Sediment Geochemistry of the Yamuna River System in the Himalaya: Implications to Weathering and Transport

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

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, Japan 2Physical 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 been analyzed for major elements and trace metals (Sr, Ba, Ni, Cu, Co, Zn, Pb and Cr). These results have been used to characterize chemical weathering and transport in the Himalaya, to assess relative mobility of elements during weathering and to understand heavy metal association. Concentrations of major and trace elements of YRS sediments vary between 20 and 50%. In general, elemental variability reduces when data are analyzed individually for the major rivers, suggesting that tributaries draining diverse lithology contribute significant variations. Comparison of sediment chemistry with composition of source rocks and average Upper Continental Crust (UCC) suggests significant loss of Na, K, Ca and Mg from source rocks during weathering, the degree of loss being more for Ca and Na. Chemical index of alteration (CIA) for YRS sediments averages at 59, indicating that weathering in the basin is of moderate intensity. This inference is also supported by 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 combined effect of higher solubility of Na and Sr, and the affinity of Ba to be adsorbed onto solid phase. Heavy metals show significant positive correlation with Al and weak correlation with Fe, Mn and P. These observations suggest that metal concentrations are controlled mainly by clay mineral abundances, and that Fe-Mn oxides and organic matter may be playing less significant role. Heavy metal concentrations of YRS sediments are lower than those of suspended particulates of 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 sediment transport and mineral sorting in influencing the YRS sediment chemistry. Enrichment factor and geo-accumulation index calculated for heavy metals in YRS sediments suggest that they are mainly of natural origin and that anthropogenic activities exert little influence on their abundances.

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

ing the Himalaya (Krishnaswami et al., 1992; Sarin et INTRODUCTION al., 1992; Pande et al., 1994; Galy and France-Lanord, The rivers draining the Himalaya contribute signifi- 1999; Dalai et al., 2002a, 2002b, 2002c, 2003). These cantly to the global sediment and water discharge studies are based mainly on isotopic and major ion com- (Milliman and Meade, 1983). They have recently attracted position of dissolved load of rivers. Available geochemical attention of several workers because of the possible con- studies of river sediments in the Indian Himalaya include nection between chemical weathering in the Himalaya and reconnaissance survey of the Ganga and the Yamuna global climate (Raymo and Ruddiman, 1992) as silicate (Subramanian, 1987; Jha et al., 1990; Chakrapani and weathering is thought to be a global sink for CO2 on geo- Subramanian, 1996; Subramanian and Ramanathan, 1996; logic time scales (Walker et al., 1981; Berner, 1995). Such Ramesh et al., 2000) and the Indus (Ahmad et al., 1998). a hypothesis has led to a number of studies on rivers drain- Geochemical studies of sediments in the headwaters of rivers in the Himalaya are limited. The river Yamuna, draining the southern slopes of the *Corresponding author (e-mail: [email protected]) Himalaya in its upper reaches, is the largest tributary of *Present address: Department of Geology and Geophysics, SOEST, the Ganga (Negi, 1991). At the confluence, water dis- University of Hawaii, Manoa 712 POST, 1680 East-West Road., charge of the Yamuna is one and half times that of the Honolulu, HI 96822, U.S.A. Ganga (Rao, 1975). The Yamuna and its major tributaries Copyright © 2004 by The Geochemical Society of Japan. in the Himalaya constitute the Yamuna River System

441 o o o o 68 76 84 92 780 13 0 0 HIGHER o Are a of 77 50’E 78 13’ 32 N G a Stu d y HIMALAYA R New Delhi n anuman h a tti Y g H C a a m R s u . n Gan o a ga R n R . 24 . o 0 T INDIA 77 50 E 0 16o . Mori 30 49 N s R on R T

r 27 LESSER Kuthnaur a

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a n

R l u d G s ir m i R. n m o Kalsi A a T Y A 5 8 m Bata R. 32 9 lawa Paonta 6 Aglar R. 2 R Dakpathar Sahib R lar R Mussoorie a g 1 A 3 n A u sa Batamandi 4 n N m R. a

Y 300 11’ N Tajewala 11 Dehradun Mussoorie 300 11 R R a Giri n R Kalsi u a m n Ya u m Dehradun a km Y 0 15

To Saharanpur ( # 33) Sampling Locations Crysta lline s boundary Towns LH-HH Carbonates Fig. 1. Map showing sediment sampling locations in the Yamuna Oth e r Sedimentaries and its tributaries in the Himalaya. Fig. 2. General lithology of the YRS drainage basin. Only some of the tributaries are shown.

