38050441

441

Geochemical Journal, Vol. 38, pp. 441 to 453, 2004

*Corresponding author (e-mail: [email protected])*Present address: Department of Geology and Geophysics, SOEST,University of Hawaii, Manoa 712 POST, 1680 East-West Road.,

Honolulu, HI 96822, U.S.A.

Copyright © 2004 by The Geochemical Society of Japan.

Sediment geochemistry of the Yamuna River System in the Himalaya:Implications to weathering and transport

TARUN K. DALAI,1,2* R. RENGARAJAN2 and P. P. PATEL3

1Ocean Research Institute, University of Tokyo, Tokyo 164-8639, Japan2Physical Research Laboratory, Ahmedabad - 380 009, India

3M.S. University of Baroda, Vadodara - 390 002, India

(Received October 23, 2003; Accepted March 24, 2004)

Bed sediments of the Yamuna River and its tributaries in the Himalaya (Yamuna River System, YRS) have beenanalyzed for major elements and trace metals (Sr, Ba, Ni, Cu, Co, Zn, Pb and Cr). These results have been used to charac-terize chemical weathering and transport in the Himalaya, to assess relative mobility of elements during weathering and tounderstand heavy metal association. Concentrations of major and trace elements of YRS sediments vary between 20 and50%. In general, elemental variability reduces when data are analyzed individually for the major rivers, suggesting thattributaries draining diverse lithology contribute significant variations. Comparison of sediment chemistry with composi-tion of source rocks and average Upper Continental Crust (UCC) suggests significant loss of Na, K, Ca and Mg fromsource rocks during weathering, the degree of loss being more for Ca and Na. Chemical index of alteration (CIA) for YRSsediments averages at 59, indicating that weathering in the basin is of moderate intensity. This inference is also supportedby major ion chemistry of YRS waters and is attributed to steep gradient and enhanced physical erosion in the basin.Available results seem to indicate that Na and Sr are effectively more mobile than Ba, which is thought to be a combinedeffect of higher solubility of Na and Sr, and the affinity of Ba to be adsorbed onto solid phase. Heavy metals showsignificant positive correlation with Al and weak correlation with Fe, Mn and P. These observations suggest that metalconcentrations are controlled mainly by clay mineral abundances, and that Fe-Mn oxides and organic matter may beplaying less significant role. Heavy metal concentrations of YRS sediments are lower than those of suspended particulatesof the Yamuna river, presumably due to higher clay mineral abundances in the latter. Strong association of metals with Al,and lower metal concentrations in bed sediments compared to suspended matter underscores the importance of sedimenttransport and mineral sorting in influencing the YRS sediment chemistry. Enrichment factor and geo-accumulation indexcalculated for heavy metals in YRS sediments suggest that they are mainly of natural origin and that anthropogenic activi-ties exert little influence on their abundances.

Keywords: Yamuna River, Himalaya, chemical weathering, sediment chemistry, elemental mobility

ing the Himalaya (Krishnaswami et al., 1992; Sarin etal., 1992; Pande et al., 1994; Galy and France-Lanord,1999; Dalai et al., 2002a, 2002b, 2002c, 2003). Thesestudies are based mainly on isotopic and major ion com-position of dissolved load of rivers. Available geochemicalstudies of river sediments in the Indian Himalaya includereconnaissance survey of the Ganga and the Yamuna(Subramanian, 1987; Jha et al., 1990; Chakrapani andSubramanian, 1996; Subramanian and Ramanathan, 1996;Ramesh et al., 2000) and the Indus (Ahmad et al., 1998).Geochemical studies of sediments in the headwaters ofrivers in the Himalaya are limited.

The river Yamuna, draining the southern slopes of theHimalaya in its upper reaches, is the largest tributary ofthe Ganga (Negi, 1991). At the confluence, water dis-charge of the Yamuna is one and half times that of theGanga (Rao, 1975). The Yamuna and its major tributariesin the Himalaya constitute the Yamuna River System

INTRODUCTION

The rivers draining the Himalaya contribute signifi-cantly to the global sediment and water discharge(Milliman and Meade, 1983). They have recently attractedattention of several workers because of the possible con-nection between chemical weathering in the Himalaya andglobal climate (Raymo and Ruddiman, 1992) as silicateweathering is thought to be a global sink for CO2 on geo-logic time scales (Walker et al., 1981; Berner, 1995). Sucha hypothesis has led to a number of studies on rivers drain-

442 T. K. Dalai et al.

(Negi, 1991). This work, which builds on our earlier stud-ies (Dalai et al., 2002a, b, c), forms a part of detailedgeochemical and isotopic investigation of the YamunaRiver System (YRS) in the Himalaya. Reported here arethe concentrations of major and trace elements insediments of the Yamuna and its tributaries in theHimalaya. Results obtained in this study, in conjunctionwith those available on bed rocks in the basin and dis-solved load of the YRS (Dalai et al., 2002a, b), are usedto (i) characterize chemical weathering in the YRS basin,(ii) assess relative mobility of elements during weather-ing and transport, and (iii) determine the origin and asso-ciation of heavy metals in river sediments.

