Project Overview

Overview:
In January 2015, Dr. Edward Buskey at the University of Texas at Austin, Department of Marine Science, was awarded an RFP-IV grant at $9,236,404 to lead the GoMRI Dispersion Research on Oil: Physics and Plankton Studies II (DROPPS-II) Consortium which consisted of 8 collaborative institutions and 115 research team members (including students). DROPPS-II builds on results from RFP-I and continues to investigate and model a series of processes affecting the fate of crude oil spills, including physical breakup and dispersion of oil patches, interactions of petroleum with marine organisms, biodegradation of oil, and the impact of aerosolized oil on public health. The experimental and numerical studies were performed at varying scales and levels of complexity, from 'bench-top' investigations that fully characterize specific phenomena, to multi-component, meso-scale experiments and simulations that mimic realistic physical and biological conditions.
Outreach:
Over its award period (3 years, plus a 12-month no-cost extension), DROPPS-II organized approximately 90 outreach activities or products, including:

 

•  Community outreach programs such as UTMSI’s “Science on Tap”, “Bay Talks”, public lecture series, seminars, and screenings of “Dispatches from the Gulf” & “Dispatches of the Gulf II” and panel discussions with the audience. JHU mentored inner city high school students by involving them with oil spill projects and JHBSPH worked with community groups to communicate health matters to the general public.
•  Educational outreach events such as “Women in Marine Science”, “Science Saturday”, “Teachers on the Estuary” (TOTE), UTMSI R/V Katy research cruises and UPENN’s “Girls in Engineering, Math, and Science Camp” (GEMS).
•  UTMSI’s Summer Science:
  •  “Adventures of a Drifter”- in collaboration with CARTHE, 3rd & 4th graders learned how ocean currents contribute to the movement of spilled oil.
  •  “Floating Habitats: A Balancing Act” – 3rd & 4th graders learned how Sargassum and the associated fauna could be affected by an oil spill.
•  Workshops and Collaborations:
  • • “Bridging the Gap Between Oil Spill Researchers and Responders” workshop was hosted by Edward Buskey and Brad Gemmell at UTMSI. The goal was to share oil spill science and to increase communication between researchers, natural resource managers, and emergency responders.
  • • Edward Buskey attended “Gulf of Mexico Workshop for International Research” to discuss opportunities for collaborations with scientists from Mexico and Cuba on studies related to past and future oil spills.
    
    

Research Highlights:
As of January 31, 2019, DROPPS-II research, which entailed around 5 research cruises/expeditions, resulted in 41 peer-reviewed publications, more than 125 scientific presentations and 44 datasets being submitted to the GoMRI Information and Data Cooperative (GRIIDC), which are/will be available to the public. DROPPS-II engaged 16 Masters and PhD students over its award period. Significant outcomes of DROPPS-II research according to GoMRI Research Theme are highlighted below.

Theme One: Breakup, Dispersion, and Settling of Petroleum by Physical Processes.

• DROPPS-II experiments carried out in the wave tank facility measured droplet size distribution from the chemical and physical dispersion of crude oil slicks by breaking waves. Scientists investigated how surface waves break up crude oil slicks into subsurface droplets, the effect of dispersants on the droplet size distributions, and the subsequent transport of these droplets by turbulence. These data are critical for modeling how oceanic currents break up and disperse crude oil.

• DROPPS-II researchers investigated the chaotic process of breaking waves using the latest version of a 3D smoothed particle hydrodynamics model (GPUSPH v4). Their study revealed that there are turbulence residuals existing prior to the generation of water waves in real-life scenarios and numerical simulations and that different turbulence residuals lead to variations of near-surface velocity at the breaking wave fronts, which causes the development of substantially different breaking wave jets and splashes.

• DROPPS-II scientists studied jet/plume fragmentation and droplet generation processes in a buoyant crude oil plume using refractive index matched surrogate fluids, fluorescent dyes, laser sheets and highspeed video to quantify the droplet size distributions. The videos revealed the presence of multi-layer compound droplets at the plume center. The presence of compound droplets changes the droplet buoyancy and the interfacial area.

• DROPPS-II researchers revealed a new pathway for the fate of oil in environments containing high sediment concentrations. They used confocal imaging techniques to examine detailed 3D structures of oil-particle aggregates formed in turbulent flows. Particles behave as projectiles penetrating the oil droplets to various depths due to the hydrodynamic forces in water. Protruding particles get torn from oil droplets and carry oil with them. Findings from this study enhance the knowledge of oil-particle interaction in nearshore environments particularly under breaking waves.

• DROPPS-II researchers studied the dissolution of soluble organic compounds contained in oil droplets rising from depth in the sea. The unsteadiness of the diffusing substances at the drop surface introduced a new phenomenon whereby gas concentration at the bubble surface changes with time as the bubble shrinks and the radius decreases, the surface tension and the gas pressure in the bubble increase, and the gas concentration at the bubble surface also increases.

