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Investigation Of The Use And Application Of Passive Sampling Methods For Understanding Potential Sources Of Mercury To Western United States
AuthorWright, Genine Clare
AdvisorGustin, Mae S.
Natural Resources and Environmental Science
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Recent work has found elevated concentrations of mercury (Hg) in fish in some remote areas in the western United States. Atmospheric deposition of Hg has become an increasing concern as a major pathway for Hg entering ecosystems. Specifically, dry deposition is being recognized as an important way for Hg to enter ecosystems in the western U.S., however little work has been done on an expanded geographic scale. To address this, our study included sampling locations on the coast of California, in the Sierra Nevada Mountains and on the eastern edge of Nevada in the Great Basin spanning elevations of sea level up to ~2800 m. Surrogate surfaces and passive samplers were deployed across nine locations at Point Reyes National Seashore, CA; Chalk Mountain, CA; Elkhorn Slough, CA; Chews Ridge, CA; Lick Observatory, CA; Yosemite National Park, CA; Hetch Hetchy Reservior, CA; Sequoia National Park, CA; and Great Basin National Park, NV. Ancillary data (ozone, temperature, relative humidity, wind speed, wind direction, precipitation and solar radiation) was available at many locations and this was used to help understand potential sources. Data indicated that regional and global Hg sources are impacting the western U.S., and deposition influenced by oxidants in the atmosphere available to form gaseous oxidized Hg from gaseous elemental Hg. In addition to investigating current air Hg concentrations, we investigated the potential for using tree cores as a long-term record of atmospheric Hg. Tree cores have been applied to understand long-term climate change and as historical monitors for various pollutants. Tree rings were collected at 11 sites spanning the same range as the surrogate surfaces and passive samplers, with the addition of 2 mining impacted sites in Nevada. Most sites showed clear increased concentrations during the gold rush era with some subtle to more aggressive increases in concentrations since the industrial era. The coastal site had the highest mean concentration, indicating differences in atmospheric chemistry between the sites. The potential for the utility of tree cores as historical records of atmospheric Hg was demonstrated.