Abstract:

The dataset contains estimation oil equivalence (EOE) concentration in the mesocosms made by fluorescence analyses that allowed to estimate changes in the oil concentration with time. The estimated EOE was determined by fluorescence (Wade et al. 2011) using Macondo surrogate oil as a standard to produce calibration curves at 5 to 7 concentrations. Water samples (5 to 20 ml) were extracted with 5 ml of dichloromethane. An aliquot of the extract was placed in a cuvette for fluorescence analyses (Horiba Scientific Aqualog Fluorometer). The EOE was determined from the calibration curve (Wade et al. 2011). Samples with fluorescence responses that exceeded the calibration curve were diluted so that their fluorescence was within the calibration range. Samples were taken at the beginning and end of the experiment and at intervals in between and at the same time point as measurements of other parameters during the experiment.

Suggested Citation:

Terry Wade, Tony Knap. 2019. Analytical measurements: Estimated Oil Equivalents (EOE) for MICROX, a mesocosm study to quantify microbial oxidation and degradation of oil. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-hwws-b079

Purpose:

To compare the potential chemical changes of microbial secretions and biological responses to change in oil concentration over time.

Data Parameters and Units:

There are 2 excel files (EOE for M6_MICROX.csv and EOE_M6_light dark bottles.csv) in this dataset and contains data on estimated oil equivalents (EOE) determined by fluorescence. Parameters: Time (days), Condition (Light, Dark), Treatment (Control 1-3, WAF 1-3, CEWAF 2-3, DCEWAF 1-3), Mesocosm tank, Estimated Oil equivalence (EOE) Concentration (mg/L). Note: Blank cells mean there is no data is available; and M6 = Mesocosm method for MICROX, a long term MICRobial oil and particle OXidation study.

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 34 PSU. Plankton (≥63 µm) were collected using a net and transferred into polycarbonate bottles after being prefiltered (115 um) to remove zooplankton, jellyfish and debris. 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 2mg/L was attempted for the concentration of oil in the water accommodated fraction (WAF) and the diluted chemically enhanced water accommodated fraction (DCEWAF). The WAF of oil was prepared by mixing 25 mL (5 ml ~ 5 min over 25 min) of Macondo surrogate oil into six baffled recirculating tanks (Wade et al., 2017) containing ~130 L of seawater were mixed vigorously for 4 hrs to create a “high energy” WAF (Knap et al. 1983). The WAF was then introduced into the WAF mesocosm tanks, filled to 104L, and mixed. From these tanks, 3.5 L WAF was removed for hydrocarbon analyses. Corexit was mixed with oil in a ratio of 1:20 to make DCEWAF. Then 25 mL of this mixture (5 ml every 5 min for 25 min) of surrogate oil plus Corexit was added to a baffled recirculating tank containing ~130 L of seawater which was not vigorously mixed for 4 hrs prior to being loaded into the mesocosm tanks. From these chemically enhanced water accommodated fraction (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. This concentrated plankton mass was introduced to each of the tanks (1.5 L to each tank which contained 104L of treated seawater, total volume of seawater 105.5L per tank) immediately prior to starting the experiments. Banks of lights were placed behind each of the glass mesocosm tanks and a 12:12 light/dark cycle employed. Treatments included controls (2), WAF (8) and DCEWAF (8). One mesocosm was sacrificed at each sampling point. Controls were sampled on Day 0 (T0) and Day 12 (T12). Sampling was more frequent at the start and less frequent with time, such that sampling was done on T0, T0.5, T2, T3, T6, T8, and T12. Oxygen, EOE and nutrients were measured each day for all remaining mesocosms. Oxygen levels were not adjusted in the mesocosms as they did not fall below 2 mg O2/L. Samples were also collected for microbial analysis for 16S/18S and a set of transcriptomes from water column and aggregates. From these DCEWAF tanks, 5L was removed for other analyses (4 L hydrocarbon analyses). The estimated oil equivalents (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, WAF and DCEWAF at the start of the experiments were close to the desired concentrations (0.15, 5.24 and 8.31 mg/L, respectively).

Instruments:

The estimated oil equivalents (EOE) were determined by fluorescence (Wade et al. 2011) using Macondo surrogate oil as a standard to produce calibration curves at 5 to 7 concentrations. Water samples (5 to 20 ml) were extracted with 5 ml of dichloromethane. An aliquot of the extract was placed in a cuvette for fluorescence analyses (Horiba Scientific Aqualog Fluorometer). The EOE was determined from the calibration curve (Wade et al. 2011). Samples with fluorescence responses that exceeded the calibration curve were diluted so that their fluorescence was within the calibration range. Samples were taken at the beginning and end of the experiment and at intervals in between and at the same time point as measurements of other parameters during the experiment.

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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