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(225) Methyl mercury production in High Arctic wetlands.
Losetto, Lisa1, Siciliano, Steven*,2, Bourdreau, Josee1, Lean, David1, 1 Department of Biology, University of Ottawa, Ottawa, ON, Canada2 LabMET, Ghent University, Gent, Belgium
ABSTRACT- Recent evidence has suggested that substantial amounts of Hg can be deposited onto the high arctic. The fate of this deposited Hg is not clear but in temperate regions methyl mercury (MeHg) is formed by sulfate-reducing bacteria (SRB). The study evaluated if MeHg is formed in arctic wetlands during the summer months and if SRB are responsible for this methylation activity. Eighteen wetlands were sampled in the High Arctic prior to ground thaw and soil samples incubated for 120 and 360 degree days. Water samples from a wetland fed by snowmelt were collected near the melting snow, in the middle of the wetland and at the outflow of the wetland. The winter soils contained only 0.066 g /kg MeHg and 45 g/kg Hg with little difference between sites. However, wetland soils incubated for 120 degree days increased in MeHg concentrations to 6.5 g/kg. Field results support this trend with water in the wetland increasing from 21 pg/L at the snow melt, to 700 pg/L in the middle of the wetland and 1500 pg/L at the outflow of the wetland. There were SRB present at almost all sites but the SRB were never present at more than 2000 cfu/g soil and sulfate reducing activity was also low, less than 18 nmoles/g/day. Analysis of the total microbial community composition indicated that the microbial communities differed between sites and that these differences were associated with higher MeHg concentrations. Our results demonstrate the MeHg is rapidly formed in arctic wetlands from initially low levels and that this formation is not strongly linked to SRB but to some undetermined biological mechanism.
Key words: mercury, arctic, wetlands, sulfate-reducing bacteria
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