黄河兰州段水体中有色溶解性有机质组成、空间分布特征及来源分析

Composition, Spatial Distribution Characteristics and Source Analysis of Chromophoric Dissolved Organic Matter in the Lanzhou Reach of the Yellow River

利用紫外-可见吸收光谱、激发发射矩阵荧光光谱(EEMs)并结合平行因子分析(PARAFAC),分析黄河兰州段水体有色溶解有机质(CDOM)的组成、空间分布以及来源.结果表明,黄河兰州段水体CDOM可能是由芳香性结构的小分子组成,解析出的4个组分中,类蛋白质(1个组分)含量最多,占总荧光强度的51.06%,类腐殖质(2个组分)次之,占36.74%,非类腐殖质(1个组分)最少,占12.20%,类蛋白质组分和类腐殖质组分来源不同.CDOM属于"类蛋白质-类腐殖质"复合主导型,以生物来源的类蛋白质为主.从上游到下游河段,CDOM的空间分布格局大体有一个先降低再升高再降低的过程,其趋势主要受到类蛋白质含量变化的影响.类蛋白质的含量受到了居民/商业污水排放、河岸及水上餐饮、娱乐设施、船舶运输以及少量工业企业废水排放等各种高强度人为活动干扰.黄河流经兰州市受到了一定的内源污染,建议对黄河兰州段水体进行内源污染的控制.

Chromophoric dissolved organic matter（CDOM） in riverine systems can be affected by environmental conditions and landuse,and can thus provide important information regarding anthropogenic activities in surrounding landscapes. It can modify the optical properties of waters and affect the balance and availability of dissolved nutrients and metals in water bodies. However, the characteristics of CDOM in the Lanzhou reach of the Yellow River have not yet been reported. In this study,the optical properties of water samples collected at 32 locations during April 2017 across the Lanzhou reach of the Yellow River were examined using UV-VIS and excitation-emission matrix fluorescence spectroscopy-parallel factor analysis（EEM-PARAFAC）,to determine CDOM compositional changes,spatial distribution characteristics,and sources. Cluster analysis was used to categorize samples into groups of similar pollution levels within a study area. Results showed that CDOM was primarily comprised of low molecular weight organic substances with aromatic structure belonging to complex ＂protein-like-humic-like ＂ substances, and dominated by protein-like substances（organism sources）. Two humic-like components（C1,C4）,one tryptophan-like component（C2）,and one non-humic-like component（C3） were identified by PARAFAC. Tryptophan-like substances were predominant in the components of CDOM,accounting for 51. 06% of average total fluorescence intensity. Humic-like materials and non-humic-like substances accounted for 36. 74% and12. 20%,respectively. Weak correlations were observed between protein-like substances and humic-like substances,indicating different sources of these components. The distribution of total fluorescence intensity showed a distinct spatial pattern; trends in fluorescence intensity were weak-strong-weak along an upstream to downstream continuum,mainly affected by changes in the content of protein-like substances. The spatial variation of the CDOM in the Lanzhou reach of the Yellow River can therefore be assessed based on protein-like materials dynamics. Public spaces along rivers offer opportunities for community gatherings and recreational activities.However,high-intensity anthropogenic activities strongly influence CDOM concentration and composition in this area in different ways;sources include increased residential/commercial wastewater,catering,water recreation facilities pollution,shipping,and a small amount of industrial discharge. In addition,it was concluded that endogenetic pollution may become the main source of internal loading in the Lanzhou reach of the Yellow River,implying that stronger endogenetic pollution control is needed to alleviate CDOM pollution and improve water quality.