Graduate Theses

The Center for Environmental Studies offers a thesis-based Masters of Science (MS) in Environmental Studies.  Here are the most recent theses from this program.


Climate Change and Mountaintop Removal Mining: A MaxEnt Assessment of the Potential Dual Threat to West Virginia Fishes - Hendrick, Lindsey R.F.  MS Thesis. Accounts of species’ range shifts in response to climate change, most often as latitudinal shifts towards the poles or upslope shifts to higher elevations, are rapidly accumulating. These range shifts are often attributed to species ‘tracking’ their thermal niches as temperatures in their native ranges increase. Our objective was to estimate the degree to which climate change-driven shifts in water temperature may increase the exposure of West Virginia’s native freshwater fishes to mountaintop removal surface coal mining. Mid-century shifts in habitat suitability for nine non-game West Virginia fishes were projected via Maximum Entropy species distribution modeling, using a combination of physical habitat, historical climate conditions, and future climate data. Modeling projections for a high-emissions scenario (Representative Concentration Pathway 8.5) predict that habitat suitability will increase in high elevation streams for eight of nine species, with marginal increases in habitat suitability ranging from 46-418%. We conclude that many West Virginia fishes will be at risk of increased exposure to mountaintop removal surface coal mining if climate change continues at a rapid pace. Read More
Forest Structural Complexity and Net Primary Production Resilience Across a Gradient of Disturbance in a Great Lakes Ecosystem - Haber, Lisa T.  MS Thesis. Forests are an important component of the global carbon (C) cycle and contribute to climate change mitigation through atmospheric C uptake and storage in biomass and soils. However, the forest C sink is susceptible to disturbance, which modifies physical and biological structure and limits spatial extent of forests. Unlike severe, stand-replacing disturbances that reset forest successional trajectories and may simplify ecosystem structure, moderate severity disturbances may instead introduce complexity in ways that sustain net primary production (NPP), leading to the phenomenon of “NPP resilience.” In this study, we examined the linkage between disturbance severity and ecosystem biological and physical structural change, and implications for NPP within an experimentally disturbed forest in northern Michigan, USA. We computed spatially resolved and spatially agnostic metrics of forest biological and physical structure before and 10 years after disturbance across a continuum of severity. We found that while biological structure did not change in response to disturbance, three of four physical structural measures increased or were unimodally related to disturbance severity. Physical structural shifts mediated by disturbance were not found to directly influence processes coupled with NPP. However, decadal changes in the spatial aggregation index of Clark and Evans, though not a function of disturbance severity, were found to predict canopy light uptake, leaf physiological variability, and relative NPP within plots. We conclude that ecosystem structural shifts across disturbance severity continua are variable and differ in their relationship to NPP resilience. Read More
Migratory patterns and population genetic structure in a declining wetland-dependent songbird - DeSaix, Matthew G.  MS Thesis. Understanding migratory connectivity is essential for assessing the drivers behind population dynamics and for implementing effective management in migratory species. Genetic markers provide a means to describe migratory connectivity, as well as incorporate population genetic analyses, however genetic markers can be uninformative for species with weak genetic structure. In this study, we evaluate range-wide population genetic structure and migratory connectivity in the prothonotary warbler, Protonotaria citrea, a wetland-dependent neotropical migratory songbird, using high-resolution genetic markers. We reveal regional genetic structure between sampling sites in the Mississippi River Valley and the Atlantic Seaboard with overall weak genetic differentiation among populations (FST = 0.0051). By ranking loci by FST and using subsets of the most differentiated genetic markers (200 – 3000), we identify a maximum assignment accuracy (89.7% to site, 94.3% to region) using 600 single nucleotide polymorphisms. We assign samples from unknown origin nonbreeding sites to a breeding region, illustrating weak migratory connectivity between prothonotary warbler breeding and nonbreeding grounds. Our results highlight the importance of using high-resolution markers in studies of migratory connectivity with species exhibiting weak genetic structure. Using similar techniques, studies may begin to describe population genetic structure that was previously undocumented, allowing us to infer the migratory patterns of an increasing number of species. Read More
