Induced respiratory pathway controls on the degradation of harmful organic contaminants in marine sediment

Terrestrially derived iron minerals can generally protect marine ecosystems from eutrophication and sulfidization, but the full extent of their ecosystem benefits has not been established. Microbial Fe(III) redox cycling can generate hydrocarbon-degrading hydroxyl radicals. These reactions may occur more frequently in sediments with elevated iron content such as those in the northern Gulf of Mexico. To determine if iron concentrations of marine sediment affect the degradation of hydrocarbons after oil spills, we exposed sediment cores with varying iron content to conditions simulating those of a post-spill seafloor environment.

Three groups of sediment cores with variable compositions were subjected to different oil treatments using crude oil from the Deepwater Horizon well. The cores were subsequently incubated in a flow-through system with saline water from the Indian River Lagoon, Florida. The sediment cores are comprised of variable ratios of quartz sand with and without iron coatings. Kaolinite clay was added to some of the cores to see if porosity differences affects the degradation by affecting the depths of oxygen penetration and intensity of the redox gradient. All cores were inoculated using mud from the Indian River Lagoon. Oil treatments included no oil, low oil (0.00223 g/mL sediment), and high oil (0.0223 g/mL sediment). Each of the sediment variations were sampled at five time periods throughout the experiment to determine the hydrocarbon content. Incubations are ongoing, but early results demonstrate significant differences in redox conditions and oil degradation extent as a function of sediment composition. The next step will be to further narrow down optimal conditions for oil degradation. The results of this research could have significant implications for environmental policy decision making; for example, if the damming of rivers has reduced the resilience of the continental shelf by stemming the flow of terrigenous sediment to ocean basins.