Environmental Science & Technology Theses and Dissertations

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    (2023) Shdaimah, Elad; Pavao-Zuckerman, Mitchell A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The effects of invasive plants on forest ecology and nutrient cycling are highly variable and poorly understood. Many studies have found that species and location make each plant invasion unique. Thus, studying invasive plants on the species and local level is necessary to understand how they impact ecosystems and how to manage them. Ninety-four percent of forest patches in Baltimore contain invasive plants. Hedera helix is one of the most prominent. My study explores how different characteristics and intensities of H. helix invasion impact ecology and nutrient cycling in Baltimore forest patches. I analyzed canopy structure, litter properties, soil properties, and steps of C and N cycling in forest patch plots. I compared findings across the invasion characteristics: presence, canopy invasion intensity, and ground cover presence. My study revealed that invasion characteristics and location strongly influence the impact of H. helix on Baltimore forest patch plots. The presence of ground cover appeared to be dictated by soil hydrology, which varied by location. Invaded plots with ground cover had significantly altered soil properties, increased soil respiration rates (2.86 times greater than control plots, p = 0.047), and may have increased decomposition rates. These differences in C cycling metrics appear to be driven by altered soil temperature, structure, and chemistry (i.e., 1.62 times more TN than control plots, p = 0.022). Canopy invasions may have caused tree loss and altered canopy structure, which indicate potentially negative consequences for forest patch ecology in the future. pH may have been higher in the presence of H. helix (1.17 times higher pH than control plots, p = 0.090). Several ecological characteristics and nutrient cycling variables may have also been more variable in the presence of H. helix. No significant differences were detected in N cycling due to invasion. These findings can help Baltimore forest patch managers to assess problematic H. helix invasions and allocate resources to control it when necessary. They also lay out further groundwork for plant invasion research, demonstrating the necessity of species-specific, location-specific studies.
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    (2023) Brooks, Nicole L; Shaffer, L. J.; Rose, Kenneth A.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Indigenous involvement in conservation and restoration practices, specifically those funded by government entities (e.g., EPA, USGS, NOAA), is not well documented in the Mid-Atlantic region of the United States. Increased Indigenous involvement in conservation and restoration projects globally, raises questions regarding this apparent environmental practice gap in the Eastern United States (McAlvay, 2021; Poto, 2021; Turner, 2010). Currently, government-led restoration projects in the Chesapeake Bay, led by the Chesapeake Bay Program, lack a strong Indigenous presence or contribution despite 7 federally-recognized Sovereign Nations in the surrounding watershed. To understand this gap, a literature review was first conducted to provide an initial context for viewing the contemporary Indigenous involvement in Chesapeake Bay restoration. The review was the basis for a detailed analysis of Virginia’s Sovereign Nation involvement in the Chesapeake Bay Program that used a series of interviews, participant observations, and a social network analysis. Interview participants were classified into one of three representative categories: Sovereign Nation, government organization, and non-government organization. Questions about working relationships between organizations were assessed to understand the political-ecological dynamics driving the interactions in the Chesapeake Bay restoration social network, specifically among the representative categories. Results showed a lack of a consistent and intentional relationship between the Sovereign Nations of Virginia and the Chesapeake Bay Program. According to the federal trust relationship, this infers that the lack of a strong Sovereign Nation involvement in the Chesapeake Bay Program may be contributing to a continued state of Environmental Injustice. To begin to address this low-level of involvement, the Chesapeake Bay Program should devote significant effort to building intentional relationships with the Sovereign Nations, including a more formal and official representation within the Chesapeake Bay Program.
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    Diel greenhouse gas emissions demonstrate a strong response to vegetation patch types in a freshwater wetland
    (2022) Taylor, Aileen; Palmer, Margaret; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Wetland methane (CH4) fluxes are highly variable over spatial and temporal scales due tovariations in the functional controls of CH4 production, oxidation, and transport. While some aspects of temporal variability in CH4 fluxes are well documented (like seasonal patterns), diurnal variability is still poorly constrained. Existing studies report conflicting evidence of diurnal patterns so we cannot make broad generalizations about diurnal patterns of CH4 flux. This is further confounded by the within-wetland spatial heterogeneity that characterizes many wetland systems: variations in topography, soil chemistry, hydrologic regime, and vegetation type can result in characteristically different “patches” that could likely influence existing diurnal patterns. Limited availability of nighttime data due to current methodological constraints also limits our ability to make broad generalizations about CH4 flux patterns. I investigated the diurnal patterns of CH4 fluxes in a seasonal-mineral soil wetland on the Delmarva Peninsula (Maryland, USA) across three functionally unique patches: two with vegetation (emergent and submerged aquatic vegetation), and one without (open water) during the summer of 2021. To explore the potential relationship between physicochemical variables and flux patterns, we also measured a series of physicochemical variables including temperature (air and water), relative humidity, PAR, DO, etc. To my knowledge, this is the first study to compare diel variability across these three patch types. We found that diel patterns in wetland systems are strongly linked to the dominant vegetation cover of a patch, but whether these differences in patterns are a direct result of vegetation impact on production, oxidation and/or transport of CH4 or on patch-specific conditions that covary with patch type will require extended study. Ultimately, this study contributes to the growing understanding of how CH4 flux vary spatially over diel cycles.
