UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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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 HYDROLOGIC DRIVERS OF SOIL ORGANIC CARBON STORAGE AND STABILITY IN FRESHWATER MINERAL WETLANDS(2019) Kottkamp, Anna Isabel; Palmer, Margaret; Tully, Katherine; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mineral wetlands comprise most of historic wetland loss, yet few studies focus on mineral wetland soil organic carbon (SOC). We explore SOC across continuous hydrologic gradients within and among seasonally flooded mineral wetlands. First, we quantify SOC stabilization (e.g., organo-mineral associations and aggregates) across a wetland–upland gradient. Second, we examine relationships between hydrologic regime and SOC stocks among wetlands. From wetland–upland, saturation was highly variable in the transition zone. Organo-mineral associations peaked in the transition zone while large macroaggregate SOC declined from wetland–upland. Across wetlands, indicators of drying (e.g., minimum water level and summertime recession rate) were more related to SOC than inundation duration. From wetland basin–upland, SOC stocks were significantly related to both mean water level and relative elevation. We highlight relationships between SOC and the dynamic hydrology of wetlands, emphasizing the need for research on how changing hydrologic regime may influence mineral wetland SOC.Item Marine Community Assembly in a Dynamic Ecotone(2016) Johnston, Cora Ann; Gruner, Daniel S; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Species distributions are shifting with climate change. By altering the presence and distribution of biogenic foundation species, climate change effectively modifies habitat. Where biogenic habitats meet, a patchy ecotone landscape forms. The impacts that range shifts and habitat modification have on broader ecological communities will depend in part on how communities assemble in frontier landscapes of patchy habitat. Here, as a case study, I investigate marine fauna community formation and habitat associations along a wetland ecotone in which tropical mangroves invade temperate saltmarsh. When foundation species shift ranges, resulting changes in geographic context and local conditions will affect the contributions of dispersal limitation and species sorting to assembly. By evaluating the presence of community structure – grouping of species – in larval supply and settlers in each pure landscape and into the ecotone, I determine that ecotone marine communities are shaped by habitat-based sorting but not dispersal limitation. Where inhabitant species can access the ecotone, the attributes that inform habitat use and the scale(s) at which inhabitants distinguish between habitat types within an ecotone should determine the apparency of emerging patches along the range edge, affecting the precision with which inhabitants occupy them. I monitored marine fauna within an experimental array that isolated physical structure from broader habitat patch attributes, revealing that nested scales of habitat sensitivity should result in increasing community divergence as habitat patches expand along the range edge. Finally, habitat associations at settlement may be driven by preference or survival. I determine habitat-specific recruitment patterns of Callinectes spp. (Decapoda: Portunidae) crabs in the ecotone and use lab trials to determine that associations are driven by preference for and superior survival in vegetation with branched architecture. Together, these results demonstrate that marine fauna are sensitive to changes in structural attributes and fine-scale emergence of mangrove habitat within marshes, which do not provide equivalent habitat. This work also contributes to our understanding of community formation in a transitional landscape, illuminating the influence of patchy foundation species expansion on community-structuring ecological processes.Item Assessing Wetland Restoration on the Delmarva Peninsula using Vegetation Characteristics(2015) McFarland, Eliza Katherine; Baldwin, Andrew H; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With wetland restoration, post-restoration monitoring is essential for determining developmental trajectories, particularly when comparing to natural reference systems. As part of the Mid-Atlantic Conservation Effects Assessment Project, 15 depressional wetlands on the Delmarva Peninsula of Maryland and Delaware were surveyed for above-ground vegetation and seed bank community composition, annual biomass production, and vegetation carbon content (10 restorations from prior-converted cropland (aged 5-31 years), and 5 natural forested depressions). Within each wetland, hydrologic zones (emergent, transition, upland) were also denoted and sampled. Restored wetlands showed more seed bank community similarity to natural wetlands than above-ground vegetation communities. Restorations also produced more annual herbaceous biomass than natural systems, and lower annual leaf litter biomass. After this period of post-restoration development, restored wetlands do not perform vegetation-related functions identical to their natural counterparts; however, these restorations are performing important vegetation-based functions that require yet more time to truly develop.Item THE DEVELOPMENT, CALIBRATION, AND USE OF A SPATIO-TEMPORAL MODEL FOR THE DESIGN AND EVALUATION OF CONSTRUCTED WETLANDS BASED ON SUSTAINABLITY METRICS(2014) Olszewski, Jennifer Marie; McCuen, Richard H; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The focus of this research was the development of a spatio-temporal model of a constructed wetland that can be used to evaluate policy elements and design practices from the perspective of wetland sustainability. The model was calibrated with data obtained from a wetland that treats runoff from an agricultural field. Sustainability metrics were developed to reflect an array of wetland functions including wildlife habitat, flood control, downstream hydrologic regime, wetland water balance, groundwater recharge and baseflow maintenance, aesthetics, and water quality functions. The model can be optimized by the user across this array of wetland functions, each of which was defined in terms of metrics relevant to sustainability. Stakeholders will be able to weight the metrics for each of these wetland functions in order to maximize