Modeling and Monitoring Subsurface Water Quality Indicators of Sistan Plain Using Geographic Information Systems

Investigating the spatial variation of groundwater quality parameters is important in identifying the quality of the aquifer and contaminating resources, and determining the most appropriate management solutions. Geostatistical and GIS methods can be useful tools in this regard. The aim of this study was to evaluate the geostatistical methods in order to investigate and analyze the spatial amount of salinity, nitrate, and total dissolved solids of subsurface waters of Sistan Plain in northern Sistan and Baluchestan province. For this purpose, ordinary Kriging (OK) and simple Kriging (SK) and certain methods such as inverse distance weigthing (IDW), local polynomial interpolation (LPI), global polynomial interpolation (GPI) and radial basis function (RBF) were used. First, the normality of the data was investigated and the non-normal data were normalized by logarithmic method. Then analysis of variograms was performed. The results were evaluated using a cross-evaluation method. The fitting results of the models showed that the EC and TDS indices follow the Gaussian model and the nitrate index follows the spherical model, and simple kriging method is suitable for salinity and nitrate mapping and ordinary kriging for zoning maps of TDS. Moreover, based on the Schuller's diagram, in terms of TDS, sub-surface waters of the region are classified as good to acceptable and in terms of salinity for agricultural use in the moderate to severe problem class.