(Negi, 1991). This work, which builds on our earlier studies (Dalai et al., 2002a, b, c), forms a part of detailed fractions were powdered either in an agate mortar or in a geochemical and isotopic investigation of the Yamuna Spex ball mill with acrylic container and methylacrate River System (YRS) in the Himalaya. Reported here are balls, and were sieved to <100 mesh size using nylon the concentrations of major and trace elements in sieves. Samples >100 mesh size were repeatedly pow- sediments of the Yamuna and its tributaries in the dered to bring all the materials to <100 mesh size. Dur- Himalaya. Results obtained in this study, in conjunction ing powdering, care was taken to ensure that samples did with those available on bed rocks in the basin and dis- not come in contact with any metal surface. After thor- solved load of the YRS (Dalai et al., 2002a, b), are used ough homogenization, powdered samples were stored in to (i) characterize chemical weathering in the YRS basin, clean plastic bottles. About 500 mg of sample was (ii) assess relative mobility of elements during weather- weighed and dissolved in PTFE dish by repeatedly treat- ing and transport, and (iii) determine the origin and asso- ing with hot HF-HCl-HNO3-HClO4 mixture and finally ciation of heavy metals in river sediments. dissolving in 1N HNO3. These solutions were used for elemental analysis after suitable dilution. Some samples were digested in replicates and analyzed to assess the pre- SAMPLING AND ANALYSIS cision of measurements. Reagents used for sample disso- Riverbed sediments were collected from the Yamuna lution were analyzed to assess their blank contribution. mainstream and its tributaries (Fig. 1) during October USGS rock standard (G-2) and an in-house laboratory 1998. Details of the sampling and analysis are given in standard (NOVA, prepared from the Pacific sediments, Dalai (2001) and Dalai et al. (2002a, b). Samples were Agnihotri, 2001) were also dissolved along with the sam- collected in zip-lock polythene bags using a plastic scoop. ples and analyzed to check the accuracy of the measure- In the laboratory, they were oven-dried at ~90°C and ments. Ca, Mg, Al, Sr, Ba, Fe, P, Ti, Pb, Zn and Cr were sieved to <1 mm size using nylon sieves. The <1 mm size measured by ICP-AES (Jobin Yvon 38S), and Na, K, Mn,

442 T. K. Dalai et al. Table 1. Results of analysis of reference standards G-2 and NOVA

G-2 NOVA

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

Cu 10.13 12 407 ± 2 392 ± 20 403 Ni 20.7 ± 0.9 13.7 244 ± 1 206 ± 15 224 Co 33.95 20.7 134 104 ± 7 101 Ti n.m. n.m. 3787 ± 234 3810 ± 245 4076 P n.m. n.m. 2009 ± 87 1875 ± 34 1702 Cr 5.89 ± 0.11 9 61 ± 2 63 ± 484 Zn 77 ± 2 85 137 ± 5 152 ± 10 146 Pb 23.3 ± 0.4 31 33.4 ± 1.2 n.m. 35.5

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

Cu, Ni and Co by flame-AAS (Perkin Elmer 4000). Car- river flows past the Higher Himalaya, it drains quartz- bonate contents were determined by coulometric titration. ites, conglomerates, slates and carbonaceous phyllites. Powdered samples were treated with 40% ortho- Further downstream, it flows through massive dolomitic phosphoric acid for 10 minutes at 70°C in the extraction limestone and marble of Mandhali and the Deoban For- unit coupled to the Coulometer (UIC Coulometer 5012). mations of the inner belt, and limestone and dolomite of The evolved CO2 was swept to the titration cell of the Krol Formation of the outer belt in the Lesser Himalaya. coulometer after being passed through columns contain- These carbonates are often associated with carbonaceous ing activated silica gel and anhydrous MgClO4. Carbon- and gray slate. Barite occurs in silisiclastic sediments of ate contents were calculated assuming that evolved CO2 Nagthat Formation in the Tons river section (Sachan and is produced from CaCO3. Sharma, 1993), and as pockets and veins in the lower Blank corrections were <2% for Zn, Pb, Cu and Ni, horizons of Krol limestone at Maldeota and and negligible for other elements. Precision and accuracy Shahashradhara (Anantharaman and Bahukhandi, 1984). of the measurements of major elements (Na, K, Ca, Mg, Southwest of Kalsi (Fig. 2), the Yamuna flows through Al, Fe), carbonate content, Sr and Ba were within about the Siwaliks comprising of channel and floodplain de- ±5% (Dalai, 2001; Dalai et al., 2002a, 2002b, 2003). Av- posits formed by Himalayan rivers in the past. erage precision was ±8% for P, ±15% for Zn and ±10% In the Himalaya, the Yamuna drains an area of ~9600 for other metals. Analysis of USGS reference rock stand- km2 and has average annual water discharge of ~10.8 × ard G-2 and the laboratory standard NOVA shows that 1012 liter at Tajewala (Rao, 1975; Jha et al., 1988; Fig. between the two standards, measured metal concentra- 1). The discharge and drainage area of the Yamuna at tions of NOVA agreed better with their reported values Tajewala is similar to that of the Bhagirathi and the (Table 1). However, measured Co concentrations of both Alaknanda (at Devprayag) prior to their confluence to the standards were ~30% higher than the reported val- form the Ganga. Among the tributaries of the Yamuna, ues. the Tons is the largest, which originates in the Higher Himalaya and merges with the Yamuna at Kalsi where its water discharge is twice that of the Yamuna (Rao, 1975). LITHOLOGY OF THE DRAINAGE BASINS Other major tributaries: the Asan, Giri, Bata and Aglar In its upper reaches, the river Yamuna drains high (Fig. 1) originate and flow through the Lesser Himalaya. grade granite-gneisses and schists of the Higher The Yamuna basin in the Himalaya, particularly its Himalayan Crystallines (HHC, Fig. 2). Occurrence of upper reaches, is not significantly influenced by agricul- carbonates is less common in HHC, however, these rocks tural and human activities. Terrace agriculture is limited are reported to contain impure limestones and calc- to a few locations in the lower reaches. The impact of silicates (Bickle et al., 2001 and references therein). These land use pattern and agricultural practices on water and rocks have schistose graphitoid quartzites (Gansser, 1964) sediment chemistry of the Yamuna and its tributaries, and graphitic/carbonaceous schists (Valdiya, 1980; therefore, is likely to be minimal. Earlier studies from Sharma, 1983). There are reports of calc-schists and mar- our group have shown that decadal variation in major ion ble in regions upstream of Hanuman Chatti which con- and Sr concentrations of the Yamuna waters is only within tain sulphide mineralization (Jaireth et al., 1982). As the 30Ð40% and about ±20% respectively, suggesting that

