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 A Data Assimilation System for Lake Erie Based on the Local Ensemble Transform Kalman Filter(2024) Russell, David Scott; Ide, Kayo; Applied Mathematics and Scientific Computation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Data assimilation (DA) is the process by which a model forecast is adjusted to account for recent observations, taking into account both forecast and observation uncertainties. Although DA is common in numerical weather prediction (NWP) and other applications at global and regional scales, DA for large lakes such as North America's Great Lakes is still at an early stage of research and is not yet used operationally. In particular, the use of an ensemble-based approach to DA has scarcely been explored for large lakes, despite its growing popularity in operational NWP centers worldwide due to its dynamic estimation of the forecast covariance. Using Lake Erie as a test case, this study investigates the potential of ensemble DA to i) propagate forecast improvements throughout the lake and across forecast variables, and ii) inform the design of in-situ observing systems. The local ensemble transform Kalman filter (LETKF) is an efficient, localized, flexible variant of the ensemble Kalman filter (EnKF) that is used in multiple operational NWP centers. This work presents the development of a DA system for Lake Erie, which uses the LETKF to adjust forecasts of temperatures, currents, and water levels throughout the lake, using only lake surface temperature (LST) and temperature profile (TP) observations. The impact of both types of observations on all three forecast variables is evaluated within the framework of observing system simulation experiments (OSSEs), in which a DA system attempts to reconstruct a nature run (NR) by assimilating simulated observations of the NR. Observing system design questions are explored by comparing three different TP configurations. Assimilation of LST observations alone produces strong improvements to temperatures throughout the epilimnion (upper layer), while assimilation of TP observations extends these improvements to the hypolimnion (lower layer) near each profile. TP assimilation also shows improved representation of strong gyre currents and associated changes to thermocline depth and surface height, particularly when profiles sample from locations and depths where the thermal stratification in the forecast has been strongly affected by erroneous gyre currents. This work shows that the LETKF can be an efficient and effective tool for improving both forecasts and observing systems for large lakes, two essential ingredients in predicting the onset and development of economically and ecologically important phenomena such as harmful algal blooms (HABs) and hypoxia.Item MOBILIZATION OF CHEMICAL COCKTAILS BY FRESHWATER SALINIZATION SYNDROME IN THE CHESAPEAKE BAY WATERSHED(2023) Galella, Joseph George; Kaushal, Sujay S; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increasing trends in base cations, pH, and salinity of urbanizing freshwaters have been documented in U.S. streams for over 50 years. These patterns, collectively known as Freshwater Salinization Syndrome (FSS), are driven by multiple processes, including applications of road salt and human-accelerated weathering of impervious surfaces, reductions in acid rain, and other anthropogenic legacies of change. FSS mobilizes chemical cocktails of distinct elemental mixtures via ion exchange, and other biogeochemical processes. Urban streams in temperate areas experience chronic salinization throughout the year punctuated by acute salinization during winter storms with associated road salting. My research analyzed impacts of FSS on stream water chemistry in the field with routine bi-weekly and targeted high frequency sampling during road salting events. Field sites were proximal to USGS stream sensors using multiparameter datasondes, allowing for additional parameters to be monitored at 5-15 minute resolution. In the laboratory incubation analyses were also conducted using sediment and water samples to assess the function of stormwater best management practices (BMPs) during road salting events. Acute FSS associated with road salting was found to mobilize chemical cocktails of metals (Mn, Cu, Sr²⁺), base cations (Na+, Ca²⁺, Mg²⁺, K⁺), nutrients (TDN), and organic matter (NPOC). Regression relationships were developed among specific conductance and major ion and trace metal concentrations. These linear relationships were statistically significant in most of the urban streams studied (e.g., R2 = 0.62 and 0.43 for Mn and Cu, respectively), and showed that specific