Consequences of the oil spill on the Gulf Coast environment revealed

Two researchers in Auburn University's College of Sciences and Mathematics have delivered preliminary results of ongoing research into the effects of the 2010 Deepwater Horizon oil spill, and results indicate potentially serious consequences for the environment. The researchers, Ming-Kuo Lee, Robert B. Cook professor of geology, and Ken Halanych, alumni professor of biological sciences, carried out two separate projects surveying different regions in the gulf, and in each location, effects of the oil spill are persistent. The research suggests the oil spill may have caused massive harm to the environment at a microscopic level, which in turn could have serious repercussions on the food chain in the long term.

Lee, along with graduate students Michael Natter and Jeff Keevan, investigated the fate and transformation of oil found in Louisiana coastal salt marshes that were contaminated by the oil spill. The team found that lighter compounds of oil are quickly degraded by natural microbes, but heavier fractions of oil still remain.

The team used advanced chemical and isotope analyses to detect and trace the presence of spilled oils in salt marsh sediments. They fingerprinted and correlated degraded oils recovered from marsh sediments to their initial sources from the BP Macondo-1 well. Lee and his team then conducted carbon depth profiling in the salt marshes. The depth profiles provided an understanding of the variation of total organic carbon contents below the water column of the marshes. Results indicate that oil contamination is not limited to surface water; elevated organic carbon contents persist in sediments and associated pore-water for months or longer, even after a significant portion of the oil in the surface water has evaporated, dispersed or been degraded by microorganisms. The persistent oil in marsh sediments could desorb slowly and lead to long-term, low-concentration tailing in pore-water. The presence of oil in elution tailing may also have deleterious effects on the aquatic and ecosystems of salt marshes, which provide habitats for many fish, shellfish, water fowl and migratory wildlife.

Lee explained that crude oil also contains a small percentage of trace metals. This trait, coupled with the fact that coastal wetlands are efficient traps of trace metals, means there is a corresponding increase in the level of trace metals in oiled wetland environments.

"Those metals are not biodegradable, thus, they can remain in the marine and coastal ecosystems longer than oil. Tracemetals such as mercury and arsenic are of particular concern because they arebioaccumulated, and in excess they become toxic to wildlife and humans," Lee said.

New research efforts, led by Lee and geology graduate student Kirsten Querra, are currently under way to model the oil intrusion dynamics and accompanying biogeochemical processes in coastal wetlands.

While Lee focused his efforts in Louisiana, Halanych studied various locations along the Alabama coast. His research indicates that small organisms living in the sediment and between sand grains underwent dramatic shifts after the oil spill. Analysis of five sites before, and several months after oiling showed reduced organismal diversity in these microscopic communities. Instead of organismal diversity, the team discovered a dominant presence of fungi. The presence of fungi is often associated with decomposition, and the particular fungal species found have previously been associated with hydrocarbons, suggesting that oiling may have been more significant than was noticeable to the eye.

These microscopic communities are particularly important at the base of the food chain and serve to couple energy flow and nutrients between the water column and sediment. Typically these communities are filled with a diversity of small organisms including various bacteria, nematodes, copepods and protists.

"Because these environments looked relatively normal after the spill, the data suggests that many impacts of the spill were potentially hidden from plain view," said Halanych. "Small perturbations to the environment or food web can often have unexpected effects a long time after the initial event."

Halanych's research represents a multi-institutional effort between Auburn's Molette Biology Laboratory for Environmental and Climate Change Studies, the University of California, Davis Genome Center, the University of New Hampshire and the University of Texas at San Antonio. The team is continuing research on these sites to assess potential ecological impacts of hydrocarbons over longer time scales.

Both studies were funded through the National Science Foundation's RAPID program for quick-response research. To read more about Halanych's research, see the report that was published in the June6, 2012 issue of the journal PLoS ONE, located at this link. Lee's work was published in the journal Environmental Science and Technology, and can be read at this link.

For more information on Lee, visit his website. For more information on Halanych, visit his website.

Last updated: 05/02/2013