CHAPTER II

REVIEW OF LITERATURE

Knowledge of geochemistry of estuarine sediments was

limited till the begin ing of 20th century. However, during the latter half

rapid industrial growh and vast urbanization has necessitated the study of

estuarine systems in view of the heavy anthropogenic input into the rivers

and oceans. From then on, there has been a steady flow of information on

the biogeochemical Londition of estuaries the world over with special

reference to accumilation of nutrients and major, minor, and trace

elements in sediments and water.

On the global scale, the bulk of sediments deposited in water

are materials derive from the land. The greater mass of the solid

products of crustal weathering,in comparison with the mass of dissolved

materials carried by rvers and the transport of solids by wind, account for

large materials entering the lakes and oceans. The relative proportion of

the terrigenous and bogenic materials in sediments may vary. The ocean

receives greater amount of terrigenous materials and the rates of

sedimentation are on the increase during the last 40 million years. Lal

(1977) has estimated the total mass of suspended sediments in the ocean

to be around 10' 6 g, most of which supplied by rivers through precipitation

17

under estuarine env .1 Of these, only 5100/o reaches deep ocean

and the rest remains in the shelf including estuaries. Holeman (1968) and

Milliman and Meae (1983) have estimated that about 50% of the

sediment transport occurs within the Indian sub continent.

A host bf investigations carried out on estuaries throughout

the world, merit attenion:

Reeder et al. (1972) Machanzie river

Trefary and Presley (976) - Mississippi river

Duinker and Nolting 1976) - fthine river

Gibbs (1977)— Amazbn and Yukan rivers

Meybeck (1978)— Zaire river

Yeats and Bewer (1982)— St. Lawrence river

Qu and Yan (1990) - hang Jiang and Don Jiang rivers.

Major Irdian rivers too, have been extensively investigated:

Sarin and Krishnaswany (1984) - Ganges and Bhramaputra rivers

Seralathan (1979a and 1987) and Subramanian et al. (1985) - Cauvery

river

Seetharamaswamy (170), Rao et al. (1988) and Ramesh et al. (1989 and

1990) - Krishna river

Biksham and Subramapian (1988) - Godavari river

Paul and Pillai (1983). Nair et al. (1990) and Padmalal and Seralathan

(1993)— Muvattupuzh river.

Estuarine 1 deposits display the transition from fluvial to

marine environments vertically and longitudinally. While there are

numerous studies o the vertical transition within modern, recent and

ancient estuaries, there are relatively fewer studies examining the

longitudinal compo ent of change within a contemporary environment.

Doi-gas and Howar (1975) have studied the indicators of the fluvial

marine transition in Ogeechee river estuary. Thomas et al. (1987) and

Smith (1988, 1989) have modelled sedimentological change along the

fluvial - estuarine reach and have formed the base to develop a

classification of estuaries. Allen (1991) has reported the presence of three

zones within Gironde estuary viz, upper estuary channel, estuarine

channel and inlet. Nicholas et al. (1991) have examined facies within the

tidal James estuary and also divided the estuary into three morphological

compartments from tie bay mouth to the meandering tidal river based on

the fluvial influence in the three zones. Cooper (1993) has argued that

river dominated estuarine morphology is controlled spatially and

temporally by the river and maintains that within this estuary, the central

zone is completely fI vially dominated.

Dairim le et al. (1992) have proposed a conceptual frame

work for estuarine classification based on geological factors and has

opined that estuaries characterize landward movement of sediments

derived from a mar ne source and accordingly classified estuaries as

wave-dominated and tide-dominated. Still, there are a number of

estuarine environments which defy any classification, according to Gibson

et al. (1997).

Sedimentation rates at various estuarine systems have been

studied using Pb21 ° method based on the exponential decrease in activity

with depth (Koide et al., 1972) and radiocarbon dating method (Roy et al.,

1984). Tidal current and river discharge were defined as two variables

19

that most often affect rates of sediment transport and accumulation in

coastal environments (Bopp and Biggs, 1973; Loring, 1978; Trefry and

Presley, 1979 and Hi11 et aL, 1987).

Generally during the monsoon season due to heavy flooding

the accumulation rate of sediments is very high but during the post-

monsoon season, re uspension of minerals occurs owing to shallow water

depth and the prevailing air currents (Jing Zhang et al., 1988). According

to Ridgeway and Price (1987), sedimentary record is an integrated record

of the pollution his ory of the area, taking into account the process of

diagenetic remobiliz tion.

Increased organic carbon preservation in marine sediments is

strongly related to increased sedimentation rate as shown by Henrichs and

Reeburgh (1987), Berner (1989), and Canfield (1989). The increase in

marine organic carbon is due to increase in surface-water productivity

(Pedersen et al., 1990; Calvert and Pedersen, 1992) and increased nutrient

supply (Ruediger Stein, 1994; Nixon et al., 1995).

Anoxic and hypersaline conditions normally result in

enhanced preservati Dn of organic matter, as aerobic degradation is

curtailed and hypersaline conditions greatly reduce bacterial

decomposition of organic matter (Klinkhammer and Lambert, 1989). Sea

floor erosion may be a major source of refractory organic carbon. There

are conflicting evi ences whether organic carbon originates from

allochthonous sources or derived from reworked marine sources.

Quantitative evidences have been presented for the allochthonous origin

of organic carbon f om comparison of primary production and carbon

accumulation ratios (leyenburg and Liebezeit, 1993).

20

Organ] carbon concentration is normally inversely related

to grain size and it increases with clay and silt fraction (Bordovskiy.

1965). The observation of Stefanini (1969) that organic carbon is mostly

associated with clayey sediments rather than silty sediments, was

contradicted by Brambati et al. (1973).

Middelurg (1999) has produced the first evidence for the

black carbon redution of sedimentary organic carbon in marine

sediments.

According to Parrish and Machanthan (1968), organic matter

serves as a pollution indicator and Mare (1942) has opined that it also

serves as a food source for deposit feeding organisms.

In Pelagic sediments, variation in biogenic carbonate content

is mainly controlled by dissolution, dilution and/or productivity changes.

Based on coarse fraction data, the carbonate could be of biogenic or

detrital in origin; however, the latter is of minor importance in pelagic

sediments (Ruediger Stein et al., 1994). In reefal sediments, the carbonate

is deposited as the reefal framework which is supplemented by various

organisms such as coralline algae, molluscs, bryozoans, foraminifera,

echinoderms, brachiopods, and sponges (Milliman, 1974). The

distribution of organic carbon concentration is higher in regions of low

calcium carbonate ^ontent, and the concentration of organic carbon is

influenced to a significant degree by the diluting effect of variable amount

of calcium carbonat (Calvert et al., 1993).

Nitrogn dynamics in the Westerschelde estuary indicates

that nitrification which mainly takes place in water column removes NH4

at a faster rate than its regeneration. Nitrification starts immediately after

the entry of NH 4 into the estuary. About 3 times as much as NO 3 is

21

leaving the estuary ompared to what enters the estuary from the river,

due to denitrificatio (Soetaert, 1995). Moreover, Ogilvie et al. (1997)

have established that nitrification occurs at the sandy mouth and

denitrifi cation at the muddy sediments.