DETERMINING TIDAL CHARACTERISTICS IN A RESTORED TIDAL WETLAND USING UNMANNED AERIAL VEHICLES AND DERIVED DATA - Thornton, Victor. MS Thesis Species’ distributions are influenced by abiotic and biotic factors but direct comparison of their relative importance is difficult, particularly when working with complex, multi-species datasets. Here, we present a flexible method to compare abiotic and biotic influences at common scales. First, data representing abiotic and biotic factors are collected using a combination of geographic information system, remotely sensed, and species’ functional trait data. Next, the relative influences of each predictor variable on the occurrence of a focal species are compared. Specifically, ‘sample’ data from sites of known occurrence are compared with ‘background’ data (i.e. pseudo-absence data collected at sites where occurrence is unknown, combined with sample data). Predictor variables that may have the strongest influence on the focal species are identified as those where sample data are clearly distinct from the corresponding background distribution. To demonstrate the method, effects of hydrology, physical habitat, and co-occurring fish functional traits are assessed relative to the contemporary (1950 – 1990) distribution of the American Eel (Anguilla rostrata) in six Mid-Atlantic (USA) rivers. We find that Eel distribution has likely been influenced by the functional characteristics of co-occurring fishes and by local dam density, but not by other physical habitat or hydrologic factors. Read More
ASSESSING THE RELATIVE INFLUENCES OF ABIOTIC AND BIOTIC FACTORS ON A SPECIES’ DISTRIBUTION USING PSEUDO-ABSENCE AND FUNCTIONAL TRAIT DATA: A CASE STUDY WITH THE AMERICAN EEL (Anguilla rostrata) - Woods, Taylor E.   MS Thesis Species’ distributions are influenced by abiotic and biotic factors but direct comparison of their relative importance is difficult, particularly when working with complex, multi-species datasets. Here, we present a flexible method to compare abiotic and biotic influences at common scales. First, data representing abiotic and biotic factors are collected using a combination of geographic information system, remotely sensed, and species’ functional trait data. Next, the relative influences of each predictor variable on the occurrence of a focal species are compared. Specifically, ‘sample’ data from sites of known occurrence are compared with ‘background’ data (i.e. pseudo-absence data collected at sites where occurrence is unknown, combined with sample data). Predictor variables that may have the strongest influence on the focal species are identified as those where sample data are clearly distinct from the corresponding background distribution. To demonstrate the method, effects of hydrology, physical habitat, and co-occurring fish functional traits are assessed relative to the contemporary (1950 – 1990) distribution of the American Eel (Anguilla rostrata) in six Mid-Atlantic (USA) rivers. We find that Eel distribution has likely been influenced by the functional characteristics of co-occurring fishes and by local dam density, but not by other physical habitat or hydrologic factors. Read More
IMPROVING THE CONSERVATION OF A CRYPTIC ENDANGERED FRESHWATER MUSSEL (PARVASPINA COLLINA) THROUGH THE USE OF ENVIRONMENTAL DNA AND SPECIES DISTRIBUTION MODELING - Roderique, Bonnie A., MS Thesis Conservation efforts that involve habitat protection, population augmentation, and species reintroductions require knowledge of the habitat requirements, distribution, and abundance of a species—information that can be challenging to acquire, especially for rare organisms with patchy distributions. In this thesis, I develop a protocol for the use of environmental DNA (eDNA) and create a Species Distribution Model for the endangered James spinymussel, Parvaspina collina (Unionidae). The results of this work show that eDNA is a robust tool for identifying species presence but not for estimating the relative abundance of populations. This study found that P. collina’s distribution is influenced by abiotic habitat characteristics related to sedimentation and runoff rather than by the distribution of its host fishes. The predicted habitat suitability was used to identify locations of priority conservation concern and these results can be used to direct future sampling efforts, identify potential dispersal routes, and inform conservation decisions. Read More
PELAGIC FISH DIVERSITY AND DENSITY ON AND OFF RESTORED OYSTER REEF HABITAT - McCulloch, Danielle.  