ena-STUDY-UNIVERSITY OF ABERDEEN-02-04-2018-10:31:05:054-3036
Evaluation of hydrocarbon transport mechanisms in deep sea sediments with and without dispersant addition and subsequent bacterial community response
Deep sea oil exploration is increasing and presents environmental challenges for deep ocean ecosystems. Marine oil spills oftenresult in contamination of sediments with oil; following the Deepwater Horizon (DwH) disaster up to 31% of released oil wasdeposited as oily residues on the seabed. Although the aftermath of DwH was studied intensely, lessons learned may not be directlytransferable to other deep-sea hydrocarbon exploration areas, such as the Faroe-Shetland Channel (FSC) which comprises coldtemperatures and a unique hydrodynamic regime. Exploration of FSC oil reserves in waters >1000 m deep increases the need tofurther understand implications of potential spills. In this work, transport of hydrocarbons into deep FSC sediments, subsequentresponses in benthic microbial populations and effects of dispersant application on hydrocarbon fate and microbial communitieswere investigated. Sediment cores from 1000 m in the FSC were incubated at 0°C for 71 days after addition of a 20 hydrocarboncomponent oil-sediment aggregate. Dispersant was added periodically from day 4. An additional set of cores using sterilised andhomogenised sediment was analysed to evaluate the effects of sediment matrix modification and biotic influence on hydrocarbonentrainment. Layers of sediments were independently analysed for hydrocarbon content and bacterial community. Oil entrainedover 4 cm deep into FSC sediments after 42 days and dispersant effectiveness on hydrocarbon removal from sediment decreasedwith time. Sterilising and homogenising sediment resulted in hydrocarbon transport over 4 cm into sediments after 7 days.Significant shifts in bacterial populations were observed in response to hydrocarbon exposure after 42 days and below 2 cm deep.The application of dispersant resulted in an accelerated and modified shift in bacterial communities. Bacterial 16S rRNA genesequencing revealed dominance of Colwellia and Fusibacter in oil and oil and dispersant treatments, respectively. The increasedrelative abundance of anaerobic hydrocarbon degraders through time suggests creation of anoxic niches due to smothering. Thestudy showed that hydrocarbons can entrain deep sediments to over 4 cm in a short time and that FSC indigenous bacteria areable to respond to a contamination event, even at a low temperature, reflecting the in-situ conditions.
Deep sea oil exploration is increasing and presents environmental challenges for deep ocean ecosystems. Marine oil spills oftenresult in contamination of sediments with oil; following the Deepwater Horizon (DwH) disaster up to 31% of released oil wasdeposited as oily residues on the seabed. Although the aftermath of DwH was studied intensely, lessons learned may not be directlytransferable to other deep-sea hydrocarbon exploration areas, such as the Faroe-Shetland Channel (FSC) which comprises coldtemperatures and a unique hydrodynamic regime. Exploration of FSC oil reserves in waters >1000 m deep increases the need tofurther understand implications of potential spills. In this work, transport of hydrocarbons into deep FSC sediments, subsequentresponses in benthic microbial populations and effects of dispersant application on hydrocarbon fate and microbial communitieswere investigated. Sediment cores from 1000 m in the FSC were incubated at 0°C for 71 days after addition of a 20 hydrocarboncomponent oil-sediment aggregate. Dispersant was added periodically from day 4. An additional set of cores using sterilised andhomogenised sediment was analysed to evaluate the effects of sediment matrix modification and biotic influence on hydrocarbonentrainment. Layers of sediments were independently analysed for hydrocarbon content and bacterial community. Oil entrainedover 4 cm deep into FSC sediments after 42 days and dispersant effectiveness on hydrocarbon removal from sediment decreasedwith time. Sterilising and homogenising sediment resulted in hydrocarbon transport over 4 cm into sediments after 7 days.Significant shifts in bacterial populations were observed in response to hydrocarbon exposure after 42 days and below 2 cm deep.The application of dispersant resulted in an accelerated and modified shift in bacterial communities. Bacterial 16S rRNA genesequencing revealed dominance of Colwellia and Fusibacter in oil and oil and dispersant treatments, respectively. The increasedrelative abundance of anaerobic hydrocarbon degraders through time suggests creation of anoxic niches due to smothering. Thestudy showed that hydrocarbons can entrain deep sediments to over 4 cm in a short time and that FSC indigenous bacteria areable to respond to a contamination event, even at a low temperature, reflecting the in-situ conditions.