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    (2023) Spivy, Annette Leah; Mullinax, Jennifer; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Typically, urban wildlife communities are made up of generalist species that are adept at utilizing human resources. However, many wildlife species struggle in the face of extensive urbanization and would benefit from increased conservation of urban green space, increased urban landscape connectivity, and proactive wildlife population management strategies. Unfortunately, maintaining and/or increasing the availability of quality habitat for biodiversity conservation in urban areas can be challenging as these conservation efforts are often influenced by the decreasing availability of critical resources and the challenges in allocating those resources among competing socioeconomic and environmental needs. Therefore, to improve the management and conservation of urban wildlife, accurate measurements of potential trade-offs between the environmental, economic, and social goals and management actions of a city’s sustainable development plan are needed. Until now, much of the effort in wildlife habitat modeling and biodiversity mapping has been across large geographic areas or broad spatial scales. Those efforts have provided valuable insights into overall biodiversity patterns, identifying key hotspots, and understanding large-scale ecological processes. However, in urban environments, the dynamics of wildlife, habitat availability, and ecosystem services operate differently than in natural or rural landscapes. As urbanization continues to expand, there is a growing need to focus on fine-scale factors to address specific conservation challenges in urban systems. This research seeks to address some of these challenges and demonstrates how new and traditional species-relevant geospatial datasets can be leveraged in urban planning and design to drive local-scale conservation decisions that put biodiversity in the forefront. This work links long-term, multi-taxon, wildlife survey data and high-resolution land use and land cover datasets (1m) to determine where high-quality, well-connected habitats exist, or could most easily be justified and acquired, within the District of Columbia. This work also evaluates the spatial patterns of ecosystem service provisions across the urban landscape to identify “win-win” areas for conservation or restoration that will benefit both biodiversity and human wellbeing. Finally, the work evaluates a local translocation effort of the vulnerable eastern box turtle (Terrapene carolina carolina) to inform mitigation strategies when a sudden loss of habitat in an urban environment is inevitable. This research is particularly relevant to wildlife managers and urban planners in highly urbanized areas, where large parcels of land with suitable habitat are minimal and municipal environmental departments are often under-resourced. Local policymakers interested in incentivizing conservation efforts to meet state or national goals can use this information for strategic urban conservation initiatives.
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    Novel Applications of Waste Treatment Technologies to Generate Energy and Treat Water
    (2023) Mahoney, Kirkland; Hassanein, Amro; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This research sought to maximize energy generation and optimize water treatment from a combined waste stream of food waste and blackwater (FW-BW) and monitored a farm-scale anaerobic digestion (AD) incorporating co-digestion and composting. The FW-BW substrate was gravity separated to obtain a liquid fraction (~90% of the volume) and a solid fraction (~10%). Solids and liquids were pretreated with hydrodynamic cavitation (HDC) to investigate changes in water treatment and energy generation from this pretreatment strategy. Energy generation from the solid fraction was assessed using biochemical methane potential tests (BMP) that quantified methane (CH4) production from AD and integrated a combined anaerobic digestion-microbial electrolysis cells (AD-MEC) design, which operated at various voltages (0.5, 0.9, and 1.2 V). Electrocoagulation (EC) at various voltages (10-25 V) and timeframes (15-90 minutes) was assessed for contaminant removal from the liquid fraction. AD at mesophilic conditions (35 °C) of solids after HDC (post-HDC solids) generated 81.2% of the cumulative CH4 (348 mL CH4/g volatile solids (VS) in 10 days. At longer digestion times (30 days), post-HDC solids generated significantly more CH4 (63%, 429 mL CH4/g VS) than solids before HDC (no-HDC solids) due to increased substrate availability and degradability. Energy generation from AD-MEC at 1.2 V was not significantly different from AD, with only 12.7% more CH4 (292 mL CH4/g VS) generated from post-HDC solids compared to no-HDC solids (259 mL CH4/g VS) after 10 days. Electrocoagulation conducted at 15 V for 90 minutes removed 96.2% of chemical oxygen demand (COD) and 100% of total suspended solids (TSS) from post-HDC liquids. Increasing EC conductivity with electrolytes decreased the timeframe (15 minutes) and voltage (10 V) needed for COD removal (66%) via increased contaminant flocculation. The performance of a farm-scale AD system co-digesting FW and dairy manure (DM) was monitored and verified by analyzing the substrates for nutrient and solids content. A combined heat and power generator produced electricity from the biogas. The system parameters were monitored with an online data-logging system that collected data every 15 minutes for biogas, temperature, hydrogen sulfide (H2S), energy generation, and CH4 content. A life cycle assessment (LCA) was applied to explore the environmental impacts of the current condition compared to four alternative scenarios. The LCA suggested the co-digestion system as currently operated had the largest reductions in environmental impact in 8 out of the 10 impact categories compared to a baseline scenario (no digestion), generating substantial reductions in global warming (81%), eutrophication (442%), and acidification (321%). Using AD can successfully convert various wastes into energy, with HDC increasing overall energy production. Moreover, farm-scale AD showed substantial reduction in global warming.
