Investigating temporal and spatial changes in the quality of underground water in Marvast plain

This research was conducted with the aim of investigating temporal and spatial changes in the quality of underground water in Marvast plain in order to be used in planning for these resources. For this reason, the underground water quality data of Marvast Plain was prepared and selected for the research through the review and test of Run Test and Makos for the statistical period of 21 years (2001 to 2021). By performing trend analysis, the presence of trend in all data was determined and during the implementation of geostatistical methods, the trend was removed. Also, for the implementation of geostatistical methods, half-variable and half-variable cross-plot were chosen and due to the higher R2, lower RSS and stronger spatial structure, the best model was selected, and the exponential model was found to be suitable for most of the parameters. Then RBF, IDW with powers of 1 and 2, normal kriging and normal cokriging were used to perform interpolation. The most accurate method was selected for each parameter with the mutual evaluation method and three error estimation indices MAE, MBE and RMSE. The results showed that the normal cokriging method is the best method for most parameters (cation, anion, Ec, Cl, Ca, K, Mg, Na and TH). For the SAR, So4 and pH parameters, the normal kriging method and for the Na percentage parameter, the radial basis function was found to be the most suitable method. The results showed that the concentration of most parameters has an upward trend from west to east and south to north. Also, with the passage of time, the trend of reducing the quality of underground water was observed.