Abstract:
This is an experiment of a series investigating the mechanisms driving the incorporation of oil into diatom aggregates using a water accommodated fraction (WAF) of oil. The diatom Skeletonema CCMP strain #776 was used, and WAF was prepared from Macondo oil (Deepwater Horizon oil spill in the Gulf of Mexico April 2010) and from Refugio oil (pipeline spill off California May 2015). Roller tank experiments mimic in situ conditions of the ocean where in that continuous sinking of particles is possible (infinity water column). Once aggregates > 1mm (operationally defined) have formed, they are harvested separately from the surrounding seawater, which contains non-aggregates cells or small aggregates. Both fractions are analyzed separately, so that the fraction of material incorporated within aggregates may be calculated. Samples were analyzed for cell abundance, particulate organic carbon (POC) and nitrogen (PON), the isotopes 13C and 15N, estimated oil equivalent (EOE), transparent exopolymer particles (TEP) and Coomassie stained particles (CSP). Sinking velocity of aggregates was determined.
Suggested Citation:
Uta Passow. 2018. EPS mechanisms in aggregation and dispersion of oil: roller tank experiment using Skeletonema CCMP strain #776. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N73N21SC
Data Parameters and Units:
GRIIDC-WAF-Agg Sinking Velocity R4x263-188-0003.csv: Experiment: exp. Treatment: WAFMac, Control, or WAFRef Water accommodated fraction of Macondo oil = WAFMAC Water accommodated fraction of Refugio oil – WAFRef Control = no oil Aggregate ID number: Agg # Equivalent spherical diameter (mm): ESD Sinking velocity (m/d) = w GRIIDC-WAF-Agg Summary R4x263-188-0003.csv: Experiment: Exp Tank number = tank # Sampling date (MM/DD/YYYY) Sampling day: number of experiment days Treatment: Control, Macondo, or Refugio Replicate number Type of sample (Slurry or SSW) Slurry = the fraction of aggregates > 1 mm with some surrounding seawater SSW = surrounding seawater fraction Tank Vol/Slurry Volume (mL): Maximum tank volume (5133 mL)/ Slurry Volume Avg POC (ug/tank): Average particulate organic carbon Std POC (ug/tank): Standard deviation particulate organic carbon Avg PON (ug/tank): Average particulate organic nitrogen Std PON (ug/tank): Standard deviation particulate organic nitrogen Avg d13CNorm: Average delta Carbon-13 (unitless) standard expressed as per mille:(δ13C = (Rsample/Rstandard -1) X 1000, where R = 13C/12C) Stdev d13CNorm: Standard deviation delta Carbon-13 (unitless) Avg d15NNorm: Average delta Nitrogen-15 (unitless) Stdev d15NNorm: Standard deviation delta Nitrogen-15 (unitless) Avg EOE corrected (ug/tank): Average estimate oil equivalent Std EOE corrected (ug/tank): Standard deviation estimate oil equivalent Avg TEP (ugGXeq/Tank): Average transparent exopolymer particles Std TEP (ugGXeq/Tank): Standard deviation transparent exopolymer particles Gum Xanthan equivalent = GXeq Avg CSP (BSAeq/Tank): Average Coomassie blue stainable particles Std CSP (BSAeq/Tank): Standard deviation Coomassie blue stainable particles BSAeq: Bovine serum albumin equivalent Avg cell numbers per tank: Average number of cells per tank Coomassie Blue stainable particles = CSP ND = no data NA = not applicable NV = not valid
Methods:
Replicate acrylic roller tanks were filled bubble free. Experiments were incubated in the dark, at 13˚C at an rpm of 1.9-3.2 Aggregate appearance and numbers were monitored during the experiments. When sufficient aggregates had formed, all treatments were harvested. Aggregates > 1mm (visually discernable) were manually collected and analyzed. After all aggregates > 1 mm were removed the remainder of the material, termed surrounding seawater (SSW), was subsampled. Both fractions were analyzed for POC/PON, cell abundance, TEP, CSP. Relative oil concentration was estimated from fluorescence using a Trilogy Turner Fluorometer with the crude oil module 7200-63, which measures at excitation wavelength of 365 nm and emission wavelength of 410-600nm. Duplicate filters (GF/F) prepared for POC/PON analysis were measured in a CEC44OHA elemental analyzer (Control equipment). Diatom cells were counted (Olympus CX41) using a hemocytometer; at least 6 subsamples and 200 cells each were counted per sample. Counts were at times only conducted on 1 of the two replicate treatments. TEP and CSP concentrations were determined in triplicate each using the respective colorimetric methods and are expressed in Gum Xanthan equivalents (GXeq.) and Bovine serum albumin equivalent (BSA eq.) respectively. All biomass results (cell abundance, POC, TEP concentration) are normalized per tank to allow budgets and make aggregate and SSW fractions directly comparable. Make WAF directly before use. Make 3L filtered seawater (0.2 µm filter), and pasteurize it for at least 2 hours at 65 degrees C. Add into 4+ L glass bottle with bottom spigot and glass stopper. Leave 20-25% headspace. Add a sterile stir bar to the bottle and add 3 mL (3000 µL) oil. Immediately cap, shake. Place on a stir table at room temperature for about 24 hours at a fairly high stirring speed (not enough to generate a vortex, but enough to keep things homogenized). Keep dark during mixing (alu foil or brown glass). Let the bottles stand for a couple hours. Then, harvest discarding the upper oily layer. Sinking velocity measurements were conducted using the column/ setcol method and the non-destructive orbit method of calculating sinking velocities based on tank rotation speed and the orbital path of aggregates within the turning tanks. Ploug, H., Terbrüggen, A., Kaufmann, A., Wolf-Gladrow, D. and Passow, U. (2010) A novel method to measure particle sinking velocity in vitro, and its comparison to three other in vitro methods. Limnology and Oceanography: Methods 8, 386-393.
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