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    Soils Developed in Freshwater Marl Sediments in The Hagerstown (Great) Limestone Valley
    (1993) Shaw, Joey N.; Rabenhorst, Martin C.; Agronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    Certain calcareous soils occupying alluvial landscape positions in the Hagerstown (Great) limestone valley of western Maryland have developed from highly calcareous ( 60-100g/100g) marl sediments of Holocene age which range in depth from .5m to over 8m. These marlderived soils have a high pH ( 7. 5-8. 5) , low bulk density, and high porosity (0.5 to 0.6). The carbonate in the marl was developed from inorganic and biogenic processes. The marl was formed in now extinct ponds which had inundated alluvial landscape positions during parts of the Holocene period. Certain algae capable of accumulating carbonate internally and externally developed the majority of the marl. Pedogenic processes have transformed the marl sediments into highly calcareous Mollisols. The presence of buried surface horizons and coarse (> fine sand) carbonate forms render classification of these soils problematic. The coarse carbonate forms were mainly biogenic deposits, but these carbonates have been altered sufficiently by coating with pedogenic carbonate to identify calcic horizons. The drainage class is difficult to interpret as a result of the gleyed appearance of the marl sediments (chroma <3) and the high pH of these soils which inhibits Fe oxide reduction. Most of the marl-derived soils (70%) are better drained than the previous classification indicates. These soils have been mapped in the Great Valley in units named for the warners series (fine-silty, carbonatic, mesic Fluvaquentic Haplaquolls) and the Massenet ta series (fine-loamy, carbonatic, mesic, Fluvaquentic Hapludolls). However, proper classification may place these soils in the Typic Calciudolls subgroup. Some soils originally mapped in the very poorly drained Dunning units are very poorly drained marl-derived soils.
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    Utilizing algal turf scrubbers for bioremediation and bioenergy production
    (2023) Delp, Danielle Marie; Lansing, Stephanie A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation researched the conversion of algal biomass that was generated as a byproduct of bioremediation by algal turf scrubbers (ATS) into bioenergy via anaerobic digestion. Anaerobic digestion is a bacterial process that converts organic material into bioenergy in the form of biogas that contains methane (CH4), the primary component of natural gas. Bioenergy yield was quantified as the volume of CH4 generated from digestion of the algae in relation to seasonal changes in algal biomass yield, different digester operational parameters, co-digestion of the biomass with more conventional digestion feedstock, and flocculation pre-treatment for dewatering of algae prior to digestion. The first study used a pilot-scale mesophilic digester at the Port of Baltimore (Baltimore, MD, USA) to continuously digest algae from a 122 m2 ATS on the Patapsco River over two years. Biomass generation was significantly correlated to maximum daily air temperature, water temperature, and flow rate in Year 1 but only water flow rate in Year 2. Algae of the taxa Ochrophyta dominated the algal turf, especially the filamentous diatom Melosira sp., in both years. In Year 1 of the study, two anaerobic digestion systems with variable hydraulic retention times (HRT), designated D1 (average HRT 45.0 ± 5.8 days) and D2-D3 (average HRT 61.0 ± 8.1 days) were used to digest the algae. The D1 generated 1090 L CH4 from 2416 L of algae over a 39-day HRT (59.1 ± 8.9 L algae/kg VS), and D2-D3 generated 1170 L CH4 from 2337 L of algae over a 53-day HRT (67.9 ± 11.0 L algae/kg VS). The difference in CH4 yield with two different HRTs was not significant. In Year 2, only the D2-D3 was operated and was modified to test the use of active recirculation and heating to improve digestion efficiency and CH4 yield. The D2-D3 system generated 4000 L of CH4 (163 ± 42 L algae/kg VS) from 3310 L of algae in Year 2. The second study consisted of laboratory-scale biomethane potential tests to test changes in CH4 yield when algae harvested from an Anacostia River (Bladensburg, MD, USA) ATS was co-digested with three wastes (dairy manure, food waste, and poultry litter) at algae:waste loading ratios of at 1:1, 1:2, 1:5, and 1:10 by organic material, or volatile solids (VS), content. The algal biomass was the least efficient substrate at generating CH4 when normalized by both mass VS digested (109 ± 4 mL CH4/g VS) and total mass of substrate digested (0.687 ± 0.025 mL CH4/g substrate). Co-digestion with all three of the wastes at all ratios tested significantly increased CH4 generation efficiency per mass VS compared to only digesting algae. However, the high moisture content of the algae (95.2%) relative to the other co-digestion wastes (29.0-84.6%) significantly decreased CH4 production on a mass basis for the dairy manure, food waste, and poultry litter when algae was added at any loading ratio. A lettuce growth experiment using the effluent of the digestion vessels showed no signs of acute toxicity when any of the diluted (8-fold) digester effluents were applied as fertilizer to the developing plants. The third and final study consisted of flocculation experiments that tested 500-mL of algae using four experimental treatments (FeCl3, electrocoagulation, chitosan, and Bacillus sp. RP 1137) to dewater algae harvested from the Anacostia River ATS and compared to gravity settling as a control. The experimental flocculants successfully increased the total solids (TS) of the ATS algae by 14-291% depending on the treatment, with electrocoagulation being the least effective and bacterial flocculation being the most effective flocculant. All treatments reduced total suspended solids (TSS) in the drained supernatant by >98%. The raw ATS algae and dewatered solids from the settling experiment were then digested for 35-days, with the algae yielding 49.6 ± 3.6 mL of CH4/g VS. The dewatered solids had reduced digestion efficiency by 29.6-71.0% compared to untreated algae. Dewatering pre-treatment increased CH4 yield from the algae when normalized by total g substrate fed to the reactor (1.65 ± 0.12 mL CH4/g substrate) for all treatments except bacteria 1x, however the effect was only significant for solids dewatered with electrocoagulation. The results from the three studies show that temperature drives algal growth patterns in temperate climates, which results in seasonally variable biomass yield from ATS, with a corresponding variability in CH4 production due to inconsistent availability of the algal feedstock. Algae can be co-digested with agricultural and food wastes that are generated year-round to reduce variability in feedstock availability. Thickening and dewatering the algae improves CH4 yield on a mass basis, however the digestion efficiency was reduced. In conclusion, the findings suggest that anaerobic digestion is a viable means of managing the algae harvested from ATS systems with and without co-digestion of the algal biomass.
