Coupling of methyl and total mercury in a minerotrophic peat bog in southeastern Sweden

Abstract

During most of an annual cycle, we studied the temporal variation of total mercury (HgT) and methyl mercury (MeHg) in unfiltered and filtered (0.45 µ) peat water from a minerotrophic peat bog in southeastern Sweden. MeHg in bulk water ([MeHgT]) and total Hg in filtered water in discharge water from the peat bog ([HgD]) were an order of magnitude higher than in upland runoff water entering the peat bog. At the discharge end, peat-water [HgD] and [MeHgD] ranged from 8 to 54 pmol·L–1 and from 1 to 32 pmol·L–1, respectively. Whereas the variation of [MeHgT] was explained by changes in [MeHgD], the variation of inorganic HgT [IHgT] = [HgT] – [MeHgT] was explained by changes in particle-bound IHg [IHgP] = [IHgT] – [IHgD]. Filterable organic matter and sulfide in the water both correlated poorly with [HgD]. Neither did the amount of HgT in precipitation and upland runoff water correlate well with the estimated discharge of HgD from the peat bog. However, there was a strong correlation between [HgD] and [MeHgT] in the peat water (r = 0.96). Furthermore, a significant fraction of HgD was MeHg (mean 28%; range 8–60%). These results suggest that methylation increased the mobility of Hg.