The Dead Zone in the Gulf of Mexico

What is a dead zone?

No, I’m not talking about a place where you don’t have cell phone coverage.  “Dead zones,” also known as hypoxic zones, are low-oxygen regions of the ocean, first discovered in the 1970s.  Ordinarily, oceans are home to some of the most astonishing biodiversity on earth.  Dead zones, however, are almost devoid of life.

A 2008 study counted 405 dead zones worldwide.  The most infamous of these areas is nearby, in the Gulf of Mexico.  The Gulf dead zone is currently over 8,000 square miles — about the size of New Jersey.

What causes dead zones?

Concentrations of phytoplankton in Gulf Coast. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio

Natural factors, such as changes in wind and water circulation patterns, can affect dead zones, but the primary causes are traced back to human activities.  Interestingly, a dead zone is produced not by toxins, but by nutrients, specifically nitrogen and phosphorus.  These chemicals are commonly used in commercial fertilizers.  Nitrogen also comes from livestock manure, wastewater treatment plants, and industry.

Nitrogen and phosphorus nutrients wash into streams and rivers, causing eutrophication, or an excess of nutrients. The streams and rivers run into larger rivers, which lead to the ocean.  Bodies of water draining 40 percent of the continental U.S. (including the heart of American agribusiness, the Midwest) empty into the Mississippi River.

The nutrient-rich waters flow into the ocean (or the Gulf, in this case).  There, the eutrophication leads to algal blooms, rapid increases in certain types of phytoplankton.  When the algae die, the bacteria that decompose them deplete the oxygen in the water.

Click to enlarge diagram. Credit: C.R.S.A.

How do dead zones affect the ecosystem?

Fish and shrimp may be able to swim farther out to sea.  But bottom-dwelling creatures like crabs, snails, starfish, and clams suffocate in the hypoxic water.

Like many ecological problems, dead zones also affect humans.  The National Oceanic and Atmospheric Administration, which monitors the Gulf dead zone, said that it presents a danger to the $2.8 billion fishing industry along the coasts of Texas and Louisiana.  Fishermen must travel farther out to find waters that support life.  This issue serves as a reminder that humans are part of the ecosystem, not separate from it.

Can dead zones be fixed?

Approx. size of dead zone. Credit: NOAA

It is possible to reverse the conditions that cause dead zones.  The Black Sea dead zone, previously the largest dead zone in the world, largely disappeared between 1991 and 2001 after fertilizers became too costly to use following the collapse of the Soviet Union.

The simplest solution is simply to decrease the use of fertilizers.  But farmers can use a number of strategies to ensure that nitrogen and phosphorus stay in the soil or are absorbed by crops, instead of running off into streams and rivers.  For instance, farmers can plant more cover crops or perennial crops that trap rainwater.  Research may produce new solutions, such as new breeds of corn that can remain in the soil from one season to the next, avoiding the need to strip fields bare and leave them susceptible to flooding.

Dead zones, especially the one in the Gulf, demonstrate that ecological issues do not recognize boundaries. Intensive farming in, say, Iowa, impacts ecosystems and industry miles away on the Gulf Coast.  Luckily, ocean hypoxia is a problem that can be solved through a combination of awareness, research, and smart management.

Learn more about dead zones:

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  1. […] a lot of pollution, and industrial use of fertilizers causes environmental problems such as ocean dead zones.  By gardening organically, you be part of the solution to large-scale issues like those, and […]

  2. […] a lot of pollution, and industrial use of fertilizers causes environmental problems such as ocean dead zones.  By gardening organically, you’ll be part of the solution to large-scale issues like those, […]

  3. […] a lot of pollution, and industrial use of fertilizers causes environmental problems such as ocean dead zones.  By gardening organically, you’ll be part of the solution to large-scale issues like those, […]



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