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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Now showing 1 - 7 of 7
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    THE EFFECTS OF LEAF LITTER MANAGEMENT PRACTICES ON OVERWINTERING INSECT COMMUNITIES AND ECOSYSTEM FUNCTION: IMPACTS AND APPLICATIONS IN RESIDENTIAL LANDSCAPES
    (2024) Ferlauto, Max; Burghardt, Karin T; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Fallen leaf management is a widespread landscaping practice in urban areas that not only influences soil health but also affects the overwintering individuals of subsequent year's aboveground arthropod communities. There has been considerable public and scientific interest in the ecological effects of this disturbance, yet little experimental research making it difficult to provide evidence-based landscaping recommendations to stakeholders. This dissertation aims to narrow this knowledge gap, provide information for the creation of best management practices, and encourage further research on this critical topic. In Chapter 2, I compare spring arthropod emergence in residential areas where fallen leaves were removed or retained across different levels of maintenance intensity. In Chapter 3, I focus on the legacies of long-term leaf removal to soil organic carbon dynamics. And in Chapter 4, I examine the efficacy of alternative leaf management practices—such as shredding and leaf piling—on soil microclimates, arthropod biodiversity, and decomposition rates while exploring if tree canopy diversity mitigated impacts to these ecosystem functions. The results of these three experimental studies were consistent across years and habitat types. Leaf removal reduced the spring emergence of Lepidoptera by about 35-45% and reduced spiders by about 50-67%, altered parasitic wasp community composition, reduced soil moisture and temperature buffering, and ultimately led to legacy effects in the soil of reduced decomposition and soil organic carbon. The context in which leaves were managed also mattered, as unique resources attracted overwintering arthropods more when they were scarce in the environment. Despite the potential for high plant diversity in leaf-managed areas to create ecosystem traps for arthropods, tree diversity actually mitigated some negative effects of fallen leaf disturbance to ecosystem function. Overall, I find that some practices like leaf removal and shredding degrade ecosystem processes while others like piling leaves and planting a diverse tree canopy can support ecosystem services. This dissertation is the first to quantify the ecological impacts of leaf management as an urban disturbance and addresses critical questions necessary for developing urban best management practices.
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    Modulus Based Compaction Quality Assurance for Unbound Materials Using Lightweight Deflectometer
    (2019) Afsharikia, Zahra; Schwartz, Charles W; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Moving away from traditional density-based methods of compaction quality assurance (QA) towards modulus-based procedures using Light Weight Deflectometer (LWD) require developing practical framework to: (1) determine soil- specific LWD target modulus, and (2) evaluate LWD modulus in the field effectively. This dissertation draws upon work from two research studies, TPF-5(285) pooled fund study and pilot projects conducted by Maryland State Highway Administration to refine the two proposed QA specifications for road base, subgrade, and embankment construction. The practical method of establishing the target modulus based on LWD drops on compacted Proctor molds was proposed and evaluated. Three types of LWDs (Zorn ZFG3000, Olson LWD-01, Dynatest 3031) were utilized and their field to target modulus ratio was compared to the percent compaction as a criterion for goodness of compaction. Results confirmed the validity of procedures for the variety of geomaterials tested and suitability for practical implementation by field inspection personnel. Target modulus values, calibrated acceptance criteria, sampling method, and frequency is presented for future implementation in the state of Maryland and other state DOTs. The LWD manufacturers collaborated to facilitate the implementation by instrument design and improvement or software/application development.
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    PARAMETRIC STUDY OF SOIL DRYING IN THE FIELD FOR COMPACTION QUALITY ASSURANCE
    (2017) Afsharikia, Zahra; Schwartz, charles W.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Moving towards modulus based methods of soil compaction quality assurance using lightweight deflectometers (LWD) requires evaluation of the LWD measured modulus in the field. The resilient modulus of geomaterials is not only influenced by the moisture content (MC) at the time of compaction, but also by the MC at the time of testing, which may be up to few hours after compaction. A parametric study was performed using SoilVision’s SVFlux analysis package to model the variation of soil moisture profile with depth versus time as a function of environmental factors. Then the drying in a compacted soil layer was modeled and compared to the volumetric water content measurements in an instrumented large-scale test pit. Finally, LWD modulus values in the field were captured immediately and a few hours after compaction to exhibit the variation of modulus with time and to identify if the stiffness gain in geomaterial is significant.
