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Tracking Oil from Deepwater Horizon Oil Spill in Barataria Bay Sediments


In April 2010, approximately 5 million barrels of oil were accidentally released to the Gulf of Mexico (GOM) during the Deepwater Horizon (DWH) Oil Spill. One and a half years after this incident, a set of oiled marsh samples (2 grab samples) coupled with nearby subtidal and intertidal cores (12 cores) were collected from Barataria Bay (BB), Louisiana to determine the concentration and probable source of hydrocarbon residues present based on their chemical composition. An archived core, collected before the DWH oil spill from the same area, was also analyzed to assess the background hydrocarbon composition of the area. The weight of evidence from aliphatic hydrocarbon, polycyclic aromatic hydrocarbons (PAHs), biomarker and stable carbon isotope data clearly indicated the presence of hydrocarbons in BB from the DWH oil spill. Based on the analysis of marsh sediment samples and sediment cores, the distribution of DWH oil in BB was patchy and limited in areal extent. Concentrations of total petroleum hydrocarbons (TPH) and PAHs in surface sediments ranged from 93.8 to 618,000 ug g-1 and 92.0 to 391,000 ng g-1, respectively. The oil present in BB sediments has undergone moderate weathering and has penetrated down to a depth of 9 cm in certain regions (via select cores) of the marsh. Additionally, to examine the decadal-scale history of sedimentation in these marshes, a sediment core was analyzed for the radioisotope 137Cs. Based on a 137Cs-derived sedimentation rate of 0.39 cm yr-1, a penetration depth of 9 cm was enhanced from biological and/or physical mixing in these sediments. Anthropogenic hydrocarbons were found in sediment core sections deposited as far back as 50 to 60 years ago. These historical background hydrocarbon concentrations increased significantly in surface sediments at a depth clearly attributed to DWH oil inputs.