Quantitative Tracking of Seasonal River Pollution Sources and Integration of Sustainable Development Goals in Hilly Regions

In line with the Sustainable Development Goals, a comprehensive understanding and precise quantification of the temporal and spatial characteristics of water quality is essential to identify sources of pollution in basins and to protect river headwaters to maintain water safety throughout basins. However, there is a lack of systematic quantitative tracking of seasonal river pollution sources in hilly areas in southwest China. In this study, the spatial and temporal characteristics of the water environmental factors in the Yaoshi River basin, the causes of pollution, and the main sources of nitrogen pollution were systematically investigated using geographic information systems and statistics. The results showed that the main pollutants in the river as a whole included five-day biological oxygen demand (BOD5), oxygen demand (COD), ammonium (NH4+), total phosphorus (TP), and total nitrogen (TN). Nitrogen pollution was the most serious, and various environmental factors caused seasonal variations and different spatial distributions in this pollutant. Temporally, the TP and COD concentrations were highest during the wet season, while the NH4+, TN, and BOD5 concentrations were highest during the dry season. Spatially, BOD5, COD, and TP concentrations were ranked upstream < downstream < midstream, while TN and NH4+ concentrations were ranked downstream < midstream < upstream. The main sources of pollution in the study area were domestic activities (34.94%), agricultural activities (40.12%), and mixed organic and natural sources (24.94%). Notably, manure effluent dominates nitrate nitrogen sources, while fertilizer inputs minimally contribute during mean-flow and dry seasons, and atmospheric deposition contributes during the wet season. These findings provide important data for improving water quality in the Yaosi River Basin, promoting sustainable agricultural practices, alleviating water scarcity, and advancing the region’s Sustainable Development Goals. In addition, this study can provide reference for the development of sustainable development management strategies for seasonal rivers in other hilly areas and promote broader environmental sustainability efforts.