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 MANAGEMENT OPTIONS FOR FARMERS FACING SALTWATER INTRUSION ON THE EASTERN SHORE OF THE CHESAPEAKE BAY(2023) Schulenburg, Alison Nicole; Tully, Kate; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rising sea levels, storms, and perigean spring tides push saltwater into coastal agricultural fields. This phenomenon, known as saltwater intrusion, alters nutrient cycling and damages crop yields. As sea levels continue to rise, saltwater intrusion will only worsen, with devastating consequences to agroecosystems along the coast of the Chesapeake Bay. Researchers and farmers alike are looking for solutions to adapt to and mitigate the effects of saltwater intrusion. Landowners may respond by altering their management practices. Farmers may 1) adapt by planting a salt-tolerant crop, 2) attempt to remediate soils with trap crops, 3) restore native marsh grasses, or 4) abandon fields altogether. My project investigates the survival of different crops and plant treatments under saltwater-intruded conditions and the potential for these plants to survive and to remove excess nutrients (e.g. sodium and phosphorus) from the soil, with the overall goal to benefit both the farming community and water quality in the Chesapeake Bay. Results from this study will help inform new management practices to increase soil health and maintain crop yields. Finally, the goal of this work is to guide local best management practices and potential easement opportunities for landowners facing saltwater intrusion, and ultimately determine optimal strategies for climate resilience.Item ORGANIC MATTER SOIL AMENDMENTS, ANOXIC SOIL BIOGEOCHEMISTRY AND WETLAND RESTORATION(2021) Scott, Brian; Yarwood, Stephanie; Baldwin, Andrew H.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Organic Matter (OM) amendments are often used in wetland restoration – a practice required in Maryland and other states. This work summarizes a literature review and lab and field experiments to evaluate the consequences of OM amendment use. The literature review showed that although OM use is widely accepted, the evidence that they are effective is weak, and there can be negative effects. Transplanted topsoil is much more effective than allochthonous OM (e.g., manure). OM amendments were largely ineffective in a field study conducted on a mitigation wetland in Caroline County, MD, and negative consequences were possible, although composting the OM relieved negative effects. One example of ineffectiveness: OM is not needed to develop anaerobic conditions in saturated soil. While in some cases OM seems to be a benefit, as in aboveground biomass production, this is usually accompanied by a loss of diversity and it selects for undesired and invasive species. One of the negative consequences OM is the increased production of methane, a greenhouse gas, which became the focus of this work. Two lab microcosm studies and a field study revealed that rewetting dried soils (as in after mitigation wetland construction) immediately releases small amounts of methane, and methane sharply increases after about 7 weeks. Using OM affects methane production in two ways. First, overall methane production usually increases. Second, the time frame before there is a sharp increase in methane production is shorter, from ~7 weeks to as little as 1 or 2 weeks. These effects are somewhat reduced with composted OM. Using a Stable Isotope Probing microcosm study, the work also helped to identify the archaeal and bacterial taxa that are responsible for the sudden increase in methane. Methanosarcina is likely the primary taxa responsible for methane generation. Understanding the conditions that result in methane emanating from wetlands could lead to practices that reduce its release into the atmosphere, where it contributes to global warming. Methane is a more potent greenhouse gas than carbon dioxide, but is short lived, so controlling methane emissions can have a more immediate effect on climate change.Item Saltwater intrusion alters nitrogen and phosphorus transformations in coastal agroecosystems(2020) Weissman, Dani; Tully, Katherine L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As sea levels rise, coastal regions are becoming more vulnerable to saltwater intrusion (SWI). In coastal agricultural areas, SWI is causing changes in biogeochemical cycling in soil and waterways. These changes are leading to the release of excess nitrogen (N) and phosphorus (P) from farm fields, which in turn can cause impaired water quality downstream. I explored the effects of saltwater intrusion on N and P concentrations of surface water and soil porewater on Maryland’s Eastern Shore in the Chesapeake Bay Watershed on three spatial and temporal scales: 1) a three-year field study through farmland and various surrounding habitats; 2) a one-month laboratory soil incubation study; and 3) a regional study of tidal tributaries (sub-watersheds) along Maryland’s Eastern Shore where I utilized 35 years of observational data on nutrient concentrations and salinity from the Chesapeake Bay Water Quality Monitoring Program. The results of the field and incubation studies suggest that SWI can cause a large release of N and P from the soils of coastal landscapes to downstream water bodies such as tidal creeks and marshes. However, the results of the regional study suggest that the relative magnitude of SWI-driven contributions of N and P to waterways as compared to other sources and drivers of N and P differ depending on the spatial and temporal scale considered. Defining mechanisms through which SWI spurs nutrient release from soils of agricultural fields and surrounding habitats as well as the magnitude of these processes is critical for quantifying N and P export in coastal watersheds. The results of these three studies can potentially be used to inform water quality models for individual tidal tributaries, which would allow for more targeted approaches to nutrient load reductions in sub-watersheds of the Chesapeake Bay and other watersheds globally.Item Soil microbial processes and community structure in natural and restored tidal freshwater wetlands of the Chesapeake Bay, Maryland, USA(2017) Maietta, Christine E.; Yarwood, Stephane A.; Baldwin, Andrew H.