Water environment status and causes analysis of Chong'an River Basin in Qiannan Prefecture

The change characteristics of water environmental quality of Chong'an River Basin in Qiannan Prefecture were studied at the watershed scale, and the water environmental status of the watershed was comprehensively analyzed. The results showed that the water quality of Chong'an River Basin in Qiannan Prefecture was generally poor before 2018. For the trunk stream, except for the section of Heitang Bridge, all other sections eliminated the water body inferior to Grade Ⅴ in 2018. In terms of tributaries, Wuliqiao section was better than Grade Ⅲ in 2019, and the downstream of Chuanheng's outfall section was better than Grade Ⅲ in 2020. The results showed a pronounced spatiotemporal heterogeneity of water environment quality, and the water quality in the upstream was overall better than that in the downstream. In terms of pollutants, total phosphorus in all the sections and fluoride in some sections exceeded the standard. In 2015, the total phosphorus in Fengshan bridge section was the highest with 17.3 mg/L. The analysis showed that agricultural sources contributed the most to the water environment pollution in the basin. In the end, the comprehensive management measures for the basin were put forward, such as continuously promoting key pollution source control projects, strengthening water ecological restoration and control measures, and strengthening joint prevention and control of water environment in Chong'an River basin.