UMD Theses and Dissertations
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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 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.Item Dual water quality responses after more than 30 years of agricultural management practices in the rural headwaters of the Choptank River basin in the Chesapeake Bay watershed(2023) Silaphone, Keota; Fisher, Thomas R; Natural Resource Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Eutrophication is the water quality response to over-enrichment by nitrogen (N) and phosphorus (P) in fresh, estuarine, and coastal waters globally. Agricultural best management practices (BMPs) are the primary tool for controlling eutrophication in rural areas, particularly in the Chesapeake Bay watershed, where BMPs are vital to achieving TMDL goals. However, despite the application of BMPs, local water quality in the headwaters of the Choptank River, a major tributary of the Chesapeake Bay on the Delmarva Peninsula, has not improved. Thus, further investigation of agricultural BMP impacts on water quality in the Greensboro watershed is needed. My overarching research question is, “Why have N and P concentrations increased at the USGS Greensboro gauge if agricultural Best Management Practices (BMPs) have been implemented?” I applied statistical approaches to three linked, testable hypotheses to systematically evaluate agricultural BMPs and their impacts on nutrient (N and P) export from the Greensboro watershed. My first hypothesis was that agricultural BMPs have increased significantly in the Greensboro watershed. To test this hypothesis, I obtained publicly available modeling data via the Chesapeake Assessment Scenario Tool (CAST) and estimated the subsequent edge-of-stream N and P export. My findings indicated that the number of BMPs in the agricultural sector increased significantly between 1985 and 2021, supporting the hypothesis. Overall, modeled agricultural N and P export significantly decreased between 2010 and 2021 (p < 0.001). However, the modeled edge-of-stream agricultural nutrient export resulted in no significant change in N export and an increase of 3% in agricultural P export resulting from BMP implementation levels in 2021 compared to 2010. This study demonstrated the use of CAST to acquire reported BMP implementation levels and increased nutrient inputs into the Greensboro watershed between 1985 and 2021. The watershed nutrient inputs mirror the upward trends in N and P export captured by the USGS long-term monitoring station at Greensboro. With this improved access to BMP implementation and nutrient data, decision-makers can consider adaptive management measures to decrease nutrient export downstream. My second hypothesis was that agricultural BMPs have an adequate basis for estimating their capacity to reduce N export. To test this hypothesis, I conducted a meta-analysis on 689 cover crop N efficiencies reported in 18 empirical and modeling studies. The cover crop N efficiency was calculated as the ratio of an N interception by cover crop biomass or a reduction in soil or groundwater N divided by an N input, e.g., previous spring fertilizer or a previous soil or groundwater N concentration or flux. These variable approaches resulted in wide ranges in mean cover crop N efficiency (10-80%) due to empirical and modeling experimental approaches, varying methods, and parameters used to calculate efficiency. The modeling approach generally resulted in N efficiency values significantly higher than the empirical approach, as did the parallel control-treatment experiments compared to the sequential before-and-after implementation method. Because of these variables, there appears to be no standard methodology to report the effects of cover crops or standardized metadata describing the variables used in the N efficiency calculations. I suggest a standard methodology and metadata that should accompany future reports of cover crop N efficiencies to improve the modeled effects of BMPs on nutrient export. My third hypothesis was that three methods of estimating N and P concentrations and yields are in agreement and show a relationship to BMP implementation in the Greensboro watershed. To test this hypothesis, I compiled annual nutrient (N and P) datasets based on (1) USGS field measurements of concentrations and discharge, (2) USGS flow-normalized weighted regression based on time, discharge, and season (WRTDS) of concentrations and yields, and (3) CAST-modeled nutrient yields. Statistical analyses revealed time, discharge, agricultural BMPs, and animal waste management