Indian Journal of Marine Sciences Vol. 16, December 1987, pp. 235- 239 Trace Element Geochemistry of Modem Deltaic Sediments of the Cauvery River, East Coast of India P SERALATHAN School of Marine Sciences, Cochin University of Science and Technology, Cochin 682016, India Received 13 February 1987; revised received 4 August 1987 In the river channel sediments, concentrations of trace elements (Cu, Co, Ni, Zn, Pb, Ga, V and Cr) increase down- stream, but near the mouth Cu, Co, Zn, Pb and Ga values decrease considerably. This is attributed partly to desorption of these elements from fresh water clay minerals and control of Fe and Mn oxides over trace elements in the estuarine region. Among elements only Ga content shows a gradational decrease from fresh to saline environment. its content shows a 2-3 fold increase in river channel sediments than in marginal environments. Ni distribution does not show any variation in the deltaic sediments except in swamps. Not much variation is found in Cu, Co, Zn and Ga distributions in mangrove, swamps and tidal channel sediments. Pb content in mangrove and swamps is more or less same. Similarly in the marine sediments, trace metals distributions do not show any systematic trend either along or across the coast. Cu, Co, Zn, Pb, Ga and Cr are enriched in river channel sediments attributing the importance of terrigenous supply of traces to the deposition site. V and Ni are concentrated in estuary and swamps respectively. Lowest average concentrations of dements are observed in the following environments: Ga and Cr in marine, V and Zn in swamps, Cu in mangrove. Pb in tidal channels, Ni in river channel and Co both in tidal channels and swamps. Apart from terrigenous supply. oxides of Fe and Mn, organic mat- ter, P and clay minerals playa significant role in the concentration of these metals in the delta. In continuation of earlier reports 1- 4 on the sediments of Cauvery delta in this communication distribution of Cu, Co, Ni, Zn, Pb, Ga, V and Cr and factors con- trolling their distribution are presented. Materials and Methods Details of study area, sampling locations, methods of sampling I, texture of sediments", drainage basin.' and lithological composition of sediments" were same as reported. Representative clay samples were digested with hy- drofluoric and perchloric acids and the solution was used for analysis. Elements were analysed using a Per- kin Elmer 303 atomic absorption spectrometers. Ac- curacy of the analysis was -for Cu and Pb 88%, Co 84%,Ga85%,NiandZn89%andVandCr90%.For calculating correlation coefficients, published data on Fe and P', organic matter? and Mn and CaC0 3 (ref. 4) were usee. Results and Discussion Concentrations of various trace elements are given in Table 1. The inter-relationships (r values) between various constituents are given in Table 2. The follow- ing inferences are made with regard to the distribu- tion of various elements in the delta: (1) In the river channel sediments, all elements increase downstream (upto sample No. 119) but near the mouth ofthe estu- ary concentrations of most elements decrease sharp- ly. (2) Cu, Co, Zn, Pb, Ga and Cr show highest con- centrations in the river channel sediments indicating the terrigenous supply. V and Ni are high in estuary and swamps. Ga and Cr are lowest in marine clays and V and Zn in swamps, Cu is lowest in mangrove, Pb in tidal channels, Ni in river channel and Co both in swamps and tidal channel sediments. (3) In marine clays trace element distribution shows no variation either along or across the coast. Similarly Cu, Zn and Ga distributions in mangrove, swamps and tidal chan- nel and Pb distribution in mangrove and swamps are more or less similar. Ga content decreases steadily from fresh water to brackish/saline environments. (4) Strong positive correlation is shown by Ga, V and Cr with Fe, a moderate positive relation by Zn and Ni with Fe, and marginal relation by Cu and Co with Fe in some environments. Significant positive relation ex- ists between V and Mn but only moderate relation ex- ists between Mn and Ga, Zn and Ni. Organic matter shows a strong relation with Pb, but the relationship ofZn, Cu and Co with organic matter is only marginal. The relationship between P and Cu, Zn, V and Cr is also marginal. Except Ni and Ga, no significant rela- tion is observed between other trace elements and CaC0 3 . (5 )Amajorpart of the trace elements are der- ived from the terrestrial source. The enrichment of trace elements in clay minerals is also significant. The decrease in Cu, Co, Zn and Pb near estuarine mouth is nearly 1 to 2 fold than their contents in up- 235
Transcript
Indian Journal of Marine SciencesVol. 16, December 1987, pp. 235- 239
Trace Element Geochemistry of Modem Deltaic Sediments of theCauvery River, East Coast of India
P SERALATHANSchool of Marine Sciences, Cochin University of Science and Technology, Cochin 682016, India
Received 13 February 1987; revised received 4 August 1987
