Theses and Dissertations from UMD
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Item THE EFFECTS OF LEAF LITTER MANAGEMENT PRACTICES ON OVERWINTERING INSECT COMMUNITIES AND ECOSYSTEM FUNCTION: IMPACTS AND APPLICATIONS IN RESIDENTIAL LANDSCAPES(2024) Ferlauto, Max; Burghardt, Karin T; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fallen leaf management is a widespread landscaping practice in urban areas that not only influences soil health but also affects the overwintering individuals of subsequent year's aboveground arthropod communities. There has been considerable public and scientific interest in the ecological effects of this disturbance, yet little experimental research making it difficult to provide evidence-based landscaping recommendations to stakeholders. This dissertation aims to narrow this knowledge gap, provide information for the creation of best management practices, and encourage further research on this critical topic. In Chapter 2, I compare spring arthropod emergence in residential areas where fallen leaves were removed or retained across different levels of maintenance intensity. In Chapter 3, I focus on the legacies of long-term leaf removal to soil organic carbon dynamics. And in Chapter 4, I examine the efficacy of alternative leaf management practices—such as shredding and leaf piling—on soil microclimates, arthropod biodiversity, and decomposition rates while exploring if tree canopy diversity mitigated impacts to these ecosystem functions. The results of these three experimental studies were consistent across years and habitat types. Leaf removal reduced the spring emergence of Lepidoptera by about 35-45% and reduced spiders by about 50-67%, altered parasitic wasp community composition, reduced soil moisture and temperature buffering, and ultimately led to legacy effects in the soil of reduced decomposition and soil organic carbon. The context in which leaves were managed also mattered, as unique resources attracted overwintering arthropods more when they were scarce in the environment. Despite the potential for high plant diversity in leaf-managed areas to create ecosystem traps for arthropods, tree diversity actually mitigated some negative effects of fallen leaf disturbance to ecosystem function. Overall, I find that some practices like leaf removal and shredding degrade ecosystem processes while others like piling leaves and planting a diverse tree canopy can support ecosystem services. This dissertation is the first to quantify the ecological impacts of leaf management as an urban disturbance and addresses critical questions necessary for developing urban best management practices.Item EXAMINING QUINONE CONTRIBUTION TO THE OPTICAL PROPERTIES OF CHROMOPHORIC DISSOLVED ORGANIC MATTER(2024) Ashmore, Rachel; Blough, Neil; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Chromophoric Dissolved Organic Matter (CDOM) in natural waters is largely responsiblefor absorption of light and photochemistry in the water, impacting environmental reactions and aquatic life. The composition of CDOM is greatly varied based on source, photochemical reactions, and natural cycles. The impact of quinone moieties on this structure and photochemical and redox reactions involving CDOM remains the subject of controversy. To investigate the impact of quinone structure on optical properties, model quinone compounds were thoroughly characterized by their optical properties and reactions with sodium dithionite and sodium sulfite. A series of methyl-substituted p-benzoquinones, a methoxy p-benzoquinone, and a range of napthoquinones and anthraquinones were investigated. These model compounds were characterized according to their quinone and hydroquinone molar absorptivities and fluorescence quantum yields. Sodium dithionite reduction of quinones and the impact of structure on the products of this reaction was investigated by reducing the quinones with both sodium dithionite and sodium sulfite and comparing the optical properties of the products to those of the quinone and hydroquinone. The spectra of dithionite reduced p-benzoquinones and napthoquinones suggested the presence of products other than the hydroquinone. Sulfite is produced in solution as a result of dithionite reduction of quinones. Model quinones were therefore also reduced with sodium sulfite to investigate the impact of this side reaction on the dithionite reduction products. High performance liquid chromatography (HPLC) was used to further investigate and quantify the products of dithionite reduction of quinones and the importance of sulfite interference. Although some of the model quinones react with sulfite to form a proposed sulfonated hydroquinone product, based on the observed extent of this reaction in dithionite reductions, the structures of quinones likely to be found in CDOM, and their relatively small contribution to CDOM optical properties, the sulfite reaction was