Massive 'Dead Zone' Threatens Gulf Marine Life

The effects of the BP oil spill on marine life in the Gulf of Mexico may be overshadowed, at least for the moment, by a more chronic threat: The arrival of the dead zone. It's an area of deep water in the Gulf where little, if anything, can live.

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RENEE MONTAGNE, host:

And we're going now from a top kill in the Gulf to the dead zone. It's an area of deep water in the Gulf where little, if anything, can live. And the threat from the oil spill to marine life there may be overshadowed - at least for the moment - but this chronic threat.

As NPR's Christopher Joyce reports, this year's dead zone is one of the biggest ever - the size of Massachusetts.

CHRISTOPHER JOYCE: The dead zone is huge blob of oxygen-deprived water that forms in the northern Gulf almost every year. It's called dead because there's too little oxygen in the zone for most sea creatures to live on. They either flee or die.

Marine scientist Nancy Rabalais has been mapping the zone, and says that this summer's is one of the biggest ever, stretching from the mouth of the Mississippi River, west to Galveston, Texas. Speaking on a dock in Louisiana after her latest survey, Rabalais says the source of the problem is what comes down the Mississippi River.

Ms. NANCY RABALAIS (Marine Scientist, Louisiana University's Marine Consortium): We're at a high river stage for the Mississippi River right now. It's above-normal flow, so there's a lot of fresh water and nutrients, such as nitrogen and phosphorous, going into the Gulf of Mexico right now. And that's what basically starts the creation, the formation of the low-oxygen area, the dead zone offshore.

JOYCE: Nitrogen and phosphorous are like plant food for tiny phytoplankton that float in the warm Gulf waters. The more nutrients, the more phytoplankton reproduce. When these tiny plants die, they fall to the bottom and decompose. That decomposition essentially burns up the oxygen in the water. The result is dead water.

The dead zone is well west of the BP oil spill. Nonetheless, scientists have been concerned that oil in the Gulf could act the same way as nutrients: become food for microscopic animals. Rabalais says it's too soon to tell about the spill's effects.

Dr. RABALAIS: This could have had an impact on the amount of low oxygen that we found because bacteria will consume those hydrocarbons, and in that process, will suck up the oxygen. We didn't see any evidence of that.

JOYCE: Rabalais, who's with the Louisiana University's Marine Consortium, says the source of most of the nutrients in the dead zone is clear: fertilizer on Midwestern farms.

Nine years ago, the federal government promised to find ways to reduce the flow of those nutrients. But for the past five years, the average nutrient load in the river has been higher than ever.

Dr. RABALAIS: It didn't seem that it would be that difficult. We thought it would only take about a 30 percent reduction in the nitrogen in the river. But, as you can see now, the average is much higher than it has been. You can see that we're well away from the goal that we want.

JOYCE: Government scientists and their colleagues in academia say it's hard to change traditional agriculture across the Midwest. Among them is Jerry Glover, an ecologist with the Land Institute, which advocates for perennial crops instead of the annuals that you have to plant every year from seed.

Dr. JERRY GLOVER (Ecologist, Land Institute): What we need to face up to is the fact that we're growing crops that aren't well-suited to that environment up there.

JOYCE: Glover points out that annuals don't put down deep, permanent roots.

Dr. GLOVER: They're not taking up nutrients and water from deep on the soil. This allows nutrients to run off the soil surface when it rains, and eventually, in the case of the Corn Belt region of North America, make their way down to the Gulf of Mexico.

JOYCE: Scientists trying to stem the dead zone say there is federal money to study solutions, such as planting cover crops in the winter to reduce runoff. But there's far more federal money in subsidizing traditional agriculture, and more money for the moment for cleaning up the oil in the Gulf.

Christopher Joyce, NPR News.

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