Weathering and geochemical processes controlling solute acquisition in Ganga headwater-Bhagirathi river, Garhwal Himalaya, India

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/km(2)/yr, higher than the Indian and global average.