The largest corn crop in decades may be good news for
the biofuel business, but it could be a disaster for
the Gulf of Mexico.
Millions of tons of fertilizer used by farmers,
carrying nutrient pollution in the form of excess
nitrogen and phosphorus, are running into watersheds
that feed the Mississippi River. This pollution
eventually flows into the Gulf, creating a massive
“dead zone” where sea life cannot be sustained. Low
oxygen levels in these waters off the coast of
Louisiana and Texas interfere with fish reproduction
by disrupting fish hormones, and bottom dwellers such
as snails, worms, starfish and crabs die off.
The dead zone, first observed during the 1970s, is a
seasonal phenomenon, forming each spring and lasting
through early fall. Almost the size of New Jersey in
2007, scientists fear the dead zone will grow even
bigger in the years to come because of increased
farming activity - and fertilizer use - to meet the
demand for biofuels like ethanol.
This summer the zone grew to 7,900 square miles
(20,461 square kilometers), the third largest since
scientists began measuring it in 1985. The dead zone
first eclipsed 10,000 square kilometers in 1991,
surpassed 15,000 square kilometers in 1993, and
reached 20,000 square kilometers in 2001.
The area where the Gulf of Mexico meets the mouth of
the Mississippi River has been lost as "a viable area
for fishing," says David Tilman, a University of
Minnesota ecology professor. "That dead zone has
become larger and larger through the last decade, and
will become larger more quickly with the big increase
in corn being grown.”
Nitrogen and phosphorus from fertilizer are the major
factor in creating these low-oxygen, or hypoxic, Gulf
waters. Nitrogen and phosphorus promote excessive
growth of phytoplankton, which eventually die off and
are decomposed by bacteria that consume much of the
oxygen in the water. In order to shrink the dead zone,
scientists say that nitrogen and phosphorus inputs
into the Mississippi River will have to be reduced.
In a draft report submitted last month, Environmental
Protection Agency science advisors recommended cutting
the amounts of nitrogen and phosphorus carried by the
Mississippi River into the Gulf by 45 percent. The
report identified several opportunities for reducing
nitrogen and phosphorus inputs: converting to crops
for producing cellulosic ethanol (which require less
fertilizer than corn), constructing or restoring
wetlands which can absorb nitrogen and phosphorus
before they enter the Mississippi, and reducing the
amounts of these pollutants discharged by wastewater
treatment plants. These changes would allow the dead
zone to be reduced to 5,000 square kilometers, or
roughly 1,930 square miles.
The dead zone "currently averages somewhere around
15,000 square kilometers (5,791 square miles).
Reducing it to a third of that size – 5,000 square
kilometers – would place it at the level it was a
couple decades ago,” said Alan Lewitus, lead scientist
with the National Oceanic and Atmospheric
Administration’s Ecosystems Stressors Research branch,
which funds projects investigating the dead zone.
University of Texas at Austin marine scientists were
recently awarded a $781,000 grant from NOAA to better
understand how nutrient pollution from the Mississippi
River affects the dead zone. These scientists are
attempting to understand each step in the formation of
low oxygen waters.
When nitrite – a form of nitrogen that fuels explosive
phytoplankton growth- enters the Mississippi River, it
doesn’t have much of an effect, says Dr. Wayne
Gardner, a professor of marine science leading the
UT-Austin project. The turbidity - or cloudiness - of
the river is so high that phytoplankton cannot grow.
However, when nutrients like nitrite enter the Gulf,
they’re entering an area where the water is clearer
and there is enough light to support growth of
phytoplankton.
The size of the dead zone seems to be dependent upon
the amount of fresh water inflow from the Mississippi
River, says Gardner. The more fresh water inflow, the
more nitrogen enters the Gulf and the more
phytoplankton can grow. A massive phytoplankton
die-off follows, depleting the water's oxygen supply.
Nutrients are not the only factor promoting low levels
of oxygen in Gulf waters. The level of stratification
- or mixing - between the fresh river water and the
heavier salt water of the Gulf also plays a role, says
NOAA’s Lewitus.
In a worst case scenario, the less dense fresh water
of the Mississippi flows into the Gulf undisturbed and
forms a surface layer where all of the oxygen is
trapped; the oxygen does not flow to the bottom and
organisms there perish. However, this result is
averted when tropical storms and hurricanes cause the
fresh and salt water to mix. High winds stir
oxygen-rich surface water into the water near the
bottom of the Gulf, and the dead zone temporarily
dissipates. The smaller size of the dead zone in 2003
has been attributed to tropical storms that caused the
water to mix.
Bottom dwelling species such as snails, worms,
starfish and crabs typically cannot escape the dead
zone’s oxygen poor water and die off. However, fish
and shrimp tend to migrate out of the dead zone,
surviving but abandoning their traditional habitats in
the process.
“It hasn’t really impacted the shrimping industry all
that greatly. The shrimp are largely displaced to the
outer boundary of the hypoxic zone,” says Lewitus.
“You have fishermen that can take advantage of fish
being aggregated like that. There doesn’t seem to be
an economic impact that has been documented.”
Lewitus does note that scientists do not have a “good
handle” on the ecological impacts on many
fish species that have been forced to migrate because
of the dead zone. As far as shrimp are concerned,
“You’re displacing them away from what used to be
their optimal habitat. What the cost is in terms of
their health is another consideration,” says Lewitus.
the biofuel business, but it could be a disaster for
the Gulf of Mexico.
