Dead Zones emerging as big threat to 21st Century fish stocks

There are nearly 150 oxygen-starved or “dead zones” in the world’s oceans and seas, a new report by the United Nations Environment Programme (UNEP) shows.

These ‘dead zones’ are linked to an excess of nutrients, mainly nitrogen, that originate from agricultural fertilizers, vehicle and factory emissions and wastes. Low levels of oxygen in the water make it difficult for fish, oysters and other marine creatures to survive as well as important habitats such as sea grass beds.

Experts claim that the number and size of deoxygenated areas is on the rise with the total number detected rising every decade since the 1970s. They are warning that these areas are fast becoming major threats to fish stocks and thus to the people who depend upon fisheries for food and livelihoods.

The issue is raised in UNEP’s first ever Global Environment Outlook Year Book which is being launched to governments attending the Global Ministerial Environment Forum (GMEF) taking place this week in Jeju, Korea.

The Year Book looks at some of the environment-related milestones of the past year both globally and regionally.

Issues covered include the coming into force of the Cartagena Protocol, an international treaty covering trade in genetically modified organisms, the costs of mainly weather-related natural disasters and the challenges that remain in improving drinking water supplies for over 1 billion people.

The Year Book also identifies the continued ‘fertilization’ of the planet and growth of oxygen starved areas in the oceans as a key emerging issue that governments need to urgently address.

In some parts of the world, such as large parts of Africa, nitrogen shortages are reducing farmers’ chances of meeting food demands. Such areas desperately need more fertilizers. However, in many other parts of the globe, excessive use of fertilizers is contributing to the escalating problem of dead zones.

Klaus Toepfer, UNEP’s Executive Director, said: “ Human-kind is engaged in a gigantic, global, experiment as a result of the inefficient and often over-use of fertilizers, the discharge of untreated sewage and the ever rising emissions from vehicles and factories. 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 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 “ he said.

“Hundreds of millions of people depend on the marine environment for food, for their livelihoods and for their cultural fulfillment. Reducing the impacts of agriculture, human wastes and air pollution on the oceans and seas will be a key component in helping us to meet the Millennium Development Goals and deliver the World Summit on Sustainable Development’s Plan of Implementation in areas ranging from fisheries and biodiversity loss, to sanitation and poverty,” added Mr Toepfer.

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. Even when carefully managed, a lot of the fertilizer applied to crops is left in the soil. From there it is easily washed into rivers and subsequently to the sea.

The fertilizers, often in combination with nutrients from sewage, and nitrogen gases from traffic and industrial fumes falling on coastal water from the air, trigger blooms of tiny marine organisms called phytoplankton.

Their rapid growth and decomposition uses up oxygen in the sea-water leading to depleted oxygen levels.

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 mass.

The economic costs associated with these oxygen depleted areas is unknown, but predicted to be significant on a global scale.

Some of the earliest recorded dead zones were in places like Chesapeake Bay in the United States, the Baltic Sea, the Kattegat, the Black Sea and the northern Adriatic Sea. Others have been reported in Scandinavian fjords.

The most well known area of depleted oxygen is in the Gulf of Mexico. Its occurrence is directly linked to nutrients or fertilizers brought to the Gulf by the Mississippi River.

Others have been appearing off South America, China, Japan, south east Australia and New Zealand.

In some parts of the world, actions have been taken to reduce the amounts of fertilizer and sewage running off the land.

An agreement for the River Rhine in Europe, in which countries agreed to reduce by half the levels of nitrogen being discharged, has cut by 37 per cent the quantities of nitrogen entering the North Sea.

However, there is concern that more oxygen starved areas will emerge in coastal waters off parts of Asia, Latin America and Africa as industrialization and more intensive agriculture increase the discharge of nutrients.

Experts believe that global warming, with its likely increase in rainfall and temperatures, may aggravate the problem. Research by a team at the College of William and Mary, Virginia Institute of Marine Science in Gloucester Point, Virginia, whose work has contributed to the GEO Year Book, indicates that there may be large changes in rainfall patterns with a doubling of levels of carbon dioxide.

In some areas, this in turn could lead to a marked increase in the levels of run-off from rivers into the seas. They calculate that dissolved oxygen levels in the Northern Gulf of Mexico, triggered by an increased discharge from the Mississippi river basin of 20 per cent and a climb in temperature of up to four degrees Centigrade, could fall by 30 to 60 per cent.

Actions to reduce the threats should focus on sources of the nitrogen overload. Numerous options are available to governments, partly as a result of new scientific understanding as to how nitrogen ‘cascades’ through the environment.

For example, forests and grasslands have a high ability to ‘soak up’ excess nitrogen and slow down its movement from the land to the rivers and the seas. Planting more forests and encouraging more grasslands in some areas of the globe might help.

Improving ‘precision agriculture’ so that less fertilizer is wasted should be another option. Producing livestock in the regions where most of their feed comes from could also reap benefits.

Large number of farm animals in Europe are fed on soya, produced in North America and Latin America. Raising the animals in the soya growing regions could reduce the exports of nitrogen to regions like the European Union where nitrogen excess is an issue.

Other actions include more widespread use of technologies that remove nitrogen compounds from vehicles fumes alongside the wider uptake of alternative energy sources that are not based on burning fossil fuels.

Better treatment of sewage, both by high tech systems such as water treatment works and low tech systems, such as wetlands and reed bed networks, will not only reduce nutrient discharges to coastal waters, but will help the world meet the water and sanitation aims in the Millennium Development Goals.

UNEP News Release 2004/14

http://mirror.unep.org/gc/gcss-viii/PressRelease_E2.asp