Theses and Dissertations from UMD
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Item INVESTIGATION OF AMBIENT METHANE CONCENTRATION, SOURCES, AND TRENDS IN THE BALTIMORE-WASHINGTON REGION(2024) Sahu, Sayantan; Dickerson, Russell Professor; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Methane, an important and not yet fully understood greenhouse gas, has a global warming potential 25 times that of carbon dioxide over 100 years, although with an atmospheric lifetime much shorter than carbon dioxide. Controlling methane emissions is a useful way to avoid some of the adverse effects of climate change at least on short time scales. Natural sources include wetlands, ruminants, and wildfires, while anthropogenic sources include the production, transmission, distribution, and use of natural gas, livestock, and landfills. In the US, natural gas and petroleum systems, anthropogenic sources, are the second-largest source of methane emissions. Urban areas are a significant source of anthropogenic methane emissions, primarily fugitive emissions from natural gas distribution and usage.We studied methane observations from five towers in the Baltimore-Washington (BWR) region – two urban towers ARL (Arlington, VA), NEB (Northeast Baltimore, MD), and one rural tower, BUC (Bucktown, MD). Methane measurements from these three towers displayed distinct seasonal and diurnal cycles with maxima at night and in the early morning, which indicated significant local emissions. We concluded from our analysis that anthropogenic methane emissions dominate at the urban sites whereas wetland emissions dominate at the rural site. We compared observed enhancements (mole fractions above the 5th percentile) to simulated methane enhancements using the WRF-STILT model driven by two EDGAR inventories – EDGAR 4.2 and EDGAR 5.0. We did a similar comparison between model and observations with vertical gradients. We concluded that both versions of EDGAR underestimated the regional anthropogenic emissions of methane, but version 5.0 had a more accurate spatial representation. We ran the model with WETCHARTs to account for wetland emissions which significantly reduced the bias between model and observations especially in summer at the rural site. We investigated winter methane observations from three towers in the BWR including a ten-year record, 2013-2022, from BUC, located ~100 km southeast of these urban areas. We combined the observations with a HYSPLIT clustering analysis for all years to determine the major synoptic patterns influencing methane mixing ratios at BUC. For methane concentrations above global background, the cluster analysis revealed four characteristic pathways of transport into BUC – from the west (W), southwest (SW), northwest (NW), and east (E) and these showed significant differences in methane mixing ratios. We corroborated our conclusions from BUC using 2018-2022 data from towers in Stafford, Virginia (SFD), and Thurmont, Maryland (TMD); results confirmed the influence of synoptic pattern, typically associated with frontal passage, on methane. No significant temporal trend over the global background was detected overall or within any cluster. For BUC, low concentrations were observed for air off the North Atlantic Ocean (E cluster) and flowing rapidly behind cold fronts (NW cluster). High methane mixing ratios were observed, as expected, in the W cluster due to the proximity of the BWR and oil and gas operations in the Marcellus. Less expected were high mixing ratios for the SW cluster – we attribute these to agricultural sources in North Carolina. Swine production, ~500 km to the SW, impacts methane in eastern Maryland as much or more than local urban emissions plus oil and gas operations 100–300 km to the west; this supports the high end of emission estimates for animal husbandry and suggests strategies for future research and mitigation.Item Methane Biogeochemistry and Microbial Communities in Natural and Restored Freshwater Depressional Wetlands(2024) Hamovit, Nora David; Yarwood, Stephanie A; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wetlands are the largest natural source of methane (CH4), a potent greenhouse gas. Wetland CH4 emissions are dependent on rates of microbial CH4 production (methanogenesis) and consumption (methanotrophy). These processes vary spatially and temporally with environmental conditions, edaphic characteristics, and microbial community structure, making it difficult to predict wetland CH4 emissions. This high variability can be further pronounced in restored wetlands that have undergone environmental and edaphic disturbances. The following work aims to understand this variability by assessing patterns of methanogenesis and methanotrophy, and their associated microbial communities, across natural and restored freshwater depressional wetlands on the Delmarva Peninsula (USA). Sites addressed in this