The explosion of the oil rig Deepwater Horizon in the Gulf of Mexico on April 20, 2010 has released ~3 million barrels of crude oil to the Gulf as of mid-June (The Economist, 2010). This oil has a range of deleterious effects on the aquatic and coastal ecosystems of the Gulf. One such effect may include alteration of biogeochemical cycling of heavy metals in the coastal wetlands. Cycling of mercury (Hg) and arsenic (As) both depend on microbial activity, particularly iron and sulfate reduction, which may be promoted by the influx of organic matter (i.e. oil). Coastal wetlands are particularly susceptible to heavy metal contamination and may therefore be especially vulnerable to altered heavy metal cycling as a result of the oil spill. This project would examine solids and pore waters from sediment cores in Weeks Bay, Alabama for changes in microbial activity, arsenic concentration and speciation, and mercury concentration and speciation over the next eight to twelve months. Results will be of broad interest to the fields of bioremediation, biogeochemistry, geomicrobiology, and environmental health. During the progress of the study, PIs will be cooperating with local scientists and government officials, and plan on presenting technical seminars and workshops in the Alabama Gulf shore region. Because ocean oil spills are a common environmental problem worldwide, the data gathered in the research should benefit many other affected regions. Research will expose students from Alabama to state of the art methods and to a timely research topic. The Weeks Bay field site will serve as an outdoor laboratory for Auburn University Water Education for Alabama Black Belt (WET) outreach activities and existing courses.
The aim of this project was to determine the effect of the Deepwater Horizon oil spill in the Gulf of Mexico on the movement of metals, such as arsenic and mercury, between the sediments (soils) and waters of the gulf coast. In general sites further to the West, such as Bay Jimmy, Bayou Dulac, and Bay Batiste in Louisiana were more heavily contaminated than those to the east in Alabama such as Weeks Bay, Wolf Bay, and Walker Island. Previous studies have shown that additional organic matter, such as oil, can change water chemistry in ways that promote higher concentrations of dissolved arsenic and a higher proportion of mercury found as the most dangerous form, methyl mercury. Data from this study indicate that this is not happening to a great extent as a result of the gulf oil spill, although numerous heavily oiled sites were sampled. At these sites the total concentrations of metals were in general higher than the concentrations at the less contaminated sites. Bacteria capabable of performing the relevant reactions, primarily sulfate-reducing bacteria, were found in all samples. This may indicate that under the proper conditions it is possible to see the higher concentrations of arsenic and methyl mercury that were expected.
