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

当前极端气候事件频发,引起了人们广泛的关注。然而,气候变化对中国典型河流溶解有机物(DOM)的影响尚且未得到充分的认识。2021年11月至2022年10月,每月于珠江下游广州段采集河水样品,并分析其中溶解有机碳(DOC)、发色溶解有机物(CDOM)和荧光溶解有机物(FDOM)的浓度和组成。采样期间, 2022年6月珠江流域遭遇百年一遇的洪水。结果显示,洪水大幅度降低了河水中的DOC和CDOM浓度,并提高了DOM的芳香化程度。尽管洪水对DOM浓度产生了明显的稀释效应,但通过分析FDOM组成,进一步发现FDOM中不同组分对洪水的响应存在较大差异。FDOM短激发波长(230～235nm)处的类蛋白质组分峰值在洪水期间出现高值;与此同时,长激发波长(280～285nm)的类蛋白质组分和激发波长在345nm处的类腐殖质组分峰值在洪水期间出现最低值。此外,与长江下游相比,珠江下游水体中往往具有较高的DOC和CDOM浓度、DOM芳香化程度以及CDOM分子量。研究将有助于进一步了解珠江等世界大河DOM浓度和组成的变化规律和控制机制,以及揭示极端洪水对大河DOM动态变化产生的影响。

IMPACT OF THE BASIN FLOOD IN JUNE 2022 ON THE CONCENTRATION AND COMPOSITION OF DISSOLVED ORGANIC MATTER IN THE LOWER ZHUJIANG (PEARL) RIVER

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.