Application of Geostatistical Methods for determining nitrate concentrations in Groundwater (case study of Mashhad plain, Iran)

ABSTRACT: Excess nitrate in the soil can be easily moved with Irrigation water, rainfall or melting snow to pass through different layers of soil and reach groundwater. Water pollution occurs when the elements in the water exceeds the limit. If nitrate in drinking water is greater than the limit it will cause disease in humans. The purpose of this study was the evaluation of geostatistical methods for estimation of the spatial variables nitrate, sodium and electrical conductivity in groundwater of Mashhad (Iran ). Samples were taken from 276 wells and the parameters nitrate, sodium and electrical conductivity were measured. Data were analyzed with software GS+. To investigate the spatial correlation of data, experimental Variogram each variable were calculated and plotted. Amounts of nitrates, sodium and electrical conductivity were estimated with using geostatistical methods. Cross validation method was used to determine the accuracy of the estimated data. After drawing the variogram, the best model was fitted based on minimum RSS. For determining the most appropriate method estimation of the root mean square error (RMSE) and scatter plot method was used. Results showed that kriging methods are more accurate. Sodium and nitrate maps were drawn based on kriging method and areas where nitrate concentrations greater than 50 mg per liter, were identified. Comparing the plans of sodium and nitrate showed that sodium and nitrate concentrations in a certain part of the scope of this study are higher than the limit.