• DROPPS researchers used the wave tank to investigate the effects of viscosity and interfacial tension on entrained oil droplet size distributions using a submersible holography system. The experimental design included varying wave types, oil-seawater interfacial tension, and oil viscosity. For the same sizes of breaking waves, mean droplet diameters decreased as viscosity and interfacial tension decreased. Droplet size distributions were quantified and used to create a scaling factor.

• DROPPS-II scientists completed experiments in their tower basin of mixed releases of oil and air as well as oil and natural gas (methane) to identify droplet and bubble size distributions associated with these releases. They also tested the effect of different dosages of dispersants applied to the mixtures.

• DROPPS-II researchers studied the role of gas phase plays in an oil jet blowout. Multiphase (air-water) bubbly and churn jets were measured using particle imaging velocimetry to evaluate the influence of the gas phase on the jet hydrodynamics, especially at the near-to-orifice region. A computational fluid dynamics approach with large eddy simulation was used to simulate the hydrodynamics of bubbly and churn jets in detail. Results indicate that the gas phase plays an important role in influencing the hydrodynamics of the underwater blowout and affects the formation of the droplet at the initial stage, as well as the effectiveness of dispersant.

 

Theme Two: Chemical Evolution and Biological Degradation of Oil by Interactions with Marine Plankton
and Bacteria.

I. Interactions with marine plankton

• DROPPS-II scientists collected marine microbiota samples shortly after the Texas City “Y” oil spill and found that exposure to crude oil can rapidly imbalance populations of marine microbiota, which leads to the proliferation of more resistant organisms after an oil spill.

• DROPPS-II researchers collaborated to examine the effect of dispersed crude oil on a natural Kareniabrevisbloom. The results demonstratedthatgrowthofK.breviswas markedly inhibited by the oil-dispersant mixture in experiments using closed Erlenmeyer’s flasks. In contrast, experiments using open beakers showed no effects on growth perhaps because the use of open beakers reduced the exposure to the volatile fraction of the crude oil. However, morphological changes were observed on the size and shape of cells exposed to the soluble toxins.

• DROPPS-II scientists investigated the effects of crude oil, dispersant-treated crude oil and dispersant alone on the structure of natural plankton assemblages in the northern Gulf of Mexico. Major grazers of phytoplankton were negatively affected in coastal waters by the exposure to oil and dispersant, whereas bloom-forming dinoflagellates increased their concentration. The removal of key grazers due to oil and dispersant disturbed predator-prey controls (“top-down”) that normally function in plankton food webs. This disruption of grazing pressure opened a “loophole” that allowed certain dinoflagellates with higher tolerances to oil and dispersants to grow and form blooms when there are no growth limiting factors (e.g. nutrients). Therefore, oil spills and dispersants can disrupt predator-prey controls in plankton food webs and indirectly lead to potentially harmful dinoflagellate blooms.

• DROPPS-II researchers looked at the effects of crude oil and dispersants on the grazing behavior of heterotrophic dinoflagellate, Oxyrrhis marina, on the autotrophic flagellate, Isochrysisgalbana. Results showed reduced grazing by O. marina in seawater with crude oil alone and chemically dispersed oil treatments, but not with dispersant alone. Growth rate experiments indicated that chemically dispersed oil could significantly reduce the growth rate of I.galbanabutnotthe grazer O. marina.

• DROPPS-II scientists conducted a series of experiments examining the effects of oil-degrading bacteria on dinoflagellate growth. Although growth promoting nutrients released by oil-degrading bacterial cultures were not found to affect the growth rate of dinoflagellates, the growth rate and yield of phytoplankton were enhanced following addition of oil-degrading bacterial cultures. These results suggest that the presence of oil-degrading bacteria may have assisted in the formation of Prorocentrum blooms after the Texas City “Y” oil spill.

• DROPPS-II researchers studied the effects of oil and dispersant on copepod swimming. The presence of dispersed crude oil after 2 days of exposure significantly decreased the swimming velocities,trajectory shape and orientation, leading to a decline in escape efficiency. Overall, this study demonstrated that hydrocarbon contamination of seawater affects prey-predator relationships through the perturbation of copepod escape mechanisms, suggesting a general impact on population fitness and dynamics.

II. Formation of biofilms and associated interfacial phenomena

• DROPPS-II scientist modeled the transport of oil, source-fingerprinted 44tarballsamplesfrom Galveston Island and Mustang Island and determined the hydrocarbon and bacterial community composition of these tar balls following the 2014 Texas City “Y” Oil Spill. Source-fingerprinting confirmed that the tar balls collected from both Galveston Island and Mustang Island originated from the spill. Tar balls from Galveston Island showed 21% depletion of alkanes and 55% depletion of Polycyclic Aromatic Hydrocarbons (PAHs), and were dominated by alkane-degrading marine bacteria. Samples from Mustang Island showed 24% depletion of alkanes and 63%PAHs, and contained mainly PAH-degrading Pseudoalteromonas. This was the first study to relate oil transport, tarball source-fingerprinting, chemistry, and microbial community composition, which provided insights on the fate of oil in the northern Gulf of Mexico.

