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.
Browse
7 results
Search Results
Item Interactions between an estuarine submersed plant bed and its physical and biogeochemical environment: Seasonal and spatial variation(2009) Gruber, Renee Kirstin; Kemp, William M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Annual cycles of growth and morphology were analyzed in a bed of the canopy-forming submersed aquatic vegetation (SAV) species, Stuckenia pectinata, in relation to seasonal water quality conditions in a Chesapeake Bay tributary. A rapid accumulation of aboveground plant material occurred during the spring period of high water clarity, which aided plants in circumventing light limitation during the summer period of low water clarity. During summer, this SAV bed strongly attenuated wave energy, which contributed to growth-promoting feedback effects that improved light and nutrient availability for plants. Modification of hydrodynamic conditions also resulted in several negative feedback effects on SAV growth. Feedbacks were regulated by plant stand size and density and seasonal changes in plant canopy architecture. The findings of this study illustrate the significant impacts SAV beds can have on their local environment, improving conditions and resulting in plant growth that could not otherwise occur in this degraded system.Item Organic nitrogen and carbon transformations in a stream network of Chesapeake Bay watershed(2009) Delaney, Katie M.; Kaushal, Sujay S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increased export of anthropogenically-derived nitrogen in streams has contributed to increased water quality problems. I investigated in-stream transformations of nitrogen and carbon at the benthic habitat and reach network scale. Both indicated large transformations of dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) along the Gwynns Falls urban stream network. In-stream transformation of DON and DOC declined from headwaters to outflow, with a mean 23% removal of DOC and 57% removal of DON. Transformation rates ranged from in-stream internal loading of 28 g/m2/day to in-stream removal of 740 g/m2/day for DOC (mean: uptake 64 g/m2/day) and in-stream internal loading of 4.8 g/m2/day to in-stream removal of 74 g/m2/day for DON (mean: uptake 3.5 g/m2/day). Urban stream networks may act as both "transporters" and "transformers" of nitrogen and knowledge regarding in-stream N transformations is critical in predicting the sources and removal of nitrogen en route to adjacent tidal waters.Item Effect of pH on phytoplankton and bacteria production(2009) Johns, Desmond Justine; Stoecker, Diane K; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In recent decades eutrophication has fueled intense phytoplankton blooms that frequently negatively impact ecosystems. Dramatic pH elevations are commonly overlooked during such blooms, which may also be harmful. Cyanobacteria blooms in the Sassafras River, MD were sampled during Autumn 2008 and measured for primary and bacterial production (PP and BP), and differences in bacteria communities composition were examined. pH elevations above 8.8 in the field corresponded to decreased PP, but had no effect on BP. Laboratory experiments demonstrated that negative effects of pH were dependant on light intensity; PP increased with pH at moderate light intensities, but decreased at low irradiance. There was some evidence that BP is affected by high pH, although bacteria community differences as determined by DGGE were not. Negative effects of high pH are probably most important during spring and summer in low salinity environments when pH fluctuations are more common and last longer.Item Transport, sources, and quality of seston in a Piedmont headwater stream(2008-05-27) Richardson, David Charles; Palmer, Margaret A; Kaplan, Louis A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Streams transport and process particulate organic carbon (POC) within the suspended load (seston) after terrestrially-fixed (allochthonous) carbon enters lotic ecosystems or as instream (autochthonous) production is suspended from the streambed. POC provides a basal resource for upstream food webs, but can also support heterotrophic metabolism in downstream rivers. Yet, the controls on transport, sources, and biological availability (quality) of POC from headwaters are poorly understood. I examined seston and POC dynamics in a 3rd-order headwater stream in SE Pennsylvania. I studied the temporal controls on seston transport, composition, and sources, and the biological quality of POC. I present evidence that seasonal patterns in seston and POC transport and composition reflect stream organism activity and cycles of autumnal leaf litter inputs and vernal algal production. This work also provides the first evidence