Seasonal variation of the solute and suspended sediment load in Gangotri glacier meltwater, central Himalaya, India

Abstract

A systematic study on the seasonal variation of major cations and anions was carried out to understand the source of dissolved ions as well as the geochemical weathering processes controlling the meltwater chemistry of Gangotri glacier. Calcium and magnesium are the major cations while sulphate is the dominant anion followed by bicarbonate. The high ratios of (Ca+Mg)/(Na+K), Ca/Na, Mg/Na, HCO3/Na and low ratio of (Na+K)/TZ+ for pre-monsoon, monsoon and post-monsoon seasons indicate the dominance of carbonate weathering, which is a major source of the dissolved ions in the meltwater of Gangotri glacier followed by silicate weathering. High equivalent ratios of Na/Cl and K/Cl as compared to sea water indicate relatively lesser contribution from atmospheric input to the chemical composition of meltwater. Correlation matrix and factor analysis were used to identify various factors controlling the major ion chemistry. Marked seasonal and diurnal variations were observed in the dissolved ions and suspended sediment concentration. Daily mean suspended sediment concentration for pre-monsoon, monsoon and post-monsoon was observed as 1719, 3281 and 445mgl−1, respectively. Highest suspended sediment load was observed in monsoon season followed by pre-monsoon and post-monsoon seasons. The cation denudation rates of Gangotri glacier meltwater were calculated to be 42.2, 46.5 and 15.9tkm−2y−1 for pre-monsoon (June only), monsoon and post-monsoon respectively. These values are higher than that of other Himalayan glaciers. Whereas physical weathering rate of the Gangotri glacier catchment was observed to be 7056, 15,344 and 588tkm−2y−1 for pre-monsoon (June only), monsoon and post-monsoon respectively, much higher than the Indian and world averages of river.