By MICHAEL MCCARTHY
It is as sinister a development as any in the lengthening list of things going wrong with the planet. Marine "dead zones" - oxygen-starved areas of the oceans that are devoid of fish - are now emerging as one of the greatest environmental problems facing the world, UN scientists warned yesterday.
There are nearly 150 dead zones across the globe, they are steadily increasing, and they pose as big a threat to fish stocks as overfishing, the United Nations Environment Program (UNEP) said in its Global Environment Outlook Year Book for 2003, released at an environment ministers' meeting 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), UNEP said.
While nitrogen is essential in the form of fertiliser for farming and is in short supply in many parts of the world, its overload in other areas is creating a crisis in the seas.
Dead zones have long afflicted the Gulf of Mexico and Chesapeake Bay off the US East Coast, 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, thereby suffocating everything from clams and lobsters to oysters and fish.
"Human kind 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 UNEP's Executive Director, Klaus Toepfer.
"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 UNEP senior environmental affairs officer Marion Cheatle.
"It hasn't been something well known by policy makers," Ms Cheatle said. "But it's been getting noticeably worse."
There is concern that even more oxygen-starved areas will emerge in coastal waters off parts of Asia, Latin America and Africa as industrialisation and more intensive agriculture increase the discharge of nutrients.
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, in part by cutting back on fertiliser use or planting more forests and grasslands along feeder rivers to soak up the excess nitrogen.
Herald Feature: Conservation and Environment
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By MICHAEL MCCARTHY