New York Times Article: “Golf of Mexico’s Dead Zone”
By Carol Kaesuk Yoon
It can stretch for 7,000 square miles off the coast of Louisiana, a vast expanse of ocean devoid of the region's
usual rich bounty of fish and shrimp, its bottom littered with the remains of crabs and worms unable to flee its
suffocating grasp. This is the Gulf of Mexico's "dead zone," which last summer reached the size of the state of
New Jersey.
Alarmed, the White House recently commissioned six teams of scientists to begin the first large-scale study of
the area, hoping for a remission or cure.
The dead zone, researchers say, is emblematic of the growing ills suffered by the planet's seas. Earlier this
month, hundreds of scientists, marking 1998 as the international Year of the Ocean, warned that unless action is
taken, overfishing, coastal development, and pollution will multiply the kinds of problems that already plague
the gulf.
The trouble with the dead zone is that it lacks oxygen, scientists say, apparently because of pollution in the form
of excess nutrients flowing into the gulf from the Mississippi River. Animals in this smothering layer of water
near the bottom of the sea must flee or perish.
"You can swim and swim and not see any fish," said Dr. Nancy Rabalais, a marine scientist at Louisiana
Universities Marine Consortium who has dived in the zone. "Anything that can't move out eventually dies."
While scientists have yet to measure the impact of the zone on fishing yields, fishermen say they already feel its
effects as they are forced to travel ever farther to escape the zone's barren limits.
"This is a very serious issue," said Jim Giattina, director of the Gulf of Mexico Program office at the Stennis
Space Center in Mississippi. Giattina said the gulf boasts an annual catch of 1.7 billion pounds of fish and
shellfish, worth $26 billion. "We've seen what can happen in other places in the world," he said. "We don't want
to see a collapse of this fishery."
In fact, researchers say, the problem of rising nutrient loads and accompanying decreases in oxygen, known as
hypoxia, is becoming ever more common in the coastal waters of the United States.
"Hypoxia in the gulf is a dramatic case," said Dr. Don Scavia, director of the National Oceanic and Atmospheric
Administration's Coastal Ocean Program and overseer of the ongoing scientific assessment, "but it's
symptomatic of what's happening coastally." More than half of the estuaries in the country experience oxygen
depletion during the summer, he said, and a third experience a complete loss of oxygen.
Dr. Rabalais and her team have led the research efforts to date on the dead zone, also known as the hypoxic, or
low-oxygen, zone. She and others involved in the new research initiative by the White House Office of Science
and Technology Policy presented their latest findings in December at a meeting of the American Geophysical
Union, in San Francisco.
The scientists trace the trouble to high levels of nutrients, in particular nitrogen, that flow out of the Mississippi
and into the gulf. As in other coastal areas, these rich stores of nutrients feed algal populations which explode
during the summer, producing oxygen, as all plants do. This oxygen stays near the gulf's surface. However,
these blooms eventually fall to the ocean floor. When bacteria begin decomposing the dead algae, they deplete
the oxygen from the ocean bottom, sometimes to the point where none is left.
At the same time, the lighter fresh water flowing in from the river forms a discrete layer on top of the heavier,
salty gulf waters, keeping oxygen in the air from reaching and refreshing the hypoxic zone near the bottom of
the sea.
Among the most compelling pieces of evidence are the maps researchers have made since 1985 of the hypoxic
zone. Scientists measure the zone each summer, when it reaches its peak. Dr. Rabalais carries out the work
along with her colleague and husband Dr. R. Eugene Turner, who is director of the Coastal Ecology Institute at
Louisiana State University and who discovered the zone in 1974.
In 1993, the team witnessed a grand natural experiment as the American Midwest was deluged and the
Mississippi flooded, pouring huge amounts of nutrient-rich runoff from waterlogged cities and agricultural
lands into the gulf. That summer the hypoxic zone doubled in size.
In contrast, 1988 was the year of a great drought in the Midwest, Turner said, and "the hypoxic zone was almost
absent," adding: "That clearly shows the influence of the river is dominant."
The team of researchers has gathered corroborative evidence from mud cores taken from the seabed of the
hypoxic zone, studying algal and animal remains in the cores that are dated using radioisotopes. From these
Turner and colleagues have been able to infer the relative levels of algae and oxygen in the gulf for the past 200
years. They found an increase in the amount of algae deposited, as well as a decrease in the animals that require
high levels of oxygen and an increase in those that can tolerate low levels, such as microscopic, one-celled
creatures known as foraminifera.
The timing of the changes, said Turner, matches well the times of known increases in nutrients in the river, with
levels lowest early in the century and striking increases since the 1950s.
The timing also matches large increases in fertilizer use, suggesting farming as a key source of nitrogen in the
river. In addition, a U.S. Geological Survey study estimated that more than half of the nitrogen reaching the gulf
appears to come from agricultural sources.