Sediment geochemistry of the Yamuna River System in the Himalaya 443 om Dalai et al. (2002b).

om Dalai et al. (2002a). Ba data fr

Al and carbonate data fr

Table 2. Major and trace element concentrations of YRS bed sediments Table

n.m.: not measured. b.d.: below detection. Carb.: carbonate content. Na, K, Ca, Mg, n.m.: not measured.

444 T. K. Dalai et al. . values are rounded off. rounded . values are

amuna mainstream and the Tons amuna mainstream

Aglar river (RS98-8) which has 44% carbonate in its sediment. C.V

Table 3. Variability in major and trace element concentrations in the bed sediments of the YRS, Y 3. Variability Table

Statistical analysis for Ca and Mg does not include data of

Sediment geochemistry of the Yamuna River System in the Himalaya 445 anthropogenic activities and land use pattern have not significantly impacted the river water chemistry (Dalai et 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 gÐ1), carbonate content (weight %) and trace elements (Sr, Ba, Ni, Cu, Co, Zn, Pb and Cr, in µg gÐ1) are presented in Table 2. Data for some of the major elements and Ba were earlier reported in Dalai et al. (2002a, b). In order to ob- serve general variability in the sediment chemistry of the YRS, statistical parameters of the data (arithmetic mean, standard deviation and coefficient of variation) were calculated (Table 3). The Yamuna and the Tons are the two largest rivers draining major part of the YRS basin. Hence statistical analysis was also done separately for these two rivers; the results are shown in Table 3. The concentrations of major and trace elements vary by 20 to 50% for the YRS. Coefficient of variation is maximum (45Ð50%) for Ca, Mn and Ni, ~35Ð40% for Mg, Fe, Cr and Cu, and is within ≤30% for other elements. It can be seen that variations in the elemental concentrations, calculated separately for the Yamuna and the Tons, are reduced when compared with the YRS as a whole. This seems to suggest that contributions from the tributaries draining multilithologic terrains may introduce significant variations to YRS sediment chemistry. For the Yamuna sediments, Fe and Mn show maximum scatter (~33 and ~23% respectively) whereas other elements have <20% variation. For the Tons sediments, the coefficient of variation is the highest for Mn (~56%), 24 to 33% for Fe, Zn, Ca, Mg and Ni, and <20% for the rest. Compared to the Tons sediments, the average concentrations of Ca, Mg, Ti and Ni in the Yamuna sediments are higher whereas the opposite holds true for Sr, Ba, Fe and Mn (Table 3).

Major elements Among the major elements, Na, K, Fe and Al show no systematic downstream variation, whereas carbonate, Ca and Mg show higher abundances in the lower reaches where Precambrian carbonates is a major lithology of the YRS catchment. In order to determine inter-relation among the major and trace elements, multiple regression analysis was car- ried out, results of which are given in Table 4. Among major elements, Na, K, and Fe show positive correlation with Al; correlation coefficient being the highest for the K-Al pair (0.73, Table 4). Ca and Mg show weak nega- tive correlation with Al. These trends suggest that concentrations of Na, K and Fe of YRS sediments are sig-

Table 4. Co-variation matrix for major and trace element concentration of YRS sediments Table nificantly controlled by clay mineral abundances that are progressively diluted by quartz content. Due to physical

446 T. K. Dalai et al. 1.25 8 Ca-Carb. Mg-Carb. 1.00 6

0.75

4 0.50

0.25 2 UCC normalized ratio normalized UCC Carbonate (% wt.)