MS Thesis The heterogeneity provided by structured habitats is important in supporting diverse and dense fish communities. The biogenic reefs created by the native Eastern Oyster, Crassostrea virginica, were once the dominant structural habitat in Chesapeake Bay, and have since declined to less than 1% of historic estimates. Conflicting results on the effects of oyster reef restoration on pelagic fish assemblages make further investigation necessary. Incorporating multiple sampling strategies may help elucidate oyster reef habitat influence on fish assemblages. This study used multi-panel gillnets, hydroacoustic technology, and day-night sampling to describe pelagic fish assemblages on and off oyster reef habitat in the lower Piankatank River, VA. Data from oyster reef habitat, adjacent sandy-mud bottom habitat, and unstructured sandy habitat outside of a reef restoration area compared fish diversity, species composition, and density among habitat types. A multivariate analysis using day of the year, day or night, and habitat type as model terms found temporal factors explained variation in fish distribution more than habitat. Fish diversity varied significantly with day or night and habitat type. Diversity and density were significantly higher at night, demonstrating the necessity of nocturnal sampling in fish assemblage research. Results from this study conclude that fish assemblages were not significantly more diverse or denser on reef than non-reef habitat. We suggest that future work should concentrate on studying areas where oyster reef habitat comprises a larger proportion of the study area. Read More
QUANTIFYING CURRENT SEDIMENT DEPOSITION, LEGACY SEDIMENTS, AND PRE-IMPOUNDMENT VERTICAL ACCRETION AND CARBON DYNAMICS FOLLOWING DAM REMOVAL IN A RECENTLY RESTORED TIDAL FRESHWATER WETLAND - Davis, Melissa J.  MS Thesis Damming disrupts natural sediment flow to downstream resulting in legacy sediment accumulation. Legacy sediments have been well investigated in streams throughout the Piedmont region; however, there is no research of legacy sediments following dam removal in low-gradient Coastal Plain streams. Research objectives were to: characterize legacy sediments in a low-gradient stream restoration, quantify pre-impoundment accretion and carbon dynamics, and assess current sediment deposition rates via 14C analyses within sediment cores and sediment collection tiles. Carbon accumulation and accretion rates of modern tidal sediment have reached that of the tidal relic benchmark and current sediment deposition rates are similar between the natural reference and restored tidal wetlands. At this site, the pattern of legacy sediment accumulation and stream incision was reversed relative to previous studies in higher gradient systems. Results suggest in dam impacted Coastal Plain streams, legacy sediment may become a benefit rather than a liability for downstream tidal wetlands. Read More
Behavioral responses of sub-adult Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus) to electromagnetic and magnetic fields under laboratory conditions - McIntyre, Andrew III.  MS Thesis Electromagnetic fields (EMF) produced by high voltage (HV), submarine transmission cables leading from offshore wind energy generation facilities could affect foraging or migratory behaviors of electro-receptive fishes, including endangered Atlantic Sturgeon. However, no published studies have quantitatively evaluated the possible behavioral effects of EMF exposure on sturgeon during residence in coastal waters. This study evaluated behavioral responses by sub-adult Atlantic Sturgeon to electromagnetic and magnetic fields under controlled laboratory conditions. Fabricated EMF generators were used to emulate a range of field EMF conditions that migratory fishes could encounter in proximity to submarine HV sources. Sensor arrays and digital video recorders synoptically quantified EMF conditions and fish behaviors during experimental trials. This thesis will describe the unique, experimental EMF generator/sensor array, present results of the behavior study, and suggest implications of the findings for Atlantic Sturgeon management and conservation. 45 trials were conducted over the course of the study. Study fish were subjected to 3 different field strengths (5µT, 100 µT, 1000 µT), generated using both AC and DC current. Time spent in generated field area, number of passes through the field area, and swimming speed were used to quantify behavioral changes in test subjects. From the data collected and analyzed there was no evidence indicating a change in fish behavior due to the influence of field strengths, field orientations, or field types used during the study. Read More
A Study of Sediment Accretion Dynamics in Mature and Restored Tidal Freshwater Forested Wetlands in the James River Watershed using Surface Elevation Tables and Marker Horizons - Lopez, Ronaldo.  MS Thesis Sediment accretion and elevation change in tidal forests, and the corresponding ability of these wetlands to keep pace with sea-level rise (SLR), represent data gaps in our understanding of wetland sustainability. Surface Elevation Tables and marker horizons were installed in three mature tidal forests and a restored tidal marsh, allowing us to measure elevation change, accretion, and subsidence. Additionally, we measured predictor variables to test for their significance in explaining accretion and elevation change rates. Mean accretion at our sites was 11.67 +/- 3.01 mm yr-1 and mean elevation change was -20.22 +/- 8.10 mm yr-1, suggesting subsidence occurring beneath the sites. Processes contributing to accretion and elevation change at our sites may be driven by hydrologic patterns. Comparing our elevation trends with SLR trends suggests that our study sites may not keep pace with SLR. However, we may be observing short-term oscillations that do not indicate true long-term trends. Read More