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.
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Item QUANTIFYING EFFECTS OF SEASONAL INUNDATION ON METHANE FLUXES FROM FORESTED FRESHWATER WETLANDS(2021) Hondula, Kelly Lynn; Palmer, Margaret A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Developing effective strategies for reducing methane and other greenhouse gas emissions requires a quantitative understanding of their global sources and sinks. Decomposition of organic matter in wet soils is one of the largest sources of methane to the atmosphere, but it is a highly variable process that remains difficult to quantify because we lack a predictive understanding of how environmental factors control methane emissions in wetlands. Hydrology is one of the most important factors controlling methane production wetlands along with temperature and vegetation, however it is unclear how to relate aspects of a wetland’s hydrologic regime to the timing, magnitude, and spatial extent of its methane emissions. Furthermore, discrepancies between the magnitude of global methane emissions calculated using different techniques indicate that current methods for measuring the extent and dynamics of wetland areas in global models may not adequately represent processes controlling methane cycling in wetlands and other small water bodies. I studied the role of seasonal hydrologic variability on methane emissions from forested mineral soil wetlands to inform modeling techniques at different scales. In Chapter 1, I show the importance of inundation extent and duration as major drivers of wetland methane emissions, that methane fluxes have a non-linear relationship with water level, and that methane fluxes are higher when water levels are falling rather than rising. In Chapter 2, I demonstrate a new technique for calculating methane emissions using high resolution satellite data to quantify wetland inundation time series, and some limits of current technology for modeling surface water dynamics in forested wetlands. Chapter 3 presents and applies a modeling framework for quantifying hydrologic fluxes of methane in the context of common forms of wetland restoration In combination, these studies establish how and why quantifying the hydrologic regime of seasonally inundated forested wetlands enables a more accurate estimation of methane emissions at multiple scales, that water level drawdown associated with the natural hydrologic regime of forested wetlands considerably reduces methane producing areas, and that improved methods for detecting and modeling surface water dynamics in low relief landscapes will improve our ability to quantify methane emissions.Item The City Symbiotic: Integrating Architecture and Hydrology in the Public Realm(2021) Piltz, Shayne Michelle; Bell, Matthew J; Hendricks, Marccus; Architecture; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis approaches climate resilience through a comprehensive urban-scale system that incorporates integrated stormwater management to address sea-level rise and urban flooding, while leveraging the power of community as a tool for environmental stewardship. The City Symbiotic has dual notions. At its core, the concept alludes to a mutually beneficial relationship between the built and natural environment. This thesis will be an exploration of designing with water through the lens of climate resilience. Built structures will incorporate an integrated stormwater management network for capturing, filtering, storing, and reusing water, bettering our understanding of the symbiotic relationship between the built and natural environment by blurring the line between the two. The City Symbiotic is also a reference to the relationship between people and their environment. In this respect, this thesis approaches climate resilience through community and connection. Climate change exacerbates existing vulnerabilities that are the result of historical planning failures like Euclidean and exclusionary zoning, urban disinvestment, car-centric planning, environmental racism, and displacement. Reimagining the civic commons as a more inclusive and resilient center of public life can help redress marginalization and inspire environmental stewardship. The outcome of this thesis will demonstrate the value of symbiotic urban design, connecting the built, natural, and human environments to build resilience to water-related impacts of climate change.Item WARM SEASON HYDROLOGIC PROCESSES IN A BOREAL FOREST HILLSLOPE AND CATCHMENT, NEWFOUNDLAND(2020) Talbot-Wendlandt, Haley; Prestegaard, Karen; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Prior investigations into boreal forest ecosystems have examined hydrological processes on plot scales, examining factors such as precipitation, soil characteristics, tree rooting depths, evapotranspiration, infiltration, and groundwater, or on the catchment scale, investigating factors such as stream discharge and water chemistry. In this study, I examine hydrological processes at both plot and catchment scales, with the goal of understanding how rooting depths influence evapotranspiration (ET) and the effects of ET on catchment discharge and water chemistry. Evapotranspiration was found to influence seasonal and diurnal fluctuations in groundwater table, stream discharge, and stream electrical conductivity. Tree rooting depths were shallow, primarily within O and Ae soil horizons, suggesting that these trees intercept infiltrating water, reducing summer groundwater recharge. Stream electrical conductivity increased with cumulative ET. Summer streamflow minima coincided with hillslope groundwater minima. Stream depth and conductivity exhibited similar diurnal patterns, suggesting variations in groundwater contributions and opportunities for future research.Item Geomorphic, hydraulic, and biogeochemical controls on nitrate retention in tidal freshwater marshes(2012) Seldomridge, Emily; Prestegaard, Karen; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal freshwater wetlands are ideal sites for nitrate retention because of their position within the landscape (near the head of tide); they receive water, discharge, nutrients (N and P), and sediment loads directly from contributing watersheds. Nitrate retention (the difference between nitrate inputs and outputs in an ecosystem), however, is difficult to predict due to the complex interactions between flow processes and the multiple retention processes. The goal of the study was to evaluate both external and internal controls on nitrate retention, and to determine whether scaling procedures could be identified to estimate nitrate retention for an entire ecosystem. The external controls included temperature, dissolved oxygen concentrations, and incoming nitrate concentrations. Internal controls are the interactions among geomorphic, hydrologic, and biological systems within individual marshes that influence nitrate retention. This study was conducted in the upper Patuxent River Estuary where the ecosystem is composed of hundreds of individual marshes that are connected to the estuary through tidal inlets; marsh inlet geomorphology governs water and nitrate fluxes into the marshes. This study therefore took a mass balance approach to determine geomorphic, hydrologic, and biological influences on nitrate retention. Nitrate retention was measured over a 4-year period in three tidal freshwater wetlands, selected to represent a range of marsh sizes. An examination of the mass balance data suggest that nitrate retention is an outcome of complex interactions among inlet geomorphic characteristics, hydrologic flux, and biogeochemical processes. In cases where nitrate concentrations and temperatures are greater than critical (limiting) values, an emergent behavior in which nitrate retention is a simple function of water volume is observed. The wetland ecosystem is composed of numerous, small wetlands that process a small percentage of total nitrate; approximately 50% of retention is processed by the large marshes that comprise only 4% of the total population, but over 80% of the marsh area; therefore, any processes that affect tidal water volumes in large marshes is likely to affect net nitrate retention. The growth of vegetation in these large channels reduced ecosystem nitrate retention.Item Redefining the ORILLA: community awareness at the water's edge in Baltimore(2012) Kelley, Joyce; Chanse, Victoria; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis proposes a redesign of a waterfront park in South Baltimore, Maryland. Middle Branch Park, located one mile south of Baltimore's Inner Harbor, offers a unique opportunity to restore a degraded shoreline in the context of watershed stewardship. This thesis strives to reestablish Middle Branch as a functional critical buffer within the urban fabric of Baltimore city by utilizing shoreline restoration techniques, stormwater management and floating wetlands. The issues of water quality within the Middle Branch and the surrounding area are reflected in the design decisions. The design focuses on visualizing the hydrology of water in the landscape and creates opportunities for people to be within the water-landscape. Moreover, within this design the dynamic overlap of water and land is used as design tool to interconnect education, health and community within the new park design.Item Impacts of Climate Change Variables on Mosquito Competition and Population Performance(2011) Smith, Cassandra Dionne; Leisnham, Paul; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rising CO2 concentrations and the resulting shifts in hydrology can have direct and indirect impacts on organisms and communities. The system studied was aquatic container habitats, where mosquito larvae often compete for food resources. I hypothesized that elevated atmospheric CO2 concentrations (Chapter 2) and extreme precipitation regimes (Chapter 3) would alter leaf chemistry and competition between two locally competing mosquito species, Aedes albopictus and Aedes triseriatus in laboratory microcosm experiments. In Chapter 2, tannin concentration was higher in leaves grown under elevated CO2 conditions than ambient, but competition was not affected. A two-fold increase was observed in leaf biomass in the elevated CO2 chamber, and increasing leaf litter to a container system could increase toxicity to mosquito larvae. In Chapter 3, simulated drought conditions decreased leaf decay rate and increased tannin concentrations compared to continuously wet and wet-dry leaves, and amplified the competitive effects of Ae. albopictus on Ae. triseriatus.Item Interregional differences in stream ecosystem responses to urbanization: causes and consequences(2010) Utz, Ryan Michael; Hilderbrand, Robert H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stream ecosystems are profoundly degraded by watershed urbanization. Hydrologic, geomorphic, chemical and thermal adjustment following urban development contributes to substantial biodiversity loss in impacted streams. However, the extent of degradation along an urban gradient may not be uniform among regions. The hydrogeologic and climatic setting in which a stream is located may influence the severity of abiotic and biotic impact induced by urban development. I explored and compared differences in stream ecosystem responses to urbanization between the Coastal Plain and Piedmont physiographic regions of the eastern United States. Taxon-specific responses of fishes and macroinvertebrates as well as the coherence of benthic invertebrate communities along gradients of landscape stressors were quantified. Hydrologic, chemical and thermal impact induced by watershed urbanization was compared between the two physiographic provinces using existent large datasets collected by various governmental entities. I also compared the severity geomorphic and sediment regime alteration in urban streams between regions using direct measurements of channel morphometry and in situ natural experiments within selected watersheds. Biotic sensitivity to urbanization was consistently found to be heightened in Piedmont streams relative to those in the Coastal Plain. Such trends were consistently observed for fish