0.00 0 Na K Ca Mg Al Fe Mn P Ti

Fig. 3. Upper Continental Crust (UCC) normalized ratios (con- Ca, Mg (% wt.) centrations of the river sediment/concentration of the UCC) Fig. 4. Scatter plot of carbonate contents with Ca and Mg in for major elements in YRS sediments. Calculations of mean and YRS sediments. Significant positive correlations suggest a com- standard deviation exclude data of the Aglar river. Data for mon phase for them, such as carbonates and plagioclase min- UCC are from McLennan (1995). erals. Data for Aglar river (RS98-8) not plotted.

transport and hydrodynamic sorting, many of the major 0.75, it is difficult to distinguish it from 1 due to the large and trace elements are known to be associated with clay error (Fig. 3). Figure 3 also shows that Na and Ca have and fine silt fractions of sediments and suspended suffered the highest loss, consistent with the knowledge particulates of rivers, whereas quartz is usually abundant that they are relatively more mobile in the natural aque- in the sand fractions (cf., Tebbens et al., 2000). The re- ous environment (Nesbitt and Young, 1982; Berner and sults obtained for YRS sediments, as discussed above, Berner, 1996; Gaillardet et al., 1997). Degree of Ca and thus underscore the importance of transport processes in Mg loss from source rocks, as evident from comparison regulating the elemental abundances of river sediments. of YRS sediments with UCC, could be more than the ac- Large scatter in Al-Ca and Al-Mg plots may be caused by tual value due to the presence of detrital and/or authigenic contributions from detrital carbonates. Mn shows signifi- carbonates in bed sediments. A significant part of the YRS cant positive correlation with Fe which is suggestive of catchment in the lower reaches comprises of Precambrian Mn-Fe association in oxide phase. carbonates, especially the massive dolomites. Wide oc- The Yamuna and its tributaries, as mentioned earlier, currence of limestone and dolomite in the basin, together have major part of their drainage basins in the Lesser with the observed co-variation of Ca and Mg (Table 4) Himalaya. Comparison of element abundances in the YRS and significant positive correlations of carbonate content sediments with those in the granites/gneisses in the Lesser with Ca and Mg (Fig. 4), support the idea that the car- Himalaya suggests that the Na, K, Ca and Mg have been bonates in YRS sediments are mainly of detrital origin lost from bedrocks during weathering. Since river with little contribution from calcite precipitation. Though sediments are composite weathering products of all the many of the YRS waters are supersaturated with calcite, lithologies in the catchments, major element concentra- evidence for calcite precipitation in the YRS has not been tions of sediments were normalized with those of the av- observed (Dalai et al., 2002a). Galy et al. (1999), based erage Upper Continental Crust (McLennan, 1995). Nor- on Sr- and C-isotopic studies of bed carbonates and sedi- malization of elemental concentration of river sediments ment carbonates of the Narayani river in the Nepal with those of the UCC is a common approach to assess Himalaya, also observed that carbonates in the river the elemental mobility during weathering and transport sediments are mainly of detrital origin. (Taylor and McLennan, 1985). In YRS sediments, the Comparison of elemental ratios in silicate source rocks UCC normalized ratio for most of the major elements is with those in sediments provides an opportunity to as- <1 (Fig. 3). This would suggest their loss from source sess their relative mobility during weathering and trans- rocks during weathering and transport. Exceptions to this port. Average Ca/Na ratio (molar) in YRS sediments is trend are P and Ti, which have UCC normalized ratios ~0.75 which is higher than the average values of 0.46 in close to 1. This observation seems to support the idea Lesser Himalaya silicates, 0.32 in Higher Himalaya sili- that Ti is relatively immobile during chemical weather- cates and 0.15 in granites from Hanuman Chatti and ing. On the other hand, P may have contributions from Sayana Chatti (Krishnaswami et al., 1999; Dalai et al., land-derived organics and/or productivity in rivers. Al- 2002a). Higher Ca/Na in bed sediments, however, can though average value of UCC normalized ratio for Mn is arise either due to higher mobility of Na relative to Ca or

