Identifier

etd-11102011-122352

Degree

Master of Science (MS)

Department

Geology and Geophysics

Document Type

Thesis

Abstract

The 2010 Deepwater Horizon oil spill in the Gulf of Mexico not only impacted open ocean and shoreline geochemical and ecological environments, but it served to promote research of microbial ecosystems in poorly studied habitats, such as Louisiana marshes. Sediment and water samples from four main marshes in southern Louisiana were collected in May 2010 (pre-oil), September 2010 (oiled), and June 2011 (post-oil). Sites near the Mississippi River had exceptionally low salinity in the immediate months following the oil spill due to freshwater diversion efforts; salinity increased by an order of magnitude one year later. Microbial diversity was evaluated from tag-encoded FLX-amplicon pyrosequencing, and phylum-level diversity decreased from pre- to post-oil sampling times. The major taxonomic groups changed from communities dominated by Proteobacteria in pre-oil conditions to communities dominated by Firmicutes or a mixed assembledge of Proteobacteria-Firmicutes-Bacteriodetes in oiled and post-oil conditions. Non-metric multidimensional scaling of taxonomic diversity against geochemical site parameters suggested that both the presence and concentration of hydrocarbon at the marsh edge, as well as the effects of changing salinity, contributed to shifts in the microbial community diversity at the phylum-level. The changes in community composition influenced the rates of community-level heterotrophic degradation of glucose, which was used as an analog to hydrocarbon. The maximum growth rate was higher for the most oiled samples, which were also samples with the greatest increase in genera associated with hydrocarbon degradation. This study provides a comprehensive investigation of the diversity of microbial communities in marsh sediments over a period of one year, which has not been previously done. Collectively, the results will aid in our understanding of how coastal marsh microbial ecosystems can respond to disturbances and how biogeochemical cycles are affected through time.

Date

2011

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Engel, Annette Summers

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