickness of the active layer underthe bate ground conditions might increaseto 60 em As only 30 em of the originalactive layer remains 60 em of the permashyfrOSt must thaw before the active layercan thicken to 60 em since 30 em ofsupernatant water will be released Thusthe surface subsides 30 em because ofthermal melting associated with thc= deshygrading permafrost to produce an overalldc=pression of 4S em

Thus the kc=y factors involvc=d inthermokarst subsidence are the state of theactive layc=r and its thermal relationshipsWhen surface vegetation is cleared forpurposes of agriculture or construction forexample the dc=pth of thaw will tend to

increase as the ground will no longer beinsulated from the effects of dirc=et sunshylight The movement of uackc=d vehicleshas been particularly harmfuJ to surfacevegc=tation and deep channels may soonrc=sult from permafrost degradation wherethe$( have been used Similar c=ffects maybe producc=d by siting hc=atc=d buildings onpermafrost and by laying oil sewer andwater pipes in or on thc= active layer

Some subsidence is creatc=d by a processcalled hydrocompaction This occurs beshycause moisture-deficient unconsolidatedlow-density sediments tc=nd to have suffishycic=nt dry strength to support considenbleeffective stresses Vtithout compacting

FURTIIER READING

However when such sediments which mayinclude alluvial fan materials or loess art

thoroughly wetted for the first time (forexample by percolating irrigation water)the inter-granular strength of the depositsis diminished Rapid compaction resultsand subsidence of the ground surface folshylows Unequal subsidence can crate probshylems for irrigation schemes

Land drainage can promote subsidenceof a different type notably in soils rich inorganic matter The lowering of the watertable makes peat susceptible to oxidationand deflation (being blown away by thewind in dust storms) so that its volumedecreases We discuss this in the context ofthe English Fenlands in part IV section S

A further type of subsidence sometimesassociated with earthquake activity rcsultsfrom the effects on the earths crust oflarge masscs of water impounded behinddams Seismic effects can be generated inareas with susceptible fault systems Thismay account for eanhquakcs recorded at

Koyna (India) and elsewhere The processwhereby a mass of water causes crustaldepression is called hydro-isostasy

It is clear from this discunion thatground subsidence is a diverse but imporshytant facet of the geomorphological impactof human activity The damage caused ona worldwide basis can be measured in bilmiddotlions of dollars each year We have menshytioned some of the forms such damagetlkes in this section They include brokendams cracked buildings offset roads andrailways fractured well casings deformedcanals and impeded drainage among manyothers

Johnson A T (ed) 1991 LAnd SubJidmu IAHS Publication no 200A large collection of research-level papers

Waltham A C 1991 LAnd Subsithnu Glasgow BlackicA lower-level inuoductory study which is particularly strong on the effects of miningon subsidence

WaS[( Disposal 191

8 WASTE DISPOSAL

Waste can be loosely defined as all unshyused unwanted and discarded materialsincluding solids liquids and gases (Costaand Baker 1981 p 397) Alternatively itcan be defined as something for which

(Il tllUlllPJamptd WUQ

we have no further use and which we wishto get rid of However it is defined thereis no doubt that waste is generated in largequantities by humans that the amount ofwaste generated develops as societies bltshycome greater consumers of materials andthat the control and disposal of waste is a

tJ -A-

(~~

~-~

H ~-~aSlltS Rcoolltl of Runoff (fOOl urban lltiddquitioll TUJi spiJLampltllI fmnbnd ldltIiriva rmllJld tnJ other Ivtd rK khgcI

-8 ttltmM~ t B lilli ft- HolINtiIliun hydfQIrigttgtts gt011 W)

p(flriiti

~_-----Dmmilt nd 0001TlCrltial9

r8 PtMpwlIpoundIhpWttrgt

Demolition and llIUQuoon 8B Irbk rMJ fIa~iP

-- bull------------~

(tl DispouJ motIwllb for~ WUltl

(UKdl - toulfOO millioo ton)

~ -------UodIiU 57 -8 _Mew

-riIeI illIItgtUII W bullbullUI

--Ii I

SCi dlllllping 1~54_4yullllilriamps__IJIlliIIUIi

itWlIriM fMjiulJ

Figure V7 The main sources of and disposal strategies for wastes that canpollute land and water early 19905Source After Woodcock (1994) fig 161

192 The Land Surface

Table V10 Wastes arising In Englandand Wales late 19805

Source House of Commons EnvironmentCommittee Second Report Toxic Waste(19889)

major environmental issue Furthermorethe disposal of waste can substantiallymodify surface conditions and produce anarray of environmental impacts

Wastes can be divided into those thatare unmanaged and those that arc manshyaged (figure V7(a) and (braquo)

Table VIO shows the amounts of difshytcrcllt cangories of waste produced in Engshyland and Wales In terms of sheer wdghtliquid industrial etfhunt is the largest comshyponent but the production of emucntfrom the agricultural sector is also imporshytant Significant amounts of primarily solidwaste arise trom mining and quarryingindustrial sources the domestic seerorsewage sludge power station ash blast furshynace slag and the building ami cOllStrucshytion industries In the USA an average dtywith 250000 inhabitants has to collecttransport and dispose of 450 tonnes ofrefuse every day In general about 2-3 kgof municipal waste and 3-4 kg of industrialwaste are produced in the USA per person

Waste type

liquid industrial effluentAgriculturalMining and quarryingIndustrial

HazardousSpecial

Domestic and tradeSewage sludgePower station ashBlast furnace stagBuildingTotal

Quantity(mtlyr)

2000250130

503915

28241463

2505

per day In the UK about 137 million tonnesofcontrolled waste (waste which is eitherincinerated or disposed of to a landfill) areproduced every year Landfill takes 90-95per cent of the controlled waste

In this section we are mainly concernedwith solid waste a category which includesmaterials from a wide range of sources(table VII) There are a number of disshyposal options for solid waste (figure V7(c)) As we have already noted the mostimportant of these in the UK is so-calledsanitary landfill (table Vl2) The relashytive importance of different methods varshyies from country to country (table VI3)For example whereas most municipal solidwaste in the UK and Australia goes to

landfills in Switzerland nearly half is inshycinerated and in Japan about two-thirds isincinerated

The content of waste is also highly varishyable Some types contain contaminants thatcan pose a series of hazards to health andproperty (table VI4) For example inshydustrial waste may contain dangerous heavymetals building waste may contain asbesshytos and household food waste may genshyerate potentially explosive methane gasIf sites are not carefully controlled wastedraining from the site (leachate) may beheavily polilited Other problems are posedby the bct that landfill ma~ graduallycompact through time

Landfilling is a cheap means of disposalIn countrie~ where there are manr oldquarries and gravel pits it may be a conshyenient way not only to dispose of wastebut also to reclaim such land lor otheruses Such sites are not always availablehowever in cloS( proximity to sourcesAlso if the~ are badly managed they canproduce environmental problems of rhetypes just discussed

There may be advantages in reducingthe amount of landfill capacity that is reshyquired A range of methods is available

Waste Disposal 193

Table V11 Refuse materials (solid waste)

Type

Garbage

Rubbish

Ashes

Street refuse

Dead animals

Abandonedvehicles

industrial wastes

Demolition wastes

Constructionwastes

Special wastes

Sewage treatmentresidue

Composition

Wastes from preparation cookingand serving of food marketwastes wastes from handlingstorage and sale of produce

Combustible paper cartons boxesbarrels wood shavings treebranches yard trimmings woodfurniture bedding

Residue from fires used for cookingand heating and from onmiddotsiteincineration

Sweepings dirt leaves catch-basindirt contents of litter receptacles

Cats dogs horses cows

Unwanted cars and trucks left onpublic property

Food-processing wastes boilermiddothouse cinders lumber scraps metalscraps shavings

lumber pipes brick masonry andother construction materials fromrazed bUildings and other structures

Scrap lumber pipe otherconstruction materials

Hazardous solids and liqUidsexplosives pathological wastesradioactive materials

Solids from coarse screening andfrom grit chambers septic-tanksludge

Sources

Households restaurantsinstitutions storesmarkets

Same as garbage

Same as garbage

Streets Sidewalksalleys vacant lots

Same as street refuse

Same as street refuse

Factories power plants

Demolition sites to beused for new buildingsrenewal projectsexpressways

New constructionremodelling

Households hotelshospitals institutionsstores industry

Sewage treatmentplants septic tanks

Source Costa and Baker (1981) table 13-1 Data from Institute for Solid Wastes of theAmerican Public Works Association and Bureau of Solid Waste Management 1970

Incineration

Sanitary landfills

Method

Open dumps

194 The Land Surface

Table V12 Methods of solid waste disposal

Description

Practices vary from indiscriminate piles to periodic levellingand compacting

little effort taken to prevent rodents flies odours andother health hazards

Often located with little planning where land was available

Consists of alternating layers of compacted refuse and soiLEach day refuse is deposited compacted and covered withsoilDaily operation and a final cover of at least 70 em ofcompacted soil prevents many health problems

Requires planning for economical operation and for suppliesof topsoil for cover Operations vary depending ontopography and supplies

Reduces combustible waste by burning at 1700F to aninert residue Ash and noncombustibles dumped or placed inlandfills

Air pollution is a problem with poor management

Increasing in use and often combined with a sanitary landfilland salvage operation

Onmiddotsite disposal Small-scale incinerators and garbage disposals

Incinerators are expensive and require considerablemaintenance

Garbage disposals are increasing rapidly in use with wastetransferred directly to the sanitarymiddotsewer system

Swine feeding A decreasingly used method which involves collection ofgarbage for swine food (pig swill)

Composting Biochemical decomposition of organic materials to a humusshylike material usually carried out in mechanical digesters

Increasingly used method with a useful end product whichis often sold

Source Costa and Baker (1981) table 13-3 from Schneider (1970)

Waste Disposal 195

Tabe V13 Selected solid waste material statistics for various countries

Country Annual per capita disposed disposedprodudion (kg) by landfill by incineration

Australia 681 98 2Austria 216 57 19Canada 642 94 6Denmark 420 64 32France 289 33 32Germany (W) 447 83 9Italy 246 38 20Japan 342 28 67Netherlands 502 66 19Sweden 300 52 38Switzerland 336 13 49UK 332 80 6USA 744 nla nla

Source UNEP (1990)

Table V14 Some commonly encountered contaminants the sites on which theyare likely to occur and the principal hazards they produce

Underground fires

Principal hazards

Harmful to health ofhumans or animals ifingested directly orindirectly May restrictor prevent the growthof plants

Explosions within orbeneath buildings

Chemical attack onbuilding materials egconcrete foundations

Contamination of watersupplies by deteriorationof service mains

Dangerous jf inhaled

Likely to occur

Metal mines iron and steelworllts foundries smeltersElectroplating anodizing andgalvanizing works

Engineering works egshipbuilding Scrap yards andshipbreaking sites

Gasworks power stationsrailway land

landfill sites filled dockbasins

Made ground includingslags from blast furnaces

Other metals egcopper nickel zinc

Type of contaminant

Toxic metals egcadmium lead arsenicmercury

Combustiblesubstances eg coaland coke dust

Flammable gases egmethane

Aggressive substanceseg sulphateschlorides acids

Oily and tarrysubstances phenols

Chemical worllts refineriesby-products plants tardistilleries

Asbestos Industrial buildings Wastedisposal sites

Source Attewell (1993) table 41

196 The Land Surface

Plate VS Landfill is one way of disposing of waste but the choice of sites to usecan be a problem This site is filling in old gravel pits near Didcot central England

bull Incineration can greatly reduce thevolume ofwaste However incineratorsare expensive to construct and maycreate pollutant emissions to the auConcerns have been expressed forexample about dioxin emissions Onthe positive side incinerators can proshyduce usable energy

bull Compaction can also reduce wastevolume Powerful hydraulic rams canbe used to compress waste

bull Shredding and baling can also reducewaste volume

FURTHER READING

However it may be mort desirable toreduce the amount of waste produced inthe first place This can be achieved by

bull substituting durable goods for dispos-able ones

bull composting garden wastebull generating less wastebull reusing materials and extending their

lives (eg by using rechargeable batshyteries and refillable bottles)

bull recycling paper glass etcbull recovering materials from waste (eg

magnetic separation of ferrous metals)

Douglas T 1992 Patterns of land water and air pollution by wastes In M Newson(ed) Managing the Human Impact on the Natural Environment Patterns and Promiddotcesses 150-71 London Belhaven PressA very useful review chapter in an introductory textbook

9 STONE DECAY IN URBAN

BUILDINGS

The natural materials we use for buildingare just as prone to weathering and alterashytion as are natural rock outcrops Simishylarly manufactured building materials suchas bricks concrete and plastics also decayand change once in contact with theatmosphere Usually such decay processesare of no real concern as they act veryslowly and produce only slight changes tothe appearance of buildings monumentsand engineering structures and do notaffect their strength safety or economiclife-span However where decay processesbecome accelerated and altered usually asa result of air pollution they can oblitershyate priceless carvings prcxiuce unsightlydecay features and lead to structural weakshyness Many buildings and monuments areat risk from the historic basilica of StMarks in Venice to Lincoln Cathedral inEngland the Parthenon in Athens and theMerchants Exchange Building in Pniladelshyphia In many cities whole groups of buildshyings and monuments are under attackExamples are the historic university townof Oxford in England and the lxautifulcity of Prague in the Czech Republic

Buildings in the urban environment areparticularly vulnerable to decay because ofthe following factors

bull urban microclimatic changes such aswarming and increased local rainfall orhumidity

bull air pollution such as increased conshycentrations of sulphur dioxide andnitrogen oxides

bull increased urban traffic levels which conshytribute to air pollution lead to applishycation of de-icing salts in winter inmany temperate-zone cities and causevibrations affecting roadside buildings

Stone Decay in Urban Buildings 197

~ DStQIttff

3 C~~ ) cpm~~ r~lt ~ Lichtns

- ron surfacfWi

)

0) () (d) () if) disroloralKln

Figure VS Some common forms ofbUilding stone decay (a) sooty andgypsum encrustations on shelteredparts of a building (b) blistering andexfoliation of gypsum crusts from (a)(c) cracking (d) pitting blistering andexfoliation of porous stone which hasbeen affected by salts (e) lichengrowths on stone with biologicalweathering underneath (f) surfacelowering and roughening by add rain

bull increased human contan with buildshyings leading to abrasion graffiti etc

Cities on coasts and within the arid zonesuffer particularly from highly corrosiveenvironments because of high concenshytrations of salt in the atmosphere andgroundwater

These environmental conditions inurban areas produce the following effectson building and monument surfaces (seefigure VS)

bull gypsum crusts produced by directchemical reaction of sulphur dioxidewith calcium carbonate-rich stone

bull soiling of building materials by sootyparticulates commonly prcxiuced by coaland oil combustion and diesel engines

bull accelerated lowering of surfaces proshyduced by acidified rainfall hitting calshycium carbonate-rich stone

198 The Land Surface

Plate V9 Decaying bUildings in Venice The sheltered portion of the columnshows the development of a black crust which contrasts sharply with the lightcolour of the portion of the column that is washed by rain (Dr 8 Smith)

bull exfoliation and blistering produced bysalt crystallization and hydration inporous materials

bull cracking produced by vibration andother stresS(s

bull pitting and surface growths producedby organic colonization especially bymicro-organisms and lichens possiblyencouraged by nitrogen oxides actingas fertilizers

Vast changes in pollution and environshyment have occurred in many cities overrecent years These changes have had conshysequent impacts on the weathering anddecay of buildings and monuments Thusa rapid increase in urban traffic andphotochemical pollution in Athens seemsto have been reflected in increasing stonedamage on the many ancient marblemonuments in the city In other cities suchas those in Britain and the USA legislamiddottion to combat air pollution has resultedin sharp decreases in sulphur dioxide andsmoke pollution over the past 40 yearsbut not in nitrogen oxides Measurementsfrom St Pauls Cathedral in London howshyever indicate that the rate of decay inbuilding stone has not yet declined Inshydeed stone decay may worsen in someplaces as nitrogen oxides act as a fertilizerfor organic growths such as bacteria andlichens which are important agents ofstone decay

How serious a problem is urban stonedecay and what can we do about it Interms of cost stone decay can be a seriousproblem for the owners of buildingsespecially when it has turned into a longshyterm problem In Oxford England forexample by the middle of the twentiethcentury 200 years or so of air pollutionfrom domestic and industrial coal burninghad produced intense damage to buildshyings constructed from the rather vulshynerable Headington Freestone (a locallimestone which weathers badly in pollutedatmospheres) Restoration work costing

FURTHER READING

Stone Decay in Urban Buildings 199

over pound24 million was carried out in the1950s and 1960s More recently trafficand other sources ofair pollution arc damshyaging these restored buildings as well asnew ones and soiling paintwork withinthe city centre Stone decay is particularlyserious when it affects monuments ofgreatcultural and spiritual significance especiallythose which attract large numbers of tourshyists and their associated income Decaycan also be hazardous as when it affectsbridges or causes bits ofstone to fall fromhigh towers In most cities however buildshying stone decay is just one symptom ofincreasing urban pollution and environshymental despoliation The impacts of airpollution on human health and urbanecology in cities are also of great concern(as discussed in paC[ II section 8 and paC[III section 6)

Suategies for combating urban buildingstone decay include

bull removing the causes of accelerateddecay by reducing air pollution stopshyping the application ofddcing salts to

roads etcbull removing vaJuable and vulnerable sculpshy

tures and carvings from the aggressiveurban environment putting them inconuolled museum environments andreplacing them with copies

bull cleaning and repairing soiled and damshyaged buildings

bull preventing future -decay by applyingprotective treatments on new or newlycleaned and repaired stone

Winkler E M 1975 Stone Properties Durability in Mans Environment ViennaSpringer-VerlagContains much information about many aspects of stone weathering

