Spatial-Temporal Variations for Pollution Assessment of Heavy Metals in Hengshui Lake of China

A comprehensive analysis of the spatial and temporal variations of heavy metals in wetland sediment can delineate the changes in possible contamination sources, providing valuable conservation strategies for further wetland management. Using pollution index, enrichment factors, and potential ecological risk index, the spatial and temporal variations in heavy metals (Cd, Hg, As, Pb, Cr, Cu, and Zn) were evaluated in Hengshui Lake in north China from 2005 to 2020. The results demonstrated that the concentrations and assessment index for most heavy metals all decreased, with that of As decreasing the most (-54.3%), which mainly benefited from the implementation of a series of ecological conservation and restoration projects. Although the assessment indexes for most heavy metals indicated non-pollution status, Hg and Cd exhibited medium enrichment and moderate potential ecological risk. Especially for Cd, the related-indexes increased by 859.3%. Furthermore, the high pollution was mainly distributed nearby the regions of dense enterprises and the spilled into of water (i.e., Wangkou sluice, the Jizhou Small Lake and its causeway). This was primarily attributed to discharge of industrial wastewater and Cd-polluted ecological diversion water. These findings demonstrated the necessity of continued and targeted implementation of wetland conservation and restoration projects, identified possible contamination sources and important pollution regions that could provide insights into contamination control options and targeted management strategies for Hengshui Lake.