Nagendernath and Mudholkar (1989) have analysed core

samples from Arabian sea as well as Central Indian Ocean - Mn nodule

area and observed t intermediate depths possible denitrification and

unoxidized organic rbon which consumes oxygen and nitrate as primary

and secondary el

in acceptors. Nitrification has been noticed in the

lithologically unifi

upper layers.

Caffrey (1995) has indicated that remineralization rates are

highest during spring when there is a phytoplankton bloom and that the

carbon and nitrogen contents in sediments are positively correlated, the

concentration of NH4 being highest with stations having high

remineralization rates. The sediment - NH 4 adsorption ability as well as

nitrification-denitrifi ation suffer due to increase in salinity as the

bacteria get deactivated (Rysgaard et al., 1999). In the Scheldt estuary,

more than 50% of the carbon and nitrogen entering the estuary are

removed as CO2, C'H 4 and N20 and the rest get accumulated in the

sediments, due to C—N cycling (Middelburg et al.. 1995).

Gillibrand et al. (1998) have established a four fold increase

of total organic nitroen during the past 30 years in the Ythan estuary.

Sahoo al. (1991) have found that the decay of foliage

increases organic n gen and carbon during monsoon season.

General low C/N ratio in areas with high organic carbon

and nitrogen, is indiative of organic matter preservation in clayey silt

22

sediments which is iue to adsorption of organic compounds on the clay

minerals (Muller, 19'7; Rosenfeld, 1979).

Faganeli et al. (1991) have suggested that C/N ratio could not

be used as an index of organic matter source as there is more of organic

nitrogen preservation than the sedimentary organic matter.

According to Ruediger Stein et al. (1994), the relatively high

organic carbon compared to open marine sediments are certainly caused

by the supply of terrgenous organic matter as indicated by high C/N ratio.

The highly varying C/N value between 5 and 20 may be due to the

complex nature of ofganic matter as well as diagenetic alteration (Trask,

1939, and 1953) an the degree of preservation of organic matter is a

function of surface 4ater productivity, rate of falling on the sea floor, and

subsequent alterati

due to oxygenated waters (Tissot and Wette, 1978).

Venk

thnam Kolla et al. (1981) have found that the high

degree of preserv of organic matter along the Indian margin is

primarily due to the impingement of low oxygenated waters on the sea

floor and due to high rate of sedimentation. Paropkari (1979) has also

indicated the enrichment of organic carbon in the sediments of the North

Western continental shelf of India.

Estuarink sediments act as a source as well as sink for

phosphorus which i desorbed under anoxic conditions into the water

column (Maher, 199 ; Larsen et al., 1994) and transferred from water to

sediments (Vaidyana han et al., 1993 and Chambers et al., 1995) under

oxic conditions. Release of phosphorus, under aerobic conditions from

sediments is a functi of pH due to the stabilization of Fe-Al phosphate

(Seitzinger, 1991) t particulate phosphorus being mostly associated with

2 3

Fe and Al as their sesquioxide (Subramanian et al., 1993 and Maher,

1994) as well as with, organic matter (Lobo, 1991).

In the Peal Harvey Estuary and Swan Canning estuary in

Australia, anthropognic phosphorus has increased 5 times in the sediment

and Dissolved Inorgtnic Phosphorus (DIP), 2-3 times, since 1940 (Geritze

et al., 1998). Prastka et al. (1998) have established that DIP levels in

rivers are a regulator of DIP in estuaries and their continuous increase in

rivers can change the source to sink, based on a general study of estuaries.

Calcite plays a modest role in phosphorus distribution in

Ems estuary and mst of the particulate inorganic phosphorus is Fe -

bound. Experiment have revealed that organic coatings on minerals

inhibit phosphate reease at a low redox potential and this phosphate

associated with iroh may be crucial for the seasonal variation of

phosphate in water (De Jonge et al., 1993).

In theganges estuary, phosphorus and silicon show negative

trend, as phosphoris is present in the non-detrital fraction of the

sediments (Subramanjan, 1993).

Padmall and Seralathan (1995) have established the

distribution of phosjhorus more in the silt and clay fractions of the

estuarine sediments compared to that in sand.

Bordovskiy (1965) and Nasnolkar et al. (1996) have viewed

that high correlation of nitrogen with phosphorus indicated their common

source.

A geochemical record of eutrophication and anoxia in

Chesapeake bay sediments indicates the history of the process of

24

eutrophication and organic matter deposition and preservation

(Zimmerman et al., 2000).

Increasing eutrophication would be reflected in high organic

carbon, total nitrogn, and phosphorus in surficial sediments (Muller et

al.. 1979; Paroni et al., 1987; Szefer and Skwarzee, 1988), due to over-

production of autotiophs like algae and cyanobacteria resulting in high

respiration rate and anoxia at bottom waters (Correll, 1998). Such

nitrogen and phosphorus cause non-point pollution (Carpenter et al.,

1998).

Seasonl variation of organic carbon, nitrogen, and

phosphorus contents in surficial and nearshare estuarine sediments have

been observed due to variation in benthic activity (Herndl et al., 1987).

Monsoonal conditiois are characterized by increased productivity, high

influx of fresh water run off, reduction in surface water salinities, and

bottom water oxygen levels, whereas there is high evaporation rates, low

precipitation and ruii off, and well ventilated bottom waters (Michael W.

Howell, 1992).

Decreae in organic carbon, and phosphorus contents

followed by C/N ad N/P increase is due to intense decomposition of

organic nitrogen and phosphorus compounds involving aerobic and

anaerobic pathways ^Faganell and Hendl, 1991).

Doering et al. (1995) have found the N/P ratio around 16,

and that the relative proportion of nitrogen and phosphorus in external

inputs is a function qf hydrodynamic mixing.

According to Ellery Ingall et al. (1990), low C/P values

(<200) are observed in low sedimentation rates and high values (>600) are

25

found with intermediate sedimentation rates and that organic phosphorus

and organic carbon 10 not correlate linearly. Froelich et al. (1982) have

varied with this ob tion and proposed that in marine sediments the

phosphorus concen tion is independent of organic carbon.

Mason and Folk (1958); Friedman (1961,1967,1979):

Visher, (1969); Stapr and Tanner (1975) have used grain size data to

differentiate beach dine and river sediments. The % S102/%Al 20 3 , ratio

has been often used s a grain size indicator according to Henning Dypvik

(1979).

Nordstrom (1977) has used grain size statistics to

distinguish between high and moderate energy environments. Samsuddin

(1986) has determin statistically the significant variation of grain size

distribution between e high water line and the plunge point wherein the

sediments are depositd under different energy conditions, aimed at firmly

establishing the depoitional environment, age and the geological history

of these sediments.