Cooke R U and Gibbs G 1994 Crumbling Heritage Studies of Stone Weatheringin Polluted Atmospheres Report for National Power picA useful summary of the recent worries over stone decay in Britain and results fromresearch aimed at elucidating the problem

200 The Land Surface

Venices decaying treasures

Venice in Italy contains many imporshytant buildings and monuments whichform a key part of the European culshytural heritage and which are underthreat from decay accelerated by airpollution and rising u=a levels Thereare also over 2000 pieces ofoutdooran mainJy stone carvings and sculpshytures within the city Studies of oldphotographs have revealed that moSdeay has occurred since the SecondWorld War The cause seems to bethe high sulphur dioxide levels resultshying from rapid post-war industrialshyization of the surrounding area (DelMonte and Vittori 1985) Since1973 laws have banned the use ofoil within the city itself replacing itwith methane However pollutionstill drifts in from elu=where and much u=rious decay has already occurred Smokeand sulphur dioxide react with marble limestone and calarcous sandstones toproduce the blackened gypsum crusts vhich now coat many ampmoos buildings inVenice These crusts are not only unsightly they are also damaging the undershylying stone A local relative sea-level rise has been a problem over the past centuryin Venice This has been caused by a combination of natural subsidence andextraction of groundwau~r (which has now ceased) As well as creating floodingsuch higher u=a levels have had a less visible impact on Venices environmentthrough encouraging the penetration of water and salts into vulnerable buildingmaterials The humid environment also encourages the transformation ofcalciumcarbonate into gypsum in the presence of sulphur dioxide

Major research is currently under way into stone decay in Venice coupled withmany schemes to restore damaged buildings and outdoor art Estimates of thecosts of restoration suggest that all the sculptures and carvings in Venice couldbe restored at a cost of some $US9S million Grime accounts for IS per centof the damagt requiring conservation corrosion or decay accounts for 35 percent and structural problems for the remaining SO ~r ctnt (Carrera 1993)

Considerable care has to be taken in attempting to clean and restore valuableobjects and buildings It is essential first to diagnose the major causes of decaycorrectly Only then can the most appropriate solutions be proposed The Churchof Santa Maria dei Miracoli for example has marble decoration slabs which arcbadly damaged Surveys revealed that salts from rising damp were the major causeof decay and techniques to remove the salts were develop=d before any restotamiddottion began

10 CONCLUSION

In this part of the book we have considshyered the impact that humans have had onthe soil on geomorphic processes and onlandforms We have drawn attemion tothe unintended acceleration of rates ofsoilerosion by water caused by a range ofhuman actions including deforestation theuse of fire and urban growth Acceleratedsoil erosion threatens soil fertility andagricultural productivity It also has otheroffarm impacts which indude a lowershying of water quality While this has oftenbeen seen as a particular problem in dcmiddotveloping countries where it has been idenshytified as onc facet of desertification andland degradation we have also shown thatit is a problem demanding attemion inthe British context Likewise acceleratedsoil erosion by wind has been a majorproblem not only in the Sahel zone ofAfrica and China but also in the techshynologically advanced farmlands of theUSA and the lowlands of Britain Thereare however a wide range of soil conshyservation measures that can be adoptedto counter both water and wind eroshysion caused by land-use and land-coverchanges

Land-use and land-cover changes arealso responsible for many other geoshymorphological changes They affect theform of river channels and the nature ofmass movements (including landslides)on slopes As is the case with soil erosionnumerous methods arc available to try tostabilize slopes and so reduce the hazardsposed by slope failures

Soil erosion and accelerated landslidesare not the only serious ways in which theEarths surface materials are transformedIn particular the spread of irrigation andthe removal of trees can lead to one ofthe most pernicious forms of soil transshyformation or metapedogenesis acceler-

Conclusion 20 I

ated salinization This is a major problemfor agricultural production especially inthe drier parts of the world Again a rangeof techniques for the eradication conshyversion or control of salinity have beendeveloped

Another form of accelerated geoshymorphological change that we hac idenshytified for a range of environments fromthe tundra regions to the worlds greatdeserts is ground subsidence However inmany parts of the world it is not so muchthe subsidence of the ground that is theproblem but where to put the cvcrshyincreasing quantities of waste which weproduce Landfill is one solution but therearc other options including incinerationcompaction shredding and baling A morefundamental solution is to reduce theamount of waste produced in the firstplace

Finally we draw attention to the factthat humans alter the weathering environshyment particularly by subjecting rocks andother building materials to corrosive airStone decay whether in Venice or Oxshyford Prague or York Athens or Agra is aserious threat to our cultural heritage Eventhough the process is slow compared withthe accelerated soil erosion mentionedearlier in this part it can have a seriousimpact on buildings and monuments

Overall the human impacts on the landsurface discussed in this section are a rathermixed bag often spatially limited in exshytent and often inadvertently caused Theyare nevertheless serious and show linkshyages with human impacts on the bioshysphere and atmosphere Many technologishycal solutions have been developed to dealwith these problems Nevertheless asseveral of our case studies have shownthe success of such schemes depends onthe willingness and ability of the peopleinvolved at all levels to implement andmaintain them

202 The Land Surface

KEy ThRMS AND CONCEPTS

accelerated landslidesaccelerated soil erosiondune reactivationforest soilshydrocompactionlandfillmass movementspermafrost

POINTS FOR REVIEW

salinitysand controlseawater incursionsoil conservatonsubsidencethetmokarstwaste

Why shouJd we be concerned about soil erosion

How would you seek to control rates of soil erosion by (a) wind and (b) water

What are the main ways in which humans unintentionally cause river channel characshyteristics to change

Why is salinization such an important issue in the worlds drylands

What are the main geomorphological hazards that are being accelerated by humanactivities

How in your own life could you reduce the need for waste to be disposed of aslandfill

Is there are evidence in your own home area that buildings are suffering from severeweathering Why might this bd

PART VI

Oceans Seas andCoasts1 lncroduction 2052 Sea-level Rise 206

bull Sea level rise and the Essex coast marshesEngbnd 208

3 Coastal Erosion 210bull Erosion at Victoria Beach Nigeria 213

4 Coastal flooding 215bull flooding at Towyn North Wales

February 1990 2165 Coastal and Marine Pollution 218

bull Pollution in the Mediterranean Sea 2206 Coastal Dune Management 222

bull Muuging dunes on the lancashire coast

England 2257 Coral ReefDegradation 226

bull Threatened reefS ofthe Red Sea 2308 Aquaculnue and Coastal Wedands 232

bull Pond culture in the Philippines 2349 Conclusion 235

Key Tenns and Concepts 235Points for Review 236

1 INTRODUCTION

Today almost 3 billion people (about 60per cent of the worlds population) livenear coasts often in large cities Furthershymore coastal popuJations are rapidly increasshying In the USA for example populationdensity is growing faster in coastal statcsthan inland ones Nearly half of all buildshying in the USA between 1970 and 1989occurred in coastal regions which accountfor only 11 per cent of the countrys totalland area Similar trends are found in manyother countries

Human activity is contributing to arange of local and regional environmentalproblems in coastal areas The main envirshyonmental impacts along the worldscoastline involve disruption to coastal sedishymentation pathways through erosion andaccelerated deposition increased floodhazard through sea-level rise and encourshyagement of local subsidence disruption ofcoastal ecology through reclamation of

Introduction 205

land and changing land uses and coastalpollution Historically attempts to manmiddotage the coastal ecosystem have involvedtrying to make the coast more stable andfixed These have made many environmenshytal problems worse In recent years an extradimension has been added to concerns overcoastal environmental problems with thethreat of accelerated sea-level rise in thefuture as a result of global warming

The worlds oceans and seas cover over70 per cent of the Earths surface and playa vitaJ role in the biosphere These vastbodies of water are also being affectedby a range of human impacts Pollution isthe major worry Some pollutants comefrom ships and oil platforms but most arefrom onshore sources reaching the sea viathe atmosphere rivers or coastal outfallsFishing and harvesting of marine resourcesaJso have adverse consequences for the mashyrine environment leading to more pollushytion and also damaging ecosystems About53 million toones ofmarioe fish are caught

TropIc ofCIJm

Tropic ofCprirom

bull~

-- CltWIII KltgtIog ltiMply inJIutllCfd by pollution

Aniflri1 lt1115S (diktbullbull hubows lind ttbmgttion tic) ofloogtr atto

Figure VI1 World distribution of major coastal problemsSource After Kelletat (1989)

206 Oceans Seas and Coasts

worldwide for human consumption everyyear with an additional 22 million tonnescollected for processing into fish mealoil etc (Taiba and EI-Kholy 1992) Atpresent the most severe problems are reshystricted to enclosed seas such as the Medishyterranean and Baltic Seas surrounded bydense populations However the evershyincreasing load of pollution entering theworlds oceans is likely to cause wider proshyblems in the future

Coastal areas particularly vulnerable toenvironmental problems include estuariesdeltas and other low-lying coasts especiallyin highly populated areas Figure Vllshows the global distribution of suchareas Parts of the Mediterranean BalticNorth Sea and Bangladesh coasts arcparticularly vulnerable to a whole range of

FURTHER READING

problems Natural and human-inducedprocesses combine to create coastal proshyblems In most cases these do not occurin isolation but rather interact to producea complex web of stresses on the environmiddotment Thus salt-marsh erosion may beexacerbated by pollution which interfereswith the plant-sediment relationship vitalto marsh development where such eroshysion occurs it may encourage floodingStresses on one part of the coastline mayaffect other parts For example deforestashytion can cause mangrove swamp erosionwhich in turn leads to downdrift degradashytion of coral reefs as they become chokedby the extra sediment load The destrucshytion ofcoral reefs in turn encourages stormdamage to the coastal zone behind thereefs that once sheltered it

GESAMP 1990 The State of the Mnrine Environment Oxford Blackwell ScientificAn authoritative global survey of marine pollution

Bird E C F 1985 Coastline Changes Chichester WileyA counrry-by-country survey of the erosional state of the worlds coastline

Viles H A and Spencer T 1995 Coastal Problems London Edward ArnoldA textbook which surveys with many examples the range of ways in which humansinteract with the natural coastal processes

2 SEA-LEVEL RISE

Sea level is perhaps a misleading termfor the relative positions of land and oceansare continually changing on a variety oftime-scales These fluctuations range fromdaily tidal cycles to vast changes in oceanvolume related to glacial and interglacialcycles over periods of thousands and milshylions of years However a practical definishytion of mean sea level is the long-termaverage (usually over 19 yean at least) ofhigh and low tide levels at a particularplace This level is affected by changes inthe volume or mass of water (eustatic orglobal changes) and movements of land

(tectonic and isostatic changes) or a comshybination of the two Over the past 18000years since the peak of the last Ice Agethe rising volume of ocean water as theicc on land melted coupled with complexisostatic changes has produced a generallyincreasing mean sea level over the world

Individual areas however have experishyenced very different sea-level histories(Clark et al 1978) Over the past 1000or so years sea level has risen (accordingto a range of evidence) at 01-02 mm peryear During the last 100 years sea-level risehas accelerated to l0-25 mm per yearaccording to many estimates This accelershyation is mainly due to climatic factors such

S~a-l~v~1 Ris~ 207

as th~ thermal ~xpansion of oc~an watersand the melting of ice on land E

bullIt is predicted that over the next 50 to -100 years global warming will lead to a tfurther acceleration of the rat~ of sea-level lris~ through a combination of two effects

bull

bull increased volume as ocean warer warmsup (call~d the steric effect)

bull addition of water to the oceans fromth~ melting of small glaci~rs and largeic~ she~ts

Th~ direct impact of human actions on sealevel may also provide an additional accelshyeration These actions and their conseshyquences include the following

extraction of oil and groundwater mayencourage coastal subsidence

bull d~forestation may encourage incrtasedfreshwater runoff to oceans

bull groundwater extraction for irrigationand damming of rivers to produce resshyervoirs may encourage evaporation ofthis water which will eventually r~turn

to the oceans (Sahagian et aI 1994)bull w~dand drainage reduces the water holdshy

ing capacity ofw~dand soils and thereshyfore adds more wat~r to the oceans

It is very difficult to predict how suchinfluenc~s might combine to aff~ct seashylevel ris~ in the futur~ The b~haviour ofsom~ of th~ compartments of the system(eg ice sheets) is not well understoodand the magnitude of global warming in

High

Middlt

1-

Y - -- ---- 1-

----- -

00Yo

Figure VI2 Best estimate high middleand low projections of sea-level riseto the year 2100 under the IPCCemissions scenario IS92aSource After Wigley and Raper (1992)fig 4

the next few decades is itselfthe subject ofmuch debate Howewr the most recentestimates suggest an average sea level riseof about 5 mm per year over the nextcentury within a range of unc~rtainty of2-9 mOl per year This will produce a totalincrease ofabout 50 cm by 21 00 as shownin the middle curve in figure VI2 andm~ans that sea level will rise two to fivetimes fast~r than over th~ last 100 years(Watson ~t aI 1996) This rat~ althoughhigh is much lower than some ~arlier

estimates which predicted wid~spread

drowning of many coastal ar~as Whatev~r

its precise magnitude future s~amiddotlevel ris~

in association with a whol~ host of small~rhuman-induced and natural disturbancesis likely to provid~ a complex seri~s of~ffects on th~ coastal ~nvironment

208 Oceans Sus and Coasts

Sea-level rise and the Essex coast marshes England

bull

N

I

ESSEX

bull

FIgure VI3 The Blackwater estuaryEssex and its associated marshes andmudflatsSource After Pethick (1993) figs 1 2

=

Much of the eastern and southerncoasdine of England is already undershygoing rdative sea-Ievd rise Isostaticreadjustments to the removal of theicc cap over northern Britain at theend of the last lee Age (some 11000yurs ago) arc causing the north ofBritain to risc forcing the southernpart down as a consequence TheEssex coast has been experiencingrelative sea-level rise of 4-5 mm peryear over the past few decades as aresult of such a process The coast-line of Essex is dominated by lowshylying estuarine and open coastmarshes which play a valuable rolein coastal protection acting as bafflesto wave energy and protecting thesea walls on the landward side Reshycent sea-Ievd risc coupled with 10-eaI human activities has led toerosion ofmany of the marshes here

The Blackwater estuary (figureVI3) provides a good example ofthe problems faced by the Essexcoast It has 680 hectares of saltmarsh and 2640 hectares of inter- ~

tidal mudflats around it and isbacked by agricultural land TheBradwell nuclear power station islocated on its margins Much ofthe coastal marshland around theestuary has been reclaimed over thecenturies to increase the area offarmland Flood embankments nowline 95 per cent of the estuary Theselimit the ways in which the marshes can react to seamiddotkvel rise Studies show thatbetween 1973 and 1988 23 per cent of the total salt marsh area around theestuary was lost to erosion (Pethick 1993) Over the past 150 years sea-level risehere has lxen accompanied by an increase in width of the main estuary channeland a decrease in its depth John Pethick an eIpcrt on this particular area of thecoast thinks that accelerated sea-Icvd rise in the future will lead to erosion ofmarshes in the outer estuary and their replacement by sand and gravel habitltsFurther inland marshes will ~come less brackish as salt Wllter penetrates further

Sea-Icvel Rise 209

Plate VI1 The salt marshes at Tollesbury Essex Marshes such as these willbe modified by any future sea-level rise Marshes nearby are the site of ascheme to stimulate marsh development (H A Viles)

up the estuary The extensive coastal defences behind the Blackwater marshesmean that unless humans intervene sea-level rise will eventually lead to thedestruction of these marshes

As the marshes help to protect the sea walls tram coastal erosion there havebeen strenuous efforts [0 help save the marshes A pilot scheme on NortheyIsland (whose location is shown in figure VI3) for example has pioneered theuse of set-back techniques to stimulate new marsh growth by removing an oldbroken-down sea wall and allowing the sea to reclaim the land behind it AtTollesbury on the northern shore of the estuary similar experiments are takingplace Here 21 hectares of arable land bought by EngJish Nature specially for thepurpose is being flooded in a policy of managed retreat There is a danger thatsuch piecemeal schemes will make the problems worse for the rest of the estuaryunless they are carefully managed John Pethick suggests that a much biggeresmary-wide project is necessary to manage these vital coastal wetlands in the faceof future sea-level rise Such a scheme would involve allowing the outer estuarinechannel to widen coupled with a general retreat of flood embankments

Further reading

Pethick J 5 1993 Shoreline adjustments and coastal management physical andbiological processes under accelerated sea level rise GeographictJl Journal 159162-8

210 Oceans Seas and Coasts

3 COASTAL EROSION

Coastal erosion is a natural processpowered by wave energy and vital tothe maintenance of a dynamic coastlineHuman activity however has increasinglybeen responsible for accelerating coastalerosion Increasing human settlementnear the coast and use of the coastal zonehave also created a serious environmentalissue which requires sensitive long-termmanagement

Recent surveys have produced somestark statistics For example net erosionhas occurred on over 70 per cent of theworlds sandy coastline over the past fewdecades However such erosion does notonJy affect sandy coastlines There havebeen spectacularly high losses of land onthe Niger delta Here 487 hectares ofcoastal plain were lost as a result of subshysidence caused by oil and gas extractionfrom the delta and mangrove deforestamiddottion Where high rates of erosion howshyever localized they may be (see table VlIfor Britain) coincide with dense humansettlement and intensive coastal useserious problems result Along the midshyAtlantic coast of the USA for example

barrier islands have retreated at about 15metres per year as sediment from the oceanside is eroded and washed over the top asa response to locally rising sea level Manysuch barrier islands are now highly builtup for example places such as AtlanticCity and Ocean City arc built almost litershyally on the beach This restricts the naturalinland migration