SAMPLING AND ANALYSIS

Riverbed sediments were collected from the Yamunamainstream and its tributaries (Fig. 1) during October1998. Details of the sampling and analysis are given inDalai (2001) and Dalai et al. (2002a, b). Samples werecollected in zip-lock polythene bags using a plastic scoop.In the laboratory, they were oven-dried at ~90°C andsieved to <1 mm size using nylon sieves. The <1 mm size

fractions were powdered either in an agate mortar or in aSpex ball mill with acrylic container and methylacrateballs, and were sieved to <100 mesh size using nylonsieves. Samples >100 mesh size were repeatedly pow-dered to bring all the materials to <100 mesh size. Dur-ing powdering, care was taken to ensure that samples didnot come in contact with any metal surface. After thor-ough homogenization, powdered samples were stored inclean plastic bottles. About 500 mg of sample wasweighed and dissolved in PTFE dish by repeatedly treat-ing with hot HF-HCl-HNO3-HClO4 mixture and finallydissolving in 1N HNO3. These solutions were used forelemental analysis after suitable dilution. Some sampleswere digested in replicates and analyzed to assess the pre-cision of measurements. Reagents used for sample disso-lution were analyzed to assess their blank contribution.USGS rock standard (G-2) and an in-house laboratorystandard (NOVA, prepared from the Pacific sediments,Agnihotri, 2001) were also dissolved along with the sam-ples and analyzed to check the accuracy of the measure-ments. Ca, Mg, Al, Sr, Ba, Fe, P, Ti, Pb, Zn and Cr weremeasured by ICP-AES (Jobin Yvon 38S), and Na, K, Mn,

11

4

3 1

2 6

532 9 8

1214

2122 25

20

3031

29

2826

27

Hanuman Chatti

Tiuni

KuwaNaugaon

Barkot

Dehradun

Minas

Dakpa tharPaonta

Sahib

Sampling LocationsTowns

Pabar R

Yam

una R

.

Tons R.

Aglar R.

Asan R.

Bata R.

Giri R. Am

law

a R

.

N

Yamun

a R

30 49’0

78 13’077 50’0 E

30 11’0 N

Tons R.

To Saharanpur ( # 33)

Yam

una R

.

Barni Gad13

Puro

la R.

Shej Khad

Batamand i

1819Pali G

ad

Ka lsi

Purola

GoduGad

Didar Gad

Mori

Tons R.

68o 76o 84o 92o

32o

24o

16o

Area ofStudyNew Delhi

Yam

una R

.G

an

ga R

. Ganga R.

Ta jewa la

Mussoorie

INDIA

Fig. 1. Map showing sediment sampling locations in the Yamunaand its tributaries in the Himalaya. Fig. 2. General lithology of the YRS drainage basin. Only some

of the tributaries are shown.

Dehradun

Ka lsi

Minas

Tiuni

Kuwa

Naugaon

Barkot

Yam

una R

Tons R

Tons R

Giri R

Aglar R

Yamuna R

Amlawa R

Crysta llines

Carbonates

Other Sedimentaries

0 15 km

N

Barni Gad

Hanuman Chatti

Mussoorie

Yamun

a R

Purola R

77 50 E0

78 130

30 110

30 490 N

Shej Khad

Mori

Purola

Kuthnaur

HI GHERHI MALAYA

LESSERHI MALAYA

LH-HH boundary

Sediment geochemistry of the Yamuna River System in the Himalaya 443

Cu, Ni and Co by flame-AAS (Perkin Elmer 4000). Car-bonate contents were determined by coulometric titration.Powdered samples were treated with 40% ortho-phosphoric acid for 10 minutes at 70°C in the extractionunit coupled to the Coulometer (UIC Coulometer 5012).The evolved CO2 was swept to the titration cell of thecoulometer after being passed through columns contain-ing activated silica gel and anhydrous MgClO4. Carbon-ate contents were calculated assuming that evolved CO2is produced from CaCO3.

Blank corrections were <2% for Zn, Pb, Cu and Ni,and negligible for other elements. Precision and accuracyof the measurements of major elements (Na, K, Ca, Mg,Al, Fe), carbonate content, Sr and Ba were within about±5% (Dalai, 2001; Dalai et al., 2002a, 2002b, 2003). Av-erage precision was ±8% for P, ±15% for Zn and ±10%for other metals. Analysis of USGS reference rock stand-ard G-2 and the laboratory standard NOVA shows thatbetween the two standards, measured metal concentra-tions of NOVA agreed better with their reported values(Table 1). However, measured Co concentrations of boththe standards were ~30% higher than the reported val-ues.

LITHOLOGY OF THE DRAINAGE BASINS

In its upper reaches, the river Yamuna drains highgrade granite-gneisses and schists of the HigherHimalayan Crystallines (HHC, Fig. 2). Occurrence ofcarbonates is less common in HHC, however, these rocksare reported to contain impure limestones and calc-silicates (Bickle et al., 2001 and references therein). Theserocks have schistose graphitoid quartzites (Gansser, 1964)and graphitic/carbonaceous schists (Valdiya, 1980;Sharma, 1983). There are reports of calc-schists and mar-ble in regions upstream of Hanuman Chatti which con-tain sulphide mineralization (Jaireth et al., 1982). As the

river flows past the Higher Himalaya, it drains quartz-ites, conglomerates, slates and carbonaceous phyllites.Further downstream, it flows through massive dolomiticlimestone and marble of Mandhali and the Deoban For-mations of the inner belt, and limestone and dolomite ofKrol Formation of the outer belt in the Lesser Himalaya.These carbonates are often associated with carbonaceousand gray slate. Barite occurs in silisiclastic sediments ofNagthat Formation in the Tons river section (Sachan andSharma, 1993), and as pockets and veins in the lowerhorizons of Krol l imestone at Maldeota andShahashradhara (Anantharaman and Bahukhandi, 1984).Southwest of Kalsi (Fig. 2), the Yamuna flows throughthe Siwaliks comprising of channel and floodplain de-posits formed by Himalayan rivers in the past.

