The treatment of biodegradation in models of sub-surface oil spills: A review and sensitivity study

Highlights • Biodegradation is a critical process that governs the fate of oil spilled subsea. • Current models use first-order decay of pseudo-components of the oil composition. • We simulated subsea oil spills varying composition, biodegradation rates, and droplet size. • The most important parameter affecting surfacing time and location was droplet size. • The choice of biodegradation model and rates was of secondary importance. Abstract Biodegradation is important for the fate of oil spilled in marine environments, yet parameterization of biodegradation varies across oil spill models, which usually apply constant first-order decay rates to multiple pseudo-components describing an oil. To understand the influence of model parameterization on the fate of subsurface oil droplets, we reviewed existing algorithms and rates and conducted a model sensitivity study. Droplets were simulated from a blowout at 2000 m depth and were either treated with sub-surface dispersant injection (2% dispersant to oil ratio) or untreated. The most important factor affecting oil fate was the size of the droplets, with biodegradation contributing substantially to the fate of droplets ≤0.5 mm. Oil types, which were similar, had limited influence on simulated oil fate. Model results suggest that knowledge of droplet sizes and improved estimation of pseudo-component biodegradation rates and lag times would enhance prediction of the fate and transport of subsurface oil.