Cliff erosion is often linked to beacherosion as removal of protective beachesexacerbates erosion of the cliffs Clifferosion is a serious problem along partsof the developed southern California coastwhere cliffmiddottop apartment buildings havehad to be demolished Here eliffi havefailed because of tectonic activity coupledwith groundwater seepage and waveundercutting of the cliffs In Britain therehave been many instances of buildingscollapsing as a result of cliff failure Arecent example was Holbeck Hall hotel inScarborough on the north-east coast ofEngland In most such cases naturally highrates of erosion on failure-prone e1iffi havebeen exacerbated by building which hasaltered the cliff hydrology

What causes coastal erosion Erosion isproduced by the interaction of natural and

Table VI1 Rapid rates of coastal retreat at sites In Britain

Area

North YorkshireHoldernessNoriolk (Cromer-Mundesley)Essex (The Naze)

Kent FolkestoneEast Sussex Seaford HeadEast Sussex Beachy HeadEast Sussex Cliff EndDorset Ballard DownDorset Kimmeridge Bay

Cliff geology

Glacial driftGlacial driftGlacial driftGlacial drift London Clay

and cragGault ClayChalkChalkSandstone (Hastings Beds)ChalkKimmeridge Clay

Average retreat rate(metres per 100 years)

2812096

11-88

281261061082339

Source After Goudie (1990 1995)

Coastal Erosion 211

Plate VI2 The jetty at West Bay Dorset southern England has plainly modifiedthe drift of sediment along the coastline In the foreground sediment hasaccumulated but in the background the beach is starved of sediment and erostenrs occurring neussrtating coastal protection engineering schemes (A S Goudie)

human hctotS both acting to increase waveenergy andor reduce sediment 2vail2bilshyity The rate of erosion depends upon theinterpl2Y between the erosive action of thewaves and other agents of erosion andthe etodibility of the rocks and sedimentsbeing affected Natural increases in thetendency of the coastal environment toerode arc caused by storms BI Ninoevents and longer-term increases in sealevd All these herotS increase wave enshyergy at the coast LocaJly human impactsmay be increasing the erodibility of coastsby the following means

bull reducing the availability ofsediment forprotection and accelenting erosion byaJtering the wave energy field and sedishyment stores with graynes breakwatersand cliff protection schemes

bull removing vegetation which stabilizes

coastal wetlands thus making the sedishyment more erodible

bull reducing the sediment supply by otTmiddotshore and onshore mining and by trapmiddotping sediment behind dams on riversthat enter the ocean

bull replacing the coastal plain over whichbarrier islands can migrate withbuilt-up areas which restrict sedimentmovements

bull reducing the stability of coastal cliffsthrough building and aJtering groundmiddotwater levels

The fact that sediment moves betweendifferent parts of the coast means thatattcrnpts to reduce erosion in one area canhave the opposite effect on areas downdriftIn New Jersey USA for example tenninalgroyncs at Sandy Hook at the southernend of Long Beach Island have encouraged

212 Oceans Seas and Coasts

Plate VI3 A sea wall and cliff stabilization measures at Weymouth Dorsetsouthern England Such engineering solutions are expensive and are not alwayssuccessful (A S Goudie)

accelerated erosion downdrift Beach nourshyishment that is feeding the beach bybringing in sediment has been utilized toovercome such problems with some success

It is clear then that managing coastalerosion can ~ a very difficuh task To besuccessful it requires understanding bothof what factors are causing erosion in aparticular area and of how remedial techshyniques will themselves affect the situationFor example a highly developed barrierisland where future sea-level rise inducedby global warming threatens to exacerbate

FURTHER READING

erosion on a naturally subsiding coast willrequire a very different management stratshyegy from a small beach where erosion canbe rdated to a specific episode of offshoresand mining Clearly the threat of afuture acceleration in sea-level rise becauseof global warming (see section 2 above) ismaking coastal erosion an increasinglyserious problem In many places managedretreat where coastal erosion is allowedto occur relatively naturally and settlementsmiddotmoved inland is perhaps the only feasiblelong-term solution

Nordstrom K F 1994 Developed coasts In R W G Carter and C D Woodroffe(eds) Coastal Evolution 477-509 Cambridge Cambridge University PressA wide-ranging review of the problems faced by coasts with large concentrations ofpeople in an edited collection of advanced papers

Bird E C E 1985 Coastline Changes A GJobfll Reliew Chichester WileyA survey of erosion and accretion on coasdines in various countries

Coast1l ElQ5ion 213

Erosion at Victoria Beach Nigeria

Around the port of Lagos is a 200kin long sttttch ofbarrier island coastcharaeteriud by a sandy barrierbacked by a mangrove-mnged lashygoon It appears to have grownseawards over the Holocene Nowhowever the coast is eroding atsometimes spectacular rates (Ibc1988) Wave energy is high in thisenvironment the coast is poundedby waves coming all the way acrossthe Adantic and there is a generaltrend from west to east in movementof material along the shore

The port and former capital cityof Lagos has a population of over 6million Much of its economic prosperity is based on the extraction of oil fromthe Niger Delta Lagos is situated where ~ere is a break in the coastal barrierand expanded rapidly in the nineteenth and early twentieth centuries on landreclaimed from mangrove swamps behind the barrier As the port developedimprovements were made to the harbour starting with dredging in 1907 Majorharbour works began in 1908 These involved the construction of two breakshywaters and a training wall or jetty to provide a safe deep-water entry for largeships These breakwaters interrupted the west-to-east longshore drift The conshysequence has been a long-term erosion problem on Victoria Beach (on the westside of the harbour) and accumulation of sand on Lighthou~ Beach to the eastVictoria Beach has eroded by up to 69 metres per year since then (by 2 km inall) and an estimated 25 sq km of beach has been lost (figure VIA)

Victoria Beach is an important recreational arca for Lagos Also its erosion wasstarting to threaten housing built on low-lying reclaimed land behind the beachwhich protects the coast under natural conditions Beach nourishment by bringshying in sediment has been used to try [Q solve the problem starting in 1976Although it was successful in the shott tetm dramatic erosion occurred in 1980necessitating further emergency nourishment using 21 million cu metres of sandbetween 1980 and 1981

The erosion problems of Victoria Beach are particularly hard to solve becausethe Lagos port must be kept open The sand accumulating on Lighthouse Beachis also proving to be a problem as eventually it will extend past the weslernbreakwater and be washed around into the harbour Long-term integrated manshyagement of the entire coast here is necessary This may involve pumping sandaround from wcst to east (mimicking the natural longshore drift) and preventingfurther development on vulnerable low-lying land

Erosion ofVictoria Beach must be set in the context of more general erosionaltrends along the Nigerian coast Altogether Nigeria has some 800 km ofcoasdineand there is much evidence of widesprcad erosion within the past few decades

214 Oceans Seas and Coasts

Figure VI4 Since breakwaters were built erosion and accretion haveresulted along the beaches around Lagos harbour NigeriaSource After Usoro (1985)

Along the Niger Delta coast which is situated to the east of the Lagos areaerosion - coupled with environmental problems related to the oil extractionindustry - is a serious problem and several schemes (usually involving beachnourishment like that at Victoria Beach) have been implemented with limitedsuccess Table VI2 below shows some recent typical erosion rates along barrierbeaches of the Niger Delta coast for comparison with those at Victoria Beach

Table VI2 Erosion on the Niser Delta cout

Location

OgboiodoEscravos(western part of the Niger Delta coast)Forcados(western part of the Niger Delta coast)Brass(central part of the Niger Delta coast)Kulama(central part of the Niser Delta coast)Bonny(eastern part of the Niger Delta coast)ImoOpobo(eastern part of the Niger Delta coast)

Erosion rate (metres per year)

18-24

20-22

16-19

15-20

20-24

10-14

4 COASTAL FWODlNG

Simply put coastal flooding is a result ofsubstantially increased water levels on thecoastal plain above high ride levd Floodsoccur therefore as the Ka level riKS orthe coast sinh or where a combination ofthe two happens The possibility of globalwarming raising sca levels worldwide ismaking coastal flooding an cver morcserious issue Currently flooding affectslow-lying coasts such as the MississippiNile and Ganges dehas the Thames estushyary Venice Bangkok and the NetherlandsIn many areas expensivc flood protectionstructures and schemes have been impleshymented usually after a serious flood Anexample is the Thames Barrier completedin 1982 In Bangladesh storm surges proshyduced by cyclones in the Bay of Ikngalhave produced particularly dcvasntingfloods such as that in April 1991 which isestimated to have killcd morc than100000 pltrople

The major causa of coastal floodingarc storm surges EJ Niio events hurrishycanes tidal waves (tsunamis) and subsidshyence through abrupt tectonic movementsThe size and severity of flooding are influshyenced by the tidal regime and the phaseof the tide when the flood event suikesIn esruanes peak river flows can also makematters worse

Factors which make places more proneto flooding by lowering the land include

bull natural compaction of delta sedimentswhich promotes subsidence

bull oil gas and groundwater extractionwhich promotes subsidence

bull removal of mangrove and marsh veg-

FURTHllR READING

Coastgtl Flooding 215

etation which reduces coast2l protecshytion for backshore areas

bull building on low-lying subsidingland

bull fli1ure of flood defences such asdikes

There are severa stages in managementof the coastal flood hazard The initialstages include understanding the majorcauses of flooding in the area buildingstructures and flood defence schemes andimproving prediction and disaster planningIn Bangladesh for example mangrovetrees have been planted on a large scale [0

encourage the stabilization and development of mangrove swamps These helpto provide a buffer and so to preventflooding inland Also the Coastal Embankmiddotment Project has been established to buildembankments and a series ofsluices to proshytect against flooding Flood hazard warnshying improvements and increased provisionofemergency shelters on high land are alsovital elements in flood management here

The management of coastal flooding inBritain is in the hands of the Ministry ofAgricuJrure Fisheries and Food (MAFF)Since 1985 MAFF has also managedcoastal protection works for example [0

control erosion The Environment Agencyformerly the National Rivers Authority alsohas an important role to play in floodwarning and flood defences The floodson the east coast in 1953 provided a majorstimulus to planning and defences in Britainin East Anglia most of the sea defencestructures date from the decade after 1953A national network of tide gauges and theStorm TIde Warning System (STWS) wasalso set up about this time

Perry A H 1981 EPiroflMnltlJl HtuImu i the British klu London Allen andUnwinWard R C 1978 FlHds A GeogrRphiuJ Perrpectipe London Macmillan

216 Oceans Seas and Coasts

Flooding at Towyn North Wales February 1990Towyn and the surrounding Clwyd coastal lowlands covering about 20 sq kmaltogether support a population of around 14000 people On 26 February 1990the sea wall at Towyn was breached as a result of a storm surge The floodwatersrose to over 5 metres above normal sea level or Ordnance Datum (00) in thecentre ofTowyn Over 64 sq km ofland was flooded including all ofTowyn andmuch of the adjacem settlement of Kinmel Bay (figure VIS) Many housesbungalows and caravans were destroyed Over 750 domestic and commercialproperties were ruined in Towyn alone The floodwaters reached up to 2 Ioninland covering much agricultural land

What caused these floods and why were the floodwaters so patchily distribshyuted Storm surges are a major cause of coastal flooding around the British coastTheir low barometric pressure and strong winds act to raise tide levels abovethose predicted When a strong depression occurs over the sea falling barometricpressure acts to suck up the water surface producing a rise of about 1 cm forevery 1 millibar (rob) drop in pressure

On 22 February 1990 there was a large anticyclone situated over central EUJopeand a strong depression over south-west Iceland Between 23 and 25 Februshyary this depression deepened and moved towards southern Scandinavia By 26February it was JUSt west of Denmark and a second related depression haddeveloped to the sourn-east of Iceland These depressions had low-pressure cores

Plate VI4 A flooded caravan and trailer park beind the sea wall at TowynNorth Wales in March 1990 (Richard SmithKatz)

~f ~

Coastal Flooding 217

bullo flood wmr in dilrhes C--

_ Roilwi) _ Majolt road

Figure VI5 (a) location of Clwyd lowlands (b) The extent of flooding westof the River Clwyd near Towyn North Wales in February 1990Source After Englefield et aJ (1990) fig 3

of between 950 and 960 mb and major storms with high winds occurred acrossthe UK between 2S and 26 February Rain hail gale-force winds and lowpressure occurred in the Clwyd lowlands coupled with exceptionally high sealevels (assisted by the storm surge conditions) This combination of circumstancesled to the floods

The Clwyd lowlands were particularly vulnerable to flooding as they are exshytremely low-lying situated on reclaimed land ranging from 35 metres 00 to 7metres 00 most of it below 5 metres Along much of the coast there is a naturalprotective shingle ridge this reaches a height of up to 7 metres at Kinmel Baybut dies out at Towyn

The history of land use and human intervention in the area also had a crucialrole to play in the flooding In 1847 the Chester to Holyhead railway wasopened running along the coast (figure VI5) This has interfered with coastalsediment movements ever since resulting in long-term coastal erosion problemsFor example between 1872 and 1899 along one section the coast eroded by 60metres in frOnt of the railway line During the nineteenth and early twentiethcentury sea defences were built to help overcome these problcms including a seawall and groynes at Towyn Very little sediment ever accumulated in front of thewall and on 26 February 1990 it faced the full force of the ocean breaking ataround 11 am

Studies carried out after the flood by Englefield et al (1990) showed theextent of the damage and explained that the pattern of flooding was controlledby microtopography and the road layout within settlements Roads and higherareas acted as flood barriers Interestingly the old bungalows nearest (0 the seaat Kinmel Bay escaped the worst 800ding as they were located on the shingleridge at 6-7 metres 00

218 Oceans Seas and Coasts

5 CoASlAL AND MARINEPOLLunON

A report in 1990 by the Group of ExpertSon the Scientific Aspects of Marine Pollumiddottion concluded that most of the worldscoasts are polluted while many parts ofthe open ocean arc still relatively cleanCoastal pollution is an important environshymental issue affecting human health andthe diversity of fisheries and coastal ecoshysystems Recent attention has focused onliner and sewage pollution on Britishbeaches red tides (algal blooms caused byan excess of nutrients sec part rv section7) in the Mediterranean and elsewhereand oil spills such as that resulting fromthe WTeck of the Braer tanker ofT the Shetshyland Islands in January 1993 and the SeaEmpress off West Wales in February 1996

Most marine and coastal pollution (over75 per cent) coma initially from landshybu4=d sources It is brought down to thesea by rivers dumped in sewage outfalls orarrives via the atmosphere The rest comafrom dumping by ships and from offsho~

mining and oil production To we oilpollution as an example a surprising 344per cent of a total of 32 million tonnaper year which reaches the sea coma fromland via urban runoff etc another 343per cent comes from marine tnnsport (oilshipment) the rcst comes from atmoshyspheric fail-out offshore oil production(only 16 per cent) and natunl sources

The major types and sources of coastalpollution are

bull nutrients from sewage agriculturalrunoff aquaculture

bull pathogenic organisms from sewagebull litter especially plastics from land and

shipsbull metals eg admium and lead from

mining and indwuybull sediments from deforestation soil

erosion mining and dredging which

may be contaminated with syntheticorganic compounds

bull orpnochJoride pesticides from agrimiddotcultural and industrial runoff

bull PCBs (polychlorinated biphenyls) fromindustry

bull oil from land and oil tanker dischargesbull radionuclides from discharges from

nuclear reactors and reprocessing plantsand naNral sources

The amounts involved can be hormiddotrifying In 1985 at least 450000 plasticcontainers were dumped by th~ worldsshipping fleet The impacts on humanscoastal ecosystems and coastal stability canbe devastating The effects can also belong-lasting Oil spilt from the Isla Payardioil refinery in Panama in 1986 for examshyple came ashore on to a mangrove coastand killed many shellfish as well as beshycoming absor~d in mangrove muds Fieyears later the oil was recycled as thesesediments eroded and started to threatennearby coral reefs

Other pollutants have more immediateand shortmiddotlived effects For examplenutrients whieh trigger algal blooms causedeoxygenation of the water killing otherspecies These algal blooms may also betoxic poisoning shellfish and affectinghuman health Many synthetic organiccompounds such as PCBs have a sinisterlong-term effect They tend to accumushylate in living organisms gradually gettingmore concentrated as they are passed upthe food chain and seriously affectingmarine mammals and sea birds

Some areas ofthe coastal and marine envirshyonment arc particularly prone to such polshylution Espccially vulnerable are areas wheretidal and wave acrion encourage the conshycenmrion of pollutants and where sedishyments can act as a sink Thus sheltued baysestuaries and coastallagoons are key areasaffected by pollution Enclosed seas such asthe Mediterranean and Baltic are now alsoseriouslyaffected by pollutionover vast areas

Coastal and Marine Pollution 219

Plate VI5 Beach pollution at Bahrain Arabian Gulf (A S Goudie)

What can we do to reduce coastal polshylution~ Great strides have already beenmade in limiting the influx of pollutantsthrough a number of international agreeshyments In 1987 for example eight counshytries bordering the North Sea agrccd tophase out the incineration of chemicalwastes at sea by 1994 Dumping of radioshyactive waste at sea was stopped worldwidein 1982 The United Nations EnvironmentProgramme (UNEP) has coordinatedmany attempts to tackle pollution in parshyticular areas such as the south-east Pacificand the Black Sea (which has already sufshyfered serious ecological damage from toxic

FURTHER READING

chemicals pathogens and eutrophication- see part IV section 7) Agriculture inshydustry urbanization maricu1turc marinetransport dumping oil extraction miningand war are all important polluters Allmust be addressed if the problem is goingto be tackled successfully In many areasit is still difficult to get accurate infonnationon coastal pollution and its effects Duringand after the Gulf War for example disshyagreements raged about how much the warhad increased coastal pollution (throughdeliberate sabotage of oil fields) or deshycreased it (through preventing oil shipshyments and their associated pollution)

GESAMP 1990 The State of the Marine Enronment Oxford Blackwell ScientificA general report by an authoritative international group on pollution of the oceans andthe coastal seas

Clark R B 1989 Mllrine Pollution 2nd edn Oxford Clarendon PressA very good overview

