The Beijiang River Basin is an important ecological security protection area and water source supply area in Guangdong Province. This study assesses the spatiotemporal distribution characteristics of watershed water quality based on on-site monitoring data and multivariate statistical analysis. The results indicate that PO43−P concentrations peak during the flood season, whereas pH, NO3−-N, and total nitrogen (TN) reach their highest levels during the autumn normal-flow period. Spatially, water quality follows a gradient of upstream > downstream > midstream, with the midstream region identified as the primary zone of water quality degradation. Future non-point source (NPS) pollution characteristics in the Beijiang River Basin are influenced by land use/cover change (LUCC) and climate change, showing significant variation across Shared Socioeconomic Pathway (SSP) scenarios. Under SSP126, precipitation increases at the slowest rate, with a peak annual value of 1599.77 mm during 2031–2040 and an average basin temperature of 19.61 °C. In contrast, SSP245 exhibits a marked increase in precipitation, reaching 1802.92 mm by 2061–2070. Under SSP585, annual precipitation rises to 2200.04 mm, with temperatures approximately 0.5 °C higher than those under SSP126. Simulations based on the improved ESP-PLUS model indicate that, under the natural development scenario (NDS), expansion of construction land increases urban runoff pollution by 32.97%. Under the economic development scenario (EDS), 1023 km2 of ecological land is lost, significantly weakening pollution interception capacity, while construction land increases by 26.01%. In contrast, the coordinated development scenario (CDS) reduces ecological land loss by more than 60% compared to EDS through balanced development and conservation, thereby maintaining the basin’s pollutant purification function. Overall, future nitrogen and phosphorus loads in the watershed are projected to first decrease and then increase. Accordingly, differentiated management strategies are recommended, emphasizing the coordinated development of economic growth and ecological protection, and providing a scientific basis for controlling NPS pollution under changing climatic conditions.
Wang et al. (Tue,) studied this question.