Historical variations of atmospheric trace metal pollution in Southwest China: Reconstruction from a 150-year lacustrine sediment record in the Erhai Lake

Abstract

A 35-cm long sediment core - retrieved from Erhai Lake - was analyzed for Pb isotope ratios (207Pb/206Pb and 208Pb/206Pb) and trace metal concentrations (Cr, Cu, Ni, Hg, Pb and Zn) to gain an understanding of atmospheric trace metal pollution over the last 150years in Southwest China. Core chronology was established by using the 210Pb and 137Cs dating techniques. Principal component analysis (PCA) and enrichment factors (EFs) were used to differentiate between the anthropogenic and detrital origins of the metals. The results indicate that the elements Hg, Pb and Zn in the sediment of Erhai Lake were affected by anthropogenic contamination. During the 1860s-1890CE, decreasing EFs of Hg, Pb and Zn and Pb isotope ratios suggest improving atmospheric quality, which may relate to the shrinking metallurgy activities during the late Qing Dynasty in Southwest China. Pollution levels of the metals remained stable during 1890–1960CE, whereas they increased after 1960CE, especially since the 1980CE, suggesting degradation of the regional atmospheric environment with the economic development after the reform and opening in the late 1970s. Pb isotopes and the PCA reveal that the atmospheric Pb is mainly from regional ore mining and smelting, which is also the dominant source of atmospheric Hg and Zn pollution in Southwest China. Our study also shows that the use of a pre-industrial background may underestimate the trace metal pollution in Erhai Lake due to the influence of early smelting activities.