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PETROMAKS2-Stort program petroleum

Marine snow flocculation and sedimentation in relation to oil spill responses

Alternative title: Marin snø flokkulering og sedimentering relatert til oljevernaksjoner

Awarded: NOK 4.6 mill.

After an oil spill to the marine environment, efforts will be made to reduce the impacts of the spill. One such oil spill response effort is to use chemical dispersants to create small oil droplet dispersions. After a sea surface oil spill these dispersions are "whipped" down in seawater column by the waves and rapidly diluted. Dispersant treatment of a deepwater blowout may result in a deepwater "plume", as a collection of small oil droplets, since the small droplets have low rising velocity and are catched by deep water currents. Recent investigations have indicated that the chemically dispersed oil may generate particles of oil droplets, biological material (bacteria, algae, feces from zooplankton, polymerer), and/or mineral particles, which may possibly sink to the seabed. We call these particles oil-related marine snow (ORMS). It has been shown that these particles are a site of continuous oil biodegradation, and the oil in these particles will be depleted of biodegradable and soluble oil compounds (highly weathered). In this project we have investigated the formation and fate of ORMS in relation to the use of chemical dispersants. We have studied these processes in experimental systems relevant for Arctic, temperate and warm seawater. We have developed experimental and analytical methods to compare oil biodegradation processes in the ORMS particles and in the surrounding seawater. Data from experiments in cold, temperate and warm seawater (simulating conditions in the Arctic, along the Norwegian coast, and in subtropical/tropical seawater) shower faster ORMS formation at higher water temperatures, and that up to 50% of the oil were associated with ORMS particles. As part of the ORMS formation process, Arctic algal species relevant for the Arctic, the North Sea/Norwegian Sea and warm water have been used. Biodegradation rates of oil compounds were also faster at higher water temperatures, and the rates were not influenced by the presence of algae and/or mineral particles, when compared to oil and seawater alone. Analyses of microbial communities showed successions of microbes associated with degradation of oil compounds, and algal associations, when these were present. Experiments were performed to determine biodegradation by chemical and respirometric analyses to compare primary and ultimate biodegradation. Studies describing ORMS formation as function of oil dilution showed that large ORMS aggregates were only formed at rather high oil concentrations, but that oil adhered to small particles even at very low oil concentrations (<1 mg/L). Data from these experiments therefore indicate that the use of dispersants may affect the fate of the oil by increased particle Associations in the seawater. Experiments in a sinking velocity chamber designed at SINTEF Ocean, showed ORMS particle sinking rates of 50-100 m/day at 20°C, but sinking rates were not necessarily associated with particle size. A literature review has been performed to evaluate the fate of the ORMS after sedimentation to the seabed, with focus on the fate of the sinking oil after sedimentation on the seabed surface and after burial in te sediments. An evaluation of how ORMS formation may influence on oil spill contingency planning (SIMA) were performed with focus on different seawater temperatures, and for coastal and offshore contingency planning. The fate of an oil spill is often predicted using oil spill models, and in Norway the OSCAR model is the common tool. This model includes biodegradation data, and our studies have shown that ORMS formation will not affect the biodegradation data for the model significantly. However, the transport ways of the oil may be affected by ORMS formation, with seawater temperature, algal blooms, concentrations of mineral particles and ORMS sinking rates as important parameters to consider.

1) Virkninger for en nasjonal kunnskapsbase: Bedre kunnskap om hvordan oljerelatert marin snø (ORMS) påvirkes av ulike vanntemperaturer, hvordan og hvor fort oljen akkumuleres og brytes ned i partiklene, hvordan fortynning påvirker ORMS dannelse, samt hvor fort og under hvilke temperaturbetingelser oljen kan synke til sjøbunnen pga. disse aggregeringsprosessene. Resultane fra prosjektet er spesielt viktig for temperert og arktisk sjøvann, der relevant kunnskap har vært spesielt mangelfull. 2) virkninger og effekter for oljeindustrien: Prosjektet har gitt svar på at nedbrytingsdata i oljeutslipps-modeller ikke trenger å revideres, men at endringer av transport-beregninger knyttet til ev. synking av olje bør vurderes, spesielt i kystnære farvann og i varmt vann. Effekter av ORMS-prosesser bør også inkluderes i planlegging av oljevernberedskap, spesielt effekten av bruk av dispergeringsmidler i farvann med mye partikler.

After the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico (GoM) in 2010, oil-related marine snow (ORMS) flocculation was suggested to play an important role for the long-term fate of the oil. It was further suggested that the use of subsurface dispersant injection (SSDI) was a driver for the ORMS processes, eventually resulting in seabed sedimentation of parts of the spilled oil. In this project we will use experimental and litterature data to investigate ORMS processes related to biological and mineral particles. We will focus on processes involving oil/biological particles (oil-degrading bacteria and phytoplankton producing extracellular polymer material), oil aggregated to mineral particles, and combinations of biological and mineral particles. Essential in the aggregation processes will be the use of chemical dispersants as oil spill response methods, since dispersants generate small oil droplets with near-to neutral buoyancies that easier come in contact with biological and mineral particles than a floating oil slick. In this context, the use of chemical dispersants may also increase oil biodegradation, and the impacts of flocculation on oil biodegradation will therefore also be important to investigate. Biological ORMS processes will be of particular relevance for oil spills during algal blooming seasons (Spring/Summer), while mineral particle processes will be relevant for oil spills in coastal and shallow water. For these studies selected scenarios will be simulated, including Arctic oil spills, spills in temperate regions of the Norwegian Continental Shelf (NCS), and oil spills in warm seawater regions where Norwegian oil companies are involved. Conditions relevant for dispersant treatment of surface spill will be focused, but conditions relevant for subsurface oil spills will also be included, as well as the influences of oil dilutions after dispersant treatment. Sinking velocities of various ORMS particles in the seawater column will be determined. Fate processes related to the ORMS processes will be focused, primarily by determination of oil biodegradation in the ORMS particles, but also by determination of succcessions of microbes involved in oil biodegradation. Finally, fate/biodegradation processes after oil sedimentation on seabed surfaces will be reviewed from previous relevant studies with sedimented oil performed at SINTEF and at other laboraties. The data from these studies will be compared to field data where ORMS processes have been analyses, in particular during the DWH oil spill in the GoM. The review will also include evaluations of toxicity changes in the sediments during biodegradation processes. The data from this project will be used to evaluate the importance of ORMS processes after oil spill treatment and to determine if ORMS processes should be included in oil spill models like OSCAR. The data from the project will also be used to determine if ORMS processes will result in needs for changed oil spill response actions, compared to situations where ORMS processes are not involved.

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Funding scheme:

PETROMAKS2-Stort program petroleum