Theses and Dissertations from UMD
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Item USING BAYESIAN ELECTRICAL RESISTIVITY INVERSION TO REVEAL HILLSLOPE DRY-UP PROCESS IN A MEDITERRANEAN CLIMATE(2024) Shahid, Saffat; Huang, Mong-Han; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hydrologic dynamics in hillslopes is essential for comprehending the processes that shape landscape evolution and sustain the Earth’s critical zone. Electrical resistivity (ER) is considered as one of the best geophysical methods to observe these dynamics due to its sensitivity to subsurface water content. To understand hillslope water dynamics and mitigating the risks of slope instability caused by extreme weather events, we studied how subsurface hydrological processes are being influenced by variations in vegetation type across different aspects of hillslopes. Thus, how accurately ER can quantify the dry-up process during the growing season on hillslopes becomes critical, particularly in regions with distinct dry summers and wet winters (i.e. Mediterranean climates). The Blue Oaks Ranch Reserve (BORR) in Central California provides an ideal location for this study due to its consistent ridge-valley systems, which well represents the regional climatic and topographic conditions. Previous work at BORR used active source seismic refraction (SR) to constrain subsurface structure. To additionally investigate moisture content in regolith, we conduct ER surveys with Schlumberger and Dipole-Dipole configurations to invert for resistivity using Transdimensional Hierarchical Bayesian (THB) inversion framework with reversible-jump Markov Chain Monte Carlo (THB rj-MCMC). We also performed 2D synthetic tests to evaluate how well THB can recover a synthetic model with imposed data uncertainty. The results indicate that Schlumberger outperforms Dipole-Dipole in the THB rj-MCMC inversion. However, these results also reveal limited depth resolution to ~10 m depth using current ERT configurations. Finally, we adopt the THB approach for a series of ER surveys at BORR between June and September 2023. The findings suggest a distinct increase in resistivity on the North-facing slope during growing seasons, indicating reduced moisture content particularly in areas with presences of oak trees as they draw water from deep regolith. On the South-facing slope, resistivity remained stable due to the dominance of grass that lacks deep roots for consuming deep moisture. Our resistivity results show that vegetation type particularly trees play a critical role in regolith moisture distribution. To compare and correlate changes in resistivity over dry periods, we analyzed soil probe data previously collected at the site. The correlation suggested that increases in resistivity are related to decreases in volumetric moisture content. Additionally, we compared ERT data with seismic survey data to better understand changes in subsurface properties like porosity and saturation along depth, as ERT and seismic velocity is sensitive to moisture content and material porosity.Item A DEEPER DIVE INTO THE WATER: A COMPARISON OF HYDROLOGIC FEATURES AS VARIABLES IN PRECONTACT SITE LOCATION PREDICTIVE MODELS FOR THE VIRGINIA PIEDMONT(2024) Johnson, Jeffrey Wade; Palus, Matthew M; Anthropology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The use of predictive modeling in Cultural Heritage Resource Management (CHRM) archaeology has become commonplace since its foundational principals were established in the 1980s, but criticisms of the practice persist, often centered around their lack of theory and dehumanization of the archaeological record. Proximity to water, typically expressed in the United States as distance to streamline data from the National Hydrography Dataset (NHD), is one of the most utilized variables when creating predictive models for Precontact period sites, but how does the variable “distance to streamline” compare to other hydrologic variables? In this thesis I seek to answer the question “how do distance to stream confluences and distance to wetlands compare to distance to streamline when attempting to predict Precontact site locations in the Virginia Piedmont?”The publication Quantifying the Present and Predicting the Past: Theory, Method, and Application of Archaeological Predictive Modeling (Altschul et al. 1988) is considered foundational to the practice of predictive modeling in archaeology; it is referenced frequently in modern theoretical works and throughout this thesis. The approaches to creating archaeological predictive models are typically divided into two camps: models that utilize an inductive, or correlative, approach and models that utilize a deductive, or theory driven, approach. Rather than establishing distance correlations between wetlands and stream confluences with previously recorded site data, I utilize a deductive approach where I establish the importance of those variables through archaeological theory pertaining to subsistence and settlement patterns and test their value with site data. Inductive associational models are very good at showing that archaeological site distribution is strongly patterned, but they often lack the explanatory framework that would be useful for management decisions based on their findings. The Study Area the models are tested on is located within Orange County, Virginia near the town of Locust Grove, and encompasses about 686 acres. The Study Area contains two main streams, named Cormack Run and Mine Run, the confluence of those streams and other lower order streams, as well as wetlands located adjacent to the streams. Precontact occupations have likely occurred in this region for the past 12,000 years, if not longer. The test results demonstrate that models created using deductively derived variables perform well enough to justify their use in CHRM contexts, but also include the added benefit of an explanatory framework. The guidelines for archaeological investigations in Virginia allow for the use of predictive models when conducting inventory surveys, meaning the archaeological predictive models (APM) created for this thesis could be utilized in a real-world context. The primary focus of this thesis was to