Development of a new oil biodegradation algorithm for NOAA's oil spill modelling suite (GNOME/ADIOS)

In recent years, it has become apparent that the rate of biodegradation of oil in the environment is of great concern to oil spill responders and the community. While it has been accepted that the long-term fate of most oil in the water column is dominated by biodegradation, the rates of degradation in the open ocean have been poorly understood, and the tools to model the process have been limited. Many environmental factors have been shown to have an effect on biodegradation rates, including temperature, nutrient load, composition of the microbial community, oil composition, and overall surface area of the oil-water interface. However, the interplay between these effects remains unclear. As part of the process to upgrade the weathering algorithms in NOAA's oil spill modeling suite, we have developed a new rate law to model the biodegradation of oil in seawater based on pseudo-first-order kinetics. The surface-area-to-mass ratio of the oil is explicitly included as a parameter that changes over the course of a modeling run, so this model can be adapted to predict biodegradation from oil droplets or surface slicks. Oil composition is accounted for by using pseudocomponents with distinct mass fractions and biodegradation rate constants. All other environmental factors that affect biodegradation are incorporated into the rate constants for each component. The values for these rate constants are derived from published experimental studies. More systematic studies are needed in order to determine the exact nature of these effects on biodegradation rates of oil.