| Abstract
| - Historical records of mercury (Hg) accumulation in lakesediments and peat bogs are often used to estimate humanimpacts on the biogeochemical cycling of mercury. Onthe basis of studies of lake sediments, modern atmosphericmercury deposition rates are estimated to have increasedby a factor of 3−5 compared to background values: i.e., from about 3−3.5 μg Hg m-2 yr-1 to 10−20 μg Hgm-2 yr-1. However, recent studies of the historical mercuryrecord in peat bogs suggest significantly higher increases(9−400 fold, median 40×), i.e., from about 0.6−1.7 μgHg m-2 yr -1 to 8−184 μg Hg m-2 yr -1. We comparedpublished data of background and modern mercuryaccumulation rates derived from globally distributed lakesediments and peat bogs and discuss reasons for thedifferences observed in absolute values and in the relativeincrease in the industrial age. Direct measurements ofmodern wet mercury deposition rates in remote areas arepresently about 1−4 μg m-2 yr -1, but were possibly ashigh as 20 μg Hg m-2 yr -1 during the 1980s. These valuesare closer to the estimates of past deposition determinedfrom lake sediments, which suggests that modern mercuryaccumulation rates derived from peat bogs tend to over-estimate deposition. We suggest that smearing of 210Pb in theuppermost peat sections contributes to an underestimationof peat ages, which is the most important reason forthe overestimation of mercury accumulation rates in manybogs. The lower background mercury accumulationrates in peat as compared to lake sediments we believeis the result of nonquantitative retention and loss of mercuryduring peat diagenesis. As many processes controlling time-resolved mercury accumulation in mires are still poorlyunderstood, lake sediments appear to be the more reliablearchive for estimating historical mercury accumulationrates.
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