MEES Theses and Dissertations

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    (2023) Avalos, Grace; Richardson, Rodney T; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Molecular taxonomic detection is now widespread across the sciences, because of advances in direct PCR, improved marker selection, and increases in sequencing throughput. Facilitated by these advances in sequencing, methodological sensitivity of sample identification has improved substantially. Metagenetic techniques to infer what species are present in a sample by sequencing unknown samples and comparing them to known references has the potential to advance our understanding of biodiversity. Metagenetic analysis of environmental DNA (eDNA) represents a novel, non-lethal method for characterizing floral-associated arthropod communities. Diverse arthropod assemblages interact with flowers, and floral surfaces have been shown to harbor arthropod DNA. We performed metagenetic sequencing on eDNA isolated from flower samples and honey bee-collected pollen samples using multiple markers and compared the frequency and taxonomic breadth of eDNA detections across these genetic markers and substrate types. Understanding which markers and substrates are most effective for eDNA characterization of floral-associated arthropod communities will guide future research and enable low-risk detection of threatened or endangered arthropods.
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    (2023) Wade, Kaitlynn Jean; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The economic and commercial importance of Jonah crabs (Cancer borealis) and Atlantic rock crabs (Cancer irroratus) has increased greatly in the USA. The objectives of my research were to determine spatial distributions, habitat preferences, and potential seasonal movements of both species. Data were obtained from the offshore Northeast Fishery Science Center bottom trawl surveys. Analyses included kernel density estimates, generalized additive models, empirical cumulative distribution functions, and ANOVAs. The spatial distributions of Jonah and Atlantic rock crabs changed over time during the 1970s – 2000s. Compared to Atlantic rock crabs, Jonah crabs preferred slightly warmer temperatures, deeper depths, and muddier sediments. Seasonally, Jonah crabs were found farther offshore in the winter and closer to shore in the fall and spring. Atlantic rock crabs were found closer inshore in the winter and spring and more offshore in the fall. Both species were found to have different seasonal patterns in the Mid-Atlantic Bight
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    (2023) Stahl, Katherine A.; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In many ditched coastal salt marshes, megapools, or large ponded areas of vegetation dieback,have formed. In combination with sea level rise, this interior marsh loss can decrease wildlife habitat suitability, resilience to storms, and other ecosystem services. However, mechanisms of megapool formation are poorly understood, hampering restoration efforts. Here, we explored differences in environmental characteristics between megapools in different stages of formation (Fully Formed, Partially Formed and Nonformed/Control) and between Elevations within megapools (High, Medium, Low). Using IRIS Films (Indicator of Reduction in Soil), we found that Fully Formed megapools had higher sulfide concentrations than Partially formed, which in turn were greater than Nonformed megapools. We additionally found that lower elevations correlated with higher sulfides, lower plant coverage, lower belowground biomass, lower Carbon Density, and predicted megapool type. We noted that in terms of elevation, vegetative cover, and biomass, Nonformed and Partially formed were more similar as were High and Medium elevations. Whereas in terms of soil characteristics, Fully Formed and Partially formed were more similar as were Medium and Low Elevations. To combat megapools and dieback, we will assess the effectiveness of two restoration techniques, the first of which is assessing the survival and growth of plantings at different spacings, elevations, and megapool formation levels. We found survival and growth was higher in Partially formed megapools than Fully formed, and no impact by spacing or elevation. Our second restoration technique is runnels, or 15” channels that reconnect megapools to ditches, which were installed in January of 2023. The data collected above will act as baseline data, repeated again. These baseline results support a close relationship between pool stages of formation, carbon storage, elevation, vegetation health, biomass production, and sulfide levels (Graphical Abstract).
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    (2023) Ahn, So Hyun; Glibert, Patricia; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The toxic mixotrophic dinoflagellate Karenia spp. forms blooms almost annually in the Gulf of Mexico, especially on the West Florida Shelf (WFS). Blooms typically initiate in early fall but can persist from months to years. Daily, Karenia vertically migrates to the surface water during the day, possibly experiencing changes in temperature, light, nitrogen (N), and prey type and availability. Therefore, this dissertation aimed to examine the interplay between Karenia’s photo-autotrophic and phago-mixotrophic metabolism and the short-term fluctuations in environmental conditions to understand how these factors may relate to the conditions under which Karenia spp. are found in the WFS.Title of Dissertation: INTERACTIONS BETWEEN NITROGEN AND TEMPERATURE ON THE METABOLISM OF THE RED-TIDE MIXOTROPHIC DINOFLAGELLATE KARENIA SPP. IN SUPPORT OF PREDICTIVE MODELS: IMPLICATIONS FOR BLOOM DYNAMICS ON THE WEST FLORIDA SHELF So Hyun (Sophia) Ahn, Doctor of Philosophy, 2023 Dissertation directed by: Professor Patricia M. Glibert, Marine Estuarine Environment Sciences A culture of K. mikimotoi balanced photon flux pressure (light availability) with consumption in overall metabolism when pulsed with 15N-NO3-, 15N-NH4+, or 15N-urea over the range of 15-25°C as shown by photosynthetic fluorescence. However, when shifted to 30°C, cells were significantly stressed, but urea-enriched cells showed a smaller decline in fluorescence, implying that urea might induce a photoprotective mechanism by increasing metabolic “pull.” Studies conducted with natural K. brevis winter and summer populations during 2021 showed that thermal history played a critical role. Unusually, summer blooms had higher biomass but were stressed photosynthetically and nutritionally. However, 15N-urea enriched summer cells had higher uptake rates as well as carbon (C) and N cell-1, especially in warmer waters, showing differential thermal responses based on N forms. Mixotrophy grazing measurements showed that K. brevis grazed both the picoplankter Synechococcus as well as the cryptophyte Rhodomonas. Grazing did not selectively target specific qualities of Synechococcus (based on differing N and P of the prey growth media), but ingestion rates were a function of prey-to-grazer ratios (R2=0.76) as well as prey amounts (R2=0.71). NanoSIMS confirmed 15N incorporation from Synechococcus in K. brevis. In natural communities of K. brevis, ingestion rates were also significantly related to prey-to-grazer ratios (p < 0.01) and by temperatures (p < 0.05) to a lesser degree (R2= 0.75) when incubated at ambient (24°C) and ambient temperature ± 5°C (19, 29°C). The grazer effects on the photosynthetic performance of grazer and prey were also examined. Grazing on Synechococcus indirectly reduce the photosynthetic performance of prey, especially at warmer temperatures but had little or no effect on the photosynthesis of K. brevis itself.