220 Oceans Seas and ~ts

Pollution in the Mediterranean Sea

It is estimated that the population ofcountries around the Mediterranean will riseto 430 million by 2000 CB These countries and especially their coastal zonesalso attract large numbers oftounsts 100 million visited the area in 1984 Thereare huge disparities between the economies of countries on the northern andsouthern sides of the Mediterranean but pollution is getting worse everywhere

The major types of pollution are

bull oilbull domestic wastebull industrial and urban wastewaterbull organochlorine pesticidesbull heavy metalsbull PCBs

All these harm wildlife affect human health and may lead to long-tenn damageto the entire Mediterranean ecosystem Oil pollution is now a chronic problemover most of the Mediterranean as a result of tankers discharging ballast and bilgewaters in the network of shipping lanes which criss-cross the sea carrying some250 million tonnes of oil per year Sewage is a severe problem especially aroundthe Italian Spanish and French coasts (see figure VI6) The costs of reducingsuch sewage pollution may be very high In 1990 GESAMP suggested it wouldcost USS150 per person to construct sewage treatment and disposal facilities forall the 132 million inhabitants of the coastal settlements around the Mediterrashynean That would amount to US$lS billion overall at 1990 prices Sewage polshylution can make swimmers ill and can also contaminate seafood In 1973 acholera epidemic broke out in Naples Italy because of contaminated molluscsand hepatitis can also be transmitted by seafood Organochlorine pesticides PCBsand heavy metals are a problem in particular areas such as the Venice lagoonwhere lack of flushing allows them to accumulate in bottom sediments Sewageleads to algal blooms and red tides under extreme circumstances which firstposed a problem in the Gulf of Venice in 1972 Eutrophication is a seriousproblem in the western Adriatic Sea where rivers coming from Italy bring around29000 cu metres of phosphates and over 120000 cu metres of nitrates everyyear Like acid rain this results in a transnational problem beaches along thecoast of Croatia are affected as seriously as Italian beaches

i

CoOStal and Marine Popution 221

shyFigure VI6 Sewage and industrial waste discharges into the MediterraneanSea (BOD = biological oxygen demand)Source After Clark (1989) fig 93

Some pollution problems affect only small areas and arc easily solved Anexample is the discharge of tannery wastes contaminated with chromium into theGulf of Geras on the Isle of Lesbos The impact of this was lessened in 1983when an effluent treatment plant was installed (Papathanassiou and Zenclos1993) Some pollution problems however are less easily solved and some areassuch as the Vcnice lagoon appear to be polluted beyond acceptable limits

In 1979 as a response to concerns about many oftheslt issues the Blue Planset up with the help of UNEP was adopted by the Mediterranean countries Thisplan aimed to help both economic development and environmental protectionand to limit pollution from land-based sources As always however dealing withinternational environmental problems is a difficult task and implementing susshytainable development and tourism has so far proved very hard amp tourism is oneof the major industries of the Mediterranean and is affected by pollution as wellas contributing to it perhaps the initiation of ecotourism would make a starttowards solving the poUution problems here

222 Oceans Seas and Coasts

6 COASTAL DUNE

MANAGEMENT

Coastal dunes provide an important bufferbetween land and sea and act as a storefor sediment They arc dosdly linked withbeaches as there is a regular interchangeof sediment nutrients and organismsbetween beach and dune systems Coastaldunes arc a common component of mostcoasdines and arc often of very impresshysive height and extent Notable examplesarc found on the west coast of Americawhere the Coos Bay dunes arc 72 kID longand reach heights of 50 metres In Eurshyope high dunes occur along the CocoDonana in southern Spain where theyreach 90 metres Coastal dunes unlikemany descrr dunes tend to be vegetatedHardy salt-tolennt plants grow on themnearest the sea as dune environments getmore sheltered and better soils occur furshyther inland and over time other plantsfollow

Coastal dunes provide many attractionsfor human society Because of this as wellas their natural dynamism and role asagents of coastal protection their successshyful management has become an irnporuntissue especially as most sandy coastlinesarc undergoing erosion As cliffs areprevented from eroding so the supply oferoded material going to beaches anddunes is reduced In Britain for exampledunes on the East Anglian coast probablynow have a diminished supply of sandbecause of coastal protection works covershying about 60 per cent of the coast hereDunes themselves are eroded by both windand waves

Sand dunes provide a harsh environshyment colonized at first by hardy plantsthat can tolerate salt and sand such as searocket (CiJtie mllritimll) and salt won(SIIsoJ4 W) whose seeds can tolente longperiods soaked in seawatec As these plants

grow they trap sand and help the dunesto grow Grasses such as A1fJmophili4llrettllrill (marram grass) and sand couchshygrass (Aaropyrtm jmuitmfIU) are themajor sand-accumulating species Gradushyally plant succession creates a diverse ecoshysystem which is attractive to birds insectsreptiles and small mammals For examplehalf the flowering plants of Britain can befound in coastal dune areas around thecountry

Important human uses ofdunes include

bull golf coursesbull sand and water extractionbull afforestation and grazingbull recreation such as horse-riding walkmiddot

ing biking and off-road vehiclesbull military training and exercisesbull housing camping and caravan parksbull transport such as coods and airfieldsbull pipelines

Most of these uses however inoledisrurbing the narura ecosystem Suchdisrurbance often encourages dune mobilmiddotiution and destabiliution and the develmiddotopment ofblowouts This can lad to sandmigrating inland ovec valuable agriculturalland or housing it also removes the coastalprotection afforded by the dunes Otherimpacts affect the groundwater level ofdunes which in turn affects the ecologyIn the Netherlands for example coastaldunes provide an important source ofdrinking watec Other human uses ofdunescan fossilize them removing any chanceof natunl dynamism through such thingsas planting grass and trecs for golf courscsFinally some human impacts affect dunesindirectly removing sand from beachesdamming rivers offshore sand mining andpoUution can aU tip the balance betweensedimentation and erosion

Because of the many and vuloW usesand abuses of coastal dunes considenblemoney and time have been invested in

trying to conserve and protect dunes inorder to save them and the wildlife theysupport Dune management schemes usushyally involve all or some of the following

bull aiding deposition of sand on beachesthrough groynes sea walls and beachnourishment

bull shaping dunes using bulldozers tomove sand

bull planting and watering dunesbull using biofabrics mulches etc to help

stabilize fragile dune surfacesbull fencing to restrict accessbull providing walkways to channel people

away from sensitive areas and preventdamage to the underlying dune

Coastal Dune Management 223

bull providing signs information displaysand education to involve the public indune conservation

However overmanagement can also be aserious problem Most coastal dunes unshyder natural circumstances are not fixedand movement ofdunes and blowouts areperfectly natural occurrences Some eleshyment of disturbance needs to be includedin successful dune management schemesFigure Vl7 shows how dune managementis also affected by natural coastal erosionon the Baltic coast of Poland a catastrophicstorm in January 1983 led to severe eroshysion of beach and foredunes which thenthreatened the stabilized dunes behind(Piotrowska 1989)

Plate VI6 Footpaths causing erosion patterns across coastal sand dunes atWinterton Norfolk eastern England This is a dear example of the effects ofrecreational pressures on the landscape (University of Cambridge Air Photographcollectlon)

224 Oceans Seas and Coasts

18th Ctntury Browndulll m

SI 8mh Fortmlll Yellow dun~ Grt)dune S v 0

EIymo-Ammophiletum HeUehryraquo-jasionetum Em~ro-Pinetum

IS

19th20th Century 10

S

0Bnch JgtuJtrd gmsn He~dllp(l-Jasionum Pine lIlQIlocult=

2nd halfof2Oth Century

After 1983 rommon slate

lkach Young pinrmonocullUn

After 198310cat slates

I Btach

IS

10

S

0Old pine monocultun

IS

10

S

0Old pi~ llJOIlocuhun

Figure VI7 The history of dune management and coastal erosion on the Balticcoast of PolandSource After Piotrowska (1989) fig 5

FURTHER RBAoING

Ranwell D S and Boar R 1986 Coast Dune Management Guide HuntingdonInstitute of Terrestrial EcologyA useful practical guide to management techniques with plenty of C~ studies

Goasral Dune Management 225

Managing dunes on the Lancashire coast EnglandThe Ainsdale-Forrnby dunes cover 800 hectares of which 490 hectares is aNational Nature Reserve The coast here faces north-west and the dunes form asuite of more or less parallel ridges with low-lying areas called dune slacks inbetween Behind these are more irregular dunes Erosion has dominated at thesouth end of the area since the beginning of the twentieth century The coast isprotected in the north towards Stockport by wide sand flats The sand here is richin calcium carbonate so dune soils are not very acidified The area is rich in plantspecies with marram dune scrub and woodland including Anm and BetultlHippophae rhamnoides (sea buckthorn) was introduced here and has spread conshysiderably over the dunes (Boorman 1993) In 1959 myxamatosis arrived decishymating the rabbit population and aiding the spread ofscrub (by preventing rabbitgrazing which maintains grass) Now the Formby dunes to the south of thenature reserve are threatened by both public pressure and coastal erosion

Detailed studies by the geomorphologist Ken Pye have revealed the long-termimportance of human activities to the dunes here (Pye 1990) Marram grass wasintroduced into the area at the start of the eighteenth century when strict lawswere introduced to encourage planting indeed planting was obligatory until1866 Marram favours the development of hummocky sand hills as found tomiddotwards the back of todays dune system In the late nineteenth and early twentiethcentury brushwood fencing and backshore planting were wed to encouragedune development resulting in the parallel dune ridges found over most of thedune system

By the late 1920s recreational pressure was causing severe erosion and producmiddoting much blown sand Other activities which have affected these dunes include

bull excavation of flat-floored depressions for asparagus cultivationbull sand miningbull waste dumpingbull development of caravan and car parksbull road-buildingbull development of golf courses

These pressures have led to dune management and restoration schemes such asthe Sefton Coast Management Scheme established in 1978 This scheme beganto restore the dunes using brushwood fencing marram planting and woodenfencing and restricting access by vehicles and pedestrians Covering some 17 kmof coast the Sefton Coast Management Scheme provides a framework for natureconservation projects within an area which includes several different landownersA Coast Management Officer has been appointed who promotes co-operationbetween the different landowners and ensures integrated management of thissensitive coastal environment

226 Oceans Seas and Coasts

7 CORAL REEF DEGRADATION

ConJ reefs arc some of the worlds mostdiverse ecosystems containing a bewildershying array ofcorUs fish and other organismsAlthough mey cover only 017 per cent ofthe ocean floor (an area roughly the sizeofTexas) they are home to perhaps 25 percent of all marine species One hundredand nine countries have bctween them over100000 km of reefs and many of theseare threatened by a series of natural andhuman-induced stresses (figure VI8)

Coral reefs require very specific envirshyonmental conditions Reef-forming coralsonly grow in waters with temperatures of2S-29degC where there is a suitable relashytively shallow platform less than 100 meshytres below sca level to grow on and wheresediment and pollution do nOt kill themof[ Thus meir growth is restricted to suitshyable tropical and subtropical shores Onesuch is the north-eastern coast ofAustraliawhere the Great Barrier Reef forms thelargest agglomeration of reefS in the worldstretching for over 2000 km and comshyprising ova 2500 individual reefs Othermajor reefs are found along the Gulf coastof Belize and around many South Pacificislands

As Charles Darwin explained in the nineshyteenth century there arc three main typesof reefS related in a genetic sequence First

there are fringing reefS which connectdirectly with the shore Then there arcbarrier reefs which arc separated from theshore by a lagoon Finally when such reefSarc growing around a gently subidingoceanic island atoUs arc produced Anaroll is a ring of coral reefs around a lashygoon in the centre ofwhich was once theisland Sand and gravel islands accumulatshying on the margins of such atolls providea precarious home for flora fauna andhumans as in the Maldives

Reefs arc remarkable in that their entiregeological structure is formed from bioshylogical growths now dead covered by athin veneer of living corals Despite thename coral reefs most reefs arc in factcomposed of a number of important reefmiddotbuilding species including coralline algaeas well as a range of corals

Stresses affecting coral reefs in todaysworld include

bull storms and hurricanesbull EJ Nino eventsbull scamiddotlevel rise and other effects ofglobal

warmingbull outbreaks of disease and preduors

(such as the Crown ofThoms starfish)bull increased sedimentation produced by

deforcstation on landbull eutrOphication produced by sewage and

other pollutants

Figure VI8 A generalized map of threatened coral reefs around the worldSource After C R Wilkinson personal communicationUnivmity of Guam

bull onshore and offshore mining producshying scdimcntenrichcd with heavy metals

bull trampling and physical damage fromboats and divers

bull overfishing and the usc of damagingfishing techniques such as dynamiting

bull direct quarrying and removal of coralsfor building or curios

bull oil pollution from land and shippingbull nuclear weapons testing and other

military activitybull pollution and damage from landfill

(used for example to create new landfor airports and sometimes constructedwith toxic waste)

Natural disturbances such as hurricanescan damage fragile corals and fling themup on to the reef flat However the imshypact of such events is probably short-livedand may in fact be good for the overallhealth of reefs providing a disturbancewhich may increase species diversity andgrowth in the long term El Nino eventswhich occur every two to ten years andinvolve widespread changes in ocean curshyrents and temperature have a potentiallymore scrious effect They temporarily warmthe water around reefs this can causecoral bleaching when the corals expel thezooxanthellae the tiny algae that livesymbiotically with them In severe casesbleaching can cause mass death of coralsGlobal warming may mue such bleachingepisodes more frequent and more seriousas it will heat the oceans and may providefurther stresses by accelerating the rate ofsea-level rise forcing corals to grow fasterin order to keep up with sea level Locallysome corals have been badly affected byoutbreaks of pests and diseases Crownof Thorns starfish for example eat coralsthese predators spread rapidly across manySouth Pacific reefs in the 19605 In 1993South Pacific reefs were first observed tobe suffering from another biological probshylem CLOD (coralline lethal orange dis-

Coral Reef Degradation 227

ease) which affects coralline algae anotherimportant part of reef frameworks (Littlerand Uttler 1995) The causes of suchbiological disturbances arc unknown andmuch-debated but they may be at leastpartly due to environmental pollution

Other stresses on coral reefs can dearlybe blamed on human impacts both dishyrectly on the reefs themselves (from divshying and fishing for example) or indirectlyfrom activities on land or offshore Inshycreased sediment load pollution fromsewage agriculture and industry and deshystructive fishing techniques all damage thereef ecosystem by upsetting the balance ofspecies At the Green Island resort on theGreat Barrier Reef sewage has led to anincrease in the area of seagrasses largelyat the expenS( of corals Thcsc seagrassestrap sediments which usually circulate freelyaround the beaches of the island Thuspollution here is damaging both reef andbeach environments Deforestation inThailand and conversion of forest to rubshyber and cocoa plantations has had severeimpacts on the reefs on southern PhuketIsland producing excessive sedimentationand killing corals

Many of these stresses on reefs are nowacting together and many reefs are goinginto the twenty-first century in an increasshyingly unhealthy state (table VI3) If gloshybal warming continues some reefs may beunable to cope How serious is the proshyblem and what can we do about it~

Reefs have many uses and roles for society

bull they are agents of coastal protectionproviding a natural sponge absorbingwave energy

bull they are major tourist attractionsbull they arc an important focus for bioshy

diversity and conservation of marinespecies

bull they contain living and nonmiddotliving reshysources ofgreat elaquogtnomic value such asfish crustaceans coral rockand sediment

228 Oceans Seas and Coasts

Plate VI7 The destruction of a coral reef by draglines used to build a new porton the island of Taketoni off Okinawa Japan (Panos PicturesJim Holmes)

Most counrries cannm afford to lose theirreefs In terms of fishing alone Pacificislanders get up ro 90 per cent of theirprotein requirements from reef fish andworldwide reefs are home ro a toral fishcatch of 4-8 million ronnes per year (Weshyber 1993)

Furure sea-level rise will affecr reefs asreef-building corals and algae only growwithin relatively shallow water Three majorreef strategies have been identified (figureVI9) Keep-up Catch-up or Give-updepending on he balance between therelative rate of sea-level rise and the growthrate of the corals involved Ifsea levels risevery fast most reefs will be unable ro keepup Given the receor predictions of 4-5mm per year mean sea-level rise over thenext 50-100 years (see section 2 above)most reefs will keep up or catch up Unshyhealthy reefs however are less able to keeptheir growth rates up and are more likelyto give up

- ---_ _-$fa~ ___~ _ - bull r

~ Z4 -- _~ampJt)

RftfswflKe

~lnb_~--~Rftfiuface (tl

--$fIlM rise -Rffi growth

Figure VI9 Coral reef growthscenarios (a) keep-up reef growthproceeds at roughly the same rate assea-level rise (b) catch-Up sea levelinitially rises faster than reef growththen reef growth catches up (c) giveshyup sea level rises too fast for slowshygrowing or unhealthy coral reefs

Area

Coral Reef Degradation 229

Table VI3 Summary of the health of coral reefs In various parts of the world

worlds reefs Reef healthfound in the area

South-east Asia 30 60-70 reefs sick Deforestation miningand fishing problems

Pacific Ocean 25 Mainly good condition because of lowpopulations

Indian Ocean 24 20 reefs lost Mining fishing and coastalpollution problems

Caribbean Sea 8 Deforestation and tourism problems

Atlantic Ocean 6 Coastal development and tourism problemsBermuda has good reef reserves

Middle East 6 low runoff low population and littletourism aid reef health oil spills a problem

Source Adapted from Weber (1993) table 3-2

Currently many reefs are protected tovarying degrees in an attempt to reducethe suesses on them The Great BarrierReef Marine Park in Australia was createdin the 19705 It contains five sectionswith different reef uses allowed in eachOil drilling and mining are prohibitedthroughout the park and in some secshytions only scientific research and traditionalfishing are permitted Where relatively poorcountries have vulnerable reefs which arealso major touriSt attractions there can bemany conflicts involved in successful reefmanagement and marine parks can be hardto monitor and control If reef manage-

