Trends in groundwater pollution with nitrate and phosphate may be an indication of water resources management. The aims of this research were to determine changes in nitrate and phosphate concentration and changes in spatial variability patterns of nitrate and phosphate and distribution over a 5-year period. To do this, 100 agricultural wells were sampled in the years 2006, 2010 and 2011, and analyzed for nitrate and phosphate concentrations. From 2006 to 2011, the mean nitrate concentration increased from 18 to 27 mg/L and the mean phosphate concentration from 0.05 to 0.15 mg/L. Spatial patterns did not change, and spherical model described the patterns throughout this period. Maps showed that the nitrate and phosphate concentrations are higher in the south, and lower in the north of the aquifer. It seems that the presence of the municipality treatment plant, intensive cattle farming, shallower water-table and inward flow gradient may be the reasons for the higher concentration in the southern part of the aquifer. From the comparison of the maps, it was clear that the areas of less polluted classes had shrunk while the areas of more polluted classes had grown from 2006 to 2011.

Keywords: Aquifer, Kriging, Mapping, Variogram.

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