Chan-Ytotai (1994) has established that grain size and

heavy mineral conten in the surface sediments are resulted to present a

changing trend from coarser to fine to coarser and higher to lower to

higher, a scope from land to sea due to leaking river water and by the

shelf's water invasion tt the river mouth.

Kapila Lahanayaka et al. (1981) have confirmed the glacial

environment in the 1Veuda region of Sri Lanka based on grain size

statistics. The 'phi' skewness is more or less zero ranging between slight

positive and slight negtive values.

26

The textural mineralogical and chemical nature of the

estuarine sediments have an important bearing on the environmental

quality of the rive basin, as the chemical composition of marine

sediments is controlled by the relative contribution of particulate

materials derived fr rn different sources. Stevens et al, (1996) have

carried out particle size characteristics of skagerrak sediments and

inferred that the coarse fraction trends are more variable.

Datta et' al. (1994) have studied the GangesBhramaputra

river system and concluded that the extremely fine sand, silt, and clay at

their lower reaches, se ve as potential trap for contaminants.

Padmalal and Seralathan (1995) have indicated the presence

of substantial quantity of Fe and Mn in fine silt and clay fraction due to

increased surface area of finer clastics which enhance absorption ability.

Lambiase (1980) has shown the relationship between grain

size distribution and hydraulics in the macrotidal Avon river estuary

indicating the hydraulic control of sediment distribution. However,

Mclaren (1982) has disputed that grain size distribution need not reflect

either the process of t ansport or the environment of deposition but its

distribution depended on its source and the sedimentary processes of

(i) winnowing (ii) select i ve deposition of the grain size distribution in

transport or (iii) total deosition of the sediment in transport.

Morten Pjrup (1988) has proposed that the conventional

triangular diagram of Shepard (1954) used to classify various sedimentary

facies from estuarine environments is not well suited for the purpose

because the single facies are clustered in an elliptical form and the major

axes are not parallel to any of the lines in the diagram. According to him

the percentage of clay in the mud fraction of an estuarine sediment can be

27

used as a simple indicator of hydrodynamic condition during deposition

(Folk, 1954).

Textural analysis of Tagus estuary sediments has indicated a

highly uniform mud sedimentation but geochemical, mineralogical, and

micropaleantological results indicated climatic and environmental changes

with arithropogenic disturbance (Freitas et al., 1999). Terry et al. (1986)

have described the interplay between the regional onshore geology and

modern as well as past shelf processes in producing clay mineral

assemblages in the sirface sediments of Western Central North Island -

New Zealand and iiferred that the clay mineral distribution patterns

largely reflect their dtrital origin.

Ramamirthy et al. (1979) have confirmed the detrital nature

of clay minerals in the north-west parts of Bay of Bengal, from the

significant presence of quartz in the fine fractions.

In the Connecticut valley illite has been identified as the

major clay mineral

mponent with subordinate amounts of chlorite,

smectite and kaolini

characteristic of the source rocks. Vermiculite

present in a few s pies must have originated either as a detrital

component of the s e or as a degradation product of illite/chiorite.

This could also be du to aggradation of vermiculite, previously abundant

before burial, to illit /chlorite causing uptake of K and Mg2 through

replacing of Fe 3 7Fe 2 , thereby relegated to a rare component (Kazantzef.

1934; Richard, 1981).

Accord]

to Douglas (1977), vermiculite and aluminous

chlorite are widespre

in soils world wide and the soils make a small

contribution to clay m nerals.

Maria Boni et al. (1979) have shown that the degree of

crystallization of ka unite is affected by the microbial changes in the

organic matter. Andres Maldonado et al. (1981) have found that large

proportion of kaolini e is transported by wind and the amount serves as an

indicator of dilution in the South-West laventine sea and low

sedimentation rate.

Study on distribution and transportation of fine grained

sediments off the Cheju Island, Korea has revealed the presence of illite

as the most abundantclay mineral in the sediment even beyond the reach

of terrigenous influence. The distribution pattern of fine grained

sediments not only d pends on regional and onland geology but also local

turbid plume and major ocean circulation (Youn-Jeung-Su, 1996).

Pehlivaiog1ou et al. (2000) have concluded that the

hydrodynamic regime and physical grain size are the main mechanism

controlling the distribution of clay minerals in the Alexandroupolis gulf.

The gechemistiy and mineralogy of marine sediments from

eastern Indian Ocean has revealed the presence of Fe in dual forms, a

terrigenous contribution with Ti and a hydrogenous contribution with Mn,

the clay minerals being common in the terrigenous and pelagic sediments

(Wijayananda et al., 994).

An am

different parts of

(Subha Rao, 1963;

1979; Kalesha et al

Rao et al., 1988) ha

and bed loads of the

of accounts on the distribution of clay minerals in

continental shelf of India along the East Coast

allik, 1976; Rao et al., 1977; Rama Murthy et al.,

1980; Subramanian, 1980; Naidu et al., 1984; and

reported the various clay minerals of the suspended

ajor rivers of India.

29

The and northern parts of Bay of Bengal are shown

to have received th6 products of weathering from the Himalayan region

through Ganges-Bhrimaputra and the sediments are dominated by illite

and chlorite. Whereas the east flowing rivers, Godavari, Krishna, and

Cauvery contribute smectite dominated assemblages, the other rivers

Mahanathi, Bhramani, Vamsadara, and Nagaveli, which drain across the

eastern ghats, are characterized by large quantities of illite, smectite, and

kaolinite (Venkatarathnam and Biscaye, 1973).

Fine fraction mineralogy of the red sediments along the

Vizag-Bhimunipa region off the east coast, reveals the dominance of

kaolinite followed

illite and in addition montmorillonite has been

formed due to d sis of illite. It has been inferred that humid and

tropical to subtrojica1 climate conditions should have prevailed

throughout the late Pleistocene and Hollocene in the region (Durgaprasada

Rao etal., 1980).

A reditribution of K in the bottom sediments of the lake

produces a greater ptoportion of montmorillonite and the process is aided

by the organic aci1s released through the decomposition of bottom

sediments and favo

the diagenetic alteration of illite (El Sabrouti et at.,

1982).

A dethiled study of Visakapatnam shelf sediments to

understand the source areas and the transport path ways of clay minerals

indicates that the variations in the surface circulation prevailing at the

time of deposition of the sediments during the geological past is

responsible for the ;ymmetric distribution of clay minerals (Murthy et

al., 1989).

30

Clay mineral distribution in the Penner delta along the east

coast of India shows a high content of smectite corresponding to the high

clay content in the sediments whereas illite distribution is just reverse and

their distribution depends on selective transport, differential flocculation,

and response to sediment depositional environment (Seetharamiah et al.,

1994). A similar distribution trend was noticed in the Vellar estuary, also

along the east coast of India, where montmori!lonite is the major clay

mineral (Mohan et al., 1992).

Raman et al. (1995) have studied the clay mineral content

between the Mahanathi river in the north and Madras in south along the

east coast of India. Chauhan et al. (1996) have established the presence of

high content of illite and chlorite which are not abundant in the soils of

the south west continental margin.

