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TRACKING OIL FROM DEEPWATER HORIZON OIL SPILL IN BARATARIA BAY SEDIMENTS Zeynep Dincer 1 , José L. Sericano 2 , Franco Marcantonio 1 , Terry L. Wade 2 , Thomas S. Bianchi 3 , Alexander S. Kolker 4 1 Texas A&M University, Department of Geology and Geophysics, College Station, TX 77843 2 Texas A&M University, Geochemical and Environmental Research Group, College Station, TX 77845 3 Texas A&M University, Department of Oceanography, College Station, TX 77843 4 Louisiana Universities Marine Consortium DeFelice Marine Center, Chauvin, LA 70344 Reference Oil A (0-1 cm) AS (0-1 cm) A1 A2 F (0-1 cm) TPH (ng/g) 1396336 77399.4 618185.7 424383.5 532187.3 93.8 TPAHs(ng/g) 119473.9 219065.3 138504.8 193396.6 263869.8 119.5 C 17 /pristane 1.658 0.689 0.689 0.765 1.03 6.79 C 18 /phytane 2.189 0.591 0.767 1.06 0.810 4.03 Pristane/phytane 1.335 0.582 0.771 0.907 0.808 0.31 CPI (Carbon Preference Index) 0.971 1.051 1.01 1.00 1.05 2.92 Figure 1. Sampling Area. 1 2 3 4 5 6 7 8 9 10 -40.00 -35.00 -30.00 -25.00 -20.00 -15.00 Samples δ 13 C (‰) Core A Grab Samples Core AS Core B1 and B2 Ref. Oil Figure 6. δ 13 C isotopic composition of oily and non-oily samples. Sample collection Freeze Dried Extraction with Methylene Chloride Sulfur Removal Si/Al Column Fractionation GC/MS Terpanes and Steranes Si/Al Column Fractionation GC/MS n-alkanes isoprenoid hydrocarbons PAH Materials and Methods Figure 2. Materials and Methods. 1 2 3 4 Table 1. Molecular characteristics of reference oil (DWH NRDA QA10 Oil 01) and BB samples. Conclusions The impact of the Deepwater Horizon (DWH) oil spill in Barataria Bay is higher in area A, closer to the spill source. One and a half years after the DWH, low-molecular weight n-alkanes were lost, and target PAHs and their alkylated homologues were moderately degraded, but high molecular weight PAHs and the biomarker compounds remain. Biomarker composition of DWH and area A samples compare well which means that the likely source of the oil in the samples is DWH. The signature of DWH can be tracked to a depth of 9 cm, which suggests that a penetration of 9 cm in the sediment column. Although weathering can have a significant impact on the composition of the oil, the ratio C 17 /pristane, C 18 /phytane, pristane/phytane and CPI can remain the same. Stable carbon isotope analysis show a significant shift between oily (avg. δ 13 C = -23.87) and non-oily (avg. δ 13 C = -17.99) samples. The calculated sediment accumulation rate, 0.39 cm/yr, is lower than the long-term rate of relative sea level rise at Grand Isle (~0.94 cm/yr). This suggests that these marshes are in a long-term elevation disequilibrium that is likely to result in marsh loss, regardless of the impacts of the Deepwater Horizon oil spill- though that spill may accelerate wetland loss processes. Figure 7. Sedimentation rate analyses of core C. The arrows represent the 137 Cs that caught at a depth of 19 cm. References • Lehr, W., Bristol, S., and Possolo, A., 2010, Oil Budget Calculator Deepwater Horizon Technical Documentation. • Graham, W., R. Condon, et al. (2010). "Oil carbon entered the coastal planktonic food web during the Deepwater Horizon oil spill " ENVIRONMENTAL RESEARCH LETTERS. Acknowledgement Authors would like to express their gratitude to Dr. Ethan Grossman, Dr. Brendan Roark, Mr. Stephen Sweet and Ms. Cyndhia Ramatchandirane for their contributions. In addition, authors would like to thank the Stable Isotope Geosciences Facility at TAMU for the stable isotope analyses. Zeynep Dincer is grateful to the Turkish Petroleum Corporation and other mentors for their financial support and encouragement. Scan code for online version. Figure 4. PAHs distributions of reference oil (DWH NRDA QA10 Oil 01) and core A. Pronounced decrease in Naphthalenes relative to other PAHs due to its higher solubility. Biodegradation alters the PAHs pattern and resulting in a C 3 >C 2 >C 1 >C 0 distribution. Time Abundance Figure 5. Terpanes (m/z 191) and Steranes (m/z 217) signatures of reference oil (DWH