南水北调中线清河溶解性有机物的光降解行为

溶解性有机物(dissolved organic matter, DOM)在水环境中普遍存在，其光降解行为与种类和来源密切相关。近年来，南水北调中线工程沿线中DOM含量过高问题逐渐引起了人们对饮用水水源水质的关注。利用三维荧光光谱与紫外可见吸收光谱表征了清河段DOM在水(Water DOM, W-DOM)、底泥(sediment-derived DOM, S-DOM)、藻胞内(intracellular DOM, I-DOM)和胞外(extracellular DOM, E-DOM)这4种典型来源中的光学性质和光降解行为。结果表明，W-DOM的主要来源是藻类代谢产生的E-DOM；S-DOM的主要形成原因是藻细胞破裂释放I-DOM。DOM的光漂白主要发生在紫外区，且UV-B波段的光漂白效率大于UV-A波段。
W-DOM、S-DOM和E-DOM中有色DOM(chromophoric DOM, CDOM)的降解率基本相同，为40%~50%；I-DOM中CDOM降解率相对较低，约为25%。光照可以将W-DOM、S-DOM和E-DOM中复杂的大分子物质分解成结构简单的小分子物质。CDOM中类腐殖质的光降解率比类蛋白质更高，W-DOM、S-DOM和E-DOM中CDOM与类腐殖质的光降解速率在相同时间下基本保持一致；S-DOM和E-DOM中CDOM与类蛋白质的光降解速率在相同时间下基本保持一致。以上结果反映了太阳辐射对水环境中DOM的转化和去除机理，为河流水质保护提供了理论依据。

Photodegradation behavior of dissolved organic matter in Qinghe river of middle route of South-to-North Water Diversion Project

Dissolved organic matter (DOM) is ubiquitous in water environment, and its photodegradation behavior is closely related to species and sources. In recent years, the problem of high content of DOM along the Middle Route Project of South-to-North Water Diversion has gradually aroused people's attention to the quality of drinking water sources. In this study, three-dimensional fluorescence spectroscopy and UV-visible absorption spectroscopy were used to characterize the optical properties and photodegradation behavior of DOM from four typical origins, i.e., water (W-DOM), sediment-derived (S-DOM) and algae-derived intracellular (I-DOM) and extracellular DOM (E-DOM) in Qinghe river section. The results showed that the main origin of W-DOM was E-DOM produced by the metabolism of algae. The main reason for the formation of S-DOM was the release of I-DOM by algal cell rupture.
The photobleaching of DOM mainly occurred in the ultraviolet region, and the photobleaching efficiency of UV-B band was higher than that of UV-A band. The degradation rates of chromophoric DOM (CDOM) in W-DOM, S-DOM and E-DOM were basically same, ranging from 40% to 50%. The degradation rate of CDOM in I-DOM was relatively low and about 25%. Irradiation could decompose complex macromolecules in W-DOM, S-DOM and E-DOM into small molecules with simple structure. The photodegradation ratio of humic-like substances in CDOM was higher than that of protein-like substances. The photodegradation rates of CDOM and humic-like substances in W-DOM, S-DOM and E-DOM were basically consistent at the same time; the photodegradation rates of CDOM and protein-like substances in S-DOM and E-DOM were basically consistent at the same time. The experimental results show the transformation and removal mechanism of DOM in water environment by solar radiation, which provides a theoretical basis for the protection of river water quality.