‘Dead zones’ threaten fisheriesMay 27, 2004, Christian Science Monitor
By Mark Clayton | Staff writer of The Christian Science Monitor
In midsummer, the northern Gulf of Mexico, where the Mississippi River
empties into it, may shimmer like any other swath of sea. But a few score
feet below, bottom-dwelling fish and other creatures struggle just to
This area – one of the world’s biggest coastal "dead zones" – is rapidly
being joined by a growing number of "hypoxic," or oxygen-depleted areas
around the world. At least 146 such zones have been documented through
2000 – from the northern Adriatic Sea to the Gulf of Thailand to the
Yellow Sea, according to a United Nations Environment Program (UNEP)
report released in March. And their number has been doubling every decade
since 1960, it adds. At risk: coastal fisheries near the most populous
A handful of efforts are under way that could mitigate the effects. But
because of lag times involved, the problem is likely to get worse before
it gets better.
"I’m convinced this is going to be the biggest environmental issue in the
aquatic marine realm in the 21st century," says Robert Diaz, a marine
biologist and professor at the Virginia Institute of Marine Science, who
coauthored the study undergirding the UNEP report. "It won’t take too much
for these annual lower-oxygen events to expand throughout the year and
actually eliminate fisheries."
Dead zones often grow where populations grow. But the real driver is the
spread of nitrogen, many observers say, caused by runoff of nitrogen-based
fertilizers, sewage outflows, and nitrogen deposits from burning fossil
fuels. Some waters remain oxygen-depleted year-around. In other waters,
the problem appears periodically.
In the northern Gulf of Mexico, one of the best-known and best-studied
dead zones, hypoxia occurs seasonally from April to September. The zone’s
size depends on the weather and how much flow the Mississippi brings each
year. Its waters are laden with fertilizer runoff from farms and lawns
across the Midwest. Sewage and fossil-fuel emissions exhaust (from power
plants and autos) are also factors, says a 1999 University of Alabama
study sponsored by the fertilizer industry.
Excess nitrogen combined with placid summer weather results in an
oxygen-poor bottom layer of water. The process works this way: In the top
layer, the nitrogen and sun feed phytoplankton, which grow rapidly, then
die and fall to the bottom. As they decay, they consume oxygen. Called
eutrophication, the cycle depletes oxygen in isolated bottom waters. In
2002, one of the worst years since it was first documented in the 1970s,
the northern Gulf’s hypoxic zone reached more than 7,700 square miles.
Despite its size, the problem is largely hidden from view, except to the
"I see massive schools of stingrays, bottom dwellers, moving on the
surface. Even shrimp come up 20 feet or so off the bottom trying to get to
oxygen," says Nancy Rabalais, a marine biologist at the Louisiana
Universities Marine Consortium in Chauvin, La. Only because they are
desperate to breathe do such bottom-dwelling creatures flee upward,
risking becoming easy prey.
More mouths to feed
Such scenes will become more common worldwide, scientists predict. As
populations grow, nitrogen and phosphorous-caused eutrophication will more
than double in coastal areas by 2050, predicts a 2001 study published in
"There’s been a big increase in these hypoxic zones that correlates
strongly with increased use of nitrogen fertilizers, particularly in the
’60s and 1970s," says Robert Howarth, a coauthor of the Science study and
professor of environmental biology at Cornell University in Ithaca, N.Y.
"About half of the nitrogen fertilizer used on Earth in all of history has
been used in the last 15 years."
One positive trend: Total global fertilizer use seems to be growing more
slowly than in the past few decades. It plateaued in 1990 then declined
after the collapse of the Soviet Union. In the mid-’90s, global growth
resumed, but much more slowly. For the decade, nitrogen fertilizer rose
only slightly from 79 million to 82 million tons.
Still, scientists say it takes time for a rise in fertilizer use to harm
coastal ecosystems. In a 2002 study, Howarth and other scientists found
that falling levels of dissolved oxygen in coastal waters lagged 10 to 20
years behind increased chemical fertilizer use beginning in the 1940s.
That lag effect is worrisome, he says, because fertilizer use has more
than quadrupled globally since 1960.
The use of nitrogen has increased, too. Nitrogen fertilizers were 37
percent of all fertilizers used in 1961, but grew to 60 percent by 2001,
according to Fertilizer Institute data. "If you look globally at what
humans are doing to the nitrogen cycle, we’re increasingly making nitrogen
available to the environment," Dr. Howarth says. "Almost 75 percent of the
increase is through fertilizers."
The fertilizer industry in the US has been working with farmers to reduce
fertilizer overuse and resulting runoff since the 1960s. But pressure from
the Environmental Protection Agency in the ’90s also has pushed the
industry toward new technologies. Global positioning satellite technology,
linked to fertilizer applicators on tractors, permits "precision farming"
in which each acre gets specific chemicals according to its soil
"Applying more won’t necessarily get more crop, and farmers understand
that it’s not good for their bottom line," says Rino Maddalena of the
Fertilizer Institute in Washington D.C.
Even so, several farm authorities say it is not uncommon for farmers to
use more nitrogen and other fertilizers than they need as a modest
insurance policy. Better to slightly overfertilize than underfertilize and
underproduce, the thinking goes.
To address this concern, the American Farmland Trust (AFT), a nonprofit
group that attempts to protect cropland, has developed a new form of crop
insurance. The risk-management program encourages farmers to apply less
nitrogen fertilizer. In this scheme, a farmer agrees to use a lesser
amount of nitrogen fertilizer, based on nutrient management advice. If the
farmer’s output falls below the output of a test plot on his land that has
the maximum nitrogen fertilizer applied to it, then he receives the
difference in cash.
So far, 27 pilot projects are under way in Minnesota, Wisconsin, Ohio, and
Illinois, says Brian Brandt of the AFT’s Agricultural Conservation
Innovation Center. In three years, the project has seen a 24 percent
reduction in nitrogen use among the farmers. Only a handful saw yields
fall. They were paid the difference, about $6 per acre.
It pays to use less
One participant, Burley Hall, a farmer with 2,100 acres north of Urbana,
Ohio, now uses some 35 pounds less nitrogen per acre of corn – a reduction
of more than 20 percent. That reduction saves him money. And once, when
his crop came in a fraction of a bushel less than his test strip, he got
reimbursed $900. But his enthusiasm for the program runs deeper than
"We’ve got creeks that run through our land," Mr. Hall says. "We live here
and drink the water. If I’m buying this stuff [nitrogen], I don’t want to
see how far down the stream I can run it. You’ve got to watch out for the
environment by all means and this is one way of doing it."
One high-tech idea in the works would take another big whack at nitrogen
use – but from the other end of the equation. Arcadia Biosciences in
Davis, Calif., is working to make corn and other plants more efficient
users of nitrogen already in the soil. For example, using genetic
engineering, it has modified canola with a gene found in barley. The
effect is to activate the plant’s roots to absorb nitrogen more
aggressively than before.
"We’ve grown the same yield as a conventional crop of canola using less
than half as much nitrogen," says Eric Rey, the firm’s president.
Arcadia has conducted three years of tests for the US Department of
Agriculture. But the first commercial canola and rice seeds won’t be ready
until 2008 or 2009, Mr. Rey says. He acknowledges, too, current concerns
over genetic engineering. On the other hand, farmers cut costs and use
less fertilizer, he adds. "So the environment is improved by farmers
making more money."
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