FURTHER READING

ment and protection is to be successful itis necessary to understand how reefs workmanage the various human uses of themand plan onshore land use (0 reduce damshyage from external sources The problemhas many dimensions as Weber (1993p 53) explains Ultimately the forcesbehind reef dedine are hard to untangleOverexploitation and coastal pollutionstem from business interests wealthy conshysumers the growing numbers of coastalpoor and governments trying to balanceconflicting development goals No singlegroup is the cause of reefs precipitousdecline yet all contribute to the tragedy

Guilcher A 1988 Coral Reef GeomorphokJgy Chichester WileyA general clearly written study of coral reefs with a useful section on human pressureson reefs

230 Oceans Seas and Coasts

Threatened reefs of the Red Sea

The Red Sea which extends from 13 N to 30 N has fringing reefs along almostall of its coastline Reefs are especially well developed along the north and centralcoasts Conditions arc particularly suitable for reef growth here There are nopermanent rivers flowing into the Red Sea from its arid hinterland andphytoplankton productivity is low both of which encourage clear water Thereare few storms and no tropical cyclones Reefs along the northernmost part of theRed Sea however are affected by occasional extremely low tides and sea temshyperatures here are near the minimum level acceptable for reef-building coralsMost countries bordering on the Red Sea are arid and sparsely populated andthere have therefore been few onshore threats to the reefs Pollution from thebusy Red Sea shipping lanes is a problem and oil pollution from oil explorationin the Gulf of Suez is especially serious

Tourism is a growth industry here most concentrated in the northern counshytries of Israel Egypt and Jordan Studies estimate that 19 per cent of Egyptsreefs are now affected by tourism and this figure is expected to rise to 73 percent by the year 2000 The Egyptian resort of Hurghada provides a good examshyple of the actual and potential impacts of tourism on Red Sea reefs The townof Hurghada was founded in 1909 to supply the oil industry It did not start toamact many tourists until the late 1970s Now it has huge tourist complexesstretching some 20 km along the coast and many more are planned (figureVIlO) Diving is a major attraction for tourists here What damage does tourismcause to these reefs~

First construction creates dust which in the dry Red Sea climate gets blownon to reefs creating a sediment nuisance Secondly construction often involvescreation of new coastal land from landfill This can cause major damage to reefsAlso enhancement of tourist beaches through beach nourishment etc can upsetregional sediment dynamics Thirdly sewage disposal desalination irrigation andrubbish disposal all pose problems At Hurghada sewage is treated before itenters the sea but observations of high algal growth on reefs nearest the shoresuggest that high nutrient inputs may still be a problem (Hawkins and Roberts1994) Fourthly tourism may encourage overfishing and the collection of coralsand shells for sale Fifthly diving and boat anchoring have been shown to damagereefs over small areas Finally it should be noted that tourism has positive benefitsfor neighbouring reefs as it reduces the industrial development in the area andbrings an added awareness of the value of natural reef habitats

A Marine Station was established at Hurghada in 1931 which has providedinvaluable data on marine biology A national park has been proposed to helpprotect the reefs Oil pollution remains a serious problem For example in 1982fresh oil was found over a wide area affecting turdes white shark spoonbill andosprey (Wells 1988)

Further north around the tourist resort of Sharm-el-Sheikh the Ras Mohamshymed Marine Park was set up in 1983 to aid reef conservation Here there is a

Coral lkef Dt=gradarion 231

WI e-J

DpIo

N

j -----

EGYPT

Figure Vl10 Present and planned coastal tourist development aroundHurghada EgyptSource After Hawkins et al (1993)

high density and diversity of corals as well as sharks giant clams green turtlesand many interesting bird species

According to a recent scudy tourism is causing worrying rather than alarmingdamage to Red Sea ~efs However the situation could easily worsen as touristnumbers grow and global warming and natural stresses compound the problemsNatural stresses include outbreaks of sea urchins and other grazing organismsSea urchins can reach high population densities on the coral reefs here Theygraze on coral and can inflict damage on the reefs Several areas of reefs alongthe Ikd Sea coast have shown signs of urchin damage in the past and similarproblems may recur in the future

Further reading

Hawkins] P and Roberts C M 1994 The growth of coastal tourism in theRJd Sea present and future effects on coral reefs Ambio 23 503-8

232 Oceans Seas and Coasu

Io 0

19t5 1986 1917 1911 1919 1990

8 AQUACULTURE AND

COASTAL WETLANDS

Figure VI11 Global aquacultureproduction 1985-1990Source After UNEP (1993) fig 310

ments where wave energy is low andwhere tidal processes dominate such asestuaries deltas and bays In the upperintertidal zone and above salHolerant vegshyetation may grow In the temperate zonesalt marsh communities such as SpRrtin4grasses dominate grading into mangrovetrees (eg speeies of Rbiuphora andApUnR) in the tropics At lower tidallevels there are mudflat surfaces which lookbare but actually support large numbersof algae and mud-dwelling animals

Coastal wetlands have often been seenas wastelands but 1ikc other wetlands (seepart II section 9) they play some veryuseful roles These include acting as anatural agent of coastal protection buffshyering the land behind them from the seaand acting as a purifying agent by removshying roxic wastes from the water enteringthem They are also invaluable in preservshying biodiversity for example they provideimportant stopping-off points for numershyous migrating birds In mangrove swampsthe mangrove trees themselves are a useshyful source of timber and firewood for manylocal communities

There arc many large areas of coastalwetlands such as nearly 600000 hectaresof salt marsh on the Atlantic coast ofthe USA and an estimated 22 millionhectares of mangrove swamps worldwideMany coastal wetlands are threatened bydevelopment Agriculture industry andurban expansions can all lead to landreclamation and the removal of naturalmangrove ecosystems Aquaculture alsoleads to disruption of the natural coastalwetland as trees and other natural vegetashytion are cleared ponds dug and filled withwater and nutrients and waste productsdischarged into the water Eutrophicationcan become a problem as a result of theinflux of nutrients The species mix maybe affected and total biodiversity reduced

In Indonesia for eumple brackish waterfishponds (locaUy known u tRmbu) nowoccupy over 269000 hectares or 65 per

Aquaculture is the water-based version ofagriculture where plants and animals aregrown and harvested for food and otherproducts Since the 1970s aquaculture hasdeveloped enormously and now accountsfor about IS million tonnes or 17 per centof world fisheries production (figureVIll) Aquaculture can take place inlandon freshwater lakes and ponds but a largeproportion of aquaculture takes place inbrackish water or seawater ponds in coastalwetlands Along tropical coasts for examshyple it is estimated that about 765000hecrares of land are currently in usc forshrimp production Shrimps oysters catshyfish tilapia salmon rainbow trout andtiger prawns among a wide range ofotherspecies are regularly farmed throughaquacultural techniques

Why are coastal wetlands commonlyconverted to aquacultural use~ And whydoes it matter Coastal wetlands whichinclude salt marshes mangrove swampsand mud flats arc found along low~lying

sheltered coastlines with a large sedimentsupply In general they form in environ-

ED] Ra1I olWoridlMOllr Dlnltil

olloulfuh (Itch

IlJ~f

I~ uoo-

-Aquaculture and Coastal Wetlands 233

---~--

Plate VI8 Aquaculture is expanding rapidly in South-East Asia These fish pondsare located on Java Indonesia The creation of fish ponds can destroy importantnatural coastal vegetation and contribute to coastal pollution (Panos PicturesJeremy Hartley)

cent of the total former mangrove areaConversion to tambak is often unsuccessshyful as erosion and pollution can becomeserious problems if the sites are not choshysen correctly As with agriculture on landaquaculture will only succeed in the longterm without causing ecological damageif there is a good understanding ofhow the natural environment works andaquacultural techniques are developed thatavoid disturbing these environmental sysshytems too much In the Far East whereaquaculture has been practised for thoushysands ofyears technological improvements

FURTHER READING

and more sensitive management techniquesare helping to reduce environmental probshylems associated with aquaculture Technoshylogical improvements include better diseasecontrol and nutrition and genetic enhanceshyment Technological advances also enablemangroves to be planted on dikes aroundponds The mangroves provide useful fuelshywood and fertilizer (from decaying leaves)and protect the ponds from erosion Moresensitive management techniques involveensuring that aquaculture ponds andmangrove forests are not seen as mutuallyexclusive

Beveridge M C M Ross L G and Kelly L A 1994 Aquaculture and biodiversityAmfri 23 497-503An introductory review in a journal that is full of important case studies on many topicscovered in this book

234 Oceans Seas and Coasts

Pond culture in the PhilippinesThe Philippines consist ofsome 7100islands in all Between 1920 and 1990the area of mangroves around theseislands shrank from 450000 hectaresto 132500 hectares Over the sameperiod the area covered by ponds in~

creased to 223000 hectares Around50 per cent of mangrove loss in thePhilippines can be ascribed [Q theconstruction ofbrackish water pondsBy 1991 27 ~r cent of the totalPhilippines fish production (some26 million tonnes) came from suchaquaculture

Brackish water pond aquaculturein south-east Asia started in Java Inshydonesia in the fifteenth century andspread to the Philippines whereponds were first constructed on theshores around Manila Bay (Primavera 1995) There have been several phases ofbrackish water aquaculture in the Philippines and several effects

bull In the 1950s and 1960s the government sponsored fishpond developmentespecially for milkfish production for local consumption

bull The 1970s was declared a conservation decade andbull The 1980s saw shrimp fever with a boom in production of shrimps and

especially tiger prawns mainly for export and the urban macket

The notable effects of brackish water pond aquaculture in the Philippines havebeen mangrove loss pollution of coastal waters and decline in production ofdomestic food crops

The loss of mangroves affects coastal stability removes protection against the20 or so typhoons which affect the Philippines each year and removes some veryversatile plants There ace 26 mangrove tree species found here many of whichhave a wide range of traditional meso The most seriously affected areas arewestern Visayas and central Luzon

The ecological damage inflicted by pond aquaculture has prompted the Philipshypines government and others to take action Rtforestation has been carried outfor example in 1984 when 650 hectares in central Visayas were replanted As of1990 8705 hectares of mangroves have been successfully planted

9 CoNCLUSION

The worlds coastlines and their immedishyate hinterlands are the focus of a greatdeal ofhuman activity They are thus undersevere pressure from humankind By conshytrast the worlds oceans which are enorshymous have so far been much less affectedby anthropogenic changes Their sheer sizeoffers them some protection from theeffects of pollution and waste disposalHowever the depletion ofworld fish stocksis an increasingly serious issue Halfwaybetween coastlines and the great oceansare the marginal seas - water bodies likethe Mediterranean the Baltic and theNorth Sea These do show the dear imshypacts of a wide range of human activities

The worlds coastlines are experiencingslowly rising sea levels (There arc someexceptions such as those areas undergoshying rapid uplift because of isostatic responseor tectonic activity) If the enhanced greenshyhouse effect causes global warming to takeplace the nHe ofsea-level rise will increaseover the coming decades Many of theworlds coastlines are also being subjectedto accelerated fates of erosion or retreatbecause of a range of human impactsSome are also being flooded more oftenpartly because of sea-level rise but alsobecause of a combination of local humanand natural stresses

Many types of coastal terrain are bothdynamic and fragile Dunes deltasbeaches reefS swamps and marshes comeinto this category They all offer many

KEy ThRMS AND CoNCEPTS

aquaculturecoral blachingcoral reefsEl Ninoeustatic changeisostatic change

Conclusion 235

ecological services to humankind Forexample they act as agents of coastal deshyfence or as highly productive ecosystemsThus we need to treat them with particushylar care and respect

Overall the issues covered in this partof the book illustrate that there are a wholerange of immediate environmental probshylems affecting many parts of the worldscoastline resulting from a combination ofhuman and natural stresses Future seashylevel rises if they do occur will be affectshying coastlines which are already stressedand therefore unlikely to be able to reshyspond as they would naturally to suchchanges Furthermore as we have showncoasts arc naturally dynamic over a rangeof time-scales and any attempts at coastalmanagement must take this into aCCOUD[We cannot fossilize the coast Because ofthe many attractions of coastal environshyments a multitude of people are involvedina wide range of activities within thecoastal zone Effective coastal zone manshyagement must involve and consider thesepeople Finally several of the examplcs wehave used show the many links betweencoastal environments and those on landand in the oceans There are also manylinks between different segments of thecoastline and between the different comshyponents of the coastal enviroment (ecolshyogy sediments water) In orGa to copesuccessfully with all these componentsand interlinkages coastal zone manageshyment schemes must be truly integratedprogrammes

salt marshessea levelsediment circulation celissurgestectonics

236 Oceans Seas and Coasts

POINTS FOR REVIEW

Why arc coastal areas being placed under increasing pressure

Why might sea levels rise in some areas in coming decades

Why are so many stretches of the worlds coastlines showing signs of erosion

How would you aim to reduce the impacts of coastal flooding

What marine environments are especially prone to [he effects of pollution

Which coastal types do you think are especially fragile and dynamic

Why should we aim to conserve coastal wetlands and coral reefs

PART VII

Conclusion1 Introduction 2392 The Complexity ofthe Human Impact 2393 Towards a Sustainable FUlUre 239

Key Tenns and Concepts 244Points for Review 244

1 INTRODUCTION

The human transformation of nature hasbeen going on for a very long time andhas been very pervasive The Earths surshyface still has areas ofsome size which showlittle obvious manifestation of the impactof humans (c=g the deep oceans pans ofthe polar regions some of the tropical rainforests) and we talk of wilderness areasin which very little human activity occursHowever there is no place on the face ofthe Earth which is not to some extentaffected by the changes in the chemicalcomposition of the atmosphere and assoshyciated changes in climate and levels ofpollution

2 THE COMPLEXITY OF THE

HUMAN IMPACT

We have demonstrated in this book thatdifferent types of human activity causedifferent types of land transformation Forexample at the one extreme we have disshycussed some of the changes in the envirshyonment that have been caused in andaround cities by the process of urbanizashytion At the other we have demonstratedhow even hunters and gatherers livingin scattered groups have contributed tosuch processes as deforestation anddesertification We have selected our casestudies to illustrate this theme We haveshown how some changes in the environshyment are made deliberately by humans butalso how many others are accidental byshyproducts of human activity Often it takessome time for the environments responsesto such impacts to become apparentOften too their exact causes are hard toidentify In many cases human impactsarc increasingly becoming interlinked andaccompanied by natural fluctuations toproduce massive and often unpredictablechanges in the environment We have idenshytified a whole spectrUm of different types

A Sustainable Future 239

of environmental response to stress Theserange from short-term fluctuations whichcan be easily reversed to long-term poshytentially irreversible changes which poseintractable problems for environmentalmanagement Our case studies have alsoillustrated the wide variety of types of atmiddottempted solutions to environmental probshylems These range from technologicalquick-fix solutions such as engineeringstructures to control coastal erosion tosofter and more ecologically friendlyinterventions such as replanting riparianbuffer zones to lessen the amount ofnitrate pollution that enters rivers fromagricultural slopes Increasingly any suchschemes need to be integrated That isenvironmental problems should nO[ beconsidered in isolation but should beviewed as linked parts of the same seriesof problems Inevitably any such schemeswill work only if the additional complexshyities of human society economy cultureand politics arc also taken into account

3 TOWARDS A SUSTAINABLE

FUTURE

It is likely that in coming decades many ofthe transformations we have described anddiscussed will become even more imporshytant and the need for effective environshymental management even more pressingHuman population levels arc increasingnew technologies are emerging and evershyincreasing quantities of energy and reshysources are being produced and consumedespecially in countries that aspire to thelevels of development achieved by someof the worlds richest nations There mustbe severe doubts as to whether these trendsarc sustainable Will the world be transshyformed by global warming Will we cutdown all our rain forests1 Will a large proshyportion of the worlds flora and faunabecome extinct Will many of the worldsdryIands tum into dust bowls Will urban

240 Conclusion

Table VII1 Some potential adverse Impacts of global warming on resources

Resource Possible effects

Agriculture Lower crop yieldsSpread of pestsSoil erosion

Forests

Conservation areas and naturereserves

Coastal areas

Fisheries

Water resources

Human health

Energy demand and production

Change in rate of growthChange in species compositionShifts in geographical distribution

Disruption or loss of habitatInvasion of new species

Inundation of land and accelerated erosion byrising sea levels

Changes in composition of stocks and theirlocation

Droughts floods changes in amount of supply

Heat stressShifts in prevalence of infectious diseases

Increases in need for summer aiHonditionlng

atmospheres continue to become morepoUuted and more health-threatening Willour water supplies dwindle in quantity anddeteriorate in quality~ These are some ofthe many questions that we can ask aboutthe future They form the basis of muchof the environmental concern that is deshyveloping throughout the world

Arc such massive and unwelcometransformations of the face of the Earthinevitabld Is human life sustainable Canhuman energies be harnessed over thecoming decades to improve rather than to

degrade the environment We arc notwithout hope We have indicated in manyof our cast studies that there are waysmeans and opportunities to overcomesome of the undesirable processes that wehave identified Each and everyone of usin our daily life has the power to makesure that the generations to come have asustaUnable future

There is now very great interest in howwe might adapt to global warming shouldit occur Such adaptations would be necshyessary if we could not limit emissions ofgreenhouse gases sufficiently to rule outthe possibility ofsignificant warming Theywould also be necessary because of thevery great range of environments activshyities and resources that might be modifiedas a result of global warming (table VIIl)It is onen said that there are two types ofadaptation that may be necessary The firstof these is reactive adaptation wherebywe respond to climatic change aner itoccurs The second is anticipatory adapshytation in which we take steps in advanceofclimatic change to minimize any potenshytially negative effects or to increase ourability to adapt to changes rapidly andinexpensively

