Death in the Gulf of Mexico
With dead creatures at its bottom and survivors fleeing its edges, an annual "dead zone" spooks fishermen and challenges scientists
- Joby Warrick
- Jun 01, 1999
Just south of Whiskey Pass, where the last of Louisiana´s barrier islands gives way to open sea, Gene Foret cuts the throttle and eases his boat across an unseen boundary. All around him the water looks as blue as ever, but beneath the boat an ocean of life quietly fades to black. Foret is entering the "dead zone."
In the space of a few dozen yards, one of America´s most productive fisheries becomes startlingly devoid of fish below the upper water layers. Shrimp disappear, too, and so do crabs and anything else that swims. A wall of dead water spreads westward across the floor of the Gulf of Mexico, beginning at this point near the Mississippi Delta, stretching as far as the Texas border and reaching up the water column toward the boats on the surface. On this breezeless August day, it covers an area the size of Connecticut.
The emptiness of the water clearly rattles Foret, a fishing-boat pilot and shrimper´s son. "You can almost feel it when you´re in it," he says of the gulf´s dead zone. "There are no fish here. None. Drop a line in the water and your bait rots on the line."
A decade ago, few outside the fishing trade had even heard of the dead zone--angler´s slang for the enormous body of oxygen-depleted water that appears in the gulf every summer south of New Orleans. Before the 1980s, small patches of lifeless water occasionally would turn up like a summer rash near the shoreline, where pollution and fertilizers from the Mississippi River promoted a toxic stew in the gulf´s warm, slow-moving currents. It´s the same pattern that occurs nearly every year in parts of the Chesapeake Bay, Pamlico Sound in North Carolina and other spots where pollution from rivers mingles with brackish water.
But in the Gulf of Mexico the dead zone has evolved from a curiosity to a colossus, a recurring environmental nightmare that just keeps getting bigger. Following the 1993 Midwestern floods, the dead zone suddenly doubled in size to 7,000 square miles--the largest on record in the hemisphere in coastal waters and one of the biggest in the world.
The gulf dead zone has grown nearly as large every year since then, and scientists say it will be back again this summer, repeating a cycle that is just now becoming fully understood. Already, gulf watermen are making preparations, budgeting for the extra travel time and fuel they´ll need to find fish and shrimp. But what happens, some ask, if the dead zone grows larger still?
"To this point we´ve learned to fish around it," says Johnny Glover, owner of a marina and a fleet of charter boats in Cocodrie, a fishing village in bayou country. "But if something isn´t done, it could expand and take over the whole gulf. And then we´re all in trouble."
The first orange streaks of sunrise are just beginning to show in the east, but Glover has already been hard at work for hours. After slapping out Cajun-spiced eggs and toast for a few dozen hungry fishermen, he sets out in a small whaler for an early reading on the kind of day he will have. Just before 6 am, he finds a shrimp boat stirring and pulls alongside for some bait and the latest fishing news.
"Lo, Johnny, I didn´t know that was you," booms a deeply accented voice. "Not much going on out here today." For Glover, this is more than idle conversation. Six of his charter boats are just now cruising toward the gulf with cash-paying sports fishermen eager to bag a red snapper. Lousy fishing is always bad for business, no matter the reason, and these days the dead zone is making the odds even tougher.
"Nobody wants to pay a few hundred dollars if they think they´re not going to catch any fish," says Glover, whose Coco Marina is a launch point for fishing trips.
So far, oxygen depletion, called hypoxia, has inflicted a greater toll on the gulf´s image than on fishing itself. Lately, some of Glover´s prospective clients are asking about the dead zone when they call, wondering if they might get sick. Others, he guesses, are simply doing their fishing elsewhere. Glover can usually reassure jittery callers, and he nearly always finds fish. But he sometimes has to do some fancy maneuvering when the dead zone oozes into his usual fishing areas. "It moves around. It shrinks and expands," he says.
For commercial fishermen the dead zone´s impact has been curiously mixed. Al "Jacko" Darda, a bayou shrimper from Dulac, Louisi-ana, describes dead-zone encounters where his nets have come up eerily empty. "Maybe you get a tire or a toilet seat," he says. But others have learned to turn adversity into advantage, trawling around the edges of the zone to vacuum up clouds of shrimp and fish fleeing to safer waters. Such tactics have helped keep the shrimp harvest high, but they haven´t relieved the anxiety many watermen say they feel. "It´s a cancer," says Bobby Theriot, a Cocodrie oysterman. "It keeps getting bigger."
Charter-boat skipper Foret suspects a connection between the dead zone and the loss of Louisiana´s tidal wetlands, which are disappearing at the astonishing rate of 30 square miles a year due to erosion and channelization of the Mississippi.
Although the wetland disappearance has little immediate connection to the dead zone, both problems are related to the mighty river. Its connection to the dead zone has become clear in part because of research that takes place in an imposing, spaceshiplike building next to Glover´s marina, the Louisiana Universities Marine Consortium. Here, since 1985, marine ecologist Nancy Rabalais´ definitive work has helped lift the fog on the dead zone´s complex causes and mysterious cycles while providing hints about possible solutions.
On the walls outside Rabalais´ office are photographs of dead crabs, mementos from her research dives into one of the most chillingly lifeless spots imaginable. The visible signs of change, she says, begin emerging in late spring, as the sun´s growing intensity plays a role in separating the water into layers. Warmer, nitrogen-rich fresh water arriving from the Mississippi slides like a glass lid over gulf waters, which are cooler and saltier and thus heavier. Nutrients "green" up the surface like fertilizer on a lawn, causing algae to multiply at a breakneck pace. Eventually the plants die and sink to the bottom, where bacteria consume them and suck up the limited amount of oxygen available.