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    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.
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    (2023) Li, Renjian; Li, Ming; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Recent observations in Chesapeake Bay showed that the interaction between lateral circulation and channel-shoal bathymetry generated internal lee waves which subsequently propagated onto shallow shoals and evolved into internal solitary waves, leading to overturning and enhanced turbulent mixing. However, it is unknown under what hydrodynamic conditions the lee waves could be generated and how the nonlinear internal waves evolved. Using an idealized straight channel representative of a coastal plain estuary, we conducted numerical simulations to investigate internal wave generation over a range of river flows and tidal amplitudes. The model results are summarized using the estuarine classification diagram based on the freshwater Froude number Frf and the mixing parameter M. Δh decreases with increasing Frf as stronger stratification suppresses waves, and no internal waves are generated under large Frf. Δh initially increases with increasing M as the lateral flows become stronger with stronger tidal currents, but decreases or saturates to a certain amplitude as M further increases. This regime diagram suggests that internal lee waves can be generated in a wide range of estuarine conditions. To examine the nonlinear evolution of internal waves, a three-dimensional nonhydrostatic model with nested model domains and increasing grid resolution was configured. The lee wave steepens into a shorter elevation wave due to shoaling and soon evolves into a depression with a train of undular waves at its tail as bottom boundary mixing elevates the halocline above the mid-depth. These nonlinear internal waves enhance the turbulent dissipation rate over the deep channel and shallow shoal, suggesting an important energy source for mixing in stratified coastal plain estuaries. In addition, a pH sensor deployed at the middle reach of Chesapeake Bay recorded high-frequency variability in bottom pH driven by along-channel winds. Though wind-driven lateral circulation can advect high pH water downward, the slow air-sea exchange of CO2 limits the lateral ventilation. With DIC and TA budget analysis and comparison with cross-sections at upper- and lower-Bay where strong lateral circulation was confined in the surface layer, we found vertical mixing and replenishment of oceanic water by longitudinal advection could be more important mechanisms to ventilate bottom pH.
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    (2023) Vona, Iacopo; Nardin, William; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Rising sea levels and the increased frequency of extreme events put coastal communities at serious risk. Due to SLR, traditional solutions such as breakwaters (or gray/artificial structures) will become ineffective for wave attenuation and shoreline erosion control. Moreover, gray solutions do not consider the ecological aspects of the coast, and may negatively affect surrounding ecosystems. The “living shoreline” technique includes natural habitat features, such as oysters and/or vegetation into shoreline stabilization, to provide both protection and ecosystem services. Oysters create three-dimensional, complex reef structures that attenuate wave energy and increase sedimentation rates. If coupled with breakwaters, oysters may maintain breakwaters’ efficiency over time as they are expected to grow with SLR. However, guidance for the correct implementation of Natural and Nature Based Features (NNBF) for coastal protection is still unclear, and many authors within the literature have been repeatedly requested more insights. In this thesis, we have therefore studied the coupling between oysters and breakwaters via field, modeling and laboratory experiments, in order to highlight the benevolent aspects of NNBF regarding coastal defense. Field results showed gray breakwaters allowed for shoreline protection (by reducing incoming wave energy) and increased sedimentation rates. However, SLR modeling scenarios showed a gradual reduction of wave attenuation over time, as well as increased sediment export from the coast. When oysters were included in the modeling, on the other hand, wave dampening and sediment retention were preserved through the time. Laboratory experiments showed oyster-reef breakwaters in emergent or near-emergent conditions produced higher drag coefficient compared to gray structures, resulting in greater dissipative features. Higher water levels simulated in our experiments produced less reliable results that will require further investigation. This thesis supports oysters for coastal protection, and emphasizes the positive aspects of NNBF regarding wave attenuation and sediment retention in the face of climate changes and SLR. However, challenges encountered during field studies underlined the importance of environmental and biogeochemical conditions (such as water level, aerial exposure, temperature and seasonality) for oyster reefs’ establishment, growth and survivability. Future restoration plans involving oysters in coastal defense should definitely take these environmental and biogeochemical aspects into account, in order to properly protect the coast in the face of climate changes and SLR, while also providing many other useful ecosystem services for the environment. The coupling between oysters and breakwaters may represent a valuable and effective methodology to protect our coast over a changing climate and a rising sea, where optimal conditions for oysters’ survivability occur and are maintained over time.
