JEJU, South Korea - The spread of oxygen-starved "dead zones" in the oceans, a graveyard for fish and plant life, is emerging as a threat to the health of the planet, experts say.
For hundreds of millions of people who depend on seas and oceans for their livelihoods, and for many more who rely on a diet of fish and seafood to survive, the problem is acute.
Some of the oxygen-deprived zones are relatively small, less than one square kilometer (0.4 square miles) in size. Others are vast, measuring more than 70,000 square kilometers.
Pollution, particularly the overuse of nitrogen in fertilizers, is responsible for the spread of dead zones, environment ministers and experts from more than 100 countries were told.
Global distribution of oxygen-depleted coastal zones. The 146 zones shown are associated with either majorpopulation concentrations or with watersheds that deliver large quantities of nutrients to coastal waters. (Annual – yearly events related to summer or autumnal stratification; Episodic – events occurring at irregular intervals greater than one year; Periodic – events occurring at regular intervals shorter than one year; Persistent – all-year-round hypoxia)
The number of known oxygen-starved areas has doubled since 1990 to nearly 150, according to the UN Environmental Program (UNEP), holding is annual conference here.
"What is clear is that unless urgent action is taken to tackle the sources of the problem, it is likely to escalate rapidly," UNEP executive director Klaus Toepfer said.
"Hundreds of millions of people depend on the marine environment for food, for their livelihoods and for their cultural fulfillment."
The world at present gets 17 percent of its animal protein from fish, UN figures show.
That supply is now endangered on at least two fronts: overfishing that has depleted stocks in recent decades and now the challenge of widening dead zones.
The issue was identified as a key emerging problem in the Global Environment Year Book 2003, a health report on the planet released at the start of the UNEP's three-day conference that concludes Wednesday.
The spread of low-level oxygen zones in seas and oceans, identified as early as in the 1960s, is closely related to the overuse of fertilizers in agriculture, whose main ingredient is nitrogen.
On land, nitrogen boosts plant growth. But when it washes into the sea in rivers and rainwater overrun, it triggers an explosive bloom of algae.
When these tiny plants growing on the ocean surface sink to the bottom and decompose, they use up all the oxygen and suffocate other marine life.
Fossil fuel waste from motor vehicles and power plants increases nitrogen content in oceans.
With oxygen depletion, fish, oysters and other marine life eventually die out along with important habitats such as sea grass beds.
Relatively large zones are found in the Gulf of Mexico, the Chesapeake Bay off the US East Coast, the Baltic and Black seas, and parts of the Adriatic.
Others have appeared off South America, Japan, China, Australia and New Zealand. Some zones are permanent, while other occur annually or intermittently.
Most of the 160 million tons of nitrogen used as fertilizer annually ends up in the sea.
UNEP said efforts should focus on cutting back on overuse of nitrogen to bring the seas back to life.
With a joint accord, European states within the Rhine River basin successfully cut the amount of nitrogen entering the North Sea by 37 percent between 1985 and 2000, it said.
The UNEP advocates planting of more forests and grasslands to soak up excess nitrogen and better sewage treatment.
Its conference is the first ever held in Asia with more than 100 ministers and high-level officials attending from 155 countries.
© Copyright 2004 AFP