A Case Study using Stable and Radiocarbon Isotope Analysis as a Tool to Assess Biodegradation of Hydrocarbon Contaminants in Permafrost, Old Crow, Yukon

English Abstract:

Old Crow is an arctic fly-in community located in northern Yukon along the banks of the Porcupine River. The village relies heavily on the use of fuel storage tanks to supply the motorized vehicles used in town, the daily airplane, and oil used for heating. All of the storage tanks are kept on a raised gravel pad located several metres from the banks of the river. Over the years, the land surrounding this tank farm has become contaminated with hydrocarbons which have leaked into the subsurface during daily fuel transfers. The clean-up of the site poses a significant challenge considering that the contamination extends into the permafrost, and natural bioremediation must be considered as an option. Natural attenuation of hydrocarbons through biodegradation can be recognized by carbon isotopes measured in the soil CO₂ which should incorporate the ¹³C and ¹⁴C signatures of any hydrocarbon being oxidized. Similarly, substrate consumption can be accompanied by a Rayleigh-type enrichment of ¹³C in the residual hydrocarbons. Furthermore, the CO₂ created during biodegradation would contain no ¹⁴C, which should be reflected in isotopic composition of the soil CO₂. In this experiment, soil gas samples as well as both active layer and permafrost cores containing the hydrocarbons have been collected from the site in order to sample CO₂. The δ¹³C isotopic ratios and ¹⁴C concentration in the carbon dioxide have been determined and show biodegradation occurring at the site. Microbial characterization of the active communities through microcosm and PCR techniques is recommended as a next step which will support these isotope studies. This method of assessing in-situ attenuation of hydrocarbons demonstrates natural bioremediation to be a viable treatment option in permafrost regions.