determined to not significantly impact the study of quinone moieties in CDOM. Dithionite selectively reduces quinones, while borohydride reduces ketones, aldehydes, and quinones. Therefore, in CDOM samples, dithionite can be used to isolate the effects of quinone moieties on the optical properties. Dithionite reduction was used to analyse CDOM standards and natural water extracts from the North Pacific Ocean and the Chesapeake Bay to investigate quinone contribution to their optical properties. These results are compared to borohydride reduction results from Cartisano and McDonnell to compare the contribution of quinones to that of ketones and aldehydes. (1, 2) Dithionite reduction showed small impacts on absorbance and fluorescence, whereas significant changes in both were observed for borohydride reduction. Therefore, the optical changes observed under borohydride reduction are attributed to primarily ketones and aldehydes rather than quinones. Model quinones showed significant changes in fluorescence intensity due to dithionite reduction, which are largely not observed for CDOM standards and natural water extracts, further supporting the conclusion that their role in CDOM optical properties is small.Item AUGMENTING TIDAL WETLAND VEGETATION AND ELEVATION MONITORING USING UNOCCUPIED AERIAL SYSTEMS (UAS)(2024) Malmgren, Benjamin A; Palinkas, Cindy M; Staver, Lorie W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal wetlands provide numerous ecosystem services that promote coastal resilience. Live vegetation coverage and elevation are key metrics for assessing the health of these crucial systems. However, traditional monitoring methods can be resource- intensive, intrusive, and lack adequate spatial and temporal resolution. This thesis explores the immense potential of Unoccupied Aerial Systems (UAS, or “drones”) for expanding coastal monitoring capabilities. Chapter 1 compared two tree-based classifiers against in situ observations for estimating live vegetation percent cover. While agreement with field observations varied among both model types, random forest models proved to be more robust than simple thresholding decision stump models when applied to validation data. Chapter 2 evaluated the accuracy of Digital Surface Models (DSMs) generated from drone imagery with Structure-from-Motion, and the influence of vegetation presence on vertical error. While vegetation presence significantly increased vertical error rates, it did not explain all differences in elevation model accuracy across sites. Together, this work underscores the role drones can play in connecting researchers and management practitioners with meaningful data to drive decision- making.Item Managing Cover Crops for Better N Efficiency and Soil Health(2024) Stefun, Melissa; Weil, Ray; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Winter cover cropping is a major tool that agriculture can use to protect soil and water quality and mitigate climate change. Unlike farmland in the world at large, most Maryland cropland has seen little tillage disturbance and some level of cover cropping for decades. With that background, field experiments on two soils with contrasting textures at the Beltsville Facility of Central Maryland Research and Education Center tested the effects of cover crop management enhancements on nitrogen (N) leaching, soil health indicators, and cover crop N uptake over three years. Two cover crops (sole rye and a mixture of forage radish, crimson clover, and rye) were compared to a control where cover cropping was ceased. The cash crops were corn and soybean grown in rotation. With best nutrient management practices applied, suction lysimeter sampling at 90 cm depth from October through April showed low levels of N leaching in general, but NO3-N concentrations were significantly lower under cover crops. Overall mean concentrations of NO3-N were 2.20 mg N/L in the control but 0.43 mg N/L under cover crops. Additionally, soil water samples were digested to determine dissolved organic N (DON) which was found to make up between 44-60% of the total dissolved N in the leaching water. In additional experiments, a small fertilizer N application was made to cover crops to stimulate rapid deep rooting with the goal of accessing soluble N deep in the profile to increase N capture by more than the amount of N applied. The response to fall N fertilization failed to accomplish this goal and was not related to the surface soil NO3-N concentration as expected. In spring, cover crops were terminated on three dates from mid-April to mid-May and rye biomass doubled with each extra two weeks it was allowed to grow whether it was in the mix or alone. The effect of cover crops on soil health indicators was evident with increased soil permanganate oxidizable carbon, total soil carbon, lower bulk density, and greater aggregation. These experiments demonstrated that cover crops with enhanced management can have marked effects on an agricultural system already using sustainable practices.Item DEVELOPMENT AND EVALUATION OF SPATIALLY-EXPLICIT POPULATION MODELS FOR ESTIMATING THE ABUNDANCE OF CHESAPEAKE BAY FISHES(2024) Nehemiah, Samara; Wilberg, Michael J.