Sediment geochemistry of the Yamuna River System in the Himalaya 447 due to presence of authigenic and detrital carbonate in ering. Assuming all carbonates in YRS bed sediments are sediments. It is also important to examine if transport CaCO3, the calculated CIA values for YRS sediments have processes also influence the abundances of Ca and Na in a range of ~51 to 69 with an average of ~60 (Dalai et al., river sediments. Given that Ca and Na are relatively more 2002a). Such calculations do not take into account of any soluble and have low affinity for particles, their concen- contribution of Ca from phosphates. The knowledge that trations in sediments are less likely to be affected by proc- carbonates in the YRS catchment comprise of both lime- esses such as exchange and adsorption. Thus, mineral stones and dolomites suggests that a part of carbonate sorting can influence abundances of Ca and Na in river would also be from dolomites. Precambrian carbonates sediments only through quartz dilution. However, the ef- from the Lesser Himalaya have average Ca/Mg weight fect of quartz dilution is cancelled out when the ratio Ca/ ratio of 2.9 (Singh et al., 1998). Assuming this is also Na is used. Thus, comparison of Ca/Na of carbonate-free valid for Ca/Mg ratio in bed carbonates, the CIA for indi- sediments with that of source rocks can avoid complica- vidual samples decreases only marginally, with an aver- tions of mineral sorting and presence of carbonates in age ~59 (Dalai et al., 2002a). It is seen that CIA values sediments. YRS sediments free of carbonates have aver- for YRS sediments in the lower reaches are generally age Ca/Na molar ratio of 0.44 ± 0.14 (based on data of higher, which suggests relatively more intense weather- five samples with carbonate content below detection limit, ing because of abundant vegetation, and higher soil CO2 Table 2), which is ~3 times higher than the average value and temperature. In the lower reaches, contact time of of 0.15 ± 0.13 in granites from Hanuman Chatti and water with the reacting minerals is likely to be longer Sayana Chatti (Biyani, 1998; Dalai, 2001; Dalai et al., due to shallower gradient. However, the average CIA in 2002a). Similarly, average Mg/Na ratio (molar) of YRS sediments is lower than that in average shale, 70Ð carbonate-free sediments is 0.51 ± 0.16, much higher com- 75 (Nesbitt and Young, 1982) indicating that chemical pared to 0.15 ± 0.08 in granites from Hanuman Chatti weathering of silicates in the Yamuna basin in the and Sayana Chatti. Such observations, though based on Himalaya is not so intense. This is also borne out from limited data set, are suggestive of higher mobility of Na low values of dissolved Si/(Na* + K) molar ratio (aver- over Ca and Mg during weathering and transport of sili- age 1.6) in YRS waters (Na* is sodium corrected for con- cates in the YRS basin. This is in line with the existing tributions from cyclic salts and halites using dissolved knowledge on relative elemental mobility (Berner and Cl as an index; Dalai et al., 2002a). Available studies on Berner, 1996; Gaillardet et al., 1997) and is consistent clay mineralogy of the Yamuna river sediments near with the observation that a major part of Na in YRS wa- Mussoorie in the Lesser Himalaya show that they con- ters is derived from silicate weathering (Dalai et al., tain abundant illite with minor kaolinites (Subramanian 2002a). et al., 1985; Sarin et al., 1989), also suggestive of incipi- Average Al content of YRS sediments (4.7 weight %) ent silicate weathering. Relatively lower values of CIA is much lower than that in the upper continental crust and in the Indus River bed sediments (48Ð52) and suspended in average sediments (8.04 and 7.1% respectively, matter (60Ð65) led Ahmad et al. (1998) to infer that ero- McLennan, 1995). Intense weathering in river basins sion and physical weathering regulate sediment chemis- yields high clay content and Al concentration in the river try of the Indus. In the Himalaya, physical erosion is en- particulates and sediments. Lower Al concentration would hanced by tectonic activity, steep gradient and monsoon indicate that chemical weathering in YRS basin is not so climate. As a result, the rock particles are flushed away intense, although this might have been partly caused by downstream rapidly before they are chemically weath- mineral sorting. Chemical index of alteration (CIA) of ered considerably. Dalai et al. (2002a) also observed that YRS sediments (Nesbitt and Young, 1982) provides a physical weathering is one of the driving factors for semi-quantitative measure of the degree of silicate weath- chemical weathering in the Yamuna basin in the Himalaya. ering in the river catchments. CIA is given by: Strontium and barium × CIA = [(Al2O3)/(Al2O3 + CaO* + Na2O + K2O)] 100, Alkaline earth metals such as Sr and Ba are known to (1) be relatively mobile in natural oxic and aqueous environ- ments (Dupre et al., 1996; Gaillardet et al., 1999). Sr where CaO* represents CaO of the silicate fraction concentration of YRS sediments ranges from ~45 to 156 (Nesbitt and Young, 1982). During chemical weathering µg gÐ1 (mean: 75 ± 22 µg gÐ1) and shows no definite down- of silicates, more soluble cations i.e., Ca and Na are re- stream trend. This range and mean are lower than those leased to solution, leaving Al in the residual products such in the Precambrian carbonates in the Yamuna basin (range: as clay. High intensity weathering results in high abun- 33 to 363 µg gÐ1, mean: 162 ± 120 µg gÐ1, Singh et al., dances of clay and consequently high Al in sediments. 1998). Four granites collected in and around Hanuman Thus, higher CIA would indicate intense silicate weath- Chatti (Fig. 1) and those from Sayana Chatti (Biyani,