In the river channel sediments, concentrations of trace elements (Cu, Co, Ni, Zn, Pb, Ga, V and Cr) increase down-stream, but near the mouth Cu, Co, Zn, Pb and Ga values decrease considerably. This is attributed partly to desorption ofthese elements from fresh water clay minerals and control of Fe and Mn oxides over trace elements in the estuarine region.Among elements only Ga content shows a gradational decrease from fresh to saline environment. its content shows a 2-3fold increase in river channel sediments than in marginal environments. Ni distribution does not show any variation in thedeltaic sediments except in swamps. Not much variation is found in Cu, Co, Zn and Ga distributions in mangrove, swampsand tidal channel sediments. Pb content in mangrove and swamps is more or less same. Similarly in the marine sediments,trace metals distributions do not show any systematic trend either along or across the coast. Cu, Co, Zn, Pb, Ga and Cr areenriched in river channel sediments attributing the importance of terrigenous supply of traces to the deposition site. V andNi are concentrated in estuary and swamps respectively. Lowest average concentrations of dements are observed in thefollowing environments: Ga and Cr in marine, V and Zn in swamps, Cu in mangrove. Pb in tidal channels, Ni in riverchannel and Co both in tidal channels and swamps. Apart from terrigenous supply. oxides of Fe and Mn, organic mat-ter, P and clay minerals playa significant role in the concentration of these metals in the delta.
In continuation of earlier reports 1 - 4 on the sedimentsof Cauvery delta in this communication distributionof Cu, Co, Ni, Zn, Pb, Ga, V and Cr and factors con-trolling their distribution are presented.
Materials and MethodsDetails of study area, sampling locations, methods
of sampling I, texture of sediments", drainage basin.'and lithological composition of sediments" weresame as reported.
Representative clay samples were digested with hy-drofluoric and perchloric acids and the solution wasused for analysis. Elements were analysed using a Per-kin Elmer 303 atomic absorption spectrometers. Ac-curacy of the analysis was -for Cu and Pb 88%, Co84%,Ga85%,NiandZn89%andVandCr90%.Forcalculating correlation coefficients, published dataon Fe and P', organic matter? and Mn and CaC03
(ref. 4) were usee.
Results and DiscussionConcentrations of various trace elements are given
in Table 1.The inter-relationships (r values) betweenvarious constituents are given in Table 2. The follow-ing inferences are made with regard to the distribu-tion of various elements in the delta: (1) In the riverchannel sediments, all elements increase downstream(upto sample No. 119) but near the mouth ofthe estu-ary concentrations of most elements decrease sharp-
ly. (2) Cu, Co, Zn, Pb, Ga and Cr show highest con-centrations in the river channel sediments indicatingthe terrigenous supply. V and Ni are high in estuaryand swamps. Ga and Cr are lowest in marine clays andV and Zn in swamps, Cu is lowest in mangrove, Pb intidal channels, Ni in river channel and Co both inswamps and tidal channel sediments. (3) In marineclays trace element distribution shows no variationeither along or across the coast. Similarly Cu, Zn andGa distributions in mangrove, swamps and tidal chan-nel and Pb distribution in mangrove and swamps aremore or less similar. Ga content decreases steadilyfrom fresh water to brackish/saline environments. (4)Strong positive correlation is shown by Ga, V and Crwith Fe, a moderate positive relation by Zn and Niwith Fe, and marginal relation by Cu and Co with Fe insome environments. Significant positive relation ex-ists between V and Mn but only moderate relation ex-ists between Mn and Ga, Zn and Ni. Organic mattershows a strong relation with Pb, but the relationshipofZn, Cu and Co with organic matter is only marginal.The relationship between P and Cu, Zn, V and Cr isalso marginal. Except Ni and Ga, no significant rela-tion is observed between other trace elements andCaC03. (5 )Amajorpart of the trace elements are der-ived from the terrestrial source. The enrichment oftrace elements in clay minerals is also significant.
The decrease in Cu, Co, Zn and Pb near estuarinemouth is nearly 1 to 2 fold than their contents in up-
235
INDIAN J MAR SCI, VOL. 16, DECEMBER 1987
stream (Fig. 1). This decrease may be due to desorp-tion of these elements that are concentrated in fresh-water clay minerals as reported earlier'-'. Anotherreason for the decrease of above said elements nearthe mouth is the partial removal of elements that areassociated with oxides of Fe and Mn when the latterwere removed to the sea by waves and currents beforetheir settlement at the mouth+". In this study mosttrace elements follow the path of either Fe or Mn nearthe mouth (Fig. 1). Therefore, the decrease of tracemetals near the mouth is due to a combined effect ofboth the processes. Ni content does not show muchreduction in the estuarine mouth and the average Nicontent in the estuary is higher than river sediments.A!5reported earlier" since Ni tends to be in solution
SampleNo.
