ag 508 aquatic biology and environment
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Ag 508 Aquatic Biology and Environment
Dr. John A. Finn, Room I1, TOB2 (Agricultural and Food Economics building,
opposite old building of Dept of Agriculture)
Email : j.a.finn@rdg.ac.uk
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AG 508 Aquatic Biology and the Environment
Lent Term (January – March 2000)
Convenor: Dr John Finn Room I1 AgEcon email: j.a.finn
Weeks 1&2 : room I1Weeks 3-10: room AG1L04 (New Building)
Week Date
1 13/1 Lecture Course Introduction. Hydrological Cycle and aquaticenvironment.
2 20/1 Lecture Energy flow in streams.
3 27/1 Lecture Floods and disturbances.
4 3/2 Visit Aquatic Weeds Research Unit, Sonning Farm.
5 10/2 Practical 1. River sampling.
6 17/2 Practical 2. River sampling :
7 24/2 Presentations
8 2/3 Lecture Aquaculture 1.
9 9/3 Lecture Aquaculture 2
10 16/3 Assessment. (50%)
Features of Lotic Environments
Lecture Outline Introduction to aquatic habitats
The hydrologic cycle Influences on streamwater chemistry in
lotic environmentsProperties of lotic habitats
Lecture outcomes• List and describe the dominant features of
stream chemistry• Relate the effects of the atmosphere, lithosphere
and biosphere to stream chemistry• Describe main properties of lotic habitats, and
what factors contribute to their variation in time and space.
Why is water important?
•It is the medium by which plant nutrients are introduced into autotrophic plants
•It is an essential part of living tissue
•It serves as a means of thermal regulation for both plants and animals
•It is the medium by which sediments (a prime source of nutrients) are removed or added to ecosystems
•It covers a large proportion of the Earth's surface
•It provides a range of services for humans
Water as a resource Estimated global demand of freshwater:
• 1950: 1360 km3 • 1990 : 4130 km3 • 2000: 5190 km3
Main water uses• Domestic supply• Industrial abstraction• Irrigation• Diversion between catchments• HEP • Transport• Flood control and storage• water transportation• Biological resources• Recreation and culture
The Hydrological Cycle How much water is there?
Whilst estimates vary between 2.5 and 5.8%, only a few percent of Earth's water is fresh. (...take these estimates of fresh water with a pinch of salt...!).
Of global fresh water, about 70% is locked in glaciers, permanent snow and aquifers more than a kilometre deep (such aquifers are generally considered inaccessible). Roughly 30 % of global freshwater remains as accessible groundwater, generally in either groundwater, streams, rivers or lakes.
The average of 30% of accessible freshwater is not stagnant, and is being driven by gravity and solar energy through a continuous cycle of water down from the air as precipitation and back up again through evaporation and transpiration. i.e. The Hydrologic Cycle
The proportion of water that ends up as stream flow depends on:
weather (arid versus temperate regions; evaporation, transpiration, ppt. held as snow or ice)
soil type and development (dry permeable soil vs moist porous soil)
vegetation slope of the land properties of aquifers
Thus, we see that the boundaries of rivers extend much further beyond the air-water interface and the bed of the river/stream.
Streams and rivers do not just get their water from a number of sources, but the water itself has intimate contact with the atmosphere , vegetation, soil, and rocks before entering the freshwater habitat.
Habitat features of lotic environments
What are important chemical descriptors of freshwater?
temperature, pH, dissolved gasses, suspended and dissolved organic matter, suspended solids, dissolved nutrients (N+P) and dissolved ions
What are important physical descriptors of freshwater?• bank width, water depth, substrate size,
substrate depth, flow rate, bankfull height What are important biological descriptors
of freshwater ?productivity (light penetration, temperature), riparian vegetation, organisms, interrelationships between species
(see Allan 1995, Chapter 2; Moss 1998, Chapter 3)
Water in lotic environments
a number of chemical influences act to change the chemical composition to a greater or lesser degree
These influences primarily include: Solute composition of rainwater Catchment geology Catchment vegetation Effects of human activities Volcanic activity
Solute composition of rainwater
Atmospheric CO2 dissolves to form the weak carbonic acid (natural pH of rainwater = 5.64).
Sea spray can increase concentrations of Na and Cl.
Atmospheric pollution: Sulphur dioxide, nitrogen oxides, hydrogen fluoride etc.
