Abstract
The quality of river water is influenced by a combination of natural and human factors, and its spatial and seasonal variations can have significant impacts on the health of aquatic ecosystems and human uses. The present study aimed to investigate and compare the summer and winter variations of chemical parameters of water, including nitrate (NO3-), phosphate (PO43-), bicarbonate (HCO3-), sulfate (SO42-), ammonium (NH4+), silica (SiO2), sodium (Na+), potassium (K+), and total dissolved solids (TDS) in the Gheshlaqh, Gaveroud, and Sirvan rivers in Kurdistan Province. Sampling was conducted at six stations during two seasons (summer and winter) of 2024, and the data were modelled using the Inverse Distance Weighting (IDW) interpolation method in the GIS environment. The results showed that in summer, due to reduced flow discharge and increased pollutant inputs, the concentrations of most parameters increased, while in winter, dilution effects caused by precipitation and runoff led to their relative decrease. Downstream of the Sanandaj wastewater treatment plant (station 3) had the highest concentrations of nitrate, phosphate, ammonium, sodium, and potassium in both seasons, indicating the dominant role of point sources in determining water quality. The Gaveroud branch acted as a diluting flow, resulting in a relative reduction in pollutant concentrations when merging with the main river. The variation patterns of bicarbonate and silica were mainly controlled by geological characteristics and hydrological conditions. The assessment of TDS indicated that high values, especially in summer, could pose a serious threat to the quality of water for agricultural and drinking purposes. Overall, the findings demonstrated that improving the efficiency of the wastewater treatment plant and land-use management in the watershed could serve as key strategies for enhancing the sustainability of water resources in the region.

Abstract
The quality of river water is influenced by a combination of natural and human factors, and its spatial and seasonal variations can have significant impacts on the health of aquatic ecosystems and human uses. The present study aimed to investigate and compare the summer and winter variations of chemical parameters of water, including nitrate (NO3-), phosphate (PO43-), bicarbonate (HCO3-), sulfate (SO42-), ammonium (NH4+), silica (SiO2), sodium (Na+), potassium (K+), and total dissolved solids (TDS) in the Gheshlaqh, Gaveroud, and Sirvan rivers in Kurdistan Province. Sampling was conducted at six stations during two seasons (summer and winter) of 2024, and the data were modelled using the Inverse Distance Weighting (IDW) interpolation method in the GIS environment. The results showed that in summer, due to reduced flow discharge and increased pollutant inputs, the concentrations of most parameters increased, while in winter, dilution effects caused by precipitation and runoff led to their relative decrease. Downstream of the Sanandaj wastewater treatment plant (station 3) had the highest concentrations of nitrate, phosphate, ammonium, sodium, and potassium in both seasons, indicating the dominant role of point sources in determining water quality. The Gaveroud branch acted as a diluting flow, resulting in a relative reduction in pollutant concentrations when merging with the main river. The variation patterns of bicarbonate and silica were mainly controlled by geological characteristics and hydrological conditions. The assessment of TDS indicated that high values, especially in summer, could pose a serious threat to the quality of water for agricultural and drinking purposes. Overall, the findings demonstrated that improving the efficiency of the wastewater treatment plant and land-use management in the watershed could serve as key strategies for enhancing the sustainability of water resources in the region.

Abstract
The quality of river water is influenced by a combination of natural and human factors, and its spatial and seasonal variations can have significant impacts on the health of aquatic ecosystems and human uses. The present study aimed to investigate and compare the summer and winter variations of chemical parameters of water, including nitrate (NO3-), phosphate (PO43-), bicarbonate (HCO3-), sulfate (SO42-), ammonium (NH4+), silica (SiO2), sodium (Na+), potassium (K+), and total dissolved solids (TDS) in the Gheshlaqh, Gaveroud, and Sirvan rivers in Kurdistan Province. Sampling was conducted at six stations during two seasons (summer and winter) of 2024, and the data were modelled using the Inverse Distance Weighting (IDW) interpolation method in the GIS environment. The results showed that in summer, due to reduced flow discharge and increased pollutant inputs, the concentrations of most parameters increased, while in winter, dilution effects caused by precipitation and runoff led to their relative decrease. Downstream of the Sanandaj wastewater treatment plant (station 3) had the highest concentrations of nitrate, phosphate, ammonium, sodium, and potassium in both seasons, indicating the dominant role of point sources in determining water quality. The Gaveroud branch acted as a diluting flow, resulting in a relative reduction in pollutant concentrations when merging with the main river. The variation patterns of bicarbonate and silica were mainly controlled by geological characteristics and hydrological conditions. The assessment of TDS indicated that high values, especially in summer, could pose a serious threat to the quality of water for agricultural and drinking purposes. Overall, the findings demonstrated that improving the efficiency of the wastewater treatment plant and land-use management in the watershed could serve as key strategies for enhancing the sustainability of water resources in the region.

Abstract
The quality of river water is influenced by a combination of natural and human factors, and its spatial and seasonal variations can have significant impacts on the health of aquatic ecosystems and human uses. The present study aimed to investigate and compare the summer and winter variations of chemical parameters of water, including nitrate (NO3-), phosphate (PO43-), bicarbonate (HCO3-), sulfate (SO42-), ammonium (NH4+), silica (SiO2), sodium (Na+), potassium (K+), and total dissolved solids (TDS) in the Gheshlaqh, Gaveroud, and Sirvan rivers in Kurdistan Province. Sampling was conducted at six stations during two seasons (summer and winter) of 2024, and the data were modelled using the Inverse Distance Weighting (IDW) interpolation method in the GIS environment. The results showed that in summer, due to reduced flow discharge and increased pollutant inputs, the concentrations of most parameters increased, while in winter, dilution effects caused by precipitation and runoff led to their relative decrease. Downstream of the Sanandaj wastewater treatment plant (station 3) had the highest concentrations of nitrate, phosphate, ammonium, sodium, and potassium in both seasons, indicating the dominant role of point sources in determining water quality. The Gaveroud branch acted as a diluting flow, resulting in a relative reduction in pollutant concentrations when merging with the main river. The variation patterns of bicarbonate and silica were mainly controlled by geological characteristics and hydrological conditions. The assessment of TDS indicated that high values, especially in summer, could pose a serious threat to the quality of water for agricultural and drinking purposes. Overall, the findings demonstrated that improving the efficiency of the wastewater treatment plant and land-use management in the watershed could serve as key strategies for enhancing the sustainability of water resources in the region.