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although fish populations typically experience spatially varying abundance and fishing mortality, stock assessments that inform management decisions commonly model a population that is assumed to be well-mixed with homogenous mortality rates. When assumptions about population mixing are not met, these models can result in biased estimates. Spatial population estimates are particularly beneficial to the Chesapeake Bay because this region faces unique challenges as a result of climate change and fishing pressure. However, use of spatial population models for fisheries management relies on models that can provide more accurate estimates of biological parameters than non-spatial models. Objectives for this research were to 1) develop and implement a multi-stock, spatially-explicit population model for Striped Bass (Morone saxatilis) to estimate abundance and fishing mortality in the Chesapeake Bay and along the Atlantic coast; 2) assess the performance of spatially-explicit models compared to spatially-implicit models (i.e., fleets-as-areas) to estimate abundance, determine how improved data quality (e.g., stock composition) affects model performance, and determine the effect of aging error on model accuracy; and 3) determine how spatial model performance is affected by potential changes in population dynamics resulting from climate change (e.g., time-varying natural mortality). The population model was a two-stock model with two sub-annual time-steps and two regions with stock and age-specific occupancy probabilities representing movement into and out of the Chesapeake Bay. Fishing mortality was estimated to be higher in the Ocean than the Chesapeake Bay, and abundance increased during 1982-2004 for both stocks before declining slightly until 2017. Simulations were conducted to test the ability of models to estimate abundance and fishing mortality under alternative scenarios of data availability and quality. Spatially-explicit estimates were approximately unbiased when they closely matched the assumptions of the data generating model. Models that ignored potential aging bias in datasets resulted in highly biased estimates of abundance and fishing mortality. Although the performance of all models degraded under most climate change scenarios, spatially-explicit models produced the most accurate model estimates compared to fleets-as-areas models. This research highlights the potential benefits of implementing spatially-explicit population models for Striped Bass and ecologically valuable fish species in the Chesapeake Bay.Item MOSQUITOES AND VEGETATION ACROSS SOCIOECONOMIC GRADIENTS(2024) Rothman, Sarah; Leisnham, Paul T; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The biomass and composition of local vegetation is a key resource for juvenile mosquitoes, affecting a suite of life history traits including survival, development rate, and body size. In cities across the United States, both plant and mosquito communities vary with socioeconomics. Vegetation is typically more abundant and biodiverse in high-income neighborhoods, whereas mosquitoes are often more numerous and more likely to vector diseases in low-income neighborhoods. While prior work has examined the effects of plant resources on mosquitoes, my dissertation evaluates how these communities interact across a socioeconomically diverse urban landscape. Chapter 1 is a scoping review of current knowledge of the individual relationships between mosquitoes, plants, and socioeconomics in cities. In Chapter 2, I describe fine-scale vegetation surveys on socioeconomically diverse residential properties in Baltimore, MD and Washington, D.C. that revealed less canopy cover, more vines, and more non-native plant species on lower-income blocks. In Chapter 3, I used leaves from the most frequently observed canopy species on low- and high-income blocks, and species common to both, as detrital resource bases in competition trials between two dominant urban mosquitoes, Aedes albopictus and Culex pipiens. Population performance for both species was greater when reared with characteristically low-income than characteristically high-income detritus, suggesting that socioeconomically diverse plant communities are an important factor in shaping urban mosquito communities. Overall, population performances were greatest when mosquitoes were reared in the regionally representative detritus, and I used this detritus base in Chapter 4 to evaluate the effects of varying temperatures. Aedes albopictus population performance was optimized at higher mean temperatures characteristic of low-income blocks, while