In situ biodegradation of hydrocarbons in arctic soil at sub-zero temperatures-field monitoring and theoretical simulation of the microbial activation temperature at a Spitsbergen contaminated site

The objective of the study has been to investigate whether cold-adapted microorganisms (CAMs) are metabolising hydrocarbons in situ at sub-zero temperatures. Since the summer 2001, soil temperatures and soil gas concentrations of oxygen (O2) and carbon dioxide (CO2) at various depths at a petroleum hydrocarbon contaminated permafrost site at Longyearbyen, Spitsbergen, have continuously been measured and compared to data from a nearby non-contaminated site. We have previously reported on unchanged microbial O2 consumption in the active layer for about 12 days after the soil temperatures decreased below 0 °C in late October 2001 and we are now reporting on the microbial activity in the soil profile from January to September 2002. The empirical data have been compared to theoretical simulations of O2 concentration as a function of soil depth and time from when the CAMs became active in spring until steady-state conditions were achieved in the summer. At the 0.7 m depth in the oil-plume site, microbial O2 consumption started in the middle of April, about 45 days before the soil thawed. There was no coincidence between the microbial activation time and the thawing time of the soil. The CAMs became active at temperatures of about −6 °C, but the main degradation activity occurred at temperatures between −1 and −3 °C. When the soil thawed, the hydrocarbon degradation was probably limited by the O2 supply. In the summer months where we expected the greatest degradation activity to occur because of positive temperatures and access to water, the degradation was limited by O2 depletion. The overall data from this arctic permafrost site indicate that without other limiting conditions such as O2 and substrate availability, the active biodegradation period can be extended to about 6 months despite periods with sub-zero soil temperatures.