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The Lateral Extent and Spatial Variation of Mercury Exposure in Birds and their Prey Near a Polluted River

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Author: Howie, Mikaela Gioia Selene
Advisor: Cristol, Daniel A.
Committee Members: Chambers, Randolph M.; Ware, Stewart A.
Issued Date: 2010-01-26
Subjects: Mercury
Avian Ecology
South River
Spatial Extent
Wildlife Exposure
URI: http://hdl.handle.net/10288/1664
Description: Mercury contamination of waterways has become a global issue with the increase of industrial emissions during the last century. The South River of the Shenandoah Valley of Virginia is contaminated with mercury from an industrial plant that deposited mercury into the river from 1929-1950. The river and its associated biota have been monitored intensively since the 1990’s and mercury levels have not decreased since then. The majority of previous studies have focused on the aquatic ecosystem; however, recent data demonstrated exposure in terrestrial songbird species sampled within 50 meters of the contaminated river. The present research investigated the distribution of mercury exposure in terrestrial songbirds and their prey across the floodplain. The first objective was to describe the lateral extent of mercury exposure in songbirds nesting in the adjacent floodplain. By comparing mercury levels of four species of songbirds captured on nests at various distances from the river, the footprint of the mercury-impacted floodplain was described. The results using both adult and nestling Carolina wrens, Carolina chickadees, house wrens and eastern bluebirds, suggest that mercury is accumulated by terrestrial bird species foraging throughout the floodplain extending at least 400 meters from the river. A second objective was to investigate the importance of flooding as a physical vector in transporting aquatic mercury to the terrestrial food chain. This was accomplished by recording various spatial variables that influence flooding at each bird nest sampling location. These spatial characteristics were then tested for their ability to predict avian mercury levels. The results suggest that flooding potential best predicts “hotspot” areas for mercury exposure. However, other variables, including distance from the proximate and ultimate sources of mercury also related to mercury exposure. Previous work has established that mercury exposure in wildlife is largely through diet. In the floodplain of the South River, spider prey, in particular, has been shown to deliver the vast majority of mercury to terrestrial insectivorous songbirds. My study investigated whether mercury exposure of songbird prey, with particular focus on spiders, followed the same spatial trends as did the birds themselves. The results concerning the lateral extent of mercury exposure in terrestrial spiders were inconclusive, most likely due to the lack of information regarding foraging territories of the spiders. However, flooding variables did relate to mercury for all types of prey collected, and especially in the case of spiders. This suggests that spiders inhabiting low-lying, flood prone areas are more likely to accumulate high amounts of mercury that they then deliver to the songbirds. This study offers the first information about the spatial variability of floodplain mercury exposure on a biological scale. The compelling finding is that exposure risk extends for at least 400 meters from the mercury contaminated South River, which should be considered in all riverine mercury risk assessments as well as in future restoration efforts. Additionally, this study implicates flood waters as a vector of importance in transporting mercury from the aquatic ecosystem into the adjacent floodplain and terrestrial food chain.
Degree: Masters of Science in Biology

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