August 2008


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Phil Gasper <[log in to unmask]>
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Science for the People Discussion List <[log in to unmask]>
Thu, 31 Jul 2008 16:42:04 -0500
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A 'Dead Zone' in The Gulf of Mexico

Scientists Say Area That Cannot Support Some Marine Life Is Near Record Size

By Joel Achenbach
Washington Post Staff Writer
Thursday, July 31, 2008; A02

The "dead zone" in the Gulf of Mexico, an area on the seabed with too 
little oxygen to support fish, shrimp, crabs and other forms of 
marine life, is nearly the largest on record this year, about 8,000 
square miles, researchers said this week.

Only the churning effects of Hurricane Dolly last week, they said, 
prevented the dead zone from being the largest ever.

The problem of hypoxia -- very low levels of dissolved oxygen -- is a 
downstream effect of fertilizers used for agriculture in the 
Mississippi River watershed. Nitrogen is the major culprit, flowing 
into the Gulf and spurring the growth of algae. Animals called 
zooplankton eat the algae, excreting pellets that sink to the bottom 
like tiny stones. This organic matter decays in a process that 
depletes the water of oxygen.

Researchers expected the dead zone to set a record -- even more than 
the 8,500 square miles observed in 2002 -- after the Mississippi, 
swollen with floodwaters, carried an extraordinary amount of nitrates 
into the Gulf, about 37 percent more than last year and the most 
since measuring these factors was begun in 1970.

The researchers set out July 20 aboard the Pelican, a 115-foot 
academic research vessel, and braved 12-foot waves and 35-mph winds 
from the outer bands of Dolly to take samples. The hypoxia began to 
appear about halfway to the bottom in waters ranging from 10 to 130 
feet deep, said Nancy Rabalais, executive director of the Louisiana 
Universities Marine Consortium, which conducted the study. Some water 
samples from the bottom of the water column showed no oxygen at all, 
and instead bore the signature odor of hydrogen sulfide emerging from 
underlying sediments.

"It smells like rotten eggs," she said. "It's really nasty."

The dead zone has been known about for decades but has been studied 
carefully only since the mid-1980s, when Rabalais began making annual 
cruises in late July to measure its extent and characteristics. She 
said the dead zone has roughly doubled in size since 1985.

"I would think an area the size of Massachusetts where you can't 
catch any fish or shrimp, that's significant," Rabalais said.

The hypoxia tends to go away after October as cooler weather slows 
algae growth and storms mix the waters. Even so, there's a "legacy" 
from year to year, said Eugene Turner, a professor of coastal ecology 
at Louisiana State University who makes annual predictions of the 
size of the dead zone. Not all organic matter on the bottom decays in 
any given year.

"For the same amount of nitrogen going in one year, you'll get more 
hypoxia the next year," Turner said.

He said the entire Mississippi watershed, and not merely the Gulf, is 
suffering the effects of agricultural runoff. About half the streams 
and rivers in the watershed are unsafe for swimming, drinking, 
recreational contact or use as drinking water, Turner said. He said a 
major factor is intensified corn production, which relies heavily on 

"The longer you wait to reduce the nitrogen, the harder it is to 
reverse course. It's like going into debt: You have compound-interest 
laws, and you have to back out of that. It's not good," he said.

The dead zone snakes east to west along the Louisiana and Texas 
coasts, starting near the mouth of the Mississippi. As the hypoxic 
region expands during the summer, commercial shrimpers and 
recreational fishermen have to find other areas to cast their lines 
and nets, typically farther out in the Gulf.

Wayne Keller, director of the Grand Isle (La.) Port Commission, said 
that in recent years many people along the Gulf coast have grabbed 
nets and poles to celebrate "jubilees" in which fish and shrimp seem 
to be rushing to the shoreline. But this was not a demonstration of 
nature's bounty, he believes:

"Unfortunately, what it was really showing was everything was going 
to the edge of the dead zone -- everything that could swim and go 
fast enough."