Table I-Trace Element Concentrations (ppm) in Var-ious Sediments
for a longer time, unlike those of Fe, Mn and other ele-ments, it is carried to a longer distance and depositedin the hydrolysed sediments.
Among trace elements only Ga shows a distinctchange from fresh to saline environment. Ga in theriver channel sediments is nearly 2-3 folds highercompared to other environments. Because of this fact
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INDIAN J MAR SCI, VOL. 16, DECEMBER 1987
Ga is considered as a strong indicator for differentiat-ing marine and fresh water sediments". Distributionsof Cu, Co, Zn and Ga do not show any marked varia-tion in mangrove, swamps and tidal channel environ-ments indicating the existence of the same set of phy-sico-chemical conditions. Similarly Pb content inmangrove and swamps is more or less same. In thenearshore sediments trace element distributions donot show any specific trend either along or across thecoast.
Trace elements can be enriched in the delta in var-ious phases. Oxides of Fe and Mn are good absorbentof many trace elements. Krauskopf'? has stated thatCu, Pb, and V are absorbed consistently by hydratedFe203· The adsorption of V onto Fe203and Fe(OH)3is due to the attraction of (H2VOs)3 - and possibly(VO4)3- anions to positively charged Fe(OH)3 sols 11.Similarly Mn02 is a good scavenger of many trace ele-ments in marine and freshwater environments 10,12-15.The control of Fe and Mn oxides over trace elementsin river channel and estuarine sediments is shown inFig. 1. It is clear that the individual elements follow thepath of either Fe or Mn at various places and at about75 km where both Fe and Mn show an upward trend,invariably concentrations of all elements increase.
Cu, Zn, V and to a limited extent Co, Pb, Ga and Crshow a strong to marginal positive correlation with P.Enrichment of Zn, V and other elements in marinephosphate is reportedv":". V'" has nearly the sameionic radius like P' + (o.s9A and o.3sA respectively)which may explain the formation of several isotypicphase for both elements. With CaC03, except Ni andGa, most trace elements show a negative relationshipand therefore the chances of concentration of ele-ment in it may be much less.
Marine organisms are considered to be good ab-sorbents and concentrators of many elements. How-ever, in the delta only Pb co-varies strongly with or-ganic matter. Other elements, except in river channeland a few other environments, show either an insign-ificant positive or negative relation with organic mat-ter (Table 2). However, studies on the concentrationof trace elements in zooplankton from the Bay of Ben-gal" and other places 19,20show the following elemen-tal (av. range in ppm) enrichment: Cu (30-41),Co (1-13),Ni (19-42), Pb (37 -49) and Zn (227 -440). Serala-than and Hartmann" have observed a negative rela-tionship between V and organic matter in the Atlanticsediments, but through chemical leaching they esti-mated an enrichment of 10- 32% V in organic phase ofthe anoxic sediments and about 3-8% V in oxic sedi-ments. In the light of the above findings, it can be attri-buted that a marginal amount of trace metals is boundin organic matter. Negative relation, particularly inthe marginal environments where high organic matter
238
is observed, may be due to the non-availability oftraces for the concentration in organic matter.
Another part of trace elements may be transportedto the delta by clay minerals. According to Wede-phol" clay minerals contain the bulk of Ga. Hirstllhas demonstrated through differential chemicals at-tack that clay minerals such as illite, kaolinite andsmectite transport Cu, Co, Ni, Pb, Ga, V and Cr to thedepositional basin mainly combined structurally inthe lattices of clay minerals. Ni is enriched in smectiteby replacing Mg in octahedral coordination+. Sim-ilarly V is concentrated in illite through the replace-ment of AI and Fe in octahedral layer+', Further,smectite has high exchange capacity specifically forcations such as Cu and Zn in acid and neutral solu-tions". Therefore, even desorption is a major processof removal of traces in brackish and saline environ-ments, an appreciable amount of traces can be en-riched in clay minerals, particularly in smectite, of thefreshwater environment where process of desorptionis not effective.