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    (2023) Poindexter , Carlton; Lansing, Stephanie; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The burgeoning global threat of antimicrobial resistance (AMR) has policy makers,veterinarians, farmers, and physicians re-evaluating antibiotic stewardship. Worldwide, millions of people are affected by multidrug resistant bacteria. Human and animal waste are primary transporters of antibiotics, antibiotic resistant bacteria (ARB), and antibiotic resistant genes (ARGs) through rural and urban systems. Resistance within biological waste, as it moves through the landscape and sanitary/manure infrastructure to adjacent natural systems, is yet to be fully understood. The various environmental conditions, bacterial composition, and genetic factors result in highly complex interdependent relationships that influence the occurrence and dissemination of ARB and ARGs. Understanding the fate of ARB and movement of ARGs is critical to evaluating environmental and anthropogenic impact. Agricultural systems and wastewater treatment plants are target locations for quantifying connections between clinical and animal antibiotic use and environmental AMR. Waste management techniques/technologies, such as compositing and anerobic digestion (AD), have been shown to be effective in combating AMR. Studies have highlighted temperature as a key environmental determinant that could influence antibiotic degradation, ARG, and ARB abundance. The proposed research examines advanced heat-based manure and wastewater technological capacity for AMR reduction, while measuring treatment impact on ARG dissemination. Focusing on the reduction of AMR within biological waste treatment and the distribution of AMR factors into the environment. A key metric to understanding AMR is accurate detection and quantitation of antibiotic concentration within manure and other biosolid waste products. The first phase of this dissertation research focused on the development of a liquid chromatography in tandem with mass spectrometry (LC-MS/MS) method for detecting multi-class antibiotics residuals in various manure substrates. To combat the challenges of manure heterogeneity, this work focused on novel extraction methodology to achieve higher recovery of tetracyclines, macrolides, sulfonamides, and beta lactams simultaneously in a complex manure matrix. The method includes a two-step, liquid-solid extraction using 10 mL of 0.1 M EDTA-McIlviane buffer followed by 10 mL of methanol. Reporting total antibiotic recoveries of 67–131% for tetracyclines, 56% for sulfonamide, 49–53% for macrolides, and 1.3–66% for β-lactams. This method is novel in its application to four different manure substrate and utilization for waste risk assessment. This developed method was used for antibiotic quantification throughout the three thermal treatment studies to determine antibiotic concentrations, degradation, and monitor agricultural contributions to environmental AMR. The following research extensively focused on the evaluation of three advanced, high temperature waste treatment technologies on the mitigation of antibiotic resistance factors, including a composting rotary drum bedding recovery unit (BRU), thermophilic (55°C) and mesophilic (35°C) AD, and thermal hydrolysis pretreatment to reduce antibiotics, ARGs, and ARB. The assessment of environmental components, such as metals, bacterial community, and nutrient composition, are also included to determine any relational trends. The BRU study was conducted as a mass balance analysis to highlight antibiotics, ARGs and ARB partitioning within the BRU system. Dairy manure samples were collected over 24-hour period as the manure was treated with a solid-liquid separator producing two streams of substrates (liquids and separated solid), with the separated solid fraction continuing to the high temperature BRU processing. This study generated a mass flow analysis of manure and partitioning of antibiotic resistance factors throughout the manure treatment system. The study indicated that most of the manure mass containing the AMR factors goes untreated following solid-liquid separation, with 95% of the mass pumped to a storage lagoon and 5% proceeding to BRU processing. The removal of antibiotic residuals during BRU processes was insignificant, yet the BRS processing was 100% effective in removing the ARB examined. Five (Intl1, sul1, tetQ, tetX and tetM) of the eight ARGs were found to have significant reduction (>95%) following the thermophilic rotary drum composting portion of the BRU system. While the three other ARGs (tetW, ermB and bla2) remained constant despite treatment. An AD experiment was implemented as lab-scale destructive assay, highlighting antibiotic removal at two temperature and over time. This destructive batch assay used 18 sets of triplicate AD reactors filled with antibiotic spiked dairy manure and incubated under anerobic conditions at 35°C or 55°C for 43 days. Triplicates bottles destructively sampled at six time points (Day 0, 3, 9, 21, 36, and 43) to generate a degradation curve. The antibiotic erythromycin was more efficiently degraded under mesophilic conditions, with 100% removal by Day 36 compared to 97% reduction for thermophilic conditions during the 43-day digestion period. Though the higher temperature conditions proved better for oxytetracycline degradation, with 66% removal compared to only 22% removal for mesophilic conditions. ARG removal was dependent on the bacterial community, as the different conditions selected for various bacteria. While both conditions proved to be effective in reducing most of the ARGs (4-5 out of 8 genes tested), enrichment of other resistance genes was also documented. The tetW gene was found to increase >81% for both digester temperatures, highlighting the variety of bacteria harboring resistance genes and their varied responses to environmental conditions. The ermB genes was found to be located on the intl1 mobile genetic element and likely resided within bacteria that was not heat tolerant. This study highlighted the role of residential digester bacteria in harboring and potentially transferring resistance genes. The thermal hydrolysis (THP) technology ability to extensively lysis substrates was examined with subsequent AD for its impact on reducing antibiotic resistance factors. Comparative analysis of THP processing on spiked diary manure and wastewater biosolids followed by mesophilic digestion at 35°C was conducted to document substrate response to the treatment. AD was conducted as a destructive assay for 30 days with a 4-point sample curve (Day 0, 10, 20 and 30). This study can be found in the appendix. In addition to the lab and field work described above, this body of research also included a review and a proposed communication model for antibiotic resistance education for the general public. Lay audiences’ exposure and understanding of complex natural issues, such as AMR and climate change, are essential to behavioral changes and potentially legislative actions. By surveying and evaluating various aspects of scientific communication, this research empathized five rhetorical elements of storytelling shown to influence audience reception to scientific messaging. Communication techniques, such as narrative structure, normalization of the subject using human scaling, non-agentive language, trusted experts for message delivery, and future simulation, were all analyzed and reviewed for their effectiveness and incorporated into a mock model for presenting information about AMR. Bridging gaps between research institutions and the public is key to generating more inclusive spaces for innovation and mitigating issues interwoven within the built and natural environment.
