Undergraduate Honors Thesis


Mercury Transfers in the Aquatic Food Web of a High Alpine Lake Ecosystem, Green Lakes Valley, Colorado Public Deposited

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  • Mercury (Hg) is a global pollutant whose cycling has been dramatically influenced by mobilization of elemental Hg (II) from anthropogenic sources. Mercury mobilization has led to a significant increase in atmospheric deposition of inorganic Hg, which can cycle within terrestrial and aquatic ecosystems. Prior research has documented the long-distance transport of Hg, thus allowing for deposition in remote regions. High elevation areas have been disproportionately affected due to increased deposition and retention of Hg in these areas. There remains, however, a lack of knowledge about the Hg cycle in these areas, particularly as it pertains to the mobilization of Hg into the food chain. Under anoxic conditions, usually in aquatic systems, Hg can be methylated by sulfate and iron-reducing bacteria into methylmercury (MeHg), a neurotoxin that bioaccumulates at each successive trophic level. Prior research at Niwot Ridge in the Colorado Rocky Mountains, U.S., showed elevated concentrations of MeHg in weasels (M. frenata), with low concentrations in its terrestrial food sources, pointing to aquatic systems of the area as a potential source of MeHg. In order to investigate the movement of MeHg into the alpine aquatic food web, I sampled fish, zooplankton, water, and lake sediments in the Green Lakes Valley, Colorado. I present total mercury (THg), methylmercury (MeHg), and stable isotope data for each sample type to determine the flows of MeHg between lakes within the Green Lakes Valley and the factors that affect the bioaccumulation of MeHg in the aquatic food web. The data suggest that MeHg production and bioaccumulation in the Green Lakes Valley increased with elevation, likely due to their proximity to Arikaree rock glacier. Results showed clear rates of MeHg bioaccumulation at each succesive trophic level. Furthermore, fish within the Green Lakes Valley showed no MeHg concentrations over set limits of 200 ng MeHg g-1 ww at which trout show no effect from MeHg concentrations. This project provides the first look into the movement of MeHg and bioaccumulation within an aquatic food web of the Green Lakes Valley. In combination with prior studies on the terrestrial food web in the area, it provides more knowledge of the Hg cycle in high elevation mountain ecosystems.

Date Awarded
  • 2022-04-05
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Last Modified
  • 2022-04-12
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