The dispersal and distribution pattern of clay minerals on the

western continental shelf of India has established a source-rock influence

on clay mineral composition than physical transport ie the south-west

monsoon drift (Nair et al., 1982).

Clay mineralogy of inner shelf sediments off Cochin on the

west coast of India has revealed that a variation of clay minerals from the

source is indicative of size sorting with coarser kaolinite depositing closer

to the source than finer montmorillonite (Reddy et al., 1992).

Clay mineral studies of the Mandovi estuary along the west

coast has confirmed the dominance of kaolinite and gibbsite originated

from the laterites whereas the minor quantities of montmorillonite is

derived from the offshore (Bhukari et al., 1996).

Van Andel (1955) was the earliest to recognize quantitative

mineralogical variation in different depositional environments of the

Rhone river delta by dividing the heavy minerals into marine and

terrestrial groups.

Kulm and Byrne (1966) used relative abundances of heavy

minerals to differentiate marine, fluviatile and marine-fluviatile realms of

deposition in Yaqina bay.

- Glen (1978) and Peterson et al. (1982), have identified the

zones of dominant marine, shoreline and river influence in the Tillamook

bay and Alsea bay respectively. The distribution of heavy minerals in

bays and estuaries should reflect the degree of sedimentary input from the

ocean through tidal transport and from drainage basins that feed the

estuaries through fluvial transport. The degree of fluvial influence in an

estuary relative to other input mechanisms, depends on the location of the

sediments within the estuary and the mass and mode of transport of

sediments by the river relative to other transport mechanisms (Guilcher,

1967).

In the Huelva estuary in Spain, the distribution of clay and

heavy minerals, illite, kaolinite, quartz, feldspar, dolomite, calcite and

aragonite is controlled by grain size, physico chemical conditions of

waters and hydrodynamic factors, with the heavy metals trapped in the

river mouth at elevated levels of concentration (Fernandez et al., 1997).

Henrik Fris (1978) has inferred from heavy mineral analysis

on the marine deposits of Miocene age, that epidote and amphibole grains

have corroded surfaces indicative of post depositional processes. The

variation in heavy mineral distribution and surface textures of that

deposits reveals the mixing of unweathered detritus with weathered

detritus of the same provenance.

Maria Augusta (1979) has identified opaque minerals like

magnetite and limonite, transparent minerals like hypersthene and

hornblende and minor quantities of tourmaline, garnet, rutile etc in the

Rio avandi and Chu] sediments of Brazil. The primary sources of these

minerals are igneous metamorphic rocks.

Xu, Maoquan (1995) has identified 46 kinds of fragmentary

minerals in surface sediments of Minjiang estuary where these minerals

have originated from the weathered and eroded bed rock of the river

valley and are closely related to the hydraulic condition, the land forms,

and topography.

Zhu-Weiging et al. (1991) have analyzed the composition,

main characteristics, content variation, and distinctive features of detrital

minerals, clay minerals and carbonate minerals in the Pearl river delta and

identified the source of sediments and origin of authigenic minerals.

Heavy mineral distribution in modern sediments of Willapa

bay, Washington has indicated the dominance of two mineralogical

assemblages one with almost equal amounts of hornblende, orthopyroxene

and pyroxene with the other dominated by clinopyroxene. These reflect

the relative influence of tidal and fluvial processes on these Late

Pleistocene deposits and suggest that the pattern of sedimentation

resembles that of a modern bay (Gretchen Luepke et al.. 1983).

Heavy mineral reconnaissance off the coast of Apalachi

Cola delta in Florida, has established that the heavy mineral suite within

the delta is composed of opaques, kyanite, staurolite, tourmaline, and

3

zircon with minor quantities of epidote, sphene, amphibole, sillimanite,

garnet, and monozite. It has been postulated that in addition to the

interpretation of grain size distribution, skewness and kurtosis that these

inner sediments are basically fluvial in origin (Jonathan et a]., 1989).

A study of sediments from Sharm Obhur, Saudi Arabia has

revealed that the heavy mineral suite is apparently derived from

metamorphic source rocks with minor contribution from basic igneous

rocks. Moreover, in these sediments, El Sabrouti (1983) has found the

presence of mixed layer chlorite-vermiculite developed during post

depositional diagenesis of chlorite.

Kuwait bay bottom sedimentological studies have

established the polygenetic origin derived from allochthonous terrigenous

materials of onshore desert and autochthonous calcareous fragmentary

shells of various fauna (Khalaf et al., 1982, 1984).

Udayaganesan (1993) has shown that apart from the river

source, additional sources such as off shore and along shore must have

contributed to the heavy mineral composition of Vaipar basin sediments.

Based on the mineral assemblage in the Vellar river estuarine

environment, Mohan (1995) has inferred that the main sources for these

minerals are the different rock types in the catchment area and the

enrichment of some heavy minerals in the nearshore environment suggests

that these minerals are derived from paleo sediments and offshore

sediments.

XRD studies on the carbonate mineralogy of recent

sediments from the western and eastern continental shelves around Cape

Comerin indicate that sediments where benthic foraminifera are the most

3

abundant, are dominated by magnesium calcite between Gulf of Mannar

and Cape Comerin (Hashmi et al., 1982). A similar XRD study of

sediment samples from the western continental shelf of India has

suggested that aragonite is the dominant carbonate mineral and concluded

that no diagenetic change has occurred in the limestone sediments after

their deposition (Nair et al., 1981).

Rajasekaran (1995) has revealed that the contribution of

terrigenous sediments of Palar river basin to the placers is meagre,

thereby confirming a source external to the beaches off this river by

shoreward migration of sediments during rising sea level. A similar

conclusion has been arrived at by Rajamanickam et al. (1995) through a

study of detrital minerals from the sediments of Gadilam river basin.

A study of beach placers between Kanyakumari and

Mandapam has established a density segregation and the nature of

concentration of heavy minerals in various size fractions is suggestive of

the influence of northern drifting currents (Angusamy, 1995).

In the upstream region of Vembanad estuary, Padmalal et al.

(1998) have found the abundance of opaques, amphiboles, pyroxenes,

garnet, zircon, and biotite as major minerals along with monazite, rutile,

and sillimanite as minor minerals and concluded the polycyclic nature of

the sands derived from beach ridges.

Heavy mineral and geochemical studies of Bharathapuzha

sediments in Kerala (Rajendran et al., 1996) have indicated an increase in

their content towards finer sizes and that opaques, hornblende, and

pyroxenes account for 90% variability.

35

Back scattered electron imaging mode in Scanning Electron

Microscope (SEM) has been used by Jennifer (1984) to study

phyllosilicate minerals and conclude that all kaolinite is authigenic and it

occurred as pore filling books of plates.