448 T. K. Dalai et al. 3

1 UCC normalized ratio 0 Sr Ba Cu Co Ni Zn Pb Cr Fig. 5. Upper Continental Crust (UCC) normalized ratios (concentrations of the river sediment/concentration of the UCC) for trace elements in YRS sediments. Calculations of mean and standard deviation exclude data of Aglar river (RS98-8). Data Fig. 6. Scatter plot of Ba with K and Al in YRS sediments. for UCC are from McLennan (1995). Significant positive correlations (r2 = 0.69 for K-Ba and 0.68 for Al-Ba) are suggestive of association of Ba with K- aluminosilicates such as clay minerals. Regression analysis 1998) have Sr in the range of 76Ð153 µg gÐ1 with a mean excludes data of the Aglar river (RS98-8, data point encircled). of 105 ± 25 µg gÐ1. The Upper Continental Crust (UCC) normalized ratio for Sr in YRS sediments averages at 0.21 ± 0.04 (Fig. 5). The average Sr/Al ratio (µg gÐ1/ the results show that Ba/Na of YRS sediments are a fac- weight %) of YRS sediments, 17 ± 8 is much lower than tor of ~4 higher than that measured in granites of the that for the UCC, ~44 (McLennan, 1995). It is borne out Yamuna basin. If these data are representative of the en- from all these comparisons that Sr is lost from bed rocks tire basin, then higher Ba/Na in sediments relative to those during weathering. In YRS sediments, Sr shows signifi- in granites would suggest preferential release of Na over cant positive correlation with Ca and Mg (Table 4) sug- Ba during weathering. This inference is based on the gesting that it is associated mainly with plagioclase and premise that the HHC granites/gneisses are the dominant carbonate minerals. source of these sediments. At present there is no data to Ba concentration of YRS sediments ranges from ~200 test if this assumption is valid. However, Derry and to 550 µg gÐ1 (mean 371 ± 95 µg gÐ1, Table 2) and shows France-Lanord (1996) concluded that the HHC is the no distinct downstream trend. Four samples of granites dominant source of the Bengal Fan sediments. It is, there- collected in and around Hanuman Chatti in the Higher fore, likely that the YRS bed sediments are also derived Himalaya (Fig. 2) have Ba concentration in the range of mainly from HHC. Measurements of diagnostic isotope ~120Ð400 µg gÐ1 (Dalai et al., 2002b) with a mean of proxies are required to confirm this conjecture. Compari- 307 ± 126 µg gÐ1, which is indistinguishable from that son of Ba/Sr in granites from the upper Yamuna basin for YRS sediments. The UCC normalized ratio for Ba in with those in carbonate-free bed sediments also allows YRS sediments averages at 0.66 ± 0.16 (Fig. 5). It is drawing similar inferences. Ba/Sr of granites of Hanuman tempting to infer from this ratio that there is overall loss Chatti is about a factor of two lower than that in of Ba during weathering of bed rocks. If source rocks in carbonate-free sediment samples. Assuming that the da- YRS basin have a wide range in Ba concentrations, the tabase is representative of the entire YRS basin, it indi- above interpretation may seem over simplified. However, cates that Sr from granites is preferentially released over based on a detailed geochemical investigation Dalai et Ba. al. (2002b) inferred that silicates in the YRS basin are an In addition to higher mobility of Na and Sr, their pref- important source of dissolved Ba in many of the rivers. erential release over Ba can also be understood in terms The mean value of Ba/Na (nmole µmole-1) in four gran- of weathering resistance of host minerals of Ba and the ites of the upper Yamuna basin is 1.4 ± 0.6 whereas Ba/ affinity of Ba to be associated with solid phases during Na ratio in bed sediments averages at 5.6 ± 1.5 (exclud- weathering and transport. Due to their similar ionic radii, ing data of three samples RS98-8, RS98-11 and RS98- Ba substitutes for K in feldspars and micas (Wedepohl, 31, which have anomalously high Ba/Na ratios, 10.4Ð 1972; Nesbitt et al., 1980; Gallet et al., 1996). Given that 24.2). The average Ba/Na of five carbonate-free samples K-bearing minerals are relatively more resistant to chemi- is also nearly the same. It is also seen that the average cal weathering (Berner and Berner, 1996), release of Ba Ba/Na in sediments of rivers draining the HHC (5.2 ± from them is likely to be relatively restricted. There is 0.3, n = 4) is nearly the same as those for rivers flowing significant positive correlation of Ba with K and Al in through the Lesser Himalaya (5.6 ± 1.7, n = 19). Thus, YRS bed sediments (Fig. 6; r2 = 0.69 and 0.68 for Ba-K

