2022 年 6 月珠江流域洪水对下游溶解有机物浓度和组成的影响

The recent frequent occurrence of extreme climate events has attracted widespread attention. However, the impacts of climate change on dissolved organic matter (DOM) in typical rivers in China are not yet well recognized. From November 2021 to October 2022, river water samples were collected monthly in Guangzhou section of the lower Zhujiang (Peral) River, and the concentration and composition of dissolved organic carbon (DOC), chromophoric dissolved organic matter (CDOM), and fluorescent dissolved organic matter (FDOM) were analyzed. During sampling period, the Zhujiang River basin encountered a “once in a century” flood in June 2022. Results show that the flood significantly reduced the concentrations of DOC and CDOM in the river water, and increased the DOM aromaticity. Although floods had a significant dilution effect on DOC and CDOM, further measurement of FDOM composition revealed that different FDOM components had different responses to the flood. The peaks of protein-like components at the shorter excitation wavelength (230~235 nm) reached its high value during the flood period. At the same time, the peaks of protein-like component with longer excitation wavelength (280~285 nm) and humic-like component (with excitation wavelength at 345 nm) showed the lowest values. In addition, compared with the lower Changjiang (Yangtze) River, the lower Zhujiang River showed generally greater concentrations of DOC and CDOM, and greater DOM aromaticity and molecular size. This study improved our understanding of the control mechanisms on the variations in DOM concentration and composition in the large rivers of the world like the Zhujiang River, and elucidated the impact of extreme flood on the DOM dynamics in large rivers.