Padmalal and Seralathan (1994) have revealed using SEM

studies that the Muvattupuzha riverine sands depict only a low amount of

diagenetic tectural features while the Vembanad estuarine sands exhibit a

wide spectrum of surface tectural features which include bulbous edges,

pitted surfaces, and diagenetic dissolution structures.

Heavy metal distribution is determined by current velocity,

proximity to open ocean, percentage of organic carbon, amount of rainfall,

and low energy conditions favourable for deposition of fine grained

organic materials with associated heavy metals (Paul Ramondetta, 1978).

Several workers have revealed that trace metal sediments are

metal-rich and some host economic deposits of metal ores (Gustafson and

Williams, 1981).

Pollution of marine coastal sediments near densely

populated areas by heavy metals has been recorded worldwide in view of

their inherent toxicity. Waste water run off and sewage effluent can be a

major source of metals (Klein and Goldberg, 1970; Appelquist et al.,

1972; Forstner and Muller, 1974; Helz et al., 1975; Papakostidis et al,,

1975; Grimanis et al., 1977; Eganhouse et al., 1978; Galloway, 1979;

Forstner, 1980; Forstner and Wittmann, 1981; Hershelman et al.. 1981:

Warren, 1981; Elsayeed, 1982; Ng and Patterson, 1982; Salomons and

Forstner, 1984; Bryan, 1984; Santschi et al., 1984; Brown et al., 1986;

Stoffers et al., 1986; Seelinger et al., 1988; Gonzalez and Brugmann,

1991; Seidemann, 1991; Li.X., et al., 2000 and Neto et al., 2000).

ffet

Importance of fine grained sediments in determining the

trace metal concentration has been emphasized by a host of researchers

(Salomons and Forstner, 1984; Jing Zhang et al., 1988; Biksham et al.,

1991; Varma et a]., 1993 and ICES, 1995) have established the presence

of heavy metals over coarse sediments too, due to the presence of heavy

minerals and high carbonate content.

The particle size in sediments has a significant role in the

accumulation and exchange processes of metals between sediments and

water which act as an efficient sink for heavy metals (Gibbs, 1977;

Ramamoorthy et al., 1978) as these heavy metals are susceptible to

sorption by clay mineral silicates present in sediments with low organic

carbon but high clay content. However high quartz and kaolinite content,

indicative of the granitic terrain in the river basin, have low sorption of

heavy metals (Allan, 1979).

Generally organic carbon is more associated with fine

grained sediments due to their high surface to volume ratio and absorption

ability (Emery, 1960; Oliver, 1973; Griggs, 1975; de Groot et al., 1976)

through complexation (Rashid and Leonard, 1973).

Enrichment of trace metals over organic matter is revealed

by high correlation between them as well as fine grain size (Narendra,

1993). Metal concentration variability is mainly related to the textural

variability of sediments (Cho et al., 1999).

In the fine grained sediments of Retalax in Finland, Na and

Ca are enriched in sand and silt fractions while Al, Co, Cr, Cu, Fe, K, Mg,

Ni, Ti, and Zn increase from sand to the clay fraction, which are mainly

due to the presence of phyllosilicates (kaolinite, vermiculite, and chlorite)

in this size fraction (1.1 - Deng et al., 1997).

Calvert and Pedersen (1993) have claimed that trace metals

are initially supplied to the site of deposition from terrestrial sources

through rivers as well as from authigenic fraction of the bottom ocean

waters and it is possible to distinguish between the elements from these

two sources.

According to Martin and Meybeck (1979) suspended matter

in rivers act as efficient scavengers for trace metals and the suspended

phase contain a larger percentage of heavy metals than the soluble phase.

The suspended organic matter could catalyze the scavenging ability of

trace metals (Sholkovitz and Copeland, 1981). However, depending on

the depositional conditions, sediments can act as a source or sink for trace

metals dissolved in water and these elements in the sediments need not

necessarily be bound to the sediments. Recycling can occur under

biological, chemical, as well as physical processes (James, 1978,

Carignan and Nriagu, 1985).

Diagenetic reactions involving remobilization of Fe and Mn

are believed to play a key role in trace metals enrichment and transport

because the hydrous oxide precipitates of these elements in the surface

sediments act as scavengers for trace metals (Krauskoff, 1956 Chester

and Aston, 1976). Flocculation of colloids of Fe and Mn oxides and

hydroxides with increase of pH on mixing with saline water, causes

sedimentary deposition of the heavy metals which are adsorbed on the

surface of the hydrolysats of Fe and Mn (Panda et al., 1999).

Jing Zhang et al. (1988) have established that a low

percentage of the Fe/Mn oxides is an index of low contamination in any

estuary, thereby confirming the trace metal scavenging ability of these

metals.

Turner (2000) has evaluated the role of hydrous iron and

manganese oxides in the trace metal contamination in several U.K.

estuaries and established the mean estuarine ratios of Fe/Mn ranging

between ten and hundred.

In the Jiulongjiang estuarine sediments, the transfer of most

trace metals is governed by salinity while the oxides of Fe and Mn control

the trace metals in the off-estuarine region (Chen-Song et al., 1995).

Mn02 acts as a good scavenger of many trace metals in marine as well as

fresh water environments (Murty et al., 1978 and Seralathan et al., 1986).

Peter et al. (1991) have noticed a depletion of Mn as a result

of oxidation of labile organic matter by Fe/Mn-oxyhydroxides resulting in

the displacement of Mn" by Fe and decrease in Mn-oxyhydroxides.

Padmalal and Seralathan (1996) have reiterated that metal scavenging

phases like Fe/Mn hydrolysats, organic carbon and clay minerals are more

in the silt and clay fractions than in sand as they possess larger surface

area.

Anoxic marine sediments in coastal and estuarine

environments are frequently found at depths of a few cm under surface

oxidized deposits. These anoxic sediments, usually sulphide rich, have

been reported to be sites of accumulation of trace metals of pollutant

origin (Manheim, 1961; Gross, 1967; Aston and Chester, 1976).

Concentration of trace metals is found to increase downshore suggesting

tidal deposition (Macky, 1995). Generally along the direction of sediment

transportation, the river influence decreased as inferred by the decrease in

concentration of trace metals (Jing Zhang et al., 1988).

3

Human activities along with hydrological, morphological

and mineralogical factors affect the chemical behaviour and distribution

of trace metals (Surija et al., 1995).

Calvert and Pedersen (1993) have observed that chalcophile

elements like Cd, Ni, and Zn behave as micronutrients, being removed

quantitatively by phytoplankton from the surface waters and liberated

from settling organic matter debris into the upper part of the water

column. These metals along with Cu are added to the sediments by

diffusion from the oxygenated waters (Davies Colley et al., 1984,1985

and Pederson et al., 1989) and precipitated as sulphide under anoxic

conditions under the sediment depth.

Padmalal and Seralathan (1996) have inferred that the

spatial distribution pattern of Cu in the finer fractions exhibits a marked

decreasing trend towards the high saline zones of a tropical estuary.

