A hydro-chemical study of a mountainous watershed: the Ganga, India

A hydro-chemical study has been carried out on a 37-km stretch of the River Ganga from Deoprayag to Rishikesh (India) during the period from April 1999 to March 2000. The assessment of sediment and nutrient load has been considered to evaluate the current state of pollution through real time measurements. The values of pH and conductance are well within the limits prescribed for drinking water. The maximum suspended sediment concentrations of 1,405 and 2,002 mg/L were recorded at Deoprayag and Rishikesh, respectively, during the rainy season. A large amount of sediment and nutrient load is transported from the watershed during the rainy season. Concentrations of N(O3-)-N and N(H3-)-N at Deoprayag varied from 0.30 to 0.50 and 0.02 to 0.12 mg/L, respectively, depending on season. Examination of the results showed clearly that N(H3-)-N was generally low as compared to N03-N. Depending on the pH and temperature of soils, NH4+ and NO3- ions are produced in the watershed through ammonification and nitrification of organic matter and mobilized into rivers through run-off. Dissolved N and P from fertilizer application, sewage and non-point source run-off contribute significant quantities of these nutrients in river water. The nitrate and phosphate are transported from the cropland either by being adsorbed on to soil particles that are subsequently eroded, or dissolved in runoff water from agricultural land. The data generated through the study will be useful for development and management planning of the hilly watershed.