Investigation of petroleum residues and microbial PLFA in Barataria Bay sediments one year after the Deepwater Horizon oil spill
Abstract
The Deepwater Horizon spill released crude oil into the Gulf of Mexico over a period of 3 months in 2010. Barataria Bay, Louisiana was among the most heavily impacted and extensively oil-contaminated coastlines. Studies conducted in the marshes show significant ecological and geologic effects from oil residues that reached the bay. Observation of the presence of an oil sheen associated with sediment disturbance raised the question as to whether petroleum residues were also present in the sediments of Barataria Bay. In order to address this question, six sediment cores were collected from non-oiled (#1 & 2) and oiled (#3-6) portions of Barataria Bay approximately one year after the Deepwater Horizon oil spill. Concentrations of n-alkanes, unresolved complex material (UCM) and polycyclic aromatic hydrocarbon (PAH) were determined in these upper sediments. In addition, concentrations of phospholipid fatty acids (PLFA) were determined to assess variations in microbial community abundance. Alkane concentrations ranged from 134 to 747 ng/g with chain lengths from C12 to C35. Most cores showed an odd over even preference (carbon preference index of 1.2 to 4.3) with highest concentrations of long chain compounds between C24 and C35 (average chain length 29 to 39), consistent with a terrestrial carbon source such as plant waxes. Core #6 however, in the southwest portion of the bay, had the lowest concentrations of alkanes, and shorter n-alkane chain lengths overall. Despite this difference, the core maintains a relatively high carbon preference index and average chain length compared to that which would be expected from oil contaminated sediments. Measured PAH concentrations were highly variable ranging from undetectable to 436 ng/g. These values are several orders of magnitude lower than what is generally seen in highly contaminated sediments. Further, UCM concentrations were negligible in the cores from the oiled regions. These findings suggest only a minimal presence of petroleum hydrocarbon in these sediments, which may be because the oil was biodegraded or because contaminated layers were covered by more recent layers of uncontaminated sediments. Total PLFA concentrations were found to vary between 0.6 ug/g and 9.6 ug/g, which is equivalent to a cell density range of 4.22x107 to 6.90x108 (using a conversion factor from Green & Scow, 2000). PLFA concentrations did not show a consistent correlation with measured petroleum parameters. Ongoing isotope analysis (Δ14C, Δ13C) of alkane and PLFA will further explore carbon sources being used by the microbial community. Further survey of Barataria Bay sediment is needed to locate Deepwater Horizon spill residues.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.B21A0337C
- Keywords:
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- 0432 BIOGEOSCIENCES / Contaminant and organic biogeochemistry