Cadmium remains mostly in the coarse fraction of sediments

and it shows no correlation with bulk sediment components (Bremner et

al., 1993). Guy and Chakrabarti (1976) have established the low affinity

of this metal for organic carbon, but a high degree of correlation reflected

an indirect control of the production of dissolved sulphide by sulphate

reduction (Pedersen et al., 1989). Low value of Cu in estuaries may be

due to selective biological intake of the metal by aquatic organisms in the

sediments (Lee, 1970).

Rajathy and Jeyapaul (1996) have reported seasonal

variations in the levels of Fe, Mn, Zn, and Cu which were highest during

post-monsoon and lower during pre-monsoon, in the Ennore estuary,

Madras.

BE

Schmidt et al. (1991) have identified a 56 year sedimentary

record in Santa Barbara basin, yielding information on climatic changes.

Concentration of Cu, Ni, Cd, and Pb in bulk sediments has reflected heavy

anthropogenic input and industrial pollution. Accumulation of Cd and Zn

is attributed to the contribution from natural sources.

Trace metal behaviour during summer (pre-monsoon) season

in a stratified Mediter '-estuary indicates that saline water intrusion

along the riverbed formed a thin salt wedge water mass acting as a sink

for most of the trace metals (Scoullos et al., 1996).

Leonordo Leoni et al. (1991) have observed that Pb, Cu, and

Zn are precipitated at low energy zones which act as sedimentary sink for

the particulates. Ni tends to be in solution for a longer time than Fe, Mn

and other trace metals and hence carried to longer distances and gets

deposited (Rankama et al., 1950).

In the Minjiang river estuary, during both high and low

discharges (post-monsoon and pre-monsoon), the increase in dissolved Cd

concentration is found, due to its regeneration from microplankton and

their organic remains (Zou Dong Liang et al., 1996).

Trace metal contamination survey of several coastal

embankments of Nova Scotia by Loring et al. (1996) has indicated that Cd

is the most ubiquitous contaminant far exceeding the background levels.

Similar inferences have been obtained for Scheldt estuary (Zwolsman et

al. 1996).

Chandrasekar et al. (1998) have recorded high

concentrations of Cu, Zn, and Ni along the industrial area of Tuticorin,

attributable to intensified anthropogeni c inputs.

rJ

Heavy metal concentration in macro algal seaweeds from

Tutjcorjn coastal areas indicates the environmental levels of Fe, Mn, Pb.

Zn, Cr, Cu, and Cd in dissolved forms (Venkataraman et al., 1999).

Normally, fluvial sediments exhibit a strong positive

correlation between the clay content and the trace metals, as the latter are

strongly adsorbed on the fine clay particles. Hence the heavy metal

concentration of any sediment should be directly proportional to its Al

content. However many of the trace metals do not show any close

relationship with clay minerals, or Al due to high degree of desorption

under the saline environment. With increase in the concentration of Na,

K,Mg2 and Ca2 , under estuarine conditions, the trace metal

concentration in sediments is found to decrease depending on the ability

of ions to undergo ion exchange and desorption in the order

Hg>Cu>Zn>Pb>Cr (Susan, 1992a).

Ramamurthy et al. (1978) have observed the cation

exchange in the order Hg>Pb>Cu>Cd and that desorption of Hg from

sediments is enhanced by the presence of Cd, Cu or Pb in a higher order.

The competitive exchange between the easily desorbable Fe and Mn with

Na, K, Mg and Ca, causes depletion of these two metals in high saline

areas (Weaver, 1967; Russel, 1970) also due to Eh-pH conditions

(Grahams, 1976 and Evans etal., 1977).

According to Prithivraj et al. (1990) the lack of significant

correlation between clay mineral and trace metals is indicative of

desorption on the surface of clay minerals on entering the marine

environment and Paropkari et al. (1980) have claimed that the desorption

mechanism is aided by the deprotonation on the surface of Fe(OH) 3 by

NaCl.

42

In the Gangolli estuarine sediments, most of the trace metals

except Cu, Zn, Pb, and Ti do not show any association with clay minerals.

They may be due to high degree of desorption in the saline environment

and it appears that the detrital source is the dominant factor influencing

the abundance of clay minerals, since organic matter and calcium do not

show any significant effect on the abundance of clay minerals

(Pandarinath and Narayana, 1992).

In the Lena river estuary in Russia, particulate Cu and Ni are

preferentially associated with organic matter and clay minerals

respectively whereas no significant distribution trend is available for Pb

and Zn, but terrigenous trace metals supply does not appear to be

significantly altered by the transfer processes in summer (Martin

et al., 1993).

Ramesh et al. (1997) have held that Si0 2 , Fe and Al present

in the labile fraction of St. Lawrence Lowlands post-glacial marine

transgressive clays are released preferentially in zero salinity waters and

there is a sharp decrease in their amounts released with increasing

salinity, may be due to the Fe and Al released as colloids of hydrated

oxides.

Kharker et al. (1968) and Richard (1971) have confirmed

that cobalt and copper are substantially desorbed from clay particles when

they are in contact with sea water.

Lars-Goran et al. (1983) have generalized that the Metal/Fe

ratio can be taken as a measure of trace metal concentration in particulate

matter and this ratio decreases from river water to saline water for Cd and

Zn, indicating significant desorption.

)

Bilinski et al. (1991) have observed that Cd is not

practically adsorbed on kaolinite whereas Pb, Cu, and Zn do and at higher

salinities, Cd is released into the water column. Concentration of trace

metals near the mouth of the estuary decreases sharply, (Fuku Shima et

al., 1992); Veer et al., 1992) and Zeuolsman et al., 1996) which is

attributed to desorption of these elements concentrated in fresh water clay

minerals (Kharkar et al. 1968 and Seralathan, 1979a). It is also due to

partial removal of Fe-Mn bound metals which are removed to the sea by

waves and currents before their settlement at the mouth (Seralathan and

Seetharamaswamy, 1987).

Windom et al. (1991, 1999) have observed a mid estuarine

maxima in their dissolved concentration for Cu, Cd, Ni, and Zn due to

desorption from suspended bottom sediments or regeneration and

recycling from degrading organic matter, but biological regeneration is

important only for Cd, in the Patos Lagoon in Brazil. Jayashree et al.

(1995) have noticed a similar trend for these metals in the sediments of

Cochin estuary.

Calvert and Pedersen (1993) have identified two sets of trace

and minor elements which behave differently under oxic and anoxic

conditions, the first being elements like Mn and Cr whose valency can

change as a function of the redox potential, forming insoluble oxides

under oxic conditions having a great affinity for organic matter and the

other category of elements form highly insoluble sulphides of Cd, Cu, Ni

and Zn under anoxic conditions. In areas of rapid sediment

decomposition, sediments become anoxic due to depletion of oxygen

levels and under such reducing conditions insoluble MnO, is replaced by

Mn 2 , soluble (Calvert and Price, 1972).

