Holocene-Anthropocene transition in northwestern Yunnan revealed by records of soil erosion and trace metal pollution from the sediments of Lake Jian, southwestern China

Accelerated soil erosion and trace metal pollution in aquatic environments have become a pervasive aspect of global environmental changes during the Anthropocene, threatening food security and ecosystem viability. Long-term records of these processes can promote an improved understanding of their timing, amplitude, and environmental impacts. Here we present a sedimentary record from Lake Jian in Yunnan Province, southwestern China, which shows that land-use changes affected the lake watershed by at least 1200 CE, and that the intensity of soil erosion increased from 1450 CE onwards, as evidenced by increases in magnetic susceptibility and high concentrations of trace metals. The timing of the increase in atmospheric lead (Pb) transport, which was possibly related to the growth of metallurgical activity in the region, occurred ~250 years earlier than the anthropogenic soil erosion. Pb emissions resulting from the mining and smelting industry, coal burning, and the use of leaded gasoline led to enhanced Pb pollution in the area since the 1950s CE. Comparison of the results with geochemical records from lakes in northwestern Yunnan reveals that environmental disturbances were relatively limited during the intervals of the Nanzhao and Dali Kingdoms. However, enhanced human disturbances of lake watersheds in Yunnan occurred from the Yuan dynasty onwards, as a result of population increases caused by immigration to the area, which was followed by the changes in the type and intensity of human activity, with an enhanced anthropogenic impact after the middle twentieth century. Overall, our study provides a case study for understanding the historical background of the Anthropocene.