Sediment Pollution Characteristics and Dredging in the Nanfei River Estuary, Chaohu Lake

To clarify the endogenous pollution characteristics of sediments in the Nanfei River estuary, Chaohu Lake, and provide a theoretical basis for the dredging works, the organic index, pollution index, and potential ecological risk were determined. The results show that the average total nitrogen (TN), total phosphorus (TP), and organic matter (OM) content of the sediment was 1 461 mg•kg-1, 438 mg•kg-1, and 1.77%, respectively, showing enrichment in the surface layer (0-10 cm). The nutrient pollution status and TP pollution index show that the organic pollution level was moderate and the TP pollution was severe. Furthermore, the pollution risk gradually reduced with sediment depth, representing a low risk at depths below 30 cm. Static release results showed that the average release fluxes of NH4+-N and TP in the sediment were 8.04 mg•(m2•d)-1 and 0.19 mg•(m2•d)-1, respectively, and showed highest release potentials consistent with areas of sediment nutrient pollution. Except for Cr and Ni, the concentrations of six heavy metals were higher than the soil background values for Anhui Province, and the concentrations of Hg and Cd far exceeded the standards. According to the assessment of potential ecological risk from heavy metals, the 0-20 cm sediments present a high level of risk and sediments below 30 cm have a low level of risk. Heavy metal leaching toxicity indicated that the risk of heavy metal release after dredging is low and non-hazardous. These results were used to determine the key dredging area (3.93 km2) and depth (30 cm) for the Nanfei River estuary, providing an important basis for future dredging activities. © 2021, Science Press. All right reserved.