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 Gulf of Mexico oil spill in 2010 resulted in the release of millions of barrels of crude oil into the environment. Crude oil and trace metals in it can adversely affect the aquatic and nearby environments. It can increase the total organic matter content of the water and surrounding environments. Organic matter promotes microbial growth and therefore can cause the release of metals and metal-like elements such as arsenic, iron, manganese and mercury. Growth of microorganisms can cause sulfate and iron reduction and the transformation of mercury to methyl-mercury which is a more available form with potential to affect living systems. Thus the overall objective of this research was to explore the effects of the increased organic matter due to the crude oil on metal cycling and microbial activities in sediments from Alabama, Mississippi, and Louisiana coastal wetlands. The specific objective of this component of the collaborative research that spans the fields of geology, chemistry, biochemistry and microbiology focused on analysis of sulfate and iron reducing bacteria. Using most probable number (MPN) method, we enumerated sulfate reducing bacteria and iron reducing bacteria in sediment cores collected from various Alabama, Mississippi, and Louisiana coastal wetlands, to better understand the biogeochemical effects of the oil spill. The sites included three heavily contaminated sites (Bay Jimmy, Bay Batiste and Bayou Dulac in Louisiana), three intermediate sites (Walker Island in Alabama, Point Aux Chenes Bay in Mississippi, and the Rigolets in Louisiana) as well as three pristine sites (Weeks Bay and Long’s Bayou in Alabama, and Bayou Heron in Mississippi). DNA analysis was employed to monitor the nature of bacterial communities in sediment cores at different layers. Overall the Rigolets, an intermediate contaminated site, displayed the highest number of sulfate reducing bacteria (≥1600 MPN/g in all the sediment core samples). In Bay Batiste sediment core samples, a heavily contaminated site, 920 MPN/g at 12-15 cm depth was recorded for sulfate reducing bacteria. A similar number of sulfate reducing bacteria was observed in the 0-3 cm layer of Bayou Dulac Core C, a heavily contaminated site. Nevertheless, MPN of sulfate reducing bacteria in pristine sites (Bayou Heron, Long’s Bayou, Weeks Bay E Core and Weeks Bay F Core), were higher than those observed in some intermediate contaminated sites (Walker Island and Point Aux Chenes Bay) and in some heavily contaminated sites (Bay Jimmy South and Bay Jimmy North). Biogeochemical differences between the sites can influence the composition of microbial communities and their activities. MPN of iron reducing bacteria were all positive for the sediment core dilutions indicating abundance of iron reducing organisms. Nonetheless, non-living processes contribute to iron reduction. DNA analysis of the sites displayed presence of diverse group of bacteria including sulfate and iron reducing bacteria which influence transformation of metals. This study provided relevant scientific information on the gulf oil spill as well as research experience to students.