practice trends of the three methods. Results indicated that the USGS field measurements and WRTDS flow-normalization methods consistently showed an increase in N and P concentrations and yields. In contrast, all CAST-modeled regressions showed significantly decreasing nutrient concentrations and yields (p ≤ 0.05), which did not support the hypothesis that all three methods are in agreement. Despite CAST-modeled results decreasing with increasing BMPs, which supports the hypothesis that N and P concentrations and yields show a relationship with BMP implementation, USGS methods resulted in increasing nutrient concentrations and trends. These results indicated significant underestimates of modeled N and P export by CAST. I recommend using adjusted BMP efficiencies during cultural and structural BMP lifespans to improve model outputs. I also suggest two approaches to reflect the role of annual poultry manure applications: (1) model nutrient transport via artificial drainage ditches that interfere with natural nutrient flow pathways and exacerbate N and P transport, and (2) model the accumulation of soil-P and saturated soil-P, resulting in increases in dissolved P and particulate P in downstream surface waters. Agronomic recommendations include developing efficient manure recycling approaches within the local agricultural systems via nutrient management practices and concurrent research and development to support alternative uses of animal waste, including composting, bioenergy generation, granulating/pelletizing, and establishing a marketplace to support the sale of these products and to offset the costs of transporting manure from areas of manure surplus to manure deficit areas. This dissertation revealed that modeling studies overestimate cover crop N efficiencies in the United States Coastal Plain province and that CAST modeling is not in agreement with the USGS field measurements. CAST-modeled nutrient concentrations and yields decrease over time, indicating improvements in water quality. In contrast, USGS methods consistently show that nutrient concentrations and yields increase, indicating that BMPs are insufficient, inadequate, overwhelmed by nutrient inputs, or efficiencies are overestimated. Indeed, nutrient-reducing BMPs have increased between 1985 and 2021. With over 35 years of BMP implementation, measurable water quality response is expected. However, BMPs that relocate and apply higher amounts of manure annually have also increased with nutrient-reducing BMPs. Rising manure application rates combined with higher fertilizer application rates due to economic pressures on farmers to increase crop yields appeared to have overwhelmed implemented BMPs. Continued manure applications onto croplands in the Greensboro watershed suggest nutrient export will continue to rise; thus, reaching water quality goals is unlikely.Item Investigating the Utility of Environmental DNA Analysis for the Monitoring and Management of Mid-Atlantic Alosine Fishes(2023) Fowler, Chelsea; Plough, Louis V; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Environmental DNA (eDNA) tools can address gaps in fish assessment data while reducing the cost and the impact of sampling on threatened anadromous alosine fishes in Chesapeake Bay. Here, I tested the ability of high-frequency eDNA sampling of river herring to predict fish abundances from sonar-based fish counts on the Choptank River and developed and validated novel species-specific eDNA assays for American and hickory shads. River herring eDNA concentrations from daily eDNA sampling were highly correlated to sonar-based fish counts (Spearman’s Rho = 0.84). This relationship informed a model that could accurately predict fish count from eDNA and relevant covariates (R2 = 0.88). The two new shad assays are highly specific and quantitative, and field testing validated detections in Delaware, Maryland, and North Carolina. This work provides a set of eDNA monitoring tools for the Mid-Atlantic alosines and highlights the capacity for eDNA data to generate quantitative metrics of fish abundance.Item A DETAILED OPTICAL ANALYSIS OF CHROMOPHORIC DISSOLVED ORGANIC MATTER AND C18 EXTRACTED ORGANIC MATTER IN THE CHESAPEAKE BAY(2023) McDonnell, Shannon Marie; Blough, Neil V; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Chromophoric dissolved organic matter (CDOM) is a large portion of the open ocean dissolved matter pool which contributes largely to ocean color. The composition and distribution of CDOM is essentially controlled by in-situ biological production, terrestrial inputs, photochemical degradation, and microbial