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    (2023) Quach, Emily; Yonkos, Lance; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Aquaponics (APs), a soilless production system, integrates aquaculture and hydroponics to provide local fresh produce while conserving natural resources. The absence of soil in APs eliminates one potential food safety risk present in typical soil-based production systems, but APs may become contaminated from a variety of sources. Escherichia coli TVS 354 long-term survival was evaluated in bench-scale, deep-water APs units. In addition, pathogen presence on basil and lettuce at the time of harvest and changes in the population density of mesophilic aerobic bacteria in APs were measured. Results showed E. coli populations significantly decreased 24 h post-inoculation in water samples and remained undetectable by day 1 post-inoculation. Lettuce harvested on day 60 had detectable E. coli on lettuce leaves and roots at harvest. These results provide new insight on E. coli survival in harvested plants, indicate potential risks for foodborne illnesses, and unreliability of water testing as a monitoring tool.
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    Social-Ecological Processes and Dynamics of Urban Forests as Green Stormwater Infrastructure in Maryland, USA
    (2023) Ponte, Sarah; Pavao-Zuckerman, Mitchell A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Urban trees are part of social-ecological systems shaped by the interactions between human components (e.g., communities, management practices, and sociodemographic characteristics) and ecological components (e.g., trees, microclimate, and soil). This dissertation investigated the social-ecological factors that shape urban trees and forest outcomes. Urban trees can reduce stormwater runoff, mitigate flood risk, increase infiltration and water storage capacity in the soil, reduce nutrient loading, and improve water quality in developed areas. This dissertation begins by quantifying the influence of management context (single vs. clustered vs. closed canopy trees) on the transpiration of red maple (Acer rubrum L.), sweetgum (L. styraciflua L), and tulip poplar (L. tulipifera L.) trees as well as the relationship between tree transpiration and environmental drivers (vapor pressure deficit and soil moisture) in Baltimore and Montgomery County, MD. Results showed significantly lower transpiration rates in closed-canopy trees when compared to solitary trees. No significant differences were observed between transpiration rates across tree species in the closed canopy site during the growing seasons of 2018 and 2019. However, species differences in sap flux density were observed at the 24-h time-scale with tulip poplar trees being the most sensitive to drought. In addition to the ecological characteristics of urban forests, it is necessary to take into consideration the human factors and the resulting outcomes (e.g., tree canopy cover and green stormwater infrastructure distribution) for a better understanding of such complex social-ecological systems. Using regression models, spatial patterns and relationships between biophysical, social, and built components were explored at the neighborhood scale in Baltimore, MD. Results showed that the presence of voluntary green stormwater infrastructure (GSI) was positively associated with stewardship activity related to GSI. Median household income and race were significantly associated with the presence of regulatory GSI, and percent impervious cover was a significant predictor for the presence of voluntary GSI. The findings from this dissertation can aid the development and refining of stormwater crediting programs as urban trees can be more accurately incorporated into planning efforts. This dissertation also provides insights on how environmental stewardship and socio-demographics relate to landscape characteristics and informs future research directions regarding social-ecological systems.
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    (2023) Epp Schmidt, Dietrich; Yarwood, Stephanie A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The advent of DNA sequencing revolutionized the field of microbiome research. Many organisms, by virtue of their codependence and/or growth rate, are either impossible or extremely challenging to get into pure culture. Sequencing allows important taxonomic and phylogenetic information to be obtained independent of culturing. Development of the sequencing technology itself has allowed for high throughput workflow that has allowed low cost and extensive sampling of microbiomes across environments. The co-development of reference datasets for taxonomy and functional assignments, along with open-source bioinformatics pipelines has further empowered scientists to explore microbiomes in many environments. However, there are limitations to sequence data that have constrained the ecological inferences in microbiome research. One such limitation, the compositional nature of sequence data, has impeded our ability to make accurate inferences about the environmental drivers of taxon abundance and covariance across conditions. In this dissertation I explore the use of quantitative PCR in combination with sequencing techniques to generate “Quantitative Sequencing” data (QSeq) that mitigates the limitations of compositionality on inferences relating to taxon abundance and covariance across environmental gradients. In chapter 1, I reviewed key characteristics of the soil environment and sequencing as a mechanism for sampling. In chapter 2, I leveraged modeling, synthesis, and literature review methods to establish the questions and data characteristics that demand QSeq methodology. I show that even small amounts of variation in total abundance make determining the effects of environment (biotic and abiotic factors) on any given taxon unreliable without QSeq. In Chapter 3, I extend the logic of quantitative sequencing to improve metagenome prediction from PICRUSt2. Using data synthesis methods, accounting for 16S gene abundance consistently improved the accuracy of predicted functional genes. This was confirmed by high correlations between predicted and measured gene abundance (QPCR). There was however a large variation in prediction accuracy, likely due in part to database biases and in part to decoupling of bacterial function from taxonomy. In Chapter 4, I applied QSeq in the context of an experimental, long-term farming system that has large gradients in total abundance with depth, and I used QSeq to identify taxa that changed in abundance due to different farming system management and soil depth. Finally in Chapter 5, I used QSeq to identify putative N-fixing taxa that responded to glyphosate in four experimental farming systems. I show that the abundance of these taxa were decoupled from other effects of glyphosate on N-fixation in soybean across farming systems.
