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Format:
Print
Author:
Davis, Eric
Dept./Program:
Natural Resources
Year:
2013
Degree:
MS
Abstract:
Vernal pools play critical ecological roles by supporting diverse invertebrate communities and providing breeding habitat for globally pressured amphibian species. However, these systems may also be effective in transfonning mercury (Hg) into a more toxic and bioavailable fonn, methylmercury (MeHg). Long-range atmospheric deposition of Hg, emitted primarily from industrial sources, has led to widespread ecosystem contamination. Upon entering aquatic systems, the anoxic conditions at the sediment-water interface in vernal pools favor anaerobic bacteria that facilitate the transfonnation ofatmospherically deposited, inorganic Hg to MeHg. MeHg is a neurotoxin that has significant adverse effects on wildlife including reduced perfonnance, maintenance, and reproductive capabilities.
Vernal pools are also characterized by low pH conditions and high amounts of dissolved organic carbon and these environmental characteristics have been linked with increased methylation in other aquatic ecosystems. The variable hydrology ofvernal pools may also favor increased methylation by shifting the redox cycle. Given the ecological role ofvernal pools and their potential for efficient methylation, the uncertainty around methylation dynamics in these systems represents an important knowledge gap.
The purpose of this research was to quantify the concentrations of Hg and MeHg that biota are exposed to in vernal pools and to detennine 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 methylmercury 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.