The impact of the Deepwater Horizon blowout on coastal wetlands can be understood through investigating carbon loading and microbial activity in salt marsh sediments. Carbon influx causes pore water sulfide to increase in wetland sediment, making it toxic and inhospitable to marsh vegetation. High sulfide levels due to increased microbial activity can lead to plant browning and mortality. Preliminary analyses at Marsh Point, Mississippi indicated that sulfate reducing bacteria are more active in contaminated marsh, producing sulfide concentrations 100x higher than in noncontaminated marsh. Sediment electrode profiles, hydrocarbon contamination, and microbial community profiles were measured at three additional locations to capture the spatial sedimentary geochemical processes impacting salt marsh dieback. Findings indicate that response to contamination is variable due to physical and biogeochemical processes specific to each marsh. Temporal evaluation indicates that there is a lag in maximum response to contamination due to seasonal effects on microbial activity.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

The molten salt reactor (MSR) is one of the advanced nuclear reactors expected to be alternatives to the conventional water-cooled nuclear reactor systems. Despite many advantages of MSRs, properties of molten salts have not been sufficiently measured in previous studies. In addition, the corrosion of structural alloys by molten salt is the biggest challenge for the operation of MSRs. This study focuses on measurements of thermophysical and thermodynamic properties of fluoride salt fuels, salt purification, and the degradation of structural materials in static and flowing molten-salt fuels. For the measurements of properties, phase transition, specific heat capacity, vapor pressure, contact angle on nuclear-grade graphite, and density were measured. The methodologies for the property measurements used in this study were validated by measuring the properties of metals or salts that have been well studied. For the flow-induced corrosion tests, the salt flow with different velocities was simulated by rotating the stainless steel 316H (SS316H) specimens in molten NaF-KF-UF4 (FUNaK) contained in glassy carbon crucibles at 1073 K. Salt samples were intermittently collected to monitor concentration changes of corrosion products in the salt, and surfaces and cross-sections of post-test SS316H specimens were analyzed to study their corrosion behaviors. Different batches of FUNaK were synthesized using different methods of purification, such as thermal purification, U-metal purification, and hydrofluorination with electrochemical purification (chemical purification) to study impacts of salt purification on the corrosion of SS316H. The corrosion test of SS316H by thermally purified FUNaK showed that the Fe concentration increased at the beginning and then decreased while the Cr concentration continued increasing while the rate decreased. In addition, (Cr, Fe)7C3 layers, Cr-metal particles, and dendritic structures concentrated with Cr and Fe were observed on the glassy carbon crucible after the 2 m/s test. The U-metal purification and hydrofluorination with electrochemical purification reduced concentrations of oxygen and hydrogen in FUNaK and mitigated the corrosion of SS316H significantly. The infiltration of the fluoride fuel salts into graphite and the fluorination of graphite by the salts at different pressures and temperatures were also studied. The salt infiltration into graphite at pressures above its threshold pressure was observed, and the formation of carbon fluorides on the surface of post-test graphite specimens was identified. / Doctor of Philosophy / As conventional water-cooled nuclear power systems showed safety issues, the Generation IV International Forum was established to expedite the development of next-generation nuclear reactor systems. Among the six advanced nuclear reactors, the molten salt reactor (MSR) stands out for its remarkable technical advantages, including low operating pressures and increased efficiency resulting from higher operating temperatures compared to water-cooled nuclear systems. Despite their advantages, further studies need to be conducted to develop and operate MSRs, as properties of molten salts have not been comprehensively measured in previous studies, and the corrosion of structural materials by molten salt is a significant challenge to their operation. The corrosion of alloys by molten salt can be attributed to many different factors, and the level of impurities in salt is an important factor directly linked to corrosion. Thus, the purification of salt is imperative to mitigate the corrosion of MSRs and needs to be well studied. In this study, methodologies for measuring thermophysical and thermodynamic properties of fluoride fuel salts were developed and validated using reference data. In addition, the corrosion of stainless steel 316H (SS316H) in a flowing fuel salt was also studied. Although various corrosion tests with static molten salts have been conducted, studies on corrosion of alloys in flowing molten salt fuels containing uranium fluorides are still limited. This study addresses this gap by developing a test apparatus equipped with a rotating disk to simulate the flow of molten salt on the surface of alloy specimens. Different batches of fuel salts with varying impurity levels, especially oxygen and hydrogen, were prepared using different purification methods. These salts were then used for corrosion tests under the same conditions, such as temperature and time duration, to explore the impacts of the non-metallic impurities on the corrosion of SS316H. The findings revealed that the salts with lower levels of oxygen and hydrogen caused less corrosion of SS316H, underscoring that the purification of salt is indispensable to the mitigation of corrosion in MSRs. This study also explored interactions of molten-salt fuels with graphite which is a promising candidate for a moderator or reflector of MSRs for enhancing neutron economy for thermal nuclear reactors. A high-pressure graphite-infiltration test apparatus was developed to investigate infiltration of fluoride fuel salts into graphite and the fluorination of graphite.