consumption. Estuarine environments contain particularly diverse CDOM composition due to their large variety of inputs and shoreline land usage in addition to the mixing of freshwater and salt water. Developing a further understanding of CDOM variation and composition will help develop and improve satellite remote sensing algorithms, help us understand CDOM’s role in the global carbon, nitrogen, and oxygen cycles, and may help to prioritize in-situ sampling for water quality monitoring in areas of concern. The use of inherent optical properties combined with pH titration and chemical reduction with sodium borohydride (NaBH4), helps to probe the molecular composition of CDOM and its spatial variability. Detailed studies of CDOM from the Chesapeake Bay are limited with many studies only investigating the main channel of the Bay and neglecting the various tributaries. Also, there is a lack of studies which specifically probe the molecular composition of the CDOM samples. To address this, an in-depth analysis of the optical properties of CDOM and C18 extracted organic matter (C18-OM) from the Chesapeake Bay, focusing on various inputs, was performed. Chemical reduction with NaBH4 and pH titration were employed to probe the presence of specific functional groups and their contribution to overall optical properties, and how they vary between locations. Spectral slope (S300-700), E2:E3 absorption ratio, fluorescence intensity, and apparent quantum yield of fluorescence (AQY) were used to analyze 170 samples from various tributaries in the Chesapeake Bay. Overall, this study suggested 1) there may be multiple inputs of CDOM within the Chesapeake Bay 2) the Top of the Bay and central channel of the Bay are impacted by the heavy terrestrial input from the Susquehanna River 3) A lack of correlation between phytoplankton fluorescence and CDOM absorption suggest phytoplankton are not an immediate source of CDOM within the Chesapeake Bay and 4) removal of protein and phytoplankton fluorescence after sample filtration indicates these species must exist in aggregates >0.2 µm. Optical analysis combined with pH titration and NaBH4 reduction investigated the variation between 9 C18-OM extracts from various regions in the Chesapeake Bay and a humic material standard Suwannee River Fulvic Acid (SRFA). Additionally, this study investigated the validity of the Charge-Transfer (CT) model using the optical properties of model compounds. This study suggested 1) certain absorbing and emitting species are lost during C18 extraction but extracts are still representative of their CDOM 2) nearly identical optical responses to pH titration and NaBH4 reduction suggest similar chromophore content throughout the Chesapeake and 3) CT interactions leading to long wavelength absorption are more prevalent in Suwannee River Fulvic Acid (SRFA) than they are in the Chesapeake. To compare the molecular and optical properties of the Chesapeake Bay to other locales, these extracts were compared to extracts from the Delaware Bay (DEL), Equatorial Atlantic Ocean (EAO) and North Pacific Ocean (NPO) in addition to reference materials Suwannee River Fulvic Acid (SRFA), Pony Lake Fulvic Acid (PLFA), and Elliott Soil Humic Acid (ESHA). This study showed 1) composition of deprotonatable and reducible chromophores within the Chesapeake and Delaware Bays is nearly identical but different from the oceans 2) despite being estuaries and containing a mixture of fresh and ocean water, CDOM within both Bays looks terrestrially dominated 3) deep ocean extracts from the Atlantic and Pacific exhibit similar optical response to pH titration, NaBH4 reduction, and NaBH4 reduction combined with pH titration suggesting the similarity of deep ocean waters from both ocean basins.Item GEOSTATISTICAL ESTIMATION OF BLUE CRAB CALLINECTES SAPIDUS ABUNDANCE IN CHESAPEAKE BAY AT LOCAL SCALES(2022) Jones, Sarah Ann; Miller, Thomas J.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increases in the sizes of container ships due to the expansion of the Panama Canal has increased the need for dredging activities in the Chesapeake Bay. Placement of dredged material in the Bay is restricted to winter months owing to concerns for threatened and endangered species. Placement of dredged material in the lower Chesapeake Bay in Wolf Trap Alternate Open Water Placement Site (WTAPS) overlaps with overwintering locations for mature female blue crab. To estimate the potential magnitude of winter mortality in WTAPS and WTAPS Northern Extension (WTAPSNE) resulting from placement of dredged material, a range of geostatistical tools (e.g., inverse distance