Theses and Dissertations from UMD
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Item Characterizing nutrient budgets on and beyond farms for sustainable nutrient management(2023) Zou, Tan; Zhang, Xin; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The production and security of food are heavily reliant on adequate nitrogen (N) and phosphorus (P) inputs in agriculture. However, ineffective management of N and P from the farm to the table can result in nutrient pollution, triggering both environmental and social issues. Moreover, another important challenge for P management is limited and unevenly distributed P resources, leading to P scarcity in many parts of the world. Inefficient use of nutrients in agriculture-food systems is the root cause of both nutrient pollution and scarcity. To improve nutrient use efficiency and reduce nutrient loss, it is crucial to address key knowledge gaps in nutrient management research, which include inadequate quantification of nutrient budgets, as well as identifying and addressing nutrient management challenges across various systems and spatial scales. This dissertation tackles the knowledge gaps in two studies, including a global-scale study and a case study of the Chesapeake Bay watershed. In the global-scale study, I establish and utilize a unique P budget database to assess historical P budget and usage patterns at the national and crop type level from 1961 to 2019. This analysis reveals the impacts of various agricultural and socioeconomic drivers on cropland P use efficiency (PUE), including N use efficiency (NUE), fertilizer-to-crop-price ratio, farm size, crop mix, and agricultural machinery. The findings indicate that P management challenges vary by country and spatial scale, necessitating tailored country-level strategies. The regional-scale study applies a framework adapted from N studies to the Chesapeake Bay watershed, analyzing nutrient (N and P) management across systems and spatial scales. This approach uncovers that nutrient loss potential beyond crop farms is larger than that at crop farms. This highlights the need to enhance nutrient management and curb nutrient loss in animal production, food processing and retail, and human consumption. This study also identifies a large potential for meeting cropland nutrient demand by increasing the recycling of nutrients in manure, food waste, and human waste. To tackle the challenges surrounding nutrient management in the watershed, it is imperative to target factors significantly related to nutrient management, such as agricultural practices, soil properties, climate change, and socioeconomic conditions. This dissertation contributes to a deeper understanding of N and P management challenges, gaps, priorities, hidden drivers, and potential solutions at various scales, from regional to national and global levels. The analytical procedures and statistical tools developed in this dissertation are generalizable, allowing for their adaptation to similar nutrient management studies in different regions and for diverse research purposes.Item NUTRIENT MOVEMENT IN A VEGETATED COMPOST BLANKET AMENDING A VEGETATED FILTER STRIP ON A HIGHWAY SLOPE(2022) Forgione, Erica Rose; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Excess stormwater runoff caused by rapid urbanization and exacerbated by climate change generates many challenges for public safety and the environment. Large runoff volumes contribute to flooding and pollutants in stormwater runoff pose risks to human and environmental health, including toxicity to the aquatic environment caused by heavy metals and nutrient pollution leading to eutrophication, the cause of harmful algal blooms. An effort is being made to improve the efficiency of existing highway stormwater control systems which have limited performance in terms of volume reduction and pollutant removal. To address this issue, amendment of highway Vegetated Filter Strips (VFS) with a Vegetated Compost Blanket (VCB), a layer of seeded compost placed on an established slope, has been proposed. Compost has high water holding capacity and organic matter content which can immobilize contaminants of concern. However, the high nutrient content of compost poses a threat to net beneficial performance since excess nutrient leaching occurs after application. This research has posed the question: Can a VCB be used as a stormwater control measure (SCM) while avoiding excessive nutrient leaching?The VCB/VFS system was assessed through lab-scale, greenhouse-scale, and field-scale experiments. Hydrologic performance was evaluated in field and greenhouse experiments through evaluation of dynamic flow modification, event volume storage, and cumulative volume retention. Water quality performance was assessed through analysis of Total Suspended Solids (TSS), Nitrate + Nitrite (NOx), Total Kjeldahl Nitrogen (TKN), Total Nitrogen (TN), Total Phosphorus (TP), filtered and total Copper, and total Zinc concentrations. Nitrogen (N) and phosphorus (P) in compost are naturally transformed from organic to inorganic, soluble forms through the microbially-mediated process of mineralization. Nutrient removal occurs through adsorption as compost leachate passes through the VFS soil layer. To further investigate nutrient movement, small scale laboratory experiments were completed to determine the N and P compost mineralization rates and theoretical soil adsorption capacities. Nutrient data from greenhouse and field experiments were empirically evaluated using the lab-obtained mineralization data. Nutrient release was simulated and compared to experimental field data using a new open-source software, OpenHydroQual, which combines hydraulic and water quality modeling. VCBs were found to have a significant impact on both flow and volume reduction, though at the highest flowrates, VCBs were unable to significantly reduce flow and instead acted as conveyance. A useful design estimate for representative storage capacity using the saturated moisture content and wilting point of both the VCB and VFS was determined. Significant TSS removal was observed in both the field and greenhouse studies and particulate metals were largely removed; however dissolved copper leaching was observed in the field experiment, as has been observed previously for some compost in stormwater systems. Highly elevated concentrations of nutrients (as high as 100 mg/L TN and 12 mg/L TP) were observed in the effluent of both field and greenhouse experiments, resulting in net nutrient leaching and concentrations above recommended EPA freshwater limits even after 1-2 years. Additionally, mass loading rates at the field site (as high as 41 kg/ac/yr for TN and 14 kg/ac/yr for TP) were 1-2 magnitudes higher than observed influent mass loading rates (~3.8 kg/ha/yr for TN and ~0.47 kg/ha/yr for TP). Through laboratory mineralization studies, N and P mineralization rates were found to differ between compost batches, with initial nutrient content and age/leaching of compost being important factors. Adsorption experiments indicated increasing P adsorption from compost leachate with increasing soil Al+Fe content. Comparisons to greenhouse and field data showed differences in N speciation, likely due to differences in moisture content and temperature causing differing amounts of nitrification and volatilization. OpenHydroQual modeling showed modest results, with varying levels of accuracy for storm hydrograph simulation and mass release. VCBs are not currently recommended for use due to the risk of nutrient and metals pollution, especially in nutrient and metals sensitive watersheds. However, several impactful factors were identified that may reduce nutrient leaching, including compost composition, compost age/leaching, and VFS soil type.Item IMPROVING STORMWATER QUALITY USING A NOVEL PERMEABLE PAVEMENT BASE MATERIAL(2018) OSTROM, TRAVIS Kyle; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A novel stormwater treatment media has been developed using expanded shale aggregate, Al-based water treatment residual (WTR), and psyllium-based binder. The media (HPMM) has sufficient structural capacity and hydraulic conductivity to serve as a permeable pavement base material and demonstrated effective phosphorus (P) retention in lab- and field-scale studies. Long-term adsorption capacity is projected to exceed 600 years of useful life before P saturation under conditions typical of urban stormwater in Maryland (i.e., 0.20 mg/L dissolved P (DP) influent and 100 cm of direct rainfall per year). A dynamic model was developed to describe DP adsorption onto the media based on lab testing and verified under field monitoring. The model predicted 62% DP concentration reduction and 65% DP mass load reduction. Actual reductions from 17 months of monitoring in a field pilot study were 67% for DP concentration and 69% DP mass load. Total Cu and Zn were also removed from stormwater in lab and field studies. Percent concentration reductions of 59-69% for Cu and 78-90% for Zn were shown in lab studies using synthetic stormwater. Mass load was reduced in field monitoring by 32 and 21% for Cu and Zn, respectively. WTR in the media was shown to be a potential source of nitrogen (N). An internal water storage (IWS) zone was established in a 5-cm permeable pavement base layer to mitigate N export by promoting denitrification. The IWS was shown to effectively lower N concentrations in simulated stormwater when carbon (C) was available in excess (~10 mg/L total C as C). Elevated Al concentrations were found in some filtrate samples from the field study, resulting from washout of fines from the media. Improved HPMM mix preparation methods have been developed and are critical to prevent Al washout and export. This research resulted in development of the first known enhanced stormwater treatment media to retain DP in a permeable pavement base layer. With appropriate N and Al control, the novel media can be an effective tool and can