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    (2022) Jacobson, Sylvia Rebecca; Baldwin, Andrew H.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Efforts have been made in U.S. wetlands to eradicate the invasive grass Phragmites australis. But eradication of Phragmites does not always lead to the return of native plants. This research investigated native vegetation recolonization across 12 tidal wetland study sites in the Chesapeake Bay watershed and tested the potential of planting perennial native wetland species to accelerate site recovery following Phragmites removal. Our study found that site salinity was a dominant driver of plant recolonization rate: low salinity sites (0.5-3 ppt) had, on average, 4.3x greater aboveground biomass and 2.5x higher vegetation cover than brackish sites (5-9 ppt) two or more growing seasons after Phragmites removal. The composition of returning plant species also differed by salinity, with a higher abundance of annuals and fewer graminoids at low-salinity sites. Site hydrology also influenced native plant recolonization—more frequently flooded sites had lower aboveground biomass of native vegetation two or more years following Phragmites removal. Experimental planting had variable results, with high die-off at several sites, but showed potential to accelerate vegetation recovery at brackish sites in the first years after Phragmites removal—plots with transplants at brackish sites had 17.5x, 2.4x, and 1.5x higher plant cover than unplanted plots in years one, two, and three, respectively, after planting. All sites had some amount of native vegetation recovery within three to four years following Phragmites removal, suggesting that native planting may not be necessary for many tidal wetland sites. Sites with especially high salinities and flooding frequencies may benefit the most from plantings, as larger plants may be able to survive in conditions that are not favorable for seedling emergence. In a mesocosm experiment, we planted six different clonal wetland species in a sand-vermiculite mixture at three different elevations in a tidal creek on the Rhode River in Maryland, USA. We found that peak plant biomass in the sandy substrate occurred at lower elevations and higher flooding frequencies than is typical in marsh environments and than was observed in other mesocosm experiments with organic soils. In well-drained, sandy substrates, wetland plants may benefit from more frequent tidal pulses, likely due to increased water supply and nutrient flux. This has implications for wetland-restoration practitioners using dredged sand to create or elevate tidal wetlands, as wetland species may grow at different elevations and flooding frequencies in these conditions than in a typical tidal marsh with organic soils.
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    (2022) Kim, Jordan; Rabenhorst, Martin C; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Tidal marsh wetlands have the capacity to store disproportionately large quantities of Cdespite their small areal extent. Good estimations of this “blue C” are now more critical than ever due to implications for the global C cycle and climate change, especially since C storage in tidal marshes has historically been understudied. In this study, we set out to measure, more accurately estimate, and conceptually model the C stocks in representative tidal marshes of the Mid-Atlantic region. We found that C storage differs significantly in marshes formed among various pedogeomorphic settings due to differences in pedogenic processes and soil morphology. Further, we have demonstrated that the mean C densities of particular soil materials can be used in conjunction with soil morphological descriptions to reliably estimate the C stocks in the absence of laboratory data. Finally, we augmented existing concepts of tidal marshes in the region by incorporating newly gained understandings of the spatial changes in morphology and C stocks across marshes within different pedogeomorphic settings.
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    (2022) SHOUSHTARIAN, FARSHID; NEGAHBAN-AZAR, MASOUD; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The water crisis caused by climate change, population growth, high urbanization rate, lifestyle changes, and industrialization has decreased global access to safe freshwater resources. As the primary food-producing and the largest water-consuming sector, agriculture heavily depends on water availability. Incorporating alternative water supplies (e.g., water reuse) can reduce freshwater demands, addressing water crisis consequences. Water reuse generally includes recycling treated effluent (known as recycled water) from wastewater treatment plants for different applications (e.g., agricultural irrigation). This alternative water resource can reliably and sustainably increase the resiliency of agriculture to water shortage. However, the complexities inherent in water resources management and the challenges associated with water reuse make planning and managing agricultural water reuse practices demanding. Agricultural water reuse projects include many interrelated/ interconnected components, including the human (e.g., farmers) and technical (e.g., engineering and natural infrastructures) components. The abilities of existing models are limited in simulating these components’ complex and adaptive behaviors. It is necessary to utilize tools capable of capturing these complexities and adaptations to plan and manage agricultural water reuse practices sustainably.The main research question of this dissertation was: How to capture the complex and adaptive dynamics of socio-hydrological systems inherent in sustainable water resources management when alternative water sources are introduced in the water supply system? The primary focus of the dissertation was to develop a dynamic decision support system that can successfully simulate the complexities and adaptations inherent in agricultural water reuse practices. It aims at increasing the existing knowledge regarding agricultural water reuse planning and management and help water resource decision-makers make sustainable and better-informed decisions in agricultural water reuse practices. To accomplish this goal, first, the literature was thoroughly reviewed to identify, collect, and analyze the data related to agricultural water reuse (e.g., current agricultural water reuse regulations and guidelines). Second, two models were developed using a “bottom-up” approach to study two agricultural water reuse practices in the Southwest (CA) and Mid-Atlantic (MD-DE) regions. These two models were used to further study the dynamics of agricultural water reuse adoption by farmers and their impacts on local water resources. The results showed that the regulations and guidelines were mainly human health centered, insufficient regarding some potentially dangerous pollutants such as emerging constituents, and with large discrepancies when compared with each other. In addition, some important water quality parameters, such as pathogens, heavy metals, and salinity, were only included in a few of the regulations and guidelines investigated in this study. Finally, specific treatment processes were only mentioned in some of the regulations and guidelines, with high levels of discrepancy. Moreover, results showed that agricultural water reuse adoption by farmers is a gradual and time-consuming process. In addition, results also showed that agricultural water reuse could significantly decrease the water shortage (by 57.7%) and groundwater withdrawal (by 74.1%) in CA. The results also showed that climate change and recycled water storage capacity and unit price were among the top factors with significant influence on agricultural water reuse practice studied in this dissertation. This study demonstrated the importance of conducting time-varying sensitivity analysis for complex simulation models. Furthermore, results demonstrated that implementing agricultural water reuse could decrease farmers' water shortage, groundwater consumption, and surface water consumption (by almost 19.5 %) in MD. This dissertation’s results can help decision-makers effectively take advantage of agricultural water reuse projects and other alternative water resources to plan and manage water resources sustainably.
