Environmental Science & Technology

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    Managing Cover Crops for Better N Efficiency and Soil Health
    (2024) Stefun, Melissa; Weil, Ray; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Winter cover cropping is a major tool that agriculture can use to protect soil and water quality and mitigate climate change. Unlike farmland in the world at large, most Maryland cropland has seen little tillage disturbance and some level of cover cropping for decades. With that background, field experiments on two soils with contrasting textures at the Beltsville Facility of Central Maryland Research and Education Center tested the effects of cover crop management enhancements on nitrogen (N) leaching, soil health indicators, and cover crop N uptake over three years. Two cover crops (sole rye and a mixture of forage radish, crimson clover, and rye) were compared to a control where cover cropping was ceased. The cash crops were corn and soybean grown in rotation. With best nutrient management practices applied, suction lysimeter sampling at 90 cm depth from October through April showed low levels of N leaching in general, but NO3-N concentrations were significantly lower under cover crops. Overall mean concentrations of NO3-N were 2.20 mg N/L in the control but 0.43 mg N/L under cover crops. Additionally, soil water samples were digested to determine dissolved organic N (DON) which was found to make up between 44-60% of the total dissolved N in the leaching water. In additional experiments, a small fertilizer N application was made to cover crops to stimulate rapid deep rooting with the goal of accessing soluble N deep in the profile to increase N capture by more than the amount of N applied. The response to fall N fertilization failed to accomplish this goal and was not related to the surface soil NO3-N concentration as expected. In spring, cover crops were terminated on three dates from mid-April to mid-May and rye biomass doubled with each extra two weeks it was allowed to grow whether it was in the mix or alone. The effect of cover crops on soil health indicators was evident with increased soil permanganate oxidizable carbon, total soil carbon, lower bulk density, and greater aggregation. These experiments demonstrated that cover crops with enhanced management can have marked effects on an agricultural system already using sustainable practices.
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    MOSQUITOES AND VEGETATION ACROSS SOCIOECONOMIC GRADIENTS
    (2024) Rothman, Sarah; Leisnham, Paul T; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The biomass and composition of local vegetation is a key resource for juvenile mosquitoes, affecting a suite of life history traits including survival, development rate, and body size. In cities across the United States, both plant and mosquito communities vary with socioeconomics. Vegetation is typically more abundant and biodiverse in high-income neighborhoods, whereas mosquitoes are often more numerous and more likely to vector diseases in low-income neighborhoods. While prior work has examined the effects of plant resources on mosquitoes, my dissertation evaluates how these communities interact across a socioeconomically diverse urban landscape. Chapter 1 is a scoping review of current knowledge of the individual relationships between mosquitoes, plants, and socioeconomics in cities. In Chapter 2, I describe fine-scale vegetation surveys on socioeconomically diverse residential properties in Baltimore, MD and Washington, D.C. that revealed less canopy cover, more vines, and more non-native plant species on lower-income blocks. In Chapter 3, I used leaves from the most frequently observed canopy species on low- and high-income blocks, and species common to both, as detrital resource bases in competition trials between two dominant urban mosquitoes, Aedes albopictus and Culex pipiens. Population performance for both species was greater when reared with characteristically low-income than characteristically high-income detritus, suggesting that socioeconomically diverse plant communities are an important factor in shaping urban mosquito communities. Overall, population performances were greatest when mosquitoes were reared in the regionally representative detritus, and I used this detritus base in Chapter 4 to evaluate the effects of varying temperatures. Aedes albopictus population performance was optimized at higher mean temperatures characteristic of low-income blocks, while C. pipiens performance was best at lower mean temperatures characteristic of high-income blocks. Population performance was often lower, however, when temperatures fluctuated around a high or low mean than when the temperature was stable, suggesting that laboratory studies may need to mimic field conditions to obtain applicable results. My research provides a deeper understanding of the mechanisms behind previously observed relationships, and may help guide management and policy strategies to address environmental injustices and public health threats.
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    MODELING GROUNDWATER FLUCTUATIONS IN THE COASTAL PLAIN OF MARYLAND: AN ANN POWERED STRATEGY
    (2024) Steeple, Jennifer Lynne; Negahban-Azar, Masoud; Shirmohammadi, Adel; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Groundwater management in the face of climate change presents a critical challenge with far-reaching implications for water resource sustainability. This study evaluates the effectiveness of Artificial Neural Networks (ANNs) as predictive tools for estimating current groundwater levels and forecasting future groundwater levels in the Aquia aquifer in the Coastal Plain ofMaryland. The groundwater levels of the Aquia aquifer have declined under the pressures of land use change, increases in agricultural irrigation, and population growth. We tested, trained, and employed eight county-level artificial neural network (ANNs) models to predict and project Aquia aquifer groundwater levels for the near (2030-2050) and far (2050-2100) future under two socio-economic pathways (SSP245 and SSP585). The models exhibited significant predictive performance during testing (R²= 0.82-0.99). Minimum temperature and population were the most influential variables across all county-based models. When used to forecast groundwater level under two climate scenarios, the models predicted declining groundwater levels over time in Calvert, Caroline, Queen Anne’s, and Kent counties, aligning with regional trends in the Aquia aquifer. Conversely, Anne Arundel, Charles, St. Mary’s, and Talbot counties exhibited projected increases in groundwater levels, likely influenced by correlations with the variable irrigated farm acreage, underscoring the importance of considering nonlinear relationships and interactions among variables in groundwater modeling. The study highlights the ability of ANNs to accurately predict county-scale groundwater levels, even with limited data, indicating their potential utility for informing decision-making processes regarding water resource management and climate change adaptation strategies. This study also assessed the usability of multiple methods to fill in the missing data and concluded that using the repeated groundwater level data still resulted in powerful ANN models capable of both predicting and forecasting ground water levels in the Coastal Plain of Maryland.
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    Sperm Quality Characterization of Male Mummichog (Fundulus heteroclitus) in Response to Legacy Contaminants
    (2024) Malik, Sabine; Yonkos, Lance; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Historically contaminated rivers persist as hazards to ecosystem and human health despite remediation attempts, impacting the species found in these ecosystems. These rivers contain complex mixtures of legacy contaminants, including dioxins, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons, many of which are classified as endocrine disrupting compounds. Due to this level of contamination, few fish species are pervasive in these systems, an exception being the mummichog (Fundulus heteroclitus), known for its acquired tolerance of contaminated environmental conditions. While female and offspring reproductive success have been well-documented in the literature, few studies have investigated the use of sperm quality as a tool for assessing reproductive harm from contaminant exposure. Therefore, this study aims to demonstrate the usefulness of sperm quality characterization through the use of three assays: computer-assisted sperm analysis (CASA), a bioluminescent adenosine triphosphate (ATP) assay, and a modified Comet assay. This novel method was developed through field-collection of F. heteroclitus in three historically-contaminated tidal rivers in the United States: the Passaic River, NJ, the Christina River, DE, and the Anacostia River, MD. The results of this study not only present a novel method for investigating fish health in contaminated aquatic environments, but also a comparison of differential outcomes that can occur in rivers with varied contaminants and histories of pollution.
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    GENERATING BIOENERGY AND HIGH-VALUE PRODUCTS FROM HIGH SALINITY FOOD WASTE
    (2024) McCoy, Emily Lim; Lansing, Stephanie; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Bioenergy generation and volatile fatty acids (VFAs) production from household food waste and high salinity food processing waste were explored using anaerobic digestion and dark fermentation processes, respectively. This study tested adding value to three organic waste streams: household food waste, high salinity food processing waste (composed of glycerin sludge from biodiesel production), and residual solids from VFAs separation after dark fermentation of food waste. The investigations were conducted using batch and semi-continuous systems in mesophilic conditions (35°C). Methane (CH4) potential tests were conducted to determine the bioenergy production of food waste and residual solids, including the addition of dark fermentation gas at four ratios of hydrogen (H2) to carbon dioxide (CO2) (1:1, 1:2, 1:3, 1:5) into the liquid portion of the reactor to enhance CH4 production and three inoculum to substrate ratios (1.5:1, 2:1, 4:1). Additionally, a semi-continuous dark fermentation study was used to determine the VFA production from household food waste and high salinity food processing waste combinations over 62 days. The anaerobic digestion of residual solids from VFAs separation had similar bioenergy potential as household food waste when normalized by volatile solids (VS) added (492 ± 11 mL CH4/g VS and 470 ± 11 mL CH4/g VS, respectively). Dark fermentation gas added into the liquid portion of the reactor during anaerobic digestion decreased CH4 yields, especially at low H2:CO2 ratios, suggesting that only dark fermentation reactors that produce high H2:CO2 ratios should have the gas sparged into anaerobic digestion systems. When the residual solids from dark fermentation were fermented at three inoculum to substrate ratios (1.5:1, 2:1, 4:1), the lowest inoculum to substrate ratio (1.5:1) had the highest VFAs concentration (28.05 ± 0.89 g/L) after nine days of fermentation, which showed that residual solids can be fermented with low inoculum levels, allowing more room for substrate fermentation. Additionally, the mono- and co-fermentation of household food waste and high salinity food processing waste showed that the high salinity waste improved VFA production due to the high pH (9 – 10) and high organic loading (6.3 – 17.8 g VS/L-day), even with high salinity levels (21.4 – 85.6 g/L Na) in this waste. There was significantly higher VFA production in high salinity food processing waste (36.04 ± 0.54 g/L) compared to household food waste (9.29 ± 1.01 g/L). The maximum VFA concentration (36.04 ± 0.54 g/L) was achieved after 51 days of high salinity food processing waste semi-continuous fermentation. The findings in this study can be used to improve operations of anaerobic digestion and dark fermentation systems by using residual solids for bioenergy generation or VFA production. The testing of mono- and co-fermentation of household food waste and high salinity food processing waste showed high VFA production in fermenting high salinity food processing waste. This work showed the valorization of three organic waste streams through bioconversion to both bioenergy and high-value products (VFAs), which redirected these waste products from municipal solids landfills and into resources, thereby reducing CH4 released into the atmosphere from landfills and reducing global warming potential.
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    INVASIVE LIANA HEDERA HELIX (ENGLISH IVY) IMPACTS ON ECOLOGICAL CHARACTERISTICS AND NUTRIENT CYCLING IN BALTIMORE FOREST PATCHES
    (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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    INDIGENOUS INVOLVEMENT IN ECOLOGICAL RESTORATION: AN ANALYSIS OF VIRGINIA’S SOVEREIGN NATIONS INVOLVEMENT IN THE CHESAPEAKE BAY PROGRAM
    (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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    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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    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.