work were restored from agricultural land between 1986 and 2004 through multiple programs funded by the United States Department of Agriculture (USDA). In the first set of experiments, we identified a high abundance of active acetoclastic methanogens in intact core incubations from a restored wetland suggesting a higher potential for methanogenesis in situ compared to the natural wetland assessed. The co-occurrence of active methanogens and Fe-reducing bacteria in these restored wetland cores contradicted the hypothesis that loss of competition may allow methanogens to be the primary users of acetate. Following assessments across vegetative-hydrologic zones in a series of restored wetlands of varying ages, and their natural counterparts, highlighted vegetation type and extent as a driver of methanogen community abundance, composition, and activity. In turn, restored wetlands showed elevated potentials rates of methanogenesis compared to natural sites. Potential rates of methanotrophy (aerobic and anaerobic), however, were also elevated in restored wetlands, which could constrain CH4 emissions in situ. Variability of environmental conditions (ie. hydrology and vegetation) and edaphic measures (ie. soil organic matter (SOM)) across all sites sampled are reflected in distinct microbial community composition and CH4 biogeochemistry. Clear patterns of SOC accumulation and CH4 biogeochemistry with restoration age were not observed for these wetlands, and variability in environmental conditions and edaphic measures across the sites (restored and natural), emphasize the need for continued monitoring and maintenance of the wetlands. Our results suggest efforts to manage herbaceous vegetation extent and maintain regular seasonal hydrology in future restorations may help prevent high potentials for CH4 production, and thus emissions.Item 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.Item MECHANISMS CONTROLLING VOLATILE FATTY ACID AND FERMENTATION GAS PRODUCTION IN THE RUMEN(2022) Scott, Jarvis G; Kohn, Richard A; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atmospheric methane accounts for less than approximately 16% of global anthropogenic greenhouse gas emission. However, it is significantly greater and trapping heat when compared to atmospheric CO2 on a molar lever and any reduction in atmospheric abundance in warranted. Enteric methane from ruminant species accounts for a fraction (< 30%) of the total atmospheric methane however its production also accounts for major dietary energy loss in ruminant species and affects feed efficiency and overall production. Major studies have investigated numerous feed additives and supplements with highly variable finding on the antimethanogenic property of these compounds or feeding strategies, however the findings have raised other questions regarding shifts in VFA profiles accompanying methane inhibition. Higher inclusion levels of concentrate and other nonstructural starch in the diet of ruminants have been shown to decrease methane production and shift volatile fatty acid (VFA) profiles in the rumen. Additionally, many studies have suggested that inhibiting methane production avails as a reducing equivalent to fuel the propionate producing pathway and therefore results in shift in VFA profiles in the rumen. However, very little is understood regarding how these VFA shifts come about. Microbial Kinetics and thermodynamics are physiochemical principles that can be used to study how concentrate inclusion in ruminant diets can change the substrate concentrations and ultimately lead to shifts in fermentation profile in the rumen. Substrate availability supports and/or limits the growth of microbial population in the rumen, while the accumulation of the products or reactants for major fermentation reactions dictate the profile of the VFA. Understanding the role of these physiochemical principles and ultimately the mechanisms involved with changes the profile of VFA and fermentations gas in the rumen would help researchers understand how VFA profiles are shifting during methane inhibition as well as possibly identifying a more targeted approach for inhibiting enteric methane production. Therefore, the objectives of this projects are: to develop an in vitro method to understand the basal kinetic parameters of metabolism in the rumen, to evaluate the effects of increasing forage-to-concentrate ratio on performance and change in in VFA and fermentation gas in vivo, and to test the effect of various perturbations (fermentation metabolites e.g. sodium acetate, sodium lactate etc.) on the fermentation profile of rumen fluid adjusted to different forage-to-concentrate ration. The results indicate that rumen fluid from cows on a high-concentrate diet have a greater capacity to make propionate compared to the high forages diet. The higher propionate production limits the availability of which is