Huge areas in the world’s waters now have almost no life. No fish swimming. No seaweed waving. Here’s the story.
DEAD ZONE: The Gulf of Mexico
The zone in the Gulf of Mexico changes from year to year, but sometimes it’s as big as 8,500 square miles. (That’s the size of New Jersey!)
THE VICTIMS: Fish, turtles, and other sea creatures
THE CULPRIT: Fertilizer runoff from farmland in U.S. states along the Mississippi River. Fertilizer used in modern farming is loaded with nitrogen. Nitrogen promotes huge “blooms” of algae: Millions of the tiny plant-like organisms fill the water. When algae die, they sink to the bottom. Microbes gobble them up and form “bacterial mats” that release toxic gases. The result: not enough oxygen for fish and other aquatic creatures to breathe. They leave the area or suffocate to death.
CHANCE OF RECOVERY: Weather can affect the size of the Gulf’s dead zone. In 2011, scientists expected the zone to reach its largest size ever because of the considerable flooding that spring along the Mississippi. But high winds from Tropical Storm Don churned up the water, helping to replenish some of the oxygen. The dead zone remained huge, but it didn’t reach the record size that was anticipated. A year later, in 2012, very dry weather caused a drought in farming regions along the Mississippi, and the dead zone was reduced to about 3,000 square miles—less than half its usual size. Scientists were mildly encouraged to see such a big effect from just one season of reduced nitrogen from fertilizer runoff. “If we could find some way to stop all that nitrate from going down the river, the problem would be solved in a year or two,” said an aquatic ecologist from the University of Michigan.
DEAD ZONE: The Black Sea
In the 1980s, this zone was the largest in the world—the size of Switzerland.
THE VICTIMS: Mussels, crabs, fish, sea grasses
THE CULPRIT: Detergents from wastewater, fertilizers, air pollution. During the 1960s, ’70s, and ’80s, the flow of nitrogen and phosphorus into Europe’s Danube River doubled. Most came from fertilizer, air pollution, and detergents in wastewater from cities in Communist countries such as East Germany, Romania, Bulgaria, and Hungary. In 1989, Communism collapsed. Fertilizer became so expensive, farmers had to cut down on its use. Within a few years, the dead zone had mostly disappeared.
CHANCE OF RECOVERY: “It’s a clear first—a successful reversal of dead zones,” says Andrew Hudson, of UN Oceans, an environmental group established by the United Nations. As the Black Sea became healthier, many species rebounded. The fertilizer reductions were unintentional, but the countries recognized the benefits and have worked to reduce other forms of pollution.