The contribution of phytoplankton productivity to higher trophic levels in salt marshes is not well understood. My study furthers our understanding of possible mechanisms controlling phytoplankton productivity, abundance, and community composition in salt marshes. Across three consecutive springs (2001 to 2003), I sampled the upper Nueces Delta in south Texas, a shallow, turbid, salt marsh system stressed by low freshwater inflow and wide ranging salinity (<15 to >300 ppt). Water column productivity and respiration were estimated using a light-dark bottle technique, and phytoplankton biovolume and community composition were determined using inverted light microscopy. To determine their effect on the phytoplankton community, zooplankton and bacterioplankton abundance and several physical parameters were also assessed. Meaningful relationships among the numerous variables evaluated in this study were identified using principal component analysis (PCA). Despite high turbidity, phytoplankton productivity and biovolume were substantial. Resuspension appeared to play a major role in phytoplankton dynamics, as indicated by a positive relationship between ash weight and biovolume that explained up to 46% of the variation in the PCA. Negative relationships between zooplankton grazers and pennate diatoms of optimal sizes for these grazers suggested a functional grazing food chain in this system. Salinity also may have been important in phytoplankton dynamics, whereas nutrients appeared to play a minor role. Salinity increases may have been responsible for a decoupling observed between phytoplankton and grazers during late spring. Findings suggest hypotheses for future studies focused on the role of phytoplankton in salt marshes, particularly those stressed by reduced freshwater inflow and high salinities.

The North Caspian Basin (NCB) contains a significant number of major oil fields, some of which are yet to be put into production. The reason why some of these fields are not yet put into production is the exploration challenge that the NCB poses. In particular, the complex geological structure of this region makes it quite difficult to image its oil fields with conventional seismic techniques. This thesis sheds more light on difficulties associated with acquiring and processing seismic data in the NCB. The two central tools for investigation of these imaging challenges were the construction of a geological model of the NCB and the use of an accurate elastic wave-propagation technique to analyze the capability of seismic to illuminate the geological structures of the NCB. Using all available regional and local studies and my knowledge gained with oil companies, where I worked on subsalt and suprasalt 2D and 3D seismic data from the North Caspian Basin, I constructed a 2D elastic isotropic 10-by-6 km geological model of a typical oil field located on the shelf of the Caspian Sea in the southeastern part of the North Caspian Basin, which has the largest oil fields. We have propagated seismic waves through this model. The technique we used to compute wave propagation is known as the Finite-Difference Modeling (FDM) technique. Generating 314 shot gathers with stationary multicomponent OBS receivers that were spread over 10 km took two weeks of CPU time using two parallel computers (8 CPU V880 Sun Microsystems and 24 CPU Sun Enterprise). We have made the data available to the public. The dataset can be uploaded at http://casp.tamu.edu in the SEGY format. The key conclusions of the analysis of these data are as follows: - Combined usage of P- and S-waves allows us to illuminate subsalt reef, clastics and complex salt structures despite the 4-km overburden. - Free-surface multiples and guided waves are one of the key processing challenges in NCB, despite relatively shallow (less than 15 m) shelf water.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2002. / Vita. Includes bibliographical references (leaves 153-161).

Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1940. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed March 9, 2010) Includes bibliographical references (p. 45-46) and index (p. 47-52).

Thesis (Ph. D.)--University of California, San Diego, 2000. / Vita. Includes bibliographical references.

