Abstract
For oil spilled at sea, the main weathering processes are evaporation, emulsification, photo-oxidation, dispersion and biodegradation. Of these, only biodegradation may completely remove hydrocarbons from the environment in the long term, as the other processes only serve to transform and dilute the oil components. As petroleum development is moving north, the probability of Arctic oil spills increases. Hence, it is imperative to develop methods for comprehensive risk assessment of oil spills in cold and ice-covered waters. Accurate biodegradation rates are an essential part of this, as they are required to predict the long-term effects of marine oil spills. In this paper, we present experimentally determined biodegradation rates for the component groups which are used to represent oil in the OSCAR oil spill model. The experiments have been carried out at seawater temperatures of −2∘C, 0∘C, 5∘C, and 13∘C. We show that for the lighter and more soluble oil components, the changes in degradation rates between 0∘C and 13∘C are well captured by a constant Q10 scaling law. At lower temperatures, and for heavier and less soluble components, the rates are not well described by a constant Q10, probably indicating that oil properties become important for the biodegradation rate.
Highlights
In the modelling of marine oil spills, there is a strong focus on predicting where the oil will end up in the short term, in order to direct response operations or evaluate different response strategies (Reed et al, 1995, 2000; Barker and Healy, 2001; McCay et al, 2005)
We present experimentally determined biodegradation rates at À 2+C, 0+C, 5+C, and 13+C, for the oil component groups used in the OSCAR oil spill model (Reed et al, 2000, 2001)
We assume that the first-order rate constant, ki, of component group i, is independent of the concentration of other component groups in the oil. The advantage to this approach is clear: Once the different properties have been established for each component group, one can model the behaviour of any oil, as long as the composition is known in terms of the same component groups
Summary
In the modelling of marine oil spills, there is a strong focus on predicting where the oil will end up in the short term, in order to direct response operations or evaluate different response strategies (Reed et al, 1995, 2000; Barker and Healy, 2001; McCay et al, 2005). Models are used to statistically analyse the possible outcomes of an oil spill (Barker, 2011; Nordam et al, 2017), and carry out environmental risk assessments (McCay et al, 2004). After response operations are over and there is no surface oil, the only relevant process determining the ultimate fate of the remaining oil compounds at sea is biodegradation. In order to properly assess the risk of these activities, there is a pressing need for oil spill models that incorporate the effects of ice and low temperatures on the transport and fate of the oil (French-McCay et al, 2018; Nordam et al, 2019). We present experimentally determined biodegradation rates for crude oil components at low temperatures, and assess the validity of a commonly used approach to temperature-scaling of these rates
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