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Polonium-210 (t1/2=138 d) is the most common among the 33 known radioisotopes of Polonium found in the natural environment. It is produced by the radioactive decay of its long-lived grandparent Lead-210(t1/2=22.3 d) via Bismuth-210 (t1/2=5.012 d) and forms as part of the natural Uranium-238 decay series. The primary hazard associated with Polonium-210 is its radioactivity, as an alpha particle emitter. Marine organisms receive their maximum radioactive dose in the natural environment from Polonium-210. Polonium has been known to bioaccumulate in the marine food web and can be potentially harmful to humans via the intake of certain marine organisms. Thus it is important to understand the source and sink of Polonium-210 in the marine environment. A number of studies in the past have observed Polonium-210 remobilization from sediments in anoxic lake environments but the release mechanism has never been studied in low oxygen marine systems. On the other hand, the biological affinity of Polonium-210 allows it to be used as an effective tracer of POC export from the upper ocean, although no such study using Polonium-210 as a tracer of POC flux has been carried out in the northern Gulf of Mexico. The present work is aimed at understanding both remobilization of Polonium-210 from sediments in the hypoxia zone of the northern Gulf of Mexico and utilizing Polonium-210 as a tracer of POC export in the northern Gulf of Mexico. Results from our study indicate Polonium-210 was enriched in bottom waters by as much as 50% compared to surface waters from sample stations in the hypoxia zone in 2011 and 2012. No strong correlation between oxygen concentration and unsupported Polonium-210 activity was apparent. However, there was a good correlation between Polonium-210 enrichment and the release of redox sensitive trace metals like Fe and Mn. Due to the affinity of Polonium-210 to Fe and Mn, the cycling of redox sensitive elements such as Fe and Mn and the degradation of organic matter in the water column are likely the driving mechanisms of Polonium-210 remobilization from sediments to the water column under hypoxic conditions. The second study utilized Polonium-210 as a tracer for POC export and was carried out along a north south transect in the Gulf of Mexico beginning near the mouth of the Atchafalaya River and ending on the slope of the continental shelf. POC fluxes were estimated using the Lead-210 Polonium-210 disequilibria in the water column and varied between 10.4 mg C m-2 d-1 and 85.6 mg C m-2 d-1 and showed a general decreasing trend further offshore similar to the decrease in net primary productivity further from shore. The efficiency of the biological pump was found to decrease from 21% at stations close to shore to 4% at stations further offshore, suggesting a transition in POC export efficiency from nutrient rich eutrophic water to nutrient poor oligotrophic water.

This dissertation attempts to better understand astronomical, meteorological, and oceanographic forcing of offshore-spawned, estuarine-dependent species from continental shelf to estuarine waters through tidal passes. The vertical distribution of zoo-/ichthyoplankton within the inner continental shelf from the Louisiana Offshore Oil Platform monitoring project (1978-1995) provided an important offshore end member for the estuarine recruitment study, and is potentially useful in predicting vulnerabilities to past and future oil spills. The role that atmospheric cold front passages may have on densities and movement of zoo-/ichthyoplankton recruiting through the Bayou Tartellan tidal pass, Louisiana, were analyzed using a Generalized Additive Model. The pre-frontal phase, with dominant southern quadrant winds, leading to coastal setup, can enhance flood tides and increase larval recruitment. Post-frontal phase strong northerly winds can enhance ebb tides, which could have negative estuarine retention implications. Lateral differences across Bayou Tartellan at a bulkheaded northern edge, center channel, and a natural-sloping southern shore edge were analyzed using a Zero Inflated Negative Binomial model to determine if behaviorally-mediated, lateral movements by larger larvae could enhance estuarine recruitment/retention. During inflows, estuarine-dependent larvae generally utilized the surface of the center channel and had much lower densities towards the edges. During outflows, larger larvae were more numerous along the southern edge, where velocities were slower. Finally, otolith age and growth data for Micropogonias undulatus and Brevoortia patronus were analyzed for growth rates and microstructure differences associated with oceanographic variability along their recruitment corridors from offshore spawning grounds through the coastal boundary layer, and into the tidal pass. Growth rates from a Laird-Gompertz model for M. undulatus were similar to previous studies. Otolith microstructure suggested ingress through the coastal boundary layer/estuarine waters occurred at approximately 40 days post hatch, and had a marked effect on growth. A two-cycle, Laird-Gompertz growth model for B. patronus suggested a growth stanza at 35 days post hatch, which most likely reflects changing oceanographic conditions during transport and biological consequences of a shift in ontogenetic feeding strategy from selective particulate feeder to an omnivorous filter feeder, with a strong initial growth rate decreasing rapidly after the beginning of the transition in feeding strategy.

