Major ion chemistry and weathering control in a high altitude basin: Alaknanda River, Garhwal Himalaya, India

An analytical study of major cations and anions of the glacier fed Alaknanda River and its tributaries has been carried out to assess the weathering and geochemical processes in the high altitude river basin. The Alaknanda and its tributaries were sampled during pre-monsoon (June 1992) and post-monsoon (October 1992) season for the present hydrogeochemical study. Calcium and magnesium are the major cations, accounting for 85% of the total cations. Among the anions, bicarbonate is the most dominant (78%) with minor contribution from sulphate (19%) and chloride (3%). The average (Ca+Mg)/HCO3 equivalent ratio of 1.2, a relatively high contribution of (Ca+Mg) to the total cations (TZ(+)) and high (Ca+Mg)/(Na+K) ratio indicate that the carbonate weathering could be the primary source of the major ions to these waters. Wide seasonal and spatial variations are observed in the total dissolved solids (TDS) and total suspended matter (TSM) concentration in the Alaknanda river basin. The chemical denudation rate of Alaknanda is 133 t km(-2) year(-1), nearly double that of the Ganga river basin and three times the world average. The sediment erosion rate of the basin is 356 t km(-2) year(-1), double that of the world physical denudation rate. The high rates of denudation are attributed to high relief, intense monsoon rainfall, landslides and glacial erosion in the Himalaya.