Aarhus University Seal / Aarhus Universitets segl

No. 347: A study of microbial crude oil degradation in water and sediment from the Greenland Sea

Johnsen, A.R., Christensen, J.H., Poulsen, K.G, Hansen, L.H. Ellegaard-Jensen, L. & Fritt-Rasmussen, L. 20xx. A study of microbial crude oil degradation in water and sediment from the Greenland Sea. Aarhus University, DCE – Danish Centre for Environment and Energy, 90 pp. Scientific Report No. 347. http://dce2.au.dk/pub/SR347.pdf

Summary

This project evaluated the capacity for microbial oil degradation in the marine environment offshore NE Greenland. Offshore oil exploration and exploitation in this area will be associated with an increased risk of accidental oil spills due to sea ice, drifting icebergs, and the depth at which the drillings may take place. Natural oil pre-exposure from seeps presumably induces microbial degrader communities with broad substrate diversity by selecting and enriching rare degraders with the necessary metabolic machinery to “handle” a great number of different oil compounds. Any indications of oil pre-exposure would therefore be important for the strategic environmental impact assessment.

Sediment and/or sea water were sampled at 11 stations within and outside of the license areas. We carried out four sub-experiments. 1) Sediment from 10 stations was analysed for the contents of natural oil compounds and the contents of oil degrader microorganisms. 2) Six sediments from the continental shelf were spiked with crude oil and/or mineral nutrients to investigate the potential for oil degradation and to which extend this potential is dependent on the addition of mineral nutrients. 3) Crude oil degradation was investigated in seawater from a selected station by comparing the intrinsic degradation and degradation in water spiked with mineral nutrients and/or a dispersion agent. 4) The metabolism of microbial oil degraders at different depths of the water column at three stations was qualitative characterized by extracting microorganisms from water samples and incubating them with crude oil under optimized conditions.

The results from our simplified laboratory experiments can only be extrapolated to the complex environment of the Greenland Sea with great caution, but some microcosms did show a large potential for biodegradation of many different oil compounds in the water column, even “difficult” compounds such as C1-pyrene and C3-phenanathrene was partially degraded after 70-90 days. This suggests, that bioremediation of surface spills may have a large potential if the intrinsic microbial degraders can be activated.

It was also clear that in-situ concentrations of mineral nutrients are strongly limiting for oil degradation. Oil biodegradation will thus be very limited in the water column without addition of mineral nutrients. Contingency strategies based on the intrinsic potential for microbial oil removal should therefore include strategies for applying mineral nutrients for degradation to be efficient. The dispersing agent Slickgone NS was efficient at dispersing the oil under the tested conditions, but may have little effect on oil biodegradation when mineral nutrients are limiting, probably because degradation of the dispersant itself requires mineral nutrients.

The concentration of alkyl-PAHs was low in sediments from the shelf break, but light alkyl-PAHs were detectable, suggesting that the shelf break stations may have had some form of limited oil pre-exposure. Alkyl-PAHs were non-detectable in the tested shelf sediments suggests that the shelf stations have had no oil pre-exposure. The potential for biodegradation of weathered PAHs in the shelf sediments was very low, even when mineral nutrients were not a limiting factor, which is in line with the absence oil pre-exposure. 

The applied methods all had benefits and drawbacks, but they were strong tools when combined. The knowledge gained from this project will be important for evaluating the potential for oil removal based on the natural microbial communities that are present in the marine environment of NE Greenland.