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 #775 was used to assess the effect of oil on marine snow formation and the incorporation of oil in marine snow. A control and a WAF was prepared from Macondo oil (Deepwater Horizon oil spill in the Gulf of Mexico, April 2010). Roller tank experiments mimic in situ conditions of the ocean in that continuous sinking of particles is possible (infinity water column). Once aggregates > 1mm (operationally defined) formed, they were harvested separately from the surrounding seawater, which contains non-aggregates cells or small aggregates. Both fractions were analyzed separately, so that the fraction of material incorporated within aggregates may be calculated. Samples were analyzed for particulate organic carbon (POC) and nitrogen (PON), the isotopes Carbon-13 and Nitrogen-15, estimated oil equivalent (EOE), transparent exopolymer particles (TEP), and coomassie-stained particles (CSP).

Suggested Citation:

Uta Passow. 2018. EPS mechanisms in aggregation and dispersion of oil: roller tank experiment using Skeletonema, POC-PON-EOE-TEP-CSP. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7ZW1JBJ

Publications:

Passow, U., Sweet, J., Francis, S., Xu, C., Dissanayake, A., Lin, Y., … Quigg, A. (2019). Incorporation of oil into diatom aggregates. Marine Ecology Progress Series, 612, 65–86. doi:10.3354/meps12881

Purpose:

Small preliminary test experiment with 2 treatments (Control and WAF) using Skeletonema CCMP 775 to assess the effect of oil on marine snow formation and the incorporation of oil in marine snow. Marine snow and surrounding seawater (SSW) sampled separately.

Data Parameters and Units:

Experiment: exp. Tank number = tank # Sampling date (MM/DD/YYYY) Sampling day = number of experiment days Treatment (Control or Macondo) Replicate #: number of replicates Type of sample (slurry or SSW) Slurry = the fraction of aggregates > 1 mm with some surrounding seawater SSW = surrounding seawater fraction Tank volume/slurry volume (mL): Total tank volume (1160 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 delta13C (unitless). Relative value compared to a standard expressed as per mille:(δ13C = (Rsample/Rstandard -1) X 1000, where R = 13C/12C) Stdev d13CNorm: Standard deviation delta13C (unitless) Avg d15NNorm: Average delta15N (unitless) Stdev d15NNorm: Standard deviation delta15N (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): Average transparent exopolymer particles Gum Xanthan equivalent = GXeq Avg CSP (BSAeq/tank): Average Coomssie Blue stainable particles Std CSP (BSAeq/tank): Standard deviation Coomssie Blue stainable particles BSAeq=Bovine serum albumin equivalent ND = no data

Methods:

Replicate acrylic roller tanks were filled bubble free. Experiments were incubated in the dark, at 22˚C at an rpm of 1.4 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). TEP concentrations were determined in triplicate using the colorimetric methods and are expressed in Gum Xanthan equivalents (GXeq. All biomass results (POC, TEP concentration) are normalized per tank to allow budgets and make aggregate and SSW fractions directly comparable. Made WAF directly before use. Made 3L filtered seawater (0.2 µm filter), and pasteurized it for at least 2 hours at 65 degrees C. Added into 4+ L glass bottle with bottom spigot and glass stopper. Left 20-25% headspace. Added a sterile stir bar to the bottle and add 3 mL (3000 µL) oil. Immediately cap and shake. Placed 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). Kept dark during mixing (aluminum foil or brown glass). Let the bottles stand for a couple hours. Then, harvested discarding the upper oily layer.

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