Evaluating the impact of land use on urban surface water quality: a case study of the Western Tehran watershed

Abstract

The quality of urban surface waters is strongly influenced by land-use patterns, and changes in the type and intensity of human activities can exert significant impacts on the ecological health of aquatic systems. This study aims to evaluate the effects of land use on the water quality of the Kan River in the western Tehran watershed using the IRWQIsc index and spatial–statistical analyses. To achieve this, land-use maps were updated using Sentinel, Landsat, and Google Earth imagery, and water-quality data were collected from 10 sampling stations during 2024–2025. Land-use characteristics were analyzed within six spatial buffer zones (100, 500, 1000, 2000, 3000, and 5000 m). The results showed a considerable decline in water-quality index scores toward the downstream sections of the river. Agricultural, industrial, and commercial land uses exhibited the strongest associations with increased levels of nitrogenous, phosphorous, and organic pollutants. Redundancy Analysis (RDA) revealed that with increasing spatial scale, the influence of land-use classes on water-quality parameters shifts from point-source to multi-factor patterns. Green spaces and barren lands showed inverse relationships with pollutant concentrations, maintaining their protective role across all spatial scales. The findings underscore the significance of multi-scale spatial analysis for integrated urban water-quality management and provide a foundation for environmental planning and water-resource policymaking in the Tehran metropolitan region.