Determination of areas vulnerable to pollution in a karstic river basin in Turkey via a decision support system based on DRASTIC,SWAT and isotopes analysis

Determination of areas vulnerable to water pollution in river basins helps to generate appropriate water management protection plans. This study aims to define areas vulnerable to pollutants in a data-scarce karstic river basin in Turkey by using a holistic approach integrating the Soil and Water Assessment Tool (SWAT), the DRASTIC framework, and selected isotopes within a decision support system based on a geographic information system to delineate vulnerable areas. DRASTIC was used to show groundwater vulnerability to pollutants. The concentrations of isotopes ¹⁸O, ²H, and ³H in groundwater were used to define the vulnerable areas of the karst region. SWAT was utilized to show watershed vulnerability to pollutants in shallow aquifers. The recharge rate parameter in DRASTIC was obtained from SWAT. This methodological approach was applied to the Yuvac?k Dam Basin in Kocaeli, part of the Marmara River Basin, as it is a good example of a karstic watershed. According to this study, each approach provides different vulnerabilities when applied separately. The final map obtained from the integrated approach shows that drinking water supplies in the northeast and northwest parts of the basin are highly vulnerable to pollution. All the karst spring catchments and areas near the basin outlet are highly vulnerable. Moreover, across all water samples taken across the basin, those exhibiting the highest concentrations in nitrate were all found in the areas mapped as highly vulnerable. The methodology was validated by analyzing nitrate concentration in 22 groundwater and surface-water samples.