Master of Science (MS)
Oceanography and Coastal Sciences
The Deepwater Horizon (DWH) oil spill in 2010 triggered extensive research on the impacts of crude oil contamination in the Gulf of Mexico. This research focuses on the impact of the longer-term presence of oil from the DWH spill on denitrification and soil reduction-oxidation (redox). Cores were collected from a salt marsh heavily oiled by the DWH spill, and a nearby, non-oiled site in Barataria Bay, LA to investigate the effects of the long-term presence. Denitrification is typically the dominant process of nitrate removal in coastal wetlands, converting bioavailable N in surface waters into gases released to the atmosphere through microbial respiration. Potential denitrification rates were lower in soils mixed well with compared to non-oiled samples, suggesting suppressed microbial activity due to the presence of oil. However, nitrate removal, a proxy measurement of denitrification, from the overlying water column in intact cores with a persistent layer of buried oil was significantly higher, compared to non-oiled cores over an 11-day period. Redox conditions in wetland soils provide an excellent indicator of oxygen levels which control biogeochemical functions. Treatments tested were a non-oiled control, weathered crude oil at the soil profile surface, fresh crude oil at the soil profile surface, and a layer of buried weathered crude oil, 5-cm beneath the soil surface. No significant differences in redox potentials were detected among treatments at any depth at the end of the 35-day flooded, anaerobic portion of the study. After draining the cores, mean redox values for each set of treatments (n=3) were calculated for each sample time to determine the time necessary for the rhizosphere to reach the aerobic threshold (+300 mV). Mean redox values for the control cores reached +300 mV after 193 h. Both fresh and weathered crude oil surface treatments reached +300 mV after 316 h. The buried crude oil treatment reached the aerobic threshold after 418 h. Future studies should investigate the fate and impact of buried crude oil released back into the environment driven by the erosion of coastal salt marshes.
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Levine, Brian Michael, "Implications of the Long-term Presence of Crude Oil from the Deepwater Horizon Spill on Salt Marsh Biogeochemistry" (2016). LSU Master's Theses. 4467.