Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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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 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 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.Item Stable nitrogen isotopes (&delta15N) in the eastern oyster (Crassostrea virginica) as an indicator of nitrogen source(2010) Fertig, Benjamin Meir; Dennison, William C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation demonstrates that stable nitrogen isotope signatures (δ15N) in oysters (Crassostrea virginica) can identify anthropogenic nitrogen sources (a cause of degraded water quality) at multiple spatial scales in Chesapeake Bay and Maryland's Coastal Bays. Fieldwork, monitoring and land use data, spatial analyses, and modeling techniques were employed. Due to minimal tissue &delta15N variations between individuals as replicates (standard error < 0.5 /), a sample size of five individuals optimally balanced error with effort. Transplantation verified convergence of oyster &delta15N after changes in nitrogen source while modeling quantified temporal integration (four months for muscle, two to three months for gill and mantle) and measurements over two years demonstrated seasonal &delta15N increases in seston (summer) and oysters (winter). At the small scale (10s of km2), oyster tissues in Monie Bay's creeks (varying by watershed land use) were dominated by anthropogenic nitrogen transported to Monie Bay from Wicomico River whose watershed inputs were predominantly manures (6.8 x 104 to 2.4 x 106 kg N yr-1), not sewage (2.0 x 105 kg N yr-1) or septic (1.1 x 105 kg N yr-1). This has large implications for Delmarva Peninsula: home to 4,630 poultry feeding houses (generating 3.9 x 106 to 1.3 x 108 kg N yr-1) and 1.2 x 106 people (combined sewage and septic generating 3.7 x 106 kg N yr-1), thus a poultry:human nitrogen generation ratio of 1:1 to 91:1. At the medium spatial scale (100s of km2), water quality in Maryland's Coastal Bays was susceptible to runoff. Macroalgae &delta15N (Gracilaria sp.) responded rapidly (4 days) over 100s of km2, while oyster &delta15N responded slowly (2 months) over 10s of km2. Broadly, in Chesapeake Bay (large scale, 10,000s of km2), oyster &delta15N was correlated to land use, stream and tributary water quality, and it reflected tributary wastewater plumes. The overall oyster &delta15N gradient (16.0 / in Eastern Bay, 8.3 / in Lynnhaven River) decreased with flushing time, with increased salinity, and with increased shell height. Denitrification remains potentially confounding as it elevates nitrate &delta15N signals, potentially before oyster assimilation (via plankton). Nevertheless, oyster &delta15N is a powerful tool for indicating nitrogen sources across spatial and temporal scales.Item CARBON AND NITROGEN SOURCES AND CYCLING IN PLANKTONIC MARINE ECOSYSTEMS(2010) Keller, David Peter; Hood, Raleigh R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbon and nitrogen are involved in many important biological and environmental processes and can even influence the global climate (i.e. CO2 as a greenhouse gas). In this dissertation the role of dissolved organic matter (DOM) in marine C and N cycling is studied. Research is also presented that looks at phytoplankton as potential sources of C and N in the upper Chesapeake Bay estuary food web. To better understand DOM cycling a model was constructed to simulate dissolved organic carbon (DOC) and nitrogen (DON) cycling in marine surface waters. Using the model DOM cycling was simulated in the context of: (1) a steady- state comparison of idealized oceanic, coastal, and estuarine ecosystems, (2) the seasonal cycle in eutrophic waters, and (3) a focus on the roles of viruses and microzooplankton. The results suggest that DOM cycling is intricately tied to the biomass concentration, ratio, and productivity of phytoplankton, zooplankton, viruses, and bacteria. The first set of simulations highlights the importance of certain processes in each ecosystem. The second set of simulations shows how DOM cycling, particularly the sources of DOM, changes seasonally. The third set of simulations highlights differences in the top-down and bottom-up roles of viruses and microzooplankton and their subsequent effect on DOM cycling and trophic interactions. To better understand C and N cycling in the upper Chesapeake Bay the biomass distribution and floral composition of the phytoplankton community was studied during the winter and spring to determine if phytoplankton could play an important role in the estuarine turbidity maximum (ETM) food web. This research suggests that the general distribution of phytoplankton in the upper Bay is somewhat like a classic estuarine "salt wedge" diagram with two distinct phytoplankton communities separated by a zone of increased mortality due to salinity stress and ETM entrapment. High concentrations of phytoplankton pigment degradation products were often observed in the ETM suggesting that this is an area of high phytoplankton mortality and/or an area where phytoplankton derived particulate organic matter was being concentrated. These results suggest that phytoplankton have the potential to play an important role in C and N cycling and the ETM food web.Item Steriod Hormones in Biosolids and Poultry Litter: A Comparison of Potential Environmental Inputs(2010) Bevacqua, Christine Elizabeth; Torrents, Alba; Rice, Clifford; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Steroid hormones can act as potent endocrine disruptors when released into the environment. The main sources of these chemicals are thought to be wastewater treatment plant discharges and waste from animal feeding operations. While these compounds have frequently been found in wastewater effluents, few studies have investigated biosolids or manure, which are routinely land applied, as potential sources. This study assessed the relative environmental contribution of steroid hormones from biosolids and chicken litter. Samples of limed biosolids collected over a four year period and chicken litter from 12 mid-Atlantic farms were analyzed for 17β-estradiol (E2), estrone (E1), estriol (E3), 17α-ethinylestradiol (EE2), progesterone, and testosterone, and the conjugated hormones E1-sulfate (E1-S), E2-3-sulfate (E2-3-S), and E2-17-sulfate (E2-17-3). Results showed that E1 and progesterone were the most prevalent compounds in both of these materials, with E1-S also present in chicken litter.Item THE EFFECTS OF ULTRAVIOLET RADIATION ON THE GROWTH, REPRODUCTION AND SURVIVAL OF THE LOBATE CTENOPHORE MNEMIOPSIS LEIDYI(2010) Rathjen, Kristen; Breitburg, Denise L; Roman, Michael R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Solar ultraviolet radiation (UVR) is an environmental stressor that can have a variety of negative effects on aquatic organisms. The ctenophore Mnemiopsis leidyi is a highly transparent organism that has not been shown to actively avoid UVR or possess photoprotective compounds and may therefore be vulnerable to deleterious effects of UVR. Results of this study indicate that summertime UVR exposure equivalent to average UVR conditions within the top 0.5 m of the water column of the Rhode River, Maryland, USA, can cause mortality and reduced size of M. leidyi. Exposures tested did not, however, affect egg production. Experiments indicated a sharp threshold for the tolerance of M. leidyi to biologically effective UVR exposure. Mnemiopsis leidyi is an important component in many ecosystems; thus, changes in its abundance have the potential to significantly affect coastal and estuarine food webs and oyster, fish and sea nettle populations in systems like Chesapeake Bay.