| The effect of resuspension energy and duration on release and subsequent redistribution of sediment bound Hg in Yangtze Estuary was measured experimentally using a particle entrainment simulator. Concentrations of HgD (Dissolved Hg) and HgP (Particulate Hg) in the overlying water were 34-268 ng·L-1 and 25-195 μg·kg-1 respectively, and sensitive to disturbance energy and time during sediment resuspension. There is no significant correlation between HgD and HgP concentration. After the first disturbance intensity experiment for 3 h, Hg was released to the overlying water in general, with HgD and HgP concentrations increasing from 179 ng·L-1to 268 ng·L-1 and from 116 μg·kg-1to 139 μg·kg-1respectively. And then concentrations of HgD and HgPdecreased after the overlying water was disturbed for 3 h at the second intensity, while after the third disturbance intensity experiment for 3 h, a slight increase was observed in HgD, and HgP concentration increased from 89 μg·kg-1 to 162 μg·kg-1 in overlying water. The distribution coefficient (lg Kd) of Hg in overlying water had no significant correlations with the water column pH, Eh, DO and TSS, but influenced by the combined physical and chemical conditions of the water column. In each disturbance energy treatment, both the content of suspended particles and lg Kd for Hg increased rapidly in the overlying water in the early stage, especially the first 5 min, indicating a strong absorption of Hg on the suspended particles. After that, a decrease of the lg Kd for Hg occurred with the time and content of suspended particles increased. It can be explained that the released Hg by oxidation of sulfide was bounded by the newly generated colloidal material such as the hydrate iron-manganese oxide. In relatively strong disturbance energy treatment, part of the coarse particles settled with time. The concentrations of HgP increased in some resuspension stage in the overlying water due to the “fine particle concentration effect". |
