Weathering in the Ganga Alluvial Plain: Geochemical signatures linking of the Himalayan source and the Bay of Bengal sink (original) (raw)
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A B S T R A C T Geochemistry of the Himalayan rivers has been a major point of contention in sedimentary geochemistry because of its global impact on ocean chemistry and climate. Among the Himalayan rivers, the Ganga and its Himalayan catchment have been studied extensively. However, the Peninsular rivers constituting a significant part of the Ganga basin have not received much attention, heretofore. In the present geochemical study of the Peninsular river's sediments, we have found that the initial chemical weathering of rocks in the catchment produces texturally, mineralogically and geochemically diverse sediments and fluvial processes further segregate them into the geochemically contrasting coarse channel and fine-grained suspended sediments. The overbank sediments possess an intermediate texture and geochemistry, but more towards the suspended sediments. The sediment geochemistry data indicates that the Peninsular river's sediments show an increase in the weathering intensity from the west (Banas river) to the east (Son river) along the climate gradient, i.e., from the arid-semiarid to the subtropical condition. The higher chemical index of alteration (CIA) values of the Peninsular river's sediments than the Yamuna and Ganga river sediments reflect the control of weatherable lithology in the tectonically stable, low relief and subtropical climate condition. The Yamuna and Ganga river sediments with lower CIA values show more physical weathering in the tectonically active Himalaya. The suspended and overbank sediments of the Yamuna and Ganga rivers show an increase in their CIA values after the confluence of the Peninsular rivers, indicating the contribution of more weathered materials by the Peninsular rivers. It has been found that there is a geochemical split between the channel and suspended sediments of the Peninsular rivers for sharing different sources, i.e., the dominant contribution of felsic sources to the channel and mafic sources to the suspended sediments. The weathering geochemistry, trace element systematics, and REE patterns suggest that the dominant sources of the channel sediments of the Peninsular rivers are the felsic crystallines and sedimentary lithologies of the Aravalli range, Bundelkhand and Chhotanagpur granite and gneisses, and Vindhyan sandstones. Whereas, the mafic lithologies such as the Deccan traps and mafic components of the felsic lithologies appear to be the major sources of the suspended sediments. Within the range of intermediate composition , the overbank sediment chemistry reflects more contribution of the mafic sources except for the Ken which shows a higher contribution of the felsic sources. The geochemical split between the channel and suspended sediments of the Peninsular river's sediments for the different provenances indicates differential weathering of the Deccan basalts, Bundelkhand crystalline, and Vindhyan sedimentary rocks; and also the hy-drodynamic control of the Peninsular rivers during erosion, transport, and deposition. However, the Himalayan rivers do not show such contrast between the channel and suspended sediments because of the higher physical weathering and sediment mixing in the high gradient topography of the Himalayan catchment.
Frontiers in Environmental Science, 2022
The Ramganga basin is an important sub-catchment of the Ganga River to study the wide-scale effects of human-induced changes on geochemical processes. The basin inhabits pristine locations in the upstream and dense human establishments in the floodplain region. Furthermore, the entrapment of upstream sediments in the Kalagarh Dam aids in creating different geochemical regimes. To reveal the geochemical heterogeneity over the multi-spatial and temporal scale, controlling factors (natural and anthropogenic), and source end-members, dissolved load samples were collected during the pre-monsoon, monsoon, and post-monsoon season of the year 2014. Major cations and anions data were analyzed using principal component analysis and mass-balancing equations-based forward modeling to quantify the contribution from the atmosphere, rock weathering, and anthropogenic sources. The results show that chemical weathering predominates the dilution effect during the pre- and post-monsoon season. A high ...
