Persistent impact of human activities on trace metals in the Yangtze River Estuary and the East China Sea: Evidence from sedimentary records of the last 60\u202fyears.

Abstract

Three sediment cores taken from the Yangtze River Estuary (YRE) and the East China Sea (ECS) in 2016 were analyzed for trace metals (Pb, Zn, Cu, Cr and As), major elements (Al, Fe and Mn), sediment composition, chemical properties (Eh and pH), and natural/artificial radionuclides (210Pb/137Cs) to decipher the high-resolution historical variation in anthropogenic metals over the past 60\u202fyears. The results showed that anthropogenic Pb was primarily derived from atmospheric deposition, while anthropogenic Zn, Cu and As were carried out by fluvial discharge. In the YRE, the recent decrease in sedimentary metals could be largely a result of intensified erosion, which was triggered by the construction of dams in particular the Three Gorges Dam (TGD) in 2003 and soil-conservation projects. In comparison, sedimentary records in the deposition-dominated environment of the ECS showed that anthropogenic Pb and Cr began to gradually increase following 1970, but a remarkable increase in anthropogenic Zn and Cu occurred in 1990, probably reflect the different origins and dispersion pathways of these elements. Anthropogenic Pb and Cr exhibited a sharp decrease near early 2000s due to increasing investment in treating pollution. Being sensitive to the substantial reduction in riverine particulate flux of Zn and Cu from the Yangtze River, the concentrations of anthropogenic Zn and Cu in the cores decreased by 5-27% in 2005-2016. Furthermore, a prominent increase trend of As record after 1990, probably due to the excessive pesticides used in agricultural activity.