The Variable Influence of Dispersant on Degradation of Oil Hydrocarbons in Subarctic Deep-Sea Sediments at Low Temperatures (0-5 °C)

Abstract

The microbial degradation of petroleum hydrocarbons at low temperatures was investigated in subarctic deep-sea sediments in the Faroe Shetland Channel (FSC). The effect of the marine oil dispersant, Superdispersant 25 on hydrocarbon degradation was also examined. Sediments collected at 500 and 1000 m depth were spiked with a model oil containing 20 hydrocarbons and incubated at ambient temperature (5 and 0 °C, respectively) with and without marine dispersant. Treatment of sediments with hydrocarbons resulted in the enrichment of Gammaproteobacteria, and specifically the genera Pseudoalteromonas, Pseudomonas, Halomonas, and Cobetia. Hydrocarbon degradation was faster at 5 °C (500 m) with 65-89% of each component degraded after 50 days compared to 0-47% degradation at 0 °C (1000 m), where the aromatic hydrocarbons fluoranthene, anthracene, and Dibenzothiophene showed no degradation. Dispersant significantly increased the rate of degradation at 1000 m, but had no effect at 500 m. There was no statistically significant effect of Superdispersant 25 on the bacterial community structure at either station. These results show that the indigenous bacterial community in the FSC has the capacity to mitigate some of the effects of a potential oil spill, however, the effect of dispersant is ambiguous and further research is needed to understand the implications of its use.

Figure 1

Mass of each aliphatic hydrocarbon group degraded during slurry incubations in FSC500 at 5 °C. Error bars are standard deviation, n = 3. Black lines are model oil and grey are model oil + dis.

Figure 2

Mass of each aliphatic hydrocarbon group degraded during slurry incubations in FSC1000 at 0 °C. Error bars are standard deviation, n = 3. Black lines are model oil and grey are model oil + dis.

Figure 3

Mass of each PAH degraded during slurry incubations in FSC500 at 5 °C. Error bars are standard deviation, n = 3. Black lines are model oil and grey are model oil + dis.

Figure 4

Mass of each PAH degraded during slurry incubations in FSC1000 at 0 °C. Error bars are standard deviation, n = 3. Black lines are model oil and grey are model oil + dis.

Figure 5

Summary of bacterial communities in slurry incubations: Panel A) Relative abundance of top 50 OTUs (No sample collected for T0 FSC1000 model oil treatments as they did not differ from control T0). Panel B) nMDS based on Jaccard index; red = FSC1000 and green = FSC500; square points = control, triangles = oil + dis, and circles = oil only; contours show total mass of hydrocarbon degraded, predicted by ordisurf(). Panel C) Cladogram output from LefSe analysis showing consistently differing taxonomic groups between oil treated and control slurry incubations. Panel D) LDA effect scores for output from LefSe analysis. For panels C and D red = control and green = model oil.