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.
Browse
6 results
Search Results
Item Anthropogenic disturbance alters plant and microbial communities in tidal freshwater wetlands in the Chesapeake Bay, USA(2019) Gonzalez Mateu, Martina; Yarwood, Stephanie A; Baldwin, Andrew H; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal freshwater wetlands are often found near urban centers, and as a result of human development they are subject to multiple environmental stressors. Increases in nutrient runoff, sedimentation, and hydrologic alterations have had significant impacts on these systems and on the ecosystem services they provide. One of the consequences of these stressors is the expansion of invasive species that can affect native biodiversity and the many biogeochemical processes that are key to wetland ecosystem function. This research looked at how human activities affect microbial communities in tidal freshwater wetlands, and explored various aspects of an invasive plant’s ecology in the Chesapeake Bay. In our first study, we found that microbial community composition differed along a rural to urban gradient and identified microbial taxa that were indicators of either habitat. Rural sites tended to have more methanogens and these were also indicators in these system, whereas in urban systems nitrifying bacteria were the main indicator taxa. This study suggested that urban wetlands have different microbial communities and likely different functions than those in rural areas, particularly concerning nitrogen and contaminant removal. Our second study looked at management of an invasive lineage of Phragmites australis which is commonly found in wetlands impacted by nitrogen enrichment. We evaluated the effects of different C:N ratios on the competitive ability of this lineage and a native North American lineage. Even though carbon addition did not improve the native’s competitive ability, we identified facilitative interactions when both lineages were growing together. This suggests that native and invasive Phragmites might coexist if there are no additional disturbances to the system. Our last study focused on plant-fungal interactions, and found that both Phragmites lineages benefitted from inoculation with fungal endophytes under salt stress. These results suggest that studies of plant-fungal interactions can yield insights into mechanisms of invasion, and could be further investigated in native wetland plants susceptible to increased salt stress following sea-level rise. Our results provide insights into plant and microbial ecology in the Chesapeake Bay’s tidal freshwater wetlands, and improve our understanding of the invasion process and management strategies of Phragmites australis.Item EFFECTS OF THE INVASIVE PHRAGMITES AUSTRALIS ON THE PREDATION OF MOSQUITOES THROUGH CHANGES IN HABITAT COMPLEXITY(2019) Weeks, Virginia Lynn; Leisnham, Paul; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ephemeral stormwater ponds in the eastern United States are often invaded by non-native Phragmites australis which has been associated with numerous negative impacts on resident systems, including changes in hydrology, displacement of native macrophytes, and degradation of wildlife habitat. Few studies have documented the impacts of invasive P.australis on macroinvertebrate communities. Vegetated edges of stormwater retention facilities are often important developmental habitat for medically significant mosquitoes and the invertebrate predators that regulate their abundances. The displacement of resident macrophytes by P.australis could alter the physical structure of pond vegetation and disrupt the interactions between mosquitoes and their visual predators. The overall goal of my thesis was to evaluate differences in habitat complexity between native macrophytes, T.latifolia and J.effuses, and P.australis, and explore how those differences may impact predation of mosquitoes. I addressed this goal by conducting a controlled laboratory predation experiment and field surveys of four stormwater ponds.Item Effects of Phragmites australis (Common Reed) Invasion on Nitrogen Cycling, Porewater Chemistry and Vegetation Structure in a Brackish Tidal Marsh of the Rhode River, Maryland(2015) Meschter, Justin; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Phragmites australis is one of the most widespread invasive species in wetland habitats of North America. Conversion of existing wetland ecosystems to Phragmites-dominated communities decreases overall plant diversity and alters biogeochemical cycles, which can negatively affect ecosystem processes. Previous studies demonstrated that Phragmites has a significantly greater above-ground nitrogen demand than native