Anthropogenic, detritic and atmospheric soil-derived sources of lead in an alpine poor fen in northeast China

Abstract

Ombrotrophic bogs are faithful archive of atmospheric metal deposition, but the potential for fens to reconstruct environmental change is often underestimated. In this study, some new data on the Pb depositional history in northeast China were provided using two ²¹⁰Pb-dated peat sequences from a poor fen in the Fenghuang Mountain of Heilongjiang province. Anthropogenic, detritic and atmospheric soil sources were discriminated using a two-step sequential digestion (weak acid leaching to liberate mobile Pb which is often regarded as anthropogenic Pb, especially for recent samples) and a ratio of unsupported ²¹⁰Pb and supported ²¹⁰Pb with the logic of that the ²¹⁴Pb mainly represents the residual detritus (constant throughout the core) and the unsupported ²¹⁰Pb arises from atmospheric fallout. A higher ²¹⁰Pb/²¹⁴Pb suggests more contributions from atmospheric deposition to the Pb content in the peat, and a ratio of 10 was defined to indicate the boundary between detritic input and atmospheric deposition. The detritic Pb was estimated to be 10–13 mg·kg⁻¹, the anthropogenic Pb ranged from 10–80 mg·kg⁻¹, and the atmospheric soil-derived Pb ranged from < 5 mg·kg⁻¹ to 30 mg·kg⁻¹. The history of anthropogenic Pb pollution over the last 150 years was reconstructed, and the calculated Pb deposition rate (AR Pb) ranged from 5 to 56 mg·m⁻²·yr⁻¹. Using Ti as a reliable reference, the enrichment factor of Pb (EF Pb) relative to the upper continental crust was calculated. Both AR Pb and EF Pb increased with time, especially after the foundation of the People’s Republic of China. This is consistent with increasing industrialization and coal burning in the last 60 years in northeast China. The present record of anthropogenic Pb deposition was consistent with the previous reports and an increasing trend of environmental pollution due to anthropogenic activities, in contrasts to Europe and North America which have experienced a major environmental cleanup. For the first time, this work estimates atmospheric Pb deposition via a minerotrophic peat core in China. This will enhance the use of peat archives for studies of environmental change.