Distribution and Pools of Mercury in Czech Forest Soils

摘要

Parts of the Czech Republic received extreme loading of acid deposition from coal combustion in the second half of the twentieth century. Although associated Hg deposition was not directly measured, Hg deposition rates calculated from peat cores approach 100 ng m~(-2) year~(-1). We quantified the soil concentrations and pools of Hg with carbon (C), sulfur (S), and nitrogen (N)—elements closely associated with soil organic matter at five sites across the Czech Republic-four sites known for extreme deposition levels of S and N compounds in the twentieth century, and one site relatively less impacted. The site-specific means of O-horizon Hg concentrations ranged from 277 to 393μg kg~(-1), while means of Hg concentrations in mineral soil ranged from 22 to 95 μg kg~(-1). The mean Hg/C ratio across sites increased from ～0.5 μg Hg g~(-1) C in the Oi-horizon to ～5 μg Hg g~(-1)C in the C-horizon due to the progressive mineralization of soil organic matter. The soil Hg/C increase was accompanied by a soil C/N decrease, another indicator of soil organic matter mineralization. Soil Hg/C also increased as soil C/S decreased, suggesting that Hg was stabilized by S functional groups within the soil organic matter. Mineral soil Hg pools (8.9-130.0 mg m~(-2)) dominated over organic soil Hg pools (5.3-10.1 mg m~(-2)) at all sites. Mineral soil Hg pools correlated more strongly with total soil S and oxalate-extractable Fe than with total soil C. Total soil Hg pools could be accounted for by a time period of atmospheric inputs that was short relative to the age of the soils. The cross site variability of Hg soil pools was not sensitive to the local Hg deposition history but rather related to the capacity of soil to store and stabilize organic matter.