The massive release of oil from the Deepwater Horizon incident has led to an unprecedented use of oil dispersants, which include a mix of surfactant compounds designed to dissolve oil and prevent slick formation. Previous research has shown mixed effects of surfactants on biodegradation and little is known about their effects on the ability of microbial communities to degrade the many hydrocarbon compounds found in crude oil. Hydrocarbon degrading bacteria differ in their substrate preferences, as well as in their response to surfactants, which will play an important role in determining the rate and extent of biodegradation.
With funding from this Grant for rapid Response Research (RAPID), researchers at the University of California at Santa Barbara will use a combination of chemical and biological tools to track changes in the composition of the oil, changes in the microbial community, and the amount of surfactant present, in order to determine the impact of these dispersants on biodegradation. Oil quantification and composition will be determined by gas chromatography, including the use of comprehensive two-dimensional gas chromatography. Microbial community changes will be determined by analysis of the 16S rRNA gene and functional genes for hydrocarbon oxidation, and specific members of the community will be quantified with quantitative real time PCR. Surfactants will be identified and quantified with LC-MS or other techniques. Initial sampling will be shore based, with deep water and sediment sampling planned as conditions allow. The opportunity to sample in the early stages of response to this spill will provide important baseline information and enable longer term studies on the fate of oil and dispersants in the Gulf of Mexico.
Broader impacts of this proposal include the involvement of an undergraduate researcher and a postdoctoral researcher, as well as collaboration with the popular news media to educate members of the public on the effects of dispersants and the fate of oil from this spill.
This award led to six primary findings, each related to the biogeochemistry of the deep hydrocarbon plume that emanated from the Deepwater Horizon blowout. The first finding resulted from an NSF-sponsored cruise in June 2010, in which project personnel identified the importance of natural gas driving respiration in the deepwater plumes. By applying a combination of chemical, isotopic and biological approaches, propane and ethane were found to drive a majority of respiration in these settings. This work was published in Science in 2010. The second finding was based on results from a series of expeditions, some funded by NSF and some by NOAA. The plumes from the deepwater horizon were identified and tracked, and found to be devoid of methane – previously the most abundant component. The regional oxygen deficit was found to match the missing methane, and methane-consuming bacteria were found to be abundant in these waters. When combined with results of a simple biodegradtion model, these results indicate that most methane released from the Deepwater Horizon event were consumed by methanotrophic bacteria within ~ 3 months of release. These findings were published in Science in 2011. The third finding comes from a series of cruises in which sampling was conducted for DiOctylSulfoSuccinate (DOSS), an anionic surfactant present in the applied dispersant formulations. DOSS was tracked in the near field to the wellhead during active flow, and then in the far field after flow had ceased. These finding show that DOSS dissolved into the deep plume and was not rapidly biodegraded. These findings were published in Environmental Science and Technology in 2011. The fourth finding for this award was in relating bacterial identities to important biogeochemical functions, namely the bacterial consumption of ethane, propane and benzene. These are based on stable isotope probing experiments and the findings implicate bacteria of the genus Colwellia as being responsible for consumption of ethane and propane in plumes from the deepwater horizon. This work was published in 2011 in the Proceedings of the National Academy of Sciences, USA. The fifth finding for this award comes from a combined physical-chemical-biological model for the deep plume horizon during and after active flow. The model correctly predicts observed patterns of biodegradation and microbial ecology, and further identifies physical features potentially responsible for observations made in the response efforts. These findings were published in 2012 in the Proceedings of the National Academy of Sciences, USA. The sixth finding for this award comes from a broad geochemical consideration of the Deepwater Horizon emissions. This collaborative work independently assessed the hydrocarbon flow rate from the Deepwater Horizon event, and further estimated the partitioning of hydrocarbons into the environment. These findings were published in 2012 in the the Proceedings of the National Academy of Sciences, USA. This work also led to a host of broader impacts, including the rapid relay of oil spill related information to the public through the popular media, and to scientists through rapid publication of results. Two graduate students and a postdoctoral researcher all received training from this award.
