Seasonal changes in mercury stocks and methylation ratios in vernal pools in the northeastern United States

Davis, Eric

University of Vermont master’s thesis examining the effects of mercury on vernal pools. The purpose of this research was to quantify the concentrations of Hg and MeHg that biota are exposed to in vernal pools and to determine the methylation efficiency of these habitats. Eight sites in two national parks in the northeastern United States were utilized for this study. Water samples were collected and analyzed for parameters shown to influence methylation, including pH, temperature, conductivity, dissolved organic carbon(DOC), sulfate, as well as Hg and MeHg concentrations. Pressure transducers that continuously recorded water level were deployed at each site to quantify the hydrologic regime. These chemical and hydrologic parameters were also used to explore how the physical environment of these systems may affect methylation dynamics.Mean total mercury concentrations at our study sites ranged from 0.53 ng/L to 8.27 ng/L. Mean methyl mercury concentration ranged from 0.24 ng/L to 4.52 ng/L. The mean methylation efficiency averaged 43% and peaked at 58%. Methylation efficiencies exceeding 10% have been linked to elevated levels of MeHg in biota and each of our study sites regularly exceeded this threshold. Vernal pools play an integral role in energy cycling in forested ecosystems, exporting as much as 140 kg of biomass per hectare annually. Thus contamination of vernal pool biota not only has implications for these organisms, but also represents a vector for MeHg to move out of vernal pools and into other trophic webs. This potential contamination could negatively affect population dynamics for a wide range of species.

Seasonal changes in mercury stocks and methylation ratios in vernal pools in the northeastern United States

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