Aquatic Geochemistry, 1999
Water and suspended sediment samples were collected along a longitudinal transect of the Bhagirathi – a headwater stream of the river Ganga, during the premonsoon and postmonsoon seasons, in order to assess the solute acquisition processes and sediment transfer in a high elevation river basin. Study results show that surface waters were dominated by HCO3 and SO4 in anionic abundance and Ca in cationic concentrations. A high concentration of sulphate in the source region indicates oxidative weathering of sulphide bearing minerals in the drainage basin. The combination of high concentrations of calcium, bicarbonate and sulphate in river water suggests that coupled reaction involving sulphide oxidation and carbonate dissolution are mainly controlling the solute acquisition processes in the drainage basin. The sediment transfer reveals that glacial weathering and erosion is the major influence on sediment production and transfer. The seasonal and spatial variation in ionic concentration, in general, is related to discharge and lithology. The sediment mineralogy and water mineral equilibrium indicate that water composition is in equilibrium with kaolinite. The river Bhagirathi annually delivers 0.74 M.tons of dissolved and 7.88 M.tons of suspended load to the river Ganga at Devprayag. The chemical and physical denudation rate of the Bhagirathi is 95 and 1010 tons/km2/yr, higher than the Indian and global average.
… et Cosmochimica Acta, 1989
The Ganga-Brahmaputra, one of the world's largest river systems, is first in terms of sediment transport and fourth in terms of water discharge. A detailed and systematic study of the major ion chemistry of these rivers and their tributaries, as well as the clay mineral composition of the bed sediments has been conducted. The chemistry of the hi~land rivers (upper reaches of the Ganga, the Yamuna, the B~mapu~ the Gandak and the Ghaghra) are all dominated by carbonate weathering; (Ca + Mg) and HCOs account for about 80% of the cations and anions. In the lowland rivers (the Chambal, the Betwa and the Ken), HCOs excess over (Ca + Mg) and a relatively high contribution of (Na + K) to the total cations indicate that silicate weathering and/or contributions from alkaline/saline soils and groundwaters could be important sources of major ions to these waters. The chemistry of the Ganga and the Yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions.
Chemical Geology, 2009
The dissolved concentrations of major ions and Sr isotopes ( 87 Sr/ 86 Sr) were measured in the headwaters of the Chambal river and its tributaries draining the Deccan Trap basalts and the Vindhyan sediments of peninsular India. The total dissolved solids (TDS) ranged from 181 to 547 mg L − 1 ; much higher than the global "mean" river water. A significant fraction of solute abundance in the Chambal river is derived from sodium salts, unlike the Himalayan rivers which exhibit dominance of (Ca + Mg) salts. It is estimated that the Chambal river supplies about one-third of sodium via the Yamuna to the Ganga at Rajshahi (Bangladesh), with only ∼ 6.5% of water discharge. The presence of Na salts not associated with chloride in the Chambal headwaters constraints the application of Na⁎ (Na corrected for Cl) as an index of silicate derived component. This finding brings out the need to revisit the estimates of silicate erosion rate (SER) and associated CO 2 consumption in the Ganga basin, downstream Allahabad, based on Na⁎ as an index. The Sr concentration in the Chambal tributaries varied from 1.9 µM to 5.9 µM and 87 Sr/ 86 Sr ratio from 0.70923 to 0.71219. Unlike the Himalayan Rivers, Sr isotope composition in the Chambal river is far less radiogenic as the major sources of Sr to the Chambal are the Deccan Trap basalts and the Vindhyan sediments, which are low in 87 Sr/ 86 Sr. The Sr isotope budget of the Ganga, based on available data of the Chambal, Betwa, Ken, Yamuna and the Ganga shows that, weathering of the Deccan Trap basalts and the Vindhyan sediments (the drainage basin of the Chambal, Betwa and the Ken) contribute ∼ 70% of the dissolved Sr to the Ganga at Varanasi. This study highlights the key role of peninsular rivers draining the Deccan and the Vindhyan regions in the major ion and Sr budget of the Ganga.
