Amy Sauer

Date of Award

9-15-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

Mark Ritchie

Keywords

Adirondack Park;Elevation;Mercury;Songbird;Sphagnum Bog;Upland Forest

Abstract

Mercury (Hg) is a globally widespread and toxic pollutant that bioaccumulates and biomagnifies within terrestrial and aquatic food webs. Numerous adverse effects been documented in wildlife species, such as avian communities, exposed to elevated environmental Hg levels, specifically those inhabiting Hg-sensitive habitats, such as wetland and montane ecosystems. The primary goals of this dissertation were to examine spatial and seasonal patterns of Hg exposure for targeted songbird species occupying Sphagnum bog, upland forest and high elevation habitat types in the Adirondack Park of New York State, a biological Hg hotspot. From 2009–2010, Catharus thrushes were sampled at 13 study plots along an elevational gradient (450-1400 meters) on Whiteface Mountain. Mercury concentrations were observed to increase along the elevational gradient to 1,075 meters, followed by declining blood concentrations with further increases in elevation. These results are consistent with studies conducted at the same study sites which documented increases in atmospheric Hg deposition and soil Hg along the gradient, with the highest concentrations also occurring within mid- and high elevation forests. A seasonal pattern of increasing, followed by decreasing, blood Hg concentrations was detected across thrush species over the course of the breeding season. During 2008, 2009 and 2011, songbird species were sampled from study sites at Sphagnum bog and adjacent upland forests. Songbirds inhabiting Sphagnum bogs displayed significantly higher blood Hg concentrations than species within the surrounding forests, and similar patterns of species-level bioaccumulation were evident across each study site. There were no overall seasonal changes in Hg concentrations documented for Sphagnum bog songbirds, which remained consistently elevated throughout the breeding season. However, an overall seasonal pattern of increasing, followed by decreasing blood Hg was observed across upland forest songbird species. A comparative analysis was also conducted utilizing subsets of data from wetland-adjacent upland forests and those sampled on Whiteface Mountain. These results indicated that forest songbirds in proximity to wetland sites had significantly higher Hg concentrations than forest songbirds sampled at Whiteface Mountain, a location well-removed from wetlands. This finding suggests the potential influence of wetland ecosystems on biota within the surrounding landscape. Taken together, these results provide evidence that high-Hg habitat types, such as Sphagnum bog ecosystems and montane forests, influence songbird Hg exposure and the associated spatial patterns that were observed as part of this dissertation research. Seasonal fluctuations in blood Hg concentrations were highly variable across study sites and are likely reflective of multiple contributing variables, including dietary selection and molting cycles. Finally, these results contribute to regional wildlife Hg databases and demonstrate the importance of monitoring efforts to further characterize Hg exposure patterns within bioindicator species inhabiting sensitive ecosystems in New York State.

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Open Access

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