Spatiotemporal Variability of Physicochemical Water Quality Parameters in the Tigris River within Kut City, Iraq

Abstract

  This study examined the spatiotemporal variations of water quality of Tigris River in Al-Kut city, Iraq to evaluate anthropogenic and hydrological effects. Sixteen physicochemical parameters were analysed from September 2025 to May 2026 and sampled monthly at four monitoring stations, according to the ISO 5667 protocols. The results showed stable baseline levels of pH (7.27±0.19) and dissolved oxygen (8.08±1.66mg/L); while pollution indicators (COD, phosphate, turbidity and nitrate) exhibited high variability (CV>70%). A distinct spatial gradient was observed, with the upstream site being optimal and sites in the urban areas being extremely degraded. Progressive deterioration was found from the autumn (WQI ≈ 50) to the spring (WQI >1300) with seasonal analysis; this was attributed to the lack of hydrological flushing and thermal changes, and possible cumulative organic loadings. Two independent drivers were found using principal component analysis: mineral concentration/dilution gradient (PC1, 51.6% variance) and an organic/nutrient enrichment axis (PC2, 19.6%). Water quality patterns were also confirmed by hierarchical clustering which showed that spatial differentiation is completely masked by the effect of seasonal forcing. These results emphasize the importance of the system during the spring season and the need for a system of seasonally adjusted management practices to lessen the effects of urban and agricultural pollution in semi-arid watersheds.