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal freshwater wetlands are integral to downstream water quality because they capture, store, and transform nutrients. Unfortunately, anthropogenic stressors are negatively impacting these habitats. While wetland restoration is helping to reinstate their presence in the landscape, restored wetlands frequently differ physically, chemically, and biologically from their natural counterparts. This research examined plant, soil, and microbe relationships and how their interactions affect soil carbon (C) storage and cycling in natural and restored tidal freshwater wetlands of the Chesapeake Bay, MD, USA. This research yielded important findings regarding differences between natural and restored habitats. First, we discovered soil microbial community composition of an urban tidal freshwater wetland retained similar composition as their less disturbed, suburban counterpart, and wetland sites constructed using similar restoration methodology produced similar microbial community structure and soil function. Additional research revealed that a natural and a restored wetland store soil C quite differently: A majority of soil C in the natural site was associated with large macroaggregates (> 2000 μm) whereas most soil C in the restored site was associated with smaller macroaggregates (> 250 to < 2000 μm). The distributions of six chemical compound classes (i.e., carboxylics, cyclics, aliphatics, lignin derivatives, carbohydrates derivatives, N-containing compounds) were relatively similar across the five soil fractions from both sites, however. In the final study, anaerobic laboratory mesocosms were used to evaluate the effects of clay content (%) and leaf litter quality on soil C cycling processes over time. This study found restored soils, regardless of clay content, mineralized more C as carbon dioxide (CO2) and methane (CH4) compared to natural wetland soils. Natural soils respired approximately half the volume of gas as restored soils, suggesting the addition of high- or low-quality C substrates to low C systems elicit a greater response from the heterotrophic microbial community. The results of these three studies suggest site history and edaphic features of restored wetlands are important drivers of microbial communities and their function. We propose that practitioners and researchers work together to identify practices that will enhance soil functions, particularly C storage, in tidal freshwater wetlands of the Chesapeake Bay region.Item Methane Emissions From A Tidal Brackish Marsh On Maryland's Eastern Shore and the Factors Impacting Them(2016) Derby, Robert Kyle; Needelman, Brian A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Methane is a potent greenhouse gas and may offset a significant portion of the carbon sequestration benefit of many brackish marshes. The objective of this study was to determine whether methane emissions varied across different hydrologic/vegetative communities within a tidal brackish marsh, and if so, what other variables varied with them. We sampled methane emissions from two brackish marshes using static flux chambers, on Maryland’s Eastern Shore. Additional data was collected from sampled marsh pore water, water level and soil temperature. We found that there was a significant difference in methane emissions between different hydrologic/vegetative communities. The results of this study help explain the factors that influence methane emissions in a tidal brackish marsh, and the vegetative communities therein; these factors could be used to develop models to better estimate methane emissions at the site-landscape level.Item Redox and Soil Manipulation Effects on Ditch Soil Phosphorus Processing(2012) Ruppert, David Emmanuel; Needelman, Brian A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ditches increase the connectivity of landscapes to open water systems, potentially facilitating the degradation of downstream waterways. A treatment and an observational experiment were conducted to identify processes behind phosphorus (P) cycling in ditch soils. If the ditch had not undergone recent dredging soils were observed in the treatment experiment to release P to surface water whether the soil system was iron (Fe)-oxidizing or Fe-reducing. Also in the treatment experiment, Fe was released to surface water in appreciable amounts only if the soil system was Fe-reducing. From the observational experiment P release due to mineralization was inferred due to a positive trend with temperature. Also in the observational experiment Fe-reducing conditions were weakly correlated with diminished P concentrations in the ditch water. It was inferred that emergent Fe(II) released from within the soil through reductive dissolution captures P from ditch surface water upon oxidation. In the treatment experiment dredging and saturated conditions resulted in similar effluent P concentrations as drained soils that were undredged. This may explain a lack of dredging effect that was observed in the field.Item Evaluation of the Effects of Bioaugmentation and Biostimulation on Natural Attenuation and Biodegradation Pathways of Chlorinated Compounds in a Tidal Wetland(2006-12-12) Devillier, Emily Nicole; Becker, Jennifer G; Biological Resources Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The usefulness of bioaugmentation and biostimulation in enhancing the natural attenuation of chlorinated compounds at a seep site at Aberdeen Proving Ground, MD was tested. The biodegradation of (1) a mixture of 1,1,2,2-tetrachloroethane, tetrachloroethene, and carbon tetrachloride, or (2) TeCA alone was compared in microcosms amended with chlorinated substrates alone, chlorinated substrates and electron donor, and chlorinated substrates, electron donor, and a TeCA-degrading enrichment culture. A third experiment evaluated the usefulness of H2 thresholds in determining the importance of co-metabolic and metabolic processes in biodegradation. TeCA biodegradation was significantly enhanced by bioaugmentation and biostimulation. However, the presence of other contaminants inhibited TeCA biodegradation, even in the presence of electron donors and the enrichment culture. H2 thresholds did not prove useful in determining the importance of metabolic and co-metabolic processes; however, evaluating each chlorinated compound individually provided insight regarding biodegradation pathways and the effects of electron donor substrates on degradation rates.