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Completed Project

Historical Analysis of Atmospheric Mercury Deposition Preserved in Ombrotrophic Bogs in the Catskill Mountains

Natasha Vargo, Vassar College ’17 and Prof. Alison Spodek Keimowitz
Atmospheric heavy metal emission and deposition have become growing concerns as industry and fossil fuel usage have dramatically increased globally over the past 200 years. Mercury is emitted into the atmosphere from natural geothermal sources and from anthropogenic sources such as fossil fuel fired power plants, mining, and metal manufacturing (Pirrone, et. al., 2010). Ombrotrophic bogs are purely rain-fed wetlands in which compressed Sphagnum mosses form peat. Chemical and hydrologic properties of ombrotrophic bogs allow peat to preserve atmospherically deposited substances including mercury; no other sources of mercury are anticipated. For this study, several 15 to 150 centimeter long cores were collected from six bogs in the Catskill Mountains using a Russian peat borer designed to not compress the obtained core. The peat cores were sectioned every 1-centimeter, air-dried and digested using potassium permanganate. The digested peat samples were analyzed for mercury concentration using Atomic Absorbance Spectroscopy and compared to NIST and ERM plant and soil standards. Results show significantly higher concentrations of mercury on the top sphagnum layers of cores relative to more baseline values towards the bottom of the cores. The maximum mercury concentration found at the top of a core is 12.8 mg/ kg (on a dry weight basis) which then stabilized to about 2 mg/kg along the bottom of a core found at Bog 303. Some bog locations had overall significantly higher concentrations of mercury than others pointing to possible geographic factors; for example, Bog 305 had a maximum concentration of 7.6 mg/kg whereas Bog 308 only had a maximum mercury concentration of 0.068 mg/kg. Further analysis and carbon dating are required to obtain a historical record of deposition and to compare between locations within and outside of the Catskills.