Atmospheric Deposition History of Trace Metals and Metalloids for the Last 200 Years Recorded by Three Peat Cores in Great Hinggan Mountain, Northeast China

摘要

A large number of studies on trace metals and metalloids (TMs) accumulations in peatlands have been reported in Europe and North America. Comparatively little information is available on peat chronological records of atmospheric TMs flux in China. Therefore, the objective of our study was to determine the concentrations and accumulation rates (ARs) of TMs in Motianling peatland from Great Hinggan Mountain, northeast China, and to assess these in relation to establish a historical profile of atmospheric metal emissions from anthropogenic sources. To meet these aims we analyzed 14 TMs (As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sr, Sb, Tl, and Zn) and Pb isotopes (206Pb, 207Pb, 208Pb) using ICP-AES and ICP-MS, respectively, in three peat sections dated by 210Pb and 137Cs techniques (approximately spanning the last 200 years). There is a general agreement in the elemental concentration profiles which suggests that all investigated elements were conserved in the Motianling bog. Three principal components were discriminated by principal component analysis (PCA) based on Eigen-values 1 and explaining 85% of the total variance of element concentrations: the first component representing Ba, Co, Cr, Mo, Ni, Sr and Tl reflected the lithogenic source; the second component covering As, Cu and Sb, and Cd is associated with an anthropogenic source from ore mining and processing; the third component (Pb isotope, Pb and Zn) is affected by anthropogenic Pb pollution from industrial manufacturing and fossil-fuel combustion. The pre-industrial background of typical pollution elements was estimated as the average concentrations of TMs in peat samples prior to 1830 AD and with a 207Pb/206Pb ratio close to 1.9. ARs and enrichment factors (EFs) of TMs suggested enhanced metal concentrations near the surface of the peatland (in peat layers dated from the 1980s) linked to an increasing trend since the 2000s. This pollution pattern is also fingerprinted by the Pb isotopic composition, even after the ban of leaded gasoline use in China. Emissions from coal and leaded gasoline combustions in northern China are regarded as one of the major sources of anthropogenic Pb input in this region; meanwhile, the long-distance transportation of Pb-bearing aerosols from Mongolia should be also taken into consideration. The reconstructed history of TMs’ pollution over the past ca. 200 years is in agreement with the industrial development in China and clearly illustrates the influence of human activities on local rural environments. This study shows the utility of taking multi-cores to show the heterogeneity in peat accumulation and applying PCA, EF and Pb isotope methods in multi-proxies analyses for establishing a high resolution geochemical metal record from peatland.