Resuspension and release of Hg from Taihu Lake sediment under different hydrodynamic disturbances

Pollutants resuspension in sediments affected by wind wave could influence on the water quality in shallow lakes. The resuspension of surface sediments from Zhushan Bay, Taihu Lake was simulated by using a pneumatic annular flume in this study. There were 6 kinds of wind speeds in this experiment, including 1.60m/s, 3.62m/s, 6.36m/s, 8.04m/s, 10.38m/s and 14.10m/s. The velocity of water column was measured by Acoustic Doppler Velocimeter (ADV) in each wind forcing. The characteristics on release of suspended solid (SS) and total Hg in the processes of sediment resuspension were studied by layered sampling technology. The experimental results show that 6m/s was a critical wind speed which could change the hydrodynamic conditions significantly. The total resuspended amount of sediments was increased with the enhancement of hydrodynamic disturbances, and during the resuspension event, the total resuspended amount changed slightly after 5 hours except the latter two wind forcing conditions. There was no significant correlation between the release amount of Hg and hydrodynamic disturbance intensity. According to the relativity analysis between total Hg and SS in the overlying water, it could be known that particulate Hg is not the main existence of total Hg in the water column. Based on the analysis of wind speed (V), mean flow velocity (u̅) and total resuspended amount of sediment particulates (W), quantitative relationships were achieved among these three variables, and they could be expressed by u̅ = 0.2939 V^1.7683, W = 1.9638 V^2.1609, and W = 11.639 exp (0.1669 u̅). These three formulas could provide calculated methods of total resuspended amount of sediment particulates in shallow lakes.