Volcanic emissions
Catchment geology
rocks give most of the inorganic substances that reach freshwaters
about 70% of the surface of the continental crust is covered by sedimentary rocks - they are soluble and readily weather
Extent of chemical change by geology is affected by• the amount of precipitation, • availability of chemical substances• local geology and soils of ecosystems• alteration by humans
Alteration of freshwater chemistry by catchment vegetation
Contributes to the formation of soil Provides a source of nitrogen (nitrogen
fixation provides nitrate for plant uptake, and easily leached into streams
Live and dead biomass forms a store of soluble ions (not leached as readily)e.g Hubbard Brook
Provide organic matter that reaches the streams
Fuller vegetation cover reduces erosion, and entry of silt and suspended solids and provides habitat ‘corridor’
Organic matter may enter waters
Increase in evapotranspiration can reduce the amount of water leaving the stream
Effects of human activities
Agricultural nutrients
Agricultural chemicals
Human settlement
Industry
Habitat simplification/modification
Physical properties of the river habitat vegetation linkage between the catchment and terrestrial
biogeochemical cycles. catchment size, stream size and order pattern of water movement affected by
characteristics such as slope, depth and permeability of soils, and local patterns of precipitation.
hierarchical organisation of patterns and processes
Physical properties (substrate particulate organic matter)
Flows and hydraulics• Discharge and current• Flow and sheer stress• Floods
Spatial and temporal variability in physical properties
Factors important to biota of streams and rivers
(Reference: Allan chapter 3)• 1. Current• 2. Substrate• 3. Temperature• 4. Oxygen• 5. Light• 6. Species interactions
We will look at each of these in turn:
1. Current• Benefits and risks• Organisms can be adapted to fast or slow-water
conditions e.g. caddis larvae• invertebrates have anatomical features that prevent
dislodging• velocity affects substrate size resource supply,and
other env. factors
2. Substrate• There are many kinds of substrates• Slower currents correlated with finer particle
size (as well as others)• But it’s not just size that counts!• Substrate can display high variability• Field surveys indicate importance of substrate to
diversity and abundance of biota in lotic habitats
3. Temperature• affects metabolism• can often set limits to geographical distribution • longitudinal temp change in long rivers • variation in temperature is buffered by aquatic
medium• diel, seasonal and geographical variation;
elevation, shading by/removal of vegetation, groundwater
4. Oxygen• Aquatic organisms have several adaptions for
gaseous exchange• Solubility of oxygen in water is related to
temperature• In unpolluted running water, oxygen usually not
limiting• High temperature, low flow, decomposition of
o.m. contribute to oxygen poor conditions. 5. Light
Summary Rivers and streams arise from that portion of the hydrologic
cycle that is surface runoff. Several factors influence the extent of surface runoff: e.g. climate, vegetation
Many factors act to cause considerable variation in water chemistry between running water habitats. e.g. rainwater composition, geology, vegetation, human influences
Water chemistry and other factors can be of importance to the biota of running water habitats (examples include temperature, oxygen, current, substrate type and light)
Next week: Food webs and energy flow in running water habitats
References (for this lecture in brackets) The biology of streams and rivers. 1998. Giller
and Malmqvist. Oxford University Press. (Chapter 1.)
Stream Ecology. Structure and function of running waters. 1995. Allen, J.D. (Chapters 1& 2.)
Ecology of fresh waters. Man and medium. 1988. Moss, B. Blackwell Scientific. (Chapter 3.)
Natural Ecosystems. 1973. Clapham, Jr., W.B. MacMillan. (Chapter on aquatic habitats.)
How many people can the Earth support? Joel E. Cohen. Chapter 14. Water: a Case Study.
Threats to the World’s Water. Maurits la Riviere. Scientific American, September 1989. Pp 48-55.
Websites http://www.execpc.com/~aqsys/index.html Institute of Hydrology:
• www.nwl.ac.uk/ih/www Aquatic life and ecology interests on the
internet (lists about thirty websites):• http://www.geocities.com/RainForest/
Vines/4301/links.html The Environment Agency (Flood relief scheme,
eutrophication, water demand, groundwater contamination):• http://www.environment-agency.gov.uk/
If you find any other websites that are particularly interesting please send me the address so that I can distribute it. Thanks.
Email: j.a.finn@rdg.ac.uk
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