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
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Application of Advanced Statistical Methods to Assess Atmospheric and Soil Pollution Mitigation and Potential Risks(2020) Yang, Zijiang; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In environmental engineering field studies, data analysis plays an important role when presenting data into useful information that can be used by engineers and policy makers. However, traditional and currently used approaches have significant limitations due to the nature of the field data, such as high temporal variability, high spatial variability, and high heterogeneity. Such uncertainty may be better handled with more realistic statistical models than traditional statistical models with normal approximation. Additionally, a more robust incorporation of heterogeneity and variability may help to modify environmental fate models to achieve more accurate predictions. Therefore, this dissertation applied some advanced data analysis techniques to four case studies.First, reparameterization was applied to modify the Gaussian plume model to predict dispersion of air pollutant emission from a ground-level active-discharge releasing source. Cross-validation was applied for model selection. The results showed that predictive accuracy of the modified GPM was greatly improved compared with the original model. Second, dispersion of particulate matter was accessed, and a dispersion correction factor was developed to enhance the performance of the regulatory air dispersion model (AERMOD) for low-level sources. Cross-validation was used for model comparison. The results showed that predictive accuracy of the corrected model was greatly improved. Third, carbon amendments were applied to a historically contaminated field to investigate the feasibility for mitigating bioaccumulation. The effect of carbon amendments on bioaccumulation were evaluated. The results showed some evidence of the mitigation effect of compost, and in the meanwhile, the need of a robust statistical method was highlighted due to great spatial variability. Lastly, the Bayesian hierarchical model (BHM) was applied to the field measurement dataset to characterize pollutant concentrations and bioaccumulation. Cross-validation and information criteria were used to evaluate model performance between the BHM and traditional model. The results showed that the BHM was preferred for smaller predictive errors and ability to handle data with larger observational error. These case studies demonstrate the capability of advanced statistical methods for dealing with different environmental research problems. Such statistical methods will be useful for model modification with more specific situations, for data analysis with limited sample size and/or great variability and observational error, for environmental and ecological risk assessment, for evaluation of environmental mitigation strategies, for simulation of real-time pollutant distribution and forecasting with integration of monitoring and modelling approaches, and for minimization of sample size to meet with the accuracy requirement and lower the cost. In conclusion, advanced statistical methods are useful tools for environmental research.Item ASSESSING THE FATE AND BIOAVAILABILITY OF HYDROPHOBIC ORGANIC POLLUTANTS IN AGRICULTURAL SOILS(2012) Almeida e Andrade, Natasha; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Persistent organic pollutants have been the cause of concern for many decades; however, little information is available about their environmental fate. One goal of this work was to assess whether land application of biosolids represents a source of persistent organic pollutants to agricultural soils. To address this goal, we developed a methodology to quantify low levels of the flame retardants polybrominated diphenyl ethers (PBDEs) in biosolids and soils and conducted field studies to determine the fate and persistence of PBDEs upon the land application of biosolids. We found that biosolids can take up to one year to completely incorporate into the soil matrix after application and biosolids-bound chemicals are released during this time. PBDEs profiles in soils that receive biosolids applications are similar to PBDEs profiles in biosolids and both reflect commercial formulations of these flame retardants, indicating that biosolids are a source of these chemicals to soil. Residence time of these chemicals was reported for the first time and it was estimated at 16 yr. for the sum of BDE-47 and BDE-99. An abiotic methodology to assess bioavailability of aged soil residues was developed and results were compared to earthworms. The study illustrated that the polymer-based abiotic methodology can be used to assess the bioavailability of soil-bound hydrophobic organic chemicals to earthworms. Measured soil-polymer equilibrium concentration ratios of organic pollutants correlated strongly with earthworm bioaccumulation factors using the same soils. A laboratory protocol to introduce the concept of fugacity and bioavailability to undergraduate and graduate environmental science and engineering students was developed based on the methodology developed for research. The experiment provided an excellent opportunity for students to become familiar with the laboratory protocols and techniques for quantitative analysis as well as graphical analysis of data. The totality of this work improves knowledge of the fate of two classes of organic pollutants in soils. This work substantially adds information and understanding of chemical behavior to the general environmental engineering field. Although this unique experiment provided original and essential pieces of information, additional research is crucial to address the difficulties involved in assessing the environmental behavior of organic pollutants.