重污染水环境中重金属在沉积物-海水界面扩散迁移及其平衡分配行为的研究：以锦州湾为例

The remobilization of heavy metals at sediment-water interface has been extensively studied in marine environmental science. In recent years, with the cut down of fluvial discharges in previously heavily contaminated bays (such as Jinzhou Bay), sediments may become an important source to the overlying water of the bay. However, systematic studies that focus on seawater, sediment and porewater are in general lacking, and the role (source or sink) of which the sediment plays is unclear, nor is its change with the environmental variables, such as redox or pH. This study is going to conduct accurate and systematic studies on heavy metal contents in seawater, porewater and sediment employing trace-metal clean protocols, in order to quantitatively determine the benthic flux of heavy metals at sediment-water interface in Jinzhou Bay, and elucidate its change with the other environmental variables. A budget model on heavy metals in Jinzhou Bay will also be constructed, and the contribution of the sediment, as a source or sink, to the metal inventory of heavy metals in the bay will be calculated, along with the time period estimation of its influence (if it is a source) to the bay. This study will provide the scientific evidence and basis for the environmental/remediation policy makers. In the meantime, this study will provide a perfect study region with higher metal concentrations for the heavy metal sediment-water chemical equilibrium model (SCEM) that is proposed by us previously. The successfully application of SCEM in Jinzhou Bay will prove the model’s validity in higher environmental metal concentrations.

重金属在沉积物-海水界面的扩散迁移和二次污染问题是当前海洋环境科学的研究热点和前沿。近年来，在我国一些重金属污染严重的海湾（以锦州湾为例），随着河流携带的污染源的治理减排，沉积物可能已经成为了重要的源，但针对海水、沉积物、孔隙水的系统性研究还相对匮乏，沉积物在该海湾的源/汇角色不明，其季节性变化规律也不清。本项目旨在通过对海水、孔隙水、沉积物三相体系的痕量洁净无污染的采样和测试分析，系统、准确地反映锦州湾重金属在沉积物-海水界面的扩散迁移行为及其季节变化规律，定量估算其扩散通量并判定其源/汇角色，并建立锦州湾重金属的源/汇模型，定量估算沉积物释放对整个海湾的贡献并预测其作用时间，为锦州湾重金属污染治理提供科学依据。同时，该研究又将为申请者提出的“重金属化学平衡模型（SCEM）”在重污染水环境中的适用性验证提供一个理想的实验场，为该模型的普适性应用提供佐证。

重金属在沉积物-海水界面的扩散迁移和二次污染问题是当前海洋环境科学的研究热点和前沿。近年来，在我国一些重金属污染严重的海湾（以锦州湾为例），随着河流携带的污染源的治理减排，沉积物可能已经成为了重要的源，但针对海水、沉积物、孔隙水的系统性研究还相对匮乏，沉积物在该海湾的源/汇角色不明，其季节性变化规律也不清。本项目在重金属污染严重的锦州湾进行了三个季节（春、夏、秋）的采样，采集了海水、孔隙水、沉积物短柱样品，得到主要结论如下：1) 锦州湾海水和沉积物中主要污染金属为Cd和Zn，其含量都远高于渤海其他海区，其主要污染源应为葫芦岛锌厂常年排放的废水；2) 沉积物未达到厌氧状态，其还原性由小到大顺序为：秋季 < 春季 < 夏季；3) 沉积物-海水界面的重金属通量存在季节性差异，夏季较高，这与夏季温度较高、沉积物颗粒表面有机质降解程度较高的现象相一致；4) 根据目前锦州海水中金属储量计算，沉积物通量只贡献了较小的一部分，分别为0.5%(Zn)、0.3%(Ni)、1.4%(Pb)、14%(Co)。该结果说明，目前锦州湾海水中金属的主要污染来源还应是河流排放的污水；5）沉积物中Pb和Zn含量处于污染状态, 按照本研究所得金属沉积物通量平均值估算其对上覆水体作用时间，将分别约为300和2000年；6）在锦州湾应用Zn、Pb、Cd的沉积物-海水界面化学平衡模型 (SCEM)，结果显示SCEM预测的上覆水体中自由离子态Zn和Pb的活度与测定值吻合较好，说明该模型在重污染水环境下的适用性。但SCEM预测的pCd含量为8-9，远高于测定值(pCd=10-12)，我们推测其原因可能是海水中藻类的抑毒机制导致的（pCd=10 即开始产生毒性）。