sustainability for their specific goals. Optimally, this model will aid design engineers and policy makers in designing constructed wetlands as a function of necessary functions, location, and influent water quantity and quality characteristics.Item The Impact of Agricultural Wetland Restoration on Adjacent Temporary and Perennial Streams(2013) McDonough, Owen Thomas; Palmer, Margaret A; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wetlands are known for the ecosystem services they provide, including hydrologic storage, sediment retention, nutrient processing, habitat provision, and carbon sequestration. Since European settlement, however, it is estimated that > 50% of wetlands within the conterminous United States have been lost, with a majority of loss attributed to drainage of freshwater wetlands for agriculture. In efforts to offset loss and restore ecosystem services, agricultural wetland restoration has become common. How wetland restoration impacts adjacent stream ecosystem structure and function, however, is poorly understood. Additionally, many freshwater wetlands have historically been considered geographically isolated and disconnected from adjacent surface waters. Recent U.S. Supreme Court rulings have called into question the jurisdictional status of so-called isolated wetlands and non-perennial streams, making investigation of wetland-stream connectivity particularly critical. Comparing native forested, historical (i.e., prior-converted cropland), and hydrologically restored freshwater wetlands within the headwaters of the Choptank River watershed (Delmarva Peninsula, Maryland, USA), I examined the impact of agricultural wetland restoration on within-wetland structure and function and influences on adjacent temporary and perennial streams. In Chapter 1, I present evidence that recently restored wetland soils, although similar to historical wetland soils in physicochemical properties and denitrification potential, may be sediment and nutrient sinks. Chapter 2 shows that so-called isolated Delmarva bay wetlands may in fact be intimately linked to perennial stream networks via temporary stream flow and that land use influences connectivity. In Chapter 3, I investigate the role of temporary stream sediment drying and wetting on denitrification potential in restored and forested wetland-stream pairs and find that alterations in flow regime, a likely outcome of both land use change and climate change, may alter the capacity of temporary streams to denitrify. Chapter 4 considers the impact of cultivation on perennial stream dissolved organic matter (DOM) quantity and quality, and suggests agricultural wetland restoration may be a tool to recover more natural fluvial DOM. Results from this research suggest geographically isolated wetlands may be both hydrologically and ecologically linked to adjacent temporary and perennial streams and that cultivation and subsequent restoration of historical wetlands exerts strong influence on these connections.Item Carbon Storage and Potential Carbon Sequestration in Depressional Wetlands of the Mid-Atlantic Region(2011) Fenstermacher, Daniel E.; Rabenhorst, Martin C; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With recent concern over climate change, methods for decreasing atmospheric levels of greenhouse gasses such as CO2 have been of particular interest, including carbon sequestration in soils that have depreciated levels of carbon from cultivated agricultural crop production. The Delmarva Peninsula contains many Delmarva Bay landforms, which commonly contain wetlands. Five pairs of Delmarva Bays were selected to examine change in carbon stocks following conversion to agriculture and to assess the potential for carbon sequestration if these soils were to be restored hydrologically and vegetatively. A loss of approximately 50 % of the stored soil carbon was observed following the conversion to agriculture. If these agricultural soils were to be restored, the wetland soils within the Delmarva Bay basin are predicted to sequester a total of approximately 11 kg C m-2 and the upland soils of the rim would be expected to sequester a total of approximately 4 kg C m-2.Item Wetland Restoration in Urban Settings: Studies of Vegetation and Seed Banks in Restored and Reference Tidal Freshwater Marshes(2005-12-12) Rusello, Kristin; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study examined the seed bank and vegetation of a restored tidal freshwater marsh located in Washington, D.C. and compared it to an older restored marsh, a natural urban marsh, and a natural non-urban marsh. A study examining the effects of a beaver impoundment on the vegetation and edaphic factors in the natural non-urban reference site was also conducted. The number of seedlings, vegetation cover, taxa density, evenness, and diversity of vegetation were compared among sites in these studies. The restored marshes were more similar to the natural urban wetland than to the natural non-urban wetland with regard to the seed bank and vegetation. Duration of flooding from the beaver impoundment was found to be an important factor affecting vegetation composition at the non-urban reference site. Findings included: urban restoration projects should likely have urban reference sites; and natural disturbances may have similar influences upon both natural and restored systems.Item Hydromorphology of Piedmont Floodplain Soils(2004-05-07) Castenson, Karen Lynn; Rabenhorst, Martin C; Plant Science and Landscape Architecture (PSLA)Alluvial soils situated on middle locations along Mid-Atlantic Piedmont floodplains lack characteristic redoximorphic features that allow them to meet a current field indicator of hydric soil. Although these soils appear to be located in wetlands based on their hydrologic, vegetative, and electrochemical status; there is no hydric soil indicator that accurately includes soils on these landscapes. Two research sites in Maryland and one in Delaware were instrumented along a hydrosequence. Depth to water table, redox potential, and soil temperature were measured. Redox potential measurements of the hydric and possible hydric soil conclude that Fe(III) is predicted to be reduced to Fe(II) for a significant period of time during the growing season. Based on data collected over three years, the possible hydric soil was confirmed hydric. An alternate hydric soil indicator has been proposed for these landscapes.