On April 20, 2010, the BP Deepwater Horizon (DWH) offshore oil platform exploded releasing ~ 795 million L of southern Louisiana (LA) light sweet crude oil into the Gulf of Mexico. Approximately 7.9 million liters of dispersant, Corexit EC9500A, were applied for remediation. The effect of BP DWH crude oil and Corexit EC9500A on two marsh soil microbial processes, (mineralizable nitrogen and denitrification), were examined in the laboratory. Surface soil samples were collected from an unimpacted salt marsh site proximal to areas that suffered light to heavily oiling in Barataria Bay, LA. Additions of oil were at a ratio of 1:10 (crude oil:wet soil), mimicking a heavy oiling scenario. Carbon and nitrate based compounds were added to investigate the toxicology of oil and dispersant on denitrifier activity. Potential denitrification rates at the 1:10 weathered crude oil:wet soil ratio were 46 ± 18.4% of the control immediately after exposure and 62 ± 8.0% of the control following a two-week pre-incubation period. Potential denitrification rates of soil oiled with fresh crude oil were 51.5 ± 5.3% of the control after immediate exposure and significantly lower at 10.9 ± 1.1% after two-week exposure. Potential denitrification rates (acetylene blockage) after immediate exposure to Corexit:wet soil at ratios of 0:10 (control), 1:10, 1:100, 1:1,000, and 1:10,000 were below detection for the 1:10 treatment while the 1:100 was 7.6 ± 2.7% of the control and the 1:1,000 was 33 ± 4.3% of the control. The 1:10,000 treatment was not significantly different from the control. Denitrification rates measured after two-week pre-incubation were below the detection limit for the 1:10 treatment and the 1:100 treatment was 12 ± 2.6% of the control. Both fresh and weathered crude oil and Corexit can significantly impact activity of denitrification in the short-term. Corexit also negatively affected other microbial measures. Microbial biomass nitrogen (N) values were below detection for the 1:10, 1:100 and 1:1,000 Corexit:wet soil treatments. Potentially mineralizable N rates were significantly lower for 1:10 and 1:100 Corexit:wet soil treatments. Future research should include additional oiling levels and extended exposure periods to determine the recovery of key wetland soil microbial processes.

This thesis advances knowledge of the diverse spatialities of gentrification by examining processes of change in coastal towns, drawing upon the case-study location of St Leonards-on-Sea, in the South East of England. Based on rich, empirical findings from semi-structured interviews, content analyses of local media sources, 2001 census data, and a household survey of 173 respondents, it is shown that processes of gentrification are unfolding in St Leonards. The findings suggest that it is beneficial to distinguish between coastal gentrification, and urban/rural gentrification. To emphasise this point, it is argued that there is merit in utilising the term coastification , in order to conceptualise the socio-cultural and economic transformations tied to in-migrants seeking the coastal idyll . The thesis disrupts some dominant theorisations of contemporary gentrification, identifying the presence of pioneer gentrifiers in a coastal town setting. It is contended that simply transferring the representations of urban gentrification to other socio-spatial locations along the urban-rural hierarchy is not a straightforward process. Therefore, gentrification-based regeneration policies should not be transferred in taken-for-granted ways from one location to another. A representation of coastification allows for a fuller appreciation of the effects of gentrification on coastal regeneration policies.