As levels of dissolved oxygen drop below 5 parts per million (ppm), many creatures begin to show signs of stress. Below 2 ppm, Rabalais says, the water is considered hypoxic. "Anything that can leave, leaves," she says. As the oxygen level drops further, slower creatures such as crabs and snails die and appear on the bottom. Below 1 ppm, the sea floor becomes strewn also with dead worms and other bottom dwellers that crawl from the mud in search of oxygen. In the dead zone the bodies often remain undisturbed for weeks because there is nothing to eat them.
Rabalais tracks the stages by boat, measuring bottom oxygen levels at monitoring stations scattered across hundreds of square miles. That´s how she detected the dramatic doubling of the dead zone after the 1993 floods. Rainfall amounts returned to normal the following year, but to Rabalais´ amazement, the dead zone did not shrink back to its pre-flood size. "The next year it was still big," she recalls.
What followed was even worse. Since 1993, the dead zone has surpassed 6,000 square miles each year, peaking at 7,032 miles in 1995. It appeared to retreat slightly in 1998, to 4,800 square miles, but in fact it merely changed its shape. Last year´s hypoxic zone grew deeper as it narrowed, moved into deeper waters and affected a large portion of the water column. "On the map it appears smaller, but the volume was about the same," Rabalais explains.
Eventually, as it does every year, the dead zone will break up when autumn´s cooler temperatures cause the gulf´s stratified layers to weaken and mix. Sometimes a hurricane accomplishes the same feat earlier in the season, but in other years the storms barely make a dent. In 1997, Hurricane Danny hovered directly over the hypoxic area for several days, yet its high winds and 15-foot seas had virtually no effect. "Every year," Rabalais says, "we learn something new."
Some of the findings by Rabalais and other scientists likely will have consequences that extend far beyond the gulf. If specific upstream sources of pollutants such as farms are found to be partly responsible for the dead zone, they certainly will face pressure to participate in a solution--one that could prove to be costly.
In recent months, in response to concerns about the dead zone, the Clinton administration has attempted to distill the newest discoveries into a single volume for use by a task force of federal and state policy makers. Also, the U.S. National Oceanic and Atmospheric Administration (NOAA) has compiled reports from six scientific teams that examined virtually every aspect of the problem, from causes to the costs of various remedies.
One key result, says NOAA Coastal Oceans Program Director Donald Scavia, is that officials now can attribute the problem to human activities farther upstream on the Mississippi, which drains 40 percent of the U.S. mainland and supplies 90 percent of the freshwater flow into the gulf. "This had been controversial but now it is clear," Scavia says. "The size and duration of the hypoxic zone is very clearly driven by the nutrient load in the Mississippi River."
The finding is important because it puts to rest the argument that the dead zone is a natural, if previously under-appreciated, part of the gulf´s ecology. Natural hypoxic zones have been found elsewhere in the United States; indeed, North Carolina´s Pamlico Sound is thought to have experienced dead zones hundreds of years before the arrival of European settlers.
But there´s no evidence of such a pattern in the Gulf of Mexico. Studies of sediments suggest that nutrient levels reaching the gulf were relatively low prior to the nineteenth century, when European settlers chopped down the great forests of the northern Great Plains to create one of the world´s most productive agricultural regions.
As farming practices modernized, the nutrients trickling into the gulf from the Mississippi River turned into a torrent by 1950, and the flow increased virtually every year thereafter until it stabilized a decade ago. About 15 percent of the nitrogen comes from fixed-point sources such as municipal wastewater plants. Another 15 percent comes from gases given off by automobiles, and the rest mostly comes from runoff from nutrient-rich pastures and croplands.
"The gulf has become the end of the pipe for American agriculture," University of Minnesota economist Ford Runge told a meeting of the dead-zone task force in Minneapolis last fall. "Dealing with the problem will require that we look at the millions of individual farm fields arrayed all the way up the Mississippi basin."
Exactly how upstream states may be asked to change their habits may not be decided for a year or more. Some of the options identified by the NOAA scientific teams include proposals for reducing agricultural sources of nitrogen--by cutting fertilizer use, for example, or tightening controls on livestock waste. Other, less painful alternatives may involve creating wetlands or wooded buffer zones along the river to remove nitrogen naturally from the water before it gets to the gulf.
Each of the proposed solutions likely would face resistance. At the task-force meeting in Minnesota, Gerald Tumbleson, president of the state´s corn growers´ association, complained that politicians were rushing to blame farmers before all the evidence was in. "Making emotional decisions instead of scientific decisions is something that scares us," he said.
Back in Cocodrie, such talk has dampened expectations for a quick demise to the dead zone, but some see the debate as a hopeful sign. At the very least, says marina-owner Glover, states along the Mississippi are being forced to consider the connections that can tie river communities a thousand miles apart. "What we now know is this: Everything that goes in the river ends up in the gulf," he says. "Things that have happened way upriver can affect us right here, today."
Joby Warrick, a reporter from The Washington Post visited the dead zone for this article.
NWF Takes Action: Stopping Runoff Before It Starts
Halting various proposed projects in the lower Mississippi River basin that would destroy critical wetlands and wildlife habitat to create more agricultural land is an NWF priority. One goal of these efforts, which involve collaborations with the Mississippi Wildlife Federation (an NWF affiliate) and other groups, is to stop new sources of nutrients from flowing into the river and ultimately the Gulf of Mexico, where they contribute to the formation of the dead zone. In one example, NWF and Trial Lawyers for Public Justice took the U.S. Army Corps of Engineers to court last fall to stop a major dredging project.