Sediment geochemistry of the Yamuna River System in the Himalaya 449 and Ba-Al regressions respectively, excluding the sam- Zn) show positive correlations among themselves (Table ple from river Aglar). It is well known that Ba is retained 4) suggesting that a common mechanism regulates their in clays and Fe-oxyhydroxides during weathering and abundance. This, coupled with the observation that these transport (Wedepohl, 1972). This property of Ba is known metals also show co-variations with Al (Table 4), leads to regulate its dissolved concentrations of rivers and its to infer that occurrence of Al-rich phases such as clay flux to oceans (Hanor and Chan, 1977; Li and Chan, minerals exert significant control on abundances of met- 1979). During weathering of alkali feldspars, release of als. Trace metal concentrations of YRS sediments show Ba to solution is limited due to its retention in the weath- very weak correlation with Fe, Mn and P (except Zn which ering profile possibly via exchange with clays (Nesbitt et correlates positively with Fe, r = 0.52; and Co which al., 1980). Association of Ba with clay minerals of stream shows a weak positive correlation with P, r = 0.36, Table sediments was also observed for the Amazon River 4). Phosphorous is known to be associated with ferric (Vital and Stattegger, 2000). The relative importance of oxides/hydroxides and organic matter in river sediments these two mechanisms (resistance of K-Al silicate min- (Berner and Rao, 1994). Jha et al. (1990) observed a sig- erals to weathering vis-á-vis retention of Ba in solid nificant co-variation between organic C and P in the phases during transport) in regulating the abundance and Yamuna river sediments. In the present study, co- distribution of dissolved Ba in YRS waters and sediments variation of heavy metals with Al and absence of the same is difficult to assess from available information. How- with P, Fe and Mn suggest that these metals are mainly ever, studies on weathered granites indicate that K is fixed associated with clay fractions and that their abundances onto clay surfaces even after complete weathering of K- are not significantly influenced by the presence of organic feldspars (Nesbitt and Young, 1982). Earlier work on matter and/or Fe-Mn oxides. Strong association of met- weathering profiles in the Middle Hills of the Himalaya als with Al-rich phase demonstrates the role of sediment showed that K and Mg were retained in clays of the soil transport and mineral sorting in influencing the distribu- profile after their mobilization from bedrocks (Gardner tion of metal abundances of YRS sediments. Ramesh et and Walsh, 1996). It is observed that Ba concentrations al. (2000) also observed that finer grain size and clay of carbonate-free YRS sediments, in general, are either mineral abundances in surficial sediments of the similar to or higher than those in granites. All these ob- Himalayan river system control metal accumulation in servations, coupled with the knowledge that silicates are them. The role of particle transport and sorting is also an important contributor to dissolved Ba of YRS waters evident from comparison of chemical composition of sur- (Dalai et al., 2002b), seem to indicate that adsorption of face sediments with those of suspended particulates of Ba onto particles, after its release to solution, is likely the Yamuna river. The heavy metal (Cr, Cu, Ni, Zn and the dominant mechanism in regulating Ba abundances of Pb) concentrations of the Yamuna river sediments (Table YRS sediments and waters. 2) are lower than those reported for total suspended matter of the river at Baghapat (the most upstream point of Heavy metals sampling in Jha et al., 1990). Suspended particles are finer Average heavy metal concentrations of YRS in size and have higher abundances of Al and clay miner- sediments, except for Pb, are lower than those reported als. Relatively higher metal contents in the suspended for the surficial sediments of the Yamuna main channel matter compared to bed sediments would also support the (Ramesh et al., 2000). Cobalt concentrations of the YRS idea that these metals are mainly associated with the clay are higher than those reported by Ramesh et al. (2000) fraction. Contributions from basaltic lithology and pos- even after considering that its concentration might have sible anthropogenic contributions in the plains may also been overestimated in this study. The samples studied by explain part of the difference in metal concentrations of Ramesh et al. (2000) are from the Yamuna at Dakpathar bed sediments and suspended matter observed in two dif- near Dehradun till its flow in the plains near Allahabad. ferent studies. In the plains, the Yamuna receives contributions from Among the heavy metals, UCC normalized ratios for tributaries draining mainly the basaltic terrains. Thus, the Cu, Zn and Pb are less than 1 (Fig. 5). This can be be- variation in metal concentrations of the river sediments cause of loss of these metals from bed rocks during weath- may be due to source rock characteristics. Furthermore, ering and/or less abundance of clay (and Al) in bed sediments in the plains are likely to have anthropogenic sediments compared to that in UCC. For Cr and Ni, UCC contributions whereas this study focuses on the headwater normalized values are indistinguishable from 1 within region of the Yamuna and its tributaries. The upper reaches errors. However, normalized ratio for Co is higher than 1 of the YRS being remote and minimally affected by agri- (this will be valid even after accounting for over estima- cultural activities, trace metals in sediments are likely to tion of Co) suggesting that it is supplied to sediments from be mainly of natural origin (see later discussion). non-lithogenic source(s). In YRS sediments, heavy metals (Cu, Cr, Co, Pb and

450 T. K. Dalai et al. 6 centrations of the metal n respectively; and 1.5 is the cor- 5 90th Percentile 75th Percentile rection factor used to account for possible variability in 50th Percentile 4 25th Percentile the background data due to lithological variation. Metal 10th Percentile concentrations of average post-Archean shale (Taylor and 3 McLennan, 1985) are used as the background concentra- 2 tions for metals. Calculation using Eq. (3) showed that 1 Igeo values for metals of YRS sediments are between 0

Enrichment factor 0 and 1. Such values indicate that YRS sediments are unpolluted for the metals analyzed in this study. Ti Mn CuCo Ni Zn Pb Cr