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    (2023) Wiltsee, Laura E.; Gray, Matthew W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Bivalves are prized for the ecosystem services they provide. The removal of particles from the water column through filter feeding and resulting water quality benefits, known as the biofiltration services, of bivalves have been studied for over a century. This has created a wealth of knowledge around the mechanistic drivers of bivalve feeding activity. Recently, Chesapeake Bay ecosystem-wide models have begun incorporating Eastern Oyster (Crassostrea virginica) biofiltration. Acute feeding variability is critically important when estimating oyster biofiltration services at ecosystem scale. Typically, natural seston clearance rate studies last a limited timeframe, with a focus on specific environmental events such as an increase in temperature, drop in salinity, or a tidal cycle.To capture the highly variable filter feeding rate of bivalves, such as the Eastern Oyster, studies have used highly controlled laboratory conditions, with single environmental variable modification. These studies often use indirect methods for estimating clearance rates that commonly lack high-resolution capability. Furthermore, these studies are labor intensive and time consuming, and as a result, few studies have monitored bivalve feeding activities over long periods to understand variation in activity or how these rates may change with seasonal shifts in conditions. These limitations have led to a shortage of knowledge around how clearance rates of oysters vary in response to ambient conditions over both short-term (hourly) and long-term (seasonal) time scales. This study leverages advances in semi-autonomous aquatic observing to track high- resolution, long-term feeding responses of bivalves to subtle variations in environmental conditions. Oyster ex situ clearance rates in the Choptank River (Maryland, USA) were estimated under flow-through conditions, and logged in real-time using fluorometers among replicate oysters over 5-day experiments for 9 months. The measured clearance rates from this system were compared to a mechanistic clearance rate model used by the Chesapeake Bay Program, which is used to estimate the role of oysters in controlling water quality in the Bay. Environmental data were evaluated to build a statistical and random forest model to predict how oyster clearance rates respond to prevailing environmental conditions. This monitoring system and resulting models enable a deeper understanding of feeding variability and how natural seston and environmental variability directly influence oyster physiology.
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    Impact of Plant-Derived Allelochemicals on Harmful Algal Blooms
    (2023) Armstrong, Christen Taylor; Place, Allen; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Harmful algal blooms (HABs) are a global concern in both freshwater and coastal systems; creating dire consequences for public health, water resources, and local economies. Thus, there is a focus among scientists and environmental managers on HAB prediction, prevention, and mitigation. Current chemical mitigation methods include algicides such as copper sulphate, chlorination, and hydrogen peroxide, which can have high financial costs and secondary pollution associated with them. The use of natural allelochemicals produced by plants and bacteria has received considerable attention as an alternative to synthetic algicides, as they can have negligible toxins, be highly selective, and easily degraded in the environment. This dissertation is a coalition of research looking into new sources of plant allelochemicals and whether natural levels of allelochemicals in the water column, can impact phytoplankton communities and the presence of toxin-producing algal species. The first objective focused on the use of the waste product: brewer’s spent grain (BSG), as a new control mechanism to inhibit the growth of toxic algae. BSG extract of doses higher than 250mg/L inhibited the growth of freshwater and marine toxin-producing cyanobacteria and dinoflagellate species (Microcystis aeruginosa and Karenia brevis), while not impacting the diatom and chlorophyte tested (Scenedesmus obliquus and Prorocentrum tricornutum). This same dosage of BSG caused cyanobacteria abundance in lake water to decline by 90% within 4 days and chlorophytes to dominate the community by day 6 during a microcosm study. However, an experiment controlling bacteria levels demonstrated that the decline of K. brevis growth was likely due to the increase in abundance or presence of certain types of bacteria growing with exposure to BSG extract rather than due to chemicals released from the BSG. The second and third objectives shifted focus to the New Jersey Pinelands and whether the chemicals released into the water from terrestrial and marine plants in these waters, like phenolic compounds, impact the phytoplankton community and toxin-producing species. The second objective focused on the spatial and temporal distribution of phycotoxins along two New Jersey estuaries using passive samplers and whether the utility of passive samplers was impacted by the excess phenolic compounds in the water. By utilizing passive samplers in New Jersey, phycotoxins not previously reported in the area were described, such as azaspiracids, goniodomin-A and yessotoxins. However, this objective also showed some of the caveats of passive samplers, especially at sites with high phenolic compounds. The third objective focused on identifying the primary environmental drivers of chlorophyll a concentration and phytoplankton community along the freshwater – marine continuum of two New Jersey Estuaries with varying levels of disturbance. This dissertation explored BSG as a novel control method of HABs, and provided new information for monitoring, managing, and modeling HABs based on phenolic content measured in the water.
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    The Role of Connectivity and Spatial Structure on the Population Dynamics of Marine Fishes
    (2023) Arai, Kohma Herbert; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Migrations regulate population structure, which can play an important role in conferring stability at aggregate scales via asynchronous responses of population sub-components to perturbation; however, little is known about the importance of spatial structure in population persistence in fishes. My dissertation aims to explore the role of spatial structure on the population dynamics of marine fishes. Two species that exhibit different types of population structure were considered: (i) Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic, comprised of two components that have distinct spawning regions off Canada (northern contingent) and the US (southern contingent); and (ii) striped bass (Morone saxatilis) in the Hudson River (HR), which exhibit early-life partial migration whereby a portion of juveniles remain in their natal freshwater habitats, while others migrate into higher salinity habitats. In Chapter 2, I used otolith stable isotopes (d18O/d13C) to understand contingent mixing of the Northwest Atlantic mackerel over two decades (2000–2019). Prevalent contingent mixing occurred within the US waters, indicating that the northern contingent may provide subsidies to the US mackerel fishery. In Chapter 3, I combined machine learning with otolith d18O isoscapes to predict the geographic origin of the Northwest Atlantic mackerel spanning four decades (1975–2019). Contingent mixing occurred over four decades, including the 1970s when intensive foreign fisheries took place in US waters. Nursery hotspots were detected within spawning regions, but shifted over time. In Chapter 4, for HR juvenile striped bass, I explored the influence of early-life conditions and environmental drivers on partial migration. Otolith chemistry uncovered four dominant early migration modes. Partial migration was associated with larval growth, albeit facultatively controlled by environmental conditions. In Chapter 5, I evaluated how HR striped bass early-stage partial migration influenced recruitment patterns to the adult population over a 3-decade span. As an outcome of partial migration, adults recruited from a variety of nurseries, which exhibited asynchronous dynamics in response to climate variables. Through a comparative analysis of two species that exhibit different types of population structure, I demonstrated how spatial structure can play key roles in the population dynamics of marine fishes, with implications for management and conservation.
