Trend analysis of water quality variation in the estuarine reach of the Xiaojiang River, a tributary of the Three Gorges Reservoir Area

Based on measured water quality data from 2010 to 2025, the water quality of the estuarine reach of the Xiaojiang River, a tributary of the Three Gorges Reservoir Area, was analyzed using the comprehensive water quality index method. Pearson correlation analysis and principal component analysis were further employed to reveal the major sources of pollution in the Xiaojiang River. The results showed that the water quality in the Xiaojiang estuary from 2010 to 2025 was mainly Class I. Significant seasonal variation was observed within each year, with more severe pollution in summer. Biochemical oxygen demand over five days, total nitrogen, total phosphorus, permanganate index, and fecal coliform were identified as the main pollution indicators. Principal component analysis showed that the estuarine reach of the Xiaojiang River was mainly affected by organic pollution, eutrophication, and fecal contamination. In response to these pollution problems, source control should be strengthened, and the discharge of major pollutants should be reduced to improve water quality. This study can provide a reference for water environment management in the tributaries of the reservoir area.