海河口DOM与Cd的微观作用机理及其复合体系迁移转化规律

On the one hand, estuary is a key area where dissolved organic matter (DOM) participates in the environmental geochemical cycle. On the other hand, estuarine sediments are important storage of heavy metals pollutants and potential sources of secondary pollution. However, there are still few reports on the microscopic complexation mechanism between heavy metals and DOM with different fractionation components and different molecular weights, neither the migration and transformation of metal-DOM complexes in the estuary. In this study, Haihe Estuary, which is heavily polluted by heavy metal Cd, is selected as the study area. DOM and Cd in the water and sediments of Haihe Estuary are selected as research objects. Firstly, the spectral characteristics, chemical fractionation components and molecular weight distribution of DOM in the pore water of sediments and in the water of Haihe Estuary will be researched in this study. And the spatial distribution characteristics and sources of DOM will be analyzed. Secondly, the Cd contents in the water and sediments of Haihe Estuary will be determinated and the occurrence forms of Cd in sediments will also be analyzed. And the spatial distribution characteristics, bioavailability, quality assessment and risk assessment of Cd in Haihe Estuary will be evaluated in this study. Moreover, the complexation mechanism between DOM and Cd will be systematically researched by using kinds of DOM in different molecular weights, in different fractionation components, or extracted from different regions. And many experiments will be carried out to study the effects of different environmental factors on the complexation of DOM and Cd. Above all, the microcosmic complexation mechanism between Cd and the characteristic functional groups of DOM will be explored deeply. And experiments will also be finished to reveal the correlation between DOM and different occurrence forms of Cd in sediments of Haihe Estuary. Finally, the migration and transformation of the DOM-Cd complexes in the horizontal and vertical directions of Haihe Estuary will be discussed in this study.

河口是溶解性有机质（DOM）参与环境地球化学循环的重点区域，同时河口沉积物是重金属污染物的重要汇库和潜在次生污染源，然而，目前针对河口不同分级组分、不同分子量DOM与重金属的微观作用机理及其复合体系的迁移转化研究仍鲜有报道。本研究拟选取受重金属Cd污染严重的海河口作为研究区域，研究海河口水体及沉积物孔隙水中DOM的光谱特征、化学分级组分及分子量分布，分析DOM的空间分布特征与来源；测定海河口水体和沉积物中Cd的含量以及沉积物中Cd的赋存形态，获悉海河口Cd空间分布特征、生物有效性、质量评估及风险评价；探究水体和沉积物中不同区域、不同分子量及不同分级组分DOM与重金属Cd的作用机制，研究不同环境因素对DOM与Cd结合作用的影响。深入探索DOM特征官能团与重金属Cd的微观作用机理，揭示河口沉积物重金属Cd赋存形态与DOM的相关性，进而探讨DOM-Cd复合体系在海河口横向和垂向上的迁移转化规律。

河口是溶解性有机质（DOM）参与环境地球化学循环的重点区域，河口沉积物是重金属污染物及有机质的重要汇库和潜在次生污染源。本课题以海河口为研究区域，通过大量的野外采样监测及室内实验研究，初步理解了如下几方面内容：（1）揭示了海河口DOM空间分布特征及来源。从垂向空间来看，孔隙水的有色溶解性有机质（CDOM）丰度显著高于上覆水，而上覆水中表层水的CDOM丰度又稍高于底层水；从横向空间来看，防潮闸上游水体的CDOM丰度普遍高于下游水体。水体腐殖化程度排序为：孔隙水＞底层水＞表层水。防潮闸附近水体DOM表现出更多的陆源影响，随着越来越靠近海洋，水体DOM受陆源影响减弱。防潮闸上游沉积物的有机质含量显著高于防潮闸下游沉积物。从沉积物样品中提取DOM存在较大的异质性，浸提方法及控制条件在一定程度上影响从沉积物中提取的DOM。为准确分析和阐明海河口沉积物DOM的分布特征及其环境效应，需进一步优化沉积物DOM浸提方法。（2）海河口水体重金属污染可以忽略，但沉积物重金属污染不容忽视。防潮上游沉积物受重金属污染的程度普遍高于下游。海河口沉积物中Cd、Zn和Cr属轻度至偏中度污染，Cu属轻度污染，As和Pb属无污染至轻度污染。Cd属于中等至强生态危害等级，其他重金属（Cu、Zn、As、Cd、Pb）属于轻微生态危害等级。海河口沉积物中Cd具有很强的活性。海河口沉积物重金属的生态风险主要源于Cd。（3）海河口水体和沉积物中不同区域、不同分级组分、不同分子量DOM与不同浓度Cd2+的络合机制存在明显差异，对DOM进行不同方式的分离及表征对于揭示重金属的迁移转化和环境效应具有重要意义。本项目研究成果可为评估海河口生态健康风险、揭示天然有机质参与重金属地球化学循环提供基础支撑。