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    Climate Change and Vibrio species: Investigation of Environmental Parameters Associated with Occurrence and Transmission
    (2023) Brumfield, Kyle David; Colwell, Rita R.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Climate change, associated with shifts in the geographical range of biological species, has become increasingly important in emergence and re-emergence of disease. Vibrio spp., native to aquatic ecosystems, are commonly associated with aquatic invertebrates, notably crustaceans and zooplankton. Some species of the genus Vibrio cause infection in humans, of which Vibrio cholerae, the etiological agent of pandemic cholera, is the most documented. Pathogenic non-cholera Vibrio spp., namely Vibrio parahaemolyticus and Vibrio vulnificus, cause gastroenteritis and also septicemia and extra-intestinal infections. They are responsible for a large number of public health emergencies in developed countries, including the United States. As sea temperatures rise and salinity profiles are altered, a pattern of poleward spreading of non-cholera Vibrio spp. has been observed globally, demonstrating significant geographic expansion of these bacterial populations, corroborated by an associated increase in the number of reported vibriosis cases. Since Vibrio spp., including pathogenic vibrios, play an important role in the degradation of polymeric substances, such as chitin, and in biogeochemical processes, they cannot be eradicated. Hence, routine monitoring and an early warning system are needed for public health preparedness. Since the 1960’s, ongoing research has focused on environmental factors linked with occurrence and distribution of clinically relevant Vibrio spp. and their role in disease transmission. We have reported that lack of, or damage to, water, sanitation, and hygiene (WASH) infrastructure, coupled with elevated air temperatures, and followed by above average rainfall promotes exposure of a population to contaminated water, hence increases the risk of an outbreak of cholera. Global predictive intelligence models applicable to diseases caused by non-cholera Vibrio spp. are in development. The research reported here describes results of intensive sampling to detect and characterize Vibrio spp. in the Chesapeake Bay, Maryland, and the Florida Gulf Coast, the latter an area significantly impacted by Hurricane Ian, September 2022, with a spike in confirmed vibriosis cases and deaths during weeks following the storm. Results of this study provide confirmation of environmental predictors for Vibrio spp. and document long-term increase and extended seasonality of Vibrio populations in the Chesapeake Bay. Using satellite remote sensing data, we demonstrate the impact of extreme heat, precipitation, and other key environmental and geophysical factors (e.g., temperature, salinity, and chlorophyll) on prevalence of pathogenic Vibrio spp. in aquatic systems. This study lays the groundwork for a predictive intelligence system for Vibrio spp. and other pathogens under varying climatic scenarios.
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    (2023) Windle, Anna; Silsbe, Greg; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Environmental remote sensing is the science of monitoring physical, chemical, and biological characteristics of the Earth through space and time, and from a distance, by measuring how these environments interact with electromagnetic energy, or more simply through changes in color. This dissertation leverages in situ, satellite, and unoccupied aircraft system (UAS, drones) data to enhance the efficacy of environmental remote sensing in Chesapeake Bay. Satellite data consists of distinct contributions of the surface under observation and the intervening atmosphere. Atmospheric correction (AC) processors seek to isolate the surface signal, and while several variants exist, their accuracy varies widely in optically complex coastal waters. Chapter 2 is a statistical evaluation of four common AC variants applied to data collected by the most recent operational ocean color sensor, the Ocean Land Color Instrument (OLCI) onboard Copernicus Sentinel-3A and -3B satellites. Remote sensing reflectance (Rrs), the product of AC processors from which a suite of water quality metrics is then derived, was obtained from each AC variant and matched in space and time with in situ Rrs data collected in the Chesapeake Bay. AC results varied widely, and the most statistically robust was a neural-net based algorithm (Case 2 Regional Coast Color, C2RCC). The resultant shape and magnitude of Rrs (e.g. color) is governed by the type and concentration of optically active constituents (OACs), namely phytoplankton pigments, chromophoric dissolved organic matter, inorganic sediment, and water itself. In coastal waters where OACs are dynamic and vary independently from each other, deriving accurate water quality metrics remains an open challenge. Chapter 3 applies a spectral clustering classification of OLCI Rrs data (2016-2022) and identifies the fifteen most dominant optical water types (OWTs) of Chesapeake Bay. OWTs were matched in space and time with Chesapeake Bay water quality monitoring data, and a statistical evaluation demonstrates how water quality data are constrained within and across OWTs. In contrast to earth-observing satellites, UAS equipped with optical sensors offer on-demand, highly resolved data. Aquatic UAS applications are in their infancy, and the critical removal of light reflected directly off the skin of water has received little attention in the literature. Chapter 4 proposes four different approaches to remove direct surface reflectance from UAS imagery and evaluates each against in situ Rrs data. The most accurate method is a simple empirical model that exploits measurements in the infrared where water strongly absorbs light; applying this model permits high resolution water quality retrievals with only modest uncertainty. Chapter 5 uses UAS imagery to monitor a wetland restoration site in the Chesapeake Bay across seasons and years. A supervised random forest model is developed with UAS data and used to classify species-specific marsh vegetation with 97-99% accuracy. Vegetation classification maps were compared to as-built planting plans to delineate instances of significant marsh migration. Chapter 6 summarizes how the environmental remote sensing methods used in this dissertation can contribute to a better understanding of coastal research, monitoring, and management by addressing challenges, gaps, and potential solutions at various scales.
