UMD Theses and Dissertations
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Item Sorption of Yttrium and the Rare Earth Elements on the Marine Macroalga Ulva lactuca(2011) Zoll, Alison M.; Schijf, Johan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Trace metal interactions with organic matter are relatively poorly understood, though organic matter is ubiquitous in aquatic environments and likely instrumental in controlling metal geochemistry. To better understand the mechanisms underlying metal interactions with organic substrates, sorption of Yttrium and the Rare Earth Elements (YREEs) on Ulva lactuca, a marine macroalga, was studied in batch laboratory experiments at different ionic strengths over a large pH range (2.7 - 8.5). At all ionic strengths and experimental pH values, colloid-bound YREEs make up a substantial portion of sorbed metals as described by a two-site Langmuir model, which has implications for bioremediation and metal sorption studies. YREE sorption on U. lactuca can be modeled as a function of pH with a three-site non-electrostatic surface complexation model, and patterns of conditional YREE complexation constants were used to determine possible identities of metal-complexing functional groups.Item GENETIC ANALYSIS OF TROPODITHIETIC ACID BIOSYNTHESIS IN MARINE BACTERIA(2011) Geng, Haifeng; Belas, Robert; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Members of the Roseobacter clade of alphaproteobacteria are among the most abundant and ecologically relevant marine bacteria. The antibiotic tropodithietic acid (TDA) produced by roseobacters is hypothesized to be a critical component of the roseobacter-phytoplankton symbiosis. TDA production is influenced by environmental conditions. Specifically, in the lab, TDA activity is highest when bacteria are cultured in standing liquid nutrient broth, whereas cells produce negligible TDA in nutrient broth with shaking. Random mutagenesis was used to construct loss-of-function mutants defective in TDA activity (Tda-). Twelve genes were identified as required for Tda activity. Six tda genes, tdaA-F, are physically linked and are carried on pSTM3, a ca. 130-kb plasmid, while the remaining 6 genes are located on the sequenced genome. Genetic and molecular biological evidence demonstrates that tdaA and tdaB form a bicistronic message, tdaCDE are part of a separate operon, and tdaF is likely a part of a third operon. The expression of tdaAB is constitutive, whereas tdaCDE and tdaF mRNA are regulated, showing significantly increased levels when cells are grown in standing liquid broth compared to shaking liquid culturing. Expression of tdaCDE is lost in Tda- strains, but could be restored- tdaA and tdaH failed to respond - by placing wild-type Tda+ strains in close proximity or by adding exogenous TDA to the mutant. These results indicate that TDA acts as an autoinducer of its own synthesis and suggest that roseobacters may use TDA as a quorum signal. Next, I focused attention on the only known regulatory protein, TdaA, involved in tda expression. Disruption of tdaA results in loss of tdaCDE expression, and expression of tdaA in an Escherichia coli background is sufficient to transcribe tdaCDE. Transcriptional activation of the tdaC promoter by TdaA is supported by data from electrophoretic mobility shift assays (EMSA) showing that purified TdaA protein binds specifically to a fragment of DNA containing the tdaC promoter. These results support a hypothesis that TdaA is a positive transcriptional regulator of tdaCDE gene expression whose function requires binding to the tdaC promoter region. One of the mechanisms used by TM1040 to regulate TDA biosynthesis is therefore through TdaA regulator.Item Desing of Click Hydrogels for Cell Encapsulation(2011) Breger, Joyce; Wang, Nam Sun; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The long-term stability of ionically crosslinked alginate hinders the development of a bioartificial pancreas for the treatment of Type I Diabetes. Ionically crosslinked alginate with divalent cations is traditionally utilized to encapsulate islets of Langerhans serving as a protective barrier between the host's immune system and the donor islets of Langerhans. However, due to ion exchange with monovalent ions from the surrounding serum, alginate degrades exposing donor tissue to the host's immune system. The overall goal of this dissertation was to explore the possibility of utilizing `click' chemistry to introduce covalent crosslinking in alginate