C. pipiens performance was best at lower mean temperatures characteristic of high-income blocks. Population performance was often lower, however, when temperatures fluctuated around a high or low mean than when the temperature was stable, suggesting that laboratory studies may need to mimic field conditions to obtain applicable results. My research provides a deeper understanding of the mechanisms behind previously observed relationships, and may help guide management and policy strategies to address environmental injustices and public health threats.Item The Impact of Marsh Sill Living Shorelines on Coastal Resilience and Stability: Insights from Maryland's Chesapeake Bay and Coastal Bays(2024) Sun, Limin; Nardin, William WN; Palinkas, Cindy CP; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Climate change and coastal urbanization are accelerating the demand for strategies to reduce shoreline erosion and enhance coastal resilience to storms and sea-level rise. Generally adverse ecological impacts of hardened infrastructure (e.g., seawalls, revetments, and dikes) have led to growing interest in alternative solutions. Living shorelines, increasingly recognized as sustainable Natural and Nature-Based Features (NNBFs; or Nature-Based Solutions (NBSs)) for their dual benefits of stabilizing shorelines while preserving or restoring coastal habitats, represent a promising approach to shoreline stabilization. Marsh sill living shorelines (created marshes with adjacent rock sills) have been extensively constructed in the Chesapeake Bay, notably in Maryland. Despite their popularity, significant uncertainties remain regarding their effectiveness and resiliency, especially during high-energy events. This dissertation investigates the dynamics of marsh sill living shorelines in Maryland’s Chesapeake Bay and Coastal Bays, aiming to fill knowledge gaps and inform effective shoreline stabilization strategies. First, the dissertation examines marsh boundary degradation into open water during high-energy conditions, contrasting mechanisms between living shorelines and natural marshes. Field surveys and numerical modeling reveal that while natural marshes experience erosion through undercutting and slumping at the scarp toe, living shorelines degrade primarily through open-water conversion at the marsh boundary behind rock sills. Differences in sediment characteristics and vegetation between the two ecosystems drive variations in marsh boundary stability between them. Next, the study assesses the impacts of rock sill placement on sediment dynamics and shoreline stability, highlighting the role of tidal gaps in enhancing sediment flux to the marsh and increasing vertical accretion during high-energy events. Numerical modeling demonstrates that while continuous sills mitigate erosion at the marsh edge of living shorelines, they diminish sediment deposition on the marsh platform compared to segmented sills with tidal gaps. Finally, the research identifies key factors driving marsh boundary degradation that are needed to assess the stability of marsh sill living shorelines. Analysis of eco-geomorphic features and hydrodynamics across 18 living shoreline sites reveals that metrics such as the Unvegetated/Vegetated Ratio (UVVR) and sediment deposition rate often used to assess the resilience of natural marshes also apply to the created marshes of living shorelines. Multivariate analyses further reveal that the Relative Exposure Index (REI) and Gap/Rock (G/R) ratio are crucial predictors of shoreline stability in marsh sill living shorelines, and thus should be particularly considered in shoreline design. By integrating remote sensing, field observations, and numerical modeling, this dissertation advances the understanding of sediment dynamics and stability in living shorelines and provides actionable insights for effective shoreline design and management to promote coastal resilience.Item MODELING GROUNDWATER FLUCTUATIONS IN THE COASTAL PLAIN OF MARYLAND: AN ANN POWERED STRATEGY(2024) Steeple, Jennifer Lynne; Negahban-Azar, Masoud; Shirmohammadi, Adel; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Groundwater management in the face of climate change presents a critical challenge with far-reaching implications for water resource sustainability. This study evaluates the effectiveness of Artificial Neural Networks (ANNs) as predictive tools for estimating current groundwater levels and forecasting future groundwater levels in the Aquia aquifer in the Coastal Plain ofMaryland. The groundwater levels of the Aquia aquifer have declined under the pressures of land use change, increases in agricultural irrigation, and population growth. We tested, trained, and employed eight county-level artificial neural network (ANNs) models to predict and project Aquia aquifer groundwater levels for the near (2030-2050) and far (2050-2100) future under two socio-economic pathways (SSP245 and