Three cotton (Gossypium hirsutum L.) germplasms (DP62, 84027, and 84033) were used to investigate the physiology of salt tolerance. Lines 84027 and 84033 were developed from the parental line DP62 and showed superior vigor under varying NaCl conditions (0.5 to 2.0 M) during germination and emergence. Proline levels increased in the leaves of all germplasms in response to increasing salinity. Varietal differences in proline levels did not reflect their variation in salt tolerance. Several physiological characteristics were also evaluated under non-saline condition in the greenhouse. There were no significant differences among germplasm sources for all parameters measured. However, salinity reduced transpiration rate, increased leaf diffusive resistance and leaf temperature for all lines. Ribosomal-RNA levels in all germplasms were evaluated after seeds were stressed for 24 hrs in various concentrations of NaCl and then germinated under normal conditions for 72 hrs. Ribosomal-RNA levels were inversely related to salt concentrations. Line 84033 followed by line 84027 had highest ribosomal-RNA content than the parental line DP62 when averaged over the four salt concentrations. Sodium content (ppm/g FW) and Cl⁻ content (ppm/g FW) were evaluated in microsomal and cell walls fractions as well as a cytoplasmic fraction which consisted of vacuoles, mitochondria, and plastids. The Cl⁻ ion exhibited a greater consistency in a concentration shift from one fraction to another as a function of time than did the Na⁺ ion. As a result, there may be a correlation between the drop in ribosomal-RNA and the amount of Cl⁻ in the microsomal fraction. Other parameters measured in the germinating seed were soluble protein (globulin), insoluble proteins (prolamin and glutelin) and fiber percentage. Variations within the germplasms were shown to exist. This study shows that even among lines that have been selected for salt tolerance from a single variety, the possibility exists that each of these lines may have a different mechanism to cope with salt stress.

The succulent, annual euhalophyte, Salicornia bigelovii was grown in 1, 10, 35, 45 and 60 ppt Instant Ocean. This range represents approximately 1/35 to nearly twice the salinity of seawater. The plants in the 4 highest salinities had common final dry weights and seed yields of about 60 and 11 g, respectively, while the 1 ppt plants had 28 and nearly 5 g, respectively. The water relations data reflected the growth and seed production of the plants. The plants in the 4 higher salinities had water potentials sufficient to generate large import gradients and osmotic potentials which contributed to substantial turgors. The 1 ppt plants had a gradient like the rest, but a very low turgor of 0.11 MPa which was barely 23% of that of the lowest of the other treatments. Higher salinities resulted in slightly greater organic and inorganic osmotica contents. Overall, these results suggest a relatively fixed genetic response to a wide range of salinities, as well as an inability to function well at very low salinities. No plant grown at 0 ppt was ever able to reproduce. Therefore, this plant is an obligate halophyte. Experiments in the plant's native coastal estuary indicated meristem water potentials fluctuate with the tides, although they remain about 1.5 MPa below the corresponding soil water potentials. The plants occupy a discrete elevational range throughout the estuary, spending about 1/3 of their daylight hours submerged, and apparently never see dryness. Phenotype differences in the estuary suggest that, within the habitat, pacing and consequent resource domination may be important parameters affecting plant size and possibly fitness. Nitrogen, which is characteristically rare in this and other estuaries, may be critical in this regard. The plants produce large quantities of glycine-betaine, which may be for simultaneous osmoticum use and nitrogen storage. Most roots occur in the first 3 inches of soil. A mechanism is proposed, based on highly efficient compartmentation at the cellular level and the shuttling of organic osmoticum across the tonoplast, by which the tidally based cyclical water potentials could be explained.