for therapeutic cell encapsulation. `Click' chemistry is customarily defined as the Cu (I) catalyzed reaction between an azide and alkyne to form a 1,2,3 triazole ring. To achieve the goal of covalently crosslinked polysaccharides, the following aims were determined: (1) synthesis and characterization of functionalized polysaccharides (alginate and/or hyaluronic acid) with alkyne or azide end groups; (2) measurement and comparison of the stability and transport properties of covalently crosslinked alginate hydrogels to that of ionically crosslinked alginate hydrogels; (3) determination of the inflammatory potential and cytotoxicity of these functionalized polysaccharides and `click' reagents by employing RAW264.7, a murine macrophage cell line under various simulated inflammatory states (with or without endotoxin, with or with out the inflammatory cytokine gamma-interferon); (4) optimization of the `click' reaction for therapeutic cell encapsulation utilizing RIN-5F, a rat insulinoma cell line, while minimizing cytotoxicity and maintaining insulin production; (5) encapsulation of primary porcine islets of Langerhans in either ionically and/or covalently crosslinked alginate capsulation and comparing insulin response to a glucose challenge. The results of these experiments demonstrate the utility of employing `click' chemistry to increase the overall stability of alginate hydrogels while maintaining therapeutic cell function.Item FOREST LOSS AND FRAGMENTATION IN SOUTHERN BAHIA, BRAZIL: IMPLICATIONS FOR THE EXTINCTION RISK OF GOLDEN-HEADED LION TAMARINS (Leontopithecus chrysomelas)(2011) Zeigler, Sara Lynn; Dubayah, Ralph; Fagan, William F; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Golden-headed lion tamarins (GHLTs; Leontopithecus chrysomelas) are Endangered arboreal primates endemic to the Atlantic Forest of Brazil, where continuing loss of forest and its connectivity are major threats. The objectives of my research were to assess the vulnerability of GHLTs to habitat loss, fragmentation, and threats related to small population size in the context of past, current, and future trends in range-wide forest cover in Brazil's Atlantic Forest. I did this by conducting a supervised classification of Landsat 5TM remotely-sensed imagery to define past and current forest cover in the region, analyzing connectivity patterns in a graph theoretical framework, projecting recent deforestation patterns into the future using a multi-layer perceptron neural network, and modeling GHLT metapopulaton viability using population viability analysis. I found that forest cover has declined throughout the range of the species by 13% over the last 20 years, and only one habitat patch is large enough on its own to support a genetically viable GHLT population able to recover from extrinsic threats such as fire and disease. Functional landscape connectivity, which is important for population persistence, acquisition of resources, and maintenance of genetic diversity, is low at the distance and movement cost thresholds likely associated with this arboreal species that is rarely seen in non-forest matrix. The majority of remaining forest cover throughout the species' range is found in patches that are either (1) too small to support even a single group of GHLTs or (2) found at low elevations, in areas of high human population density, or in close proximity to previously cleared areas--conditions that are associated with past deforestation patterns and that make current habitat vulnerable to loss. Finally, I found that many of the known GHLT populations have a moderate to high risk of local extinction even over short time scales and assuming no further forest loss, and their presence may represent extinction debt. Continued deforestation will accelerate population declines and local extinction events. The results of my dissertation research suggest that GHLTs and their habitat face significant threats and low viability in the future because of both ultimate and proximate drivers of extinction.Item COMPETITION BETWEEN HYDRILLA VERTICILLATA AND VALLISNERIA AMERICANA IN AN OBSERVATIONAL FIELD STUDY AND GREENHOUSE EXPERIMENT.