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    (2023) Tingler, Aubrey; Leisnham, Paul; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The worldwide spread of the Asian Tiger Mosquito (ATM), Aedes albopictus, demands effective and sustainable urban mosquito management, due to their disease vector capacity and potential for causing high nuisance levels. Agency-led mosquito management is often ineffective at controlling ATM or unwanted by residents. In 2016 and 2017, citizens of University Park, Maryland, USA led a town-wide campaign to encourage residents to purchase Gravid Aedes Traps (GATs), a lethal oviposition trap successful at capturing Aedes mosquitoes. This campaign resulted in significant reductions of adult female ATM in areas with >80% GAT coverage among yards. The goal of this study was to test the continued effectiveness of University Park’s citizen-led program and explore social and environmental predictors of household GAT deployment in 2021. We conducted adult trapping at 18 sites in University Park to test if current levels of GAT deployment still predicted reductions in area-wide adult female ATM, distributed an online questionnaire to gather data for testing relationships of demographic, environmental, knowledge, and attitude predictors with household GAT deployment, and conducted environmental yard surveys to assess relationships of GAT deployment with container habitat and mosquito container infestation. We found that only 24.9% (130/523) of University Park households deployed GATs in 2021, which is substantially lower than the 46.0% (439/954) of households that deployed GATs in 2017. GAT coverage in 2021 did not exceed 50% (3/6) in any adult-trapping area, well below the 80% threshold thought needed to reduce area wide adult Aedes. Nevertheless, we found a significant negative relationship between household GAT deployment and adult female ATM, indicating that GATs are still effective at controlling Aedes at lower coverages. Households that deployed GATs had lower numbers of total, but not infested, water-filled containers, suggesting GAT deployment was often a part of a household's overall effort to reduce mosquitoes alongside source reduction, but that source reduction and GATs may not limit mosquito infestation at the yard scale. Households with middle incomes, further from town greenspace were less likely to deploy GATs along with respondents who spent less time outdoors, were less favorable toward University Park's GAT Program, and could not name ATM as University Park's most common human-biting mosquito. Respondent familiarity of ATM was lower in renters than homeowners, and respondent favorability towards University Park's GAT program was lower in households with children, and with respondents that do fewer yard activities and who had resided for less time in the town. The results of this study show that a citizen-led mosquito-control program using a passive lethal oviposition trap is still effective, four years after its inception, and that there were specific social and environmental predictors of household participation. In this thesis, I will discuss these results and their implications for bottom-up, citizen-led, control of ATM and other Aedes in other residential communities and demonstrate a framework for understanding drivers of participation and success in community-led environmental management.
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    Assessing vertebrate biodiversity across the Chesapeake Bay using environmental DNA metabarcoding
    (2023) Rodriguez, Lauren Kelly; Bailey, Helen; Woodland, Ryan J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Through the collection and sequencing of trace genomic evidence from environmental samples (e.g., water, air, and soil), environmental DNA (eDNA) metabarcoding can detect a range of vertebrates. Despite the dynamic characteristics of estuarine environments, which often hinder the persistence of genomic material, this project successfully employed metabarcoding to assess the distribution of vertebrates in the Chesapeake Bay. Primarily, the study evaluated the effects of using various eDNA sampling, laboratory, and post-hoc analysis techniques when investigating species presence and biodiversity of an area. This study also identified spatially-explicit fish communities along salinity gradients as described by a Generalized Additive Mixed Model (GAMM) and a Permutational Multivariate Analysis of Variance (PERMANOVA). Community compositions were similar to previous findings by traditional trawling and seining methods. This research supports the usefulness of eDNA metabarcoding to assess species presence across spatiotemporal extents, making it a promising tool for future biomonitoring efforts in the Chesapeake Bay.
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    Expanding the Fisheries Management Tackle Box: A Multiple-Model Approach to Support Better Decisions
    (2023) Hayes, Christopher Glenn; Wainger, Lisa; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Marine fisheries provide critical ecosystem services but face an array of stressors like climate change and overfishing. Managing fisheries is challenging due to limited information and the need to make complex tradeoffs among ecological and social objectives. Decision processes that include integrated social-ecological models and equitable stakeholder engagement are increasingly recognized as approaches to improve the likelihood of achieving management goals compared to those that rely solely on stock assessment models with limited stakeholder input. Additionally, advanced technologies offer new opportunities to understand marine ecosystem dynamics, including human behavior. This research adds two examples of underutilized tools: multi-criteria decision analysis (MCDA) and agent-based models (ABMs). In the first case, I compared management recommendations for the Chesapeake Bay oyster fishery arising from A) stakeholder engagement using group negotiations and B) preferences elicited from individuals using an MCDA approach. The recommendations were consistent across methods, suggesting that group effects did not bias group negotiation outcomes. The second case investigated New England groundfish reporting behavior based on stock dynamics, quota markets, and fishery observer coverage. First, having an observer onboard was found to significantly reduce the probability and magnitude of reporting error (ie., an observer effect) using a linear mixed effects model of data from vessel trip reports and remote vessel monitoring systems. Next, an ABM was used to explore emergent responses to policy changes - varying levels of observer coverage and the strength of the observer effects - on fish catch, reporting error, and profit outcomes, given fisher interactions and responses to fish population dynamics. Scenarios with strong observer effects resulted in increasing marginal improvements in reporting accuracy at high levels of observer coverage. MCDA and ABM can contribute to a multiple-model approach by allowing fisheries managers to integrate diverse stakeholder perspectives and use additional data sources that could lead to better fishery outcomes.
