Spatial Variability of Nitrate and Phosphate and Their Mapping in the Shahrekord Groundwater

Groundwater in many parts of the world is the main source of drinking water. The Shahrekord aquifer (Iran) supplies the drinking water to the residents of Shahrekord. The aim of this research was to geostatistically analyze and map nitrate and phosphate concentrations in this aquifer. For this purpose, 100 agricultural wells, located in the Shahrekord plain, were sampled on three different dates during 2010 and water samples were analyzed for nitrate and phosphate. The results presented here are based on the average concentrations of the three samples. The mean concentrations of nitrate and phosphate were 25.9 and 0.09 mg/L, respectively. Comparison shows that these mean concentrations have increased since 2007. The spatial variability of nitrate and phosphate were better described by spherical semivariogram models. Examination of maps shows that the southeast of the aquifer had the highest concentrations of both nitrate and phosphate. In some wells, located in the southern part of the aquifer, the concentration of nitrate sometimes exceeded the permissible level of 45 mg/L. This may be attributed to the presence of the Shahrekord municipal wastewater treatment plant, the shallower water table in this part, and also due to the inflow of groundwater.