Influence of dredging on sedimentary arsenic release for a tide-influenced waterfront body.
We evaluated the influence of sediment dredging on sedimentary As release for the Inner Lake, a typical tide-influenced waterfront body in the middle to lower reaches of the Yangtze River in Zhengjiang, China. By field investigation and laboratory experiment, the As content in the deposited sediment before dredging was analyzed and the relationship between dynamic disturbance and sedimentary As release intensity was established. Using a numerical model in which the factors of water current, suspended sediment, and As were coupled, the processes of As migration were simulated for typical years and tidal cycles before and after dredging. The results show that: (i) the amounts of sedimentary As release during the tidal cycles in the flood season and the dry season after dredging were reduced by 14.6 and 28.1%, respectively, compared with before dredging; (ii) after removal of the surface polluted sediment, the annual volumes of internal released As in the high-water year, common-water year, and low-water year were decreased to 11.89, 4.94, and 4.89 Mg, respectively; and (iii) the highest reduction rate could reach 27.5% in the common-water year, while the lowest was 10.92% in the high-water year because the massive water exchange with the Yangtze River in the high-water year resulted in an enhanced dynamic disturbance that played a more dominating role in the internal As release than the surface sediment removal. The results of this study may be useful for other researchers of water environment protection for waterfront bodies.