X-/EPA
United States
Environmental
Protection Agency
The Gulf Dead Zone
The Gulf of Mexico is the
largest area of hypoxia
in the United States. In
the summer of 2002, the
hypoxic zone measured
larger than ever before.
In fact, it covered an
area greater than the
size of Massachusetts.
Hypoxia in the Gulf of
Mexico has raised
considerable concern
throughout the United
States because many
people in coastal states
make their livelihood
fishing in the Gulf and
many Americans
vacation on the Gulf. It
is also an indication of
the quality of the waters
that feed the Gulf,
including the Mississippi
River Basin. The
nitrogen concentration
in Mississippi River Basin
water has doubled since
the 1950s.
What Is Hypoxia?
Hypoxia is the condition in which dissolved oxygen is
below the level necessary to sustain most animal life.
For many members of an aquatic community,
hypoxia is like drowning, because life-giving dissolved
oxygen levels in a body of water drop much lower
than normal. Hypoxia often occurs when high
concentrations of nutrients enter water as a result of
human actions.
1
ust as on land, nutrients like nitrogen and
phosphorus, which are found in fertilizer,
stimulate plant growth in water. In water, algae is
the predominant plant. Although algae is integral
to a healthy aquatic ecosystem, addition of
nitrogen and phosphorous beyond natural levels
can lead to the formation of large, unattractive
algal mats on the surface of lakes and algal
blooms in lakes and coastal waters. The
decomposition of algal blooms consumes
oxygen, and the resulting low oxygen condition,
or hypoxia, is inhospitable to many aquatic
organisms that then must flee or die.
Where Does Hypoxia Occur?
Hypoxia occurs throughout the world. In the
United States, the largest known area is off the
Louisiana Coast (see sidebar). Other known
areas in the United States are the Long Island
Sound and the Chesapeake Bay. Hypoxia can
The six major sub-
basins of the Mississippi
River Basin and the Gulf of
Mexico. Nutrients transported
from these areas contribute to
Gulf of Mexico hypoxia.
occur naturally; however, there is no doubt that
human activites have increased the frequency,
areal extent, and severity of hypoxia around the
world. Although nutrient enrichment is the
primary contributor to hypoxia, landscape
changes such as the loss of coastal and
freshwater wetlands that naturally remove
nutrients from the water also contribute to the
problem. Many of the original freshwater
wetlands and riparian zones that were
connected to streams and rivers are now gone.
Mitigating Hypoxia Through
Wetland Restoration
There is growing interest and expertise in the
field of wetland restoration. Federal, state,
tribal, and local agencies, as well as private and
nonprofit groups, are working not just to slow
wetland loss, but to actually increase wetland
acres. This trend is good news for hypoxia-
affected waters since some wetlands can
significantly reduce the amount of nutrients
reaching our inland and coastal waters.
Restoring these wetlands can help reduce
nutrient loading to our nation's streams and
rivers. The following two examples highlight
such efforts.
Effects of Hypoxia
• More expensive water treatment
• Threat to commercial fisheries
• Harmful algal blooms and shellfish
toxicity
• Unattractive or smelly water
• Fish kills
• Damage to ecosystems and wildlife,
including "dead zones"
• Decreased diversity of aquatic plant
and animal life
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Winter ricefield management protects the Gulf of Mexico from sediments and nutrients.
Iowa and the US Department of
Agriculture (USDA)
Iowa farmers, in coordination with USDA. are
presently hard at work creating and restoring
9,000 acres of wetlands that are strategically
located and designed to be especially effective
at removing nutrients and herbicides from
agricultural fields. Their project targets the
Raccoon River which produces one of the
highest nitrogen loads in the Mississippi River
Basin. Not only will this project improve
conditions in the Gulf of Mexico, but it will
also protect drinking water in Iowa.
Hunters Increase Wetland Acres
The conservation group Ducks Unlimited is
working with rice farmers to provide habitat
for migrating birds at a critical time of year.
Farmers flood their fields between crops
creating temporary wetlands that are needed by
the birds and that also reduce the
concentration of nutrients in runoff water.
Much of this same runoff water will finally
make its way to the Gulf less laden with
harmful concentrations of nutrients. Ducks
Unlimited hopes to enroll 150,000 acres of
such wetlands in Arkansas alone. This win-win
situation benefits farmers, waterfowl, and
downstream water users.
Restored Wetland in Northeastern Iowa
To protect your local waters and those downstream, you can
take some precautions:
1. Use fertilizers on your farm prudently, and on your yard and
garden sparingly or not at all. When you do use fertilizers, be
sure to follow application time and amount recommendations
closely. One useful tool to avoid over-applying (which can also be
bad for plants) is a soil test. A test kit can be obtained from your
local USDA extension office. Find yours at: www.reeusda .gov/
1 700/statepartners/usa.htm
2. Protect the wetlands and stream-side vegetation on your own
property and in your community. Visit a wetland near your home
and learn about its contributions to your local watershed.
3. Help restore a wetland or a stream bank. Visit EPA's restoration
website atwww.epa.gov/owow/wetlands/restore
4. Properly maintain septic systems.
5. Support local efforts to reduce contamination of the water in your
community. The first step is to determine the condition of water
supplies and local streams in order to identify and then mitigate
or eliminate sources of pollutants.
EPA843-F-02-002
Office of Water
For more information, call EPA's Wetlands Helpline at
1-800-832-7828, or visit www.eoa.gov/owow/wetlands
Selected Refences:
EPA's Mississippi River Basin Webpage www.epa.gov/msbasin
U.S. EPA 2001. National Coastal Condition Report. Office of Research and Development, Office of Water, U.S.
Environmental Protection Agency, Washington, DC. EPA-620/R-01/005. www.epa.gov/owow/oceans/nccr
CENR. 2000. Integrated Assessment ofHypoxia in the Northern Gulf of Mexico. National Science and Technology
Council on Environment and Natural Resources, Washington, DC. www.nos.noaa.gov/pdflibrary/hypox final.pdf
National Oceanic and Atmospheric Administration (NOAA). 1998. Oxygen Depletion in Coastal Waters by Nancy N.
Rabalais. NOAAs State of the Coast Report. Silver Spring, MD: NOAA. state-of-coast.noaa.gov/bulletins/html/hyp 09/
hyp, html
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