Just 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.

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.

What Is 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 hypoxiaaffected 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.

The Gulf Dead Zone 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.

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

United States

Environmental

Protection Agency

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 subbasins of the Mississippi

River Basin and the Gulf of

Mexico. Nutrients transported

from these areas contribute to

Gulf of Mexico hypoxia.
Winter ricefield management protects the Gulf of Mexico from sediments and nutrients. Ducks Unlimited

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.

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/

1700/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 at www.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.

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.

United States Office of Water EPA 843-F-01-002h

What Can You Do? What Can You Do?

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 of Hypoxia 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. NOAA’s State of the Coast Report. Silver Spring, MD: NOAA. state-of-coast.noaa.gov/bulletins/html/hyp_09/

hyp.html

Restored Wetland in Northeastern Iowa

Lynn Betts, USDA NRCS

EPA 843-F-02-002

Office of Water

For more information, call EPA’s Wetlands Helpline at

1-800-832-7828, or visit www.epa.gov/owow/wetlands