Power generation through decentralized small scale CHP would facilitate the use of biomass as an energy source, with the externally fired gas turbine (EFGT) being a promising technology due to its high electrical efficiency. In an EFGT hot flue gases are heat-exchanged with an air cycle, driving the turbine. The operation requires higher flue gas temperatures than other technologies, for example steam turbines, to achieve optimal performance.  The operating conditions subjects the high temperature heat exchanger (HT-HE) to both physical and chemical stress, with the corrosion related issues yet to be solved. Problems concerning deposit formation and corrosion, on for example super heaters and heat exchangers, when firing biomass are important issues even in commercially available technologies, where the choice of fuel and fuel additives together with component design and choice of material plays important roles in order to minimize the problems. The significantly higher temperatures of the heat transferring surfaces for an EFGT entails combustion deposit related problems less studied. The evaluation of turbine control, deposit formation and corrosion as well as design of the HT-HE and system integration will enable the development of the EFGT technology for applications with small- and medium-size biomass combustion. In this work four potential HT-HE alloys of various grades have been evaluated with respect to corrosion resistance, when exposed to alkali salts and salt mixtures in the KCl-K2CO3-K2SO4 system. The exposures were done in a tube furnace during 24 h for each experiment at four temperature levels between 700–1000oC. Morphological and elemental analysis of the alloy surface and corrosion layers was performed with SEM-EDS. The presence of KCl in the salt caused the most severe corrosion attacks while the corrosion attacks of the pure sulfate and carbonate were more modest. Significant differences between the four materials were observed. X20 experienced severe corrosion, with corrosion scale formation in most cases. The KCl-containing salts caused 253MA to form corrosion scales at all temperatures, while the corrosion resistance to other salts was fairly good. Inconel 600 had the second best overall corrosion resistance. However, it should be pointed out that in some cases the alloy was surpassed by 253MA. Kanthal showed the best overall performance, with limited corrosion scale formation and surprisingly high corrosion resistance to the KCl-containing ternary salt mixture at 900°C and 1000°C.

Estuarine wetlands and salt marshes are fundamentally driven by variations in freshwater inflow. In semi-arid salt marshes, such as the Nueces River Delta, TX, the stochastic nature of freshwater inflow events exposes resident organisms to a wide range of environmental conditions. In this study, we investigate (1) the relative importance of environmental variables on porewater salinity and (2) determination of freshwater inflow needs based on the response of emergent plants to salinity variations. Porewater salinity variations were tracked on a continuous basis with deployed conductivity sensors and on a synoptic basis with soil water extracts. We found that spatial patterns of porewater salinity were characterized by a high degree of variability in creekbank areas (23.8 ± 7.68) relative to interior marsh areas (44.2 ± 3.4). Our observations were used to test a simple model capable of predicting porewater salinities based on environmental variables. Both empirical measurements and model simulations indicated that semiannual tides play a critical role in controlling porewater flushing from precipitation and freshwater inflow events. Estimation of freshwater inflow needs for the Nueces Delta proceeded in two steps. First, we examined the response of three common emergent plants species (Borrichia frutescens, Spartina alterniflora, and Salicornia virginica) to variations in salinity. The abundance of one species in particular (S. alterniflora) was tightly coupled to salinity variations whereby salinities exceeding 25 ± 5 resulted in dramatic declines in coverage. Next, the relationship between freshwater inflow and porewater salinity was examined with respect to the salinity “tolerance” of S. alterniflora. Estimated inflow needs based on maintenance of substantial (> 20%) S. alterniflora coverage was comparable to both previous inflow needs estimates and mean annual inflows observed over the course of the study. The results of this study suggest that S. alterniflora abundance provides a reliable indicator of overall estuarine hydrological condition in the Nueces Delta. / text

Hydrocarbon exploration involves drilling into or near salt deposits in the Gulf of Mexico, Brazil, Egypt, and the Middle East. Drilling these systems has proven to be quite dangerous, challenging, and expensive due to the pressure and stress perturbations that exist around the salt. My study focuses on characterizing the pressure and stress distribution at the Mad Dog field, which is a large oil field below an allochthonous salt body in the deepwater Gulf of Mexico. The Mad Dog field lies beneath the Sigsbee Escarpment, which represents the surface and seaward-most indicator of a mobile salt in Green Canyon blocks 781, 782, 825, and 826, 190 miles southwest of New Orleans in 4,500-6,500 feet of water. I characterize the pressure distribution within the Lower Miocene sandstone reservoir which has produced over 100 million barrels to date. I map the reservoir horizon using 3D seismic data and that the reservoir is a complex regional anticlinal structure that is separated by numerous normal faults that cause it to be segmented into compartments. The in-situ pore pressures show that the compartments are not in pressure communication across the field and that multiple aquifer phase pressures are present. The in-situ pore pressure measurements are used to characterize the pressure distribution in the Miocene sediments below the salt body and in front of the mobile salt body. These measurements show that between the upper Miocene to middle Miocene there is an absolute pressure decrease and between the middle to lower Miocene there is a large pressure increase. This pressure distribution is seen both within the Miocene sediments below salt and in front of salt. A porosity and effective stress relationship from shallow Pleistocene sediments was developed to predict the pressure behavior observed within the Miocene and compare the predicted pressure with in-situ pore pressure measurements. The mudstone pressure prediction overestimates the in-situ sand pore pressure. The mudstones bounding regional sandstone have a constant porosity throughout the field, suggesting that the vertical effective stress is constant. These observations can be used to estimate the mudstone pore pressure in a new well location. If the vertical effective stress in an offset well is known and given knowledge of the total vertical stress in the new well location, the mudstone pore pressure can be estimated. / text

