Spatiotemporal variation in water quality of the Lianjiang River Basin: A multimetric assessment using index-based, statistical, and isotopic approaches

Assessing regional water quality and evaluating the potential health risks posed by water pollutants are critical for protecting surface water resources and informing evidence-based environmental policies. Based on a March 2021–February 2022 survey of the Lianjiang River Basin using CWQI, NPI, PCA, and dual-isotope techniques,we assessed water quality and health risks. CWQI and NPI results demonstrate distinct spatiotemporal patterns of water quality, with a peak value of 3.21 in June followed by a drastic 79.44% reduction to 0.66 in November. Simultaneously, a gradual degradation in water quality was observed from upstream to downstream. PCA and isotopic analysis indicated that soil nitrogen–related agricultural non-point source pollution served as the dominant force driving water quality degradation. With TP being the principal contaminant, followed by COD Mn and TN in sequence. To improve water quality management, targeted strategies should prioritize controlling non-point source pollution in the Xin’anjiang River sub-basin and mitigating eutrophication risks in Thousand Island Lake.