Dead zone may set record

By Nikki Buskey, Houma Courier
15 June 2011

HOUMA — The colossal flow from this year’s record river flooding could trigger the Gulf’s largest-ever dead zone, scientists say.

The area of low-to-no oxygen, which scientists attribute to fertilizer runoff flowing the Mississippi River from Midwest farms, blooms off the coasts of Louisiana and Texas each summer.

This year’s dead zone could be as large as 9,421 square miles, as big as both New Jersey and Delaware combined, said Nancy Rabalais, director of the Louisiana Universities Marine Consortium in Cocodrie.

Oxygen-starved waters create an inhospitable area of marine landscape that organisms, especially bottom-feeders like crabs and shrimp, must either flee or die. This creates large areas of “dead” sea that give the zone its name.

The largest dead zone on record was recorded in 2002, measuring 8,484 square miles. Last year’s dead zone measured almost 7,722 square miles, about the size of Massachusetts, and extended far into Texas waters.

The dead zone, known to scientists as hypoxia, is fueled by nutrient pollution, excess amounts of nitrogen and phosphorus that are introduced into the Mississippi River through human activities like large-scale agriculture.

The increased nutrients, coupled with the warm summer sun, work as fertilizer in the Gulf and trigger an explosion of algae growth that soon sinks and decomposes, consuming most of the life-giving oxygen in the water.

Scientists measure the load of nitrogen in the Mississippi River system to predict the size of the dead zone each year.

This year saw the biggest flow of river water into the Gulf in the last 38 years, said Gene Turner, a marine scientist at Louisiana State University and lead dead zone forecaster.

“Even though we’re past the peak of the flood right now, the river flow is at least two times greater than it usually is, and it’s expected to remain that way for awhile,” Rabalais said.

According to U.S. Geological Survey estimates, 164,000 metric tons of nitrogen flowed down the Mississippi and Atchafalaya rivers to the northern Gulf in May. That’s 35 percent higher than average.

That’s not a record-breaking amount of nitrogen, Turner said, but it’s enough to ensure a possibly record-breaking dead zone.

The Gulf is more sensitive to nutrient influence now because the dead zone builds on itself every year, Turner said. Nutrients that weren’t consumed during last year’s dead zone remain on the Gulf floor, feeding the phenomenon this summer as part of a legacy effect.

Though the dead zone happens every year, it could deal yet another blow to fishermen still suffering from repeated hurricanes and last year’s BP oil spill, which shut down fishing grounds in much of the state. Its effects on the environment and Gulf fisheries are largely unknown, though scientists have discovered the stress of the dead zone may cause drastic biological changes in some species.

Croakers, a species of Gulf fish, have been found to change their sex in the dead zone.

“That’s a serious environmental effect,” Turner said. “We have the one of the largest fisheries in the U.S., but we’ve got fishermen having to travel further to find fish and shrimp and wasting fuel to do that. We believe some migratory paths of species might be blocked for species that feed on the bottom, and there’s a loss of prey that affects the food chain.”

Whether this year’s dead zone will have a big impact on fishermen depends on the “extent, timing and where it ends up laying,” said George Barisich, a shrimper and president of the United Commercial Fishermen’s Association.

Many inshore commercial and recreational fishermen never even encounter the dead zone, said Allen Estay, owner of Blue Water Shrimp Co. in Dulac.

But when the dead zone lines up with prime offshore fishing grounds, it can create a mess, Barisich said.

“The impact shoots through the roof,” Barisich said. “And any shrimp larvae that comes through there, it ends up harming them.”

Fishermen are struggling this year already after getting hit with repeated hurricanes, struggles to receive claims payments for missed fishing time during last year’s Gulf oil spill and now low prices for their catch. This will be another hurdle that some fishermen may not be able to jump, Barisich said.

“We may be dead before the dead zone,” he said.

The size of the dead zone could change if early tropical storms churn up the Gulf and dispel the low-oxygen waters, Rabalais said.

LUMCON’s annual research cruise to map the dead zone will leave from Cocodrie July 25.

Nikki Buskey can be reached at 857-2205 or

The Courier, Houma, Louisiana.

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