Spatial Assessment of Reservoir Water Quality Using GIS-Based Thematic Mapping: A Case Study of Kesikköprü Dam Lake, Türkiye

Assessing the water quality of reservoirs used for drinking water supply is essential for sustainable water resource management. This study evaluates the spatial distribution of key water quality parameters in the Kesikköprü Dam Lake, an important drinking water source located in the Kızılırmak Basin, Türkiye. Monthly monitoring data collected from five reservoir stations (R-1–R-5) between April 2022 and March 2023 were analyzed, and annual average values of selected physicochemical and chemical parameters, including electrical conductivity (EC), total Kjeldahl nitrogen (TKN), total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), biochemical oxygen demand (BOD), arsenic (As), and iron (Fe), were calculated. Spatial distribution maps of these parameters were generated using the Kriging interpolation method within a Geographic Information System (GIS) environment (ArcGIS 10.8). The obtained results were evaluated in accordance with national surface water and drinking water quality regulations. EC values ranged between 1658 and 1735 µS/cm and corresponded to moderate surface water quality while remaining within the A1 drinking water category. Nutrient parameters generally indicated very good to good water quality conditions, although localized increases in TKN suggested potential agricultural runoff influence. Organic pollution indicators (COD and BOD) remained within very good to good quality classes across the reservoir. Arsenic and iron concentrations showed moderate spatial variability but remained within the A2 treatment category, indicating that conventional treatment processes would be sufficient for potable water production. Overall, the results demonstrate that reservoir water quality is mainly influenced by diffuse agricultural pressures and natural geological conditions rather than industrial sources. The integration of monitoring data with GIS-based spatial analysis provides an effective framework for identifying spatial variability in reservoir water quality and supporting basin-scale water resource management.