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TECHNICAL REPORTS

Heavy Metals in the Environment

Are Methylmercury Concentrations in the Wetlands of Kejimkujik National Park, Nova Scotia, Canada, Dependent on Geology?

^a Dep. of Soil Science, Univ. of Saskatchewan, 51 Campus Drive, Saskatoon, SK, Canada S7N 5A8
^b Dep. of Biology, Univ. of Ottawa, 30 Marie Curie, Ottawa, ON, Canada K1N 6N5
^c Geological Survey of Canada, 601 Booth Street, Ottawa, ON, Canada K1A 0E8
^d Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand

^* Corresponding author (Siciliano{at}sask.usask.ca).

Received for publication October 17, 2002. In the relatively pristine ecosystem in Kejimkujik Park, Nova Scotia, methylmercury (MeHg) concentrations in loons, Gavia immer, are among the highest recorded anywhere in the world. This study investigated the influence of bedrock lithology on MeHg concentrations in wetlands. Twenty-five different wetland field sites were sampled over four different bedrock lithologies; Kejimkujik monzogranite, black sulfidic slate, gray slate, and greywacke. Soil samples were analyzed for ethylmercury (EtHg), MeHg, total Hg, acid-volatile sulfides (AVS), organic matter, and water content as well as the biological parameters, mercury methyltransferase (HgMT) activity, sulfate reduction rates, fatty acid methyl ester (FAME) composition, and acidity. Methylmercury concentrations in the wetlands were highly dependent (P < 0.08) on lithology with no significant difference between bogs, fens, and swamps. Methylmercury concentrations in wetland soils developed on Kejimkujik monzogranite averaged 900 ng kg^-1 compared with only 300 ng kg^-1 in wetland soils developed on black sulfidic slate. Fatty acid methyl ester composition was also lithologically dependent (P < 0.001) with biomarkers for Desulfobulbus spp. discriminating between sites containing high and low MeHg concentrations. Levels of MeHg in wetlands were predicted mainly (41% of the sum of squares) by HgMT activity that differed (P < 0.009) between wetlands, with activity in bogs almost three times that present in swamps. Wetland MeHg concentrations are highly dependent on the lithology on which they have developed for largely biological reasons.

Abbreviations: AVS, acid-volatile sulfides • EtHg, ethylmercury • FAME, fatty acid methyl esters • HgMT, mercury-methyltransferase • MeHg, methylmercury • Q3, third quartile • SAM, S-adenosylmethionine • SCM, surface complexation model • SRB, sulfate-reducing bacteria • U, one unit of HgMT activity was defined as the formation of 1 nmol of tetrahydrofolate formed in response to the addition of 1 ng of Hg to the reaction vessel