Fig. 7. Distribution of enrichment factors for heavy metals in SUMMARY AND CONCLUSIONS YRS sediments. See text for calculation of enrichment factor. The major focus of this study has been to characterize chemical weathering and transport in the upper Yamuna basin in the Himalaya and to understand heavy metal as- Evaluation of metal pollution sociation in river sediments. This has been achieved Metal concentrations in river sediments is a net result through measurements of major elements and trace met- of variability in source rock composition, sediment tex- als of bed sediments of the Yamuna and its tributaries ture, redox reactions, adsorption/desorption, sediment draining the Lesser and the Higher Himalaya. Results transport, mineral sorting and anthropogenic activity. obtained in this study, in conjunction with data available Contributions of metals to sediments from non-lithogenic for YRS waters and bed rocks of the drainage basin, have sources can be gauged by calculating their enrichment led to the following conclusions. factors (EF). EF is given by: In YRS sediments, major and trace element concentrations vary between 20 to 50%. Elemental variations

EF = (X/Al)sample/(X/Al)shale. (2) observed for the YRS as a whole are more compared to those for major rivers such as the Yamuna and the Tons, Such estimation minimizes dilution effects caused by suggesting that tributaries draining multiple lithologies variable matrices such as quartz. For calculation of EF, introduce significant variation to YRS sediment chemis- we have used the composition of Post Archaean try. Na, K, Ca and Mg show significant loss from bed Australian Shale (PAAS, Taylor and McLennan, 1985). rocks during weathering. Among these, Na shows the Distribution of EF for heavy metals is shown in Fig. 7. It highest loss compared to the rest, presumably due to its can be seen that Co, Zn and Pb are enriched in YRS higher solubility and limited tendency to be influenced sediments relative to PAAS whereas other metals do not by processes such as exchange, scavenging and precipi- show clear enrichment. A value of EF ≤ 2 can be consid- tation during weathering and transport. Average CIA value ered to be of lithogenic origin for a metal whereas EF > 2 for YRS sediments is ~59, suggestive of incipient weath- is suggestive of sources such as biogenic and anthropo- ering in the basin, a result supported by major ion chem- genic (Grousset et al., 1995). Metals analyzed in this istry of YRS waters. Lack of intense weathering in the study, except Co, have EF ≤ 2 suggesting that they are upper Yamuna basin is because of steep gradient, high mainly of natural origin. This inference is consistent with physical erosion and less time of contact between bed- the finding of Dalai et al. (2002a) that anthropogenic ac- rock and weathering solution. tivities have not significantly impacted major ion chem- Results on Sr and Ba concentrations of YRS sediments istry of the Yamuna waters over decadal time scale. It has suggest their loss from bedrocks during weathering. Sr already been mentioned that Co may have been over esti- seems to be associated with Ca-Mg rich phases of mated in this study by about 30%. If higher EF for Co in sediments such as plagioclase and carbonate minerals. Na YRS sediments is indeed real, it may be supplied to and Sr are released to waters preferentially over Ba. This sediments by non-lithogenic source(s). observation is a combined result of higher mobility of Na Another approach of quantitative assessment of metal and Sr, and affinity of Ba to be adsorbed onto clay miner- pollution in sediments is to determine geo-accumulation als as seen from its significant positive correlation with index (Igeo) of metals as proposed originally by Müller K and Al. Strong positive correlations among heavy metal (1979). Igeo is expressed as: concentrations of YRS sediments suggest that their abundances seem to be controlled by a common mechanism,

Igeo = log2Cn/1.5Bn, (3) i.e., abundance of clay minerals. This inference is supported by co-variation of metals with Al, and observation where Cn and Bn are the measured and background con- of higher Al and metal concentrations in riverine

Sediment geochemistry of the Yamuna River System in the Himalaya 451 particulates compared to those in bed sediments. Weak Dalai, T. K., Krishnaswami, S. and Sarin, M. M. (2002a) Major correlations of metals with P, Fe and Mn, suggests that ion chemistry in the headwaters of the Yamuna river sys- Fe-Mn oxides and organics play secondary role in regu- tem: Chemical weathering, its temperature dependence and lating metal concentrations of YRS sediments. Associa- CO2 consumption in the Himalaya. Geochim. Cosmochim. tion of metals with clay minerals highlights the role of Acta 66, 3397Ð3416. Dalai, T. K., Krishnaswami, S. and Sarin, M. M. (2002b) Barium mineral sorting in regulating metal abundances of YRS in the Yamuna River System in the Himalaya: Sources, sediments. Enrichment factor and geo-accumulation in- fluxes and its behavior during weathering and transport. dex of metals indicate that they are mainly of natural ori- Geochem., Geophy., Geosyst. 3, 10.1029/2002GC000381. gin and YRS sediments are unpolluted for metals analyzed Dalai, T. K., Singh, S. K., Trivedi, J. R. and Krishnaswami, S. in this study. (2002c) Dissolved rhenium in the Yamuna River System and the Ganga in the Himalaya: Role of black shale weath-

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Sediment geochemistry of the Yamuna River System in the Himalaya 453