NRDA QA10 Oil 01) and core A. 110.00 115.00 120.00 125.00 130.00 135.00 140.00 145.00 150.00 155.00 160.00 10000 20000 30000 40000 50000 60000 70000 80000 90000 00000 10000 20000 30000 40000 50000 60000 70000 80000 90000 T im e --> 1 0 0 .0 0 1 1 0 .0 0 1 2 0 .0 0 1 3 0 .0 0 1 4 0 .0 0 1 5 0 .0 0 1 6 0 .0 0 0 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 m/z 191 m/z 217 A (0-1 cm) A (0-1 cm) 110.00 115.00 120.00 125.00 130.00 135.00 140.00 145.00 150.00 155.00 160.00 20000 40000 60000 80000 00000 20000 40000 60000 80000 00000 20000 100.00 110.00 120.00 130.00 140.00 150.00 160.00 0 10000 20000 30000 40000 50000 60000 70000 80000 90000 00000 10000 Reference oil Reference oil 100.00 110.00 120.00 130.00 140.00 150.00 160.00 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 55000 60000 65000 70000 75000 80000 85000 90000 --> 100.00 110.00 120.00 130.00 140.00 150.00 160.00 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000 24000 26000 28000 30000 32000 34000 36000 38000 40000 42000 44000 46000 > A (8-9 cm) A (8-9 cm) Abstract The Deepwater Horizon (DWH) was the largest offshore oil spill in history. To track the oil residues from this spill, marsh and sediment cores and marsh grab samples were collected from ten different locations in Barataria Bay (BB). On selected samples, total aliphatic and polycyclic aromatic hydrocarbons (PAHs) concentrations were determined by GC-MS analysis. Surface total petroleum hydrocarbons (TPH) range from 93 to 3,000 ug/g throughout the area with the exception of samples collected nearest the source (Area “A”: average = 410,000 ug/g). Similarly, concentrations of aromatic hydrocarbons (PAHs) in the surface samples range from 39 to 490 ng/g in contrast with the average concentration encountered for samples in area “A” (21,000 ng/g). Most cores collected in the area showed a nearly homogeneous distribution with depth while concentrations in area “A” decreased from 30,000 ng/g at the surface to 430 ng/g at a depth of 9 cm. Comparison of hydrocarbons in the sediment samples to Macondo oil is complicated due to confounding factors (e.g., already present hydrocarbons and weathering processes). Our preliminary data indicates that oil in sediments have similar signature to DWH, and the impact of the DWH in BB is limited to area A. Introduction In April 2010, approximately 4.9 million barrels (205.8 million gallons) of light, sweet Louisiana crude (SLC) oil, including 205,000 mT of methane (CH 4 ), were accidently released into the Gulf of Mexico during the Deepwater Horizon Macondo Mc252 Oil Spill (Lehr et al., 2010). The initial impact on the environment was significant; It affected marsh and marine ecosystems of Louisiana, and many beaches in Mississippi and Alabama. 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 probable source of petroleum residues present, and to characterize the chemical composition of the oil. On selected samples, n-alkanes, PAHs and biomarker analysis were done using GC-MS. Additionally, to examine the decadal-scale history of sedimentation in these marshes, a sediment core was analyzed for the radioisotope 137 Cs, and to identify the stable carbon isotopic compositions ( 13 C/ 12 C ratios ) of samples from A and B sampling locations. Figure 3. Aliphatic distributions of reference oil (DWH NRDA QA10 Oil 01) versus A (0 -1) cm AS (0-1 cm), A1 and A2. The loss of low molecular weight n-alkanes in BB samples is apparent relative to the reference oil. Results and Discussion 0 2M 4M 6M 8M n-C10 n-C13 n-C16 n-C18 n-C20 n-C23 n-C26 n-C29 n-C32 n-C35 Concentration (ng/g) n-Alkanes Reference Oil - A (0-1 cm) A Ref. Oil 0 2M 4M 6M 8M n-C10 n-C13 n-C16 n-C18 n-C20 n-C23 n-C26 n-C29 n-C32 n-C35 Concentration (ng/g) n-Alkanes Reference Oil - A1 A1 Ref. Oil 0 2M 4M 6M 8M n-C10 n-C13 n-C16 n-C18 n-C20 n-C23 n-C26 n-C29 n-C32 n-C35 Concentration (ng/g) n-Alkanes Reference Oil - AS (0-1 cm) AS Ref. Oil 0 2M 4M 6M 8M n-C10 n-C13 n-C16 n-C18 n-C20 n-C23 n-C26 n-C29 n-C32 n-C35 Concentration (ng/g) n-Alkanes Reference Oil - A2 A2 Ref. Oil Gulf of Mexico
