Ocean dead zones become a worldwide problem

Randolph E. Schmid, Associated Press 14 Aug 08;

Like a chronic disease spreading through the body, "dead zones" with too little oxygen for life are expanding in the world's oceans.

"We have to realize that hypoxia is not a local problem," said Robert J. Diaz of the Virginia Institute of Marine Science. "It is a global problem and it has severe consequences for ecosystems."

"It's getting to be a problem of such a magnitude that it is starting to affect the resources that we pull out of the sea to feed ourselves," he added.
Diaz and co-author Rutger Rosenberg report in Friday's edition of the journal Science that there are now more than 400 dead zones around the world, double what the United Nations reported just two years ago.

"If we screw up the energy flow within our systems we could end up with no crabs, no shrimp, no fish. That is where these dead zones are heading unless we stop their growth," Diaz said in a telephone interview.

The newest dead areas are being found in the Southern Hemisphere — South America, Africa, parts of Asia — Diaz said.

Some of the increase is due to the discovery of low-oxygen areas that may have existed for years and are just being found, he said, but others are actually newly developed.

Pollution-fed algae, which deprive other living marine life of oxygen, is the cause of most of the world's dead zones. Scientists mainly blame fertilizer and other farm run-off, sewage and fossil-fuel burning.

Diaz and Rosenberg, of the University of Gothenburg in Sweden, conclude that it would be unrealistic to try to go back to preindustrial levels of runoff.

"Farmers aren't doing this on purpose," Diaz said. "The farmers would certainly prefer to have their (fertilizer) on the land rather than floating down the river."

He said he hopes that as fertilizers become more and more expensive farmers will begin seriously looking at ways to retain them on the land.

New low-oxygen areas have been reported in Samish Bay of Puget Sound, Yaquina Bay in Oregon, prawn culture ponds in Taiwan, the San Martin River in northern Spain and some fjords in Norway, Diaz said.

A portion of Big Glory Bay in New Zealand became hypoxic after salmon farming cages were set up, but began recovering when the cages were moved, he said.

A dead zone has been newly reported off the mouth of the Yangtze River in China, Diaz said, but the area has probably been hypoxic since the 1950s. "We just didn't know about it," he said.

Some of the reports are being published for the first time in journals accessible to Western scientists, he said.

Nancy N. Rabalais, executive director of the Louisiana Universities Marine Consortium, said she was not surprised at the increase in dead zones.

"There have been many more reported, but there truly are many more. What has happened in the industrialized nations with agribusiness as well that led to increased flux of nutrients from the land to the estuaries and the seas is now happening in developing countries," said Rabalais, who was not part of Diaz' research team.

She said she was told during a 1989 visit to South America that rivers there were too large to have the same problems as the Mississippi River. "Now many of their estuaries and coastal seas are suffering the same malady."

"The increase is a troubling sign for estuarine and coastal waters, which are among some of the most productive waters on the globe," she said.

Fertilisers kill all ocean life in spread of ‘dead zones’
Lewis Smith, The Times 15 Aug 08;

Aquatic dead zones, stretches of water where little or nothing can survive, have increased by a third in little over a decade. More than 400 dead zones were identified last year, covering a total area of 95,000 square miles, about the size of New Zealand.

The dead zones suffer from hypoxia, a lack of oxygen, which scientists believe is caused by fertilisers washing off the land. When hypoxia sets in, it can drive away tens of thousands of marine animals and, in severe cases, kill them.

Scientists believe that hypoxia ranks with overfishing and habitat destruction as one of the most damaging problems facing sealife.

Since the Sixties, when there were 49 dead zones, the number has increased rapidly and from 1995 to 2007 it rose from 305 to 405. Among the most alarming outbreaks of hypoxia were those in major fishing areas of the Baltic, the Black Sea, the Gulf of Mexico and the East China Sea. One of the largest was identified at the mouth of the Mississippi River and was 8,500 square miles.

“Dead zones were once rare. Now they’re commonplace. There are more of them in more places,” said Professor Robert Diaz, of the Virginia Institute of Marine Science, College of William and Mary, in the United States. He said that dead zones were rarely “a naturally recurring event”.

In a paper published in the journal Science, Professor Diaz and his colleague, Rutger Rosenberg, of the University of Gothenburg, in Sweden, said that dead zones “now rank with overfishing, habitat loss and harmful algal blooms as major global environmental problems”. They wrote: “There is no other variable of such ecological importance to coastal marine eco-systems that has changed so drastically over such a short time.”

According to the scientists, the dead zones occur when nutrients used to enhance farmland, such as nitrogen and phosphorus, wash into the sea and fertilise huge blooms of algae. When dead, the algae are eaten by bacteria, which absorb oxygen from the water as the algae decompose.

The scientists said that keeping fertilisers out of the sea was the best way to reduce the number of dead zones.


Suffocating dead zones spread across world's oceans
Critically low oxygen levels now pose as great a threat to life in the world's oceans as overfishing and habitat loss, say experts

David Adam, guardian.co.uk 15 Aug 08;

Man-made pollution is spreading a growing number of suffocating dead zones across the world's seas with disastrous consequences for marine life, scientists have warned.