and macroinvertebrate taxa as well as for invertebrate community coherence. The most tolerant macroinvertebrate communities were associated with low channel slopes, effective soil permeability and high levels of wetland cover. Rural Coastal Plain streams exhibited fewer flood events that were longer in duration; however, flood hydrology was more impacted by urbanization in Coastal Plain streams relative to those of the Piedmont. Conversely, thermal impact induced by urbanization was greater in Piedmont streams. Experimental observations concluded that benthic sediment size structure, deposition and transport were more impacted by urban development in Piedmont streams relative to those of the Coastal Plain. My findings highlight interregional heterogeneity in stream ecosystem responses to landscape change, suggesting that effective watershed management decisions may need to consider the physiographic setting in order to improve efficacy. Furthermore, results suggest that watersheds characteristic of hydrogeomorphic attributes that effectively transfer water to channels during precipitation events may be acutely vulnerable to urban development.Item Importance of channel networks on nitrate retention in freshwater tidal wetlands, Patuxent River, Maryland(2009) Seldomridge, Emily Dawn; Prestegaard, Karen; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Freshwater tidal marshes border stream channels near the upstream end of the tidal limit, and are likely to undergo significant changes in salinity, tidal inundation, and biogeochemical processes due to sea-level rise. Tidal channel networks enhance nutrient processing by delivering nitrate-rich water far into the marsh. The purpose of this study is to examine the geomorphological, hydrological, and biogeochemical processes that influence the delivery and processing of nutrient-rich waters into tidal marshes. In this study, field measurements were made to calculate water and nitrate flux for stream channels of varying order. These mass balance calculations indicate there is an exponential increase in net nitrate retention with channel order. This calculation could be compared with calculations of denitrification at different sites within the system to evaluate the role of these processes in total nitrate loss.Item RADAR MONITORING OF HYDROLOGY IN MARYLAND'S FORESTED COASTAL PLAIN WETLANDS: IMPLICATIONS FOR PREDICTED CLIMATE CHANGE AND IMPROVED MAPPING(2005-08-05) Weiner Lang, Megan; Kasischke, Eric; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wetlands provide important services to society but Mid-Atlantic wetlands are at high risk for loss, with forested wetlands being especially vulnerable. Hydrology (flooding and soil moisture) controls wetland function and extent but it may be altered due to changes in climate and anthropogenic influence. Wetland hydrology must better understood in order to predict and mitigate the impact of these changes. Broad-scale forested wetland hydrology is difficult to monitor using ground-based and traditional remote sensing methods. C-band synthetic aperture radar (SAR) data could improve the capability to monitor forested wetland hydrology but the abilities and limitations of these data need further investigation. This study examined: 1) the link between climate and wetland hydrology; 2) the ability of ENVISAT SAR (C-HH and C-VV) data to monitor inundation and soil moisture in forested wetlands; 3) limitations inherent to C-band data (incidence angle, polarization, and phenology) when monitoring forested wetland hydrology; and 4) the accuracy of forested wetland maps produced using SAR data. The study was primarily conducted near the Patuxent River in Maryland but the influence of incidence angle was considered along the Roanoke River in North Carolina. This study showed: 1) climate was highly correlated with wetland inundation; 2) significant differences in C-VV and C-HH backscatter existed between forested areas of varying hydrology (uplands and wetlands) throughout the year; 3) C-HH backscatter was better correlated to hydrology than C-VV backscatter; 4) correlations were stronger during the leaf-off season; 5) the difference in backscatter between flooded and non-flooded areas did not sharply decline with incidence angle, as predicted; and 6) maps produced using SAR data had relatively high accuracy levels. Based on these findings, I concluded that hydrology is influenced by climate at the study site, and C-HH data should be able to monitor changes in hydrology throughout the year. Larger incidence angles should be explored when using C-HH data to monitor forested wetland hydrology, and C-band SAR has the potential to increase the ability to map forested wetlands throughout the year. The methods developed have the potential to fill the need of managers for increased hydrologic information and improved forested wetland maps.Item Characterization of the spatial differences in hydrological functioning in a tidal marsh, Patuxent River, MD: A framework for understanding nutrient dynamics(2004-12-08) Phemister, Karen; Prestegaard, Karen L.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study investigates spatial variations in sediment hydraulic conductivity (K), network channel shape and horizontal groundwater flux magnitude toward tidal network channels in a freshwater tidal marsh. Results showed the average value of K at zero meters from the creekbank was significantly higher than the K at both 5 and 15 meters from the network channel creekbank. Creekbank gradient did increase with increasing distance from the main channel and some data indicated that channel width-to-depth ratio (F), which is inversely related to creekbank gradient, correlates well with K. In addition, horizontal groundwater flux magnitude at a depth of 11 cm was significantly greater than flux magnitude at 22 cm below the ground surface at the first-order network channel location. Horizontal flux magnitude was also significantly higher from 5 to 0 meters than from 15 to 5 meters from the network channel creekbank at both the first- and second-order channel locations.