Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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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 WARM SEASON HYDROLOGIC PROCESSES IN A BOREAL FOREST HILLSLOPE AND CATCHMENT, NEWFOUNDLAND(2020) Talbot-Wendlandt, Haley; Prestegaard, Karen; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Prior investigations into boreal forest ecosystems have examined hydrological processes on plot scales, examining factors such as precipitation, soil characteristics, tree rooting depths, evapotranspiration, infiltration, and groundwater, or on the catchment scale, investigating factors such as stream discharge and water chemistry. In this study, I examine hydrological processes at both plot and catchment scales, with the goal of understanding how rooting depths influence evapotranspiration (ET) and the effects of ET on catchment discharge and water chemistry. Evapotranspiration was found to influence seasonal and diurnal fluctuations in groundwater table, stream discharge, and stream electrical conductivity. Tree rooting depths were shallow, primarily within O and Ae soil horizons, suggesting that these trees intercept infiltrating water, reducing summer groundwater recharge. Stream electrical conductivity increased with cumulative ET. Summer streamflow minima coincided with hillslope groundwater minima. Stream depth and conductivity exhibited similar diurnal patterns, suggesting variations in groundwater contributions and opportunities for future research.Item USING A HIGH ORGANIC-MATTER PERMEABLE REACTIVE BARRIER TO REMEDIATE TRICHLOROETHYLENE-CONTAMINATED GROUNDWATER AT THE BEAVER DAM ROAD LANDFILL(2018) Nino de Guzman, Gabriela Tejeda; Kjellerup, Birthe V; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Trichloroethylene (TCE) is an effective industrial degreaser and known carcinogen. It was frequently improperly disposed of and has become one of the most common groundwater and soil contaminants in the USA. Clean up continues to be difficult due to its physical and chemical properties. TCE and several of its degradation products were detected in the groundwater of the Beaver Dam Road Landfill (Beltsville, MD) at concentrations above their maximum contaminant levels (MCLs). The US Department of Agriculture-Agricultural Research Service together with the University of Maryland, College Park and BMT Designers and Planners designed a permeable reactive barrier, or biowall, to remediate the contaminated groundwater. A series of batch reactor studies were conducted at 12°C to examine biowall fill-material combinations including the effects of zero-valent iron (ZVI) and glycerol amendments. Headspace samples were analyzed over the course of several months to monitor TCE degradation. An unamended, 4:3 mulch-to-compost combination was chosen based on no detectable TCE at the conclusion of the experiment. To increase the biowall degradation capacity, microbial infiltration and colonization of the structure were also studied. PCR, qPCR, and next-generation sequencing were used to survey the site’s indigenous population for dechlorinating clusters. Numerous clusters were identified affirming the use of the native population for bioaugmentation efforts. The ability of the biowall to support said community was investigated by monitoring continuously-fed column reactors containing biowall material spiked with a commercially-available, surrogate population, with and without a 5 mg/L dose of ZVI. The groundwater-fed column sans ZVI had the greatest Dehalococcoides population and while ZVI without biostimulation did decrease the overall population, it did not cause a statistically significant difference. Thus, if ZVI were to be used as a future biowall amendment, biostimulation would not be required to maintain a dechlorinating population. A sacrificial carbon source may be necessary to slow the biological degradation of the biowall’s organic fill-material. These findings will be utilized in future remediation and/or biowall expansion plans to fully employ the site’s natural resources. The biowall was constructed in July 2013 containing the 4:3 mulch-to-compost ratio and has reduced the upstream TCE concentration by ~90%.Item Investigation into the Potential Toxicity of Zero-Valent Iron Nanoparticles to a Trichloroethylene-Degrading Groundwater Microbial Community(2013) Zabetakis, Kara Margaret; Torrents, Alba; Yarwood, Stephanie A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The microbiological impact of zero-valent iron remediation of groundwater was investigated by exposing a trichloroethylene-degrading anaerobic microbial community to bare and coated iron nanoparticles. Changes in population numbers and metabolic activity were analyzed using qPCR and were compared to those of a blank, negative, and positive control to assess for microbial toxicity. Additionally, these results were compared to those of samples exposed to an equal concentration of iron filings in an attempt to discern the source of toxicity. Statistical analysis revealed that the three iron treatments were equally toxic to total Bacteria and Archaea populations, as compared with the controls. Therefore, toxicity appears to result either from the release of iron ions and the generation of reactive oxygen species, or from alteration of the redox system and the disruption of microbial metabolisms. There does not appear to be a unique nanoparticle-based toxicity.Item WATER QUALITY IN MANAGEMENT INTENSIVE GRAZING AND CONFINED FEEDING DAIRY FARM WATERSHEDS(2005-07-12) Gilker, Rachel Esther; Weil, Ray R.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dairy farm size has increased in the United States, while the profit margin has decreased. An alternative to confined feeding dairy farming is management intensive grazing (MIG), a grass-based system relying on rotational grazing for most of the herd's dietary requirements. Previous research has measured high levels of nitrate leaching under MIG, citing the liquid nature and high nitrogen (N) content of urine. However, this research included heavy N fertilizer applications or was conducted on monolith lysimeters with artificial leaching processes and did not accurately represent mid-Atlantic MIG dairy farms. Phosphorus (P) losses have typically been attributed to runoff and erosion but are now being ascribed to leaching as well. To measure the magnitude of N and P losses to groundwater, we sampled shallow groundwater and pore water on one confined feeding and two MIG-based Maryland dairy farms between 2001 and 2004. Transects of nested piezometers and ceramic-tipped suction lysimeters were installed in two watersheds on each farm. Two streams running through two of the grazed watersheds were also sampled to measure the effects of grazing on surface water. For three years, groundwater and surface water samples were collected biweekly and pore water was collected when conditions made it possible. Samples were analyzed for inorganic N and dissolved reactive P and were digested for determination of dissolved organic N and P, pools previously not considered major sources of nutrient loss. Seasonal mean nitrate concentrations under the grazed watersheds remained below the EPA maximum contaminant load of 10 mg L-1 with only two exceptions on the grazed watersheds. Mean nitrate concentrations in the four grazed watersheds ranged from 3 to 7.44 mg L-1. Nitrogen losses were closely correlated to farm N surpluses. Groundwater P concentrations exceeded the EPA surface water critical levels in all six watersheds. Geologic factors, rather than dairy farm management, played a large role in P losses. In all watersheds, substantial pools of dissolved organic N and P were measured in groundwater. Low nitrate losses under MIG as well as the environmental advantages inherent in a grass-based system make grazing a viable Best Management Practice.Item Characterization of the spatial differences in hydrological functioning in a tidal marsh, Patuxent River, MD: A framework for understanding nutrient dynamics(2004-12-08) Phemister, Karen; Prestegaard, Karen L.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study investigates spatial variations in sediment hydraulic conductivity (K), network channel shape and horizontal groundwater flux magnitude toward tidal network channels in a freshwater tidal marsh. Results showed the average value of K at zero meters from the creekbank was significantly higher than the K at both 5 and 15 meters from the network channel creekbank. Creekbank gradient did increase with increasing distance from the main channel and some data indicated that channel width-to-depth ratio (F), which is inversely related to creekbank gradient, correlates well with K. In addition, horizontal groundwater flux magnitude at a depth of 11 cm was significantly greater than flux magnitude at 22 cm below the ground surface at the first-order network channel location. Horizontal flux magnitude was also significantly higher from 5 to 0 meters than from 15 to 5 meters from the network channel creekbank at both the first- and second-order channel locations.