Determination of dredging depth of Xingyun Lake based on heavy metal pollution and ecological risk assessment of sediment

It is necessary to determine rational dredging depth for environmental dredging projects of polluted sediment in lakes. Eight columnar sediment samples were collected from Xingyun Lake, and the vertical variation characteristics of heavy metals including As, Cr, Cu, Ni, Pb and Zn in the sediment of Xingyun Lake were analyzed. Geo-accumulation index and potential ecological risk index were used to assess the pollution degree and potential ecological risks posed by heavy metal contaminations, based on which the reasonable dredging depth was determined. The results showed that the average concentrations of As, Cr, Cu, Ni, Pb and Zn in the sediments of Xingyun Lake were 14.76, 35.76, 46.14, 46.08, 115.76 and 109.82 mg/kg, respectively. Compared with Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land (Trial) (GB 15618-2018), As, Pb and Zn contents in the sediments of Xingyun Lake exceeded the screening value of agricultural land soil pollution risk. The pollution of heavy metals in the sediment was mostly clean, and the pollution of Pb and Zn in some sampling sites was relatively moderate, and the overall performance was Pb>Zn>As>Ni>Cu>Cr. The potential ecological risk of heavy metals in sediment was at the level of mild ecological hazard, and the ecological hazard level of each sampling point was 1^#>7^#>2^#>6^#>4^#>3^#>8^#>5^#. The environmental dredging depth of Xingyun Lake sediment was recommended to be 20-30 cm by using the method of critical cumulative depth combined with the inflection point of ecological risk change.