Mercury deposition in the Adirondack State Park has been of great concern due to the bioaccumulation of methylmercury (MeHg) through various trophic levels. The present study focused on sediments collected from riparian/wetland regions of Sunday Lake. Samples amended with ²⁰³Hg and ¹⁴C-MeHg were used to determine potential rates of Hg methylation and demethylation. Abiotic and biotic factors such as temperature, sediment saturation, organic content, and inhibitors/stimulators of sulfate reducing bacteria leading to methylmercury production were all found to affect rates of mercury methylation. Despite repeated efforts to quantify degradation it was not possible to detect significant demethylation activity in terrestrial sites of Sunday Lake. MeHg binding to organic matter did not drastically curtail demethylation. The lack of demethylation may be due to the inability of methanogenic bacteria to use C-one compounds in these acidic habitats. Hence, without demethylation, even low rates of MeHg formation can result in significant MeHg accumulation.