determine if using hydrologic features other than streams, specifically stream confluences and wetlands, to express the distance to water variable would improve the performance of an APM. I demonstrated that, yes, other hydrologic features may be better predictors of Precontact site locations in the Virginia Piedmont. Secondarily, I hoped to show that an APM created using a deductive approach would perform well enough to be considered appropriate for use in CHRM contexts. The high probability areas of all three of the APMs I created yielded Kg values high enough to be considered as having predictive utility. This demonstrates that the use of all three of the APMs I created could be considered appropriate to guide survey efforts in a CHRM context.Item HYDROLOGY, SOIL REDOX, AND PORE-WATER IRON REGULATE CARBON CYCLING IN NATURAL AND RESTORED TIDAL FRESHWATER WETLANDS IN THE CHESAPEAKE BAY, MARYLAND, USA(2017) Keshta, Amr El Shahat Sedik; Baldwin, Andrew H; Yarwood, Stephanie A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal freshwater wetlands are key sites for carbon (C) sequestration and main component in the global C budget. The overall research objective of my dissertation was to examine the physical and biogeochemical processes that impact C cycling in tidal freshwater wetlands. One natural and one restored tidal freshwater wetland (salinity < 0.3 ppt) were selected in Maryland, USA along the Patuxent River. Data logging water recorders were installed in wells at each habitat in February 2014 for monitoring water level at 10-minutes interval and for two years. Soil organic matter and C stocks were estimated and a novel soil C bioassay (CARBIO) was developed and tested to assess C stability (change of soil organic matter concentration over time) and decomposition rates in both sites. A total of 162 CARBIO units were deployed in the natural and restored sites, and 81 were retrieved after 1 year while the others were retrieved after 2 years. Static chambers were used to quantify methane (CH4) and carbon dioxide (CO2) flux rates during day and nighttime. My results indicated that the natural wetland had significantly higher soil C stocks than the restored site (14.8±0.50 and 8.9±0.99 kg C m-2, respectively, P <0.0001). The swamp habitat had the highest soil organic matter (36.8%), while restored mudflat has the lowest (2.8%). Higher soil organic matter was partially correlated with shallower groundwater level relative to soil surface. Soil redox data with soil pH indicated that the soil of the natural wetland habitats was more reducing than the soil at the restored habitats. Based on CARBIO index, the soils in CARBIO units that were deployed in the natural wetland was significantly higher in C sequestration rate than the restored wetland (535±291.5 and -1095±429.4 g C m-2 year-1, respectively, P site<0.05). Under the current hydrological conditions, the restored wetland habitats were not able to accumulate C inside the CARBIO units after 1 or 2 years from deployment. In-situ CARBIO units can be employed in the newly constructed wetlands as in-situ sensors that reflect the C biogeochemical processes in the ambient soil to help better understanding C stability. The restored wetland had significantly higher annual CH4 emission rates than the natural wetland (1372.1±35.89 and 880.7±144.73 g CH4 m-2 y-1, respectively, P <0.05) and the log CH4 flux rate had a significant and strong negative correlation with the pore-water total available iron. Nighttime CH4 fluxes had very low concentration (<3650 µmole m-2 h-1). Future restoration efforts should focus on soil properties that will help increase C accumulation in newly constructed wetlands, but even more important every effort should be made to conserve the natural wetlands so that ecosystem function and services including wildlife habitat, water quality improvement, and offsetting the greenhouse gas emissions are maintained.Item EVALUATING RESTORATION POTENTIAL AND STORM SURGE ATTENUATION IN DITCHED AND UNDITCHED COASTAL MARSHES(2017) Lundberg, Dorothea June; Prestegaard, Karen; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The effects of ditching on the hydrological regime and ecosystem services of ditched coastal marshes—as well as the effects of hydrologic restoration of these systems—have yet to be extensively studied. The goals of this project were (1) to determine differences between ecohydrological processes in Ditched and Unditched coastal marshes, (2) to determine the effects of ditch plugging restoration projects on Atlantic Coast and Chesapeake Bay marsh hydrology, and (3) to evaluate Hurricane Sandy storm surge in the coastal marshes. Two separate pairs of Ditched and Unditched marshes were used in this study. The paired sites were adjacent, with similar topography, vegetation, and tidal patterns. Data collection included hydrological properties such as ditch density, tidal stage, water table fluctuations; as well as soil properties. Soil properties were similar in Ditched and Unditched marshes, while ditched marshes had lower water table elevations than Unditched marshes. Ditch plugging restoration partially restored the hydrological regime. A comparison of Chesapeake and Atlantic coastal marshes during Hurricane Sandy indicated similar storm surge elevations, but shorter durations of inundation at the Chesapeake Bay marshes when compared with the Atlantic marshes.Item Comparison of Hydrologic and Hydraulic Characteristics of the Anacostia River to Non-Urban Coastal Streams(2016) McDowell, Mallori; Prestegaard, Karen L; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Streams in urban areas often utilize channelization and other bank erosion control measures to improve flood conveyance, reduce channel migration, and overbank flooding. This leads to reductions in evapotranspiration and sediment storage on floodplains. The purpose of this study is to quantify the evapotranspiration and sediment transport capacity in the Anacostia Watershed, a large Coastal Plain urban watershed, and to compare these processes to a similar sized non-urban watershed. Times series data of hydrologic and hydraulic changes in the Anacostia, as urbanization progressed between 1939-2014, were