Millions of tons of fertilizer used by farmers,
carrying nutrient pollution in the form of excess
nitrogen and phosphorus, are running into watersheds
that feed the Mississippi River. This pollution
eventually flows into the Gulf, creating a massive
“dead zone” where sea life cannot be sustained. Low
oxygen levels in these waters off the coast of
Louisiana and Texas interfere with fish reproduction
by disrupting fish hormones, and bottom dwellers such
as snails, worms, starfish and crabs die off.
The dead zone, first observed during the 1970s, is a
seasonal phenomenon, forming each spring and lasting
through early fall. Almost the size of New Jersey in
2007, scientists fear the dead zone will grow even
bigger in the years to come because of increased
farming activity - and fertilizer use - to meet the
demand for biofuels like ethanol.
This summer the zone grew to 7,900 square miles
(20,461 square kilometers), the third largest since
scientists began measuring it in 1985. The dead zone
first eclipsed 10,000 square kilometers in 1991,
surpassed 15,000 square kilometers in 1993, and
reached 20,000 square kilometers in 2001.
The area where the Gulf of Mexico meets the mouth of
the Mississippi River has been lost as "a viable area
for fishing," says David Tilman, a University of
Minnesota ecology professor. "That dead zone has
become larger and larger through the last decade, and
will become larger more quickly with the big increase
in corn being grown.”
Nitrogen and phosphorus from fertilizer are the major
factor in creating these low-oxygen, or hypoxic, Gulf
waters. Nitrogen and phosphorus promote excessive
growth of phytoplankton, which eventually die off and
are decomposed by bacteria that consume much of the
oxygen in the water. In order to shrink the dead zone,
scientists say that nitrogen and phosphorus inputs
into the Mississippi River will have to be reduced.
In a draft report submitted last month, Environmental
Protection Agency science advisors recommended cutting
the amounts of nitrogen and phosphorus carried by the
Mississippi River into the Gulf by 45 percent. The
report identified several opportunities for reducing
nitrogen and phosphorus inputs: converting to crops
for producing cellulosic ethanol (which require less
fertilizer than corn), constructing or restoring
wetlands which can absorb nitrogen and phosphorus
before they enter the Mississippi, and reducing the
amounts of these pollutants discharged by wastewater
treatment plants. These changes would allow the dead
zone to be reduced to 5,000 square kilometers, or
roughly 1,930 square miles.
The dead zone "currently averages somewhere around
15,000 square kilometers (5,791 square miles).
Reducing it to a third of that size – 5,000 square
kilometers – would place it at the level it was a
couple decades ago,” said Alan Lewitus, lead scientist
with the National Oceanic and Atmospheric
Administration’s Ecosystems Stressors Research branch,
which funds projects investigating the dead zone.
University of Texas at Austin marine scientists were
recently awarded a $781,000 grant from NOAA to better
understand how nutrient pollution from the Mississippi
River affects the dead zone. These scientists are
attempting to understand each step in the formation of
low oxygen waters.
When nitrite – a form of nitrogen that fuels explosive
phytoplankton growth- enters the Mississippi River, it
doesn’t have much of an effect, says Dr. Wayne
Gardner, a professor of marine science leading the
UT-Austin project. The turbidity - or cloudiness - of
the river is so high that phytoplankton cannot grow.
However, when nutrients like nitrite enter the Gulf,
they’re entering an area where the water is clearer
and there is enough light to support growth of
phytoplankton.
The size of the dead zone seems to be dependent upon
the amount of fresh water inflow from the Mississippi
River, says Gardner. The more fresh water inflow, the
more nitrogen enters the Gulf and the more
phytoplankton can grow. A massive phytoplankton
die-off follows, depleting the water's oxygen supply.
Nutrients are not the only factor promoting low levels
of oxygen in Gulf waters. The level of stratification
- or mixing - between the fresh river water and the
heavier salt water of the Gulf also plays a role, says
NOAA’s Lewitus.
In a worst case scenario, the less dense fresh water
of the Mississippi flows into the Gulf undisturbed and
forms a surface layer where all of the oxygen is
trapped; the oxygen does not flow to the bottom and
organisms there perish. However, this result is
averted when tropical storms and hurricanes cause the
fresh and salt water to mix. High winds stir
oxygen-rich surface water into the water near the
bottom of the Gulf, and the dead zone temporarily
dissipates. The smaller size of the dead zone in 2003
has been attributed to tropical storms that caused the
water to mix.
Bottom dwelling species such as snails, worms,
starfish and crabs typically cannot escape the dead
zone’s oxygen poor water and die off. However, fish
and shrimp tend to migrate out of the dead zone,
surviving but abandoning their traditional habitats in
the process.
“It hasn’t really impacted the shrimping industry all
that greatly. The shrimp are largely displaced to the
outer boundary of the hypoxic zone,” says Lewitus.
“You have fishermen that can take advantage of fish
being aggregated like that. There doesn’t seem to be
an economic impact that has been documented.”
Lewitus does note that scientists do not have a “good
handle” on the ecological impacts on many
fish species that have been forced to migrate because
of the dead zone. As far as shrimp are concerned,
“You’re displacing them away from what used to be
their optimal habitat. What the cost is in terms of
their health is another consideration,” says Lewitus.
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