Spatial variation of nitrate concentrations in groundwater by Geostatistics (Case Study: Kurdan Plain)

Spatiality assessment of groundwater pollution is very important to determine water quality condition، pollution sources and management decisions. In this case، GIS and geostatistics methods can be useful tools. Spatiality of groundwater quality parameters، in relation with various land uses، can be very extremely. Therefore water samples from 52 wells in the Kurdan area were analyzed in this study. The results show that nitrate concentrations are less than maximum acceptable concentration in drinking water (i. e. 50 mg/L as nitrate recommended by ISIRI and WHO guideline values) except to one sample (2 percent of samples) in the study area. Various geostatistics methods، e. g. IDW (power 1-4)، ordinary Kriging and RBF (five Kernel functions) were compared after assessing the variograms and the spatiality of nitrate samples. Then the model parameters were calibrated and through the specific methods، predicted and standard errors maps were prepared. Errors criteria show that Kriging is the best fitting model in the study area. Finally، probability map of NO3 concentrations exceeding the threshold value of 50 mg/L، is generated using the Indictor Kriging method. Spatiality of NO3 show that Nitrate concentration is increased where the rock type is permeable، land use is agriculture and slope is enough low to infiltrate polluted water into the wells. This research also tries to describe how to assess the spatiality of groundwater parameters by GIS.