Comparison of spatial interpolation methods and selecting the appropriate method for mapping of nitrate and phosphate in the Shahrekord Aquifer

Selecting appropriate interpolation method can lead to the production of more accurate maps. The aim of this study was to determine the appropriate method of interpolation and mapping for nitrate and phosphate in the Shahrekord Aquifer from the kriging، co-kriging and inverse distance weighting. For this purpose، the concentrations of nitrate and phosphate were measured in 97 agricultural wells. For both nitrate and phosphate، the ordinary kriging was appropriate and enough. For nitrate، ordinary kriging resulted in R2 =0. 99، RMSE <1 mg / L and ME <0. 1 for nitrate; and R2 close to the unity، RMSE =0. 01 and ME close to zero for phosphate. Efficiency of the inverse distance weighting method was weaker than kriging and its efficiency statistic further deteriorated by increasing its exponent from 1 to 5. However، this method is a good alternative for kriging. Co-kriging did not improve the interpolation over kriging and therefore، is not worth the costs and efforts involved. Maps showed that the concentrations of both pollutants increased from the northwestern to the southwestern part of the aquifer. Examination of conformity of observations statistical summary to maps further indicated the applied kriging was appropriate. In general، using ordinary kriging is recommended for mapping of nitrate and phosphate in the Shahrekord Aquifer، due to higher accuracy، less calculation and less required data.