Trace elements, except Ni and V,are enriched in theriver channel sediments attributing the importantcontribution made by the country rocks to the delta.Several authors have attributed that many elements indepositional environments are controlled by the con-tinental weathering products+-". Further in the Cau-very deltaic clay samples, Ni, V and Cr are highlyabundant than other elements. Concentration ofthese three elements in the delta are much higher thanin Mahanadi deltaic clays?" and in clay fractions of thecontinental shelf sediments between off Madras andHoogly river'". Co, Pb and Ga contents of the Cau-very delta are very much same or comparable withthose areas. But Cu content of the Cauvery delta ismuch less. The richness of Cr in the delta may bemainly due to the occurrence of vast deposits ofchromite such as the Sithampundi complex and theNuggihalli schist belt within the Cauvery drainage ba-sin29,30 and also Cr supply from other rock types(Table 3). In addition the chromite deposits also be-come a contributor of Co, Ni and V (Table 3).Ni con-tent of various rock types is very much significant(Table 3). V on the other hand may be contributedmainly by the titaniferous-vanadiferous magnetiteore bodies of the ultrabasic rocks of Dharwar Systemand other rock types through which the river Cauveryflows. In addition V is preferentially enriched in ironoxide minerals (magnetite, heamatite and ilmenite)and in iron containing silicates (pyroxene and biotite).In the river bed and beach of the Cauvery delta abun-dant opaques (magnetite and ilmenite), pyroxene andto a lesser extent mica contents are reported? andtherefore a part of V is derived from the clay sizedgrade of these minerals as reported earlier".
SERALATHAN : TRACE ELEMENT GEOCHEMISTRY OF DELTAIC SEDIMENTS
Table 3- Trace Element Contents (ppm) in Various Rock Types of Cauvery Drainage BasinElement 1 2 3 4 5 6. 7 8 9 10 11
(1) Nuggihalli schist belt and (2) Sithampundi complex": (3) Granite plutons around Chamundi hill, Mysore!'. (4) Amphibolite, (5) Pyr-oxenite, (6) Basic granulite and (7) Intermediate charnockite of Salem District" (8) Ultramafic rocks of Chalk hill, Salem+'. (9) Basicgranulite and (10)Anorthosite of Oddanchatram, Palani ". (11)Peninsular gneisses around Bangalore "
AcknowledgementThe author expresses his sincere thanks to Dr. A.
Seetaramaswamy. Professor, Department of Geol-ogy, Andhra University, for valuable advice and help-ful criticism.
References1 SeraiathanP & Seetaramaswamy A, Indian I MarSc~8(1979)
9 Keith M L & Degens E T, Researches in geochemistry, (Per-gamon Press, New York) 1959, 38.
10 KrauskopfK B, Geochim CosmochimActa, 9 (1956) 1.11 Hirst D M, Geochim Cosmochim Acta, 26 (1962) 1147.12 MorganJ J & Stumm W,lColloidSci, 19(1964) 347.13 Murray J W, Geochim CosmochimActa, 39 (1975) 519.14 Moorby S A & Cronan D S Geochim Cosmochim Acta, 45
(1981) 1855.15 SeraJathan P & Hartmann M, Meteor Forsch Ergebnisse, 40
(1986) 1.
16 Altschuler Z S, The geochemistry of trace elements in marinephosphorites, Part 1, Characteristic abundances and en-richment-SEMP Spec Pub~ 29 (1980) 19.
17 Mullins H T & Rasch RF, Econ Geol; 80 (1985) 696.18 GeorgeMD&KureisbyTW,lnduml MarSci,8(1979) 190.19 MartinJ M, Limnol Oceanogr, IS (1970) 756.20 SzaboRJ, Caribl Sci, 8 (1968) 185.21 Wedephol K H, Geochim Cosmochim Acta, 10 (1956) 69.22 Hawkins D B & Roy R, Geochim CosmochimActa, 27 (1965)
1047.23 Nicholls G D & Loring D H, Geachim Cosmochim Acta, 26
(1962) 181.24 DemumbrumL E & JacksonML, Soil Sci, 81 (1956) 353.25 Chester R & Hanna R G M, Geochim Cosmochim Acta, 34
(1970) 1121.26 FilipekLH & OwenRM, Chem Geo~ 26 (1979) 105.27 Satyanarayana K, Studies on some aspects of the modem del-
taic sediments of the Mahanadhi River, Indian; Ph. D. the-sis, Andhra University, 1973.
28 Durgaprasada Rao N V N' & Poornachandra Rao M, MarGeoOS (1973) 43.
29 Krishnan M S, Geology of India and Burma (HigginbothamsPrivate Ltd, Madras) 1960,604.
30 Nijagunappa R, Damodaran K T, Suresh B & Somasekar S,4th Indian Geological Congress (Indian Institute of Tech-nology, Bombay) 1984, 135.
31 Babu S K GeolSurv India Special Publication, 12 (1984) 287.32 Rajasekaran K C & Ram Mohan V, Geol Surv India Special