weighting and kriging) were used to map the distribution and estimate the abundance of blue crab in Chesapeake Bay, WTAPS, and WTAPSNE (i.e., small-scale estimation) from 1990–2020 using data from the winter dredge survey. These analyses indicated that a low proportion of the age-1+ female blue crab population occurs within WTAPS and WTAPSNE (<1.18% and <1.5% respectively). Variability of abundance estimates was high when female age-1+ abundance was less than 150 million in the Chesapeake Bay. Therefore, we suggest the Port limit placement of dredged materials in WTAPS and WTAPSNE when female age-1+ abundance is less than 150 million; we recommend the Port not undertake placement activities when the stock is declared overfished (i.e., when female age-1+ abundance is less than 72.5 million).Item Discerning the roles of ocean acidification, eutrophication, and river alkalization in driving long-term pH trends in the Chesapeake Bay(2022) Guo, Yijun; Li, Ming; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rising anthropogenic CO2 in the atmosphere and oceanic uptake of CO2 have led to a gradual decrease in seawater pH and ocean acidification, but pH changes in estuaries and coastal systems are more complicated due to a multitude of global and regional environmental drivers. Increasing global fertilizer use due to agricultural production has led to a doubling of riverine nutrient loading since the 1950s, leading to widespread eutrophication in estuarine and coastal waters. Excessive nutrient loading stimulates primary production in the surface euphotic layer, which consumes CO2 and elevates pH, but unassimilated organic matter sinks and decomposes in bottom waters, producing CO2 and reducing pH. In the meantime, human-accelerated chemical weathering, such as acid rain and mining, has resulted in rising alkalinity in many rivers and basification in estuarine and coastal waters. To discern how these environmental drivers influence long-term pH trends in coastal waters, a coupled hydrodynamic-biogeochemical-carbonate chemistry model was used to conduct hindcast simulations of the Chesapeake Bay between 1951 and 2010. The model reproduced the observed chlorophyll increase and hypoxia expansion due to the increased nutrient loading. In contrast, low-pH bottom waters and acidic volume shrank from 1950 to 1980. GAM analysis of long-term pH trends in different regions of Chesapeake Bay revealed increasing pH in the upper Bay driven by the river alkalinization, a peak pH in the mid-Bay in the 1980s coincident with the peak nutrient loading and decreasing pH in the lower Bay driven by ocean acidification. Four scenario runs were performed to assess the individual effects of rising pCO2, river alkalinization, riverine nutrient loading, and climate change (warming and sea-level rise) on long-term pH changes in the Chesapeake Bay. The model results suggested that river alkalinization was more important than ocean acidification in driving the long-term pH changes in the estuary.Item MICROBIAL BIOFILMS ON MICROPLASTICS: A LOOK INTO THE ESTUARINE PLASTISPHERE OF THE CHESAPEAKE BAY(2021) Sosa , Ana Paula; Chen, Feng; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microplastics are plastic particles that are smaller than 5 millimeters and are often found as pollution in our waterways. These polymer particles are globally distributed and are a direct result of human activity. Because of their rigidity and durability, microplastics are an ideal substrate for enhanced microbial growth and biofilm development. While microplastics have been studied in various contexts, only few studies have characterized the microbial communities on different types of plastic particles, but no study has been done in the estuarine water. In this study, we exposed three different types of plastics (polypropylene, polystyrene, and polylactic acid) to the water of Baltimore’s Inner Harbor, along with a non-plastic glass control. We used both in situ and in vitro incubations to understand the development of biofilm communities on microplastics. Microbial communities were analyzed based on the 16S rRNA gene sequences. We found that microbial composition on biofilm is distinct from that in the surrounding water, and different microplastic types have a minor impact on the composition of biofilm communities. The similarity between microbial communities on plastic and non-plastic particles suggests that surface supports rather than material types could be more critical for biofilm formation. Succession of microbial communities on the microplastics and interesting bacterial groups were