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 WATER REUSE FOR FOOD PRODUCTION IN THE WEST BANK AND ISRAEL: ASSESSING THE EFFICACY OF HOUSEHOLD GREYWATER TREATMENT SYSTEMS, AND CONSUMER PERCEPTIONS OF REUSE APPLICATIONS(2019) Craddock, Hillary Anne; Sapkota, Amy R; Maryland Institute for Applied Environmental Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Greywater is increasingly reused for agricultural irrigation in the Middle East. However, there is a dearth of data regarding antibiotics, herbicides, and antibiotic-resistant bacteria in household greywater reuse systems. Additionally, there are minimal data assessing consumer perceptions of water reuse practices. To address these gaps, my dissertation aims were to: 1) evaluate the presence of antibiotics and herbicides in greywater and treated effluent; 2) assess the prevalence of antibiotic-resistant Enterobacteriaceae in greywater and treated effluent; and 3) explore consumer perceptions of water reuse practices in Israel and the West Bank. For Aims 1 and 2, household greywater (n=23), treated effluent (n=23) and pond water (n=12) were collected from four farms in the West Bank from October 2017 to June 2018. The presence of antibiotics and herbicides was quantified using high performance liquid chromatography-tandem mass spectrometry, E. coli were enumerated via membrane filtration, and isolates were tested for antimicrobial susceptibility using microbroth dilution. For Aim 3, surveys (n=236) were administered in Eilat, Israel and Bethlehem, West Bank. Statistical analysis included ANOVA, chi-squared, and Fisher’s exact tests. Multiple antibiotics and herbicides were detected in greywater influent. Removal during treatment was variable across compounds. The majority of influent (76.5%) and effluent (70.6%) samples had detectable levels of E. coli. Resistance was most commonly observed against ampicillin, trimethoprim-sulfamethoxazole, tetracycline, and cefazolin. Regarding consumer perceptions, >50% of Israeli respondents were willing to serve raw and cooked produce irrigated with reused water. Palestinian respondents were more willing to engage in high-contact uses than Israeli respondents. The successful completion of this research has advanced knowledge regarding 1) the persistence of chemical and microbiological contaminants in treated household greywater that is used for food crop irrigation; and 2) consumer acceptance of water reuse practices. Farmers in the West Bank and around the world are combating decreasing quality and quantity of water and will increasingly rely on consumers willing to purchase produce irrigated with treated wastewater. Future work must ensure that farmers have access to safe and abundant irrigation water, and that consumers can be confident that they are purchasing safe food.Item SPATIAL AND TEMPORAL VARIANCE OF MICROBIAL WATER QUALITY IN TWO MARYLAND IRRIGATION PONDS(2019) Kierzewski, Rachel Annette; Hill, Robert; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Farm ponds must be regularly sampled for Escherichia coli (E. coli) concentrations to evaluate the health risks of using pond water for irrigation. However, no guidance is available regarding sampling locations and/or irrigation pump placement. We hypothesized that there exists spatial and/or temporal patterns of E. coli concentrations across ponds. To test this hypothesis, we sampled two irrigation ponds in Maryland biweekly during the summers of 2016 and 2017. Results from data analysis of mean relative differences and Spearman correlation coefficients are presented. Empirical orthogonal functions indicated spatial patterns of Log E. coli concentrations were temporally maintained. More sample variance existed over time in the pond interiors versus near shore locations. Furthermore, larger patterns of sample variance existed within the spatial analysis variance versus the temporal analysis variance over both ponds for this study. Therefore, the spatio-temporal E. coli variance may have significant impacts on sampling and pump intake locations.Item Assessment of Zero-Valent Iron Capabilities to Reduce Food-borne Pathogens via Filtration and Residual Activities in Irrigation Water(2017) Bradshaw, Rhodel; Sapkota, Ph.D., Amy R; Maryland Institute for Applied Environmental Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Inadequate disinfection of contaminated freshwater that is used to irrigate food crops that are eaten raw can result in foodborne illnesses. Therefore, in this study we assessed the efficacy of a low-cost, water treatment technology, zero-valent iron (ZVI), in reducing microbiological contamination of synthetic irrigation water. Specifically, we compared the capabilities of a ZVI-sand filter versus a sand filter in reducing levels of Salmonella Newport MDD314 and E. coli TVS 353 through filtration or residual disinfection. Our data showed that ZVI-sand filtration was more effective than sand filtration alone in reducing levels of both of these microorganisms. Our results also showed that, after filtration, there seemed to be no residual disinfection capabilities associated