Date of Award

Summer 6-12-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geosciences

First Advisor

Dr. Daniel Deocampo

Second Advisor

Dr. W. Crawford Elliott

Third Advisor

Dr. Seth Rose

Fourth Advisor

Dr. Jack Spadaro

Abstract

Salt marshes are one of the most difficult environments to remediate due to their sensitive and important ecosystems. Traditional cleanup methods can do more harm to the marsh than the oil itself. Bioremediation is the preferred cleanup approach for these delicate environments. Typically bioremediation has been carried out by the addition of nutrients but the results have been inconsistent. Previous laboratory studies conducted in oiled seawater demonstrated that clay minerals enhanced microbial growth and hence oil degradation. However, this had not been tested at field sites or on oiled marine sediments where oil is known to persist. The main objectives of this research were to test clay minerals as a bioremediation alternative for enhancing degradation of oiled salt marsh sediments and evaluate the geochemistry of sediment profiles for heavy metal enrichment. Laboratory experiments were carried out to evaluate the application of montmorillonite or kaolinite clay minerals on salt marsh sediments impacted by diesel oil. Oil biodegradation in control experiments was significantly more successful than in clay amended experiments. Clay minerals may have caused an increase in pH which inhibited enzyme-catalyzed processes required for metabolism. Field experiments were carried out in control and clay treatment plots in Louisiana salt marshes impacted by the Deepwater Horizon oil spill. In this research it was demonstrated for the first time that biodegradation of n-alkanes and PAHs was significantly enhanced by the addition of montmorillonite compared to controls. Vegetated treatment plots were slightly more effective than non-vegetative treatment areas. It is suggested that bivalent cations adsorbed to montmroillonite’s surface suppressed the diffuse double layer. This allowed the oil along the clay’s surface to be accessible to the bacteria where oil could be readily consumed. Clay minerals may serve as a new and unique bioremediation strategy for oiled salt marsh sediments. Geochemical sediment profiles from Louisiana salt marshes showed elevated concentrations of selected heavy metals (Zn > Cu > Pb > V > Cr > Fe > Ni). The Deepwater Horizon oil spill is a likely source of metal enrichment as many of these same metals are also constituents of the Deepwater Horizon oil.

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