conductance could be used as a proxy to predict concentrations of major ions and trace metals. Principal component analysis (PCA) showed co-mobilization (i.e., correlations among combinations of specific conductance, Mn, Cu, Sr²⁺, and all base cations during certain times of year and hydrologic conditions). Co-mobilization of metals and base cations was strongest during peak snow events but could continue over 24 hours after specific conductance peaked, suggesting ongoing cation exchange in soils and stream sediments. Increased salt concentrations of all three major road salts (NaCl, CaCl₂, and MgCl₂) had profound effects on major and trace element mobilization, with all three salts showing significant positive relationships across nearly all elements analyzed. Salt type showed preferential mobilization of certain elements. NaCl mobilized Cu, a potent toxicant to aquatic biota, at rates over an order of magnitude greater than both CaCl₂ and MgCl₂. Hourly mass fluxes of TDN in streams were also found to be elevated during winter months with peaks coinciding with road salting events. Targeted winter snow event sampling and high-frequency sensor data suggested plateaus in NO₃⁻ / NO₂⁻ and TDN concentrations at the highest peak levels of SC during road salt events between 1,000 and 2,000 μS/cm, which possibly indicated source limitation of TDN after extraction and mobilization of watershed nitrogen reservoirs by road salt ions. My results may help guide future regulations on road salt usage as there are currently no federally enforceable limits. NaCl is the most commonly used deicer in the United States, largely because it is often the least expensive option. Other technologies such as brines and other more efficient deicers (CaCl₂ and MgCl₂) should be considered in order to lessen the deleterious effects of FSS.Item An investigation of the physio-chemical characteristics of a river estuary(1952) Provenza, D. Vincent; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Item A limnological investigation of acid ponds with particular reference to the factors influencing the distribution and abundance of the phytoplankton(1948) Galler, Sidney Roland; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Item STUDIES OF PERIPHYTIC ALGAE ON ALGAL TURF SCRUBBERSTM ALONG THE CHESAPEAKE BAY: COMMUNITY STRUCTURE, SYSTEMATICS, AND INFLUENCING FACTORS(2012) Laughinghouse, Haywood Dail; Kangas, Patrick C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This is an ecological and systematic study of periphytic algae growing in an ecologically-engineered system used for water quality improvement: the Algal Turf Scrubber or ATSTM. This technology consists of an attached algal community growing on screens in a shallow floway through which water is pumped. The study was conducted on small-scale, experimental floways at three sites within the Chesapeake Bay watershed: on the Susquehanna River in southeastern Pennsylvania (freshwater) and on the Great Wicomico and York Rivers in Virginia (brackish water). A total of 330 taxa were identified at the sites from 2008-2011. The majority of taxa at all three sites belonged to the phylum Bacillariophyta, but a large number of taxa from Chlorophyta and, to a lesser degree, Cyanobacteria were also found at the freshwater site. Algae found in the ATSTM exhibited a diversity of life forms and modes of attachment within the community. Although these system appear to be dominated by a "canopy" of attached, filamentous species, more than half of the total abundance (cell density) were solitary, unattached taxa that grow as an "understory" within the three dimensional structure of the community. Longitudinal patterns were examined on the longest floways (90 m long) at the freshwater site. The community nutrient uptake rate (mass of nitrogen or phosphorus m-2 day-1) for the harvested algal biomass was found to decline from the top to the bottom of the floway for a system constructed at 2% slope but no distinct pattern was found for a system constructed at 1% slope. The majority of algal taxa were evenly distributed along the floway from top to the bottom, in terms of frequency of occurrence, suggesting a general lack of longitudinal specialization within the community. A detailed review of the systematics of the Order Oscillatoriales (Cyanobacteria) found on the ATSTM was undertaken since this group has not been studied much in the Chesapeake Bay watershed. Twenty-four taxa were examined, described morphologically and their nomenclature reviewed. Comparing 16s rRNA gene analyses of planktonic and periphytic Pseudanabaena, it was suggested that periphytic Pseudanabaena be revised and elevated to a new genus, Ilyonema.