The influx of Sr responsible for increase in marine Sr has been attributed to rise of Himalaya and weathering of the Himalayan rocks. The rivers draining Himalaya to the ocean by the northern part of the Indian sub-continent comprising the Ganga Alluvial Plain (GAP) along with Central parts of the Himalaya and the northern part of the Indian Craton are held responsible for the transformation of Sr isotopic signature. The GAP is basically formed by the Himalayan-derived sediments and serves as transient zone between the source (Himalaya) and the sink (Bay of Bengal). The Gomati River, an important alluvial tributary of the Ganga River, draining nearly 30,500 km2 area of GAP is the only river which is originating from the GAP. The river recycles the Himalayan-derived sediments and transport its weathering products into the Ganga River and finally to Bay of Bengal. 11 water samples were collected from the Gomati River and its intrabasinal lakes for measurement of Sr isotopic composition. Sr concentration of Gomati River water is about 335 μg/l, which is about five times higher than the world’s average of river water (70 μg/l) and nearly three times higher than the Ganga River water in the Himalaya (130 μg/l) The Sr isotopic ratios reported are also higher than global average runoff (0.7119) and to modern seawater (0.7092) values. Strong geochemical sediment–water interaction appearing on surface is responsible for the dissolved Sr isotopic ratios in the River water. Higher Sr isotopic rations found during post-monsoon than in pre-monsoon season indicate the importance of fluxes due to monsoonal erosion of the GAP into the Gomati River. Monsoon precipitation and its interaction with alluvium appear to be major vehicle for the addition of dissolved Sr load into the alluvial plain rivers. This study establishes that elevated 87Sr/86Sr ratios of the Gomati River are due to input of chemical weathering of alluvial material present in the Ganga Alluvial Plain.
The Narmada River in India is the largest west-flowing river into the Arabian Sea, draining through the Deccan Traps, one of the largest flood basalt provinces in the world. The fluvial geochemical characteristics and chemical weathering rates (CWR) for the mainstream and its major tributaries were determined using a composite dataset, which includes four phases of seasonal field (spot) samples (during 2003 and 2004) and a decade-long (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000) fortnight time series (multiannual) data. Here, we demonstrate the influence of minor lithologies (carbonates and saline-alkaline soils) on basaltic signature, as reflected in sudden increases of Ca 2+ -Mg 2+ and Na + contents at many locations along the mainstream and in tributaries. Both spot and multiannual data corrected for non-geological contributions were used to calculate the CWR. The CWR for spot samples (CWR spot ) vary between 25 and 63 ton km À2 year À1 , showing a reasonable correspondence with the CWR estimated for multiannual data (CWR multi ) at most study locations. The weathering rates of silicate (SilWR), carbonate (CarbWR) and evaporite (Sal-AlkWR) have contributed 38−58,28−45and8−2338-58, 28-45 and 8-23%, respectively to the CWR spot at different locations. The estimated SilWR (11-36 ton km À2 year À1 ) for the Narmada basin indicates that the previous studies on the North Deccan Rivers (Narmada-Tapti-Godavari) overestimated the silicate weathering rates and associated CO 2 consumption rates. The average annual CO 2 drawdown via silicate weathering calculated for the Narmada basin is 38−58,28−45and8−230.032 Â 10 12 moles year À1 , suggesting that chemical weathering of the entire Deccan Trap basalts consumes approximately 2% ($0.24 Â 10 12 moles) of the annual global CO 2 drawdown. The present study also evaluates the influence of meteorological parameters (runoff and temperature) and physical weathering rates (PWR) in controlling the CWR at annual scale across the basin. The CWR and the SilWR show significant correlation with runoff and PWR. On the basis of observed wide temporal variations in the CWR and their close association with runoff, temperature and physical erosion, we propose that the CWR in the Narmada basin strongly depend on meteorological variability. At most locations, the total denudation rates (TDR) are dominated by physical erosion, whereas chemical weathering constitutes only a small part (<10%). Thus, the CWR to PWR ratio for the Narmada basin can be compared with high relief small river watersheds of Taiwan and New Zealand (1-5%) and large Himalayan Rivers such as the Brahmaputra and the Ganges (8-9%).
