Oil Spill: What’s Going On Under the Gulf?

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Map of Gulf dead zone from the Louisiana Universities Marine Consortium

With the coastal cleanup apparently downshifting and BP in the final stages of preparing for a static kill operation to help close the well, we may all soon need something new to obsess/post about. But the battle on the spill is actually just shifting fronts—from the Gulf coast and wetlands that have been the focus of coverage and concern since the Deepwater Horizon exploded on April 20, to the Gulf itself, and the abused waters that lie beneath its surface.

The truth is that the oil spill was just the latest outrage committed against the Gulf of Mexico, the aquatic equivalent of heavily polluted, heavily industrialized northern New Jersey. For years hypoxic events—areas of low-oxygen water called “dead zones“—have bloomed, thanks to the runoff of nitrogen and other nutrients used in farm fertilizer that are carried downstream by the Mississippi and Atchafalaya rivers and dumped into the Gulf. When those nutrients hit the water, they stimulate the growth of algae. When the algae eventually dies, sinking to the bottom of the ocean, they’re decomposed by bacteria—and the process of decomposition sucks the oxygen out of the water, leaving vast parts of the Gulf as lifeless as the surface of the moon. Fish, crabs and other sealife that can flee the area do—those that can’t, die.

How vast is it? Try the size of Massachusetts—or, if you’re like me and don’t really have a solid idea of how big the Bay State is, try 7,838 sq. mi. (20,300 sq. km). That comes from a just released report by Nancy Rabalais of the Louisiana Universities Marine Consortium, who says this summer’s dead zone is one of the largest  since she began documenting hypoxia in the Gulf in 1985. (See Rabalais’s exhaustive dead zone website here.) The record-breaking dead zone is a sign that, despite long-term government goals of reducing hypoxia in the Gulf, the problem only seems to be getting worse, according to Rabalais’s research note:

The size of the summer’s hypoxic zone is important as a benchmark against which progress in nutrient reductions in the Mississippi River system can be measured. The Mississippi River/Gulf of Mexico Nutrient Management Task Force supports the goal of reducing the size of the hypoxic zone to less than 5,000 square kilometers, or 1,900 square miles, which will require substantial reductions in nitrogen and phosphorus reaching the Gulf. Including this summer’s area estimate, the 5-year average of 19,668 square kilometers (7,594 square miles) is far short of where water quality managers want to be by 2015.

The agriculture industry has generally been skeptical of the connection between fertilizer runoff and hypoxia in the Gulf, but it’s unavoidable. Rabalais’s colleague Eugene Turner of Louisiana State University tried to predict the size of the dead zone back in May based on the amount of nutrients flowing into the Gulf, and he was almost perfect. “The size of the hypoxic zone and nitrogen loading from the river is an unambiguous relationship,” he said in a statement. “We need to act on that information.”

Dealing with the dead zone won’t be easy—the nonprofit Environmental Working Group recommends improving soil conservation to prevent runoff, reducing the overuse of nitrate-loaded fertilizers and protecting the coastal wetlands that can help capture that runoff before it reaches the Gulf. But its very existence is a reminder that just because pollution is happening out of view, under the water, doesn’t mean that it’s not real. And even though Rabalais says that it’s unlikely the BP spill has had a positive—or negative—effect on the 2010 dead zone so far, it’s possible that could change in the future. (Just as the bacterial decomposition of algae fuels the hypoxic zones now, bacteria breaking down oil in the Gulf could have a similar effect—though government scientists haven’t yet found evidence of severe oxygen depletion due to the spill.)

Dead zones aren’t the only thing to worry about under the waves. If the oil spill has seemingly vanished overnight, at least some of that credit has to go to the use of nearly 2 million gallons of chemicals dispersants on the oil—including under water. Environmentalists have fretted since the start of the spill about the impact all those chemicals might have on marine life—and Environmental Protection Agency (EPA) head Lisa Jackson pushed BP to limit its use of the chemicals during the spill response. (As it turned out, BP seems to have mostly ignored her—Representative Edward Markey released documents over the weekend indicating that BP had continued heavy use of dispersants even after Jackson’s request, and that the Coast Guard had done little to stop them.)

At the end of June—more than 70 days after the spill had begun—the EPA released toxicity tests on Corexit 9500A, the main dispersant being used in the response. The news was mostly good: Corexit—which is banned in Britain—was “practically nontoxic” in its effects on marine life. Many writers—including myself—noted that the EPA had only tested the effect of the dispersants directly on marine life, even though they’re being mixed with crude oil. Today the agency filled in the missing gap—part of the way—releasing the results of tests that measured the toxicity of dispersants when mixed with oil:

EPA’s results indicate that the eight dispersants tested have similar toxicities to one another when mixed with Louisiana Sweet Crude Oil. These results confirm that the dispersant used in response to the oil spill in the gulf, Corexit 9500A, when mixed with oil, is generally no more or less toxic than mixtures with the other available alternatives. The results also indicate that dispersant-oil mixtures are generally no more toxic to the aquatic test species than oil alone.

Though the agency acknowledged that dispersants represent an environment tradeoff, EPA assistant administrator for research and development Paul Anastas told reporters the widespread use of the chemicals “seems to be a wise decision, and that the oil itself is the hazard that we’re concerned about.” (Read the EPA’s full report here.)

Problem solved? Not exactly, as David Biello of Scientific American notes:

Of course, the new data does not determine where the dispersed oil has ended up; the U.S. National Oceanic and Atmospheric Administration has detected large plumes of it throughout the water column and some scientists have found dispersed oil in crab larvae, among other animals. Nor do the tests mimic the actual conditions faced by the dispersant-oil mixture in the cold, dark, deep waters of the Gulf of Mexico. And it does not dispel fears that the dispersed oil may have long-term toxic effects as it breaks down, both in the water and in Gulf sealife. “In toxicology, it’s quite often not the original compound that’s the toxic entity,” says toxicologist Carys Mitchelmore of the University of Maryland, who co-authored a 2005 National Research Council report on dispersants.

As Anastas indicated, research will surely continue on dispersants—as will the controversy. (The Senate Committee on the Environment and Public Works will hold a hearing on dispersant use on Wednesday.) And I hate to sound like a movie tagline—but the battle under water is just beginning.