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Bringing Coastal Dead Zones Back to Life

Robert Howarth


Dead zones, or areas that cannot support life, are increasing along the coast due to:

  • agricultural runoff and fertilizers
  • industrial waste
  • acid rain, which is produced by the burning of fossil fuels

September 2000


Areas in the Gulf of Mexico turn into dead zones at certain times of the year. Source: Gulf of Mexico Foundation.

Parts of the Gulf of Mexico turn into a dead zone each spring.

It’s springtime, and everything seems to be blooming. Unfortunately, this isn’t good news for the Gulf of Mexico, just off the Louisiana and Texas coasts. Each spring, the area turns into a “dead zone.”

What is a “dead zone”?

Agriculture and industry produce too much nitrogen and phosphorous.
  • Excessive amounts of nitrogen and phosphorus — which make their way to the Gulf from the atmosphere and via rivers polluted with agricultural runoff and municipal and industrial waste — trigger algal blooms.

  • The algae use up available oxygen, killing bottom-dwellers such as oysters, clams, and snails, and driving away fish, shrimp, and crabs.

  • Excess nitrogen is particularly harmful for marine ecosystems, and can be linked to everything from increased outbreaks of red tides to the deaths of marine mammals and the loss of biodiversity.

Dead zones are areas that cannot sustain marine life.

And it isn’t just the Gulf area that is affected by an overabundance of nitrogen and phosphorus. All of our coasts are being damaged. Of 139 U.S. coastal areas assessed recently, 44 were identified as severely affected by high levels of these nutrients. What’s more, many scientists predict that the problem will worsen in the coming decades unless action is taken now to reduce nutrient excesses in U.S. waters.

Only national policies can stop nutrient pollution of oceans and waterways.

Who or what is responsible?

State and local governments often are responsible for identifying and dealing with nutrient pollution, and their efforts can significantly improve coastal environmental quality. But state and local agencies can’t do it all, and they certainly can’t do it alone. To truly protect our coasts, rivers, and lakes, our nation needs a comprehensive strategy to prevent excessive amounts of nitrogen and phosphorus from entering our waterways. Nutrient pollution is a complex problem that is taking on ever-larger proportions.

  • For example, human activities have more than doubled the amount of nitrogen globally from 1960 to 1990, with the use of synthetic fertilizers accounting for the majority of that growth.
Human activity has caused an increase in nitrogen levels.
  • More than half of all synthetic fertilizers ever produced has been used in the past 15 years.

  • In the United States, approximately 20 percent of the nitrogen in these fertilizers seeps into ground water, rivers, and streams, gradually making its way into coastal waters.

  • Other sources of nitrogen include animal wastes, waste-water treatment plants, and the combustion of fossil fuels.

  • When these fuels burn, nitrogen compounds are released into the atmosphere, and then fall in acid rain, adding significant amounts of nitrogen to some coastal waters.

  • Nutrient pollution often crosses local and state boundaries, making it difficult for various government agencies to act cohesively.

  • Rivers can carry pollution for long distances. One of the many sources of excess nitrogen in the Gulf, for instance, might be runoff from a farm in Iowa.

  • And nitrogen from the atmosphere is a nationwide problem.

Governments must set guidelines for release of nutrients into the environment.
Nutrient levels in waterways must be continually monitored.
An online database would help local communities understand the problem.

How can we address the problem?

Large watersheds that cut across several states need uniform protection. Much needs to be done to help state and local authorities address this problem.

  • The federal government should take the lead on issues that span multiple jurisdictions or threaten federally protected natural resources.

  • The government also should continue to set clear guidelines for the maximum allowable amounts of nutrients that are released in waterways and address overlaps in existing and proposed federal legislation.

  • Developing accurate estimates of nutrients in waterways that lead to the coast is essential for forming effective strategies to curb excesses.

  • Federal, state, and local agencies should form partnerships with academic and research institutions to create a national monitoring program.

  • And every 10 years, a nationwide assessment should be conducted to determine the extent of nutrient problems and the effectiveness of efforts to combat them.

  • But just as importantly, the federal government should be more effective in providing data, information, and technical assistance to state and local coastal authorities.

  • A national information clearinghouse that provides assistance on request, or a complete database on the Internet with links to information could go a long way toward helping regional authorities make more informed decisions.

Conclusion: A nationwide plan could reduce the damage to coastal areas by 25%.

Putting these practices into place, along with strengthening state and local efforts, could realistically reduce the number of severely damaged coastal areas by at least 25 percent in the next 20 years and ensure that no other healthy coastal areas become affected. By developing a systematic, nationwide plan to attack nutrient pollution at its many sources, the government will make huge strides in protecting the many precious natural resources in and around our waterways. It’s time to put an end to coastal “dead zones” and bring marine ecosystems back to life.

Robert Howarth, Ph.D., is Editor-in-Chief of Biogeochemistry and the David R. Atkinson Professor of Ecology and Environmental Biology at Cornell University, Ithaca, New York. He also co-chairs an international project, Nitrogen Transport and Transformation at Regional and Global Scales, under the auspices of SCOPE (the Scientific Committee on Problems of the Environment of the International Council of Scientific Unions) and the United Nations Environment Program. Recently, Dr. Howarth chaired a National Research Council committee examining coastal waters.

