Effects of spatially varying association between land use and water quality in Bali Province, Indonesia using geographically weighted regression

Due to the rapid increase of land use in Bali province, there would be a gradually effect on water quality since has been widely agreed by the scientific community that there is a significant relationship between land use and water quality. For evaluating this association, this study examined the effect of spatial variation between land use categories like built-up, rice field, farm and forest and water quality in three selected known rivers (Ayung, Badung and Mati river). The study employed Geographically Weighted Regression (GWR), which consider local parameters drawn from Landsat 8 OLI in October 2015 and water quality data consists of 22 parameters and grouped into four aspects (i.e., physical, chemical, microbial and radiological aspect) are collected from Bali-Penida river region office in July 2015. Some of the key research results exhibit that the physical (Conductivity, TSS and Turbidity) and chemical (DO, KMnO₄, COD, BOD, NO₃, NO₂, NH₃ and PO₄) aspects have a strong correlation (R² > 0.5) with built-up and rice field, however, microbial and radiological water quality parameters have low relationship (R² < 0.4) with all land uses except Pb and total Fe (R² > 0.6) under radiological aspect.