It is as sinister a development as any in the list of things going wrong with the planet. Marine "dead zones" - oxygen-starved areas of the oceans that are devoid of fish - are one of the greatest environmental problems facing the world, UN scientists warned yesterday.
There are nearly 150 dead zones across the globe, they are increasing, and they pose as big a threat to fish stocks as over-fishing, the United Nations Environment Program (Unep) said in its Global Environment Outlook Year Book 2003, released at a meeting of environment ministers in Korea.
These lifeless areas of the sea are caused by an excess of nutrients, mainly nitrogen, that originate from heavy use of agricultural fertilizers, from vehicle and factory emissions and from human wastes. They have doubled in number over the last decade, with some extending over 70,000 square kilometers (27,000 square miles), about the size of Ireland, Unep said.
Dead zones have long afflicted the Gulf of Mexico and Chesapeake Bay off the East Coast of America but they are now spreading to other bodies of water, such as the Baltic Sea, the Black Sea, the Adriatic, the Gulf of Thailand and the Yellow Sea as other regions develop, Unep said. They are also appearing off South America, Japan, Australia and New Zealand.
The nutrient run-off from farm fertilisers, sewage and industrial pollutants triggers blooms of microscopic algae known as phytoplankton. As the algae die and rot, they consume oxygen, suffocating all marine life.
"Humankind is engaged in a gigantic, global experiment as a result of inefficient and often overuse of fertilisers, the discharge of untreated sewage and the ever-rising emissions from vehicles and factories," said Klaus Toepfer, Unep's executive director.
"The nitrogen and phosphorous from these sources are being discharged into rivers and the coastal environment or being deposited from the atmosphere, triggering these alarming and sometimes irreversible effects. Unless urgent action is taken to tackle the sources of the problem, it is likely to escalate rapidly."
Dead zones are especially dangerous to fisheries because they afflict coastal waters where many fish spawn and spend most of their lives before moving to deeper water, said Marion Cheatle, Unep's senior environmental affairs officer. "It hasn't been something well known by policy-makers," Ms Cheatle said. "But it's been getting noticeably worse."
The economic costs associated with dead zones is unknown, but predicted to be significant on a global scale. Unep is urging nations to co-operate in reducing the amount of nitrogen discharged into their coastal waters, by cutting back on fertiliser use or by planting more forests and grasslands along feeder rivers to soak up the excess nitrogen.
