Geochemical records in Holocene lake sediments of northern China: Implication for natural and anthropogenic inputs

摘要

Daihai Lake is located in a hydrologically closed basin within the transitional zone of the East Asian monsoon, which has experienced significant lake-level fluctuations. The sedimentary sequence of a 12.08 m core was analyzed for mobile (Ca, Mg, and Sr) and immobile elements (Al and Fe) and trace metals (e.g., Co, Ni, Cu, Zn, and Pb) in order to study the changes of natural chemical compositions and the potential influences of the historical mining and use of metals during the Holocene period. Climate changes have a significant influence on the concentrations of mobile elements in the Holocene lake sediment; high concentrations occurred during the times with high lake level, resulting from enhanced catchment weathering due to strong monsoon effects. Different from these mobile elements, the variation of immobile elements and trace metals in Daihai Lake sediment shows clear anthropogenic impact of the mining and use of metals in the last several millenniums. A gradual increase in the concentrations and fluxes of metals from ～5000 cal. a B.P. is correlated well with the emergence of Chinese civilization. The concentrations and fluxes of these metals and immobile elements in the sediments increased rapidly between 2100 and 1250 cal. a B.P., indicating the extensive use of metals during the Warring States Period (475-221 B.C.), and the early Han Dynasty (206 B.C.-220 A.D.). Further increase of trace metals, such as Cu, Ni, Co, and Pb, after the Medieval Warm Period (1200-800 a B.P.) likely reflects the increased metal emissions associated with extensive mining and utilization activities. Similar patterns of sedimentary metals between Daihai Lake in northern China and Liangzhi Lake in central China further indicate significant environmental impacts of the mining and utilization of metals in the progress of Chinese civilization in the past several thousand years.