Comparison of Spatial Interpolation Methods to Mapp Heavy Metals Concentrations in Surface Soil of Aran-O-Bidgol City

Selecting a suitable interpolation method is a main factor of surface analysis and it is a difficult task in geostatistical analysis since different methods of interpolation can result in different surfaces and ultimately different results. Hence, the aim of this study is to evaluate the performance of different interpolation methods in determining the spatial concentration of Cd, Zn and Cu in the Surface soil of Aran-O-Bidgol City.
A total of 135 surface soil (0-20 cm) samples were collected in the study area and the soil heavy metals concentrations were determined. The spatial distribution of heavy metals concentration in Surface Soil of Aran-O-Bidgol was evaluated using different interpolation methods including ordinary Kriging, CoKriging, Inverse Distance Weighting, Local Polynomials and Radial Basis Function. Cross validation and MSE, MBE, RMSE, NSE, PBIAS were applied to estimate their accuracy.
Findings: According to the results Ordinary Kriging (spherical model) had the best efficiency for estimating Cd and Cu concentrations and Ordinary Kriging (exponential model) had the best efficiency for estimating distribution pattern of Zn concentration in the soil of this region. The weight parameter has a significant influence on the accuracy of interpolation. The higher the order of local polynomial, the larger the accuracy of cross validation, whereas, the greater the weighting power of IDW for Cd and Zn, the greater error and larger accuracy of the interpolation will be for Cu.
Discussion and Although all of the considered interpolation methods had a high prediction accuracy of the mean content for soil heavy metals, but taking all cross validation indicators into consideration, Ordinary Kriging (OK) method shows a generally better performance than other methods.