Predominant floodplain over mountain weathering of Himalayan sediments (Ganga basin)
Geochimica et Cosmochimica Acta, 2012
We present an extensive river sediment dataset covering the Ganga basin from the Himalayan front downstream to the Ganga mainstream in Bangladesh. These sediments were mainly collected over several monsoon seasons and include depth profiles of suspended particles in the river water column. Mineral sorting is the first order control on the chemical composition of river sediments. Taking into account this variability we show that sediments become significantly depleted in mobile elements during their transit through the floodplain. By comparing sediments sampled at the Himalayan front with sediments from the Ganga mainstream in Bangladesh it is possible to budget weathering in the floodplain. Assuming a steady state weathering regime in the floodplain, the weathering of Himalayan sediments in the Gangetic floodplain releases ca. (189 ± 92) Â 10 9 and (69 ± 22) Â 10 9 mol/yr of carbonate bound Ca and Mg to the dissolved load, respectively. Silicate weathering releases (53 ± 18) Â 10 9 and (42 ± 13) Â 10 9 mol/yr of Na and K while the release of silicate Mg and Ca is substantially lower, between ca. 0 and 20 Â 10 9 mol/yr. Additionally, we show that sediment hydration, [H 2 O + ], is a sensitive tracer of silicate weathering that can be used in continental detrital environments, such as the Ganga basin. Both [H 2 O + ] content and the D/H isotopic composition of sediments increases during floodplain transfer in response to mineral hydrolysis and neoformations associated to weathering reactions. By comparing the chemical composition of river sediments across the floodplain with the composition of the eroded Himalayan source rocks, we suggest that the floodplain is the dominant location of silicate weathering for Na, K and [H 2 O + ]. Overall this work emphasizes the role of the Gangetic floodplain in weathering Himalayan sediments. It also demonstrates how detrital sediments can be used as weathering tracers if mineralogical and chemical sorting effects are properly taken into account.
An investigation using environmental isotopes (δ18O and δD) was conducted to gain insight into the hydrological processes of the Ganga Alluvial Plain, northern India. River-water, shallow-groundwater and lake-water samples from the Gomati River Basin were analyzed. During the winter season, the δ18O and δD compositions of the Gomati River water ranged from −1.67 to −7.62 ‰ and −25.08 to −61.50 ‰, respectively. Deuterium excess values in the river water (+0.3 to −13 ‰) and the lake water (−20 ‰) indicate the significance of evaporation processes. Monthly variation of δ18O and δD values of the Gomati River water and the shallow groundwater follows a similar trend, with isotope-depleted peaks for δ18O and δD synchronized during the monsoon season. The isotopically depleted peak values of the river water (δ18O = −8.30 ‰ and δD = −57.10 ‰) can be used as a proxy record for the isotopic signature of the monsoon precipitation in the Ganga Alluvial Plain. Une étude faisant appel aux isotopes présents dans l’environnement (δ18O and δD) a été conduite dans le but de parvenir à bien comprendre le fonctionnement hydraulique de la Plaine Alluviale du Gange, Inde du Nord. Des échantillons de l’eau de la rivière, de la nappe superficielle et du lac ont été analysés dans le Bassin de la Rivière Gomati. Pendant l’hiver, les concentrations du δ18O et du δD dans l’eau de la Rivière Gomati s’échelonnent respectivement entre −1.67 et −7.62 ‰ et entre −25.08 et −61.50 ‰. Les valeurs extrèmes du deuterium dans l’eau de la rivière (+0.3 à −13 ‰) et dans l’eau du lac (−20 ‰) révèlent l’importance des phénomènes d’évaporation. La variation mensuelle de δ18O et δD dans l’eau de la Rivière Gomati et dans l’eau de la nappe superficielle suit une même tendance, avec des pics isotopiques moins prononcés synchronisés pour δ18O et δD pendant la mousson. Les valeurs réduites du pic isotopique de l’eau de la rivière (δ18O = −8.30 ‰ et δD = −57.10 ‰) peuvent être utilisées comme données de substitution à la signature isotopique des précipitations de mousson dans la Plaine Alluviale du Gange. Um Einblick in die hydrologischen Prozesse des Ganges-Schwemmebene (Nordindien) zu gewinnen, wurden Untersuchungen mittels der Umweltisotope δ18O und δD durchgeführt. Flusswasser, oberflächennahes Grundwasser und Binnenseewasser vom Gomati-Flussbecken wurden dazu untersucht. Das Flusswasser des Gomati zeigt während der Winterzeit Schwankungen der δ18O-Werte zwischen −1.67 bis −7.62 % und der δD Werte zwischen −25.08 und −61.50 ‰. Überwerte3) von Deuterium im Flusswasser (+0.3 bis −13 ‰) und dem Binnenseewasser (−20 ‰) zeigen die Bedeutung von Verdunstungsprozessen an. Die monatlichen Schwankungen der δ18O- und δD-Werte im Flusswasser des Gomati und des oberflächennahen Grundwassers zeigen mit an Isotop abgereicherte Spitzen für δ18O und δD eine ähnliche Tendenz und verlaufen synchron1) mit der Monsunzeit. Die an Isotopen abgereicherten Maximalwerte des Flusswassers (δ18O = −8.30 ‰, und δD = −57.10 ‰) können als Aufzeichnung2) für die Isotopen-Zusammensetzung des Monsun-Niederschlags in der Ganges-Schwemmebene verwendet werden. Se realizó una investigación usando isótopos ambientales (δ18O y δD) para conocer los procesos hidrológicos de la planicie aluvial de Ganga, norte de la India. Se analizaron muestras del agua del río, del agua subterránea somera y del agua del lago en la cuenca del Río Gomati. Durante la estación invernal, las composiciones de δ18O y δD en el agua de río Gomati varía de −1.67 a −7.62 ‰ y de −25.08 a −61.50 ‰, respectivamente. Los valores en exceso de Deuterio en el agua del río (+0.3 a −13 ‰) y en el agua del lago (−20 ‰) indican la significación de los procesos de evapotranspiración. La variación mensual de los valores de δ18O y δD en el agua del Río Gomati y en el agua subterránea somera sigue una tendencia similar, con picos de isótopos empobrecidos para δ18O y δD sincronizados durante la estación monzónica. Los valores de picos empobrecidos isotópicamente del agua de río (δ18O = −8.30 ‰ y δD = −57.10 ‰) pueden ser usado como un proxy de registro para la firma isotópica de la precipitación monzónica en la planicie aluvial de Ganga. Foi realizada uma investigação com isótopos ambientais (δ18O e δD) para o estudo dos processos hidrológicos que ocorrem na Planície Aluvial do Rio Ganges, no norte da Índia. Foram analisadas amostras de água do rio, de águas subterrâneas pouco profundas e de água de lago, provenientes da Bacia Hidrográfica do Rio Gomati. Durante a estação de inverno, a composição em δ18O e δD da água do Rio Gomati variou entre −1.67 e −7.62 ‰ e −25.08 e −61.50 ‰, respetivamente. O excesso nos valores de Deutério na água do rio (+0.3 a −13 ‰) e na água do lago (−20 ‰) indicam que os processos de evaporação são significativos. A variação mensal dos valores de δ18O e δD da água do Rio Gomati e da água subterrânea pouco profunda segue uma tendência similar, com picos de depleção de isótopos de δ18O e δD sincronizados durante a estação das monções. Os valores dos picos de depleção isotópica da água do rio (δ18O = −8.30 ‰ e δD = −57.10 ‰) podem ser usados como indicadores para a assinatura isotópica da precipitação da monção na Planície Aluvial do Ganges.