Honors Theses (Environmental Studies Program)

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Browsing Honors Theses (Environmental Studies Program) by Author "Cleveland, Rachael"

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    Mercury Concentration and Speciation in Sediments Throughout the Watershed Affected by Black Butte Mine in Oregon
    (2018-06) Cleveland, Rachael
    The history of mining in Oregon has left a legacy of contaminated and abandoned sites that threatens environmental and human health. The goal of this research is to better understand mercury (Hg) cycling within an Oregon watershed that is being contaminated by an abandoned mine. The chosen site is the Superfund site at Black Butte Mine, where contaminated sediment has washed down a series of streams that drain into Cottage Grove Reservoir. The specific objectives of this work are to determine how Hg sediment concentrations and forms (reactivity) change from the mine site to the reservoir and how these factors change within the different areas of the reservoir. Sediment sampling was conducted at the Black Butte Mine site, along drainage creeks and streams, and throughout the Cottage Grove Reservoir. Sediment composites were collected and used for total Hg and speciation analysis. The concentrations of mercury decreased with distance from the mine site to the reservoir. Mercury in sediment was found in progressively more reactive forms from the mine site to the reservoir. Within the reservoir, reactivity of Hg was higher in the floodplains that experience seasonal variations than the permanently inundated areas. The creek immediately adjacent to the mine site posed the most dangers to human and environmental health in terms of total Hg. Above the mine tailings and at the reservoir, conditions are supporting the transformation of inorganic Hg to organic Hg. This information, particularly the forms of mercury found, has significant implications for Hg bioaccumulation and the resulting safety of humans and species that live within the watershed. Data gaps in the US Environmental Protection Agency and Oregon Department of Environmental Quality's previous work on mercury analysis have been filled, which will inform future work at this site and allow them to target areas of most concern. A new site of organic mercury transformation has been identified, and future work can address this site. Additionally, mercury cycling in sediment is now better understood at this site, which will inform future research looking at mercury cycling at the watershed scale.