Dead Zone

[Plane]

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

That flood made the oxygen problem substantially worse, which may 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.

http://www.msnbc.msn.com/id/25288457/