Spatial analysis of total dissolved solids in Dezful Aquifer: Comparison between universal and fixed rank kriging.

The spatial structure and auto-correlation of total dissolved solids (TDS) in an aquifer located in southwestern part of Iran were investigated by both Moran's index and variography. Since the feature of interest was non-stationary so, conventional methods of spatial analysis were not applicable and Universal kriging (UK) as a common method for spatial prediction of features with a spatial trend along with a novel geostatistical method known as fixed rank kriging (FRK) were utilized in this respect. The results of Moran's index were consistent with that of spatial analysis by geostatistical methods indicating the dominance of spatial clusters within the extent of study area. The spatial analysis by FRK was more efficient than that of its UK counterpart however the performance of UK was reasonable enough, as well. A variable selection by random forest (RF) was applied on eleven other water quality parameters that were the main constituents of TDS to identify the main parameters influencing the observed variability of TDS. It was turned out that RF is a viable method for variable selection in the realm of environmental sciences.