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    Decentralizing Stormwater Management: Shifting Infrastructure and Evolving Hydrosocial Relationships
    (2022) Wilfong, Matthew Tyler; Pavao-Zuckerman, Mitchell; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Stormwater management has historically remained in the technocratic realm of engineers and scientists disconnecting society from stormwater to protect public and environmental health. Despite incremental improvements, state and local governments are beginning to change their management practices and techniques in response to climatic changes, increased urbanization, and intensifying regulatory pressures. Scholars and practitioners have argued that this paradigm shift in stormwater management is required to continue to protect public and environmental health and reach regulatory goals. Despite the need for this paradigm shift, there continues to be slow progress towards decentralization. Thisshift is characterized by two key developments: the increased implementation of decentralized green infrastructure and increased involvement of individuals in managing stormwater. Broadly, this dissertation sets out to investigate two key aspects of this paradigm shift: (1) the hydrologic performance of these decentralized practices and (2) the social, political, cultural, and economic dynamics that are currently underpinning this paradigm shift. This dissertation begins with a chapter investigating the hydrologic performance ofdecentralized, green infrastructure treatment trains in Clarksburg, MD. Using stormwater monitoring methodology, we analyze how effectively treatment trains can hydrologically manage stormwater and the effects of precipitation dynamics on the ability of these treatment trains to manage stormwater. This research suggests that these treatment trains are generally highly effective at managing stormwater volumes across a host of storm events with an average of 93% of discharge abated throughout the monitoring period. We also demonstrate that precipitation intensity was the most influential precipitation dynamic on the performance of each treatment train suggesting that designing these treatment trains with the potential higher prevalence of higher intensity storm events due to climate change. To begin the social science portions of the dissertation research, we utilize an alternative framework, the hydrosocial cycle, to analyze how stormwater and society have and continue to shape each other over time. Building upon this work, we investigate the political, social, and cultural dynamics influencing and arising within this paradigm shift occurring within stormwater management. Through semi-structured interviews and Q-methodology within two urban watersheds in Maryland and Washington DC, we assess changes in the hydrosocial relationships between stakeholders and stormwater. Using these insights, we discuss the potential for alignment and cooperation among these diverging hydrosocial relationships and continuing the shift towards decentralizing stormwater management. Arising from this holistic and critical analysis, we seek to provide actionable recommendations focused on how, where, and who manages stormwater to reach more sustainable, resilient, and equitable outcomes. Additionally, we aim to demonstrate the effectiveness of theseframeworks and methodologies to better attend to political and power dynamics involved in water governance and management, more broadly
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    Biosolids and Compost For Urban Soil Restoration and Forestry
    (2022) Keener, Emily Cathryn; Pavao-Zuckerman, Mitchell A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Elements of urban soil quality such as compaction and low organic matter are underexamined, important challenges to urban afforestation. In this Beltsville, Maryland field experiment, I examined biosolids and compost as amendments to improve soil quality and planted tree survival in a degraded urban proxy soil and identified correlations between soil properties and tree survival. Organic amendments increased organic matter content, decreased bulk density, and had no effect on tree survivorship compared to controls. Effects on soil were more profound and lasting with compost than with biosolids. Soil organic matter and bulk density were correlated with tree survival early in the study and microbial respiration was correlated with tree survival throughout the study. High tree mortality was driven by transplant shock, limiting insights from tree response data. This study highlights the importance of soil quality and good planting practices in future research.
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    (2022) Smith, Jaclyn Elizabeth; Hill, Robert L; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The dynamics of phytoplankton community structure in two agricultural irrigation ponds located in Maryland, USA were evaluated. Stable spatiotemporal patterns and zones of consistently higher and consistently lower phytoplankton functional group concentrations were established for both ponds. Moderate and strong correlations were found between the spatial patterns of several water quality parameters and phytoplankton concentrations. Additionally, zones of consistently higher and lower concentrations were found for the cyanobacteria pigment, phycocyanin. Chlorophyll, colored dissolved organic matter, and turbidity were the most influential predictors for phycocyanin concentrations. The prediction of phytoplankton community structure from water quality measurements with the random forest machine learning algorithm was possible and easily measured physicochemical parameter models offered the best model performance. Results of this work indicate that in-situ water quality measurements may be a cost-effective and faster alternative to time-intensive microscopy analysis of phytoplankton, allowing for more efficient water quality monitoring.
