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Browsing by Author "Kramar, David E."

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    Estimating Hg Risk to the Common Loon (Gavia immer) in the Rangeley Lakes Region of Western Maine: A Regression Based GIS Model
    Kramar, David E. (Virginia Tech, 2004-04-21)
    This research relates Hg levels in the Common Loon (Gavia immer) to a variety of physical factors. Constructed within the framework of a GIS system, this model analyzes the spatial relationships and the influence of physical land cover factors as a function of distance from the individual loon territories. Thiessan polygons were used to generate the territory for each loon. Buffering of the thiessan polygons was done to establish the boundaries of the individual distance classes and to gather information on the percentage of individual land cover classes within each distance class. Information on precipitation was also gathered. Results from the regression analysis (R2 = 57.3% at the 150m distance class) performed on the variables suggest that the proximity of certain land use types such as cropland, shrub land, and wetlands influence the rates at which Hg is available within an individual territory. Within the 150m and 300m buffers, crop land, shrub land, and wetland exhibited the strongest relationship with the Hg levels in the common loon, with cropland exhibiting a negative relationship suggesting that the proximity of cultivated lands plays a role in decreasing the amount of available Hg in a territory.
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    Evaluation, assessment, and determination of risk to high trophic level piscivores in the Mid-Atlantic: A spatial, biological, and comparative case study of mercury in Virginia bald eagle populations
    Kramar, David E. (Virginia Tech, 2014-05-08)
    This research is focused on explaining the concentrations of mercury found in juvenile bald eagles (Halieattus leucocephallus) as a function of the physical and anthropogenic landscape. Due to it's location in the food chain this species is susceptible to a wide range of contaminants (xenobiotics), particularly those that bioaccumulate and biomagnify as they move through the food chain. Previous research has indicated that areas in coastal environments are less susceptible to methylation than those in freshwater environments. Sampling efforts for this research were conducted in such a manner as to obtain an equivalent number of samples from the coastal plain (expected to be low mercury) and the inland regions (expected to be statistically significantly higher). In all cases, results indicated that both feather and blood mercury concentrations were higher in the inland population (Blood: Prob > t = 0.0003, Feather: Prob > t = 0.0002). Utilizing classification and regression tree models (CART), we were able to relate metrics such as the percent of deciduous forest, percent of mixed forest, percent of pasture, and percent of wetland to measured blood mercury concentrations. We also found that the best models were produced using the USGS HUC 12 watersheds (the smallest watershed produced by the USGS). Moreover, we found that metrics describing the amount and type of fragmentation within the watersheds exhibited a significant influence on measured blood mercury concentrations. Contrary to previous research, we found wetlands to be negatively associated with higher blood mercury, whereas the abundance of core forest and a larger patch density (PD) in the deciduous and mixed land cover classes was positively associated with higher blood mercury concentrations. We also found that a higher percentage of pasture was associated with higher blood mercury.
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    Mercury concentrations in blood and feathers of nestling Bald Eagles in coastal and inland Virginia
    Kramar, David E.; Carstensen, Laurence W.; Prisley, Stephen P.; Campbell, James B. Jr. (2019-01-19)
    Background Mercury (Hg) and methylmercury are widely considered significant issues for wildlife, and in particular, piscivorous birds due to their widespread availability and neurotoxic properties. Whereas a substantial number of studies of Hg contamination of Bald Eagles (Haliaeetus leucocephalus) have been conducted throughout the east coast of the United States, little has been done that directly addresses Hg contamination in Bald Eagles in Virginia, particularly the inland population. Methods We collected blood and feather samples from nestling Bald Eagles in the coastal plain, piedmont, and western regions of Virginia in an effort to determine which areas of the state were more likely to contain populations showing evidence of Hg toxicity. We analyzed the samples for total Hg using a Milestone DMA-80. Results Samples collected from individuals located in the coastal region exhibited low concentrations of Hg compared to those further inland located on freshwater rivers and reservoirs. Samples collected from the inland population exhibited levels in some areas that are approaching what may be considered to be sub-lethal to avian health (blood: mean 0.324 mg/kg, SE = 0.13, range = 0.06‒0.97 mg/kg; feather: mean = 8.433 mg/kg, SE = 0.3, range = 3.811‒21.14 mg/kg). Conclusions Even after accounting for known point-sources of Hg, the inland eagle population in Virginia is susceptible to concentrations of Hg that are significantly higher than their coastal counterparts. Moreover, several locations besides those currently known to be impacted by point-sources are exhibiting concentrations that are approaching a sub-lethal level.