Assessment of groundwater contamination from fertilizers in the Delhi area based on O-18, No-3(-) and K+ composition

Increasing application of nitrogen fertilizers in the irrigated lands of the studied area is likely to create a blanket non-point source of nitrate. Groundwater contamination from fertilizers, in this context, has been reported as derived from NO3-, K+ and O-18 composition of groundwater. The data suggest both point and non-point sources of groundwater pollution. Thirty-three percent of the groundwater samples showed nitrate contents exceeding the general acceptable Limit of 20 p.p.m. and 15% of the samples crossed the maximum permissible limit of 45 p.p.m. High nitrate levels are associated with high delta(18)O values, clearly indicating that significant quantities of evaporated (isotopically enriched) irrigation water infiltrate along with fertilizer nitrate to the groundwater system. Different delta(18)O-NO3- trends suggest isotopically distinct, non-point source origins which vary spatially and temporally, due to different degrees of evaporation/recharge and amounts of fertilizer applied. A scatter diagram of NO3- vs K+ suggests a common source of these ions when the concentration is less than 40 p.p.m. The investigation indicates that a combination of isotope (O-18) and hydrochemical data can clearly characterize the impact of fertilizer on groundwater. Application of high nitrate, high potassium groundwater irrigation can minimize the requirement for inorganic fertilizers and bring down the cost of cultivation considerably, through appropriate management of fertilizer and water and modifications in agronomic practices and strategies on crops grown. Such practices will help protect groundwater from further degradation. (C) 1997 Published by Elsevier Science B.V.