In the Himalaya, the Yamuna drains an area of ~9600km2 and has average annual water discharge of ~10.8 ×1012 liter at Tajewala (Rao, 1975; Jha et al., 1988; Fig.1). The discharge and drainage area of the Yamuna atTajewala is similar to that of the Bhagirathi and theAlaknanda (at Devprayag) prior to their confluence toform the Ganga. Among the tributaries of the Yamuna,the Tons is the largest, which originates in the HigherHimalaya and merges with the Yamuna at Kalsi where itswater discharge is twice that of the Yamuna (Rao, 1975).Other major tributaries: the Asan, Giri, Bata and Aglar(Fig. 1) originate and flow through the Lesser Himalaya.

The Yamuna basin in the Himalaya, particularly itsupper reaches, is not significantly influenced by agricul-tural and human activities. Terrace agriculture is limitedto a few locations in the lower reaches. The impact ofland use pattern and agricultural practices on water andsediment chemistry of the Yamuna and its tributaries,therefore, is likely to be minimal. Earlier studies fromour group have shown that decadal variation in major ionand Sr concentrations of the Yamuna waters is only within30–40% and about ±20% respectively, suggesting that

Table 1. Results of analysis of reference standards G-2 and NOVA

*Reported value from Potts et al. (1992).**ICP-AES and ICP-MS data of NOVA from Agnihotri (2001).n.m.: not measured.

G-2 NOVA

Element Measured Reported* Measured ICP-AES** ICP-MS**

Cu 10.13 12 407 ± 2 392 ± 20 403Ni 20.7 ± 0.9 13.7 244 ± 1 206 ± 15 224Co 33.95 20.7 134 104 ± 7 101Ti n.m. n.m. 3787 ± 234 3810 ± 245 4076P n.m. n.m. 2009 ± 87 1875 ± 34 1702Cr 5.89 ± 0.11 9 61 ± 2 63 ± 4 84Zn 77 ± 2 85 137 ± 5 152 ± 10 146Pb 23.3 ± 0.4 31 33.4 ± 1.2 n.m. 35.5


Tabl

e 2.

M

ajor

and

tra

ce e

lem

ent

conc

entr

atio

ns o

f Y

RS

bed

sedi

men

ts

n.m

.: n

ot m

e asu

red.

b.d

.: b

e low

de t

e cti

on.

Car

b.:

c arb

onat

e c o

nte n

t. N

a, K

, C

a, M

g, A

l an

d c a

rbon

ate

data

fro

m D

alai

et

al.

(200

2a).

Ba

data

fro

m D

alai

et

al.

(200

2b).


Tabl

e 3.

Var

iabi

lity

in m

ajor

and

trac

e el

emen

t con

cent

rati

ons

in th

e be

d se

dim

ents

of t

he Y

RS,

Yam

una

mai

nstr

eam

and

the

Tons

Stat

isti

c al

anal

y sis

for

Ca

and

Mg

doe s

not

inc

lude

dat

a of

Agl

ar r

ive r

(R

S98-

8) w

hic h

has

44%

car

bona

te i

n it

s se

dim

e nt.

C.V

. v a

lue s

are

rou

nded

off

.


anthropogenic activities and land use pattern have notsignificantly impacted the river water chemistry (Dalaiet al., 2002a, 2003).

RESULTS AND DISCUSSION

The concentrations of major elements (Na, K, Ca, Mg,Al, and Fe in weight %; Mn, P and Ti in µg g–1), carbon-ate content (weight %) and trace elements (Sr, Ba, Ni,Cu, Co, Zn, Pb and Cr, in µg g–1) are presented in Table2. Data for some of the major elements and Ba were ear-lier reported in Dalai et al. (2002a, b). In order to ob-serve general variability in the sediment chemistry of theYRS, statistical parameters of the data (arithmetic mean,standard deviation and coefficient of variation) were cal-culated (Table 3). The Yamuna and the Tons are the twolargest rivers draining major part of the YRS basin. Hencestatistical analysis was also done separately for these tworivers; the results are shown in Table 3.

The concentrations of major and trace elements varyby 20 to 50% for the YRS. Coefficient of variation ismaximum (45–50%) for Ca, Mn and Ni, ~35–40% forMg, Fe, Cr and Cu, and is within ≤30% for other ele-ments. It can be seen that variations in the elemental con-centrations, calculated separately for the Yamuna and theTons, are reduced when compared with the YRS as awhole. This seems to suggest that contributions from thetributaries draining multilithologic terrains may introducesignificant variations to YRS sediment chemistry. For theYamuna sediments, Fe and Mn show maximum scatter(~33 and ~23% respectively) whereas other elements have<20% variation. For the Tons sediments, the coefficientof variation is the highest for Mn (~56%), 24 to 33% forFe, Zn, Ca, Mg and Ni, and <20% for the rest. Comparedto the Tons sediments, the average concentrations of Ca,Mg, Ti and Ni in the Yamuna sediments are higher whereasthe opposite holds true for Sr, Ba, Fe and Mn (Table 3).

