UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item USING AN INDIVIDUAL BASED MODEL TO EVALUATE THE EFFECTS OF CLIMATE CHANGE ON THE REPRODUCTIVE PHENOLOGY OF EELGRASS (ZOSTERA MARINA L.) ALONG A LATITUDINAL GRADIENT(2017) Foley, Jessica Lynn; Harris, Lora A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)I explored the effects of climate change on the reproductive biology of the clonal marine angiosperm Zostera marina L. (eelgrass) using an individual-based model. The model captures whole plant ontogeny, morphology, and ecophysiology from seed to reproductive adult to simulate the plasticity of eelgrass in response to environmental variables. Using a latitudinal gradient as a proxy for climate change, virtual seeding experiments were performed in three locations along the East coast of the United States. I simulated the impacts of increased temperatures on Z. marina’s biomass, reproductive phenology, and life history. Warmer temperatures resulted in a modeled decrease of Z. marina’s total biomass, as well as altered reproductive timing and strategy. These results have implications for long term predictions of Z. marina persistence in its traditional biogeographic range, and indicate adaptation via shifts in phenology and reproductive strategy may interact to dampen some negative consequences of increased temperatures.Item Dynamics of a large submersed plant bed in upper Chesapeake Bay(2016) Gurbisz, Cassie; Kemp, Michael; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A large SAV bed in upper Chesapeake Bay has experienced several abrupt shifts over the past half-century, beginning with near-complete loss after a record-breaking flood in 1972, followed by an unexpected, rapid resurgence in the early 2000’s, then partial decline in 2011 following another major flood event. Together, these trends and events provide a unique opportunity to study a recovering SAV ecosystem from several different perspectives. First, I analyzed and synthesized existing time series datasets to make inferences about what factors prompted the recovery. Next, I analyzed existing datasets, together with field samples and a simple hydrodynamic model to investigate mechanisms of SAV bed loss and resilience to storm events. Finally, I conducted field deployments and experiments to explore how the bed affects internal physical and biogeochemical processes and what implications those effects have for the dynamics of the system. I found that modest reductions in nutrient loading, coupled with several consecutive dry years likely facilitated the SAV resurgence. Furthermore, positive feedback processes may have played a role in the sudden nature of the recovery because they could have reinforced the state of the bed before and after the abrupt shift. I also found that scour and poor water clarity associated with sediment deposition during the 2011 flood event were mechanisms of plant loss. However, interactions between the bed, water flow, and waves served as mechanisms of resilience because these processes created favorable growing conditions (i.e., clear water, low flow velocities) in the inner core of the bed. Finally, I found that that interactions between physical and biogeochemical processes led to low nutrient concentrations inside the bed relative to outside the bed, which created conditions that precluded algal growth and reinforced vascular plant dominance. This work demonstrates that positive feedbacks play a central role in SAV resilience to both chronic eutrophication as well as acute storm events. Furthermore, I show that analysis of long-term ecological monitoring data, together with field measurements and experiments, can be an effective approach for understanding the mechanisms underlying ecosystem dynamics.Item Light available to the seagrass Zostera marina when exposed to currents and waves(2009) McKone, Katie Lynn; Koch, Evamaria W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aquatic organisms are regularly exposed to varying degrees of hydrodynamic forces such as currents and waves. Seagrasses, which are rooted in the sediment, have flexible leaves, allowing them to sway back and forth with waves and deflect with currents. Furthermore, seagrasses can acclimate to local hydrodynamic forces exerted upon them by changing their morphology, which may benefit the organism via reduced drag, but may also bring disadvantages such as increased self-shading. We examined the interaction between water flow and morphology of the seagrass Zostera marina, and how this interaction affects light availability to the plant. We also assessed carbon and nutrient content of Z. marina, as the uptake of these constituents has been linked to hydrodynamic conditions and sediment composition. Our results indicate that local hydrodynamics and sediment composition induce morphological variation in the seagrass Z. marina, and that this variation influences light availability to the seagrass canopy.Item Plant-sediment Interactions and Biogeochemical Cycling for Seagrass Communities in Chesapeake and Florida Bays(2007-12-17) Nagel, Jessica; Kemp, William M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Seagrasses are prominent, productive components of shallow coastal ecosystems worldwide. The role of seagrasses in biogeochemical cycling varies widely across ecosystems, and this is due in large part to the complex interactions and feedbacks among processes controlling dynamics of carbon, oxygen, nutrients, and dissolved organic matter (DOM). This dissertation examines the importance of the keystone seagrass species, Thalassia testudinum, to biogeochemical cycling at the community and ecosystem levels in Florida Bay. The research presented here also describes the consequence of disturbances, such as shifts in species composition and seagrass dieback, on biogeochemical processes in both Florida and Chesapeake Bays. In Florida Bay, T. testudinum was shown to stimulate sediment microbial activities and benthic production of oxygen, inorganic nitrogen, and DOM relative to adjacent benthic communities without seagrass but containing benthic microalgae. Strong diel patterns in net fluxes of these solutes in both communities underscore the importance of photosynthesis. Ecosystem-level production (P) and respiration (R) rates were also enhanced in T. testudinum communities. Clear seasonal and regional variations in P and R were evident across Florida Bay, with lowest rates reported in the northern regions. Seagrass dieback had a negative effect on sediment nitrification rates and net ecosystem production (P-R) at one site in Florida Bay, and loss of seagrass habitat may result in significant changes to biogeochemical budgets within this system. In mesohaline Chesapeake Bay, the ephemeral submersed plant species, Ruppia maritima was also shown to stimulate organic production, nutrient cycling, and sediment biogeochemical processes compared to benthic communities without seagrass; however, the more persistent native species, Potamogeton perfoliatus, had an even greater impact on these processes. Collectively, the results of this research reveal the potential significance of seagrass to biogeochemical cycling in Chesapeake and Florida Bays and suggest that disturbances, such as seagrass dieback or shifts in species composition, may substantially alter biogeochemical budgets within these systems.Item The effect of sea level rise on seagrasses: Is sediment adjacent to retreating marshes suitable for seagrass growth?(2005-12-13) Wicks, Elinor Caroline; Koch, Evamaria W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Salt marsh retreat resulting from sea level rise creates new subtidal substrate (old marsh peat) for seagrasses, which is usually unvegetated. The hypothesis that sediment characteristics of old marsh peat are limiting to <em>Zostera marina</em> was tested in Chincoteague Bay, Maryland and in controlled experiments. A unique aspect of the study site is an eroding dune within the marsh that supplies sand to the subtidal. The organic content and sulfide concentrations of old marsh peat were not limiting <em>Z. marina</em> growth and seagrasses were able to colonize the old marsh peat if a layer of sand covered it. The lack of <em>Z. marina<em/> in old marsh peat may be due to a plant morphology that is highly susceptible to dislodgement. These findings suggest that seagrass distribution may be negatively affected by sea level rise as seagrasses may be unable to migrate shoreward due to unsuitable sediments adjacent to retreating marshes.