UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item LONGITUDINAL STREAM SYNOPTIC (LSS) MONITORING TO EVALUATE WATER QUALITY IN RESTORED STREAMS(2023) Malin, Joseph Thomas; Kaushal, Sujay S; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Many kilometers of streams are being restored in the Chesapeake Bay watershed and elsewhere in efforts to stabilize streambanks, protect infrastructure, and improve water quality. Urban development and impervious surface cover increase peak flows, which degrade streams. Restoration strategies often employ engineering approaches to enhance stream-floodplain reconnection, dissipate erosive forces from urban runoff, and enhance contaminant retention. In this study, longitudinal stream synoptic (LSS) monitoring (sampling multiple points along flowpaths across both space and time) was conducted to assess the effectiveness of different forms of stream restoration in attenuating pollutants downstream. Spatial and temporal monitoring of carbon, nutrients, salt ions, and metals were conducted across five watersheds experiencing varying levels of stream-floodplain reconnection and stormwater management within the Chesapeake Bay region. Study sites included Sligo Creek (minimal floodplain reconnection), Paint Branch (streambank stabilization without significant reconnection), Scotts Level Branch (engineered stream-floodplain reconnection), Little Paint Branch (natural floodplain reconnection from sedimentation), and Campus Creek (regenerative stormwater conveyance with engineered floodplain reconnection). We investigated: (1) whether changes in water chemistry can be detected along longitudinal flowpaths in response to stream-floodplain reconnection, and (2) which monitoring scales across space and time can provide useful information regarding the effectiveness of restoration. Results from this work suggest that longitudinal synoptic monitoring can track the fate and transport of multiple contaminants and evaluate restoration strategies across high spatial-resolution scales. Along all five watersheds, stream water chemistry varied substantially across finer spatial scales (sometimes within hundreds of meters) in response to changes in landscapes, restoration features, or local hydrology. There were significant declining concentrations (p<0.05) or stable concentrations of nutrients, salts, and metals as streams flowed through restoration features. There were significant increasing trends in chemical concentrations (e.g. Na+, Ca2+, K+) in unrestored stream reaches with increasing impervious surface cover. Principal component analysis (PCA) also indicated that there were changes in the chemical compositions of mixtures of salts, metals, and nutrients in response to restoration projects, storm events, and seasons. Interestingly, dissolved Fe and Mn concentrations showed significant increasing trends along some stream reaches with hydrologically connected floodplains. Fe and Mn also showed significant decreasing trends along some unrestored stream reaches surrounded by increasing impervious surfaces. Increased concentrations of dissolved Fe and Mn may have been an indicator of increased hydrologic connectivity between groundwater and surface water and decreased redox potentials. Overall, longitudinal water quality changes over meters and kilometers can be useful in detecting effects of stream restoration on water quality at the watershed scale. Results suggest that water quality in urban streams can change locally in response to restoration projects for multiple chemicals, but the incremental changes associated with different forms of stream restoration and riparian conservation can also be overwhelmed across broader watershed spatial scales and during storm events.Item A MULTILEVEL ANALYSIS OF LANGUAGE PROFICIENCY GROWTH(2023) Mackey, Beth; Gor, Kira; Bolger, Donald; Second Language Acquisition and Application; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The U.S. Military Services employ thousands of servicemen and women in language-related positions that are critical to the nation’s national security. These positions require personnel with high-level capability in various languages and dialects (Asch & Winkler, 2013). A complex accession and training system that begins at local recruiting stations across the nation leads to worldwide placement of language professionals who serve multiyear tours in the U.S. Air Force, Army, Navy and Marine Corps. High levels of cognitive ability, as measured by two cognitive aptitude batteries, one general (ASVAB) and one language (DLAB), are required for selection into these positions. Following significant investments in basic levels of training, the jobs themselves demand high level skills, and the service members find themselves constantly challenged to grow their skills. Traditional research on the effectiveness of the accession and training processes focuses on learning outcomes, rather than growth. This research used a longitudinal design to investigate how general aptitude, language aptitude, non-cognitive and language distance measures impact language proficiency growth. Hierarchical linear models and hierarchical generalized linear models were used and the significant findings were similar. The study found that overall, while language test scores followed a drop-and-recover pattern, there was very little growth overall. Three aptitude subtests, one from ASVAB (Mechanical Comprehension) and two DLAB subtests (Part 3 and Part 4) were found to constrain initial growth in the listening modality. Language distance was found to constrain initial and subsequent growth in listening and reading.Item