Resuscitating the Gulf’s dead zone

Every spring for many years now, a dead zone has formed in the Gulf of Mexico just south of the Mississippi River Delta. This patch of water contains less than 2 milligrams of oxygen per liter, which is too little to sustain most aquatic life. For the past 5 years, this dead zone reached its maximum size—on average, 5,500 square miles, or roughly the size of Connecticut—around midsummer and disappeared in the fall.

Last month, 10 federal agencies entered an agreement with nine states and two Indian tribes to work together to stem the pollution that creates this parcel of oxygen-starved water. Their goal is to halve the Gulf’s dead zone by 2015.

Throughout the Midwest, nutrients—principally nitrogen and phosphorus—rain out of the air or run off farms and other lands and end up in streams. Eventually, these remnants of fertilizers and other sources of pollution flow down the Mississippi and spew into the Gulf. There, the nutrients spur algae blooms. As the algae die and decompose, they deplete much of the dissolved oxygen from a huge volume of water.

Over the next 2 years, the plan’s participants pledge to identify major contributors of nitrogen and phosphorus to water. They also promise to create financial incentives for businesses to reduce the runoff of such pollutants. Farmers, for instance, will be encouraged not only to restore or enhance wetlands but also to plant vegetation along streams to sop up the polluting nutrients before rains wash them toward the Gulf.

To largely eliminate the annual dead zone, nutrient flow into the Mississippi must drop by 40 percent, according to estimates by the Environmental Protection Agency. If fully implemented, the new plan would only cut the nutrient input by 30 percent.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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