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    Characterizing nutrient budgets on and beyond farms for sustainable nutrient management
    (2023) Zou, Tan; Zhang, Xin; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The production and security of food are heavily reliant on adequate nitrogen (N) and phosphorus (P) inputs in agriculture. However, ineffective management of N and P from the farm to the table can result in nutrient pollution, triggering both environmental and social issues. Moreover, another important challenge for P management is limited and unevenly distributed P resources, leading to P scarcity in many parts of the world. Inefficient use of nutrients in agriculture-food systems is the root cause of both nutrient pollution and scarcity. To improve nutrient use efficiency and reduce nutrient loss, it is crucial to address key knowledge gaps in nutrient management research, which include inadequate quantification of nutrient budgets, as well as identifying and addressing nutrient management challenges across various systems and spatial scales. This dissertation tackles the knowledge gaps in two studies, including a global-scale study and a case study of the Chesapeake Bay watershed. In the global-scale study, I establish and utilize a unique P budget database to assess historical P budget and usage patterns at the national and crop type level from 1961 to 2019. This analysis reveals the impacts of various agricultural and socioeconomic drivers on cropland P use efficiency (PUE), including N use efficiency (NUE), fertilizer-to-crop-price ratio, farm size, crop mix, and agricultural machinery. The findings indicate that P management challenges vary by country and spatial scale, necessitating tailored country-level strategies. The regional-scale study applies a framework adapted from N studies to the Chesapeake Bay watershed, analyzing nutrient (N and P) management across systems and spatial scales. This approach uncovers that nutrient loss potential beyond crop farms is larger than that at crop farms. This highlights the need to enhance nutrient management and curb nutrient loss in animal production, food processing and retail, and human consumption. This study also identifies a large potential for meeting cropland nutrient demand by increasing the recycling of nutrients in manure, food waste, and human waste. To tackle the challenges surrounding nutrient management in the watershed, it is imperative to target factors significantly related to nutrient management, such as agricultural practices, soil properties, climate change, and socioeconomic conditions. This dissertation contributes to a deeper understanding of N and P management challenges, gaps, priorities, hidden drivers, and potential solutions at various scales, from regional to national and global levels. The analytical procedures and statistical tools developed in this dissertation are generalizable, allowing for their adaptation to similar nutrient management studies in different regions and for diverse research purposes.
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    Building Flood Resilience in Social-Ecological Systems
    (2023) Snider, Natalie L.; Dennison, William C.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Historic driving forces of economic development, continually growing population and expanding inequities, are already challenging the resilience of the social-ecological system (SES) on multiple fronts, including socially, economically and environmentally. Existing and increasing threats from climate change will exacerbate the challenges in managing for resilience. The dynamic nature, involvement of multiscale feedback mechanisms between the natural and social sub-systems, possible existence of multiple states of the social-ecological system and inability to ever gain full control or understanding make it a challenge for institutions and actors to define and manage the system boundaries, its components and feedbacks. This complexity requires a transdisciplinary approach that integrates those most impacted into building knowledge and solutions across the environmental, economic and social fields. Similarly, institutions managing these systems will need to develop new approaches and strategies to integrate social, ecological, economic and political aspects of the SES and expand the participation of individual actors in the system, including a redistribution of power to successfully achieve resilience outcomes. The Social-Ecological Resilience Framework, proposed here, seeks to build resilience in the SES through purposeful interventions to maintain or change the forms, functions or both. This framework relates the key terms of sustainability, adaptation, transition and transformation, under the overall umbrella term of resilience. Within this framework, resilience is defined as the ability of the system to sustain, adapt, transition or transform in the face of acute or systemic change. Each subsequent term is then defined by the level of change in forms and functions: (1) sustainable maintains the same forms and functions, (2) adaptation changes the forms while maintain the functions, (3) transition changes the functions while maintaining the forms and (4) transformation changes both forms and functions. The framework can be used to manage the changes that society is experiencing in these systems. Adaptive management and social learning are two examples of approaches for managing the SES under the overarching construct of the Social-Ecological Resilience Framework. Adaptive management, an iterative decision-making process to address uncertainties and adapt to future conditions, should be combined with social learning, a participatory process where knowledge, skills and values are gained or modified through social interactions and collective learning. This dissertation demonstrates the framework and these approaches through five case studies focused on building resilience to flood impacts. Flooding is the costliest natural disaster in the world. However, the calculation of disasters costs typically only includes the cost of flood damages to infrastructure. But flooding is also putting a toll on society’s ability to provide social services, maintain important social factors, such as community cohesion, impacting both physical and mental health, exacerbating inequities and deteriorating the environment and ecosystem services, all with significant costs. In China’s Sponge Cities Program, the key takeaway is that defining the SES, both geographically and in terms of important forms and functions relevant to achieving the resilience goals, should be identified early to be able to address any barriers to success. The key takeaway of the Coastal Structures case study is that roles and responsibilities need to be clearly defined for institutions and actors, by which they can collectively achieve both institutional goals of reducing the societal impacts of flooding and the actors’ goals of reducing their own impacts to well-being. In the Honduras case study, the