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    Monitoring and Predicting the Microbial Water Quality in Irrigation Ponds
    (2022) Stocker, Matthew Daniel; Hill, Robert L; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Small- to medium-sized farm ponds are a popular source of irrigation water and provide a substantial volume of water for crop growth in the United States. The microbial quality of irrigation waters is assessed by measuring concentrations of the fecal indicator bacteria Escherichia coli (E. coli). Minimal guidance currently exists on the use of surface irrigation waters to minimize consumer health risks. The overall objective of this work was to provide science-based guidance for microbial water quality monitoring of irrigation ponds. Spatial and temporal patterns of E. coli were evaluated in two Maryland irrigation ponds over three years of observations. Patterns of E. coli were stable over the three years and found to be significantly correlated to patterns of water parameters such as temperature, dissolved oxygen, turbidity, and pH. The EPA Environmental Fluid Dynamics Code model was used to evaluate the spatial 3D heterogeneity of E. coli concentrations within the ponds. Significant differences in E. coli concentrations by sampling depth were found. Spatial heterogeneity of E. coli within the pond also resulted in substantial temporal variation at the irrigation pump, which was dependent on the intake location. Diurnal variation of E. coli concentrations was assessed for three farm ponds. E. coli concentrations declined from 9:00 to 15:00 for each pond, but statistically significant declines were only observed in two of the three ponds. Dissolved oxygen, pH, and electrical conductance were found to be the most influential environmental variables affecting E. coli concentrations. To better describe the relationships between E. coli and the environmental variables, four machine learning algorithms were used to estimate E. coli concentrations using water quality parameters as predictors. The random forest algorithm provided the highest predictive accuracy with R2 = 0.750 and R2 = 0.745 for Ponds 1 and 2, respectively, in the multi-year dataset containing 12 predictors. Temperature, electrical conductance, and organic matter content were identified as the most influential predictors. It is anticipated that the recommendations contained in this dissertation will be used to improve microbial monitoring strategies and protect public health.
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    (2021) Scott, Brian; Yarwood, Stephanie; Baldwin, Andrew H.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Organic Matter (OM) amendments are often used in wetland restoration – a practice required in Maryland and other states. This work summarizes a literature review and lab and field experiments to evaluate the consequences of OM amendment use. The literature review showed that although OM use is widely accepted, the evidence that they are effective is weak, and there can be negative effects. Transplanted topsoil is much more effective than allochthonous OM (e.g., manure). OM amendments were largely ineffective in a field study conducted on a mitigation wetland in Caroline County, MD, and negative consequences were possible, although composting the OM relieved negative effects. One example of ineffectiveness: OM is not needed to develop anaerobic conditions in saturated soil. While in some cases OM seems to be a benefit, as in aboveground biomass production, this is usually accompanied by a loss of diversity and it selects for undesired and invasive species. One of the negative consequences OM is the increased production of methane, a greenhouse gas, which became the focus of this work. Two lab microcosm studies and a field study revealed that rewetting dried soils (as in after mitigation wetland construction) immediately releases small amounts of methane, and methane sharply increases after about 7 weeks. Using OM affects methane production in two ways. First, overall methane production usually increases. Second, the time frame before there is a sharp increase in methane production is shorter, from ~7 weeks to as little as 1 or 2 weeks. These effects are somewhat reduced with composted OM. Using a Stable Isotope Probing microcosm study, the work also helped to identify the archaeal and bacterial taxa that are responsible for the sudden increase in methane. Methanosarcina is likely the primary taxa responsible for methane generation. Understanding the conditions that result in methane emanating from wetlands could lead to practices that reduce its release into the atmosphere, where it contributes to global warming. Methane is a more potent greenhouse gas than carbon dioxide, but is short lived, so controlling methane emissions can have a more immediate effect on climate change.
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    Extending the Cover Crop Growing Season to Reduce Nitrogen Pollution
    (2021) Sedghi, Nathan; Weil, Ray R; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Maryland currently has the highest rate of cover crop use in the United States. The Cover Crop Program, started as an initiative to clean nutrients from the Chesapeake Bay, has made it a common practice to plant a cereal cover crop after cash crop harvest in fall, and kill it several weeks before cash crop planting in spring. In Maryland, this practice does not allow enough growing time with warm conditions for optimal cover crop growth. Planting earlier in fall and killing a cover crop later in spring could improve soil N cycling. We hypothesized that interseeding into a cash crop in early fall, and delaying spring cover crop termination could increase cover crop biomass, carbon accumulation, and nitrogen uptake and decrease nitrate leached. We tested these hypotheses over four years with five field experiments, consistently using a brassica-legume-cereal cover crop mix. We evaluated the relationships between cover crop planting date and fall cover crop N uptake and reduction in nitrate leaching. In spring, we tested termination timing effects on cover biomass C and N, soil mineral N concentration, soil moisture, and corn yield. We tested multiple dates for broadcast interseeding cover crops into standing soybean cash crops. We partnered with farmers on Maryland’s Eastern Shore to test if our methods are feasible at a realistic scale. We measured nitrous oxide emissions to test if our recommended cover crop practice has the negative drawback of increasing emissions of nitrous oxide, a powerful greenhouse gas. The nitrate leached under late drilled and early interseeded methods were comparable under conditions which favored late drilling, but interseeding outperformed drilling when there was adequate rainfall for seed germination. The result was lower nitrate porewater concentrations under early planted cover crops. Nitrous oxide emissions increased slightly with cover crops relative to no cover crop, but the increase was negligible when compared to the nitrous oxide produced from applying N fertilizer. Our research showed that extending the cover crop growing season of a brassica-legume-cereal mix has multiple environmental benefits and few drawbacks.