Reactive adaptation may well be feasibleand effective In many parts of the world

A Sustainable Future 241

Table VII2 Examples of no-regrets policies In response to possible global warming

Policy area and measures

Coastal zone management

Wetland preservation andmigrations

Integrated development ofcoastal datasets

Improved development ofcoastal models

land-use planning

Water resources

Conservation

Market allocation

Pollution control

Benefits

Maintains healthy wetlands which are morelikely to have higher value than artificiallycreated replacements Maintains existing coastalfisheries that are difficult to relocate

Integrated data allow formation ofcomprehensive planning and identification ofregions most likely to be affected by physicalor social changes Allows effects of changes tobe examined beyond the local or regional scale

Improved modelling allows more accurateevaluation of how coastal systems respond toclimate change and also to other shocks

Sensible land-use planning such as the use ofland setbacks to control shoreline developmentbetter preserves the landscape and alsominimizes the concerns of beach erosion fromany cause

Reducing demand can increase excess supplygiving more safety margin for future droughtsUsing efficient technologies such as dripirrigation reduces demand to some extentPreserving some flexibility of demand is usefulas less valuable uses allow reduced demandduring droughts

Market-based allocation allows water to bediverted to its most efficient uses in contrastwith non-market mechanisms that can result inwasteful uses Market allocations are able torespond more rapidly to changing supplyconditions and also tend to lower demandconserving water

Improving water quality by improving thequality of incoming emissions prOVides greaterwater quality safety margins dUring droughtsand makes water supply systems lessvulnerable to declines in quality because ofclimate change

Table continues overleaf

242 Conclusion

Table VII2 Continued

Policy area and measures

River basin planning

Drought contingency planning

Human health

Weatherhealth watch warningsystems

Improved public health andpest management procedures

Improved surveillance systems

Ecosystems

Protect biodiversity and nature

Benefits

Comprehensive planning across a river basincan allow for imposition of cost-effectivesolutions to water quality and water supplyproblems Planning can also help cope withpopulation growth and changes in supply anddemand from many causes induding climatechange

Plans for short-term measures to adapt todroughts These measures would help offsetdroughts of known or greater intensity andduration

Warning systems to notify people of heatstress conditions or other dangerous weathersituations will allow people to take necessaryprecautions This can reduce heat stress andother types of fatalities both now and if heatwaves become more severe

Many diseases which will spread if climatechanges are curable or controllable and effortsin these areas will raise the quality of humanlife both now and if climate change occurs

More and better data on the incidence andspread of diseases are necessary to betterdetermine the future patems of infection anddisease spread This information is helpfulunder any scenario

Biodiversity protection maintains ecologicaldiversity and richness preserves variety ingenotypes for medical and other research Amore diverse gene pool proVides morecandidates for successful adaption to climatechange One possibility is to preserveendangered species outside of their naturalhabitat such as in zoos

Table continues opposite

A Sustainable Future 243

Table VII2 Continued

Policy area and measures

Protect and enhance migrationcorridors

Watershed protection

Benefits

Such policies help maintain an ecosystem andanimal and tree species diversity Corridors andbuffer zones around current reserve areas thatinclude different altitudes and ecosystems aremore likely to withstand climate change byincreasing the likelihood of successful animaland tree migration

Forest cover provides watershed protectionincluding protection from bank erosionsiltation and soil losss All of these functionsare extremely valuable whether climatechanges occur or not

Agriculture

Irrigation effiCiency Many improvements are possible and efficientfrom a cost-benefit standpoint Improvementsallow greater flexibility to future change byreducing water consumption without reducingcrop yields

Development of new crop types Development of more and better heat- anddrought-resistant crops will help alleviatecurrent and future world food demand byenabling production in marginal areas toexpand Improvements will be critical as worldpopulation continues to increase with orwithout climate change

Source After Smith et al (1995) table 3

we may well be able to adapt to the mostlikely ways in which the climate maychange For example we could substituteheat- and drought-resistant crops for thosewhose yields are reduced Infrastructure isgenerally replaced on a much faster timeshyscale than climatic change so it could beadapted to changes in climate It can alsobe argued in favour of reactive adaptashytion that it does not involve prematurelyspending money in advance of uncertainchanges

On the other hand one can argue thatrapid climate change or significant in-

creases in the intensity and frequency ofextreme events such as floods storms ordroughts could make reactive adaptationsdifficult and could pose immediate probshylems for large numbers ofpeople Equallysome policies would have significant beneshyfits even under current environmentalconditions and would be valuable from acost-benefit perspective even if no climaticchange toolc place These types of anticishypatory policies are often called no regretspolicies because they will succeed whetheror not climatic change takes place meaningthat policy-makers should never have to

244 Conclusion

regret their adoption No regrets policiesmay none the less be expensive TableVII2 illustrates a selection of these policies

One can argue that the central challengefor policy-makers in coming decades willbe to find ways of allowing the globaleconomy to grow at a moderate rate whileat the same time maintaining or enhancingthe protection of wilderness the prevenshytion of pollution and the sustenance ofecological resources We cannot be sure

KEy TERMS AND CoNCEPTS

anticipatory adaptationno-regrets policiesreactive adaptation

POINTS FOR REVIEW

that we will find policies that enable thisto happen Governments and society willinevitably need to make difficult trade-ofTsbetween economic growth and environshymental protection We cannot envisage asituation where there is indefinite growthin the human population and indefinitegrowth in the consumption of resourcesWe need to ensure to use Sir CrispinTickells phrase (Tickdl 1993) that hushymans are nOt a suicidal success

Which environmental issues wiU become increasingly important in coming decades

Can human energies be harnessed over the coming decades to improve rather than todegrade the environment

How might we adapt to global warming should it occur

GLOSSARYIn each definition any words that themselves ap~ar in the glossary are printed in iudieltyplt

adiabatic compression The process bywhich as a parcel of air falls the internalenergy is increased and its temperature israisedacid rain Rain which because of the preshysence ofdissolved substances derived fromair pollution has a pH of less than 565aerosol (atmospheric) An aggregation ofminute particles (solid or liquid) suspendedin the atmosphere The term is often usedto describe smoke condensation nucleifreezing nuclei or fog or pollutants suchas droplets containing sulphur dioxide ornitrogen dioxideaggradation The building upwards oroutwards of the land surface by the deposhysition of sedimentalbedo A measure for the reflectivity ofabody or surface defined as the total radiashytion reflected by the body divided by thetotal radiation falling on it Values are exshypressed on a scale ofeither 0-1 or 1-100alluvial floodplain A flat-lying area comshyposed ofsedim~nts (sands silts clays gravshyels etc) deposited by riversamphibian A creature that can live onland or in wat~r

anthropogenic Caused by human activshyitiesanthropogeomorphology The study ofthe human impact on landforms and landshyforming processesaquaculture The cultivation or rearingof plants or animals that grow or live in ornear wateraquifer An underground water-bearinglayer of porous rock through which watercan Row

arid Dry with limited vegetation rainshyfall less than about 250 mm and a greatexcess of evaporation over precipitationarterial drainage A system of majordrainage channels into which numeroussmall channels feedatoll An irregular annular (ring-shaped)coral algal reef enclosing or almost enclosmiddoting a central lagoon The reefS are oftenbreached by channelsbackscatter To send back rather thanlet through incoming radiation from thesunbadlands Areas that have been erodedby deep systems of ravines or gulliesbarrier island An elongated mainlysandy ridge feature running parallel to thecoast and separated from it by a lagoonbase levd The lower limit down to whicherosion on land may operate usually deshyfined with reference to the role of runshyning water For example sea level acts asa general base level though there can bea wide range of local base levels above andbelow sea levelbasin The area that drains into a partishycular river It has the same general meaningas catchment (British usage) or watershed(American usage)biodegradable A term used to describea substance that can be rendered harmlessor be broken down by natural processesbiodiversity A term used to describe thevariety of species both floral and faunalcontained within an ecosyrtembiofabrica Fabrics made of organicmaterialbiological magnification The increased

246 Glossary

concentration of toxic material at consecushytive higher trophic levels in an ecosystemToxins such as heavy metals and persistentpesticides become incorporated into livshying tissue from the environmentbiomass The total mass of biologicalmaterial contained in a given area of theEarths surface (expressed as dry weightper unit area)biorne A major ecological community orcomplex ofcommunities that extends overa large geographical area and is charactershyized by a dominant type ofvegetation (egtundra desert rain forest)bioremediation The use of microshyorganisms to restore the qualities of enshyvironments contaminated by hazardoussubstancesbiosphere The interlinked communitiesofanimals plants and micro-organisms thatlive on the land and sea of the Earthbiota The animal and plant life of aregionbiotechnology The manipulation ofliving organisms and their components(eg genes or gene components) for speshycific tasksbloom A scum produced by algae on thesurface of standing waterblowout An area of dune that has beenbreached by wind excavationboreal Of northern regions A termapplied both to a climatic zone charactershyized by cold snowy winters and shortsummers and to the coniferous forests ofthe high mid-latitudes in the NorthernHemisphere also known as taigabrecciate Break lip into angular fragmentscarbon budget The balance between theamount of carbon which accumulates in asystem and the amount that is releasedcarcinogen Any substance that producescancercarrying capacity The maximum popushylation of a given organism which a parshyticular environment can sustain without atendency to decrease or increase

catalyst A substance that without itselfundergoing any permanent change setsoff a change or increases the rate at whicha change occurscatchment The area that drains into ariver It is bounded by a drainage divideor watershed (British usage)centre-pivot irrigation The artificialdistribution of water to land for agriculshytural use in which Broundwater is pumpedand from a central point is dispersed in acirclechannelization The modification of riverchannds for the purpose of flood controlland drainage navigation and the reducshytion or prevention of erosionchaparral A type of stunted (scrub)woodland found in temperate regions withdry summers It is dominared by droughtshyresistant evergreen shrubschlorofluorocarbons A range of synshyrhetically manufactured chemically inertcompounds containing atoms of carbonfluorine and chlorine They have beendeveloped and widely used as solventsrefrigerants and aerosol propellanrs and inrhe manufacture of foam plasticscolloidal Composed of ultramicroscopicpaniclesconvection The transfer of heat in theatmosphere by the upward flow of hot airor the downward flow of cold airdeflation The removal of dry unconshysolidated material eg dust or sand froma surface by winddeflocculate To disperse or break up anaggregate so that particles become susshypended in a solution This may be achievedby the presence of sodium cationsdefolianr An agent tha[ removes foliage(eg leaves) from a plantdeforestation The permanent removal ofuees from an area of forest or woodlanddesertification The spread of desenmiddotlikeconditions in arid or semi-arid areas dueto human interference or climatic changeor both

desiccation Drying up of the environshymentdiatom A microscopic single-celled algawith a siliceous cell walLdieback A diseased condition of plantsoften applied to the dying-offoflarge tracts

of similar species at the same timedimethylsulphide A volatile sulphurcompound in seawater produced by bacshyterial decay and planktonic algae It oxishydizes in the atmosphere to form a sulphateaerosoldischarge (rivers) The amount of waterthat flows in a riverDNA (deoxyribonucleic acid) The subshystance that is the carrier of genetic inforshymation found in the chromosomes of thenucleus of a celldomestication The taming and brecdshying of prcviously wild animals and plantsfor human usedrainage basin That part of the landsurface which is drained by a particularriver system and is defined by a divide orwatershed (British usage)drawdown The reduction in groundshywater level by pumping out water fasterthan it can be replenisheddwt storm A storm in a semi-arid areawhich carries dense clouds of dust someshytimes to a great height often obscuringvisibility to below 1000 metresecology The science which studies therelations between living organisms andtheir environmenteagtsystem A biological community ofany scale in which organisms interact withtheir physical environmentecotone A transition zone marking anoverlap rather than a distinct boundarybetween two plant communities It maybe a zone of tensionedaphic A term used to describe soilconditions which influence the growthof plants and other organisms Edaphicpoundactors include physical chemical andbiological properties of soils such as

Glossary 247

pH particle-size distribution and organiccontentEI Niiio events A term applied to theextensive intense and prolonged wanningof the eastern tropical Pacific Ocean whichoccurs every few years It is associated withmajor anomalies in the patterns of atmosshypheric circulation and rainfallendemic Normally found only among aparticular people or in a certain regionewtasy A worldwide change in sea levelindicating an acmal rise or fall of the seaeutrophication The process by which anaquatic eeosystem increases in productivityas a result of increased nutrient inputOften this is due to humanmiddotinduced addishytions of elements such as nitrogen andphosphorus However the process mayalso be a natural phenomenonevapotranspiration The combined lossof water by evaporation from the soil surmiddotface and transpiration from plantsex situ methods A term used to describemeans of conserving species outside theirnatural habitat (eg in zoos or botanicgardens)feral Term describing an animal or plantonce domtJticated that has gone wildfilling The deposition ofdredged matershyial to make new landfluvial Relating to a river or riversfood chain The transfer of energy fromgrecn plants through a sequence oforganshyisms in which each eats the one below itin the chain and is eaten by the one aboveforest decline The decline of forestvitality characterized by decreased andabnormal growth leading eventually todeath The causes are poor managementpractices climatic change fungal viral andpest attack nutrient deficiency and atmosshypheric pollutionfriable Easily crumbled (ofsoil rock orother material)gabion A wire-framed container full ofboulders or cobbles used to make wallsto stop erosion

248 Glossary

general circulation mood (GeM) Adynamic computer model which simulateslarge-scale features of atmospheric andoceanic circulationgenetic ~lating to genes which arcunits of heredity composed or DNA orRNA and fanning part of a chromosomethat determines thc particular characterisshytics of an individualgeomorphology Thc science of the orishygin and developmcnt of landformsglaciated Term used to dcscribe an areathat has becn at some point covcred ormoulded by glaciers or icc sheetsglobal warming Thc process by whichthe Earth may becomc warmcr because ofthe role of mcchanisms such as the greenshyhouse ejJeClgneiss A c03nC-grained metamorphicrock composed of feldspars quartz andferromagnesian mineralsgreenhouse effect A climatic cffcctcaused by permitting incoming solar 4shyriiation but inhibiting outgoing radiationIncoming short-wave radiation is absorbedby matcrials which thcn re-radiatc longerwavelengths Certain substances in theatmosphere eg carbon dioxide absorblong-wave radiation resulting in a warmshying effectgross primary production The totalamount of organic material synthesized ina given time period by living organismsfrom inorganic materialgroundwater Water occurring below thesoil surface that is held in the soil itself orin a deeper aquifergypsum A rock fonned ofnatural calciumsulphate caused by its crystallization as saltywater is concentrated by evaporationhabitat The place in which an organismlives characterized by its physical featuresor the dominant plant typesbalons Members of the halogenatedfluorocarbon (HF) group of ethane- ormethane-based compounds in which H+ions arc partially or completely replaced

by chloride fluoride andor bromideThey arc long-lived and nave been implishycated in ozone depletionha1ophytic Tolerant of high concentrashytions of saltsheathland An area of evergreen JwJeroshypbyOUJ shrubland where beath families(eg Ericaceae) are present though nOtnecessarily dominant Heathlands developon areas where soil is low in nutrient statusheavy metal Any metal or alloy of highspecific gravity especially one that has adensity higher than 5 g per cu cm eglead zinc copper mercuryherbicide Any agent organic or inorganicwed to destroy unwanted vegetationHolocene The most recent epoch of theQuaternary following the PleistoceneOften called the post-glacial it has exmiddottended from about 10000 years ago tothe present day It has been marked byvariow climatic 8uctuarionshumus The organic constituent ofa soilusually formed by the decomp05irion ofplants and leaveshydro-isostasy The reaction ofthe Eanh 5

crust to the application and removal of amass of water For example efMtlltic seashylevel changes have affected the depth ofwater over the continental shelvcs causingthe crust to be depressed at times of highsea level and elevated at times of low sealevelhydrocarbons Compounds of hydrogenand carbon some with minor or tracequantities ofoxygen suJphur nitrogcn andothcr elementshydrocompaetion The process by whichsediments arc compressed by an overlyingbody of waterhydrology The science concerned withthe study of the different fonns of wateras they exist in the natural environmentIts cenual focus is the circulation and disshytribution of wattChydrostatic uplift Uplift of land surfrcecaused by upward water pressure

hypoxia The condition experienced whenoxygen levels are low in blood and tissuesinbreeding Breeding from closely relatedanimals or personsinfiltration The movement ofwater intothe soil from the ground surfaceinterglacial A time period between twoglacial stages during which temperaturesare relatively highinterpluvial A time period between twopiuPiRI stages during which conditions arerelatively dryisopleth line on map connecting placeswhere a particular meteorological factoreg thunderstorms occurs with the samefrequencyisostasy A process that causes the Earthscrust to rise or sink according to whethera weight is removed or added to it Sucha weight could be for example an icecapkarst A limestone region with undershyground drainage and many cavities andpassages caused by the solution of the rocklandfill The disposal of waste by tippingit on land often in old mine workings orlow-lying landlaterite The residual deposits formed bythe chemical weathering of rock composedprimarily of hydrated iron and aluminiumoxides Extensively devcloped in the hushymid or subtropical regionsleachate The solution or soluble matershyial that results from a leRching processleaching The removal of dissolved mashyterial by the percolation of water througha soil or sedimentLessepsian migration An almost unishydirectional migration of biotR from one seaor lake to another Named after the manwho built the Suez Canal which allowedorganisms to pass from the Red Sea to theMediterraneanlevee A natural or man-made embankshyment along a riverlichenometry A method of time estimashytion (dating) on rock surfaces based on

