Natural anaerobic degradation of methane and petroleum in marine sediments: geochemical gradients, degradation succession and microbial zonation
Final Report Abstract
In this project, a sediment-oil-flow-through (SOFT) System was established where a small-scale oil seep simulation was set up. This system enabled us to monitor in-situ biogeochemical changes and to study the microbial response within a sediment core, where oil was advecting towards the sediment-water interface. Different study sites were compared. Caspian Sea, Santa Barbara and North Alex Mud Volcano sediments were selected due to their subjection to nearby or direct natural hydrocarbon seepage. Eckernfoerde Bay sediment was selected as a reference, as it is a pristine site without any prior subjection to hydrocarbon seepage. A vertical zonation of biogeochemical parameters developed in all sediments during the SOFT process, leading to a formation of distinct redox zones. Sulfate reduction showed a strong response to oil seepage at all the sites. However, the response time was longest in the originally pristine Eckernfoerde Bay sediment. A methanogenic zone was observed below the sulfate penetration depth in the Caspian Sea, Santa Barbara, and the Eckernfoerde Bay core. Methanogenesis in the Caspian Sea core was potentially linked to oil degradation, supported by enrichment culturing. The volatile hydrocarbons (C1-C6) in the Caspian Sea sediment were degraded in the upper half of the core indicating the preferential degradation of lower hydrocarbons in the sulfate-reducing zone. 16s rRNA studies showed a vertical zonation of different sulfate reducers, which changed from the initial conditions prior to the seepage until after the seepage experiments. Desulfobacula and Desulfosarcina, which are known for their presence in hydrocarbon-rich environments, were relatively more abundant in Caspian Sea after the seepage experiment. Further hydrocarbon and molecular analyses of samples from the other sites are finished until end of 2015.
Publications
- Methanogenic hydrocarbon degradation: evidence from field and laboratory studies. J. Mol. Microbiol. Biotech. 2016;26:227-242
Jiménez, N., H.H. Richnow, C. Vogt, T. Treude, M. Krüger
(See online at https://doi.org/10.1159/000441679)