of recurrent nighttime peaks of seston transport; I attribute this pattern to bioturbation of streambed sediments that suspends particles during stream-organism nest digging, foraging, and movement. I present the first effort to demonstrate that stream salamanders contribute to ecosystem level processes such as modification of seston and organic carbon flow. Mixing model analyses of seston composition indicate that seston in small streams is predominantly mineral-core particles; however, POC fluxes are primarily organic-core particles. Furthermore, the traditional view of headwater POC as leaf detritus should be expanded to include algal-derived particles, even in forested headwater streams. Finally, I report a new method for measuring the quality of suspended POC from aquatic environments using heterotrophic respiration as a metric for lability. Heterotrophic respiration rates for suspended POC measured using this method were an order of magnitude higher than respiration rates previously reported for benthic POC. The results from this research highlight the importance of seston for both headwater streams and as a longitudinal linkage of allochthonous and autochthonous organic matter to downstream ecosystems. The magnitude of this connection is controlled by the quality, quantity, and timing of POC delivery.Item Nitrogen Uptake and Physiology of Dinoflagellate Blooms in the East China Sea(2008-05-06) Li, Ji; Glibert, Patricia; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Frequent and large scale harmful algal blooms have developed in the highly eutrophic water in the Changjiang River estuary and East China Sea coast in the past decade. Sampling and experiments were conducted during late spring and early summer of 2005 to study the dinoflagellate blooms in this region when large scale (> 15,000 km2) mixed dinoflagellate blooms developed. Karenia mikimotoi was the dominant harmful algal bloom (HAB) species in the first stage of the bloom and was succeeded by Prorocentrum donghaiense approximately 2 weeks later. Samples were collected from different stations along both north-south and west-east transects during 3 cruises. Nitrogen (N) uptake experiments were conducted during the time period that covered pre-bloom, bloom development and bloom decline. Kinetics of N uptake by phytoplankton assemblages were measured as a function of substrate concentration (4 N sources, NO3−, NH4+, urea, glycine) with 15N isotope techniques. The bloom progression was related to the change in available N and phosphorus (P) composition. Reduced N, especially NH4+ and urea, were preferentially taken up during the blooms. Both the biological availability of reduced N and the N:P ratio were suggested to be important factors for the bloom development. High inorganic nitrogen loading from the river and phosphorus from coastal water supported the bloom development. Relatively high organic nitrogen levels, and low DIN:DIP led to a succession of dinoflagellates. The temporal and spatial variability in kinetics parameters were reported as N-specific maximum uptake rates (Vmax, h-1), absolute maximum N uptake rates (ρmax, µM h-1) and half-saturation constant (Ks, µmol L-1) during the bloom progression. The results of comparison these indices with ambient nutrients and bloom progression confirmed the preferentially taken up of N by different species during the blooms. Remarkable correspondence was found about the nutrient ratios and specific uptake rates of urea between blooms in the East China Sea and in analogous blooms on the West Florida Shelf. Similar N uptake rates were also shown between the East China Sea and the Chesapeake Bay. These findings suggest that there may be general relationships between these blooms species and the availability of different nutrients and the N:P ratio. To more firmly estimate these relationships, additional laboratory experiments and more comparison among different ecosystem will be required. Such relationships will contribute to our understanding of, and ability to model, these bloom dynamics.Item THE INTERELATIONSHIP BETWEEN CD14 AND LPS DURING MASTITIS: RELEASE OF SOLUBLE CD14 AND CYTOKINES BY BOVINE PMN FOLLOWING ACTIVATION WITH LPS(2005-08-11) sohn, eun j; Peters, Robert R; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Understanding the immune defense of the mammary gland is important in devising and developing measures to control mastitis. Lipopolysaccharide (LPS) is the predominant factor causing pathogenesis in Gram-negative bacterial infections. The cluster of differential antigen14 (CD14), which is located on the surface of leukocytes, is the receptor for LPS. The binding of LPS to CD14 results in release of pro-inflammatory cytokines that recruit polymorphonuclear neutrophil leukocytes (PMNs), to the site of