Nagendernath et al. (1997) have determined the CaCO

content, organic carbon, trace elements and rare earth element

composition of surface sediments collected from across the oxygen

minimum zone in the Arabian Sea and concluded that the high supply of

organic matter might have caused reducing conditions and such conditions

helped the reduction of tetravalent Uranium.

In the sediments of Minamata bay in Japan during the early

sixties, the concentration of Hg shot up to 713 ppm, dry weight (Fujiki,

1973) and Kitamura (1968) has reported it to be as high as 2010 ppm.

According to Bloom ad Ayling (1977) sediments from the Derwent

estuary contained 1130 ppm Hg and 862 ppm Cd.

In the Tagus estuary, Hg has a value 20 times the natural

background value and the level is uniform in all three segments which

may be due to the mixing of older uncontaminated sediments or a

mobilization process from the river particulate matter to the dissolved

phase. As the metal associated with suspended particulates is more easily

mobilized than that in the sediments, the estuary may act as a source for a

long time to influence the levels in water, biota and sediments (Fig.ueres

et al., 1985).

The presence of chlor-alkali plants along the estuarine sites

is found to be the most important contributor to Hg in sediments

(Fimreite, 1970; Jens M. Skei, 1978). Though the emission of Hg from a

chlor-alkali plant has receded from 105g ton - ' to Ig ton 1 , the decrease has

not been reflected in the surface sediments or biota even after 12 years

(Hava Hornrung et al., 1989).

The upper Spencer gulf contains about 150 ppm Cd and 8

ppm Hg in the dredged harbour sediments (Tiller et al., 1989). Charles

im

(1986) has reported a high concentration of 130 ppm for Cd which is

positively correlated with Zn, having a maximum of 11,000 ppm

indicating a common source in the Corpus Christi bay.

Concentration and reactivity of Hg in sediments is

determined by the type of sediment (Thomas, 1972), grain size (Cranston

and Bucklay, 1972), redox conditions (Burton and Leatherland, 1971)

bacterial activity (Verner and Thomas, 1972) and organic content

(Lindberg and Harris, 1974).

Lack of significant correlation between organic carbon and

Hg in sediments indicates that the metal is not organically bound with

sediments even though both accumulate in the saline region (Cranston,

1976).

Hg residues in organisms though primarily depend on

sediment concentration, are also influenced by complexation with

particulate organic matter which reduces the bioavailability of the metal

and in effect, organic carbon has a limiting effect of Hg on species

(Langston, 1986).

The reactive forms of Hg viz, methyl mercury and dimethyl

mercury formed due to remineralization after sinking to the sediments, is

found on the surface waters of North Atlantic in the colloidally bound

form (Mason et al., 1998). Mercury speciation studies in the water

column and sediment pore waters in the St. Lawrence estuary has

indicated that total mercury in sediment pore waters is ten times as high as

methyl mercury levels (Cossa et al., 2000).

Sequential extraction studies have been used in the recent

years for estimating the relative bonding strengths of metals in different

ITIO

phases with sediments and soils (Gibbs, 1973; Tessier et al., 1979, 1982;

Kersten and Forstner, 1988).

According to Togwell (1978), leaching experiments

indicated that equilibrium concentration of metals leached from sediments

increases if the sediments are allowed to dry out for long period of time

before the conduct of leaching experiment and may be due to the

oxidation of minerals by air to compounds that are more readily soluble.

Bothner et al. (1980) have reported that low concentration of acid

leachable Cr, Zn, and Cu are characteristic of an uncontaminated area of

coarse grained sediments. Herbert et al. (1984) have established that

strong acid leachable (SAL) concentration of Fe, Mn and Co do not show

any relationship to Al and that the regression of Cu and Ni against Al in

both SAL and total digests are parallel, suggesting that these two metals

are not enriched in either fraction and their concentrations are controlled

by natural processes.

Cosmo et al. (1982) have identified stations with maximum

organic carbon, Cr, Cu, and Pb which show an elevated percentage of

extraction with acid leaching and reducing agents and that these metals

exhibit a significant correlation with organic carbon but not with Fe,

confirming the origin of these metals from independent sources of

probable anthropogenic nature.

Arakel (1992) has shown that the carbonate phase

representing the part of trace metals bound to the original or secondary

carbonate is the bioactive phase of the metals and that the reducible

fraction represents the Fe/Mn-oxide-hydroxide bound metals which are

mobile under acidic and reducing conditions and is the important criterion

deciding the pollution status of the area.

47

Chemical partitioning of heavy metals in the Pearl river

estuarine sediments has indicated that residual fraction was the dominant

phase for Zn, Cu, Ni. and Co and among the non-residual fractions, Zn, Ni

and Co were mainly associated with the Fe-Mn oxide carriers (Li-

Xiangdong et al., 2000).

Chandrasekar (2001) has carried out sequential extraction

studies in suspended sediments of salt marsh creeks adjoining Tuticorin

harbour and concluded that most of the leachable fractions of Fe, Cr, Cu,

Cd, Zn, Ni, and Pb are present in an acid-labile form.

Analytical speciation procedure through chemical sequential

extraction is helpful to deduce sedimental diagenetic processes in a

tropical estuary where Nair et al. (1993) have established the selective

accumulation of Mn and Ni in the carbonate bound fraction and the easily

reducible Co, Cr, and Fe below detectable levels. Esad Prohic et al.

(1987) have suggested a similar distribution pattern for Pb and Cu in

sediments with Zn and that Zn is largely anthropogenic and immobilized

through coprecipitation with carbonate confirming the detrital nature.

However, the distribution pattern of Pb and Cu in the carbonate and

reducible fractions has indicated a common source.

Mats Astrom (1998) has studied the mobility of Al, Co, Cr,

Cu, Fe, Mn, Ni, and V in fine grained sulphide sediments through strong

acid leaching followed by extraction with ammonium acetate and H202,

indicating high mobility for Fe and Al, extensive leaching of Co, Mn and

Ni, moderate leaching of Cu; and limited leaching of Cr and V.

Panda et al. (1999) have observed that Mn, Zn and Co are

the dominant trace metals in the carbonate phase bound to the non-

lithogenic fraction, since Mn 2 having close ionic radius with Cal

48

replaces the latter in the lattice sites of calcite and the easily reducible

Mn/Fe fraction is the most dominant phase with high scavenging ability

for Fe, Mn, Ni and Cr.

Miliward et al. (1999) have carried out a two stage sequential

extraction which removed non-detrital and detrital metals. Gerritse et al.

(1998) have observed that the concentration of acid extractable Zn, Cd,

Pb, and Cu in the surface sediments of Peel-Harvey estuary increases year

by year.

Lutz Brugmann (1988) has indicated that only a low

percentage of Cd was leachable by 0.5N HCI, proving the excessive

sulphidic nature of the metal and concluded that it was still nearly

impossible to isolate anthropogenically accumulated trace metals from

those due to post depositional redistribution.

