A Smaller Than Predicted Dead Zone Is Still Toxic for the Gulf of Mexico

It may not be as big as researchers predicted last month, but this year's Gulf of Mexico dead zone is larger than average—and a sign of things to come.

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LUMCON (Rabalais)

A map shows the extent of the 2013 dead zone in the Gulf of Mexico

Good news from the Gulf of Mexico—sort of. Last month researchers predicted that the annual summer dead zone in the Gulf—a hypoxic or oxygen-starved stretch of water caused chiefly by fertilizer runoff from the Midwest farm belt—would be among the biggest on record. It was a reasonable enough guess—after a 2012 that saw much of the Midwest gripped by drought, reducing runoff and shrinking that year’s dead zone, the spring of 2013 brought heavy rainfall and flooding to states like Minnesota and Illinois, which usually translates into lots of runoff and a very big dead zone. Researchers from the University of Michigan, Louisiana State University and Louisiana Universities Marine Consortium (LUMCON), supported by the National Oceanic and Atmospheric Administration (NOAA) forecast a dead zone as large as 8,561 sq. miles—roughly the size of New Jersey—which would have made it the largest such hypoxic event on record.

But the results from the summer mapping expedition in the Gulf are in, and the actual dead zone turned out to be somewhat smaller: 5,800 sq. miles, or about the size of Connecticut. Of course, as anyone who’s had to drive through the Nutmeg State on a winter’s day, 5,800 sq. miles isn’t that small. 2013 is still nearly twice as large as last year’s drought-starved dead zone, which came in at 2,889 sq. miles (the size of Delaware, for what it’s worth), and larger than the average hypoxic event as measured since 1985.

Nancy Rabalais, the executive director of LUMCON and the leader of the survey cruise, noted that some later weather conditions likely mixed oxygen into the hypoxic waters of the Gulf, keeping the dead zone smaller than it would have otherwise been:

A near-record area was expected because of wet spring conditions in the Mississippi watershed and the resultant high river flows which deliver large amounts of nutrients. But nature’s wind-mixing events and winds forcing the mass of low oxygen water towards the east resulted in a slightly above average bottom footprint.

As I wrote last month when covering the dead zone projections, hypoxia is a consequence of the use and abuse of nitrogen-based fertilizers in the farm belt:

The nitrogen nutrients that flow into the Gulf, especially during the rainy spring season, encourages the growth of explosive algal blooms, which feed on the nitrogen. Eventually those algae die and sink to the bottom, and bacteria there get to work decomposing the organic matter. The bacteria consume oxygen in the water as they do, resulting in low-oxygen (hypoxic) or oxygen-free (anoxic) regions in the bottom and near-bottom waters.

That’s what a dead zone—water, essentially, without air. Sealife—including the valuable shellfish popular in Gulf fisheries—either flee the area, much as you or I would if someone were to suck all the oxygen out of the room, or die. That’s why the dead zone matters—the larger it is, the greater the populations of fish that might be affected. With commercial fisheries in the Gulf worth $629 million as of 2009—and still recovering from the impact of the 2010 oil spill—the dead zone means business.

We got lucky this summer—and that’s a relative term. This year’s dead zone is still three times larger than the 1,900 sq. mile goal that was set in 2001 and reaffirmed in 2008 by the Mississippi River Gulf of Mexico Watershed Nutrient Task Force, which I have to say could really use an acronym. The reality is that with commodity prices for crops like corn and soybeans sky high—thanks in part to government mandates for corn ethanol—farmers are taking advantage by planting every square inch they can. In North Dakota, land set aside for the Conservation Reserve Program has dropped in half since 2007, largely because farmers can make more money planting than they can from the government for leaving their fields fallow.

More acres planted means more fertilizer, which means more runoff—and a bigger dead zone. Which is how 5,880 sq. miles of oxygen-starved water in one of the most productive fisheries in the U.S. somehow seems like a victory.