key takeaway is that building institutional support requires a redistribution of power dynamics to facilitate bottom-up approaches that can increase the utility of resilience actions to solving more than one social, ecological or economic problem within the SES. In Indonesia’s case study, by identifying the key forms and functions for each resilience goal, the range of possible vulnerabilities can be better defined, and timelines of potential changes and strategies to safeguard that positive outcomes are achieved can be developed. And finally, in Louisiana, the key takeaway is that institutions should not be defining the future of the SES without all the key actors engaged or represented. Institutions should support building a common vision of a resilient future through an integrated adaptive management and social learning program. The dissertation discusses a proposed Social-Ecological Resilience Framework (Chapter 1) to define key terms that integrates the notion of resilience, sustainability, adaptation, transition and transformation in relationship to each other and in relationship to the form and function of the SES. Several case studies from around the world demonstrate various aspects of operationalizing the framework. Technical aspects of adaptive management are developed and applied to a case study in Louisiana (Chapter 2). Lastly, social learning is then integrated into adaptive management using the same case study (Chapter 3). Both of these two chapters discuss actions to build resilience in the SES at a localized scale. Managing a social-ecological system (SES) can be an arduous task, and many institutions, such as governmental, non-profit, and research entities, may feel overwhelmed by the complexity and scope of this challenge. It's tempting to concentrate on a particular aspect of the system that seems more manageable or familiar. Nevertheless, without adopting a systems-thinking approach and examining the interactions within and beyond the SES, there is a risk of unintended and cascading consequences and missed opportunities to tackle multiple vulnerabilities collectively. Although this dissertation focuses on flood-related risks, the underlying themes and methodologies are relevant to any disaster, whether caused by nature or humans. Ultimately, our shared efforts to shape a more equitable, resilient, and sustainable world for present and future generations can benefit from these approaches.
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    (2023) Nemes, Claire E.; Cohen, Emily B; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Billions of birds undertake migratory movements each year, traveling distances that range from several hundreds to tens of thousands of kilometers. Migratory birds must be flexible enough to cope with the fluctuating conditions they encounter during these journeys and at their destinations. However, humans are rapidly and dramatically changing the environment across all portions of migratory species’ ranges through habitat destruction and conversion, introduction of invasive species, climate change, and other alterations. My dissertation research seeks to understand the constraints and threats facing birds during two understudied phases of the annual cycle: migration and the non-breeding stationary period. In Chapter 1, I explore how human activities may nonlethally affect birds during migration. I reviewed the scientific literature for evidence of nonlethal effects and of interacting threats that may compound fitness costs to migrating birds. In general, I found that scientific understanding of nonlethal effects during migration lags behind research on direct mortality. Because birds migrate through increasingly anthropogenic landscapes and airspaces, I identify this knowledge gap as a hindrance to effective conservation of migratory birds. In Chapter 2, I investigate if individual songbirds adjust the rate and timing of spring migration based on the vegetation phenology they encounter within North America which may allow them to keep pace with advancing spring phenology under climate change. In the spring, migrating birds must quickly reach their breeding grounds to secure territories and mates ahead of the competition, but individuals that arrive too early may encounter inclement weather or food shortages. Using the Motus automated radio telemetry network, I tracked individual songbirds as they traveled from the southern U.S. towards their breeding areas in spring. I used estimates of spring onset timing at different points on their migration routes to determine if birds traveled in sync with the “green wave” of emerging vegetation or if they used a different strategy. I found that birds migrating from their non-breeding areas arrived in the southern U.S. well after local spring onset, but were able to catch up to the wave of emerging spring vegetation as they traveled northwards, following a “catching up” strategy rather than a “surfing” one. In Chapter 3, I examine how individual songbirds respond to the threat of predation during migratory stopover, when they must balance conflicting demands of refueling and avoiding predators. Migrating birds must contend with both native avian predators such as hawks (Accipiter sp.) and abundant introduced predators such as free-roaming domestic cats (Felis catus), yet their behavioral responses to cats have been little studied during migration. Using an aviary experiment, I exposed wild Gray Catbirds Dumetella carolinensis to either a hawk or a domestic cat and observed their behaviors before and after exposure to determine if they responded appropriately to the threat posed by each predator. When compared with a control group, Catbirds responded differently to both types of predators in the short term, but I detected no differences in their behavior after release. This study provides novel insights into the possible nonlethal effects of introduced predators that birds may encounter during migration. In Chapter 4, I shift focus to explore the threat that free-roaming domestic cats pose to birds in the Caribbean within a Neotropical city. Urban regions are increasingly recognized to provide valuable wildlife habitat but may also contain hazards such as introduced predators, and we currently lack information on the effects of free-roaming cats on migratory and resident bird species during non-breeding seasons. I designed a camera trapping project in San Juan, Puerto Rico to estimate free-roaming cat densities across a gradient of urbanization as a step towards understanding their potential impacts on wildlife. I deployed cameras across 16 trapping grids at three levels of urbanization and used photographic captures of cats to build spatial capture-recapture models. Estimated cat densities ranged from 48  8 (SE) cats/km2 in exurban areas to 473  40 cats/km2 in the most heavily urbanized parts of the city. These data may prove useful for conservation practitioners in San Juan deciding where to target cat management efforts for the benefit of urban wildlife and public health.
