Gulf's future depends on oil-eating bacteria, lingering toxicity

of North Carolina, Chapel Hill, collected water samples from 26 May to 8 June aboard the University of Miami’s research vessel Walton Smith. They found that alkane-digesting bacteria have colonized the Deepwater Horizon oil plumes and have begun to consume significant amounts of dissolved oxygen. According to the Environmental Protection Agency, the average concentration of dissolved oxygen in the Gulf of Mexico is 4 mg/L.

  • Likewise, David Valentine, a microbial geochemist at the University of California, Santa Barbara, has observed microbe-associated oxygen declines in plumes of oil and methane gas. In these “gassy” plumes located within a 5- to 7-mile radius of the wellhead and at depths greater than 2,500 feet, oxygen levels have dropped by between 5 and 35 percent, he says. Valentine gathered his samples from June 11 to June 20 while aboard the research vessel Cape Hatteras,operated by the Duke/University of North Carolina Oceanographic Consortium.

    • Schmidt notes that scientists do not know yet exactly which bacterial species are present in these plumes. The Gulf has a “leaky” seafloor, populated with natural seeps that discharge between 560,000 to 1.4 million barrels of crude oil every year, according to “Oil in the Sea III,” 2003 National Research Council report on oil spills. Also hydrocarbons in general are ubiquitous in the ocean and can be found not only in seeping oil but also in plant waxes and lobster shells.

     

    “Many marine bacteria have evolved to consume these hydrocarbons, and now the spill has allowed these bacteria to follow their food beyond their natural habitat near oil seeps at the bottom of the Gulf,” Schmidt writes.

    Oxygen-depleted dead zones

    Microbes may degrade the oil quickly, Valentine points out, but their activity could eventually pose risks to the Gulf’s ecosystem, particularly in the deep ocean. A tremendous increase in the amount of oil available for consumption by bacteria that feed on hydrocarbons in the deep Gulf could generate bacterial blooms that eventually die off, leaving behind vast quantities of biomass. Other bacteria would then metabolize this biomass and deplete oxygen to levels low enough to be dangerous for other organisms, Valentine says. The Gulf of Mexico already suffers from an enormous hypoxic dead zone, measuring more than 8,000 sq miles, generated by nutrient-laden runoff from the Mississippi River (see “Midwest floods to create record dead zone in Gulf