News

June 21, 2008

With floods, a larger ‘dead zone’ feared

Farm runoff could enlarge area of Gulf of Mexico that can’t support sea life.

SETH BORENSTEIN AP Science Writer

WASHINGTON — Floodwaters loaded with farm runoff are heading down the Mississippi River, and scientists fear the deluge will dramatically increase this summer’s dead zone in the Gulf of Mexico, covering an area the size of Maryland.

The dead zone is a region of the gulf that becomes starved for oxygen during much of the summer and cannot support fish or other sea life.

There are hundreds of dead zones around the world that wreak havoc with marine ecology and cut off vast areas for commercial fishing. The zone in the gulf is the largest in the Western Hemisphere.

“It’s going to be a very interesting summer out there just because of this,” said Steven DiMarco, a professor of oceanography at Texas A&M University. “The last time something like this happened, we did see a huge difference” in the size of the dead zone from one year to the next.

The zone off the Louisiana and Texas coasts was first seen in 1972. Its size varies each year, but it has tended to grow through the decades, with a major jump in 1993, after the last big Mississippi River flood.

That flood made the oxygen problem substantially worse, which might happen again this year, DiMarco said Friday.

Even before the flooding, scientists had predicted that the gulf this summer would see its largest-ever dead zone — more than 10,000 square miles. Now experts say it’s likely to be even bigger.

Oxygen in the dead zone is depleted by excess nutrients, mostly nitrates from farm fertilizer runoff, that cause algae blooms. After the algae dies, bacteria on the bottom feast on the remains, removing crucial oxygen from the water.

The dead zone in the gulf forms in early summer and lasts through early fall.

This year’s massive floods will bring a heavier load of fertilizer into the gulf, DiMarco said.

But it’s more than the nitrates. The trillions of gallons of floodwater help trap the oxygen-depleted water near the gulf floor. The fresh water, which stays at the surface because it is less dense, forms a physical barrier that keeps oxygen in the air from mixing with the water covering the dead zone area, DiMarco said.

Scientists are just starting to study how the increasing size of the dead zone is affecting fish.

Think of a giant corridor from Des Moines to Chicago and “you took a great big piece of Saran Wrap over all that area and sucked all the oxygen out,” said Nancy Rabalais, executive director of the Louisiana Universities Marine Consortium. “You would have a big problem.”

Even without the flooding, signs from early spring flooding and heavy fertilizer use were pointing to a record year for the dead zone, said Louisiana State University professor R. Eugene Turner. Earlier this month, using data from before the floods, Turner predicted the zone would break the 10,000-square-mile mark. Last year it covered 7,900 square miles.

Scientists are also worried that the jump in corn production triggered by heightened demand for ethanol fuel could worsen the dead zone because of the increased use of fertilizers. The big question is whether it will make the zone larger, cause it to last longer or become more oxygen-starved, or some combination of those, DiMarco said.

In May, nearly 500 million pounds of nitrates flowed down the Mississippi, Rabalais said. The algae bloom — the first step of dead zones — started a month early this year, in February, she said.

Small towns suffer; more rain likely

• Flooding continued to rip apart small towns along the Mississippi River Friday. As urban areas were spared — the flood highs in St. Louis were some 10 feet below expected near-record levels — little communities took a bashing. Some were protected by levees that were simply not designed to hold back such high waters and couldn’t resist the river. Others had no protection at all and saw the Mississippi surge into their properties.

• Overnight rains made the misery worse and more storms were expected this weekend. But they are not expected to add a significant amount of water to the already swollen river.

• Missouri Gov. Matt Blunt said Friday that the high number of levee breaches shows that the federal government should soon survey the nation’s levees to find out what can be done to provide better flood protection. He said the biggest problem seems to be with dirt levees built privately and by communities to protect farmland.

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