Spatio-temporal variation characteristics of water quality and pollution source analysis of main rivers in Lijiang section of Jinsha River Basin

In order to explore the temporal and spatial variation characteristics of water quality in the main rivers in Lijiang section of Jinsha River Basin and analyze the pollution sources, based on pH value, dissolved oxygen(DO), permanganate index(COD_Mn), ammonia nitrogen(NH₃-N), and total phosphorus(TP) monitoring data from 13 monitoring sections in the basin from 2020 to 2023, the comprehensive water quality index method(WQI) was used to analyze the water quality changes. and the principal component analysis(PCA) and absolute principal component-multiple linear regression(APCS-MLR) models were used to analyze the water quality characteristics and pollution sources in the study area. The results showed that the overall water quality categories in the study area were mainly Class I and Class II. WQI was generally at a ' good ' level ; in terms of time, the average WQI was the lowest in summer(81.89) and the highest in winter(88.76); spatially, the water quality of Jinjiang Bridge S5 was better, and the water quality of Longxing Village S10 section was relatively poor. The typical pollution factors in the study area were COD_Mn, NH₃-N and TP; the types of pollution sources could be divided into agricultural activities and domestic sewage mixed sources, meteorological factors and natural environmental factors. Overall, the water quality of the main stream was better than that of the tributaries. The contribution rate of unknown sources to water quality in the study area was 32.16%, the contribution rate of meteorological factors was 27.71%, the contribution rate of natural environmental factors was 26.95%, and the contribution rate of mixed sources of agricultural activities and domestic sewage was 13.18%. The main sources of COD_Mn were unknown sources, and the main sources of NH₃-N and TP were mixed sources of agricultural activities and domestic sewage. The research results can provide reference for the protection and management of water resources in Lijiang section of Jinsha River Basin.