Major elementsAmong the major elements, Na, K, Fe and Al show no

systematic downstream variation, whereas carbonate, Caand Mg show higher abundances in the lower reacheswhere Precambrian carbonates is a major lithology of theYRS catchment.

In order to determine inter-relation among the majorand trace elements, multiple regression analysis was car-ried out, results of which are given in Table 4. Amongmajor elements, Na, K, and Fe show positive correlationwith Al; correlation coefficient being the highest for theK-Al pair (0.73, Table 4). Ca and Mg show weak nega-tive correlation with Al. These trends suggest that con-centrations of Na, K and Fe of YRS sediments are sig-nificantly controlled by clay mineral abundances that areprogressively diluted by quartz content. Due to physical

Tabl

e 4.

C

o-v a

riat

ion

mat

rix

for

maj

or a

nd t

rac e

ele

me n

t c o

nce n

trat

ion

of Y

RS

sedi

me n

ts


transport and hydrodynamic sorting, many of the majorand trace elements are known to be associated with clayand fine silt fractions of sediments and suspendedparticulates of rivers, whereas quartz is usually abundantin the sand fractions (cf., Tebbens et al., 2000). The re-sults obtained for YRS sediments, as discussed above,thus underscore the importance of transport processes inregulating the elemental abundances of river sediments.Large scatter in Al-Ca and Al-Mg plots may be caused bycontributions from detrital carbonates. Mn shows signifi-cant positive correlation with Fe which is suggestive ofMn-Fe association in oxide phase.

The Yamuna and its tributaries, as mentioned earlier,have major part of their drainage basins in the LesserHimalaya. Comparison of element abundances in the YRSsediments with those in the granites/gneisses in the LesserHimalaya suggests that the Na, K, Ca and Mg have beenlost from bedrocks during weathering. Since riversediments are composite weathering products of all thelithologies in the catchments, major element concentra-tions of sediments were normalized with those of the av-erage Upper Continental Crust (McLennan, 1995). Nor-malization of elemental concentration of river sedimentswith those of the UCC is a common approach to assessthe elemental mobility during weathering and transport(Taylor and McLennan, 1985). In YRS sediments, theUCC normalized ratio for most of the major elements is<1 (Fig. 3). This would suggest their loss from sourcerocks during weathering and transport. Exceptions to thistrend are P and Ti, which have UCC normalized ratiosclose to 1. This observation seems to support the ideathat Ti is relatively immobile during chemical weather-ing. On the other hand, P may have contributions fromland-derived organics and/or productivity in rivers. Al-though average value of UCC normalized ratio for Mn is

0.75, it is difficult to distinguish it from 1 due to the largeerror (Fig. 3). Figure 3 also shows that Na and Ca havesuffered the highest loss, consistent with the knowledgethat they are relatively more mobile in the natural aque-ous environment (Nesbitt and Young, 1982; Berner andBerner, 1996; Gaillardet et al., 1997). Degree of Ca andMg loss from source rocks, as evident from comparisonof YRS sediments with UCC, could be more than the ac-tual value due to the presence of detrital and/or authigeniccarbonates in bed sediments. A significant part of the YRScatchment in the lower reaches comprises of Precambriancarbonates, especially the massive dolomites. Wide oc-currence of limestone and dolomite in the basin, togetherwith the observed co-variation of Ca and Mg (Table 4)and significant positive correlations of carbonate contentwith Ca and Mg (Fig. 4), support the idea that the car-bonates in YRS sediments are mainly of detrital originwith little contribution from calcite precipitation. Thoughmany of the YRS waters are supersaturated with calcite,evidence for calcite precipitation in the YRS has not beenobserved (Dalai et al., 2002a). Galy et al. (1999), basedon Sr- and C-isotopic studies of bed carbonates and sedi-ment carbonates of the Narayani river in the NepalHimalaya, also observed that carbonates in the riversediments are mainly of detrital origin.

Comparison of elemental ratios in silicate source rockswith those in sediments provides an opportunity to as-sess their relative mobility during weathering and trans-port. Average Ca/Na ratio (molar) in YRS sediments is~0.75 which is higher than the average values of 0.46 inLesser Himalaya silicates, 0.32 in Higher Himalaya sili-cates and 0.15 in granites from Hanuman Chatti andSayana Chatti (Krishnaswami et al., 1999; Dalai et al.,2002a). Higher Ca/Na in bed sediments, however, canarise either due to higher mobility of Na relative to Ca or

0.00

0.25

0.50

0.75

1.00

1.25

UC

C n

orm

aliz

ed r

atio

Na K Ca Mg Al Fe Mn P Ti0

2

4

6

8

Ca, Mg (% wt.)

Car

bo

nat

e (%

wt.

)

Ca-Carb.

Mg-Carb.