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    Soil microbial processes and community structure in natural and restored tidal freshwater wetlands of the Chesapeake Bay, Maryland, USA
    (2017) Maietta, Christine E.; Yarwood, Stephane 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 integral to downstream water quality because they capture, store, and transform nutrients. Unfortunately, anthropogenic stressors are negatively impacting these habitats. While wetland restoration is helping to reinstate their presence in the landscape, restored wetlands frequently differ physically, chemically, and biologically from their natural counterparts. This research examined plant, soil, and microbe relationships and how their interactions affect soil carbon (C) storage and cycling in natural and restored tidal freshwater wetlands of the Chesapeake Bay, MD, USA. This research yielded important findings regarding differences between natural and restored habitats. First, we discovered soil microbial community composition of an urban tidal freshwater wetland retained similar composition as their less disturbed, suburban counterpart, and wetland sites constructed using similar restoration methodology produced similar microbial community structure and soil function. Additional research revealed that a natural and a restored wetland store soil C quite differently: A majority of soil C in the natural site was associated with large macroaggregates (> 2000 μm) whereas most soil C in the restored site was associated with smaller macroaggregates (> 250 to < 2000 μm). The distributions of six chemical compound classes (i.e., carboxylics, cyclics, aliphatics, lignin derivatives, carbohydrates derivatives, N-containing compounds) were relatively similar across the five soil fractions from both sites, however. In the final study, anaerobic laboratory mesocosms were used to evaluate the effects of clay content (%) and leaf litter quality on soil C cycling processes over time. This study found restored soils, regardless of clay content, mineralized more C as carbon dioxide (CO2) and methane (CH4) compared to natural wetland soils. Natural soils respired approximately half the volume of gas as restored soils, suggesting the addition of high- or low-quality C substrates to low C systems elicit a greater response from the heterotrophic microbial community. The results of these three studies suggest site history and edaphic features of restored wetlands are important drivers of microbial communities and their function. We propose that practitioners and researchers work together to identify practices that will enhance soil functions, particularly C storage, in tidal freshwater wetlands of the Chesapeake Bay region.
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    Classical Tragedy in Contemporary Violence: Writing, Devising, and Performing "Sacred Soil"
    (2013) Demke, David Michael; Felbain, Leslie; Theatre; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    "Sacred Soil" is a play about a young man's search for redemption. It poses the question of whether or not we can be redeemed by violent means. It is the story of the young man's struggle to make sense of the violence that is around him and a part of him set against the backdrop of the harsh and beautiful North Dakota landscape. This backdrop provides a mirror for the complexities and paradoxical truths at play in the human condition, revealing the fundamental tragedy within contemporary violence. Echoes of Classical Greek tragedy are heard throughout the play, as the young man discovers his fate, and the question of redemption is left unanswered.
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    Redox and Soil Manipulation Effects on Ditch Soil Phosphorus Processing
    (2012) Ruppert, David Emmanuel; Needelman, Brian A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Ditches increase the connectivity of landscapes to open water systems, potentially facilitating the degradation of downstream waterways. A treatment and an observational experiment were conducted to identify processes behind phosphorus (P) cycling in ditch soils. If the ditch had not undergone recent dredging soils were observed in the treatment experiment to release P to surface water whether the soil system was iron (Fe)-oxidizing or Fe-reducing. Also in the treatment experiment, Fe was released to surface water in appreciable amounts only if the soil system was Fe-reducing. From the observational experiment P release due to mineralization was inferred due to a positive trend with temperature. Also in the observational experiment Fe-reducing conditions were weakly correlated with diminished P concentrations in the ditch water. It was inferred that emergent Fe(II) released from within the soil through reductive dissolution captures P from ditch surface water upon oxidation. In the treatment experiment dredging and saturated conditions resulted in similar effluent P concentrations as drained soils that were undredged. This may explain a lack of dredging effect that was observed in the field.
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    Oxidation-Reduction Transformations of Chromium in Aerobic Soils and the Role of Electron-Shuttling Quinones in Chemical and Microbiological Pathways
    (2008-05-05) Brose, Dominic; James, Bruce R; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Soils from three toposequences in Maryland with minimal heavy metal contamination were sampled to investigate oxidation-reduction transformations of chromium in whole soil samples. Chromium (VI) reduction to Cr(III) was observed in all 18 samples, and 11 demonstrated enhanced reduction with the electron shuttle anthraquinone-2,6-disulfonate (AQDS). Oxidation of Cr(III) to Cr(VI) was observed in 12 samples, and 7 samples demonstrated diminished oxidation with AQDS. Lactate was added to the Watchung series to enhance biological activity, and high salt concentration was added to inhibit it. Both treatments reduced Cr(VI) to below detection limits by 11 d, suggesting abiotic reduction. The control treatment demonstrated reduction of Cr(VI) without soil. To further investigate, increasing lactate concentrations were added to Cr(VI) and AQDS. Reduction increased with increasing concentration; 60 mM lactate reduced all Cr(VI) within 1 hr. Other organic acids were tested for similar interactions; tartrate and citrate reduced Cr(VI), which was enhanced with AQDS.