Area-differentiated modelling of excess nutrient and contaminant leaching risks at the river-basin scale using a hydrological approach in India

Application of excess nutrients, such as fertilizers, is a significant and sometimes even major component of groundwater pollution. Diffuse inputs of nutrients and contaminants to the groundwater are related to runoff generated from precipitation on a catchment. This implies that the analysis of diffuse fluxes from the land surface to the groundwate- r requires an analysis of water fluxes for a catchment. This requires the simulation and modelling of total runoff, groundwater recharge, and plant-available water as a function of the regional interaction of the climate, soil, hydrogeology, topography and land-use conditions in the river basin. A model has been developed for large river basins in India, and has been applied to the Upper Yamuna basin, to quantify the exchange probability of plant-available soil water, which can be taken as a measure to determine the nutrient and contaminant leaching risk of a site. It was found that, with the available large-scale databases and methods, regional patterns of the total runoff could be simulated successfully. In this way, about 7500 km2 of the total 12 000 km 2 of the Upper Yamuna basin was classified as an area sensitive to nutrient and contaminant leaching.