Microbial Mercury Methylation in Winooski River and Englesby Brook, Vermont

Mercury methylation is the harmful process by which mercury (Hg) is converted to methylmercury (MeHg). Biotically, this is done by mercury-methylating microbes such as sulfate-reducing bacteria (SRB) in ecosystems such as wetlands and aquatic sediments. Due to legacy Hg and sulfate deposition along the eastern US, there likely remains a moderate concentration of Hg in Winooski River (W) and Englesby Brook (E), sites which have been identified as having relatively higher mercury concentrations in Vermont. If the microbial community consists partially of mercury-methylating microbes, there is a higher potential of conversion of Hg to MeHg. Further, climate change is expected to impact biotic mercury methylation due to flooding leading to redox oscillations in the riparian region of the streams. To investigate this potential, sediment cores were taken from the sites to analyze microbial community composition and concentrations of Hg, C, and N. Results suggest that the microbial communities of Winooski River and Englesby Brook are different. Further, the Riparian Land samples had a significantly greater relative abundance of 16S rRNA ASVs that matched to Hgmethylating genera compared to Riparian Water samples, as well as a greater THg concentration in Englesby Brook, indicating a higher potential for Hg-methylation within the Riparian Land of both streams.