Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
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 give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Evaluating feedbacks between vegetation and sediment dynamics in Submersed Aquatic Vegetation (SAV) beds and created marshes of living shorelines in Chesapeake Bay(2020) Bolton, Miles Charles; Palinkas, Cindy M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intertidal marshes and subtidal submersed aquatic vegetation (SAV) provide similar ecosystem services such as wave attenuation, provision of nursery habitat, water filtration, and sediment and nutrient retention. They are often found together in the coastal zone, especially when marshes have been created for shoreline protection in living shorelines. This study examines sediment dynamics within the created marshes of living shorelines and adjacent nearshore SAV habitat in mesohaline Chesapeake Bay, and within emergent, patchy SAV beds of the Susquehanna Flats. The naturally occurring radioisotopes 7Be (half-life: 53.3 days) and 210Pb (half-life: 22.3 years) were used to calculate seasonal- and decadal-scale sedimentation rates. Mud content, organic content, and nutrient concentrations were analyzed to describe sedimentary characteristics. Coastal habitats in the Chesapeake Bay exert significant influence on local sediment dynamics, further research on feedbacks between coastal vegetation and sediment dynamics can improve our understanding on how coastal ecosystems interact with Bay-wide shifts in sediment dynamics.Item SUBAQUEOUS SOILS OF CHESAPEAKE BAY: DISTRIBUTION, GENESIS, AND THE PEDOLOGICAL IMPACTS OF SEA-LEVEL ALTERNATIONS(2020) Wessel, Barret Morgan; Rabenhorst, Martin C; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Soils and sediments make up a substantial portion of the resource base that supports human societies and other life on Earth, yet in the subaqueous environment our understanding of these materials pales in comparison to our understanding and management of upland soils. We must develop an understanding of how subaqueous soils/sediments are distributed, how they form and change over time, and how they will be impacted by rising sea-levels as a result of climate change if we are to wisely manage these resources. The goal of this study is to improve this understanding in Chesapeake Bay subestuaries. The Rhode River subestuary was first surveyed to identify rates of bathymetric change in these settings and to characterize the common material types found in these settings. Bathymetric change was evaluated using hydrographic surveys dating back to 1846, and though the river bottom does change slowly, it has been more or less stable during the years evaluated. Several types of morphologically distinct materials make up the soil profiles in Rhode River. Materials highest in organic matter are easy to identify in the field, and commonly become ultra-acidic if disturbed. Also present were submerged upland soils, colored and structured like soils in the surrounding landscape. To better understand the impacts of submergence on these materials, a sampling campaign was conducted on shallow marine sediments, reclaimed land, and restored aquatic environments under both seawater and freshwater. This demonstrated that shallow marine sediments develop upland soil features and biogeochemical characteristics within 150 years of drainage, and that these characteristics do indeed persist in the subsoil two years after submergence. Topsoil changes more radically, releasing anomalous amounts of Fe while accumulating anomalous amounts of reduced S minerals, a process exacerbated by seawater flooding. Using these results, a soil-landscape conceptual model was developed and used to predict subaqueous soil distribution in the West River subestuary. These predictions were evaluated with a sampling campaign, and found to be significant. This model can now be used in other subestuaries to quickly and efficiently survey subaqueous soils, supporting the development of future land-use interpretations in these environments.Item Spatial and Temporal Variability in Suspended Sediment Characteristics in the Surface Layer of the Upper Chesapeake Bay(2020) Barletta, Stephanie Marie; Sanford, Lawrence P; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Periodic high discharge events flush suspended sediments from the Susquehanna River and Conowingo Dam reservoir into the upper Chesapeake Bay, which extends from the mouth of the Susquehanna River to the Bay Bridge near Annapolis, MD. Sediment characteristics in the surface layer of the upper Bay and changes in these characteristics with varying river discharge and distance downstream are not well known. In order to develop an integrated understanding of surface layer sediment dynamics, several in-situ data sets were examined at the Bay head and downstream along the Bay’s center channel, providing data on the spatial and temporal variability of suspended particle characteristics including concentration, settling speed, bulk density, and size. It was found that particles are entirely disaggregated at the Dam, later aggregating to a limited extent down Bay, and that downstream characteristics are more weakly linked to Susquehanna flow at lower flows and longer distances.Item Melt extraction and crustal thickness variations at segmented mid-ocean ridges(2017) Bai, Hailong; Montesi, Laurent G. J.