described. Isolation and microscopic observations were also applied in this study. The presence of phototrophic organisms like filamentous cyanobacteria and Auxenochlorella on microplastic biofilms is interesting, and little is known about their contribution to carbon fixation in the ocean. Biofilms formed on microplastic surfaces could potentially affect the ecosystems via different mechanisms, including local nutrient cycling and the transportation of invasive or harmful species. As plastic production and mismanagement continues to be pervasive in our society, it is paramount that we include biofilm development into the framework of general ecology in order to truly understand the impact of plastic pollution and safeguard our ecosystems.Item NUTRIENT RETENTION BY RIPARIAN FORESTED BUFFERS IN WESTERN MARYLAND: DO THEY WORK AND ARE THEY WORTH IT?(2021) Siemek, Stephanie Melissa; Eshleman, Keith N; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Riparian buffers are a best management practice (BMP) implemented to improve water quality. In 1997, Maryland established the Conservation Reserve Enhancement Program (CREP) to give landowners incentives to install riparian buffers that would help restore the Chesapeake Bay. Although many studies support riparian buffers as a BMP, many have also reported a wide range of nutrient reductions. It is uncertain what factors control buffer function, yet they continue to be installed with high expectations. Water quality predictions become less accurate in hydrogeologically complex systems such as the Ridge and Valley (R&V) physiographic province. The purpose of this research was to assess the riparian buffer’s nutrient removal function of dissolved nitrogen and phosphorus in the R&V to understand the hydrologic controls further. Throughout western Maryland, we conducted two synoptic stream chemistry studies that contained forest buffers planted under CREP and a range of pre-existing natural forested riparian zones. We used a steady-state reach mass balance model to estimate lateral groundwater inputs and tested several nutrient models to describe the nutrients in groundwater discharge. We then aimed to understand if incentives given through CREP to landowners were adequate by performing a benefit-cost analysis (BCA) using three scenarios. We used the BCA results to estimate nutrient reduction costs using results from the Chesapeake Bay Watershed Model (CBWM) and our synoptic studies. Streams along CREP sites did not show strong evidence of nutrient retention. However, those containing a mix of natural forests with planted buffers showed significant nutrient declines in both synoptic studies. Several models tested (i.e., The Nature Conservancy model, Gburek and Folmar (1999), our base model) inadequately described nutrient discharge; however, our actual flow model performed best. Our BCA results found newly planted forest buffers under CREP provide the greatest financial gains to landowners, but grass buffers are the most cost-effective practice based on CBWM’s estimated nutrient reductions. Although our research did not assess grass buffers, our synoptic studies showed little indication that newly planted forest buffers significantly reduce nutrients in the R&V, suggesting stream water quality greatly depends on the watershed’s hydrogeomorphology that controls how major contributing sources filter through the landscape.Item SUBAQUEOUS SOILS OF SOUTH RIVER, MARYLAND: SOIL-LANDSCAPE MODEL EVALUATION(2021) Park, Cedric Evan; Rabenhorst, Martin C; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The way soils form, their distribution on the landscape, and their interactions with their ecosystems must be understood if they are to be managed well. Our incipient understanding of subaqueous soils limits successful management, but recent research efforts have sought to address this problem. The goal of this study was to evaluate the protocols for describing, characterizing, classifying, and mapping subaqueous soils. To this end, a subaqueous soil-landscape model (Wessel, 2020) was used to predict the distribution of soils in South River, a western shore Chesapeake Bay subestuary. The soils of South River were surveyed, and the observed soils were compared to the predictions. The model provided significant positive guidance for mapping subaqueous soils, confirming that a pedological approach is useful in subaqueous settings. Pedological data were used to generate a subaqueous soils map for South River and make recommendations to refine the model. Protocols related to soil porewater halinity and mineralogy were also investigated.