necessary for the synthesis of CH4. The finding also suggests that methanogenesis is process limited by substrate concentration. Finally, our studies indicate that feeding strategies targeting enzymatic activity favoring propionate production may be more beneficial than targeting methanogens in a high forage diet.Item A 20-YEAR CLIMATOLOGY OF GLOBAL ATMOSPHERIC METHANE FROM HYPERSPECTRAL THERMAL INFRARED SOUNDERS WITH SOME APPLICATIONS(2022) Zhou, Lihang; Warner, Juying; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atmospheric Methane (CH4) is the second most important greenhouse gas after carbon dioxide (CO2), and accounts for approximately 20% of the global warming produced by all well-mixed greenhouse gases. Thus, its spatiotemporal distributions and relevant long-term trends are critical to understanding the sources, sinks, and global budget of atmospheric composition, as well as the associated climate impacts. The current suite of hyperspectral thermal infrared sounders has provided continuous global methane data records since 2002, starting with the Atmospheric Infrared Sounder (AIRS) onboard the NASA EOS/Aqua satellite launched on 2 May 2002. The Cross-track Infrared Sounder (CrIS) was launched onboard the Suomi National Polar Orbiting Partnership (SNPP) on 28 October 2011 and then on NOAA-20 on 18 November 2017. The Infrared Atmospheric Sounding Interferometer (IASI) was launched onboard the EUMETSAT MetOp-A on 19 October 2006, followed by MetOp-B on 17 September 2012, then Metop-C on 7 November 2018. In this study, nearly two decades of global CH4 concentrations retrieved from the AIRS and CrIS sensors were analyzed. Results indicate that the global mid-upper tropospheric CH4 concentrations (centered around 400 hPa) increased significantly from 2003 to 2020, i.e., with an annual average of ~1754 ppbv in 2003 and ~1839 ppbv in 2020. The total increase is approximately 85 ppbv representing a +4.8% change in 18 years. More importantly, the rate of increase was derived using satellite measurements and shown to be consistent with the rate of increase previously reported only from in-situ observational measurements. It further confirmed that there was a steady increase starting in 2007 that became stronger since 2014, as also reported from the in-situ observations. In addition, comparisons of the methane retrieved from the AIRS and CrIS against in situ measurements from NOAA Global Monitoring Laboratory (GML) were conducted. One of the key findings of this comparative study is that there are phase shifts in the seasonal cycles between satellite thermal infrared measurements and ground measurements, especially in the middle to high latitudes in the northern hemisphere. Through this, an issue common in the hyperspectral thermal sensor retrievals were discovered that was unknown previously and offered potential solutions. We also conducted research on some applications of the retrieval products in monitoring the changes of CH4 over the selected regions (the Arctic and South America). Detailed analyses based on local geographic changes related to CH4 concentration increases were discussed. The results of this study concluded that while the atmospheric CH4 concentration over the Arctic region has been increasing since the early 2000s, there were no catastrophic sudden jumps during the period of 2008-2012, as indicated by the earlier studies using pre-validated retrieval products. From our study of CH4 climatology using hyperspectral infrared sounders, it has been proved that the CH4 from hyperspectral sounders provide valuable information on CH4 for the mid-upper troposphere and lower stratosphere. Future approaches are suggested that include: 1) Utilizing extended data records for CH4 monitoring using AIRS, CrIS, and other potential new generation hyperspectral infrared sensors; 2). Improving the algorithms for trace gas retrievals; and 3). Enhancing the capacity to detect CH4 changes and anomalies with radiance signals from hyperspectral infrared sounders.Item YEAR-ROUND DETERMINATION OF METHANE (CH4) SOURCES AND SINKS IN ARCTIC LAKES USING CONTINUOUS AND AUTONOMOUS SAMPLING(2020) McIntosh Marcek, Hadley; Lapham, Laura L; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Methane (CH4) is a potent greenhouse gas and its concentration has been increasing in the atmosphere. While natural emissions from inland water bodies are known to be important, there is large uncertainty in the amount of methane released from lakes to the atmosphere, especially from Northern latitudes. Part of this is due to limited sampling in these systems during dynamic periods, such as ice-over and ice-melt. To better understand these temporal dynamics, I used autonomous, continuous samplers (OsmoSamplers) to collect lake water year-round over two years (2015-2017). Lake water was collected at a fine temporal resolution to provide time-integrated (~1 