[Impact of Rainfall on River Water Quality and Source Identification： An Example in the Maoming Section of the Jianjiang River].

To investigate the effects of rainfall on river water quality in a mixed-industrial-agricultural urban area and to analyze the sources of pollution, this study focused on the Jianjiang River, the primary tributary of the western reaches of the Pearl River system. To investigate the impact of rainfall on river water quality in an urban area with mixed industrial and agricultural activities, six river monitoring sections along the Maoming segment of the Jianjiang River, along with three meteorological stations, were chosen as the research sites. Utilizing box-and-whisker plots, correlation analysis, and the absolute principal component-multiple regression model, this study examined the rainfall-water quality relationship within the Maoming section of the Jianjiang River. Additionally, it assessed the contributions of various pollutant sources to water quality in the region. The results showed that： ① The river water quality in the Jianjiang River's Maoming section was generally better in spring and winter compared to that in summer and autumn. Specifically, the Zhensheng, Jiangkoumen, and Luojiangqiao sections consistently maintained water quality that exceeded Surface Water Category III standards. However, the Shibi, Mijidu, and Tangkou sections were at a higher risk of exceeding water quality standards during summer and autumn, particularly with increasing rainfall intensity. In these seasons, dissolved oxygen （DO）, chemical oxygen demand （COD）, turbidity （WT）, and total phosphorus （TP） tended to increase with rainfall intensity, while electrical conductivity （EC）, ammonia nitrogen （AN）, and total nitrogen （TN） showed opposite trends. Notably, the pH, DO, EC, and TN in the Shibi, Mijidu, and Tangkou sections decreased with rainfall intensity, whereas COD, AN, and TP exhibited the opposite pattern. ② River water quality was influenced by seasonal variations, meteorological factors, and rainfall intensity, with rainfall having a significant impact on water temperature, ammonia nitrogen, and total phosphorus. During summer and autumn, river water quality deteriorated with increasing rainfall. Moreover, as rainfall intensity rose, the relationship between season, spatial location, water quality indicators, and meteorological factors weakened, while the coupling between meteorological factors and water quality strengthened. ③ In the absence of rain, urban pollution sources and meteorological factors were the primary contributors to river water quality, with urban pollution sources accounting for 66.25% of electrical conductivity and chemical oxygen demand and 51.94% of other parameters. The contribution of other sources was relatively low but increased with rainfall intensity. Agricultural surface sources generally showed an increasing and then decreasing trend of contribution with rainfall intensity. During heavy rainfall, the contribution of other sources to water quality ranged from 35.17%-93.46%. In conclusion, the study indicates that heavy rainfall during summer and autumn is a significant factor leading to water quality standard exceedance in the Maoming section of the Jianjiang River. It underscores the critical need for enhanced management of urban pollutants, agricultural surface runoff, and other sources including industrial, aquaculture, and endogenous releases to improve and maintain water quality in the river.