Fig. 3. Upper Continental Crust (UCC) normalized ratios (con-centrations of the river sediment/concentration of the UCC)for major elements in YRS sediments. Calculations of mean andstandard deviation exclude data of the Aglar river. Data forUCC are from McLennan (1995).

Fig. 4. Scatter plot of carbonate contents with Ca and Mg inYRS sediments. Significant positive correlations suggest a com-mon phase for them, such as carbonates and plagioclase min-erals. Data for Aglar river (RS98-8) not plotted.


due to presence of authigenic and detrital carbonate insediments. It is also important to examine if transportprocesses also influence the abundances of Ca and Na inriver sediments. Given that Ca and Na are relatively moresoluble and have low affinity for particles, their concen-trations in sediments are less likely to be affected by proc-esses such as exchange and adsorption. Thus, mineralsorting can influence abundances of Ca and Na in riversediments only through quartz dilution. However, the ef-fect of quartz dilution is cancelled out when the ratio Ca/Na is used. Thus, comparison of Ca/Na of carbonate-freesediments with that of source rocks can avoid complica-tions of mineral sorting and presence of carbonates insediments. YRS sediments free of carbonates have aver-age Ca/Na molar ratio of 0.44 ± 0.14 (based on data offive samples with carbonate content below detection limit,Table 2), which is ~3 times higher than the average valueof 0.15 ± 0.13 in granites from Hanuman Chatti andSayana Chatti (Biyani, 1998; Dalai, 2001; Dalai et al.,2002a). Similarly, average Mg/Na ratio (molar) ofcarbonate-free sediments is 0.51 ± 0.16, much higher com-pared to 0.15 ± 0.08 in granites from Hanuman Chattiand Sayana Chatti. Such observations, though based onlimited data set, are suggestive of higher mobility of Naover Ca and Mg during weathering and transport of sili-cates in the YRS basin. This is in line with the existingknowledge on relative elemental mobility (Berner andBerner, 1996; Gaillardet et al., 1997) and is consistentwith the observation that a major part of Na in YRS wa-ters is derived from silicate weathering (Dalai et al.,2002a).

Average Al content of YRS sediments (4.7 weight %)is much lower than that in the upper continental crust andin average sediments (8.04 and 7.1% respectively,McLennan, 1995). Intense weathering in river basinsyields high clay content and Al concentration in the riverparticulates and sediments. Lower Al concentration wouldindicate that chemical weathering in YRS basin is not sointense, although this might have been partly caused bymineral sorting. Chemical index of alteration (CIA) ofYRS sediments (Nesbitt and Young, 1982) provides asemi-quantitative measure of the degree of silicate weath-ering in the river catchments. CIA is given by:

CIA = [(Al2O3)/(Al2O3 + CaO* + Na2O + K2O)] × 100,(1)

where CaO* represents CaO of the silicate fraction(Nesbitt and Young, 1982). During chemical weatheringof silicates, more soluble cations i.e., Ca and Na are re-leased to solution, leaving Al in the residual products suchas clay. High intensity weathering results in high abun-dances of clay and consequently high Al in sediments.Thus, higher CIA would indicate intense silicate weath-

ering. Assuming all carbonates in YRS bed sediments areCaCO3, the calculated CIA values for YRS sediments havea range of ~51 to 69 with an average of ~60 (Dalai et al.,2002a). Such calculations do not take into account of anycontribution of Ca from phosphates. The knowledge thatcarbonates in the YRS catchment comprise of both lime-stones and dolomites suggests that a part of carbonatewould also be from dolomites. Precambrian carbonatesfrom the Lesser Himalaya have average Ca/Mg weightratio of 2.9 (Singh et al., 1998). Assuming this is alsovalid for Ca/Mg ratio in bed carbonates, the CIA for indi-vidual samples decreases only marginally, with an aver-age ~59 (Dalai et al., 2002a). It is seen that CIA valuesfor YRS sediments in the lower reaches are generallyhigher, which suggests relatively more intense weather-ing because of abundant vegetation, and higher soil CO2and temperature. In the lower reaches, contact time ofwater with the reacting minerals is likely to be longerdue to shallower gradient. However, the average CIA inYRS sediments is lower than that in average shale, 70–75 (Nesbitt and Young, 1982) indicating that chemicalweathering of silicates in the Yamuna basin in theHimalaya is not so intense. This is also borne out fromlow values of dissolved Si/(Na* + K) molar ratio (aver-age 1.6) in YRS waters (Na* is sodium corrected for con-tributions from cyclic salts and halites using dissolvedCl as an index; Dalai et al., 2002a). Available studies onclay mineralogy of the Yamuna river sediments nearMussoorie in the Lesser Himalaya show that they con-tain abundant illite with minor kaolinites (Subramanianet al., 1985; Sarin et al., 1989), also suggestive of incipi-ent silicate weathering. Relatively lower values of CIAin the Indus River bed sediments (48–52) and suspendedmatter (60–65) led Ahmad et al. (1998) to infer that ero-sion and physical weathering regulate sediment chemis-try of the Indus. In the Himalaya, physical erosion is en-hanced by tectonic activity, steep gradient and monsoonclimate. As a result, the rock particles are flushed awaydownstream rapidly before they are chemically weath-ered considerably. Dalai et al. (2002a) also observed thatphysical weathering is one of the driving factors forchemical weathering in the Yamuna basin in the Himalaya.