Salinity is a significant barrier to the distribution of diatoms, and though it is generally understood that diatoms are ancestrally marine, the number of times diatoms independently colonized fresh waters and the adaptations that facilitated these colonizations remain outstanding questions in diatom evolution. Resolving the exact number of freshwater colonizations will require large-scale phylogenetic reconstruction with dense sampling of marine and freshwater taxa. A more tractable approach to understanding the marine--freshwater barrier is to study a group of diatoms with high diversity in each habitat. The "centric" diatom order Thalassiosirales affords an excellent opportunity to study the origin and evolution of diatoms in fresh waters. Thalassiosirales is a well-supported monophyletic group common in marine, brackish, and freshwater habitats. Thalassiosirales species historically are classified into the marine Thalassiosiraceae or freshwater Stephanodiscaceae, reflecting the more generally held hypothesis that diatoms are naturally split along marine--freshwater lines. The fossil record suggests that Stephanodiscaceae traces to a single colonization of freshwater in the mid-Miocene, and in addition, Stephanodiscaceae species share a suite of complex cell wall characters, which has been interpreted as corroborating evidence for their monophyly. I reconstructed the phylogeny of Thalassiosirales and used the phylogeny to test these and other hypotheses and to address a number of other problems related to the marine--freshwater boundary in diatoms. Phylogenetic analyses showed strong evidence for multiple colonizations of freshwater and reject all previous colonization hypotheses. Results further show that part of Stephanodiscaceae is an early diverging lineage within Thalassiosirales, indicating that these two distantly related and separately derived Stephanodiscaceae lineages independently evolved a similar set of complex morphological features upon or shortly after the colonization of fresh waters. Finally, marine and freshwater diatoms, including Thalassiosirales, show several important differences in silicon physiology. In addition to containing an order of magnitude more silica in their cell walls, freshwater diatoms have a drastically lower enzymatic affinity for silicic acid, the dissolved form of silica used by diatoms. I sequenced the silicon transporter genes from marine and freshwater Thalassiosirales and show that physiological differences are not due to differences in the coding sequence. / text

Chiral molecules as with biological activity are plentiful in nature and the chemical literature; however they represent a smaller portion of the pharmaceutical drug market. As asymmetric methodologies grow more powerful, the tools are becoming available to synthesize chiral molecules in an enantioselective and efficient manner. Recent breakthroughs in our understanding of phosphoric acid now allow for Lewis acid catalysis via pairing with alkaline earth metals. Using alkaline earth metals with chiral phosphates is an emerging approach to asymmetric methodology, but already has an influential record. The development of new conditions for the phosphoric acid-catalyzed highly enantioselective ring-opening of meso-aziridines with a series of functionalized aromatic thiol nucleophiles is described in this thesis. This methodology utilizes commercially available aromatic thiols, a series of meso-aziridines, and a catalytic amount of VAPOL calcium phosphate to explore the substrate scope of this highly enantioselective reaction. Additionally, the development of new conditions for a catalytic asymmetric aza-Darzens aziridine synthesis mediated by a vaulted biphenanthrol (VAPOL) magnesium phosphate salt is described in this thesis. Using simple substrates, this methodology explores the scope and reactivity of a new magnesium catalyst for an aziridination reaction capable of building chirality and complexity simultaneously.