with either the ZVI-sand system or the sand system alone. Our findings suggest that ZVI-sand filtration can effectively reduce microbial contaminants in irrigation water; however, there seem to be no residual disinfection capabilities after filtration.Item Essays in Greenhouse/Nursery Economics(2016) Saavoss, Monica Renee; Lichtenberg, Erik; Agricultural and Resource Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation focuses on the greenhouse and nursery industry in the United States. Two major issues are explored: irrigation and plant disease. The first two essays examine wireless soil-moisture sensor networks, an emerging technology that measures soil moisture and optimizes irrigation levels in real time. The first essay describes a study in which a nationwide survey of commercial growers was administered to generate estimates of grower demand and willingness to pay for sensor networks. We find that adoption rates for a base system and demand for expansion components are decreasing in price, as expected. The price elasticity of the probability of adoption suggests that sensor networks are likely to diffuse at a rate somewhat greater than that of drip irrigation. In the second essay, yields, time-to-harvest, and plant quality were analyzed to measure sensor network profitability. Sensor-based irrigation was found to increase revenue by 62% and profit by 65% per year. The third essay investigates greenhouse nursery growers’ response to a quarantine imposed on the west coast of the United States from 2002 to present for the plant pathogen that causes Sudden Oak Death. I investigate whether growers choose to 1) improve their sanitation practices, which reduces the underlying risk of disease without increasing the difficulty of detecting the pathogen, 2) increase fungicide use, which also prevents disease but makes existing infections much harder to detect, or 3) change their crop composition towards more resistant species. First, a theoretical model is derived to formalize hypotheses on grower responses to the quarantine, and then these predictions are empirically tested using several public data sources. I do not find evidence that growers improve their sanitation practices in response to the quarantine. I do, however, find evidence that growers heavily increase their fungicide use in response to a quarantine policy that requires visual (as opposed to laboratory) inspection for the disease before every crop shipment, suggesting that the quarantine may have the adverse effect of making the pathogen harder to identify. I also do find evidence that growers shift away from susceptible crops and towards resistant crops.Item BIORETENTION/CISTERN/IRRIGATION TO ELIMINATE STORMWATER RUNOFF AT THE UNIVERSITY OF MARYLAND(2015) Doan, Loc Nguyen; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Water quality of parking lot (~1,858 m2) stormwater runoff and its treated effluent flow were analyzed for total phosphorus (TP), total nitrogen (TN), total suspended solids (TSS), electrical conductivity (EC), copper, lead and zinc. The novel system under investigation, located at the University of Maryland, College Park, Maryland, includes a standard bioretention facility, underdrained to a cistern to store treated stormwater, and pumped to a vegetable garden for irrigation. The site abstraction, the average bioretention abstraction, and bowl volumes were estimated to be 8500, 4378, and 895 L, respectively; this indicates that rain events of more than 0.45 cm are necessary to produce runoff and more than 0.75 cm will produce system overflow. The cistern water quality indicates good-to-excellent treatment by the system. Compared to local tap water, cistern water has lower concentrations of TP, TN, EC (non-winter), copper, and zinc, indicating a good water source for irrigation.Item CALIBRATING CAPACITANCE SENSORS TO ESTIMATE WATER CONTENT, MATRIC POTENTIAL, AND ELECTRICAL CONDUCTIVITY IN SOILLESS SUBSTRATES(2009) Arguedas Rodriguez, Felix Ruben; Lea-Cox, John D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The nursery and greenhouse industry requires precise methods to schedule irrigations, since current practices are subjective and contribute to water and nutrient runoff. Capacitance sensors were calibrated to precisely estimate substrate water content, matric potential, and pore water electrical conductivity (EC) in five soilless substrates. Regression coefficients (R2) ranged from 0.29 - 0.88 and 0.16 - 0.79 for water content in 5-cm and 20-cm column heights; matric potential R2 ranged from 0.10 - 0.98 and 0.79 - 0.98, respectively. Pore water EC calibrations were investigated, contrasting two sensor types and two prediction models. Results were applied to an empirical greenhouse dataset. Better precision and accuracy were achieved with ECH2O-TE sensor and Rhoades model. Capacitance sensors provide precise estimates of plant-available water in most soilless substrates, while pore water EC accuracy and precision depends on the sensor-model combination. These results will enable growers to precisely schedule irrigations based on water content and pore water EC.