Strontium and bariumAlkaline earth metals such as Sr and Ba are known to

be relatively mobile in natural oxic and aqueous environ-ments (Dupre et al., 1996; Gaillardet et al., 1999). Srconcentration of YRS sediments ranges from ~45 to 156µg g–1 (mean: 75 ± 22 µg g–1) and shows no definite down-stream trend. This range and mean are lower than thosein the Precambrian carbonates in the Yamuna basin (range:33 to 363 µg g–1, mean: 162 ± 120 µg g–1, Singh et al.,1998). Four granites collected in and around HanumanChatti (Fig. 1) and those from Sayana Chatti (Biyani,


1998) have Sr in the range of 76–153 µg g–1 with a meanof 105 ± 25 µg g–1. The Upper Continental Crust (UCC)normalized ratio for Sr in YRS sediments averages at0.21 ± 0.04 (Fig. 5). The average Sr/Al ratio (µg g–1/weight %) of YRS sediments, 17 ± 8 is much lower thanthat for the UCC, ~44 (McLennan, 1995). It is borne outfrom all these comparisons that Sr is lost from bed rocksduring weathering. In YRS sediments, Sr shows signifi-cant positive correlation with Ca and Mg (Table 4) sug-gesting that it is associated mainly with plagioclase andcarbonate minerals.

Ba concentration of YRS sediments ranges from ~200to 550 µg g–1 (mean 371 ± 95 µg g–1, Table 2) and showsno distinct downstream trend. Four samples of granitescollected in and around Hanuman Chatti in the HigherHimalaya (Fig. 2) have Ba concentration in the range of~120–400 µg g–1 (Dalai et al., 2002b) with a mean of307 ± 126 µg g–1, which is indistinguishable from thatfor YRS sediments. The UCC normalized ratio for Ba inYRS sediments averages at 0.66 ± 0.16 (Fig. 5). It istempting to infer from this ratio that there is overall lossof Ba during weathering of bed rocks. If source rocks inYRS basin have a wide range in Ba concentrations, theabove interpretation may seem over simplified. However,based on a detailed geochemical investigation Dalai etal. (2002b) inferred that silicates in the YRS basin are animportant source of dissolved Ba in many of the rivers.The mean value of Ba/Na (nmole µmole-1) in four gran-ites of the upper Yamuna basin is 1.4 ± 0.6 whereas Ba/Na ratio in bed sediments averages at 5.6 ± 1.5 (exclud-ing data of three samples RS98-8, RS98-11 and RS98-31, which have anomalously high Ba/Na ratios, 10.4–24.2). The average Ba/Na of five carbonate-free samplesis also nearly the same. It is also seen that the averageBa/Na in sediments of rivers draining the HHC (5.2 ±0.3, n = 4) is nearly the same as those for rivers flowingthrough the Lesser Himalaya (5.6 ± 1.7, n = 19). Thus,

the results show that Ba/Na of YRS sediments are a fac-tor of ~4 higher than that measured in granites of theYamuna basin. If these data are representative of the en-tire basin, then higher Ba/Na in sediments relative to thosein granites would suggest preferential release of Na overBa during weathering. This inference is based on thepremise that the HHC granites/gneisses are the dominantsource of these sediments. At present there is no data totest if this assumption is valid. However, Derry andFrance-Lanord (1996) concluded that the HHC is thedominant source of the Bengal Fan sediments. It is, there-fore, likely that the YRS bed sediments are also derivedmainly from HHC. Measurements of diagnostic isotopeproxies are required to confirm this conjecture. Compari-son of Ba/Sr in granites from the upper Yamuna basinwith those in carbonate-free bed sediments also allowsdrawing similar inferences. Ba/Sr of granites of HanumanChatti is about a factor of two lower than that incarbonate-free sediment samples. Assuming that the da-tabase is representative of the entire YRS basin, it indi-cates that Sr from granites is preferentially released overBa.

In addition to higher mobility of Na and Sr, their pref-erential release over Ba can also be understood in termsof weathering resistance of host minerals of Ba and theaffinity of Ba to be associated with solid phases duringweathering and transport. Due to their similar ionic radii,Ba substitutes for K in feldspars and micas (Wedepohl,1972; Nesbitt et al., 1980; Gallet et al., 1996). Given thatK-bearing minerals are relatively more resistant to chemi-cal weathering (Berner and Berner, 1996), release of Bafrom them is likely to be relatively restricted. There issignificant positive correlation of Ba with K and Al inYRS bed sediments (Fig. 6; r2 = 0.69 and 0.68 for Ba-K

0

1

2

3

UC

C n

orm

aliz

ed r

atio

Sr Ba Cu Co Ni Zn Pb Cr

Fig. 5. Upper Continental Crust (UCC) normalized ratios (con-centrations of the river sediment/concentration of the UCC)for trace elements in YRS sediments. Calculations of mean andstandard deviation exclude data of Aglar river (RS98-8). Datafor UCC are from McLennan (1995).

