U.S. Water News Online
DAVENPORT, Iowa -- Two years after university researchers
said the Gulf of Mexico's dead zone covered a record 8,006 square
miles -- about the size of Massachusetts -- it has shrunk to about
3,300 square miles, a recent mapping shows.
The dead zone, a summertime phenomenon, is formed where
Mississippi River freshwater enters the salty Gulf. Microscopic
plants called phytoplankton feed on nitrogen and phosphorus in the
river water, but when they die, they decompose and use up the oxygen
in the Gulf.
The zone was smaller this year, about half the average size for
the last decade, because of three tropical storms that re-oxygenated
the water, said Don Scavia, a scientist with the National Oceanic and
While fishermen in the area weren't happy about the weather, they
were pleased that the zone wasn't as large this year, Scavia said.
``The storms came through, stirred up water and broke it into
smaller patches,'' he said. But, ``the overall trend and the overall
problem are still there.''
Hypoxia occurs when algae, stimulated by nutrients such as
nitrogen and phosphates from the Mississippi and Atchafalaya rivers,
settles. Ultimately, it decays at the bottom of the Gulf, NOAA
Researchers believe hypoxia wasn't common in the area before the
mid-1970s, Scavia said.
Between 1985 and 1992, the zone averaged 3,200 square miles,
officials said. Between 1993 and 2001, the area doubled to an average
size of 6,200 square miles. The zone extends about 375 miles west
from the mouth of the Mississippi River.
Forecasters had thought the area would be bigger this year because
of nutrient loads coming from the two rivers in May and June, Scavia
Iowa and Illinois contribute to the nutrients flowing down the
Mississippi. Research projects are underway to determine how city
dwellers and farmers can reduce runoff into streams and rivers.
The new forecast will allow those who study it to predict what
will happen to the area in a specific year, as well as look back and
study what did happen, said Nancy Rabalais, a researcher with
Louisiana State University.
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