But farm fertilizers are not the only likely culprit. A report released in December by the Senate Agriculture
Committee estimated that 1.37 billion tons of manure was produced by livestock in the United States last year
alone, much of it making its way to the sea.
Despite the evidence, scientists remain reluctant to blame the dead zone entirely on farmers.
"We're all fairly convinced that it's going to be agriculture that's going to have to kick in and change to some
degree to make a big difference," said William Battaglin, hydrologist at the Geological Survey, in Denver, and
part of a team tracking the sources of nitrogen in the Mississippi River Basin. "But we don't want to point the
finger at the farmer unless we're absolutely sure. He's the one that's going to suffer."
Agriculture, researchers are quick to note, is not the only source of nitrogen in the river, which drains 31 states
from Montana to New Mexico to New York, including nearly every state between the Rockies and the
Appalachians. Sewage treatment waste water, industrial wastes, and atmospheric pollutants all contribute
nitrogen to the Mississippi. At the same time, difficult questions remain.
Despite the significantly decreased flow of the Mississippi since the great flood of 1993, the dead zone has
grown to essentially the same size every summer. But Dr. Rabalais says there may be explanations for that.
Theoretical models predicted a large dead zone in 1994, the first year after the flood, and every year since then
the gulf has been hit with either floodwaters or pulses of water from the river at just the right time to boost
growth of the algae, making it impossible to say with absolute certainty that the flood of 1993 caused the
explosive growth of dead zone.
"I haven't had a normal year since 1994," Dr. Rabalais said. "The gulf is an uncontrolled experiment."
In addition, researchers say that while the growth of algae and the hypoxic zone appear to be controlled largely
by nitrogen, complicating roles are now known to be played by silica from rocks and phosphorus from
municipal waste waters and fertilizers. But their influence remain less well understood. Another risk with
increasing nutrient loads is an increase in harmful algal blooms, like those seen with Pfisteria and Pseudonitzschia, the algae causing amnesic shellfish poisoning, an illness that can result in permanent memory loss.
Dr. Quay Dortch, an oceanographer at the Louisiana Universities Marine Consortium, said she has already
found blooms of toxic Pseudo-nitzschia in the gulf.
"These are the highest concentrations of this organism registered anywhere," Dr. Dortch said of the Pseudonitzschia found in the plume of the Mississippi. She said they reach their peak when the river's flow into the
gulf peaks. To her surprise, there has been no documented harm so far to humans from these blooms, leaving
Pseudo-nitzschia in the gulf "a potential threat."
Though researchers agree that cutting the levels of nutrients in the river is the way to tame the hypoxic zone, the
best method to do so remains unclear.
For example, Scavia said, though much of the nitrogen appears to be coming from the middle Mississippi, a
region including Illinois and parts of Iowa, that region may not be the best one to try to control first. "It's pretty
far from the gulf," he said. "It may be more appropriate and feasible to control lesser loads in other places."
Until researchers know more, Scavia and others say they are working to find changes that benefit farmers and
the gulf. For example, Giattina said, farmers could turn riverside land into wetland reserves, receiving
compensation at the same time that they create a buffer that reduces the nutrient load draining out of the area.
Such federal and state programs to protect riverside land are now being considered in a number of areas that
have water quality problems linked to agriculture.
In the meantime, each summer brings on a new dead zone that blots out vast stretches of ocean, driving away
fish, shrimp, and the people searching for them. Cynthia Sarthou, campaign director for the Gulf Restoration
Network, in New Orleans, said: "If there was a dead zone 6 to 7,000 square miles in the middle of Iowa, people
would sit up and take notice. This is a problem that needs to be solved."
Reading Questions:
1. Where exactly is this dead zone located (be specific) and how large is it?
2. Using the bar graph, what year had the smallest dead zone & what was the size?
3. What year had the largest & what was the size?
4. What is a “dead zone”? What causes it?
5. What is the scientific term for the increase of nutrients, leading to a decrease in oxygen?________________
6. What nutrient in particular is most responsible for the “Dead Zone”, and where does it come from?
7. The increase nutrients create a bloom of what? _____________________________
8. These organisms that bloom live on the surface and create oxygen. So how is it possible that they are also responsible
for creating an area of low oxygen (what is the process…)?
9. Why doesn’t oxygen from the air reach the oxygen depleted zones?
10. What did researchers learn from taking core samples
11. What do scientists believe could be responsible for providing the excess nutrients (list at least 5)?
12. What is amnesic shellfish poisoning, and how can you get it?
13. Why is it so hard to pinpoint exactly where the nutrients are coming from (geographically speaking)?
Further Analysis
14. What do you believe is the best way to solve this crisis? Let’s assume you get elected president. What will be your
plan of action to end the “Dead Zone”?
15. If you were a researcher, what test would you use to determine if an area of water was suitable for life?