A 'Dead Zone' in The Gulf of Mexico
Scientists Say Area That Cannot Support Some Marine Life Is Near
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
"It smells like rotten eggs," she said. "It's really
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
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."