Spatiotemporal evolution of surface water quality and driving factors across varying levels of human interference in a major subbasin of the Yellow River Basin, China

The Dahei River Basin, a sub-basin of the Yellow River Basin, was selected for this study. Encompassing population centers and villages in Inner Mongolia, it supports vital ecosystems and underscores the need to address its unique challenges in water management and protection. This study examines surface water quality dynamics in the Dahei River Basin, a key aspect of sustainable water management. Predicting spatiotemporal variations and driving factors remains challenging. Using 2013–2023 datasets on water quality, hydrology, and meteorology, the composite pollution index (CPI), ANOVA, and generalized additive models were applied to provide insights for effective management. The study identified three water quality phases in the Dahei River Basin: deterioration (2013–2015), improvement (2016–2020), and stabilization (2021–2023). Seasonal variations showed better water quality (lower TN, NH 4 + -N, TP, DO, CPI) in wet seasons. Spatial variability was highest in plains and urban areas, driven by runoff, industrial pollution, and sewage, while hilly areas showed minimal variation due to low human impact. Precipitation and sediment dynamics affected water quality in hilly areas, with large runoff events worsening contamination. Solutions include sediment removal, vegetation enhancement in hilly areas, and pollutant management during rainfall and dry seasons. • Water quality varied across regions, with better conditions observed during the wet season. • In hilly regions, water quality improved with increased precipitation. • In plain regions, water quality was influenced by both precipitation and sediment dynamics. • In urban regions, human activities were primary drivers of water quality, with natural factors playing a secondary role. • Implementing region-specific measures that account for both human and natural factors is essential for improving water quality.