Assessing the Impact of Typical Variations in Stressful Life Events on Hippocampal Development in Childhood(2021) Botdorf, Morgan; Riggins, Tracy; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The negative impact of extreme stress on early brain development is well-documented. An emerging body of work suggests that less extreme and more typical variations in stressful experiences (e.g., parental divorce, changing schools) may also exert an impact on the brain, especially in early childhood; however, more systematic research is needed. Across, three studies, this dissertation addressed this gap by exploring effects of typical variations in stressful life events on development of the hippocampus, a brain region highly susceptible to stress. Study 1a assessed the impact of stressful life events on the development of hippocampal subfield volumes (i.e., CA1, CA2-4/dentate gyrus (DG), subiculum) in an accelerated longitudinal sample of 102 4- or 6-year-old children who were each followed for 3 years. Analyses revealed that experiencing more stressful life events was related to smaller CA1 and CA2-4/DG volumes in the 6- (but not 4-) year-old cohort. Study 1b used the same sample described in Study 1a to investigate the impact of stressful life events on functional connectivity between the hippocampus and stress-related cortical regions. Analyses revealed a significant association in the 4- (but not 6-) year-old cohort, such that experiencing more stressful life events was related to greater connectivity between the hippocampus and the insula, a region important for emotional processing. Study 2 assessed moderating effects of sex and socioeconomic status (SES) on the association between stressful events and hippocampal subfield volumes using a large (n = 4,348), diverse subsample of 9-10-year-old adolescents from the Adolescent Brain and Cognitive Development Study. Analyses revealed that stressful life events were related to smaller subiculum volumes, but these associations did not vary by sex or SES. Overall, these findings provide evidence of the impact of typical variations in stressful life events on both hippocampal structure and functional connectivity. Findings also highlight the complexity of stress effects on the brain as these experiences may impact the hippocampus in an age-dependent manner. These results advance our current understanding of how stress influences hippocampal development and pave the way for studies to assess the implications of findings both for cognitive processes and the development of stress-related disorders.Item The Chick or the Egg? Multi-Group, Short-Term Longitudinal Relations Between Grit and Literacy Achievement(2019) Boyars, Michal Yablong; O'Neal, Colleen R; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The impact of grit on achievement is well established, but it is unclear whether achievement impacts grit. This short-term longitudinal study examined the direction of relations between grit and literacy among diverse elementary school student groups. Most grit research features a unidirectional design (e.g., grit affects achievement). Yet, recent research supports cross-lagged models in which socioemotional skills and achievement affect one another. In addition to testing cross-lagged effects, this study examined the direction of grit-literacy relations for different demographic groups (i.e., age, gender, and dual language status). Method: Participants included upper elementary students (N = 396; 3 schools; Mage = 9.61; 55% female; 59% dual language learners; 11% Black, 6% Asian, 29% Latino/a, 8% Multiracial; 39% White). Measures were student-reported grit, teacher-reported grit, and a student literacy achievement performance task (Test of Silent Reading Efficiency and Comprehension, TOSREC). Analytic Approach: An autoregressive cross-lagged design included two time points over 4 months. A cross-lagged model was compared to unidirectional models (i.e., direct and reverse) for best fit. Multi-group analyses were then used to examine whether grit-literacy relations differed as a function of demographics. Results: The data fit the cross-lagged model better than the direct or reverse models. Within the context of a cross-lagged model – which contained both the direct and reverse effects – there was a significant relation between Time 1 literacy achievement and Time 2 student-reported Grit-PE, suggesting that literacy achievement can predict later Grit-PE. There were no demographic differences in the fit of the data with the cross-lagged model between gender, DLL status, and age groups. Findings of the current study support the examination of reciprocal effects in grit-literacy relations and its generalizability among students. Longer-term cross-lagged studies are needed to further understand the temporal sequence between grit and literacy.Item ESTIMATING THE LONGITUDINAL COMPLIER AVERAGE CAUSAL EFFECT USING THE LATENT GROWTH MODEL: A SIMULATION STUDY(2018) Liu, Huili; Hancock, Gregory; Stapleton, Laura; Human Development; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)When noncompliance happens to longitudinal experiments, the randomness for drawing causal inferences is contaminated. In such cases, the longitudinal Complier Average Causal Effect (CACE) is often estimated. The Latent Growth Model (LGM) is very useful in estimating longitudinal trajectories and can be easily adapted for estimating longitudinal CACE. Two popular CACE approaches, the Standard IV approach and the Mixture Model Based (MMB) approach, are both readily applicable to the LGM framework. The Standard IV approach is simple in modelling and has a low