Scottish Marine and Freshwater Science Volume 5 Number 3: The Science of Deepwater Oil Spills - Results from the 2013 Marine Scotland Science Workshop

Session 4 - Oil Behaviour (Weathering, Sedimentation, Chemical Dispersion)

State Of The Art

Presentations

1. Importance of microbial systems to the fate of oil in the marine environment: the case at Deepwater Horizon (Tony Gutierrez, Heriot Watt University).
2. Oil in sediments (Ursula Witte, University of Aberdeen).
3. Modelling deepwater blowouts with subsurface dispersant applications (Nicole Mulanaphy, RPS ASA).

The three talks in this themed session covered how oil can be incorporated into sediments, the microbial breakdown of oil, and the application of subsurface dispersants. The Deep Water Horizon incident was referenced a number of times, with examples of the microbial breakdown of the oil and the area of seabed affected given. The capabilities of the RPS ASA OilMap software suite were presented by examining model output where dispersants were applied in different ways and quantities. An analysis of the sensitivity of OilMap to different current and wind forcing was also shown.

Items identified in the discussions (beyond introductory talks) to characterise the state of the art are:

• Sediment/Water Interface: This interface, and the interaction between dissolved components in the water and the sediment, has been neglected in observational studies, and is absent from much of the modelling. When it is included in models there is little validation of these processes.
• Sediment Component: We are currently unsure about the scale of how much of a release enters the sediment (cf. other oils sources e.g. drill cuttings etc.)
• Oil Identification Methods: We need more work on oil identification methods, such as biomarkers to identify specific oil .
• Weathering: No information was presented on the effect of weathering of released oil. We need more information on these processes in order to include them in models correctly, particularly under the environmental conditions that may be relevant to the FSC.

Knowledge Gaps

Degradation Timescales: We need to know more about the time for degradation to occur under a variety of environmental conditions relevant to the FSC.

Toxicological Effects: Similarly we need to know a great deal more about the toxicological effects of oil and dispersants on fauna typical of the FSC.

• Relevant Species: There are currently no studies on deep water sedimentary species. This is partly due to pressure issues.
• Bacterial Blooms: We know very little about the implications of bacterial blooms - e.g. on filter feeders, and how these might be imp acted by released oil and/or dispersants.
• Sediment Biodiversity: We need to know more about the resident faunal populations in the sediment and the potential changes that might result from introduced oil.
• AUVs: Is it possible to develop and use bacterial sensors for AUVs, such as gliders and drifters?
• Communication: How does research get into operational response?
• Definition of Degradation?: The workshop participants questioned whether there was sufficiently good definitions of the degree of degradation of oil. This is needed when assessing spill impact especially using models.
• Baselines: A spill will have an impact on the bacterial biodiversity in the FSC. But what is the baseline population structure to compare change against? What is the impact of climate change on bacterial population baselines?
• Microbes/Marine Snow/Sediments: There is little research on microbes/marine snow/sediments in the FSC - e.g. there are few, if any, estimates of fluxes.

Future Directions

• Laboratory Experiments: Laboratory experiments can still tell us a great deal about the behaviour of oil at the extreme temperatures and pressures found in the FSC. aboratory experiments could also look at the effect of intermittent mixing on oil.
• Multiple Dispersants: If sub-surface multiple dispersants are to be considered, we need to investigate the possible interactions between them, and between dispersants and oil.
• Release Rates of Sub-surface Dispersant: If sub-surface dispersants are to be considered, more research is needed into what release rates should be used - i.e. efficiency vs environmental protection.
• Baselines: More research is needed on biological and chemical baselines in the FSC prior to a spill occurring.
• An Effect Proxy: Can we use within-sediment oxygen profiles as proxy for biological effect?
• GM Bacteria: There is a need for research into whether genetically modified bacteria could be used to consume oil.
• National Significant Spill: A spill in the FSC is likely to be a National significant spill. However, the same kind of NSS has never been seen twice, i.e. each one is different and we need to be prepared to be flexible and adaptive in our approach.
• Response Strategy?: Do we really have yet a viable response strategy for the FSC?
• A New Super Model? Is there a need for industry/science/government to pool resources and develop a much more advanced model of the FSC region?
• User Needs: We need to put more effort into understanding user needs as well as developing "model interpreters" in order to communicate model results to users.
• Dispersants - use them or not?: We need to gain a joint understanding of dispersant use, and an agreed strategy. For example, following a deepwater spill in the FSC, should we rely on natural degradation? We could be using models now to help with this decision.