This is a RAPID award to respond to the Deep Horizon oil spill in the Gulf of Mexico. The work involves the time series collection of samples to examine the changes, from baseline conditions to maximum exposure, to the oil leaking out of the deepwater well head to a variety of coastal sites along the Northern Gulf of Mexico. Sampling sites include the intertidal zone at Belle Fontaine Point in eastern Mississippi and the New Harbor Islands in Louisiana. Samples and analytical work will determine hydrocarbon transformations and changes due to biogeochemical processes, changes in bioturbation rates, and changes in the assemblages of benthic macro- and meiofauna over time. Implications of these variables for physical and sedimentary processes and for macrofauna will be assessed. Broader impacts of the work will have immediate implications for understanding the impacts of the oil spill on coastal ecosystems and provide data to examine the time scale of ecosystem crash and recovery. The work will have potential for mitigating the long term effects of the oil spill on coastal systems. The work will also train students and provide public outreach activities that will be carried out in collaboration with the Northern Gulf Institution and with NOAA.
Heavy contamination of marshes by BP oil affected the animals living in the marsh sediment by reducing their numbers, reducing their depth of habitation, and likely as a consequence of these changes, reducing the mixing of surface sediments. This last point is critical to the breakdown and removal of oil, because bacteria consume oil effectively only in aerated sediment. Other research (e.g., oil in the marsh at Buzzards Bay, Ma.) has shown that marsh sediment that is not effectively mixed can sequester toxic oil for many years. We chose coastal marshes in Mississippi and Louisiana that were unoiled, some that were lightly to moderately oiled, and one marsh that was heavily coated by petroleum from the Macondo blowout (Fig. 1). We initially chose these sites using daily observations published by NOAA on their website. We confirmed the quantity of oil at each site by measuring it upon collecting our samples. We then examined the density, depth of habitation, standing crop, and assemblage composition of foraminifera, which are small animals the size of coarse silt and fine sand, and the macrofauna, which are larger animals that do most of the sediment mixing. Then we measured directly the physical rate of mixing using radionuclide tracers. We found that the infauna was reduced at the sites that were heavily oiled. The abundance of foraminifera and their depth of habitation were greatly reduced compared to the uncontaminated and lightly-to-moderately contaminated sites, and we found deformed foraminifera at the heavily polluted site (Fig. 2). We found similar results for the macrofauna. The results suggest that oil contamination from the BP spill, in addition to reducing the numbers of infaunal organisms able to live in the sediment, adversely affects heavily oiled marshes in a way that hinders their ability to break down the oil naturally. By reducing the numbers of animals that mix and aerate the sediment, the oil can persist in the subsurface for decades to come.
