Source Analysis and Ecological Risk Assessment of Heavy Metals in Sediments from Western Lake Area of Taihu Lake

[Objective] Heavy metal pollution in sediments is a major factor contributing to the deterioration of lake water quality. To accurately assess the sources and potential ecological risks of heavy metals in lake sediments, it is necessary to conduct source analysis and risk assessment at the watershed scale. [Methods] Concentrations of Cr, Ni, Cu, Zn, As, Cd, and Pb in soil and sediments were measured at the small watershed scale in the western lake area of Taihu Lake, and a comprehensive ecological risk evaluation of heavy metals was performed using the enrichment factor (EF), geoaccumulation index (Igeo), and potential ecological risk index. [Results] The heavy metal contents in sediments were generally higher than those in soil. Moreover, the heavy metal contents in sediments from the northern lake area were higher than those in the central and southern lake areas. About 88.4% of the increase in heavy metal content in sediments came from exogenous inputs such as terrestrial rivers and runoff discharged into the lake. Additionally, the EF and Igeo demonstrated that the sediments experienced various degrees of heavy metal accumulation and pollution. The ecological risk values of Cr, Ni, Cu, and Zn were significantly higher than those of the corresponding elements in soil, indicating a relatively high potential ecological risk. Finally, the assessment using the potential ecological risk index showed that Cd exhibited a relatively high ecological risk value, and the sediments exhibited moderate to high comprehensive ecological risks. [Conclusion] Overall, the potential ecological risks of heavy metals in sediments from the western lake area of Taihu Lake are attributed to terrestrial inputs, including surface soil erosion. By coupling comparative analysis of exogenous and endogenous pollution levels of heavy metals at the small watershed scale of the lake, this study provides important management information and a scientific basis for heavy metal control in the Taihu Lake watershed.