Mercury, sulfur-metabolizing bacteria and organic matter in the sediments of subarctic Kusawa Lake, Yukon.

Recent studies of Arctic and Subarctic environments have detected rising levels of natural and anthropogenic mercury (Hg), putting northern residents at risk for Hg exposure. Within lake sediments, Hg can be methylated by certain species of Sulfate-Reducing Bacteria (SRB), a subset of Sulfur-Metabolizing Bacteria (SMB). This research assessed the controls of Subarctic SRB Hg-methylation in proglacial Kusawa Lake, Yukon, Canada. Kusawa was found to be oligotrophic, with very low primary productivity and an orthograde oxygen profile, conditions that inhibit Hg-methylation. In addition, the SMB proportion of total bacteria was small (1.9x10⁻³ %), no known SRB Hg-methylators were detected, the total Hg sediment concentration was 0.022 ± 0.0009 μgg⁻¹ (±SE) and methylmercury was undetectable. The results support previous research that suggests the factors influencing SRB Hg-methylation in Kusawa Lake are: (i) the rate of algal-derived Hg-scavenging, (ii) the sediment concentration of total Hg and (iii) the diversity of sediment SRB.