Water Quality in the Haihe River Basin, China: Spatial and Seasonal Variations, Sources and Sustainable Strategies

A two-year dataset was collected to investigate the spatial and seasonal variations in water quality within the Haihe River Basin (HRB), China. Potential pollution sources and influencing factors were identified, and their contributions were quantified using absolute principal component scores-multiple linear regression (APCS-MLR) and Positive Matrix Factorization (PMF) models. The average water quality index (WQI) was 80.2, indicating that the overall water quality was classified as “good”. TN pollution was severe. WQI values followed the order: Luanhe River system (84.7) > North Haihe River system (80.0) > South Haihe River system (76.6). The WQI value during the non-flood season (77.2) was lower than that during the flood season (82.0). Grassland and forest exhibited negative correlations with water-quality parameters. Construction land and farmland negatively influenced water quality but were not the primary land-use types contributing to TN variability. Higher pH and TN occurred in mountain areas and during the non-flood season, while higher CODMn, COD, BOD, AN, and TP occurred in plain areas and estuaries, respectively, and during the flood season. Four potential sources or factors were identified as domestic and industrial wastewater, meteorological and hydrological conditions as environmental driving factors, non-point sources, and unrecognized sources. Source apportionment using APCS-MLR and PMF models revealed that domestic and industrial wastewater contributed 28.6% and 47.2% of pollution, respectively, while non-point sources contributed 27.7% and 22.2%. Meteorological and hydrological conditions, as environmental driving factors, accounted for 17.9% and 21.0% of the variability, respectively, and unrecognized sources accounted for 25.8% and 9.6%. Sustainable control strategies were proposed to improve water quality in the HRB in the future.