Spatial and Temporal Distribution Characteristics of Water Quality and Pollution Sources in Mountainous Watershed

Identifying pollution sources and quantifying their contributions are essential for water environment management in mountainous watershed. This study used PCA-APCS-MLR receptor modeling to analyze monthly water quality indicators in the Longxi River basin. Results showed no significant difference between the water quality of the main stream and tributaries. The water quality of the upstream and downstream was better than the middle reaches. Significant differences were found in wet and dry seasons. In the wet season, agricultural non-point source pollution was the main driver of water quality, contributing 42.9%, followed by watershed background levels and surface runoff. In the dry season, rural domestic wastewater (39.3%) was the leading pollution source. For CODMn exceedance, basin background and agricultural non-point sources in the wet season were the main contributors (46.8% and 44.7%, respectively). For NH3-N, agricultural non-point sources in the wet season and rural domestic pollution in the dry season were the key contributors (44.4% and 71.8%, respectively). Agricultural non-point sources were the dominant pollution source for TN in the wet season (84.2%). Effective measures for improving water quality in the Longxi River Basin may include optimizing fertilization strategies and enhancing the collection and treatment of domestic sewage to control the agricultural non-point sources and rural domestic sewage. This study deepens the distribution and quantitative analysis of water pollution sources in mountainous watersheds, and also provides an important reference for water environment management.