Last summer every sea creature across an area twice the size of Lesotho was asphyxiated by severely depleted oxygen levels in the Gulf of Mexico. The same phenomenon, the marine equivalent of the ozone hole, happened off South America, China, Japan, south-east Australia, New Zealand and up to 150 other places.
A United Nations agency warned on Monday that the number of these ”dead zones”, caused mainly by the run-off of nitrogen fertilisers from intensive farming and sewage from large cities, had doubled in the past 15 years and was increasing all over the world.
In a new report, the UN Environment Programme (Unep) said that 150 sea areas were now regularly starved of oxygen and were becoming major threats to already declining fish stocks, including those in Europe, where areas of the Baltic Sea were lifeless for several months, as were parts of the Irish Sea and the Adriatic.
The Black Sea — the largest and oldest ”dead zone” in the world — supported only a few bacteria to a depth of 150m.
”Humankind is engaged in a gigantic, global, experiment as a result of the inefficient and often over-use of fertilisers, the discharge of untreated sewage and the ever rising emissions from vehicles and factories,” said Klaus Toepfer, the Unep 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.”
Some of the dead zones are less than one square kilometre, whereas others are up to 70 000 square kilometres. Many have been found near the outlets of big rivers such as the Mississippi and the Yangtze, which drain huge industrial areas. Most lie off countries which heavily subsidise their agriculture.
”What is clear is that unless urgent action is taken to tackle the sources of the problem, it is likely to escalate rapidly,” he said.
”Dead zones are especially dangerous to fisheries because they afflict coastal areas where many fish spawn and spend most of their lives before moving to deeper water”, said Unep officer Marion Cheatle. ”It is getting noticeably worse.”
She advised countries, which often share water basins, to co-operate in reducing nitrogen discharges by cutting fertiliser use or planting forests along rivers to soak up excess nitrogen.
The ”creeping dead zones” have been noted since the 1970s but the speed of their growth has surprised scientists who are only now beginning to understand their mechanism.
Robert Diaz, professor of marine science at Maryland University and author of the marine section of the report, said dead zones were fast becoming a bigger threat to fish stocks than over-fishing.
He warned that global warming, with its likely increase in rainfall, was likely to aggravate the problem, because it would increase significantly the discharge of polluted water from rivers into oceans.
The report, launched in South Korea at a meeting of 150 of the world’s environment ministers, ranked dead zones as one of the top 20 threats to the global environment. Others included dust and sand storms, more frequent around the world as land is degraded, and impending global water shortages.
More than one in three of the world’s population is likely to suffer chronic water shortages in the next few decades, according to the report, while more than 2,4-billion people lack access to basic sanitation. – Guardian Unlimited Â