Dead zone expected to expand

By AMY WOLD–Jul 17, 2007

The hypoxic zone of low oxygen off the Louisiana coast will be as large or larger this summer than ever before measured, according to researchers at the Louisiana Universities Marine Consortium and LSU.

The hypoxic zone — also known as the “dead zone” — will reach 8,543 square miles this summer, researchers said.

The previously largest measured size of the zone was 8,494 square miles in 2002.

This hypoxic zone forms after nutrients such as fertilizer, urban runoff and sewage flow down the Mississippi River and into the Gulf of Mexico. This nutrient-rich water encourages the growth of microscopic organisms. When these organisms die, they fall to the water bottom and use up oxygen as they decompose.

In the summer, this low-oxygen level of water doesn’t get mixed in with the more oxygen rich top layer of water which creates a “dead zone” where the oxygen levels are too low to support life.

The prediction will soon be tested as LUMCON Executive Director Nancy Rabalais leaves for the annual hypoxia mapping trip in the Gulf later this week.

Although the prediction calls for a very large “dead zone” this year, there’s always the possibility that the zone will not be as bad as predicted, Rabalais said.

“This weather we’ve been having has had the tendency to turn up the bottom a little bit,” Rabalais said. That has resulted in better than expected readings of dissolved oxygen at some of the stationary monitoring stations, she said.

The prediction model used by the researchers takes into account the amount of nitrogen found in the Mississippi in May and the amount of water flowing down the river to the Gulf, said Eugene Turner, professor with the School of Coast and Environment at LSU.
Turner, who is married to Rabalais, said this year’s measurements showed higher than average amount of nitrogen in the water while the river flow was below normal. That means the concentration of nitrogen in the water reaching the Gulf is higher than usual, he said.

It takes about two to three months for the nitrogen to have an effect, so the prediction should match what Rabalais will find when the survey starts Friday and will run for about a week,  Turner said.

“We’d love to measure it (the hypoxic zone) in June and August, but we don’t have the money for it,” Turner said. So instead, he said, the mapping survey takes place in July.

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