动力和盐度影响下长江口近岸沉积物中汞的再悬浮行为

利用PES(particle entrainment simulator)装置, 实验测定了不同的扰动强度和盐度条件下长江口近岸沉积物中Hg的再悬浮迁移和释放过程. 在盐度再悬浮试验中, 上覆水中HgD(溶解态Hg)和HgP(颗粒态Hg)含量分别在0.06~0.176 μg/L和0.033~0.723 μg/g之间变化, 在盐度×动力耦合再悬浮试验中, 上覆水中HgD和HgP含量分别在0.024~0.112 μg/L和0.05~0.958 μg/g之间变化. 在盐度较低(< 1‰)的水环境中, 动力条件是影响上覆水中Hg行为的重要因子, 动力条件改变后, 沉积物中的部分HgD和HgP存在短期释放行为, 但随扰动时间延长, 被扰动起来的悬浮颗粒对上覆水中的Hg起了较强的吸附作用. 当盐度在1‰以上时, 上覆水中的HgP出现解吸行为, 动力条件的耦合影响促进了Hg的解吸作用, 当动力条件达到250 r/min以上时, Hg的解吸作用增强, 上覆水中的HgD出现正通量, 表现为向上覆水的释放. 此外, 在较强动力条件下, 孔隙水中大量HgD的扩散释放也增加了其释放通量.

Effect of dynamic and salinity conditions on activities of Hg during sediment resuspension event in the Yangtze Estuary

The effect of resuspension energy and salinity on translocation and release of sediment bound Hg in the southern coastal areas of Yangtze Estuary was measured experimentally using a particle entrainment simulator. In the salinity resuspension test, concentrations of HgD (Dissolved Hg) and HgP (Particulate Hg) in the overlying water were 0.06–0.176 μg/L and 0.033–0.723 μg/g respectively. In the dynamics and salinity coupling test, concentrations of HgD and HgP in the overlying water varied between 0.024–0.112 μg/L and 0.05–0.958 μg/g respectively. Dynamic condition was one of the most important factors influencing the activities of Hg in overlying water. Once disturbance began, part of HgD and HgP was released from the sediments during short period, and then HgD was absorbed on the resuspended particles in the overlying water with time. Desorption of Hg from particles occurred when salinity was above 1‰ and this desorption was promoted by the dynamic condition. When salinity was above 1‰ and the disturbance energy was greater than 250 r/min, desorption of Hg enhanced and positive flux of HgD occurred in the overlying water, which was characterized by the release of Hg from sediment to overlying water. In addition, diffusion of HgD from porewater also increased the release flux.