Why huge areas in the oceans are dying

The number of oxygen-deprived “dead zones” in the world’s oceans has been increasing since the 1970s and is now nearly 150, threatening fisheries as well as humans who depend on fish, the U.N. Environment Program announced Monday in unveiling its first-ever Global Environment Outlook Year Book.

These “dead zones” are caused by an excess of nitrogen from agriculture fertilizers, sewage and emissions from vehicles and factories. In what experts call a nitrogen cascade, the chemical flows untreated into oceans and triggers the proliferation of plankton, which in turn depletes oxygen in the water.

While fish might flee this suffocation, slow moving, bottom-dwelling creatures like clams, lobsters and oysters are less able to escape.

“Humankind is engaged in a gigantic, global experiment as a result of the inefficient and often overuse of fertilizers, the discharge of untreated sewage and rising emissions from vehicles and factories”, program executive director Klaus Toepfer said in a statement accompanying the report.

From small to vast zones

Toepfer noted that 146 dead zones most in Europe and the U.S. East Coast range from under a square mile to up to 45,000 square miles. “Unless urgent action is taken to tackle the sources of the problem,” he said, “it is likely to escalate rapidly.”

The program noted that some of the earliest recorded dead zones were in Chesapeake Bay, the Baltic Sea, Scandinavia’s Kattegat Strait, the Black Sea and the northern Adriatic Sea.

The most infamous zone is in the Gulf of Mexico, where the Mississippi River dumps fertilizer runoff from the Midwest.

Others have appeared off South America, China, Japan, southeast Australia and New Zealand, the program said.
Preventive measures

The report was released in Jeju, South Korea, where governments from around the world are sending officials this week for a Global Ministerial Environment Forum.

The program noted preventive steps can be taken, citing these examples: