College of Agriculture & Natural Resources
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item 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.Item 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.Item 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.Item 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.Item 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.Item THE USE OF ORGANIC WASTE PRODUCTS AS SOIL AMENDMENTS FOR TURFGRASS ESTABLISHMENT: EFFECTS AND REGULATORY INFLUENCES(2024) Morash, Jennifer Dawn; Lea-Cox, John; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The use of organic waste products as soil amendments in highly disturbed urban soil is poised to grow due to rising fertilizer costs, waste-management issues, and greater emphasis on creating sustainable circular economies. Despite the advantages of using waste products as organic amendments to enhance fertility, their incorrect use may result in short-term unintended consequences such as nutrient losses or the immobilization of plant-essential nutrients, which could diminish efforts to establish vegetation on disturbed soil. To avoid these consequences, transportation authorities – cited as the largest users of compost in some states – have implemented measures to improve product specifications. This research details the efforts of one such organization, the Maryland Department of Transportation State Highway Administration (MDOT SHA), and the results of an initiative to increase the quality of manufactured topsoil and compost use through agency topsoil specifications. After determining which products were most likely to be incorporated into manufactured topsoil (finely shredded wood mulch and composted leaf yard waste), two greenhouse microcosm experiments were conducted to evaluate plant growth responses and the efficiency of nutrient uptake compared to leachate losses when those amendments were used in accordance with MDOT SHA specifications. Composted yard waste provided excellent results while wood mulch suppressed growth in the short-term studies. A biosolids treatment was included in the experiments due to widespread availability and growing interest. Biosolids improved soil fertility and plant growth. However, the difference between nitrogen (N) uptake and leachate mass losses required a second set of experiments, to quantify the effects of four biosolids amendments on plant growth, nutrient uptake, and leachate losses. Treatments were applied at the rate recommended by UMD for turfgrass establishment (2.54 cm, incorporated) and included fresh biosolids, biosolids that were stockpiled for two years, two blended products made from either the fresh or aged biosolids and fine wood mulch, an inorganic fertilizer, and a control. Aging and wood fines reduced N leaching losses but at the expense of N inputs to soil. The cumulative N leachate mass loss from the new biosolids treatment was 63 times greater than the cumulative fertilizer total. Aging did not reduce phosphorus (P) leaching losses but wood fines did by diluting the concentration of P in blends. However, biosolids mostly retained P in the soil and cumulative fertilizer losses were 2 times higher. Overall, growth measurements showed that biosolids enhanced growth during the first and second growing seasons. However, based on the results of this research, 2.54 cm of pure biosolids is not required to enhance turfgrass establishment. An application of 1.27 cm of pure biosolids or 2.54 cm of a biosolid/wood fine blend should provide comparable enhanced turfgrass growth results while reducing overall nutrient leachate losses.Item 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.Item 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.Item Dual water quality responses after more than 30 years of agricultural management practices in the rural headwaters of the Choptank River basin in the Chesapeake Bay watershed(2023) Silaphone, Keota; Fisher, Thomas R; Natural Resource Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Eutrophication is the water quality response to over-enrichment by nitrogen (N) and phosphorus (P) in fresh, estuarine, and coastal waters globally. Agricultural best management practices (BMPs) are the primary tool for controlling eutrophication in rural areas, particularly in the Chesapeake Bay watershed, where BMPs are vital to achieving TMDL goals. However, despite the application of BMPs, local water quality in the headwaters of the Choptank River, a major tributary of the Chesapeake Bay on the Delmarva Peninsula, has not improved. Thus, further investigation of agricultural BMP impacts on water quality in the Greensboro watershed is needed. My overarching research question is, “Why have N and P concentrations increased at the USGS Greensboro gauge if agricultural Best Management Practices (BMPs) have been implemented?” I applied statistical approaches to three linked, testable hypotheses to systematically evaluate agricultural BMPs and their impacts on nutrient (N and P) export from the Greensboro watershed. My first hypothesis was that agricultural BMPs have increased significantly in the Greensboro watershed. To test this hypothesis, I obtained publicly available modeling data via the Chesapeake Assessment Scenario Tool (CAST) and estimated the subsequent edge-of-stream N and P export. My findings indicated that the number of BMPs in the agricultural sector increased significantly between 1985 and 2021, supporting the hypothesis. Overall, modeled agricultural N and P export significantly decreased between 2010 and 2021 (p < 0.001). However, the modeled edge-of-stream agricultural nutrient export resulted in no significant change in N export and an increase of 3% in agricultural P export resulting from BMP implementation levels in 2021 compared to 2010. This study demonstrated the use of CAST to acquire reported BMP implementation levels and increased nutrient inputs into the Greensboro watershed between 1985 and 2021. The watershed nutrient inputs mirror the upward trends in N and P export captured by the USGS long-term monitoring station at Greensboro. With this improved access to BMP implementation and nutrient data, decision-makers can consider adaptive management measures to decrease nutrient export downstream. My second hypothesis was that agricultural BMPs have an adequate basis for estimating their capacity to reduce N export. To test this hypothesis, I conducted a meta-analysis on 689 cover crop N efficiencies reported in 18 empirical and modeling studies. The cover crop N efficiency was calculated as the ratio of an N interception by cover crop biomass or a reduction in soil or groundwater N divided by an N input, e.g., previous spring fertilizer or a previous soil or groundwater N concentration or flux. These variable approaches resulted in wide ranges in mean cover crop N efficiency (10-80%) due to empirical and modeling experimental approaches, varying methods, and parameters used to calculate efficiency. The modeling approach generally resulted in N efficiency values significantly higher than the empirical approach, as did the parallel control-treatment experiments compared to the sequential before-and-after implementation method. Because of these variables, there appears to be no standard methodology to report the effects of cover crops or standardized metadata describing the variables used in the N efficiency calculations. I suggest a standard methodology and metadata that should accompany future reports of cover crop N efficiencies to improve the modeled effects of BMPs on nutrient export. My third hypothesis was that three methods of estimating N and P concentrations and yields are in agreement and show a relationship to BMP implementation in the Greensboro watershed. To test this hypothesis, I compiled annual nutrient (N and P) datasets based on (1) USGS field measurements of concentrations and discharge, (2) USGS flow-normalized weighted regression based on time, discharge, and season (WRTDS) of concentrations and yields, and (3) CAST-modeled nutrient yields. Statistical analyses revealed time, discharge, agricultural BMPs, and animal waste management practice trends of the three methods. Results indicated that the USGS field measurements and WRTDS flow-normalization methods consistently showed an increase in N and P concentrations and yields. In contrast, all CAST-modeled regressions showed significantly decreasing nutrient concentrations and yields (p ≤ 0.05), which did not support the hypothesis that all three methods are in agreement. Despite CAST-modeled results decreasing with increasing BMPs, which supports the hypothesis that N and P concentrations and yields show a relationship with BMP implementation, USGS methods resulted in increasing nutrient concentrations and trends. These results indicated significant underestimates of modeled N and P export by CAST. I recommend using adjusted BMP efficiencies during cultural and structural BMP lifespans to improve model outputs. I also suggest two approaches to reflect the role of annual poultry manure applications: (1) model nutrient transport via artificial drainage ditches that interfere with natural nutrient flow pathways and exacerbate N and P transport, and (2) model the accumulation of soil-P and saturated soil-P, resulting in increases in dissolved P and particulate P in downstream surface waters. Agronomic recommendations include developing efficient manure recycling approaches within the local agricultural systems via nutrient management practices and concurrent research and development to support alternative uses of animal waste, including composting, bioenergy generation, granulating/pelletizing, and establishing a marketplace to support the sale of these products and to offset the costs of transporting manure from areas of manure surplus to manure deficit areas. This dissertation revealed that modeling studies overestimate cover crop N efficiencies in the United States Coastal Plain province and that CAST modeling is not in agreement with the USGS field measurements. CAST-modeled nutrient concentrations and yields decrease over time, indicating improvements in water quality. In contrast, USGS methods consistently show that nutrient concentrations and yields increase, indicating that BMPs are insufficient, inadequate, overwhelmed by nutrient inputs, or efficiencies are overestimated. Indeed, nutrient-reducing BMPs have increased between 1985 and 2021. With over 35 years of BMP implementation, measurable water quality response is expected. However, BMPs that relocate and apply higher amounts of manure annually have also increased with nutrient-reducing BMPs. Rising manure application rates combined with higher fertilizer application rates due to economic pressures on farmers to increase crop yields appeared to have overwhelmed implemented BMPs. Continued manure applications onto croplands in the Greensboro watershed suggest nutrient export will continue to rise; thus, reaching water quality goals is unlikely.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.