Distribution and ecological risk assessment of heavy metals in sediments of Dajiuhu Lake Wetland in Shennongjia, China

Abstract The rapid development of modern industrialization led to the discharge of high number of heavy metals into wetlands, which continued to accumulate and cause pollution. Located in the Shennongjia Forest District of Hubei Province in China, Dajiuhu is one of the list of international key wetlands, which is a typical representative of the wetland ecosystem and has certain scientific research value. In this study, the surface sediments of nine sub-lakes in Dajiuhu were collected in August 2020, and the total contents of Cd, Cr, Cu, Ni, Pb and Zn in the sediments have been measured. The occurrence and speciation characteristics of heavy metals have been analyzed by an improved BCR extraction method. Potential ecological risk index, geo-accumulation index, risk assessment code and pollution factor method were used to evaluate the pollution degree and ecological risk of heavy metals. The possible sources of heavy metals were estimated based on the total contents of heavy metals. The results show that the heavy metal content in lake sediments of Dajiuhu wetland is Zn>Cr>Ni>Pb>Cu>Cd in sequence, and only the average content of Cd exceeded the standard of the national nature reserve. Although Pb did not exceed the standard value, due to the proportion of different forms caused it and Cd both brought some pollution as well as ecological risk to the lakes and wetlands. The spatial distribution of heavy metal content in the nine sub-lakes does not vary regularly. The sources of heavy metals in the lake sediments of Dajiuhu wetland among which Ni, Cr and Cu are mainly natural factors, Cd and Pb are mainly anthropogenic factors, and Zn is caused by both sources together. This study can further improve the study of heavy metal pollution in the lake wetlands and provide a relevant basis and direction for the management of heavy metal pollution in the Dajiuhu wetland.