Comprehensive assessment and spatio-temporal variation characteristics of the water environment in the river network of Nantong city

To systematically assess the spatiotemporal distribution characteristics and differences of water environmental quality in the river network of Nantong city, water quality data from nine monitoring sections in the river system from 2021 to 2024 were analyzed. The Water Pollution Index (WPI) and the Comprehensive Water Quality Identification Index (Iwq) were employed to evaluate the overall water quality, while cluster analysis and discriminant analysis were applied to examine the spatiotemporal variation patterns of the assessment results. The findings indicate that the water quality in Nantong’s river network is generally affected by nitrogen and phosphorus pollution, with TN being the primary pollutant, especially exceeding standards during the non-flood season. During the flood season, approximately half of the monitoring sections were rated as Class V or worse according to WPI, and the proportion of worse than Class V increased significantly in the non-flood season. Among them, the Beilingxin Sluice and Xiaoyangkou sections in the Jiaogang-Inshore Diversion River system exhibited the most severe pollution, consistently classified as worse than Class V throughout the year. The Iwq evaluation results for most monitoring sections were primarily Class II-III, though some sections still showed potential pollution risks from TN, TP, and COD_Mn. Spatially, pollution in the river network displayed clustering characteristics, with the Beilingxin Sluice monitoring section identified as an independent pollution cluster in both evaluation methods, highlighting prominent compound pollution involving TP, COD_Mn, and TN. Cluster and discriminant analyses further validated the significant spatial differentiation of water quality in Nantong’s river network, with relatively stable clustering outcomes across different hydrological periods. The research outcomes provide a scientific basis for precise management and comprehensive remediation of the water environment in the river network of Nantong city.