inflammation, allowing them to kill bacteria through the process of phagocytosis. This research was designed to produce and characterize monoclonal antibodies (mAb) against recombinant bovine soluble (rbos) CD14, express rbosCD14 in plants and characterize the biological activity of plant-derived rbosCD14 in vitro and in vivo. The release of inflammatory cytokines and expression of CD14 on bovine PMN and the secretion of IL-8 by PMN in response to LPS was also invesitigated. A panel of ten murine mAb reactive with rbosCD14 were produced and a sandwich ELISA was developed using the mAbs and rabbit polyclonal antibodies. The mAbs recognized rbosCD14 (40 kDa), solubleCD14 (sCD14) (53 and 58 kDa) in milk and blood, and a 47 kDa mCD14 in lysates of macrophages obtained from involuted bovine mammary gland secretions by Western blot analysis. Flow cytometric analysis showed that the mAb bound to macrophages isolated from involuted mammary gland secretions. The addition of anti-rbosCD14 mAb to monocytes stimulated with LPS reduced TNF-alpha production in vitro. The anti-rbosCD14 mAbs generated in this study will be useful in studying CD14, an accessory molecule that contributes to host innate recognition of bacterial cell wall components in mammary secretion produced during mastitis. This study demonstrates the functional activity of a recombinant animal receptor protein made in plants, and the use of a plant-derived protein as a potential animal therapeutic for bacterial infections. A truncated form of sCD14, carrying a histidine residue affinity tag was incorporated with potato virus X for transient expression in Nicotiana benthamiana. CD14 from crude plant extracts was recognized by Western blot analysis. Biological activities of plant-derived rbosCD14 (prbosCD14) were characterized in vitro and in vivo. Biological activity of prbosCD14 demonstrated in vitro by LPS-induced apoptosis, an increase of caspase activity and IL-8 production by bovine endothelial cells. In vivo, prbosCD14 enhanced LPS-induced PMN recruitment and in bovine mammary quarters challenged with Escherichia coli that resulted in decreased bacterial counts and elimination of clinical symptoms. In this disseration, shedding of sCD14 from the surface of PMN in response to LPS was negatively correlated with IL-8 release. Shedding of sCD14 from the surface of PMN increased in the absence of serum and at high concentrations of LPS. The use of real time RT-PCR showed that CD14 gene expression was not different between control and the LPS stimulated cells. This demonstrates that shedding of sCD14 comes from membrane-boundCD14 (mCD14). However, in contrast to the shedding of sCD14, IL-8 secretion by PMN was decreased at high concentrations of LPS in the absence of serum. Moreover, sCD14 secretion from PMN stimulated with LPS was increased in parallel with the decrease of IL-8 secretion at varying PMN cell densities. This result suggests that the release of CD14 leads to the down-regulation of IL-8 secretion by PMN in response to LPS. Bovine PMN produced different types of cytokines in response to LPS in this disseration. The secretion of TNF-alpha, IL-1beta, IL-8 and INF-gamma by PMN increased in a dose-dependent manner, but IL-12 secretion by PMN was decreased with increasing concentrations of LPS. Co-incubation of LPS with either TNF-alpha or IL-1beta increased secretion of IL-8 when compared to LPS alone. These studies contribute to a better understanding of the interrelationship between bovine CD14 and LPS during mastitis and provide new insights into events that resolve inflammation following bovine PMN activation.Item Assessing evapotranspiration rates of a Mid-Atlantic red maple riparian wetland using sap flow sensors.(2005-04-13) Renz, Jennifer Theresa; Momen, Bahram; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Riparian forests are unique due to increased exposure of trees to winds and radiation and the subsequent effects on the quality and quantity of water discharge from the system. Since "edge effects" can enhance evapotranspiration (ET) of exposed trees, ET rates of a first-order red maple riparian wetland were assessed with thermal dissipation probes during the 2002 growing season to address: a) if edge trees transpire more water daily than interior trees, b) correlations among sap flow rates and energy balance-derived estimates, c) variations in ecosystem ET estimates based on 6 scaling variables, and d) diurnal correlations between maximum sap flow rates and streamflow losses. Results from this study indicate that: a) edge trees transpire more water daily than interior trees during early summer, b) choice of scaling variable affects estimation of ecosystem ET rates, and c) maximum sap flow rates correlate with streamflow losses diurnally under specific environmental conditions.