enhance permeable pavements to improve urban stormwater quality.Item Dynamics of a large submersed plant bed in upper Chesapeake Bay(2016) Gurbisz, Cassie; Kemp, Michael; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A large SAV bed in upper Chesapeake Bay has experienced several abrupt shifts over the past half-century, beginning with near-complete loss after a record-breaking flood in 1972, followed by an unexpected, rapid resurgence in the early 2000’s, then partial decline in 2011 following another major flood event. Together, these trends and events provide a unique opportunity to study a recovering SAV ecosystem from several different perspectives. First, I analyzed and synthesized existing time series datasets to make inferences about what factors prompted the recovery. Next, I analyzed existing datasets, together with field samples and a simple hydrodynamic model to investigate mechanisms of SAV bed loss and resilience to storm events. Finally, I conducted field deployments and experiments to explore how the bed affects internal physical and biogeochemical processes and what implications those effects have for the dynamics of the system. I found that modest reductions in nutrient loading, coupled with several consecutive dry years likely facilitated the SAV resurgence. Furthermore, positive feedback processes may have played a role in the sudden nature of the recovery because they could have reinforced the state of the bed before and after the abrupt shift. I also found that scour and poor water clarity associated with sediment deposition during the 2011 flood event were mechanisms of plant loss. However, interactions between the bed, water flow, and waves served as mechanisms of resilience because these processes created favorable growing conditions (i.e., clear water, low flow velocities) in the inner core of the bed. Finally, I found that that interactions between physical and biogeochemical processes led to low nutrient concentrations inside the bed relative to outside the bed, which created conditions that precluded algal growth and reinforced vascular plant dominance. This work demonstrates that positive feedbacks play a central role in SAV resilience to both chronic eutrophication as well as acute storm events. Furthermore, I show that analysis of long-term ecological monitoring data, together with field measurements and experiments, can be an effective approach for understanding the mechanisms underlying ecosystem dynamics.Item ENERGY-POSITIVE METHODS OF WASTEWATER TREATMENT-- AN EXAMINATION OF ANAEROBIC DIGESTION & BIO-ELECTROCHEMICAL TECHNOLOGY(2013) Gregoire, Kyla Patricia; Tender, Leonard; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The results presented here demonstrate plausibility of a hybrid Anaerobic Digester-Microbial Fuel Cell (AD-MFC) system for anaerobic primary (AD) and secondary (MFC) treatment and resource recovery from high-strength wastewater. We empirically determine the treatment efficiencies and energy densities achieved by the AD and MFC processes, both separately and when integrated as primary and secondary unit operations. On the basis of current production, undigested wastewater yielded an stable anodic current of 131 A/m3 when continuously fed to triplicate MFCs (chronoamperometry, Ean, -0.200V vs. Ag/AgCl). Substrate limitations in digested sludge reduced anodic current--36 A/m3, 17 A/m3, and 9 A/m3 were achieved from 6d, 13d, and 21d digestate, respectively. Cathodic limitations severely limited power/energy production by the MFC, with maximum power output of 11 W/m3 (69 mW/m2). Presumably, this was due to mass transport of oxygen reduction intermediates. When AD and MFC processes are de-coupled (i.e. each fed with undigested wastewater), the energy realized from AD (as biogas) was, on average, 29.6 kJ per m3 wastewater treated (8.2 Wh/m3), whereas the MFC produced, on average, 2.1 kJ per m3 wastewater treated (0.58 Wh/m3). On the basis of COD removal, AD separately generated 9,110 kJ per kg COD removed (2,530 Wh/kg COD) whereas MFC separately generated 0.18 kJ per kg COD removed (0.05 Wh/kg COD). When combined as primary and secondary unit processes with a 6-d digestion period (reaction period which yielded the highest net energy production), the energy output from AD (as biogas) was 23.9 kJ per m3 wastewater; the energy output from MFC (as electrical power) was 2.1 kJ per m3 wastewater. MFC treatment rates exceeded 90% COD removal, 80% VS removal and 80% TS removal, likely owing to the upflow, baffled reactor design that maximized interaction between wastewater and the anodic biofilm. Results indicate an inverse logarithmic relationship between digester retention time and subsequent MFC current production, i.e. maximal MFC current production is achieved with undigested waste, and an inverse linear relationship between digester retention time and subsequent COD/VS removal in MFCs. Breakthroughs must be made to address cathodic limitations of MFCs, before scaling is practically or economically viable.Item STUDIES OF PERIPHYTIC ALGAE ON ALGAL TURF SCRUBBERSTM ALONG THE CHESAPEAKE BAY: COMMUNITY STRUCTURE, SYSTEMATICS, AND INFLUENCING FACTORS(2012) Laughinghouse, Haywood Dail; Kangas, Patrick C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This is an ecological and systematic study of periphytic algae growing in an ecologically-engineered system used for water quality improvement: the Algal Turf Scrubber or ATSTM. This technology consists of an attached algal community growing on screens in a shallow floway through which water is pumped. The study was conducted on small-scale, experimental floways at three sites within the Chesapeake Bay watershed: on the Susquehanna River in southeastern Pennsylvania (freshwater) and on the Great Wicomico and York Rivers in Virginia (brackish water). A total of 330 taxa were identified at the sites from 2008-2011. The majority of taxa at all three sites belonged to the phylum Bacillariophyta, but a large number of taxa from Chlorophyta and, to a lesser degree, Cyanobacteria were also found at the freshwater site. Algae found in the ATSTM exhibited a diversity of life forms and modes of attachment within the community. Although these system appear to be dominated by a "canopy" of attached, filamentous species, more than half of the total abundance (cell density) were solitary, unattached taxa that grow as an "understory" within the three dimensional structure of the community. Longitudinal patterns were examined on the longest floways (90 m long) at the freshwater site. The community nutrient uptake rate (mass of nitrogen or phosphorus m-2 day-1) for the harvested algal biomass was found to decline from the top to the bottom of the floway for a system constructed at 2% slope but no distinct pattern was found for a system constructed at 1% slope. The majority of algal taxa were evenly distributed along the floway from top to the bottom, in terms of frequency of occurrence, suggesting a general lack of longitudinal specialization within the community. A detailed review of the systematics of the Order Oscillatoriales (Cyanobacteria) found on the ATSTM was undertaken since this group has not been studied much in the Chesapeake Bay watershed. Twenty-four taxa were examined, described morphologically and their nomenclature reviewed. Comparing 16s rRNA gene analyses of planktonic and periphytic Pseudanabaena, it was suggested that periphytic Pseudanabaena be revised and elevated to a new genus, Ilyonema.Item Evaluation of the effects of wetland restoration design on hydraulic residence time and nutrient retention(2009) Strano, Stephen; Felton, Gary K; Biological Resources Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hydraulic residence time (HRT) is a critical factor that can be integrated into wetland restoration designs to promote nutrient retention, but HRT in the context of wetlands with storm-driven hydrology is not well understood. A model for nutrient retention optimization based on HRT was evaluated using three indicators of HRT and nutrient stocks in above-ground plant biomass. Results indicated that a commonly used indicator of HRT, the ratio of wetland to watershed area, may be insufficient, while nominal HRT provided an overestimate for wetlands receiving storm runoff. While there was little relationship between total nitrogen and HRT, results suggested that HRT may explain some variation in total phosphorus. Results also indicated that the studied wetland restorations were not designed to provide sufficient HRT to promote the retention of dissolved nutrients, and that staged outlets could be used to provide significant HRT's for a range of storm events.Item Watershed land use and nutrient dynamics in Maryland Coasal Bays, U.S.A.(2008) Beckert, Kristen A.; O'Neil, Judith M.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Upstream and inshore regions of the Maryland Coastal Bays exhibit degraded water quality. Six streams and three shallow bays were sampled in May and July 2006 and 2007 to compare spatial patterns in relation to land use and nutrient loading. St. Martin River, having a high percentage of crop agriculture and a low percentage of forest and wetlands, experienced the most degraded water quality of the three regions, and stream total nitrogen in its watershed was linked to feeding operations and anthropogenic land use. Despite having a much less developed watershed, Johnson Bay experienced degraded water quality, especially in inshore regions. Sinepuxent Bay had the best water quality of the three bays, but still demonstrated anthropogenic impacts. Nutrient loading from land use is directly related to the observed patterns in St. Martin River, while residence time, groundwater flows, and within-bay cycling has led to water quality degradation in Johnson Bay.Item Plant-sediment Interactions and Biogeochemical Cycling for Seagrass Communities in Chesapeake and Florida Bays(2007-12-17) Nagel, Jessica; Kemp, William