Project Overview

OverviewDr. Edward Buskey at The University of Texas at Austin Marine Science Institute was awarded an RFP-I grant of $5,945,000 to lead the GoMRI Dispersion Research on Oil: Physics and Plankton Studies (DROPPS) Consortium that consisted of 6 collaborative institutions and 92 research team members. The goals of DROPPS were to investigate the breakup of crude oil patches into droplets under varying environmental conditions and to quantify and model the interaction of oil with the base of the marine food web, including hydrocarbon-degrading bacteria, phytoplankton and zooplankton. DROPPS also focused on characterizing and modeling complex oil-seawater interfacial processes that affect the breakup of crude oil droplets in the presence of physical and chemical agents of dispersal, and when droplets were covered by elastic interfacial bacterial colonies. DROPPS studies were designed to provide datasets to inform predictive models to assess the dispersal and fate of oil spills in the sea.  

Outreach

Over its award period (3 years, plus a 12-month no-cost extension), DROPPS organizednearly 100 outreach activities or products, including but not limited to:

• Hosting a workshop to bridge the gap between first responders and oil spill researchers that was jointly sponsored by UTMSI, Sea Grant, and the US EPA, amongst others. The intent was to prepare for (and break down) the barriers that happen when an event occurs.
• Providing a DROPPS oil spill research information panel and videos featuring DROPPS oil spill research for UTMSI’s Estuary Explorium that opened to the public in July 2014.
• UTMSI’s 2015 Summer Science program taught 120 kids about the importance of ocean currents in oil spills through the use of drifters, in collaboration with CARTHE.

 

Research Highlights

DROPPS research, which entailed 3 research cruises or expeditions, resulted in  23 peer-reviewed publications, 87 scientific presentations, and 31 datasets being submitting to the GoMRI Information and Data Cooperative (GRIIDC), which are/will be available to the public. DROPPS engaged 56 students over its award period. Significant outcomes of DROPPS research according to GoMRI Research Theme are highlighted below.

Theme 1: Physical Processes

• A series of experiments performed by DROPPS researchers investigated the effect of raindrops on the dispersal of surface oil slicks, specifically examining how oil layer thickness and dispersant concentration affect the formation of aerosolized droplets when raindrops fall on an oil slick. Results demonstrated that the generation and breakup of the splash crown, as well as the resulting concentration and size distribution of airborne droplets, vary substantially with slick thickness and dispersant concentration.
• DROPPS experiments performed in the wave tank investigated the effects of dispersants and breaking wave characteristics (wave height, speed and plunging versus spilling) on the breakup of oil slicks, as well as the generation and transport of subsurface and aerosolized oil droplets. Ongoing data analyses by the DROPPS team involving the application of digital holography show an increase in droplet concentration and reduction in droplet size with increasing wave height and dispersant concentration. This continuing effort will provide a comprehensive database on the time evolution of droplet size and spatial distributions of oil droplets created by surface waves, which is critical for modeling oil transport.
• DROPPS experiments in the towing tank investigated the effect of dispersant concentration on the shape of a subsurface oil jet/plume subjected to a cross flow. Results demonstrated that increasing the dispersant concentration reduces the thickness of the main, nearly horizontal part of the plume. This trend is attributed to a reduction in the characteristic size of the oil droplets, which suppresses the expansion of the upper part of the plume. However, dispersants increase the concentration of micron-size droplets in the wake region behind and under the plume.
• DROPPS scientists found that a variety of seemingly different phenomena which lead to the formation and detachment of very small liquid drops from a much larger liquid mass actually have a common cause in a specific physical process. They found that the presence of dispersants considerably enhances the process leading to a much finer fragmentation of dispersed oil masses.
• DROPPS investigators simulated the dissolution of soluble oil components from oil droplets dispersed in a turbulent field, with the objective of determining the time scale of the process in relation to turbulence intensity, soluble fraction content, drop size distribution and others. They have developed the code to include the mass transfer from the particles to the water and the solution of the diffusion equation of the soluble oil components in the water.

Theme 2: Chemical/Biological Processes

• DROPPS researchers found that sunlight plays an important role in determining the composition and dynamics of microbial communities found within surface marine watersthat contain oil and/or oil and dispersants.
• DROPPS investigators provided one of the first datasets of chemical composition and bacterial community structure in oil-seawater mousse from the sea surface and salt marshes during the spill, and oil deposited in sediment one year after the oil spill. These data offer insights into the weathering and changing toxicity of the oil in Gulf of Mexico.
• DROPPS scientists developed a new pyrolysis technique to follow weathering trends in environmental samples collected after the Deepwater Horizon spill and to gain insight into the weathering patterns of complex petroleum hydrocarbons that are not traditionally amenable to gas chromatography.
• DROPPS on-deck incubation experiments quantitatively evaluated the roles of biodegradation and photooxidation of oil sheens on the sea surface, validating field observation.  In particular, they found that solar irradiance preferentially promotes certainoil-degrading bacteria; a novel finding that leads to a better understanding of biodegradation and development of bioremediation strategies.
• DROPPS investigators examined oil-bacteria interactions, specifically bacterial migration near a chemically heterogeneous surface in which they measure the motility and responses of bacteria over the surface as well as the hydrodynamic role in assemblage formations. Results from experiments with Pseudomonas P62 show that bacteria swimming motility is not affected by the presence of an oil-water interface.
• DROPPS investigators developed a novel correlation-based de-noising algorithm to be used with in-line digital holographic microscopy to measure bacteria motility. This algorithm removes background noise and enhance the quality of hologram images.
• DROPPS scientists found that Films of Bacteria at Interfaces (FBI) form at oil-water interfaces. Film characteristics depend on bacterial species and strain, and evolve over time, from active films of swimming bacteria, to elastic films, posited to hinder diffusion of nutrients. Through RNA sequencing, the genetic response of bacteria cells, via metabolic pathways, to entrapment at interfaces is being studied.  For active films, simulation predicts that hydrodynamic interactions between bacteria alter the path each takes, which is posited to contribute to micromixing of the suspension and associated nutrients and quorum sensing molecules.