Estimation of Nitrate Leaching in Groundwater in an Agriculturally Used Area in the State Karnataka, India, Using Existing Model and GIS

Water pollution is one of the biggest environmental problems and nitrate is among the most common and widespread pollutants in groundwater. There has been an increasing demand for fresh water in the last two decades due to a progressive increase in population. In addition, people face serious water shortages, because groundwater has been used faster than it is naturally replenished. At the same time an increasing amount of wastes and chemicals causes contamination of water resources, especially of groundwater. Although the movement of groundwater through the aquifer has often the effect of removing a lot of impurities from the water by filtering it through the porous rocks, so that groundwater is generally much cleaner than surface water, there are many contaminants which are not easily degraded in the subsurface. Such is the case for nitrate which is impounded into the groundwater by agricultural activities, namely fertilizers and livestock manure. Since nitrate is soluble and negatively charged, it has high mobility and is thus easily leached from the unsaturated zone. In this research work, an attempt has been made to estimate nitrate leaching to groundwater at six different places around the village of Srirangapatnataluk where organic manure and inorganic fertilizers, together with irrigation water and cesspools are the major sources of nitrate in the area. Existing models and Arc-GIS have been used for the analysis. The results indicate that, except for Belagola village, the groundwater nitrate concentrations underneath the irrigated lands are still within the permissible limit, which means that the water of these villages can be used for both drinking and irrigation purposes. The average leached nitrate amounts in the sampled areas supplied from irrigated land have been estimated to range between 51.23 and 74.93 kg/ha/year. For the groundwater nitrate concentrations underneath the cesspools, the results of the analysis show that they are all within the permissible limit, except for the villages of Karekura and Bommuragrahara. Nitrate leaching amounts supplied from the cesspools lie between 87.81 and 381.96 kg/year. The reasons for this wide margin are likely losses due to denitrification and volatilisation processes. (C) 2015 The Authors. Published by Elsevier B.V.