Bringing Coastal Dead Zones Back to Life

BioScience Article

“Dead Zones Spreading in World Oceans.”
In the July 2005, BioScience article, Cheryl Lyn Dybas states, the phrase “dead zone”—coastal waters too low in oxygen to sustain life—is almost synonymous with the Gulf of Mexico. But a similar situation now exists in many other places, says Donald Boesch, president of the University of Maryland Center for Environmental Studies in Cambridge, Maryland. “There’s a dead zone right outside my office window every summer in the Chesapeake Bay,” says Boesch. “Since the 1970s, this lifeless zone has become a yearly phenomenon, sometimes affecting 40% or more of the bay.” Read the citation, or log in to purchase the full article.

Dead zone woes

A short news article on how dead zones affect coastal economy and fisheries.

Gulf of Mexico Hypoxia Assessment

Read the full report by the National Centers for Coastal Ocean Science (1999). Other links will take you to more information about hypoxia in the Gulf of Mexico.

The Aquatic Net

This site has news and science information on oceans and fisheries.

Scorecard: your community’s pollution

“Enter your [U.S.] zip code and find out what pollutants are being released into your community — and who is responsible.” Part of the Environmental Defense Network, the second link below.

Read a book

Song for the Blue Ocean: Encounters Along the World’s Coasts and Beneath the Seas. Marine scientist Carl Safina encourages readers to take a wider interest in the oceans, especially because so much of that great blue expanse is now threatened by human progress. Henry Holt & Company, Inc., Jan. 1999.

Protect the oceans and marine life

The Ocean Conservancy offers a variety of advocacy campaigns, listed right on their home page, for your participation.

Reef Relief

“A nonprofit membership organization dedicated to preserving and protecting living coral reef ecosystems through local, regional and global efforts.” Includes tips for boaters and divers.

The Surfrider Foundation

“A non-profit environmental organization dedicated to the protection and enjoyment of the world’s oceans, waves and beaches, for all people, through conservation, activism, research and education.” The second link takes you to their current campaigns.

How to reduce water pollution

There are many ways to directly and indirectly protect your area’s waters, using these tips when “in your household, in your backyard, on the road, or on the water.”

Helping coral reefs

The Nature Conservancy offers tips on how to help protect coral reefs. original lesson

This lesson has been written by a science educator to specifically accompany the above article. It includes article content and extension questions, as well as activity handouts for different grade levels.

Lesson Title: Dead Zones: Why Are the Waters Dying?
Levels: high school - undergraduate
Summary: This lesson explores the effects of pollution, in particular nitrogen pollution, on marine ecosystems. Students can brainstorm the effects of pollution on marine life, find out what the “total maximum daily load” for nutrient pollution is in their area, conduct local water quality studies… and more!

Download/view lesson. (To open the lesson’s PDF file, you need Adobe Acrobat Reader free software.)

Lessons for middle school
The following link will take you to middle school lessons available on other web sites:

  • » Oceans and Marine Life This site, a project of the North American Association for Environmental Education, provides links to a variety of lesson plans, teacher’s guides and activities on ocean and coast subjects.

Useful links for student research

In addition to the links in the “learn more” section above:

  • » Surf Your Watershed
    The EPA Surf Your Watershed site focuses on water quality from a watershed perspective. You can look up information on water quality and on your own local watershed.
  • » Chesapeake Bay Program
    The website has extensive information on water pollution, as well as wildlife and culture of coastal bay areas. It includes a section specifically focused on nutrient pollution. It also includes sections aimed at teachers and at students.
  • » The Ocean Sciences Resource Center
    The center has much material on ocean and coastal processes. It includes links to readily accessible data sets that can be used in the classroom.
  • »Glossary of Marine Biology
    Marine Biology definitions from Marine Biology: Function, Biodiversity, Ecology by Jeffrey Levinton (Oxford Univ. Press)
  • »Glossary of Water Environment Terms
    Useful definitions for water-related class activities, including common words such as acidity as well as uncommon ones such as evapotranspiration.
  • » Coral Reef Animal Printouts
    Pictures of animals that make up the coral reef, which can be printed to use in activities.
  • » Images of Life on Earth
    ARKive “is harnessing the latest in digital technology to bring together, for the first time, the world’s most important nature films, photographs, sound recordings, and memories, then using them to build vivid and fact-backed portraits of Earth’s endangered plants and animals.”

General References:

  • » Committee on the Causes and Management of Eutrophication, Ocean Studies Board, Water Science and Technology Board, National Research Council . 1999. “Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution.” National Academy of Sciences report.
  • » National Centers for Coastal Ocean Science Gulf of Mexico Hypoxia Assessment. 1999. “Hypoxia in the Gulf of Mexico.” NOAA National Centers for Coastal Ocean Science report.
  • » Coastal Assessment and Data Synthesis System — a NOAA resource for data on estuaries and coastal watersheds.
  • » Scott W. Nixon. 1998. “Enriching the sea to death,” Scientific American, August issue.
  • » World Resources Institute. 1998-9. “Nutrient Overload: Unbalancing the Global Nitrogen Cycle” at
  • » John Tibbetts. 1998. “Toxic tides,”Environmental Health Perspectives, Volume 106, Number 7, July issue. John Tibbetts. 1998. “Toxic tides,”Environmental Health Perspectives, Volume 106, Number 7, July issue.


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