Nearly 150 oxygen-starved “dead zones” in the world’s oceans and seas, linked to an excess of nutrients, mainly nitrogen, from synthetic agricultural fertilizers, vehicle and factory emissions and wastes, threaten the survival of marine animals and plants, the United Nations Environment Programme (UNEP) says in a new report.
UNEP’s first Global Environment Outlook (GEO) Year Book 2003 says, “The emergence of areas of artificially low oxygen levels can be closely correlated with the use of synthetic fertilizers in agriculture. Nitrogen is a main ingredient of these fertilizers.”
The Year Book will be launched at this week’s Global Ministerial Environment Forum (GMEF) meeting in Jeju, Republic of Korea.
Human beings are conducting a gigantic, global experiment because of the inefficient and often excessive use of fertilizers, the discharge of untreated sewage and the ever-increasing emissions from vehicles and factories, UNEP Executive Director Klaus Toepfer says.
“The nitrogen and phosphorus 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,” he says.
“Some of these so-called dead zones, or oxygen-starved areas, are relatively small, less than one square kilometre in size, whereas others are far larger at up to 70,000 square kilometres. What is clear is that unless urgent action is taken to tackle the sources of the problem, it is likely to escalate rapidly.”
The fertilizers trigger blooms of tiny marine organisms called phytoplankton, whose rapid growth and decomposition use up oxygen in seawater, the report says.
“Sometimes, the effects are mild. But sometimes they can be dramatic, with fish fleeing the ‘suffocating waters’ and creatures, like clams, lobsters, oysters, snails and other slow-moving, bottom-living creatures, dying en masse,” Mr. Toepfer says.
Dead zones have been found in Chesapeake Bay in the United States, the Baltic Sea, the Kattegat Strait between Sweden and Denmark, the Scandinavian fjords, the Black Sea and the northern Adriatic Sea.
As already flagged in 2000, the best-known area of depleted oxygen is in the Gulf of Mexico, caused by nutrients or fertilizers from the Mississippi River. Other zones have appeared off South America, China, Japan, southeast Australia and New Zealand.
More oxygen-starved areas may emerge in coastal waters off parts of Asia, Latin America and Africa as industrialization and more intensive agriculture increase the discharge of nutrients, UNEP says.