Hava Hornung (1989) and Balls et al. (1997) have used

normalization technique to infer the metal concentration in an estuarine

environment which can reflect the background levels or contaminated

levels by comparing these levels with that of a non-polluting conservative

element such as Fe. Forstner and Wittmann (1981) have also established

the use of Fe as a conservative element. In sedimentalogical studies of

Chesapeake bay (Heltz et al., 1985), the metal has been used as a

conservative element and for calculations to characterize polluted marine

sediments (Lee et al., 1998). Sven Blomquist et al. (1992) have shown

that normalizing metal concentrations to a reference constituent such as

Fe suggests the decline in the trace metal concentration of the Baltic bay

sediments, primarily due to dilution. Calvert and Pedersen (1993) have

used Al as normalizer, assuming that it is located entirely in the

Aluminosilicate lattices in the clay.

Ruiz et a]. (2000) have normalized trace metals using organic

content and concluded that both natural and man-induced processes

account for the rise and fall of contamination pattern of Cd, Co, Cu, Pb,

Zn, Cr, Fe, and Ni in the Bilbao estuary.

Normalization of absolute concentration of trace metals to

Al, illustrates a stable distribution of metals in the estuarine mixing zone,

according to Jing-Zhang (1999) in the Yangtze river estuary.

Normalization using Al is reported to have been used to minimize grain

size effect thereby distinguishing fine sediments from surface sediments

as well as natural sources from anthropogenic sources (Cho, et al., 1999

and Sharma etal., 1999).

Nagendernath et al. (2000) have concluded that Upper

Continental Crust (UCC)-normalized patterns of three sub-environments

viz. fluvial, brakish and marine are identical in the Vembanad lake along

the south west coast of India. They have also ascertained the weathering

trends of the sediments using the chemical index of alteration (CIA) to

quantify the degree of weathering.

Lithium has been used as an ideal normalizer (Loring,

1990), since it is a conservative lattice constituent of fine grained

aluminous silicate minerals with which most metals are associated.

Aluminium normalized enrichment factors indicate the

pristine nature of the Sabine-Neches estuarine sediments in Texas

(Ravichandran et al., 1995) and the lack of enrichment attributed to low

salinity, short residence time and possibly strong complexation of trace

metals with organic matter especially Cu. High M/A1 ratios have been

reported in the carbonate rich sediments in the shallow regions with high

temperature and salinity (Basham et al., 1998).

50

Rajendran et al. (1996) have reported high values for

enrichment factors of Cd and Pb whereas those of Cu, Zn, Cr and Mn are

close to background values. Abu and Ghrefat (2001) have calculated

enrichment factors and anthropogenic factors for Yarmouk river

sediments which indicate that they are moderately contaminated with Ni,

Co, Zn and Pb but strongly to extremely contaminated with respect to Cd.

Assessment of heavy metal pollution in the monsoon - dominated

environment near Karwar, south west coast of India, through enrichment

factor and geo accumulation index calculations has revealed that most of

the heavy metals are within the background level (Manjunatha et al.,

2001). Iron normalized enrichment factors are in the order

Kcd>Kpb>Kc l,>Kz T, reflecting the presence of authigenic sediments of US

origin (Sun-Huili et al., 1993). The values range between 35 and 171 for

Co, Cu, Zn, Ni, Al, Pb, and Hg, indicating high pollution levels in the Ria

de Huelva estuary (Perez et al., 1991).

Ergin et al. (1991) have calculated and compared the

enrichment factor for various heavy metals spread with major estuaries

world over and has established that Golden Horn estuary has high levels

of metal pollution due to anthropogenic influences. Panda et al. (1995)

have carried out geochemical fractionation of heavy metals in Chilka lake

sediments and attempted to assess the pollution status of the lake through

calculation of Geo accumulation Index (lgeo).

In the Ganges - Bramaputra - Meghna drainage basin, for

most of the heavy metals, lgeo lies below zero indicating unpolluted

sediment quality, but the lower reaches indicate higher concentration of

non detrital fl-action of heavy metals due to the presence of petroleum

refinery, mining and industrial effluents and agricultural run off (Dilip et

51

al., 1998). The Yamuna river sediments are reported to be moderately to

very highly polluted with Cr, Ni, Cu, Zn, Pb and Cd in the Delhi and Agra

urban centres, based on Muller's geoaccumulation index calculations

(Munendrasingh, 2001).

Hamouda and Wilson (1989) have expressed the pollution

status of Libyan coast line in terms of Pollution Load Index which was

around ten for most of the areas indicating a clean environment.

Numerous studies on sediments have reported positive

relationship between trace metal concentration and loss on ignition (LOl)

as shown by Ryding and Borg (1973); Garrett and Hombrook (1976);

Edgren (1978); Turekian et al. (1980); Di Giulio and Scanlon (1985); and

Krumgalz and Fainshtein (1991). However, Sven Blomqvist et al. (1992)

have observed the reverse, years after the setting up of the sewage

treatment plant to check the concentration of Cu, Fe, Pb and Zn, in the

surface sediments of Baltic bay near the point of effluent discharge. Craft

et al. (1991) have observed a positive correlation between LOl and

organic carbon content.

Togwell (1978) has indicated that partitioning of heavy metal

between sulphide and organic matter occurs in sediments and the

proportion of sediment bound metal decreases in the order

Hg>Cd>Cu>Fe>Zn.

Nagendernath et al. (1989) have established five important

sources viz. detrital, hydrogenetic - diagenetic, biogenic, sea salts and

dissolution residue for major and minor elements of the Mn-nodule-

bearing central Indian basin sediments, through R-mode factor analysis.

52

Natural waters contaminated with trace metals tend to be

purified by natural processes leading to their accumulation and

immobilization in bottom sediments, due to : (1) Plankton blooms which

act as scavengers (Nicholls et al., 1959: Goldberg. 1965: Martin, 1970;

Andelman, 1973; Craig, 1974, de Groot et al., 1975) and (2) the binding

of the metals by sulphide and organic matter in fine grained anaerobic

bottom sediments (Miller, 1950; Krauskopf, 1956; Hutchinson, 1957;

Manheim, 1961; Szalay, 1964; Goldberg, 1965; Manskaya et al., 1968

Thomas, 1972; Jernelov and Lann. 1973; Rashid, 1974; Nissenbaum,

1976).

Bilinsky et al. (1991) have established self purification of

Kirka river as Pb, Zn, Hg and Cu, are adsorbable on kaolinite clay which

is high for Pb, Zn and Hg but lesser for Cu and little for Cd.

Gota alv estuary in Sweden has a high accumulation rate for

Zn and Hg close to the outlet of a sewage treatment plant and decreases

by a factor of 5 for Zn and a factor of 2 for Hg in the outer estuary (Brack

et al., 2001).

Dariusz Ciszewski (1998) has discussed various channel

processes as a factor, controlling accumulation of heavy metals in rivers

of Poland and concluded that the smallest variation in heavy metal

concentration in the homogenous, fine grained bank sediments which are

trapped by plants below water level, is a feature which is recommended as

the most suitable for monitoring of river pollution.

5-)