嘉陵江中上游段沉积物中镍的形态分布及其在沉积物-水界面迁移特征

The study of Ni fraction in the sediment and mitigation characteristics of Ni cross the sediment-water interface in the mid-upstream of Jialing River

本研究使用沉积物柱状采样器对嘉陵江中上游废弃工矿区附近的沉积物进行采样,利用连续提取法和薄膜扩散梯度技术(diffusive gradient in the thin film technique,DGT)研究嘉陵江中上游段沉积物中镍元素(Ni)的在沉积物中赋存形态及其在沉积物-水界面的迁移扩散规律和释放机制.结果表明,各样点表层沉积物中总Ni含量均超过了我国水系沉积物的低标准物质值(GBW07311,14.3 mg·kg^(-1)),并有3个工矿区附近的点位超过了高标准物质值(GBW07309,32 mg·kg^(-1)),表明曾经的工矿作业等人为活动所引起的含Ni废水排放已经对当地水生生态系统构成严重的威胁.但连续提取各位点的主要存在形态为残渣态(F4),而最弱的结合态(F1,酸可交换态)的在所有采样点位的平均占比不足10%表明Ni对周边水体生态系统的实际环境风险可能并不高.DGT结果显示,CDGT-Ni浓度在S1和S2点位的深层沉积物(-9 cm—-12 cm)显著升高,在这两个采样点位表现出明显的释放趋势.通过对Ni在沉积物-水界面的扩散通量进一步计算发现Ni具有潜在内源释放风险,具有从沉积物向水的迁移趋势,会对研究区域水体形成潜在的污染.通过对连续提取中Ni的各个形态与DGT有效态Ni相关性分析发现沉积物中Ni在深层沉积物的释放过程主要受到铁、锰氧化物和含硫化合物等潜在因素的影响.

This study used sediment core samplers to collect core sediments near the region of abandoned industrial mine along the mid-upstream of Jialing River.The fraction of Ni in the sediment was studied by sequential extraction.The mitigation characteristics and release mechanism of Ni at the sediment water interface(SWI)were analyzed by diffusive gradient in the thin films technique(DGT).The results showed that total concentration of Ni in all sites exceeded the low sediment reference material(GBW07311,14.3 mg·kg^(-1))of China and three sites near the mining areas even exceeded high sediment reference material(GBW07309,32 mg·kg^(-1)).This indicates that Ni contained effluent discharged by past mining industry and other anthropogenic activities may pose a serious environment risk to aquatic ecosystem.However,the main fraction of Ni was bounded in residue fraction while the acid/changeable fraction was no more than average 10%,which indicated that Ni had little environmental risk to local water ecosystem.DGT results showed that CDGT-Ni significantly increased at the bottom sediment(-9 cm to-12 cm)presenting an obvious release trend at this depth.Further calculation of Ni diffusion flux at the sediment water interface shows that Ni can be released into the sediment and pass through sediment-water interface,which will cause potential pollution of overlying water.The correlation analysis between the different Ni fractions and DGT labile Ni shows that the release process of Ni in deep sediment was mainly controlled by potential factors such as iron,manganese oxides and sulfur compounds.