also analyzed. The data indicates lower values of warm season runoff in the non-urban stream, suggesting a shift from evapotranspiration to runoff in urban streams. Channelization in the Anacostia also increased flow velocities and decreased high flow width. The high velocities associated with channelization and the removal of floodplain storage sites allows for the continued downstream transport of sediment despite stream bank stabilization.Item Addressing New Stormwater Policies in the Redesign of the National Grove of State Trees at the United States National Arboretum(2012) Kreiseder, Kory Anne; Myers, David N; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The National Grove of State Trees at the United States National Arboretum is in need of redesign to meet ecological and social needs. The Grove serves as a scientific and cultural landscape and can be repurposed to serve the public as an ecological demonstration for contemporary environmental issues. In an intensive effort to clean up the local rivers of the District of Columbia and the Chesapeake Bay, the two agencies of the District Department of the Environment and DC Water have enacted stormwater runoff fees, based on impervious surface fees, on all property owners located in the District of Columbia. The redesign of the Grove is compounded by the Arboretum's need to add more parking to the area where the Grove is currently located. The objective of this thesis is to reimagine the design and interpretation of the Grove as well as address the impervious area charge assessments.Item EFFECTS OF BAR FORMATION ON CHANNEL STABILITY AND SEDIMENT LOADS IN AN URBAN WATERSHED(2009) Blanchet, Zachary; Prestegaard, Karen L; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study investigates channel adjustment due to urbanization in the Little Paint Branch creek of the Anacostia River watershed. In the past 15 years, large gravel bars have formed in the channels, more than doubling the active channel width of some reaches. Field data was collected to analyze downstream hydraulic geometry and the effects of gravel bars on shear stress, turbidity, and morphological change. The watershed was gauged at three locations to document the contributions of discharge and sediment to the downstream Anacostia Estuary. The results indicate that Little Paint Branch Creek generates proportionally more runoff per basin area than the watershed does as a whole, even though the impervious surface area is lower in the upstream tributaries, like Little Paint Branch Creek. Bar formation induces channel widening, which decreases flow depth and thus shear stress for bankfull and higher stages. This shoaling limits bed transport and will eventually limit bank erosion.Item SPATIAL MODELING AND UNIT HYDROGRAPH DEVELOPMENT WITH RADAR RAINFALL(2009) Rew, Stephanie Nicole; McCuen, Richard H.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Most hydrologic models use point rainfall data. Point data do not account for spatial characteristics of a storm. This research investigated the benefits of spatially- and temporally-varying rainfall data. Semivariogram analyses were made to assess the importance of the following storm characteristics: size, shape, type, and velocity. Rainfall and flow gage data from the aridlands Walnut Gulch Watershed and regional data were used. A model was developed to estimate transmission losses (TL) using hydrograph routing (temporally-varying data), then a procedure was developed to use radar rainfall data (spatially-varying data) to develop unit hydrographs (UH). Exponentially shaped UHs resulted from TLs. UHs developed from radar data agreed closely with Thiessen-averaged UHs developed from rain gage data, indicating that radar UHs better represented the overall watershed processes than a UH based on a single rain gage. Therefore, accurate UHs can be developed from radar data.Item Scales of Bank Roughness and Their Relationship to Bank Erosion Processes(2009) Hankin, Erik Ravnholt; Prestegaard, Karen L; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stream bank erosion rates and the stabilization of channel width are poorly understood processes. There have been two distinct approaches to the study and prediction of bank erosion rates in natural streams. In order to predict bank shear stresses, scientists either define a reach as being meandering or straight, even though most river channels are neither meandering nor straight but a combination of the two. This thesis aims to determine if river segments can be divided into straight reaches and curved reaches with different bank erosion prediction approaches applied to each as well as investigating the role of bank roughness element size and spacing in bank erosion. The results show that straight reaches are affected by upstream curvature and that large isolated bank protrusions that are widely spaced generate erosion-causing, stable, macroturbulent eddies. The thesis has implications for stream restoration practices regarding bank stability and erosion.Item Importance of channel networks on nitrate retention in freshwater tidal wetlands, Patuxent River, Maryland(2009) Seldomridge, Emily Dawn; Prestegaard, Karen; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Freshwater tidal marshes border stream channels near the upstream end of the tidal limit, and are likely to undergo significant changes in salinity, tidal inundation, and biogeochemical processes due to sea-level rise. Tidal channel networks enhance nutrient processing by delivering nitrate-rich water far into the marsh. The purpose of this study is to examine the geomorphological, hydrological, and biogeochemical processes that influence the delivery and processing of nutrient-rich waters into tidal marshes. In this study, field measurements were made to calculate water and nitrate flux for stream channels of varying order. These mass balance calculations indicate there is an exponential increase in net nitrate retention with channel order. This calculation could be compared with calculations of denitrification at different sites within the system to evaluate the role of these processes in total nitrate loss.
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