computational burden, but it is also criticized for ignoring distributions of subgroups and leading to biased estimations. The MMB approach is capable of not only estimating the CACE but also answering research questions regarding distributions of subpopulations, but this method may yield unstable results under unfavorable conditions, especially when the estimation model is complicated. Previous studies laid out a theoretical background for applying LGMs to longitudinal CACE estimation using both approaches. However, 1) very little was known regarding the factors that might influence the longitudinal CACE estimation, 2) the three compliance classes scenario was not thoroughly investigated, and 3) it was still unclear about how and to what extent the Standard IV approach would perform better or worse than the MMB approach in the longitudinal CACE estimation. The present study used an intensive simulation design to investigate the performance of the Standard IV and the MMB approaches while manipulating six factors that were related to most experimental designs: sample size, compliance composition, effect size, reliability of measurements, mean distances, and noncomplier-complier Level 2 covariance ratio. Their performance was evaluated on four criteria, estimation success rate, estimation bias, power, and type I error rate. With the analysis result, suggestions regarding experiment designs were provided for researchers and practitioners.Item THE UNDISCOVERED COUNTRY: HOMICIDE, DYNAMIC CHANGE, AND DETERRENCE IN WASHINGTON, D.C. NEIGHBORHOODS, 1998-2006(2014) Goodison, Sean Edmund; Paternoster, Raymond; Criminology and Criminal Justice; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Studies examining homicide rates often have two limitations. First, there is a lack of rich, dynamic data to account for change, and second, no consideration of formal social controls at the neighborhood-level. To address these limitations, longitudinal data from Washington, D.C. was collected at the neighborhood level. This homicide incident and neighborhood demographic data, which spans from 1998-2006, allow for a test of two theoretical perspectives within a classical/social control sphere, namely social disorganization and deterrence. This work poses two main questions: Do dynamic structural factors influence homicide rates across neighborhoods? Does aggregate deterrence influence homicide rates across neighborhoods? Results suggest that dynamic structural factors predict homicide rates better than static factors, though deterrence results are insignificant. Implications and avenues for future research are also discussed.Item Internet Searching in Children and Adolescents: A Longitudinal Framework of Youth Search Roles(2014) Foss, Elizabeth; Druin, Allison; Library & Information Services; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The current landscape of literature investigating youth Internet searching focuses mainly on how youth search in classrooms or libraries at a single point in time and highlights problems youth encounter, rather than taking an expansive view of the entire search process. This research uses a framework of searching roles, or patterns of search behavior, to provide a complete picture of how youth behave as searchers in the home environment. The searching behavior of the youth participating in this research is examined by viewing the whole searcher, where search problems are important, but equally important are factors such as affect, context, and the process of search. This longitudinal study examined participants at ages 7, 9, and 11 in 2008 to 2009 and again at ages 10 to 15 in 2012 to 2013. The searching behaviors displayed during the study's in-home interviews were analyzed according to qualitative methods that evolved throughout the research. Results of the research provide a comprehensive picture of how youth search roles and search behaviors change over time, and through case study analysis of selected participants. The research also provides in-depth description of how individuals change as searchers over time. Additionally provided is a graphic to summarize the main characteristics of search roles in youth searchers. This research concludes with recommendations to adult stakeholders such as teachers, librarians, search engine designers, researchers, and parents to aid in promoting search literacy for youth.Item An Examination of the Pathways of Depressive Symptoms and Heavy Drinking from Adolescence to Adulthood(2011) Gustafson, Emily Anne; Stein, William; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study examined the dynamic interaction of heavy alcohol use and depressive symptoms at three points over a time period of 11 years from adolescence to adulthood using a subset of data from the nationally representative, multi-year, longitudinal data source, the National Longitudinal Study of Adolescent Health (Add Health). Results revealed that, in general, those that drink heavily with greater frequency are more likely to have a greater number of depressive symptoms. Conversely, those with more early depressive symptoms are more likely to be early heavy drinkers, but less likely to be heavy drinkers six years down the road. Additionally, early depressive symptoms affect later trajectories in binge drinking. Gender, racial/ethnic group, and college attendance all affected the relationship over time for heavy drinking and were generally related to the average but not the change over time of depressive symptoms. Results are discussed in the context of Elder's life course theory that views developmental trajectories in relation to social pathways.