Spatial and Temporal Variations in Heavy Metals in Lake and Reservoir Sediments in China: A Pollution Status and Risk Assessment

As ubiquitous pollutants, understanding the levels of contamination, eco-risks, and potential sources of heavy metals in lake and reservoir sediments is essential for the development of pollution control policies to ensure the ecological safety of the aquatic environment. However, large-scale studies of heavy metal elements in sediments face many limitations, and most of them are characterized as small and staged. Therefore, in order to evaluate the level of heavy metal contamination in lake and reservoir sediments in China and to explore the pattern of spatial distribution of heavy metals, this article systematically collected the concentrations of seven heavy metals, Pb, Cd, Hg, Cr, As, Zn, and Cu, in the sediments of the lakes and reservoirs in question since 2000, evaluated the calculation of the accumulation index and the assessment of health risk, analyzed the spatial and temporal variations, and conducted a preliminary investigation of the sources. The results of the study showed that the contents of the seven elements were higher than the national soil pollution control standards, and various elements were enriched to different degrees, among which Cd and Hg exceeded the standard more seriously. The overall pollution level of reservoir sediments was lower than that of lake sediments, and the pollution of reservoirs was relatively light; from the distribution characteristics, the pollution level and ecological risk of different heavy metal elements showed an obvious imbalance in distribution. The heavy metal concentration, ground accumulation index, and ecological risk in the southern region are overall high. There is a good agreement with the Hu Huanyong line; from the historical change characteristics, except for the average Igeo of Hg, which shows an obvious upward trend, the average Igeo of several other heavy metals basically shows a decreasing or stable trend; the sources of heavy metals are complex and extensive in terms of the national scale, and industry, transportation, and agriculture are the main sources.