• DROPPS-II scientists investigated the motion of passive colloids at interfaces between oil and aqueous suspension of bacteria for a strain of bacteria that remains motile for prolonged periods of time. The effective diffusivities of the colloid–bacteria aggregates are up to fifty times greater than those absent bacteria. This enhanced transport might pose a concern, for example, if the colloidal cargo itself was a toxin, or if it released small molecule contaminants, as in the case of colloidal-sized aggregates that might adhere to bacteria after oil spills.

III. Degradation of crude oil

• DROPPS-II researchers examined the community composition and hydrocarbon metabolism of deep-sea sediment bacteria when exposed to light Louisiana sweet crude oil. PAHs were readily degraded when oil was added, but alkane degradation occurred more slowly. Using 16S rRNA gene sequencing and metagenomics they showed that marine bacteria increased in abundance with addition of oil. Genes related to hydrocarbon degradation were highly enriched in the oiled treatment suggesting that the hydrocarbons were biodegraded and the indigenous microflora have a remarkable potential for the natural attenuation of spilled oil in the deep-sea surface sediment.

• DROPPS-II scientists studied the fate of aromatic hydrocarbons in light Louisiana sweet crude oil after exposure to natural sunlight in the Gulf of Mexico. They traced the fates of 13C-labeled phenanthrene that was amended to crude oil during photooxidation through a 44-day natural light exposure experiment, including the conversion of the 13C-phenanthrene among the pools of saturate, aromatic, resin, asphaltene and dissolved inorganic carbon (DIC). These results can help evaluate bioavailability and toxicity of the oxygenated or polar hydrocarbons after photooxidation.

• DROPPS-II researchers conducted a series of microcosm incubations to determine if photoheterotrophic bacteria are present during oil degradation, and to what extent and how these heterotrophic bacteria contribute to the process. Preliminary data showed that concentrations of both alkanes and PAHs decreased with time in light incubation, while they stayed relatively constant in dark incubation. In light incubation, the most significant decreases in alkanes and occurred between day 5 and day 20, coinciding with the increase of bacterial abundance.

• DROPPS-II researchers conducted microcosm experiments to investigate bacteria at the crude oil droplet-water interface and demonstrated that when bacteria encounter and attach to a rising oil droplet they produce extracellular polymeric substance (EPS) threads (streamers) extruded directly from the oil-water interface. These streamers increase the drag substantially on a crude oil droplet which causes it to slow down. The slowing down of a rising oil droplet encourages interactions by nearby microbes and leads to the formation of MOS particles. These streamers have a profound impact on the hydrodynamics of rising micro-droplets and subsequently affect their fate.

• DROPPS-II researchers worked in collaboration with ADDOMEx to study EPS extracted from various microbial isolates and consortia. EPS exhibited drastic differences in aggregate growth rate, size, and shape with some aggregates growing in under an hour and others taking weeks. Previous results suggested a positive correlation between EPS protein/carbohydrate ratio and aggregation rate, but recent experiments have challenged this correlation.

Theme Five: Public and Occupational Health Impacts of Exposure to Oil Spills.

• DROPPS-II researchers investigated toxicity impacts on human bronchial cells when exposed to oily marine aerosols. They designed, created and tested the novel Real-Time Examination of Cell Exposure system. The major advantage of this system over other available commercial devices is its ability to allow in situ observations of human lung cell cultures throughout exposure, enabling direct assessment of physiological changes, e.g. cell morphology, migration and changes to the ciliary beat frequency.

• DROPPS-II scientists developed an underwater bubble-generating system to estimate the emission rate of particulate matter and gases emitted when bubbles burst on the surface of crude oil slicks. Comparisons between the concentrations of airborne particles, measured before, during, and after bubbles burst, confirmed the emission of oily aerosols which increased with the introduction of dispersants. For the same volume of air entrained in the bubbles, decreased bubble size increased the total mass of the aerosolized particles.

Theme One & Two: Incorporating the Data to Improve Modeling of Spills: Modeling of Response Option.

• DROPPS-II researchers improved the Oil Spill Contingency and Response (OSCAR) model by adding a Droplet Size sub-model (DS), which calculates crude oil-water interfacial tension using the dispersant-oil ratio. This allowed them to test the effects of dispersant application in the OSCAR model with the new DS model under breaking wave conditions. It was tested successfully with previously published data on weathered crude oils as well as recent data on fresh and low-interfacial tension crude oils.

• DROPPS-II scientists worked on an atmospheric transport model for the initial simulation of oil reaching the sea surface. Evaporated oil components were arranged onto a grid to enable the OSCAR model to estimate mass fluxes of oil components per simulation time-step. Atmospheric data time series for the Deepwater Horizon oil spill were downloaded from European Centre for Medium-Range Weather Forecasts (ECMWF) global high resolution weather simulation. These data were used to simulate transport and dispersion of evaporated oil from the DWH spill, comparing conditions before and after dispersion injection at the wellhead.