M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Seagrasses are prominent, productive components of shallow coastal ecosystems worldwide. The role of seagrasses in biogeochemical cycling varies widely across ecosystems, and this is due in large part to the complex interactions and feedbacks among processes controlling dynamics of carbon, oxygen, nutrients, and dissolved organic matter (DOM). This dissertation examines the importance of the keystone seagrass species, Thalassia testudinum, to biogeochemical cycling at the community and ecosystem levels in Florida Bay. The research presented here also describes the consequence of disturbances, such as shifts in species composition and seagrass dieback, on biogeochemical processes in both Florida and Chesapeake Bays. In Florida Bay, T. testudinum was shown to stimulate sediment microbial activities and benthic production of oxygen, inorganic nitrogen, and DOM relative to adjacent benthic communities without seagrass but containing benthic microalgae. Strong diel patterns in net fluxes of these solutes in both communities underscore the importance of photosynthesis. Ecosystem-level production (P) and respiration (R) rates were also enhanced in T. testudinum communities. Clear seasonal and regional variations in P and R were evident across Florida Bay, with lowest rates reported in the northern regions. Seagrass dieback had a negative effect on sediment nitrification rates and net ecosystem production (P-R) at one site in Florida Bay, and loss of seagrass habitat may result in significant changes to biogeochemical budgets within this system. In mesohaline Chesapeake Bay, the ephemeral submersed plant species, Ruppia maritima was also shown to stimulate organic production, nutrient cycling, and sediment biogeochemical processes compared to benthic communities without seagrass; however, the more persistent native species, Potamogeton perfoliatus, had an even greater impact on these processes. Collectively, the results of this research reveal the potential significance of seagrass to biogeochemical cycling in Chesapeake and Florida Bays and suggest that disturbances, such as seagrass dieback or shifts in species composition, may substantially alter biogeochemical budgets within these systems.Item The roles of nutrients and herbivory in controlling the microbioerosion of tropical reefs(2007-08-31) Silva, Marina Carreiro; Mihursky, Joseph A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Coral reefs worldwide are suffering degradation from increasing fishing pressure, pollution, diseases, and coral bleaching. One important ecological consequence of such degradation is an increase in biological erosion, or bioerosion, of the coral framework by boring and grazing organisms. Therefore, it has become essential to understand the factors that control the processes and agents of bioerosion. The aim of my dissertation is to understand how organic and inorganic nutrients and herbivory affect the bioerosion of carbonate substrates by microbial endolithic organisms (bacteria, fungi and algae), an often overlooked component of bioerosion processes in coral reefs. Results of controlled experiments using herbivore-exclusion cages and fertilizers at Glovers Reef, Belize consistently showed significant effect of nutrients in stimulating microbial endoliths' substrate colonization and bioerosion rates of Strombus gigas shells. The addition of inorganic nutrients increased bioerosion rates by a factor of 8 to 15 in comparison to control treatments. Changes in nutrient ratios changed microbial endolithic community structure. The addition of nitrogen alone or in combination with phosphorus stimulated green algae, the addition of phosphorus alone stimulated cyanobacteria, and the addition of organic matter alone stimulated fungi. The inclusion of herbivores reduced observed bioerosion rates by half, demonstrating the importance of herbivory in modifying bioerosion processes. Field experiments on the relationship between water quality and the amount of microbioerosion in Lambis chiragra shells in nine coral reefs in East Africa demonstrated that other factors within reefs may interact with nutrients in determining bioerosion rates. Results suggested that epilithic algal cover, particularly crustose coralline algae, may decrease microborer colonization and bioerosion rates by reducing light conditions within substrates, so that no direct effects of nutrients on bioerosion rates are detected. A critical review of the evidence for nutrients as a primary control of bioerosion by different bioeroder groups (microborers, macroborers, and grazers) suggests that macroborer abundances reflect increases in nutrient conditions and may therefore represent a useful indicator of eutrophication and coral reef "health". This dissertation contributes to a better understanding of the factors affecting bioerosion by microbial endolithic organisms, which are important but often overlooked agents of bioerosion in coral reefs.