Date of Award

12-2014

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Aria Amirbahman

Second Committee Member

Thomas G. Huntington

Third Committee Member

Stephen A. Norton

Abstract

Wetlands are well-known hotspots for storing mercury (Hg) and converting it to its more toxic form, methylmercury (MeHg). MeHg is subsequently released into adjacent water bodies and accumulated by fish. In 2010-2012, an expansive survey of more than 125 lakes and ponds in Maine suggested that fish with the highest MeHg burdens occurred in waters with a large wetland contribution (Bacon, personnel communication, 2014). Among these systems, Hodgdon Pond, Acadia National Park, Maine, had the highest levels of fish MeHg thought to be due to the large proportion of adjacent wetlands. As such, a sustainable remediation of wetlands with respect to Hg contamination is of interest to the public.

The objective of this work was to determine if zero-valent iron (ZVI) or granular activated carbon (GAC) application is an appropriate MeHg remediation strategy for the pond. Twelve mesocosms were constructed in the inundated fringing wetland of Hodgdon Pond, and ZVI and GAC were applied as treatments. Sediment and porewater samples were collected at different times, and analyzed for relevant parameters. Results indicate that both ZVI and GAC significantly lower the concentration of MeHg in porewater, and that more MeHg is present in porewater in summer than fall, likely due to plant induced redox and chemical changes.

A laboratory experiment was also conducted using intact plant containing sediment “cores” from Hodgdon Pond. Twelve microcosms were assembled from this material and kept in the laboratory with several centimeters of overlying Hodgdon Pond water; ZVI and GAC treatments were applied. Approximately ten snails (L. stagnalis) were added to each microcosm and sacrificed after 28 days. Porewater, sediment, and snail tissues were analyzed. Results for porewater and sediment corroborate trends seen in the field, and snail tissue results indicate that snails in treated microcosms uptake less MeHg than control snails.

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