(2010) McChesney, Lauren Dalton; Engelhardt, Katharina; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Invasive species continue to have a pervasive influence on biodiversity but it is often unclear how invasive species affect native species. In field observations and greenhouse experiments, I examined the effect of the non-native submersed aquatic plant Hydrilla verticillata on the native species Vallisneria americana. Field monitoring from 2002 to 2006 showed that coverage of species peaked in 2004 after initial invasion of the estuarine study system in 2002. Substrate characteristics did not limit species distribution. In contrast, substrate and planting density affected plant growth and the outcome of intra- and inter-specific competition in the greenhouse. Although other environmental variables, such as water depth and turbidity, appear to override the effect of substrate in the field, the greenhouse experiment suggests that substrate can be an important driver of submersed aquatic plant community dynamics. Sediment characteristics should therefore be a factor in restoration design and the management of invasive species.Item THE EFFECT OF AMBIENT N:P RATIO AND LIGHT ON THE NITROGEN UPTAKE AND GROWTH OF SELECT ESTUARINE AND OCEANIC DINOFLAGELLATES(2011) Li, Ji; Glibert, Patricia M.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increasing frequency of harmful algal blooms (HABs) have been observed in eutrophic coastal ecosystems. The relationship between environmental factors (nutrients and light) and bloom-forming dinoflagellates were explored in this dissertation by both historical data analysis and laboratory experiments. The growth and nitrogen (N) acquisition of the HAB dinoflagellates Prorocentrum minimum, P. donghaiense, Karlodinium veneficum and Karenia brevis, were studied. It is hypothesized that estuarine species Prorocentrum spp. develops blooms in relative high N:P ratio water, while K. veneficum blooms near or lower than the Redfield ratio; these species will grow faster in the N:P ratio in which they develop blooms, even when these nutrients are not at limiting levels; Prorocentrum spp. preferentially take up more DIN in high DIN:DIP ratio water, while Karlodinium can better use other source of N in the low DIN water; low-light-adapted nitrogen acquisition by Prorocentrum spp. serves as an adaptive advantage to grow in low light waters. Historical data analysis showed that P. minimum generally develops blooms in high DIN, high N:P ratio, but turbid water in Chesapeake Bay, while K. veneficum blooms near or lower than the Redfield ratio, when DIN was depleted, but organic N sources were still available. Following these results, the effects of ambient N:P ratio and light on the growth and N acquisition of P. minimum and P. donghaiense were studied in both batch and continuous culture (turbidistat). Prorocentrum spp. were grown in a wide range of N:P ratios, and across a wide range of light intensities in turbidistat. Experiments to determine rates of N acquisition of different N sources were conducted using 15N tracer techniques at each N:P ratio and light treatment. However, in culture, the growth of the Prorocentrum species was not regulated by the ambient N:P ratio. When nutrients were sufficient, light, instead of ambient N:P ratio, regulated the algal ability to acquire N. The adaptive strategies of the two types of dinoflagellates, Prorocentrum spp. and Karlodinium/Karenia spp., are different. Prorocentrum minimum was shown to take up N in the dark. This light independent N uptake allows it to be more competitive in the relative low light near-shore water. Karlodinium/Karenia spp. apparently only takes up N in the light phase, but it can be mixotrophic and directly use organic sources, and thus may be more competitive after DIN was depleted. The Droop model, which describes the growth rate regulated by the cell quota, was used to interpret the relationship between N acquisition and the growth rate over the diel cycle of growth. Prorocentrum spp. continuously take up nitrogen at night to supplement the cell quota, and reaches the maximum cell quota at the beginning of light phase, when they reach the higher growth rate in a diel cycle. In eutrophic coastal systems (e.g., Chesapeake Bay), the ambient N:P ratio, as well as light may be critical factors for HAB growth. The dinoflagellates studied here have different adaptive strategies to grow in low light and to take advantage of high nutrients in the eutrophic waters. Prorocentrum spp. may dominant the high DIN water, while Karlodinium/Karenia spp. prefers organic nutrients.Item Green Facade Energetics(2010) Price, Jeffrey; Tilley, David R; Biological Resources Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rising energy costs and a warming climate create the need for innovative, low-carbon technologies that help