Assessing spatial trends and land use impacts on surface water quality: A case study of the Saigon and Vam Co Rivers in southern Vietnam

This study evaluates the spatial distribution of heavy metals, water quality parameters, and ecological risks in the Saigon and Vam Co Rivers, two hydrologically connected systems in southern Vietnam. Using a multi-index assessment approach, incorporating the Heavy Metal Evaluation Index (HEI), Water Pollution Index (WPI), and Risk Quotient (RQ), we identify pollution hotspots, dominant contamination sources, and ecological threats associated with urban-industrial discharges and agricultural runoff. Due to the release of untreated domestic and industrial wastewater effluents, the Saigon River exhibits localized pollution peaks in its densely populated urban section, where Cd, Zn, and Ni concentrations exceed WHO and Vietnamese water quality standards. In contrast, the Vam Co River demonstrates a gradual downstream increase in contamination, driven by diffuse agricultural inputs and aquaculture discharges, with elevated Zn, Cu, and Cd levels presenting significant ecological risks (RQ > 1). Principal Component Analysis (PCA) showed that natural vegetation is important in improving water quality by pollutant buffering, while agriculture and urbanization tend to increase contamination loads. These findings emphasize the necessity for integrated management strategies, including improved wastewater treatment, sustainable agricultural practices, and forest conservation to maintain river water quality. Future research should incorporate seasonal variability to refine long-term water quality assessments and develop adaptive mitigation strategies for urban-industrial and agricultural watersheds in tropical regions.