Nutrient modelling in the Ganga river basin

Abstract:

Ganga river basin (GRB) is one of the most important river basins in the Indian subcontinent and the world. This river basin alone is responsible for supporting one-third of the population of India through agriculture. The central region of the river basin is a huge fertile floodplain which aids the production of crops. Further, GRB is also one of the most populous river basins in the world supporting almost 400 million people of India. With the increasing use of fertilizers in agriculture and untreated sewage waste from the industries, there is a need to assess the water quality and the contamination in surface water. We use the Soil Water Assessment Tool (SWAT) to model the hydrology and the impact on hydrology, sediment, and nutrients load, due to physical changes brought in the large ungauged river basins. We used gridded climate data from Indian Meteorological Department (IMD) and water quality data from CWC as well as SRTM 90 m DEM, 300 m Land use/land cover map from Climate Change Initiative (CCI) and 7 km soil map from Food and Agriculture Organization (FAO). We calibrated the SWAT model for 1951-1960 with three years of the warm-up period. We validated the SWAT model for 1964-1973 to evaluate the performance of the calibrated model. Our model performed well in both calibration and validation phase with Nash-Sutcliffe Efficiency (NSE) of 0.88, and 0.68 respectively. We observed that the peaks and low flows were accurately captured by the model during both phases. Further, we used the calibrated model to simulate the nutrient loading at 100 locations spread across the river basin from 1990 to 2016. We found that the upper reach locations had low nutrient loading and we did not find any significant changes in the nitrogen and phosphorous loading at the upper reach locations. Middle reach locations like Kanpur and Varanasi were found to have an increase in the loading after the 2000s.