Master of Science (MS)
Civil and Environmental Engineering
Weathering of MC252 oil from the Deepwater Horizon oil spill is taking place in coastal Louisiana marsh and mangrove wetland systems. Alkylated phenanthrenes and dibenzothiophenes, which are the most prominent PAHs found at MC252 contaminated sites, are weathering at rates up to 5% per year relative to alkylated chrysenes 3 years after initial oiling. Flux chambers at marsh locations trapped CO2 that exhibited δ13C signatures lower than indigenous organic matter signifying hydrocarbon mineralization to CO2. Weathering rates at each of these locations are heavily influenced by the biogeochemistry of the surrounding environment. High-resolution nutrient profiles were obtained at different locations within each site during the winter and summer using dialysis samplers. Dialysis sampler results determined that there is an adequate amount of nitrogen and phosphorous in the marsh and mangrove locations to support cell synthesis and enough sulfate to serve as a terminal electron acceptor in the absence of oxygen. Zones of sulfate depletion accompanied by increased ammonia and phosphorous were found in nutrient depth profiles at certain marsh and mangrove locations signifying more anoxic zones in the soils. Aerobic and anaerobic laboratory enrichment cultures were used to observe biodegradation potential of PAHs and n-alkanes in a controlled environment to supplement field findings. In the aerobic enrichment culture experiment, total reduction of n-alkanes and alkylated naphthalenes, fluorenes, phenanthrenes, dibenzothiophenes, and chrysenes were found to be 77, 96, 93, 87, 90, and 47% after 120 days, respectively, in the Fourchon marsh soil and 51, 92, 93, 83, 84, and 38% after 120 days, respectively, in the Bay Jimmy marsh soil. First order rate constants for the loss of these alkylated PAHs ranged from 0.88-18 (1/years) for the two sites, with rates decreasing with increased molecular weight and alkylation. Porewater nutrient and electron acceptor data in the anaerobic enrichment cultures indicate microbial activity may be taking place; however, no anaerobic degradation of the aforementioned PAHs were observed over the course of the experiment.
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Rodrigue, Matthew Paul, "Biogeochemical Controls on Biodegradation of MC252 Crude Oil in Coastal Wetland Systems" (2014). LSU Master's Theses. 2971.