Examining the Impact of Mercury on Waterfowl with Implications for Human Health and Water Management in Arid Environments
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Authors
Byrne, Morgan
Issue Date
2023
Type
Thesis
Language
Keywords
Bayesian , Mercury , Nevada , Waterfowl , Wood Duck
Alternative Title
Abstract
The work described in this thesis provides detailed insight into total mercury concentrations ([tHg]) observed in wood ducks along the lower Carson River watershed in western Nevada. Mercury (Hg) contamination of the Carson River dates back to the Comstock era mines in the late 1800’s, where Hg amalgamation methods were used to extract silver and gold from ore deposits. Wood ducks frequently use this river system, and thus may be impacted by the Hg contamination in the system. Mercury is of concern due to the impacts that it has on wildlife and humans; these include neurotoxicity, decreased reproductive success, and physiological and behavioral effects. The objectives for this thesis were to develop a predictive function that could be used to estimate internal waterfowl tissue [tHg] using feather [tHg], and examine the impact of several covariates (i.e., age class, site location, year) and environmental samples on Hg in wood ducks on the Carson River. Feathers were used from an archived data set and tissues obtained in 2020 and 2021 from harvested specimens donated by local hunters. Mercury concentrations ([Hg]) in water, sediment, macroinvertebrates, and terrestrial and aquatic vegetation samples were collected in 2020 and 2021 to assess sources of Hg to wood ducks. Hunter donated samples were used to examine correlations in [Hg] among tissues (feathers, breast and liver tissue) to explore potential nonlethal waterfowl sampling techniques to estimate Hg exposure to hunters. A contemporary Bayesian hierarchical model was used to estimate relationships between feathers and internal tissue [Hg]. A prediction function was developed that allowed for estimation of internal tissue [Hg] using flank feather [Hg]. This model was tested using harvested mallards from Stillwater National Wildlife Refuge. A Bayesian analysis of [Hg] in wood duck data, using archived flank feather samples collected from 2010�"2019, was conducted to characterize trends of Hg in this population. Over time, hens (adult females with nests) consistently had lower feather [Hg] than offspring (hatch years observed hatching or in a brood). There was a large increase in feather [Hg] in higher water flow years. Environmental samples collected from 5 field sites, extending from the U.S. Geological Service (USGS) gauge at the Carson River below Lahontan Reservoir to the USGS gauge at Tarzyn Road, demonstrated no spatial trends in [Hg] among sites. However, there were clear temporal trends. As water flows increased between sampling occasions, increases in water and duckweed [Hg] were observed. Based on observed [Hg] measurements, important vectors of Hg to wood ducks occur through duckweed consumption and exposure to contaminated waters. Mercury concentrations in wood duck tissues indicate a consumption advisory is warranted.