Fig. 6. Scatter plot of Ba with K and Al in YRS sediments.Significant positive correlations (r2 = 0.69 for K-Ba and 0.68for Al-Ba) are suggestive of association of Ba with K-aluminosilicates such as clay minerals. Regression analysisexcludes data of the Aglar river (RS98-8, data point encircled).


and Ba-Al regressions respectively, excluding the sam-ple from river Aglar). It is well known that Ba is retainedin clays and Fe-oxyhydroxides during weathering andtransport (Wedepohl, 1972). This property of Ba is knownto regulate its dissolved concentrations of rivers and itsflux to oceans (Hanor and Chan, 1977; Li and Chan,1979). During weathering of alkali feldspars, release ofBa to solution is limited due to its retention in the weath-ering profile possibly via exchange with clays (Nesbitt etal., 1980). Association of Ba with clay minerals of streamsediments was also observed for the Amazon River(Vital and Stattegger, 2000). The relative importance ofthese two mechanisms (resistance of K-Al silicate min-erals to weathering vis-á-vis retention of Ba in solidphases during transport) in regulating the abundance anddistribution of dissolved Ba in YRS waters and sedimentsis difficult to assess from available information. How-ever, studies on weathered granites indicate that K is fixedonto clay surfaces even after complete weathering of K-feldspars (Nesbitt and Young, 1982). Earlier work onweathering profiles in the Middle Hills of the Himalayashowed that K and Mg were retained in clays of the soilprofile after their mobilization from bedrocks (Gardnerand Walsh, 1996). It is observed that Ba concentrationsof carbonate-free YRS sediments, in general, are eithersimilar to or higher than those in granites. All these ob-servations, coupled with the knowledge that silicates arean important contributor to dissolved Ba of YRS waters(Dalai et al., 2002b), seem to indicate that adsorption ofBa onto particles, after its release to solution, is likelythe dominant mechanism in regulating Ba abundances ofYRS sediments and waters.

Heavy metalsAverage heavy metal concentrations of YRS

sediments, except for Pb, are lower than those reportedfor the surficial sediments of the Yamuna main channel(Ramesh et al., 2000). Cobalt concentrations of the YRSare higher than those reported by Ramesh et al. (2000)even after considering that its concentration might havebeen overestimated in this study. The samples studied byRamesh et al. (2000) are from the Yamuna at Dakpatharnear Dehradun till its flow in the plains near Allahabad.In the plains, the Yamuna receives contributions fromtributaries draining mainly the basaltic terrains. Thus, thevariation in metal concentrations of the river sedimentsmay be due to source rock characteristics. Furthermore,sediments in the plains are likely to have anthropogeniccontributions whereas this study focuses on the headwaterregion of the Yamuna and its tributaries. The upper reachesof the YRS being remote and minimally affected by agri-cultural activities, trace metals in sediments are likely tobe mainly of natural origin (see later discussion).

In YRS sediments, heavy metals (Cu, Cr, Co, Pb and

Zn) show positive correlations among themselves (Table4) suggesting that a common mechanism regulates theirabundance. This, coupled with the observation that thesemetals also show co-variations with Al (Table 4), leadsto infer that occurrence of Al-rich phases such as clayminerals exert significant control on abundances of met-als. Trace metal concentrations of YRS sediments showvery weak correlation with Fe, Mn and P (except Zn whichcorrelates positively with Fe, r = 0.52; and Co whichshows a weak positive correlation with P, r = 0.36, Table4). Phosphorous is known to be associated with ferricoxides/hydroxides and organic matter in river sediments(Berner and Rao, 1994). Jha et al. (1990) observed a sig-nificant co-variation between organic C and P in theYamuna river sediments. In the present study, co-variation of heavy metals with Al and absence of the samewith P, Fe and Mn suggest that these metals are mainlyassociated with clay fractions and that their abundancesare not significantly influenced by the presence of organicmatter and/or Fe-Mn oxides. Strong association of met-als with Al-rich phase demonstrates the role of sedimenttransport and mineral sorting in influencing the distribu-tion of metal abundances of YRS sediments. Ramesh etal. (2000) also observed that finer grain size and claymineral abundances in surficial sediments of theHimalayan river system control metal accumulation inthem. The role of particle transport and sorting is alsoevident from comparison of chemical composition of sur-face sediments with those of suspended particulates ofthe Yamuna river. The heavy metal (Cr, Cu, Ni, Zn andPb) concentrations of the Yamuna river sediments (Table2) are lower than those reported for total suspended mat-ter of the river at Baghapat (the most upstream point ofsampling in Jha et al., 1990). Suspended particles are finerin size and have higher abundances of Al and clay miner-als. Relatively higher metal contents in the suspendedmatter compared to bed sediments would also support theidea that these metals are mainly associated with the clayfraction. Contributions from basaltic lithology and pos-sible anthropogenic contributions in the plains may alsoexplain part of the difference in metal concentrations ofbed sediments and suspended matter observed in two dif-ferent studies.

Among the heavy metals, UCC normalized ratios forCu, Zn and Pb are less than 1 (Fig. 5). This can be be-cause of loss of these metals from bed rocks during weath-ering and/or less abundance of clay (and Al) in bedsediments compared to that in UCC. For Cr and Ni, UCCnormalized values are indistinguishable from 1 withinerrors. However, normalized ratio for Co is higher than 1(this will be valid even after accounting for over estima-tion of Co) suggesting that it is supplied to sediments fromnon-lithogenic source(s).


