Ecological risk assessment of heavy metals in sediments of Longyang Lake and Moshui Lake in Wuhan

In order to assess the current status of the ecological environment of urban lake wetlands, the present study employs various methods, including mathematical statistics, ground accumulation index, and potential ecological risk index. These methods are used to evaluate the enrichment levels, spatial distributions, and ecological risks of nitrogen, phosphorus, and heavy metal elements in the surface sediments of Longyang Lake and Moshui Lake, located in Wuhan, China. The results indicate that the surface sediment samples from Longyang Lake have total nitrogen (TN) and total phosphorus (TP) contents ranging from 265.03to 729.68mg/kg and 888.64 to 1694.86mg/kg, respectively. On the other hand, Moshui Lake samples have TN and TP contents ranging from 306.14 to 857.27mg/kg and 671.48 to 2674.39mg/kg, respectively. Thus, Moshui Lake exhibits higher pollution levels compared to Longyang Lake. Moreover, when compared to typical lakes in other domestic cities, both Longyang Lake and Moshui Lake exhibit low TN and high TP contents in their sediments. The concentrations of As, Cd, Cr, Cu, Pb, and Zn in Longyang Lake are 14.27mg/kg, 0.58mg/kg, 59.20mg/kg, 55.61mg/kg, 33.20mg/kg, and 176.94mg/kg, respectively. In Moshui Lake, the concentrations of these elements are 19.26mg/kg, 0.62mg/kg, 85.53mg/kg, 53.67mg/kg, 41.69mg/kg, and 266.64mg/kg, respectively. Additionally, the average concentration of heavy metal elements in the surface sediments, except for Cr, exceeds the background levels of soil in Wuhan. Moreover, the Cd content in Longyang Lake and Moshui Lake are significantly higher than the background values, being 4.83 and 5.17times greater, respectively. Comparing the current conditions with those from 20 years ago, it is evident that the content of heavy metal elements (except Cd) in Moshui Lake's sediments has decreased. This suggests that efforts to clean the lake's mud have improved the sediment conditions, although pollution has not been completely eliminated. The accumulated index indicates that the Cd level in both lakes is in a roughly moderate polluted state, while Cu, Pb, Zn, and As are generally in a mildly polluted state, and Cr is in a clean state. The potential ecological risk index suggests that the overall potential ecological risk is at a low to medium level, but the Cd content in both lakes poses a moderate to severe risk. The study area's heavy metal elemental pollutants may be sourced from a combination of fluxes, including early industrial discharge, fishery farming, animal feces, and emissions from human domestic sewage. © 2023 Chinese Society for Environmental Sciences. All rights reserved.