week) samples from multiple Arctic lakes within the Mackenzie Delta. The Mackenzie Delta is a lake-rich, productive environment that is expected to be a significant source of methane to the atmosphere. Lakes spanning the central delta and outer delta were sampled for methane concentration and stable carbon isotope ratio (δ13C-CH4) changes, ion concentrations, and water column characteristics were measured with continuous sensor data (temperature, water pressure, conductivity, light, and dissolved oxygen). These unique time-series datasets show lakes exhibit a close coupling of dissolved oxygen, and other electron acceptors, with the timing of methane increasing during ice-cover. The increase in methane concentrations is primarily from diffusion out of sediments and possibly water-column methanogenesis. One lake in the outer delta exhibited thermogenic gas bubble dissolution that contributed to under-ice methane concentration increases. Following ice-melt, lake depth appears to impact methane release to the atmosphere. Shallower lakes exhibit rapid fluxes followed by significant microbial methanotrophy. Deeper lakes in the central delta are connected to groundwater, though it does not appear groundwater transports methane. This is the first study of dissolved methane and gas bubble 14C-age in the Mackenzie Delta and shows that dissolved methane is produced primarily from modern carbon sources, such as macrophyte biomass and terrestrial material, but some methane transported in gas bubbles is significantly older, with seeps in the outer delta rapidly releasing radiocarbon-dead, thermogenic methane. This study demonstrates the importance of multi-lake studies particularly with fine scale temporal sampling to understand methane processes in seasonally ice-covered lakes.Item Fate of antimicrobials and nutrients in dairy manure management systems(2018) Schueler, Jenna E; Lansing, Stephanie; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Anaerobic digestion (AD) and composting manure management strategies were explored at the field scale to monitor antimicrobial degradation, nutrient transformations, and optimize mitigation of these pollutants in manure fertilizer to decrease their entry to waterways. Removal of antimicrobials and antimicrobial resistance genes (ARGs) were explored at the bench scale, where AD degraded >85% of antimicrobials. At the field-scale, antimicrobials were not consistently removed, persisting in concentrations up to 34,000 ng/g DW in the AD effluent. The tetM genes were reduced during bench-scale AD suggesting that AD could be an effective treatment for removing tetracycline ARGs from manure. The 100% reduction of sulfadimethoxine antimicrobials during AD did not correspond with Sul1 reduction, illustrating differences in antimicrobial versus gene reductions during manure treatment. Antimicrobials did not degrade significantly during field scale composting, likely due to a shortened composting period (33-days). The field-scale results illuminate limitations of tracking antimicrobials in complex treatment systems.Item HYDROLOGY, SOIL REDOX, AND PORE-WATER IRON REGULATE CARBON CYCLING IN NATURAL AND RESTORED TIDAL FRESHWATER WETLANDS IN THE CHESAPEAKE BAY, MARYLAND, USA(2017) Keshta, Amr El Shahat Sedik; Baldwin, Andrew H; Yarwood, Stephanie A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal freshwater wetlands are key sites for carbon (C) sequestration and main component in the global C budget. The overall research objective of my dissertation was to examine the physical and biogeochemical processes that impact C cycling in tidal freshwater wetlands. One natural and one restored tidal freshwater wetland (salinity < 0.3 ppt) were selected in Maryland, USA along the Patuxent River. Data logging water recorders were installed in wells at each habitat in February 2014 for monitoring water level at 10-minutes interval and for two years. Soil organic matter and C stocks were estimated and a novel soil C bioassay (CARBIO) was developed and tested to assess C stability (change of soil organic matter concentration over time) and decomposition rates in both sites. A total of 162 CARBIO units were deployed in the natural and restored sites, and 81 were retrieved after 1 year while the others were retrieved after 2 years. Static chambers were used to quantify methane (CH4) and carbon dioxide (CO2) flux rates during day and nighttime. My results indicated that the natural wetland had significantly higher soil C stocks than the restored site (14.8±0.50 and 8.9±0.99 kg C m-2, respectively, P <0.0001). The swamp habitat had the highest soil organic matter (36.8%), while restored mudflat has the lowest (2.8%). Higher soil organic matter was partially correlated with shallower groundwater level relative to soil surface. Soil redox data with soil pH indicated that the soil of the natural wetland habitats was more reducing