Spatial–temporal variations of river water quality under human-induced land use changes in large river basins

Land use patterns and anthropogenic activities exert diverse impacts on river water quality and ecosystem health across spatial and temporal scales. Under ongoing pressures from human activities and climate change, it is urgently needed to understand the pollution mechanisms and associated ecological risks in surface waters through cross-basin assessments that incorporate a broad set of water quality parameters. This study investigated the spatial-temporal variations of 22 water quality parameters, including physico-biochemical indicators, nutrients, and heavy metals, at 39 sampling sites across the Daliao River (DLR), Shuangtaizi River (STR), and Naoli River (NLR). Field observations were conducted in September 2019, December 2020, and June 2020, covering the wet, dry, and agricultural seasons to assess the influencing mechanisms of natural factors and human activities on river water quality and human health. Principal Component Analysis revealed a notable seasonal variation in water quality components for DLR and STR, which indicated substantially high concentrations of TN, NO₃^- and NH₄⁺ in the dry season. The heavy metal risk for children was calculated at 8.44E-05 year^-1 in NLR during the agricultural season, which exceeded the maximum acceptable limit, with carcinogenic arsenic being the primary contributor. Redundancy analysis (RDA) was employed to examine the influence of land use patterns on water quality across different seasons and spatial scales. DO and COD showed a strong correlation with dry land and woodland, while nutrients and Chl-a were strongly correlated with paddy fields and building areas. This study underscores the critical role of land use management in harmonizing development with ecological sustainability and provides scientific evidence supporting the achievement of Sustainable Development Goal 6 (SDG 6), which focuses on clean and safe water.