Heavy metal in water deposits over the past 60 years in karst depression

Similar to a dam or reservoir, karst depression can trap sediment and is globally spread in karst areas. However, the effect of soil erosion by water on the migration and redistribution of heavy metals in recent decades remains unclear. This study investigates the temporal variation in heavy metals (Cu, Pb, Zn, Ni, As, Cd and Cr) of water deposits over the past 60 years, quantifies the influence of sediment deposition rates on heavy metal loss, and evaluate the potential sources and contamination levels of heavy metals in karst areas of southwest China. Totally, 194 soil samples collected from three sediment cores in a karst depression were analyzed for radionuclide activities (¹³⁷Cs and ²¹⁰Pb_ex), particle size distribution, and heavy metal concentrations. Results indicated that heavy metal deposition rates peaked during 1949-1956, followed by a rapid decline in 1957-1964 and a gradual decrease from 1965 to 2015. The Pb/Cs ratio better reflected heavy metal dynamics compared to individual radionuclides. Sediment deposition rate was significantly positively correlated with all seven heavy metal deposition rates, and the Cu, Zn, Ni, and As concentrations, while it significantly and negatively correlated with Pb, Cd, and Cr concentrations. These results implied that variations in heavy metal deposition rates over the past 60 years were primarily driven by soil erosion. Cd exhibited the highest level of contamination among the investigated heavy metals and was primarily associated with anthropogenic activities. This study offers new insights into the mechanisms of heavy metal deposition and pollution, and is thereby helpful for heavy metal pollution control and national food security.