chapter ii review of literature knowledge of geochemistry...
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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-)