Nitrate and Phosphate Contamination in an Intensively Cultivated River Delta: Role Of Surface water and Groundwater Interaction

Non - point sources of contamination in surface water and groundwater is a serious environmental concern. The aim of this study is to identify the spatiotemporal variation in surface water- groundwater interaction and its effect on nitrate and phosphate concentration, in an intensively irrigated Cauvery river delta, India. This river is non-perennial and flows for about 4 months in a year. Surface water and groundwater sampling was carried out thrice in a year from 2013 and were analysed for organic carbon, major and minor ions. Statistical methods and geochemical modelling were used to identify the surface water-groundwater interaction. Generally, the ionic concentrations in surface water and groundwater is low while the river flows, whereas the concentration increases during no flow periods. The concentration of nitrate and phosphate were high in groundwater than the river water. There is a significant spatiotemporal variation in the interaction between the river and groundwater which thereby controls the concentration of major and minor ions and organic carbon. Agricultural runoff, soil organic matter and domestic sewage disposal along the riverbanks are the major causes of increased nutrient fluxes in the deltaic regions. The study therefore indicates the role of surface water and groundwater interaction in influencing the pollutant concentrations derived from non-point sources in a non-perennial river.