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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    ECOLOGICAL SIGNIFICANCE OF DISSOLVED ORGANIC MATTER COMPOSITION AND REACTIVITY IN DEPRESSIONAL FRESHWATER WETLANDS
    (2022) Armstrong, Alec William; Palmer, Margaret; Gonsior, Michael; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Dissolved organic matter (DOM) plays a central role in the biogeochemistry of aquatic ecosystems and is an important flux of carbon (C) from terrestrial to aquatic systems. Wetlands are rich sources of DOM to downstream waters, but the origins of wetland DOM and its role in biogeochemical processes in wetlands and downstream are not fully understood. To better understand the role of wetlands in mediating the movement and transformation of organic matter between terrestrial and aquatic ecosystems, I characterized the chemical composition and the microbial and photochemical reactivity of wetland DOM in a depressional wetland setting in the interior Delmarva Peninsula. I used laboratory experiments to understand DOM reactivity. I characterized sensitivity to photodegradation, concluding most wetland DOM was somewhat sensitive though site differences affected sensitivity. In another experiment, wetland DOM showed little biodegradability, but C losses to microbes were enhanced after photodegradation. This suggested photochemical and biological degradation may have interacted to influence wetland DOM composition within wetlands and in downstream waters. I also found terrestrial sources of DOM (plant and soil leachates) were more biodegradable than wetland surface water. I concluded wetland DOM was largely comprised of leftover material from previous microbial metabolism in soils or wetland water. To characterize wetland DOM and explore its environmental influences, I undertook a field sampling campaign of 22 wetlands over 18 months. Samples were characterized using a suite of DOM measurements, and variability in these data was modeled using water level, regional air temperature, a proxy for site canopy cover, estimated photosynthetically active radiation, and others. DOM varied considerably seasonally and among sites, and modeling suggested that complex seasonal and site-related interactions influenced DOM, not including water level. This research indicates that depressional freshwater wetlands accumulate and process DOM, some of it likely originating from soils and some within wetlands, but spatial and seasonal variability lead to DOM variability. Wetland DOM exported to downstream waters has intrinsically low biodegradability, though this may be enhanced by photodegradation downstream. This research may be useful for efforts to improve representation of depressional freshwater wetlands in mineral soils in C cycle models and inform policy concerned with wetland biogeochemical functions and connections with downstream waters.
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    Evaluation of the Effects of Bioaugmentation and Biostimulation on Natural Attenuation and Biodegradation Pathways of Chlorinated Compounds in a Tidal Wetland
    (2006-12-12) Devillier, Emily Nicole; Becker, Jennifer G; Biological Resources Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The usefulness of bioaugmentation and biostimulation in enhancing the natural attenuation of chlorinated compounds at a seep site at Aberdeen Proving Ground, MD was tested. The biodegradation of (1) a mixture of 1,1,2,2-tetrachloroethane, tetrachloroethene, and carbon tetrachloride, or (2) TeCA alone was compared in microcosms amended with chlorinated substrates alone, chlorinated substrates and electron donor, and chlorinated substrates, electron donor, and a TeCA-degrading enrichment culture. A third experiment evaluated the usefulness of H2 thresholds in determining the importance of co-metabolic and metabolic processes in biodegradation. TeCA biodegradation was significantly enhanced by bioaugmentation and biostimulation. However, the presence of other contaminants inhibited TeCA biodegradation, even in the presence of electron donors and the enrichment culture. H2 thresholds did not prove useful in determining the importance of metabolic and co-metabolic processes; however, evaluating each chlorinated compound individually provided insight regarding biodegradation pathways and the effects of electron donor substrates on degradation rates.