Fluctuations in Cd release from surface-deposited sediment in a river-connected lake following dredging

Lakes connected to rivers have highly fluctuating hydrological conditions and therefore processes involving the retention and release of heavy metals are complex. Jinshan Lake is a typical river-connected lake in China, was selected to estimate Cd distribution in the surface-deposited sediment after dredging. Sediment samples with low, medium and high Cd contents were collected for annular flume experiments. The shear stress-induced Cd releases from these sediments were explored and incorporated into a numerical model using the finite volume method (FVM). The process of Cd release was studied for different temporal scales by numerical simulation. We observed that, because of the adequate water exchange between Jinshan Lake and the Yangtze River, the high-water year featured the largest annual release of Cd at 8777 kg, which was 2722 kg and 2033 kg higher than that of normal and low-water years, respectively. A balance between the upstream runoff and downstream tide resulted in the lowest Cd release in a normal-water year. The Cd release during a tidal cycle fell from 48 kg during the flood season to 11 kg during the dry period, whereas the variation coefficient increased from 0.59 to 0.67 during this period. Dredging project generally reduced the release of Cd from sediment in Jinshan Lake and this impact became more prominent in the presence of sufficient water exchange and strong bed shear stress.