Abstract:

The dataset contains the estimation oil equivalence (EOE) concentration in the mesocosms made by fluorescence analyses that allowed to estimate changes in the oil concentration with time. The EOE were determined using Macondo surrogate oil as the calibration standard (Wade et al. 2011; Wade et al., 2017) for the fluorescence analyses (Horiba Scientific Aqualog Fluorometer).

Suggested Citation:

Terry Wade, Tony Knap. 2019. Estimated Oil Equivalents (EOE) for LTOPOS, a mesocosm to quantify microbial oxidation and degradation of oil. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/3RTQ512B

Purpose:

To estimate changes in the oil concentration with time in different treatments and compare to potential corresponding changes in the chemistry and microbiology.

Data Parameters and Units:

Treatment (Control, Slick Tank, DCEWAF), Mesocosm tank # (D1-10, C1-4, S1), Time (days), Estimated Oil equivalence (EOE) Concentration (mg/L). Note: M7 = Mesocosm method for LTOPOS, a Long Term Oil and Particle Oxidation Study, DCEWAF = diluted chemically enhanced water accommodated fraction.

Methods:

Eighteen 110L capacity glass mesocosm tanks were filled with Gulf of Mexico seawater collected 8 km offshore south of Galveston (TX) that had been pre-treated with a charcoal filter to remove large particles and debris. The salinity was 25 PSU. Plankton (≥63 µm) were collected using a net and transferred into polycarbonate bottles after being pre-filtered (115 um) to remove zooplankton, jellyfish and debris. Salinity of the phytoplankton concentrate was 15 PSU. The goal was to collect enough surface and bottom particles for detailed particle chemical characterization and to provide enough sample material for detailed particle chemical characterization, ~20L each from the bottom layer and the surface layer was collected. As in earlier mesocosm experiments, the target concentration of 2 mg/L was attempted for the concentration the DCEWAF (diluted chemically enhanced water accommodated fraction). Corexit was mixed with oil in a ratio of 1:20 to make chemically enhanced water accommodated fraction (CEWAF) prepared by mixing 25 mL (5 ml per each ~ 5 min over 25 min) of Macondo surrogate oil/ surrogate oil in two baffled recirculating tanks (Wade et al., 2017) containing ~130 L of seawater, which were mixed 24 hrs to create CEWAF (Knap et al. 1983). From these CEWAF tanks 5L was removed for other analyses (3.5 L hydrocarbon analyses). Diluted CEWAF (DCEWAF) was prepared by mixing 10.4 L of CEWAF with 93.6 L of the original seawater for a total volume of 104 L. Next concentrated plankton mass was introduced to each of the tanks (3 L to each tank which contained 104L of treated seawater, total volume of seawater 105.5L per tank) immediately prior to starting the experiments. To simulate an oil slick, to one mesocosm tank of 105L, 42 mL of Macondo surrogate oil was added to the surface. Banks of lights were placed behind each of the glass mesocosm tanks and a 12:12 light/dark cycle employed. Treatments included controls (4), DCEWAF (10), and 1 oil slick. Surface water column particles (WCP) were sampled on days T0, T4, T8, and T16 from control (C) tanks 2, 3, 4 and DCEWAF (D) tanks 1, 2, and 3. The bottom particles (BP) were sampled on T0 from the stock waters for the control and from D4 for the DCEWAF. For T0.5, tank D4 was sampled. From then on, the BP tank sampled on each specific time point was sacrificed for the sample. So for T1, tank D5 was sampled and sacrificed, then for T2, D6; for T3, D7; for T4, D8; for T8, D9; for T16, both C1 and D10 were sampled. EOE (estimated oil equivalents) were measured each day for all remaining mesocosms. Oxygen levels were adjusted so the mesocosms do not fall below 2 mg O2/L. From DCEWAF tanks, 5L was removed for other analyses (4 L for hydrocarbon analyses). The EOE were determined using Macondo surrogate oil as the calibration standard (Wade et al. 2011; Wade et al., 2017) for the fluorescence analyses (Horiba Scientific Aqualog Fluorometer). The EOE mean concentration of the treatments for the control and DCEWAF at the start of the experiments (T0) were 0.05 and 0.54 mg/L, respectively. The EOE mean concentration of the treatments for the control, DCEWAF, and oil slick treatments on T4 were 0.01, 0.30, and 0.10 mg/L, respectively. At the end of the experiment, T16, the EOE mean concentration of the treatments for the control, DCEWAF, and oil slick treatments were 0.01, 0.04, and 0.08 mg/L, respectively.

Provenance and Historical References:

Knap, A. H., T. D. Sleeter, R. E. Dodge, S. C. Wyers, H. R. Frith, and S. R. Smith. 1983. The effects of oil spills and dispersants use on corals: A review and multidisciplinary experimental approach. Oil and Petrochemical Pollution, 1(3), 157–169. doi: 10.1016/S0143-7127(83)90134-5 Wade, T.L., Sweet S.T., Sericano, J.L., N.L. Guinasso Jr., Diercks, A.-R., Highsmith, R.C., Asper, V.L., Joung, D., Shiller, A.M., Lohrenz, S.E. and Joye, S.B. 2011, Analyses of Water Samples from the Deepwater Horizon Oil Spill: Documentation of the Sub-Surface Plume. in Monitoring and Modeling the Deepwater Horizon Oil Spill: A Record-Breaking Enterprise, Geophysical Monograph Series, vol. 195, edited by Y. Liu et al., pp. 77–82, AGU, Washington, D. C., doi:10.1029/2011GM001103 Wade, T.L., Morales-McDevitt, M.E., Bera, G., Shi, D., Sweet, S.T., Wang, B., Gold-Bouchot, G., Quigg., A. and Knap A.H. 2017 A method for the production of large volumes of WAF and CEWAF for dosing mesocosms to understand marine oil snow formation. Heliyon 3e00419 doi: 10.1016/j.heliyon.2017.

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