than the soil at the restored habitats. Based on CARBIO index, the soils in CARBIO units that were deployed in the natural wetland was significantly higher in C sequestration rate than the restored wetland (535±291.5 and -1095±429.4 g C m-2 year-1, respectively, P site<0.05). Under the current hydrological conditions, the restored wetland habitats were not able to accumulate C inside the CARBIO units after 1 or 2 years from deployment. In-situ CARBIO units can be employed in the newly constructed wetlands as in-situ sensors that reflect the C biogeochemical processes in the ambient soil to help better understanding C stability. The restored wetland had significantly higher annual CH4 emission rates than the natural wetland (1372.1±35.89 and 880.7±144.73 g CH4 m-2 y-1, respectively, P <0.05) and the log CH4 flux rate had a significant and strong negative correlation with the pore-water total available iron. Nighttime CH4 fluxes had very low concentration (<3650 µmole m-2 h-1). Future restoration efforts should focus on soil properties that will help increase C accumulation in newly constructed wetlands, but even more important every effort should be made to conserve the natural wetlands so that ecosystem function and services including wildlife habitat, water quality improvement, and offsetting the greenhouse gas emissions are maintained.Item THE UPGRADING OF METHANE TO AROMATICS OVER TRANSITION METAL LOADED HIERARCHICAL ZEOLITES(2017) WU, YIQING; Liu, Dongxia; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the boom of shale gas production, the conversion of methane to higher hydrocarbons (MTH) promises a great future as the substituent for hydrocarbon production from crude oil based processes. Among various MTH processes, direct methane aromatization (DMA) is promising since it can achieve one-step methane valorization to aromatics. The molybdenum/zeolite (Mo/MFI or Mo/MWW) has been the most active catalyst for the DMA reaction, which, however, is impeded from industrial practice due to the rapid deactivation by coke deposition. To address this challenge, in this work, transition metal loaded hierarchical 2 dimensional (2D) lamellar MFI and MWW zeolites have been studied as catalysts for the DMA reaction. The effects of micro- and mesoporosity, external and internal Brønsted acid sites, as well as particle size of 2D lamellar zeolites on the DMA reaction have been investigated. Firstly, the spatial distribution of Brønsted acid sites in 2D lamellar MFI and MWW zeolites has been quantified by a combination of organic base titration and methanol dehydration reaction. The unit-cell thick 2D zeolites after Mo loading showed mitigation on deactivation, increase in activity, and comparable aromatics selectivity to the Mo loaded 3D zeolite analogues. A detailed analysis of the DMA reaction over Mo/hierarchical MFI zeolites with variable micro- and mesoporosity (equivalent to variation in particle sizes) showed a balance between dual porosity was essential to modulate the distribution of active sites (Mo and Brønsted acid sites) in the catalysts as well as the consequent reaction and transport events to optimize performance in the DMA reaction. External Brønsted acid sites have been proposed to be the cause of coke deposition on Mo/zeolite catalysts. Deactivation of the external acid sites have been practiced to improve the catalyst performances in the DMA reaction in this work. Atomic layer deposition (ALD) of silica species was conducted on the external surface of 2D lamellar MFI and MWW zeolites to deactivate the external acid sites in Mo/2D lamellar zeolites for the DMA reaction. Another strategy to deactivate external acid sites in Mo/zeolite catalysts was the overgrowth of 2D lamellar silicalite-1 on the microporous zeolites. The as-prepared catalysts showed higher methane conversion and aromatics formation as well as higher selectivity to naphthalene and coke in comparison with Mo loaded microporous analogues.Item NANO STRUCTURED MATERIALS FOR ENERGY APPLICATIONS(2017) Liu, Lu; Zachariah, Michael R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation addressed the applications of nanostructured materials as oxygen carriers (OCs) and catalysts in poly lactic acid (PLA) thermal decomposition. In chapter 1~4, the stability and cyclibility of metal oxides and supported metal oxides as OCs were evaluated in an isothermal fixed bed reactor at different temperatures for 50 cycles with methane as fuel, up to 15h while their structural, physical and chemical properties were identified using XRD, SEM, TEM, BET, XPS and Ar/H2-TPR. In chapter 5, aerosol synthesized Bi2O3 was found to be a useful catalyst in thermal PLA decomposition, which could lower the on-set decomposition temperature by ~75 T. The developed study protocol could be applied to various metal oxides and polymers to study their catalytic thermal decompositions as well.