Abstract: The North mainstream of Dongjiang River is located at Guangzhou’s eastern drinking water source protection zone, with a target water quality of Class II. The Dadun section, as the last assessed section designated by the government in the North mainstream, holds significant importance in evaluating the overall water quality. However, the dissolved oxygen (DO) level in this section have failed to meet required standards over the past five years. We collected water quality data from the mainstream of Dongjiang River and the Dadun section during 2018-2022 and analyzed the temporal and spatial variations of DO concentration. Using Pearson correlation analysis and multiple linear regression analysis, we investigated the causes of low oxygen levels in the Dadun section based on recent hydrometeorological data and water quality remote sensing images. Our results revealed that the DO concentration in the lower reach of the north mainstream was significantly lower than that in the upper and middle reaches. Additionally, the DO concentration was higher during dry seasons compared to wet seasons. The DO concentration in Dadun section were influenced by numerous factors. It positively correlates with pH value, conductivity, and tidal current velocity, while negatively correlating with water temperature, total phosphorus (TP), turbidity, and rainfall. Furthermore, the upstream incoming water quality plays a crucial role in affecting the DO concentration of the north mainstream. Among these factors, water temperature emerges as the primary influencing factor, contributing 62.1% to the overall DO concentration variation. The research findings provide essential support for ensuring the stability of the Dadun section during national assessments, and moreover, contribute to strengthening the region’s capacity for water pollution prevention and control, ultimately enhancing the effectiveness of water pollution management efforts.

Key words: dissolved oxygen, spatial-temporal distribution, influencing factors, correlation analysis, the north mainstream of Dongjiang River