plants, likely due to its greater biomass. To evaluate how invasion by Phragmites alters standing stock nitrogen, I measured above- and below-ground biomass and nitrogen stocks in both the invasive and native plant communities to examine how Phragmites is meeting its documented increased nitrogen demand in the Rhode River, a sub-estuary of the Chesapeake Bay in Edgewater, Maryland. I also quantified deep N uptake using a 15N tracer study. I found that Phragmites roots significantly deeper than native marsh grass communities and has the ability to utilize deeper nitrogen pools and take up nitrogen from deeper depths. This enhanced rooting structure gives the invasive Phragmites the ability to potentially access lower salinity water, as well as tap nutrients unavailable to native marsh plant communities.Item A Competitive Interaction and Dominance Experiment Between the Vegetative Marsh Species Phragmites australis and Spartina Cynosuroides Under Elevated Nitrogen and Salinity Levels(2013) Arthur, Michelle Lynn; Baldwin, Andrew; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In recent decades the invasive plant Phragmites australis (common reed) has spread throughout Chesapeake Bay marshes, lowering plant community biodiversity. Excess nutrient loading and salinity intrusion due to sea-level rise make these marshes vulnerable to invasions. This study examined the interaction between Phragmites australis and the native Spartina cynosuroides (big cordgrass) to determine whether dominance of one species was detected across a range of salinity and nitrogen treatments. Aboveground biomass production of P. australis was greater than S. cynosuroides at lower salinities; however, S. cynosuroides maintained biomass production as salinity increased. Fv/Fm ratios were measured as an indirect measurement of plant tissue physiological health; only Spartina maintained the ratio at higher salinities. Nitrogen addition increased Phragmites biomass and Fv/Fm ratio at higher salinities. Results suggest salinity and nitrogen interactively affect Phragmites biomass production, and that the negative effect of increased salinity on Phragmites spread can be mitigated by nitrogen runoff.Item Plant Biomass Allocation and Competitive Interactions in Coastal Wetlands of the Chesapeake Bay: Experimental and Observational Studies(2011) Clark, Jenna; Baldwin, Andrew H.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wetlands are diverse environments whose vegetation provides numerous natural services including flood and erosion control and excess nutrient absorption; however conditions created by sea level rise and nutrient pollution could lead to possible wetland loss. To assess the responses of vegetation in these conditions in the Chesapeake Bay tidal wetlands, an observational study and a competition greenhouse study were conducted. An aboveground to belowground biomass relationship assessment was done along a salinity gradient within a subestuary of the Chesapeake Bay. The competition study focused on the relationship between a native and a non-native species in the aforementioned conditions. These studies revealed Phragmites australis had more biomass and lower rooting depths than the native Spartina cynosuroides under varying conditions of salinity, competition, and fertilization. Growth of S. cynosuroides may facilitate the growth of P. australis through salinity uptake and root aeration, which could have important impacts on wetland management practices.Item GRAZING AS A MANAGEMENT TOOL FOR CONTROLLING PHRAGMITES AUSTRALIS AND RESTORING NATIVE PLANT BIODIVERSITY IN WETLANDS(2010) Brundage, Jennifer Emilienne; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study examined the feasibility of grazing as a sustainable and low-impact means of controlling Phragmites. In addition, this study examined whether grazing of Phragmites by large herbivores (goats) in a wetland affects soil and soil water nutrient pools, and thus how grazing might affect nutrient export from the wetland. An isolated, created wetland at USDA's Beltsville Agricultural Research Center (BARC) in Beltsville, MD was divided into four grazed and four ungrazed plots. Two rounds of grazing significantly reduced Phragmites height, stem count, and biomass and increased some measures of plant diversity. Grazing significantly elevated soil water total nitrogen and total phosphorus levels and reduced soil water-soluble phosphorus levels. The nutrient pool analysis indicates that grazing reduced the fertility of the system. The results of this study will inform the development of an alternative, sustainable approach to controlling Phragmites that integrates the local agricultural community while benefiting the local ecology.