Do Mercury Records in Ombrotrophic Peat Bogs Solely Reflect Atmospheric Deposition?
Vortragender: Dr. Harald Biester, Institut für Umweltgeochemie der Universität HeidelbergDo. 29.04.2004 (16:15), H6
Ombrotrophic peat bogs have been widely used to evaluate long-term records of atmospheric mercury (Hg) deposition. One of the major aims of these investigations is the estimation of the increase of atmospheric Hg fluxes during the industrial age compared to pre-industrial fluxes. Comparability of Hg accumulation rates calculated from density, peat accumulation rates, and Hg concentrations requires linearity between these parameters. Peat formation is a dynamic process accompanied by intense mass loss and alteration of the organic material. Our investigations on three peat cores from the Magellanic Moorlands, Chile, indicate that Hg concentrations in peat strongly depend on peat humification. Moreover, differences in mass accumulation rates during peat evolution are not compensated by linear changes in density, peat accumulation or Hg concentrations. We suggest normalizing Hg accumulation rates to carbon accumulation rates to achieve comparability of Hg accumulation rates derived from differently altered peat sections. Normalisation to the carbon accumulation rates reduces Hg accumulation rates in low degraded peat sections in the upper peat layers by factors of more than two. Our results suggest that the modern times increase in Hg deposition rates derived from ombrotrophic peat bogs are potentially overestimated if Hg accumulation rates are not corrected for mass accumulation rates.
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