SSP585). The models exhibited significant predictive performance during testing (R²= 0.82-0.99). Minimum temperature and population were the most influential variables across all county-based models. When used to forecast groundwater level under two climate scenarios, the models predicted declining groundwater levels over time in Calvert, Caroline, Queen Anne’s, and Kent counties, aligning with regional trends in the Aquia aquifer. Conversely, Anne Arundel, Charles, St. Mary’s, and Talbot counties exhibited projected increases in groundwater levels, likely influenced by correlations with the variable irrigated farm acreage, underscoring the importance of considering nonlinear relationships and interactions among variables in groundwater modeling. The study highlights the ability of ANNs to accurately predict county-scale groundwater levels, even with limited data, indicating their potential utility for informing decision-making processes regarding water resource management and climate change adaptation strategies. This study also assessed the usability of multiple methods to fill in the missing data and concluded that using the repeated groundwater level data still resulted in powerful ANN models capable of both predicting and forecasting ground water levels in the Coastal Plain of Maryland.Item Sperm Quality Characterization of Male Mummichog (Fundulus heteroclitus) in Response to Legacy Contaminants(2024) Malik, Sabine; Yonkos, Lance; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Historically contaminated rivers persist as hazards to ecosystem and human health despite remediation attempts, impacting the species found in these ecosystems. These rivers contain complex mixtures of legacy contaminants, including dioxins, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons, many of which are classified as endocrine disrupting compounds. Due to this level of contamination, few fish species are pervasive in these systems, an exception being the mummichog (Fundulus heteroclitus), known for its acquired tolerance of contaminated environmental conditions. While female and offspring reproductive success have been well-documented in the literature, few studies have investigated the use of sperm quality as a tool for assessing reproductive harm from contaminant exposure. Therefore, this study aims to demonstrate the usefulness of sperm quality characterization through the use of three assays: computer-assisted sperm analysis (CASA), a bioluminescent adenosine triphosphate (ATP) assay, and a modified Comet assay. This novel method was developed through field-collection of F. heteroclitus in three historically-contaminated tidal rivers in the United States: the Passaic River, NJ, the Christina River, DE, and the Anacostia River, MD. The results of this study not only present a novel method for investigating fish health in contaminated aquatic environments, but also a comparison of differential outcomes that can occur in rivers with varied contaminants and histories of pollution.Item EXPANDING THE HISTORIC NARRATIVE OF AFRICAN AMERICAN WATERMEN IN CHESAPEAKE BAY COMMERCIAL FISHERIES: PRESERVING CULTURAL HERITAGE AND ENSURING FUTURE AFRICAN AMERICAN MARITIME PARTICIPATION THROUGH A SOCIAL-ECOLOGICAL SYSTEMS PERSPECTIVE(2024) Black, Imani; Gray, Dr. Matthew; Shaffer, Dr. Jen; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis investigates African Americans' historical and contemporary contributions to the Chesapeake Bay commercial fishing industry, employing a social-ecological system (SES) framework to explore their roles, challenges, and the decline in their participation. Utilizing methods such as oral histories, participant observations, and historical analysis, the research highlights the significant yet underrecognized contributions of African American communities to the maritime heritage of Chesapeake Bay. Through in-depth interviews with African American watermen, historians, and community members, the study examines their achievements, obstacles, and the impacts of ecological and social change on their participation trends. Additionally, it assesses the influence of prominent African American coastal communities on commercial fisheries and discusses strategies for future engagement and adaptation in a rapidly evolving industry. The findings challenge prevailing perceptions of marginal involvement by revealing substantial African American participation across various aspects of the fisheries, emphasizing the importance of acknowledging this legacy and promoting diversity and inclusion for industry sustainability. By showcasing the rich heritage and ongoing excellence of Black maritime traditions in Chesapeake Bay, this thesis underscores the critical need for greater recognition of African American contributions to the Bay’s preservation, restoration, and strong ties to the cultural heritage that have built the coastal communities along its shoreline.