What the Gulfs low-oxygen dead zone means for you

By Robert Morris
September 17, 2007, Daily Comet, Thibodaux

GULF OF MEXICO — The sun glinting off the wave swells was like a false promise, a trick of light that inspired fantasies of mighty fish and schools of shrimp below.

Instead, the divers said as they surfaced, all they found was a lifeless wasteland.

“No fish, nothing on the bottom,” said Melissa Baustian, an LSU Ph.D. candidate. “No barnacles down there, either.”

Replacing oxygen meters on the 65-feet-deep leg of an oil platform 11 miles out in the Gulf, Baustian had emerged from ground zero of a yearly genocide. Every summer, a complex chain of chemical reactions causes the runoff from fertilizer on Midwestern cornfields to rob the Gulf floor of its oxygen and, subsequently, its sea life.

This phenomenon, known as Gulf hypoxia to scientists and the dead zone to most everyone else, has implications for not only south Louisiana’s seafood-dependent culture, scientists say, but its land rebuilding efforts as well.

“I’m surprised not more people in this area know about it,” said Lora Pride, another researcher on the Pelican during last week’s tour of the dead zone. “This is your area. This is your culture.”


Why should you care about the dead zone? For starters, it’s simply an environmental disaster, said Baustian, whose Ph.D. dissertation examines one aspect of the dead zone.

If calamity is not cause enough for concern, the dead zone is destroying your livelihood if you are a shrimper, or your playground if you enjoy sportfishing, the scientists said.

What starts as the basic nutrients necessary to grow corn in the nation’s breadbasket ends up a several-thousand-square-mile swath of the Gulf coastline uninhabitable for most marine life. In the spring, rain and mountain snow thaw sweep fertilizer down the Mississippi and into the Gulf.

That fertilizer then does its job, prompting explosive growth of algae on the top of the water. The algae then dies, sinks to the bottom and rots, where its decomposition sucks up the oxygen.

Meanwhile, the top layer of water infused from the Mississippi is substantially fresher than that at the bottom, creating a sort of barrier, so oxygen from the top can’t diffuse down to the bottom where shrimp and many fish species feed. Unable to breathe, the sea creatures flee, and those that can’t die.

Very few species will try to live at the top.

“You know they’re stressed and just trying to survive,” Baustian said.

The dead zone forces most other species out to the edges, and the fishermen who make their living off them have no choice but to chase them. That can lead to either high gas expenses, as fishermen must go farther and farther offshore to pass the dead zone and find a catch, or stiffer competition for the seafood remaining inshore.

“It can affect the season as well,” Pride said. “It could be a boom one year, and next year not be so great.”

The dead zone has obvious effects on sportfishing, as the big game fish are pushed farther out to sea, Pride said.

The low oxygen levels also prevent some species, such as large clams, from living on the sea bottom at all. They start growing over the winter, but as soon as the spring dead-zone cycle begins, they are all killed off.

“They’re just not there. They never get the chance to fully develop,” said Nancy Rabalais, executive director of LUMCON and a pioneer in Gulf dead zone research. “They get knocked back every year.”

The dead zone has another ill effect. The same conditions that create it can also lead to the formation of red tide, a poisonous algae bloom that leads to beach closings and fish kills.

The dead zone emerges at the mouth of the Mississippi in the late spring and early summer, gets swept west toward Texas by the current, and peaks in size in the late summer. In late July, scientists measured it at 7,900 square miles, its third-highest in more than 20 years. As the fall storms start in the Gulf, however, the oxygenated water along the top is being mixed with the dead zone on the bottom, wiping it away until next year.


Some research indicates that the dead zone may also be related to the controversial environmental scapegoat of late, global warming.

“You’re always going to have some people who think global warming contributes to things, and some people who don’t,” Pride said. “You’re always going to have two sides, with believers on both sides.”

Global warming’s effect could be at least twofold, Rabalais said. It could cause increased rainfall upriver, sending more fresh water and more nutrient runoff downstream into the Gulf, increasing the ingredients for hypoxia. Second, the heat and light could ripen the conditions for algae growth on the top of the water, also increasing the hypoxia underneath.

On an ironic note, one proposed side effect of global warming may decrease the size of the dead zone: More hurricanes, Rabalais said, will mix up the water and increase oxygen at the bottom.

Closer to home, the chain of chemical events that lead to the dead zone every year also has consequences for south Louisiana’s vanishing coastline. A number of land building projects call for diversion of freshwater from the river, but the nutrient load in the Mississippi River could have serious consequences – some good, some bad – for Terrebonne’s disappearing swamps and marshes if dumped incautiously upon them, scientists say.

On the one hand, the nutrients could do the same thing for swamp plants that they do for corn and Gulf algae: make them grow.

On the other, an overdose of nutrients might serve as a poison, or lead to the growth of the poisonous fish-killing red tides.

“It’s an ecological fact that you can overwhelm a system with too much nutrients,” said Kerry St. Pé, director Barataria-Terrebonne National Estruary Program.

While the swamps do have the effect of pulling some nutrients out of the freshwater, it is not nearly enough to stop the hypoxia cycle in the Gulf, Rabalais said.

“To remove the amount of nitrogen that needs to be removed,” Rabalais said, “you would need to have many, many, many more acres of wetlands than are available in coastal Louisiana for that to be effective.”


Even acknowledging the potential for damage, the swampland desperately needs that infusion of fresh water.

“The bottom line is, we can’t afford to wait for these nutrient issues to be fixed to start to restore the coast,” St. Pé said. “Given the choice between algae blooms and complete loss of wetlands, I’ll take algae blooms.”

The key for the marsh is to bring the water in cautiously, St. Pé said. Bring in small amounts, enough to help without overwhelming the system, and pass it over wetlands before it reaches open water. Don’t drop it directly into bays or lakes, or algae blooms and fish kills like those seen in Lake Ponchartrain are likely to appear.

Relying on the swamp to clean up the farmlands’ mess, however, would be both naïve and dangerous, the scientists said.

Instead, the government should proceed with what it has already promised to do, clean up the fertilizer pollution, the scientists said. That way, the wetlands can be watered without fear, and the dead zone will shrink.

“The most effect way to reduce the nutrients in the dead zone is to get them at the source,” Rabalais said.

How to clean up the river, however, is a thorny question. The so-called polluters are not regulator-dodging chemical factories; they are farmers, simply growing the food that the rest of the country eats.

In 2001, the Environmental Protection Agency fostered the draft of an “Action Plan” to reduce the size of the dead zone to a fraction of its current size, using management practices that reduce the amount of nutrients in the river. State and local governments all the way up the river signed on, but the dead zone has continued to grow.

Is there hope?

“At some point, has to make a decision about what needs to be done,” Rabalais said.

Until that time, what should be an ocean kingdom will continue to transform, every summer, into a desert.