Evaluation of metal pollutionMetal concentrations in river sediments is a net result

of variability in source rock composition, sediment tex-ture, redox reactions, adsorption/desorption, sedimenttransport, mineral sorting and anthropogenic activity.Contributions of metals to sediments from non-lithogenicsources can be gauged by calculating their enrichmentfactors (EF). EF is given by:

EF = (X/Al)sample/(X/Al)shale. (2)

Such estimation minimizes dilution effects caused byvariable matrices such as quartz. For calculation of EF,we have used the composition of Post ArchaeanAustralian Shale (PAAS, Taylor and McLennan, 1985).Distribution of EF for heavy metals is shown in Fig. 7. Itcan be seen that Co, Zn and Pb are enriched in YRSsediments relative to PAAS whereas other metals do notshow clear enrichment. A value of EF ≤ 2 can be consid-ered to be of lithogenic origin for a metal whereas EF > 2is suggestive of sources such as biogenic and anthropo-genic (Grousset et al., 1995). Metals analyzed in thisstudy, except Co, have EF ≤ 2 suggesting that they aremainly of natural origin. This inference is consistent withthe finding of Dalai et al. (2002a) that anthropogenic ac-tivities have not significantly impacted major ion chem-istry of the Yamuna waters over decadal time scale. It hasalready been mentioned that Co may have been over esti-mated in this study by about 30%. If higher EF for Co inYRS sediments is indeed real, it may be supplied tosediments by non-lithogenic source(s).

Another approach of quantitative assessment of metalpollution in sediments is to determine geo-accumulationindex (Igeo) of metals as proposed originally by Müller(1979). Igeo is expressed as:

Igeo = log2Cn/1.5Bn, (3)

where Cn and Bn are the measured and background con-

centrations of the metal n respectively; and 1.5 is the cor-rection factor used to account for possible variability inthe background data due to lithological variation. Metalconcentrations of average post-Archean shale (Taylor andMcLennan, 1985) are used as the background concentra-tions for metals. Calculation using Eq. (3) showed thatIgeo values for metals of YRS sediments are between 0and 1. Such values indicate that YRS sediments are un-polluted for the metals analyzed in this study.

SUMMARY AND CONCLUSIONS

The major focus of this study has been to characterizechemical weathering and transport in the upper Yamunabasin in the Himalaya and to understand heavy metal as-sociation in river sediments. This has been achievedthrough measurements of major elements and trace met-als of bed sediments of the Yamuna and its tributariesdraining the Lesser and the Higher Himalaya. Resultsobtained in this study, in conjunction with data availablefor YRS waters and bed rocks of the drainage basin, haveled to the following conclusions.

In YRS sediments, major and trace element concen-trations vary between 20 to 50%. Elemental variationsobserved for the YRS as a whole are more compared tothose for major rivers such as the Yamuna and the Tons,suggesting that tributaries draining multiple lithologiesintroduce significant variation to YRS sediment chemis-try. Na, K, Ca and Mg show significant loss from bedrocks during weathering. Among these, Na shows thehighest loss compared to the rest, presumably due to itshigher solubility and limited tendency to be influencedby processes such as exchange, scavenging and precipi-tation during weathering and transport. Average CIA valuefor YRS sediments is ~59, suggestive of incipient weath-ering in the basin, a result supported by major ion chem-istry of YRS waters. Lack of intense weathering in theupper Yamuna basin is because of steep gradient, highphysical erosion and less time of contact between bed-rock and weathering solution.

Results on Sr and Ba concentrations of YRS sedimentssuggest their loss from bedrocks during weathering. Srseems to be associated with Ca-Mg rich phases ofsediments such as plagioclase and carbonate minerals. Naand Sr are released to waters preferentially over Ba. Thisobservation is a combined result of higher mobility of Naand Sr, and affinity of Ba to be adsorbed onto clay miner-als as seen from its significant positive correlation withK and Al. Strong positive correlations among heavy metalconcentrations of YRS sediments suggest that their abun-dances seem to be controlled by a common mechanism,i.e., abundance of clay minerals. This inference is sup-ported by co-variation of metals with Al, and observationof higher Al and metal concentrations in riverine

Fig. 7. Distribution of enrichment factors for heavy metals inYRS sediments. See text for calculation of enrichment factor.

Ti Mn Cu Co Ni Zn Pb Cr

0

1

2

3

4

5

6

En

rich

men

t fa

cto

r 90th Percentile75th Percentile50th Percentile25th Percentile10th Percentile


particulates compared to those in bed sediments. Weakcorrelations of metals with P, Fe and Mn, suggests thatFe-Mn oxides and organics play secondary role in regu-lating metal concentrations of YRS sediments. Associa-tion of metals with clay minerals highlights the role ofmineral sorting in regulating metal abundances of YRSsediments. Enrichment factor and geo-accumulation in-dex of metals indicate that they are mainly of natural ori-gin and YRS sediments are unpolluted for metals analyzedin this study.

Acknowledgments—We thank J. R. Trivedi and S. K. Singhfor their help during sampling, R. Bhushan for assistance incoulometric analysis, authorities of Wadia Institute ofHimalayan Geology for logistics, and S. Krishnaswami for con-structive criticism. Comments of two anonymous reviewers aregratefully acknowledged.

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