The Gulf's Growing 'Dead Zone'

The American Midwest is essentially the granary of the world, supplying corn, wheat and other crops to markets from Chile to China. But all that food doesn't grow by itself. In 2006 U.S. farmers used more than 21 million tons of nitrogen, phosphorus and other fertilizers to boost their crops, and all those chemicals have consequences far beyond the immediate area. When the spring rains come, fertilizer from Midwestern farms drains into the Mississippi river system and down to Louisiana, where the agricultural sewage pours into the Gulf of Mexico. Just as fertilizer speeds the growth of plants on land, the chemicals enhance the rapid development of algae in the water. When the algae die and decompose, the process sucks all the oxygen out of the surrounding waters, leading to a hypoxic event — better known as a "dead zone." The water becomes as barren as the surface of the moon. What sea life that can flee the zone does so; what can't, dies.

Since 1990 the dead zone, which begins in summer and lasts until early fall, has averaged about 6,046 sq. mi. But the threat is growing. A study released last week by scientists from Louisiana State University (LSU) and the Louisiana Universities Marine Consortium estimated that this year's dead zone would be more than 10,000 sq. mi., roughly the size of Massachusetts. But that prediction was made before massive floods hit the Midwest: with the flow of the Mississippi at dangerous levels, and with rains sweeping fertilizer off drowned farms, the dead zone could grow even bigger. The Louisiana fishing industry, the second largest in the nation, is already hurting, with shrimp catches falling in the dead zone's wake. The U.S. is not alone in grappling with this aquatic byproduct. As modern, chemically intensive agricultural practices spread around the globe, so does hypoxia; a 2004 U.N. report documents nearly 150 dead zones globally. But none compare to the black hole in the Gulf of Mexico. "This year would be the largest since we've started keeping records," says R. Eugene Turner, a zoologist with LSU who led the modeling effort. "It's definitely getting worse."

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