Glossary 249

the rate of growth of lichens (eg Rhizoc4rpon geogrRphicum)lithosphere The solid earthloess A deposit of primarily silt-sizedmaterial that was originally dust transshyported by the windmacrobenthic Relating to large organshyisms that live on or near the bottom of abody of watermacropore A particularly large pore orvoid in the soilmammal A warm-blooded creature witha backbone which if female can nourishits youngmangrove Plant communities dominatedby mangrove trees RhizopherJl BruguieriRand ApicenniR which colonize tidalmudflats estuaries and other shelteredareas in tropical and subtropical areasmlllJuis Scrub vegetation of evergreenshrubs characteristic of the western Medishyterranean broadly equivalent to chJlparrRImarginal land Land that is difficult to

cultivate or unprofitablemariculture Farming of the seamarsupial A mammRI characterized bybeing born incompletely developed and sousually carried and suckled in a pouch onthe mothers belly for a timemeander The winding pattern of a sinushyous river channelMediterranean climate A climatic typecharacteristic of the western margins ofcontinents in the worlds warm temperatezones between latitudes 30 and 40 (egcentral Chile central California)megafauna The largest types of animalsin a communityMesolithic A cultural period foUowingthe Palaeolithic from 10000 BC to 4000BC characterized by the use of microlithicimplementsmetamorphie Term used to describerocks which have been altered by externalsowces of heat pressure or chemical subshystances rather than merely by burial underother rock

250 Glossary

metapedogenesis Human modificationof soilsmicroclimate The physical state of theatmosphere close to a very small area ofthe Earths surface often in relation toliving matter such as crops or insectsmonsoon A wind with seasonal reversalsof directionmorphology The form or shape of anobject or organismnanoplankton The smallest of the phytoshyplanktonnecrosis The localized death ofceUs tissueor an organ resulting from disease or injuryNeolithic A cultural period following theMesolithic from the fourth millennium Beuntil the onset of the Bronze Age It marksthe beginning of the domestication of anishymals and the cultivation of cropsnet biological primary production Seenet primary productionnet primary production The amount oforganic material produced by living organshyisms from inorganic sources in excess ofthat used in respirationnutrient sink A location in which nutrishyents accumulatenutrient source A location from whichnutrients are rcleasedoceanic conditions Climatic conditionsthat arc modified by the presence of ancarby sea or ocean in contrast to continshyental conditionsomnivore An animal which ears bothplant and animal matterorganochlorides Organic compoundswhich contain chlorine Often used asactive ingredients for pesticides they arevery persistent due to their chemical stabshyility and low solubility An example is theinsecticide DDTorographic A tenn used to describe climshyatic conditions or phenomena caused bythe presence ofhigh relief(eg mountains)osmosis The passage ofa solvent througha semi-permeable partition or membraneinto a more concentrated solution

oxidation A chemical reaction in whicha substance decreases its number of elecshytrons The most frequent oxidant is moshylecular oxygenpalaeolimnology The study of the envirshyonmemal history of a lake most imporshytantly from evidence preserved in itsbottom sedimentspastoralism A form of land use relatingto flocks and herds of animalspathogen An organism which causesdiseaseper capita For each personperennial Lasting through a year orseveral years Used to describe plants thatare not merely annuals and streams thatnormally flow through all seasons of theyearpermafrost The thermal conditions insoil and rock where temperatures ate bemiddotlow OC ror at least two consecutive yearspH The measure of the acidity or alkashylinity of a substance based on the numberof hydrogen ions present in a litre of thesubstance and expressed in terms of pH _logIO(lH) where H is the hydrogen ionconcentration The centre point on thescale is 7 representing neutrality Acidsubstances have a pH of less than 7 andalkaline substances have a pH of morethan 7photochemical reaction A chemical reshyaction which is speeded up by particularwavelengths ofelectromagnetic radiationphytoplankton Microscopic organismsespecially algae that live near the surfaceof the sea and form the basis of food formany other forms of aquatic lifepiezometric swface A subterranean surshyface marking the level to which water willrise within an lIiJuiftrPleistocene The first epoch of the Quashyternary including glacial and interglllcillstages between about 2 million and10000 years agopluvial A climatic phase with plentifulmoisture

podzol A soil characterized by the acidshyification of the A horizon the downwardle4ching ofcations metals and humic subshystances and their deposition in the B horishyzon often precipitating to form a panThe process is most prominent in cool andwet climatespollen analysis The analysis of plantpollen under the microscope to reconshysttuct the vegetation conditions underwhich the sediment in which it occurs wasdepositedprecipitate In chemistry the depositionin solid form from a solutionprecipitation Moisture that falls on theground including rain snow dew and fogpredator An animal which kills othersfor food by preying on them A secondaryconsumer in a food ch4inprofile An outline seen from one side(eg the cross profile of a river channel) ora vertical cross-section (eg of a soil andits various layers)radiation solar Electromagnetic wavesemitted by the sunradiation budget A term used in meshyteorology to describe the difference beshytween incoming and outgoing radi4honradiocarbon dating A method ofdetershymining the age ofan organic material (egwood charcoal peat) by measuring theproportion of the He isotope containedwithin its carbon contentrangeland Alarge area ofopen land usedfor grazing or huntingreclamation Bringing land into a newform This can involve either returningsomething to its original state (eg somedegraded land) or transforming it into anew state (eg by filling in a lake to makeland)redox potential A measurement of thewillingness of an electron carrier to act asa reducing or oxidizing agentrendzina A type of soil with dark surshyface layers or horizons that developes onsoft limestones

Glossary 251

rill A small channel in a soil or rocksurface often only a few centimetres longriparian Of or on a river bankrip~rap Large fragments of broken rockdumped along a shoreline to protect itagainst wave actionrunoff The water leaving a drainage areaIt is normally regarded as the rainfall mishynus the loss by evaporationsalinization The process whereby saltseg sulphates nitrates and chlorides beshycome concentrated in the soiLsanitization The process by which someshything is made more sanitary hygienic ordisinfected so that health conditions areimprovedsaturation excess overland flow Surfacerunoffthat is g~nerated wh~n rain falls onground that is already saturated withwatersavanna A grassland of the tropics andsubtropicsscarification The process by which seedsare cleaned by abrasion of the epidermisCan also refer to changes caused to sc~ds

by passing through th~ gut of an animalor by fireschist A met4morphic rock composed oflayers of different materials split into thinirregular platessderophyUous A term referring to speshycies ofevergreen trees and shrubs that haveadapted to lengthy seasonal droughtscrub A type of vegetation consistingmainly of brushwood or stunted forestgrowthsecondary forest Woodland which hasregenerated and colonized an area afterthe original forest has been removedsediment yield sediment load Sedimentyield is the mean sediment load carried bya stream giving some measure of the rateof erosion in a dr4in1JBt b4Sin The sedishyment yield is express~d as weight per unitareaseedbed An area of soil in which seedsare plant~d and take root

252 Glossary

seep An area moistened by the ~epage

of water from or into the ground$CIIlimiddotarid Dry with a shortage of moisshyture for much of the year but not so dryas an lind areashear strength The maximum resistanceof a material to the application of stressMajor sources of such resistance arc coheshysion and frictionsheet flow The flow ofwater in thin filmsover a low-angle surfaceshifting cultivation Cultivation of asmall area of land in which forest is clearedand the biomass removed or burned folmiddotlowed by the use of the site for the proshyduction of mixed agricultural crops forseveral years Eventually the area is abanshydoned as soil ~rtiliry decreases and thecultivators move on to a [(w area SJ4shshyut-bNrn is a type of shifting cultivationsink-hole A hole or depression in thelandscape into which water drains causedby concentration of solution of the bedshyrock usually limestone or chalkslash-and-burn A system of land useespecially prevalent in the tropics in whichland is cleared of forest by cutting andburning so that cultivation can take placeAJ fertility rapidly declines in the cultiv4

ated areas the farmer moves on to a newarea after a few yearssmectite A type of day often made upof montmorillonite that may have theproperty of swelling in watersmog A fog in which smoke or otherforms of atmospheric pollutants play animportant role in causing the fog to formand thicken It often has unpleasant ordangerous physiological effectssplash erosion Erosion produced by theimpact of raindrops splashing on theground surface particularly if it is notprotected by vegetationspontaneous combwtion Fire cawed bythe natural build-up ofheat within inflamshymable materialspp Abbreviation for specics (pluraJ)

steppe A generally dry grassy plainlandstratosphere The region of the aCDlOSshy

phert lying betwccn the tropopllllSe andabout 20 kIn in which there is lime changein temlXrature with heightsubstrates Material underlying thesurfacesuccession The sequence of changcs ina plant community as it devdops over timesupernatant Term describing liquidfloating on a surfacesustainable devdopment Dcvdopmentthat meets the needs of the prescnt withmiddotout compromising the ability of futuregenerations to meet their own needssymbiosis An interaction between twO

different organisms living in close contactand usually to the advantage of bothtalus A sloping mass of fragments simmiddotilar to scree at the foot of a clifftectonic A term describing the broadstructUreS of the Earths lithosphere andmovcments within the Earths crusttcrnperate A term used to describe aregion or climate characterized by mildtemlXraturestemperature inversion Normally airtemperature decreases as height increasesHowever under certain weather conditionsair temlXrature may increase with heightso that a layer of warmer air overlies acolder layer This is temperature inversionterracing The construction of banks orsteps on a hillside to give areas of lowgradient either to enable cultivation or toconserve soilthalweg Line where opposite slopes meetat the bottom of a valley river or lakethermokacst Topographical depressionsresulting from the thawing of ground icethreshold A condition which marks thetransition from one state of operation of asystem to another Rapid and irreversiblechange may occurtrace dementi Elements thl[ are requiredby living organisms to ensure normalgrowth development and maintenance

They occur at lower concentrations thanmajor elements and include iron mangashynese zinc copper iodine etctrau gases Gases which occur in verysmall amounts in the atmospheretrophic levels The positions that organshyisms occupy in a food chaintropopause The interface between thetroposphere and the stratospheretroposphere The lowest level of theatmosphere in which most of ourweather occurs It lies beneath the stratoshysphere and its thickness ranges from about7 km at the poles to about 28 km at theequatortundra The zone between the latitudishynal limits of tree growth and polar icecharacterized by severe winters and a shortgrowing seasonturbidity A measure of the lack of clearshyness in a liquid caused by the presence ofsuspended materialunderstory A layer ofvegetation beneaththe main tree canopyUV radiation Radiation from the sunwith shorter wavelengths than visiblelight It is classified into three rangesaccording to its effect on human skinUV-A is not normally harmful UV-Bproduces reddening and tanning uv-e(with the shortest wavelengths) is the mostdamagingvector-borne A term used to describe adisease that is passed on by an organism

Glossary 253

often an insect (eg as malaria is transmitshyted by the mosquito)volatilization Evaporation or the proshycess of turning from solid or liquid forminto a vapourwater table The level below which theground is saturated with waterwatershed (American usage) The areaoccupied by a drainage basin or streamcatchmentwatershed (British usage) A line ofseparation between waters flowing intodifferent rivers basins or seasweather front A sloping boundary surshyface separating two air masses that exhibitdifferent meteorological propertieswetlands The collective term for ecosysshytems whose formation has been dominatedby water and whose processes and characshyteristics are largely controlled by waterwilderness An area leA untouched andthus in a natural state with little or nohuman control or interferencewind reactivation The renewed moveshyment of sand and other material by thewind especially when vegetation cover isreducedwind throw The blowing over of treesby the windxerophilous A term describing plantswhich live in dry habitats and can endureprolonged drought Many such plantseg cactus have developed physiologicaladaptations to cope with these conditions

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INDEXNote Alphabetical arrangement ofheadings and subheadings is word by word ignoringand by in through etc Page numbers in italics refer to illustrations Rememberto consult the Glossary (pp 245-53) for definitions

Aberfan disaster 185 186accelerated landslides 185-8accelerated sedimentation 182accelerated soil erosion 165-74

180-2 201acid rain 116-20

and forest decline 45reduction in 118 120

Adriatic Sea eutrophication of 221aerosols atmospheric 83-9afforestation

hydrological effects 126 136-7144

ste also deforestationAfrica

fire use 20-1savanna ecosystem 4041see aso individual countries

Africanized honey bee 66 67Afromontane grassland 39-40agricultural empires 6agricultural revolutions 4-5agriculture

arid areas 27-8biotechnology in 76 77and dust storms 84 87 172energy use 10and global warming 97habitat destruction 69hydrological impact 126land drainage for 142-5machinery 46 168-9 170-1no regrets policies 243pollution from 145 151-2seasonally flooded wetlands 57soil conservation measures 169 174and soil erosion 166-7 168-9

172-4

technological developments 5 67-8 10

and tree damage 46air conditioning 100air pollution

and forest decline 44-6 47health effects 85 102 106 108-9increasing scale 83legislation controlling 44 85 104and stone decay 197-200urban areas 49 50 52 8599

102-9 197-200vehicle emissions 114115199Jee also acid rain

albedoland use changes affecting 90 92sulphate aerosol effects on 85urban areas 98

algal blooms 150 155 218alpine grasslands 43Amazon basin deforestation in 90

91America

Africanized honey bee spread 6667

Jtt aho USAanimals

channelization effects on 131domestication 4feral 66introduced species 66-7space requirements 70-1urban 48-9

Antarctic ozone hole 110 111 114anthropogeomorphology 165 167anticipatory adaptation 240 243-4apartheid 13 108-9aquaculture 232-4

aquif~rs

d~pletion and rccharg~ 159-61s~awat~r incursion 184

Aral Sea d~siccation of 155-8 184Arctic ozon~ depl~tion abov~ 114arid ar~as

agricultur~ 27-8 159d~forestation 28groundwat~r depletion 159urban groundwater recharge 142urban ston~ d~cay 197see IIlso d~sertification

arterial drainage systems 142asbestos 109ash trees di~back of 46Aswan Dam 125 128 129Atlantic industrial ~ra 6atmospheric carbon dioxide 22-3

9396atmospheric circulation

and global warming 94see tllso climate climate change

atolls 226Australia

alien plant species 68graring and grasslands 43groundwater abstraction 159introduced parasites 66savanna 41soil salinization 183 184

autumn-sown cereals 169 170

backscatter 84badlands 168Bahrain beach pollution in 219Baltic Sea dune managemem on 224Bangladesh coastal floods in 215barchans 176 177barrier islands 210 213beaches

nourishment 212 213pollution 219

biodiversity 58 -63preservation 60-3 78 242rain forests 35 36urban ar~as 48-9wetlands 55 232

Ind~x 265

bioeconomic analysis 60biological magnification 147218biomass burning 20-1 22-3

see also firebiotechnology 8 76-7bird habitat losses 69-70Biwa Lake eutrophication of 152153Black Sea eutrophication of 150Blackwater estuary sea-level rise in

208-9blowouts 222Blue Plan 221bogs 54Brazos River Texas channel changes

in 182Britain

acid rain 117air pollution 104 105dean air legislation 85 104coastal erosion 209 210 lll 212coastal flooding 215 216-17dunes and dune management 222

225field drainage 142fog 85 86 105forest decline 45-6global warming and agriculture 97groundwater recharge 160habitat loss and fragmentation

69-70heathland decline 42sea-level rise 208-9soil erosion 168-9 170-1 173waste and waste disposal 192wetland drainage 143wind erosion 173

buildingsrestoration 199 200weathering 118 197-200

butterfly habitat loss 69

Californiacliff erosion 210dust storms 172inter-basin water transfers 156subsidence 189see IIUO Los Angeles

266 Index

Cameroon rain forest management in36-7

canals animal migration along 67Canary Islands artificial channel in

179Cape Town air pollution in 109capitalism 13-14carbon dioxide atmospheric 22-3

9396see also greenhouse effect

carrying capacity 4centre-pivot irrigation 160CFCs 93 96 110 113channel straightening 178-80channelization 131chaparraJ 21Chicago

groundwater abstraction 159vegetation changes 51-2

Chinadesertification 30-1nature conservation 61 62-3

citiesair pollution 49 50 52 85 99

102-9 114 115 197-200ancient 5animals 48-9climate 98-101derelict land 49ecological footprint 48environmental improvement 50flood runoff 140 141groundwater depletion 159groundwater recharge 141-2

160-1less developed countries 7stone decay 118 197-200veget1ltion 48vehicle emissions 114115199wastes 192water pollution 49 148-9

clay soils drainage of 144clean air legislation 4485 104clear-felling

and debris ava1anches 188and runoff 136-8

clear-water erosion 128

cliff erosion 210climate

increasing human impact on 83urban 98-101

climate changeadaptation to 240-4aerosol effects 83-9deforestation causing 35 90 91

92and desertification 28-9inter-basin water transfers causing

155land use changes causing 90-2and megafauna extinctions 75-6and savanna development 40and sea-level rise 206-7see also global warming

cloud-condensation nuclei 84-5Clyde River pollution of 148-9coal waste tips 185 186coastal areas

aquaculture 232-4dune management 222-5erosion 208-9 210-14 223-4

225flooding 215-17managed retreat 209212management 235 241marshes 208-9pollution 218-21227red tides 150sea-level rise 206-9seawater incursion 184urban stone decay 197vulnerability 205 206 235

Colorado River regulation of133-5

communism 106see also Eastern Europe

conifer plantations 69conservation 14 58 60-1 62-3

242see also nature reserves

constructioncoral reefs damaged by 230soil erosion caused by 167

contributing factors 15

controlled burning 21coral

bleaching 227eutrophication effects 151

co~ reeamp 226-31crops drought resistant 243cumulative global change 10-11Czechoslovakia urban air pollution in

106

dams 125-31 133-5channel morphology effects 180ecological explosions caused by

65-6landslip caused by 185 186-7salinization caused by 183-4wetlands affected by 57

debris avalanches 188debt-for-nature swaps 34deflation see wind erosiondefoliants 13deforestation 32-7

arid areas 28climatic effects 909192and coral reef degradation 227and debris avalanches 188hydrological effects 136-8and soil erosion 165-7and soil salinization 184see aso afforestation forests

derelict land urban 49 50desertification 26-31

and dust storms 84deserts dune reactivation in 174-7desiccation

inter-basin water transfers causing155-8

and soil salinization 184developing countries

air pollution 104-5aspirations 239urbanization 7

diatoms 117dieback temperate forest 44-7dikes 142 143dimethylsulphide 84-5dinosaur extinction 73