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    (2022) Zhu, Qiurui; Davidson, Eric A.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Excess nitrogen resulting from agricultural fertilizer and manure applications on the Eastern Shore degrades the Chesapeake Bay's water quality and causes environmental issues such as algal blooms and "dead zones". Drainage water management (DWM) is an effective best management practice (BMP) to reduce hydrological nitrate export from croplands to surface and ground water by controlling the timing and the amount of ditch discharge and retaining water within ditches and adjacent fields using drainage control structures (DCS). While promoted denitrification in the subsurface and reduction in nitrate leaching are intended consequences of maintaining higher water table level, an unintended environmental consequence is possible production of nitrous oxide (N2O) from denitrification and methane (CH4) from methanogenesis, which are both potent greenhouse gases (GHGs). Whether the application of DWM leads to a "pollution swapping" concern (i.e., trading reduction of nitrate concentrations in ditch water for increases in emissions of N2O and CH4 to the atmosphere) is a question that must be addressed before more widespread implementation of DWM can be endorsed. In this dissertation, I employed a micrometeorological method called the flux gradient (FG) method to a corn-soybean rotation agricultural system with DCS in eastern Maryland on the Delmarva Peninsula to answer this question. This method was chosen because it allows near-continuous measurements of soil trace gas exchanges at multiple locations with a single laser spectrometer at a fine temporal resolution without disturbing the microclimate between soils and the atmosphere. Soil N2O and CH4 fluxes were quantified using the FG method on this drainage water managed farm for three consecutive years when no fertilizer, synthetic fertilizer, and biosolids were applied in 2018 (soybean), 2019 (corn), and 2020 (corn), respectively. Statistical tests indicated that there were no consistent treatment effects of DWM on soil GHG emissions between DWM and non-DWM conditions, suggesting that DWM did not trade the intended consequence of reduced nitrate leaching for the unintended consequence of increased soil GHG emissions. The biosolid addition in 2020 led to the largest N2O emissions among the three years, while the lowest N2O emissions in the growing season were found in the unfertilized soybean year of 2018. In contrast, different fertilization regimes did not yield distinct differences between the three years for CH4 fluxes. In addition, some potential methodological concerns associated with this tower-based micrometeorological approach were addressed and resolved, conferring confidence that the FG method can be applied simultaneously to multiple plots for N2O and CH4 measurements. This research adds to the existing understanding of the impacts of DWM on soil GHG emissions and suggests that this BMP could be applicable in other regions of the Chesapeake Bay as well as other watersheds. This work also contributes to the efforts of studying the impacts of soil organic amendments on soil GHG emissions and deriving improved estimates of emission factors (EFs) for organic amendments.
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    Understanding the Reproductive Biology and Endocrinology of the Female Red Deep-Sea Crab, Chaceon Quinquedens
    (2022) Green, Shadaesha Renee; Chung, J. Sook; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The red deep-sea crab, Chaceon quinquedens, a cold-water decapod found along the continental shelf and slope of the eastern United States has a limited amount of literature available describing their physiological processes. The present research aimed to advance the current knowledge of the reproductive physiology of C. quinquedens females by investigating essential hormones regulating vitellogenesis and ovarian development. In decapod crustaceans, members of the crustacean hyperglycemic hormone (CHH) superfamily control molting, growth, and reproduction, while reproduction and somatic growth are antagonistic. The red deep-sea crab with an extended intermolt period may adopt a similar approach to the blue crab, Callinectes sapidus, which utilizes the molt-inhibiting hormone (MIH) as a gonad-stimulating factor. Hence, a relationship between MIH and CHH levels and vitellogenin is examined, together with the potential role of other eyestalk neuropeptides in vitellogenesis using a transcriptomic analysis. Ten of the 28 eyestalk-neuropeptides found in the de novo assembly are differentially expressed between ovarian stages 1 and 3, suggesting their role in vitellogenesis. The onset of vitellogenesis (synthesis of vitellogenin, the precursor of vitellin) initiates the ovarian development of all oviparous animals. Decapod crustaceans mainly utilize two tissues for vitellogenesis: hepatopancreas and ovary. The hepatopancreas of most crab species is the primary site for vitellogenesis, producing >99.9% of vitellogenin for ovarian development, while the ovary takes up vitellogenin subunits from the hemolymph. It is found using qPCR assay that the hepatopancreas of C. quinquedens also is the main site and provides >99.9% of vitellogenin. The following is then investigated on how the vitellogenin is cleaved into two subunits using a transcriptomic analysis. First, two transcripts are pieced together to obtain the putative 2,570 amino acid vitellogenin protein. Following three subtilisin-like endopeptidases are found in the de novo assembly, potentially cleaving vitellogenin into subunits: trypsin-like serine protease, furin, and proprotein convertase subtilisin/Kexin7. Since the 1970s, the red deep-sea crab has been supporting a small fishing industry in the Atlantic Ocean, mainly harvesting adult males with >94 mm carapace width. However, a recent study reports that there is a reduction in the size of the males. To address the population structure of this species in the future, microsatellite markers are developed using MiSeq data combined with a bioinformatic pipeline. Over 37,000 microsatellites are identified, from which 122 markers are considered for initial PCR testing with a limited number of crabs. Overall, 14 novel, polymorphic microsatellite markers are developed. In conclusion, the reproduction of female C. quinquedens is regulated by eyestalk neuropeptides. With this study, the reproductive role of MIH needs investigating in the decapod crustaceans experiencing an extended intermolt stage. Novel microsatellite markers developed here will assist to study population structure and connectivity that will help towards the conservation of this species facing increasing fishing pressure.