Identifier

etd-06252014-171237

Degree

Master of Science (MS)

Department

Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

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.

Date

2014

Document Availability at the Time of Submission

Student has submitted appropriate documentation to restrict access to LSU for 365 days after which the document will be released for worldwide access.

Committee Chair

White, John R.

DOI

10.31390/gradschool_theses.2078

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