Index 267

dischargeand deforestation 136-8and flood control works 180and land drainage 144regulation by dams 125 133and urbanization 140 180

diseaseand megafauna extinctions 75-6

diseases plantaccidental introduction 65

domestication 4 19dongas 168drainage 142-5

and subsidence 190drainage basin

planning 242stresses and responses to 14-15

drawdown 159-60dredging 132drought

crops resistant to 243planning for 242and soil erosion 172

dry deposition 116dunes

coastal 222-5reactivation and stabilization 30

174-7dung beedes 66dust atmospheric 84dust storms 84 87 155 172-3

earthquakes 190Eastern Europe

air pollution 47 106-7forest decline 45

ecological explosions 65-6ecological footprint 48ecological succession see successioneconomic development stages of 6ecotones wedands as 55ecotourism 12edaphic conditions see soilsE1 Niilo events 227dephants

in savanna ecosystem 41embankments river 131

268 Index

energy renewable 77energy conservation 96energy consumption 8-10environment

naturaJ changes 14systems approach to 14-15

environmental impact of humanactivity

complexity 239increasing scale 8 10-11 12 19trends 8-11uncertainties 1495 120

erodibility 174erosion

coastal 208-9210-14223-4225

dunes 223-4 225land use changes affecting 126

127river regulation affecting 128see also soil erosion

erosivity 174Essex marshes sea-level rise and

208-9estuaries red tides affecting 150Ethiopia river sediment load in 130Europe

forest decline 44see also individual countries

eustatic change 206eutrophication 146 150-3 221evaporation

from forest 136and salinization 183-4

evapotranspiration irrigation and 91-2evolution 58extinctions

global 73and habitat area 60through habitat fragmentation 70

71increasing rate 58 78Late Pleistocene 73-6

falls 187fens 54

drainage 143

feral animals 66fertilizers eutrophication caused by

151field drainage 142 152fire 20-5 77

early usc 3 4in heather management 42oil-well 85 88-9in savanna formation 40soil erosion following 167suppression 21 24systemic and cumulative effects

10-11vegetation adapted to 22 33 40see also smoke

fibacid rain affecting 118 119pollution affecting 148 150 154

fisheries coastal wetland 232-4fishing 205-6 228fishponds 232-4flood control

and channel morphology 180channel straightening for 17880

flood peakltand deforestation 136-7and land drainage 144and river regulation 133

flood protection schemes coastal215217

floodand afforestation 144coastal 215-17and deforestation 138and land use changes 126 127and soil erosion 171urbanization effects 140see aho flood peaks

floodwaters channelization effects on131

flows 187flue gas desulphurization 120fog 85 86 105food chain biological magnification

through 147 218food production 12

see also agriculture aquaculture

forest decline 44-7forest fires 21 22 23 24-5forestry

and surface water acidity lISforests

clearance lee deforestationecological roles 32economic uses 32 37evaporation 136expansion 33fire suppression 21 24fragmentation 69hot spots S9management and protection 37runoff from 136-7soils 165-6Ile alIo trees

fossil fuel combustionand acid rain 117and air pollution 104-8atmospheric carbon dioxide from

93reduction 118IU Iso vehicle emissions

frOSts urban 100fuel domestic poUution from 108-9fuelwood 28 37fungi accidentaJly inrroduced 65Pynbes heathland 64

game management controlled burningfor 21

gardens 52general circulation models 90genetic engineering 76Georgia (USA) land usc and channel

morphology in 180-2Germany forest decline in 44 47Glasgow watu pollution in 14S-9global environmental change 10-11global warming 93-7

adaptation to 240-4and coral reef degradation 227impact on resources 240no regrets policies on 95 96

241-4and sea-level rise 207

Index 269

Gobi Descn 30grassland 39-41

grazing effects 43mid-Iatimde 22origins and maintenance 22 39-41runoff on 136

grazing 43Great Barrier Reef 226 227 229greenhouse effect 83 92-7

III alIo global warminggreenhouse gases 83 92-3

policies for reducing 95 96groundwater

dam construction affecting 186-7groundwater abstraction 159-60

and salinization 183 184and subsidence 189

groundwater recharge 141-2 160-1Gulf War

and coastal pollution 219oil-well fires 85 88-9

gypsum crusts 197 200

habitatschanges in ecological explosions

caused by 65-6edge effects 71heterogeneity loss 71hot spots 59loss and frtgmentation 69-72size 60

halons 110health

air pollutants affecting 85 88 102106 108-9

coastal pollution affecting 220-1ozone concentrations affecting 114policies on 242wastes hazardous to 192 195water pollution affecting 146 147

heat island urban 98-101heathlands 41-2 64

hot spots 59hedgerow removal 169High Plains (USA)

groundwater abstraction 160irrigation effectS on rainfill 91-2

270 Index

Holme Fen Post 143Hoover Dam 133hot spots biodiversity 58 59human environmental impact see

environmental impacthuman life origins of 3humidity atmospheric land use

changes affecting 91hunter-gatherers 4 6 12hunting megafauna ntinctions

through 73-5Hurghada coral reefs in 230-1hydro-isostasy 190hydrocompaction 190hydrological systems suesses affecting

14hydrology

forests 136-8land use changes affecting 126-7river regulation effects 125-35urban 48 140-2

inbreeding 70incineration 194 196inciting factors 15India

plantations 137river regulation 131

Indonesia aquaculture in 232-3Indus River 131industrialization 5-7 12

air pollution 84 105 117coastal pollution 221greenhouse gases 93wastes 145 192water pollution 148221

infiltration capacityforests 136 137urban areas 140

insects introduced 66 67inter-basin water transfers 131-2

155-8and soil salinization 184

Intergovernmental Panel on ClimateChange 93

international agreementson coastal pollution 219

international environmentalconventions 56

introduced species 64-8urban 49 50 51

invasions biological 64-8irrigation

channel morphology effects 180climatic effects 9091-2early developments 5 6 7efficiency 243groundwater abstraction for 159

160inter-basin water transfers for 155-8river regulation for 131salinization effects 28 183-4

islandsbiogeography 70introduced species 65

isostatic change 206 208Israel groundwater recharge in 161

Japan eutrophication in 152 153Java fishponds in 233

Kakadu National Park alien plants in68

karst 189Kenya sustainable environmental

management in 29keystone species 41Kuwait oil-well fires in 88-9

Lagos harbour coastal erosion in213-14

lakesacidification 118artificial ecological explosions in

65-6desiccation 155-8 184sediment cores 117

Lancashire dune management in 225land degradation

through deforestation 138see Iso desertification

land drainage 142-5and nitrate pollution 152and subsidence 190

land-use changeschannel morphology effects 180-2climatic effects 90-2hydrological effects 126-7lee also particular ehangu eg

dc=forestation urbanizationland-use planning 241landfill 192 194 196landforms human impact on 165 167landslides 185-8legislation

dean air 44 85 104watc=r pollution control 148 153

Lesbos coastal pollution in 2211c=ss devdopc=d countries lee developing

countriesLessepsian migration 67Lesset Snow Goose 70 72lignite 106-7limestone

overpumping and ground subsidence189

weathering in buildings 199limestone pavements 8London

building stone decay 199groundwater levds 159 160precipitation 99smog 85

Los Angelesair pollution 104 lOS 106inter-basin water transfers 156subsidence 189vehicle emissions 114 115

Machacos District Kenya sustainableenvironmental management in 29

Malidust storms 87wetland management 57

mammoth 74managed retreat 209212mangrove swamps

aquaculture threats to 232 233234

in coastal flood protection 215Vieblam War effects 13

Index 271

malJuis 22 33marginal land 13marine parks 229 230-1marine pollution 218-21Marsh George Perlcins 83 136

138-9marshes 54

coastal 208-9mass movements hazardous 185-8Mauritania dust storms in 172-3meanders 178Mediterranean area deforestation in

32-3Mediterranean Sea pollution of

220-1megafauna extinctions 73-6metals water pollution from 146metapedogenesis 165 166methane increase in 93Mexico City subsidence in 189migration corridors 243mining

charmel morphology effects 182early developments 5open-cast 10and subsidence 189

Montreal Protocol noMorocco dune stabilization in 175municipal waste 145

Namibia dune stabilization in 176-7nature conservation 62-3 242nature reserves 14 61-3

alien plant species in 68coastal dunes 225marine 229 230-1size 70-1tropical forests 37

Nepal deforesration in 33-4net primary production

human domination and destruction12 13

Niger delta 56coastal erosion 210 213-14wetland management 57

Nile River regulation of 125 128129

272 Index

nitrate pollution 146 151 152nitrogen

in eutrophication process 150 153nitrous oxide emissions 93 1I 7no regrets policies 95 96 241-4non-point pollution sources 145North America debris avalanches in

188North Platte River 180nuclear winter 85nutrient enrichment

algal blooms caused by 218let also eutrophication

nutrientseffects of fire on 22losses under shifting cultivation 22let also nitrogen phosphorus

oceansimportance 205-6limited human impact on 235

oil abstraction subsidence due to189

oil pollution 218 220oil-well fires 85 88-9Olduvai Gorge 3open-cast mining 10osmotic pressure 182overcultivation 27-8overgrazing 28 84Oxford building stone decay in 199ozone layer

role 110thinning 110-14

ozone tropospheric 105 114

Pacific global era 6Pacific Ocean coral reefs in 227 228paired watersheds 136palaeolimnology 117pandas 61 62parasites introduced 66Paris urban heat island in 100 101particulate concentrations urban

102-4 105 106lee also PM 1Os

pastoralists 28

pasNres loss of 69peadands 54

drainage 143 144permafrost subsidence of 189-90Persian Gulf stawater incursion in

184pesticides water pollution by 147pests urban 49pH 116-17Philippines aquaculture in 234phosphate pollution 146phosphorus

in eutrophication process 150153

photochemical reactions 114phytoplankton 150 151piezometric surface 159planktonic algae 84-5plantations 137plants

acid rain damage 118domestication 4introduced 51 52 64-5 68salinization effects on 182-3

Pleistocene overkill 73-5ploughing 168PMI0s 85 88 106point sources of pollution 145Poland

acid rain damage 45dune management and coastal

erosion 224pollutants classification of 145-7pollution

coastal and marine 218-21coral reefs 227and forest decline 45urban areas 49 50Set abo air pollution waste water

pollutionpollution abatement

biotechnology in 77coastal 219 221

population growth 3-4 5arid areas 27 29coastal 205projections 7 60 220

136-8140-2

and sustainable environmentalmanagement 29

see also urbanizationpore-water pressure 186poverty 60power stations

emissions 85 108 118 120thermal pollution 154

prairies urbanization of 51precipitation

global warming effects on 94relationship with vegetation 40see also acid rain rainfall

predisposing factors 15prehistoric extinctions 73-6prescribed burning 21

rain forestsbiodiversity 35 36removal 34-5 90 91 92

rainfallarid areas 27~8 29irrigation affecting 91-2land-usc changes affecting 90

91-2in savanna development 40urban areas 98-9 100 101see also acid rain

Ramsar Convention 55-6reactive adaptation 240 243recreation erosion caused by 223

225Red Sea coral reef degradation in

230-1red tides 150reefS coral 226-31rendzinas 170renewable energy 77reservoirs

channel morphology effects 180evaporation from 183-4size 128thermal poUution effects 154

resource recovery biotechnology in76

respirable suspended particulates(PMIOs) 8588 106

Index 273

rice cultivation 72rills 167-8rivers

accelerated sedimentation 182channel changes 178-82inter~basin water transfers 131-2

155-8 184pollution 145-9 150 151regulation 125-35sediment load 125 128-31 133

178 180set also discharge floods runoff

roads tree dieback alongside 46runoff

deforestation affectingurbanization affecting

Sagan River sediment in 130Sahel dust storms in 87salinization 28 182-5 201

inter-basin water transfers causing155

salt marsh erosion of 208-9sand control of 175-7sand dunes see dunessanitary landfill 192 194 196sanitization 22Saudi Arabia groundwater depletion in

159savanna 20-139-41Scarborough cliff erosion in 210sea-level rise 206-9 235

and coral reef growth 228sea urchins 231seasonal flooding 56 57seawater incursion 184secondary forest uopical 38-9sediment load effect of dams on

125 128-31 133sediment movement coasta 211-12

213sediment transport

straightened channels 178 180sedimentation accelerated 182

following dam construction 129-31seed germination effects of fire on

21-2

274 Index

seedbeds effects of fire on 21-2sewage pollution

coastal 220 227coral reefs 227

sewers 140 141shear strength 186sheet flow 167shifting cultivation 22 38-9ships ocean-going 5

accidental species introductions 66silt

dredging effects on 132effect of dams on 125 128-31

Sinai-Negev region albedo differencesin 90

Sindcanals 131salinization 183

sink-holes 189slash and burn cultivation 22 38-9slides 187slope instability 185-8smog 85smoke

effects 84from oil-well fires 88 89trends lOS

socialist economies 13soil conservation 169174

channel morphology effects 180-2soil erosion middot8

grasslands 43prevention 169 174by water 165-71 180-2201by wind 172-4201see also dust storms

soil formation 165 166soils

acidification 118and deforestation 138drainage 142-5 190and fire 22forests 165-6salinization 182-5 201and savanna development 40tundra subsidence of 190see also soil erosion

South Africamarginal land 13urban air pollution 108-9

South Downs soil erosion on170-1

South Platte River 180Soviet Union

dust storms 172urban air pollution 107

Soweto air pollution in 50 108-9Sphagnum moss 144splash erosion 167squatter settlements 50 108-9steam engine 7Stone Age megafauna extinctions

during 73-5storm surges 216-17stratospheric ozone depletion

110-14stresses drainage basin 15subsidence 143-4 189-90succession

coastal dunes 222in response to fire 24 25in secondary forest formation 38

Suez Canal animal migration along67

sulphate aerosols 85sulphur dioxide emissions 103 104

105 108and acid rain 117and forest decline 45reduction 118 120and urban building decay 200

sunshine trends 105sustainable development 14 239-44

and biodiversity conservation 60cities 50rain forest 34

sustainable environmental managementand population growth 29

swamps 54channelization effects on 131see also mangrove swamps

Swaziland gully erosion in 173synthetic organic pollutants 146-7

218

systemic global change 10 11systems 14-15

tank landscape 131tannery wastes 221technology

agricultural 5 6 7-8 10early human 3

temperate forests decline of 44-7temperature

atmospheric aerosols affecting 8485

landmiddotusc changes affecting 9092

urban areas 98-101see bD global warming

Texas Gulf coast habitat changes on72

Thames River poUution of 151thermal pollution 154-5thermokarst 189-90thunderstorms urban 99Tokyo subsidence in 189tools see technologytourism

and coastal pollution 220 221230

coral reefs threatened by 230-1ecotourism 12

Towyn (Wales) flooding at 216-17trace clements toxic water polluted by

146tractors 10170-1ttaffilt

emissions from 114 115 199urban stone decay associated with

197 199transport 12Transvaal ground subsidence in

189trees

acid rain damage 119beneficial effects 96urban areas 51-2

tropical areasdeforestation 34-5fire usc 20-1

Index 275

savanna 39-41secondary forest 38-9

tropospheric ozone 105 114

ultraviolet radiation 110uncertainty

global warming predictions 95120

in understanding environmentalimpact 14

underdrainage 142United Nations Environment

Programmedesertification data 26pollution control measures 219

urban buildingsstone decay 197-200

urban heat island 98-101urbanization 567 1248

climatic effects 98-101ecological effects 48-52hydrological effects 48 140-2

160-1 180and pollution 49 SO 52 85 99

102-9 197-200and soil erosion 167thermal pollution 154see also cities

USAacid rain 116-17coastal erosion 210 211-12coastal population 205dust bowl 87 172groundwater abstraction 160irrigation effects on rainfall 91-2waste disposal 192

Vaiont Dam disaster 185 186-7vegetation

acid rain effects on 118 119burning 10-11 20-5coastal dunes 222 225destruction through dredging 132dune stabilization through 175fire adaptation 22 33 40human domination and destruction

12 13

276 Index

and precipitation 40river banks 182river regulation affecting 135urban areas 48see Iso forests plants etc

vegetation removalclimatic effects 90-2and dune reactivation 174-5and soil erosion 165-7 172

180-2and soil salinization 184and thermokarst subsidence 190see Iso deforestation

vehicle emissions 114 115 199Venice

building decay 198 200water pollution 221

Vietnam War 13

Walesafforestation and floods 144coastaJ flooding 216-17

Walvis Bay (Namibia) dunestabilization in 176-7

war 13Washington DC urban heat island in

100 101waste

channel morphology effects 182disposal and management 12-13

191-6 201water

importance 125inter-basin transfers 131-2

155-8misdirected efforts at controlling

125soil erosion by 165-71see also rivers

water consumption 125 132 159

water pollution 145-9coastal and marine 218-21control 148 153 219 241thermal 154-5urban 49see also eutrophication

water quality land use changesaffecting 126 127

water resources policies 241water table

falling 142 143 159-60 189rising 160-1 183 184

water-spreading 161watersheds

paired 136see also dC1inage basin

waterways animal migration along67

weatheringby acid rain 118buildings 197-200and slope instability 186

weeds 66West Bay (Dorset) erosion in 211wetlands 53-7

aquacultural usc 232-4conservation 55-6 241drainage 127 142-4ecological importance 53 55 232

wilderness 19 239wind erosion 172-7wind urban 99wood

as domestic fuel 28 37

Yellowstone Park fires 23 24-5

Zimbabwe gullies in 168

Index compiled by Ann Barham

Printed in the United Kingdom byLightning Source UK Ltd Milton Keynes137029UKOOOOI B123-132P