| Summary: | Understanding the fate of oil discharges in cold marine environments has become a key issue as oil and gas industry is expandig exploration activities into frontier regions such as the Arctic Ocean. The aim of this research project was to assess a currently applied modelling approach for predicting crude oil biodegradation rate in the sea and evaluate its limitations. Furthermore, a relatively new static respirometry method was adapted for studying hydrocarbon (HC) biodegradation in seawater and to examine the effect of geographical origin of seawater on inherent biodegradation rate and temperature response. The Oil Spill Contingency and Response (OSCAR) model, the industry standard in Norway to evaluate possible effects of accidental oil releases, takes biodegradation into account based on experimentally determined rate coefficient values. These values are adjusted to local ambient conditions by temperature compensation. Based on literature data and experimental observations, the compensation method implemented in the OSCAR model has been found to be debatable. Literature data and experimental results did not corroborate the rule of thumb approach used in the OSCAR model. The 32 different temperature compensation factors (Q10 values) calculated from published HC biodegradation rates ranged from 1.1 to 16.2 with an average of 2.8. The Q10 values for crude oil biodegradation obtained during laboratory tests were 2.6 and 9.9 at 5 and 0.5 °C, respectively. Crude oil type, incubation temperature range and other experimental factors were identified as important factors causing the high variation observed among Q10 values. Results showed that substrate limitation (reduced bioavailability) occurs at low temperature due to the effect of temperature on physico-chemical properties of oil. This temperature dependence of bioavailability implies that properties of crude oil influence the Q10 value. Hence, applying the same Q10 value for different oil types is not suitable. Besides bioavailability, initial number of bacteria ...
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