Metal accumulation and contamination in sediments of 12 plateau lakes in Southwest China in response to human activities over the past century

Abstract

Historical metal accumulation and contamination in individual lakes have been studied extensively, but a comprehensive understanding at the regional scale remains limited, which is essential for establishing baselines and formulating management strategies. The present study addresses this knowledge gap by analyzing the concentrations and accumulation rates of lithogenic and heavy metals in sediment cores from 12 lakes on the Yunnan–Guizhou Plateau (YGP) of China over the past century. The lakes were categorized into urban-industrial (UI) and agricultural-natural (AN) groups according to catchment-specific socioeconomic data. The decreasing concentrations and accumulation rates of lithogenic metals in the lakes, e.g., Al, K, Fe and Ti, typically since the mid-20th century, indicated changes in human-induced soil erosion. The enrichment factors (EFs) identified Cr, Cu, and Ni as mainly lithogenic sources, and they presented temporal variations similar to those of lithogenic elements, whereas Cd was the predominant contaminant despite low accumulation rates, followed by As, Hg, Pb and Zn, with the UI lakes displaying greater contamination than the AN lakes. Metal contamination also exhibited clear historical differences between the UI and AN lakes. Contamination of most metals began in the 1950 s in the UI lakes, 30 years earlier than in the AN lakes, due to early industrial development and discharges. Contamination of As, Cd, Hg, Pb and Zn has increased since the 1980 s with rapid economic development in both types of lakes, and the accumulation rates of anthropogenic metals have indicated slightly decreasing contamination since the 2000 s due to the implementation of environmental policies, although the enrichment factor has continuously increased. The variations in mass accumulation of heavy metal contamination (ACC_a) in lake sediments were positively correlated with catchment-specific socioeconomic indicators, e.g., the proportion of industrial output, proportion of cropland area and urbanization rate, highlighting the causal link between economic development and metal contamination.