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mid-ocean ridges are underwater volcanic mountains extending more than 55,000 km in ocean basins worldwide, accounting for nearly 80% of the Earth’s volcanism. They are the birthplace of new seafloor, resurfacing two thirds of the planet over about 100 million years. At mid-ocean ridges, tectonic plates move away from each other, a phenomenon known as seafloor spreading, at rates ranging from slow (~10 cm/yr) to fast (~100 cm/yr). Plate divergence induces the underlying mantle to rise and melt. Buoyant melts segregate from the mantle and collect toward axes of mid-ocean ridges, where they are extracted and solidify into new oceanic crust. The thickness of oceanic crust, the final product of ridge magmatism, contains integrated information about plate motion, mantle flow, mantle temperature, melt generation, melt extraction and crustal accretion. In this dissertation, I investigate three types of crustal thickness variations at mid-ocean ridges to provide insights into the Earth’s deep, less accessible interior. Mid-ocean ridges are broken into segments bounded by transform faults. At fast-spreading ridges, transform faults exhibit thicker crust than adjacent ridge segments, while the crust along transform faults at slow-spreading ridges is thinner. I show that these observations are compatible with melt being extracted along fast-slipping transform faults, but not at the slow-slipping ones. The plates on either side of a ridge axis may move away from the ridge at different rates. I reveal a discrepancy between the expected and observed topography at such asymmetrically spreading ridges, and argue that the discrepancy is best explained by asymmetric crustal thickness, with thicker crust on the slower-moving plate and thinner crust on the faster-moving plate. Crustal thickness may differ between ridge segments separated by a transform fault, in a way that correlates with the relative motion between the ridge and the underlying mantle. I study the three-dimensional effects of background mantle flow, and demonstrate that the pattern of along-axis crustal thickness variations is controlled by the relative angle between ridge and background mantle flow. This dissertation systematically examines the origins of crustal thickness variations at mid-ocean ridges, and provides constraints on mantle and melt dynamics.Item CONSTRAINTS ON THE LITHOSPHERIC STRUCTURE OF MID OCEAN RIDGES FROM OCEANIC CORE COMPLEX MORPHOLOGY(2016) Larson, Mark Oscar; Montési, Laurent GJ; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Mid-oceanic ridge system is a feature unique to Earth. It is one of the fundamental components of plate tectonics and reflects interior processes of mantle convection within the Earth. The thermal structure beneath the mid-ocean ridges has been the subject of several modeling studies. It is expected that the elastic thickness of the lithosphere is larger near the transform faults that bound mid-ocean ridge segments. Oceanic core complexes (OCCs), which are generally thought to result from long-lived fault slip and elastic flexure, have a shape that is sensitive to elastic thickness. By modeling the shape of OCCs emplaced along a ridge segment, it is possible to constraint elastic thickness and therefore the thermal structure of the plate and how it varies along-axis. This thesis builds upon previous studies that utilize thin plate flexure to reproduce the shape of OCCs. I compare OCC shape to a suite of models in which elastic thickness, fault dip, fault heave, crustal thickness, and axial infill are systematically varied. Using a grid search, I constrain the parameters that best reproduce the bathymetry and/or the slope of ten candidate OCCs identified along the 12°—15°N segment of the Mid-Atlantic Ridge. The lithospheric elastic thicknesses that explains these OCCs is thinner than previous investigators suggested and the fault planes dip more shallowly in the subsurface, although at an angle compatible with Anderson’s theory of faulting. No relationships between model parameters and an oceanic core complexes location within a segment are identified with the exception that the OCCs located less than 20km from a transform fault have slightly larger elastic thickness than OCCs in the middle of the ridge segment.Item Water Flow and Sediment Texture as Co-Varying Submersed Aquatic Vegetation (SAV) Habitat Requirements(2013) Swerida, Rebecca M.; Koch, Evamaria W; Sanford, Lawrence P; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study examined the importance of water flow and sediment texture as co-varying habitat parameters of submerged aquatic vegetation (SAV) in the Chesapeake Bay. An outdoor mesocosm experiment was conducted to test the response of SAV (Zostera marina and Ruppia maritima) to combinations of water flows and sediment grain sizes characterized by sediment deposition, bedload transport and erosion. Water flow, sediment and SAV characteristics were also determined at vegetated and adjacent unvegetated areas at 11 study sites and sediment motion conditions assessed. Greater SAV biomass was developed by Z. marina and R. maritima experiencing sediment motion than sediment deposition. Although habitat parameter thresholds in situ were site-specific, overall SAV presence was limited to moderate ranges of both water flow and sediment grain size. All SAV habitat observed was characterized by sediment bedload transport. Consideration of both water flow and sediment habitat requirements will improve SAV restoration success.