Holocene mercury accumulation calibrated by peat decomposition in a peat sequence from the Sanjiang Plain, northeast China

Abstract

Peatlands are ideal archives that are widely used to reconstruct historical Hg accumulation around the world. However, decomposition of peat soils leads to Hg enrichment or depletion in peat profiles. To evaluate the impact of peat decomposition on historical Hg accumulation records, a 7800-year peat sequence from the Shenjiadian peatland (SJD-2, Sanjiang Plain, northeast China) was selected in this study. Based on the degree of peat humification and a generalized additive model (GAM), Hg accumulation rates (Hg ARs) were reconstructed and calibrated from the middle Holocene onward. The results showed that the Hg concentrations in the SJD-2 peat profile ranged from 11.9 to 55.3 ng g−1 and that the Hg AR ranged from 0.4 to 7.0 μg m−2 yr−1; these values for both parameters were lower than their corresponding values observed in other peatlands around the world. Peat decomposition led to Hg depletion in peat soils to some extent, and the GAM could be used to evaluate the impact of peat decomposition on historical Hg ARs in peat sequences based on the degree of peat humification and calibration of Hg ARs. Before the Industrial Revolution, anthropogenic Hg sources caused the calibrated Hg ARs in the SJD-2 peat profile to slightly increase around 1300 cal yr BP. Similar to other regions around the world, the calibrated Hg AR on the Sanjiang Plain also obviously increased from 3 to 8 μg m−2 yr−1 after global Hg emissions began to increase during the Industrial Revolution.