cool buildings. We constructed four small buildings and instrumented them to measure the cooling effect of a green façade on their south and west walls. The green façade significantly reduced the temperature of the building's ambient air, exterior surface, and interior air, and the heat flux through the vegetated wall. Using a mathematical model, we determined that the whole-building cooling load reduction (1.4 to 28.4%) depended on building construction, green façade placement, and especially whether the windows were covered. An emergy analysis of a south-facing green façade revealed that the total emergy consumed could be balanced by the electricity saved from reduced air conditioning if the cooling load was reduced by at least 14%. With thoughtful design and placement of a green façade it can sustainably and effectively help cool buildings.Item Relating pollutant and water quality parameters to landuse in a subwatershed in the Choptank River watershed(2010) Nino de Guzman, Gabriela Tejeda; Torrents, Alba; Hapeman, Cathleen J; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Agriculture and animal feeding operations have been implicated as sources of water pollution along the Choptank River, an estuary and tributary of the Chesapeake Bay. This survey examined a subwatershed within the Choptank River watershed for impacts of a poultry facility on its adjacent surface water. Water and sediment samples were collected May - October 2009 under mostly baseflow conditions and analyzed for antibiotics, nutrients, heavy metals, and selected bacteria. Of the antibiotics recovered, no significant difference was observed spatially, but a significant difference emerged between spring and fall/winter. For nutrients, the greatest phosphorus concentrations were at the subwatershed outlet (4) and at two branches not containing the poultry house (3 and 5); nitrogen concentrations at sites 2 and 5 were as high as site 4. Arsenic concentrations at 2 were lower than both the low-agriculture (control) site and a site neighboring 3. Bacterial counts in water and sediment remained fairly constant throughout the sampling regime.Item INTERACTIONS BETWEEN NATURAL ORGANIC MATTER COMPOSITION AND MERCURY TRANSPORT IN A BOREAL WATERSHED(2010) Ghorpade, Sarah; Heyes, Andrew; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Natural organic matter (NOM) composition affecting mercury (Hg) transport along a watershed transect were examined in the Lake 658 system at the Experimental Lakes Area, Canada. This watershed was dosed with an enriched stable isotope of Hg, allowing for distinction between recently deposited and historic Hg. Newly deposited Hg was not detected in significant quantities in upland flow or the lake, and occurred only in upper soil horizons, indicating that Hg has not reached steady state 8 years following deposition. Characterization of dissolved phase NOM was conducted by molecular weight fractionation, and analysis of absorbance properties and lignin phenols. Low molecular weight compounds were more mobile in the upland, while high molecular weight fractions contained more Hg. Spectral properties were not consistent predictors of Hg, but supported findings on molecular weight distribution. Source material composition, as indicated by lignin phenols, did not vary widely and was not correlated with Hg.Item Hindcast Study: Predicting the distribution of Vibrio vulnificus in Chesapeake Bay(2010) Banakar, Vinita; Colwell, Rita; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Vibrio vulnificus, is an ubiquitous bacterium which primarily causes seafood related gastroenteritis, primary septicemia, and wound infections worldwide. It occurs as part of the normal micro-flora in the coastal marine environment and has been frequently isolated from water, sediment and oysters. A hindcast prediction study was undertaken to determine the likelihood of occurrence of V. vulnificus in the surface waters of Chesapeake Bay. Hindcast predictions were achieved by forcing a multivariate habitat suitability model with simulated sea surface temperature and salinity in the Bay. Predictions of V. vulnificus occurrence were generated for the period between 1991 and 2005. Potential hotspots of occurrence of V. vulnificus in Chesapeake Bay were identified. The likelihood of V. vulnificus occurrence during wet and dry years was analyzed. Hindcast prediction can provide a better understanding of the environmental conditions optimal for occurrence of V. vulnificus in Chesapeake Bay.