The experts say the hundreds of regions of critically low oxygen now affect a combined area the size of New Zealand, and that they pose as great a threat to life in the world's oceans as overfishing and habitat loss.

The number of such seabed zones – caused when massive algal blooms feeding off pollutants such as fertiliser die and decay – has boomed in the last decade. There were some 405 recorded in coastal waters worldwide in 2007, up from 305 in 1995 and 162 in the 1980s.

Robert Diaz, an oceans expert at the US Virginia Institute of Marine Science, College of William and Mary, at Gloucester Point, said: "Dead zones were once rare. Now they're commonplace. There are more of them in more places."

Marine bacteria feed on the algae in the blooms after it has died and sunk to the bottom, and in doing so they use up all of the oxygen dissolved in the water. The resulting 'hypoxic' seabed zones can asphyxiate swathes of bottom dwelling organisms such as clams and worms, and disrupt fish populations.

Diaz and his colleague, Rutger Rosenberg of the department of marine ecology at the University of Gothenburg, call for more careful use of fertilisers to address the problem.

Writing in the journal Science, the researchers say the dead zones must be viewed as one of the "major global environmental problems". They say: "There is no other variable of such ecological importance to coastal marine ecosystems that has changed so drastically over such a short time."

The key solution, they say, is to "keep fertilisers on the land and out of the sea". Changes in the way fertilisers and other pollutants are managed on land have already "virtually eliminated" dead zones from the Mersey and Thames estuaries, they say.

Diaz says his concern is shared by farmers who are worried about the high cost of fertilisers. "They certainly don't want to see their dollars flowing off their fields. Scientists and farmers need to continue working together to minimise the transfer of nutrients from land to sea."

The number of dead zones reported has doubled each decade since the 1960s, but the scientists say they are often ignored until they provoke problems among populations of larger creatures such as fish or lobsters. By killing or stunting the growth of bottom-dwelling organisms, the lack of oxygen denies food to creatures higher up the food chain.

The Baltic Sea, site of the world's largest dead zone, has lost about 30% of its available food energy, which has led to a significant decline in its fisheries.

The lack of oxygen can also force fish into warmer waters closer to the surface, perhaps making them more susceptible to disease.

The size of marine dead zones often fluctuates with the seasons. A massive dead zone, some 8,000 square miles across, forms each summer in the Gulf of Mexico as floodwater flushes nitrogen-rich fertiliser into the Mississippi River.

Experts said it was slightly smaller than expected this year because Hurricane Dolly stirred up the water. Dead zones require the water to be separated into layers, with little or no mixing between.

As well as fertilisers rich in nitrates and phosphates, sewage discharges also contribute to the problem because they help the algal blooms to flourish.

Diaz and Rosenberg say: "We believe it would be unrealistic to return to pre-industrial levels of nutrient input [to oceans], but an appropriate management goal would be to reduce nutrient inputs to levels that occurred in the middle of the past century," before the rise in added nutrients began to spread dead zones globally.

Climate change could be adding to the problem. Many regions are expected to experience more severe periods of heavy rain, which could wash more nutrients from farmland into rivers.

In May, scientists reported that oxygen-depleted zones in tropical oceans are expanding. They analysed oxygen levels in samples of seawater and found the effect was largest in the central and eastern tropical Atlantic and the equatorial Pacific. The increase could push oxygen-starved zones closer to the surface and give marine life such as fish less room to live and look for food.

The scientists, led by Lothar Stramma from the Leibniz Institute of Marine Sciences in Kiel, Germany, say the change could be linked to warming seas. At 0C, a litre of seawater can hold about 10ml of dissolved oxygen; at 25C this falls to 4ml. Stramma said: "Whether or not these observed changes in oxygen can be attributed to global warming alone is still unresolved." The reduction could also be down to natural processes working on shorter timescales, he said.

Ocean dead zones free of oxygen double every decade
Roger Highfield, The Telegraph 14 Aug 08;

Dead zones that are free of oxygen have approximately doubled in number each decade since the 1960s, with many in the coastal waters around Britain.

Scientists warn today that they are now one of the most dire environmental problems of the 21st century.

The alarm about the number of "dead zones"- areas of seafloor that have so little oxygen they suffocate most marine life- is raised by a global study led by Prof Robert Diaz of the Virginia Institute of Marine Science, College of William and Mary.

Working with Dr Rutger Rosenberg of the University of Gothenburg in Sweden, he says that dead zones, where the waters are described by scientists as "hypoxic", are now "the key stressor on marine ecosystems" and "rank with over-fishing, habitat loss, and harmful algal blooms as global environmental problems."

They warn that this issue may quickly become the most important factor controlling humans' use of the sea.

The new study, published in Science, shows that the number of dead zones has increased at an alarming rate.

The first review of dead zones by Prof Diaz in 1995 counted 305 worldwide. That was up from his count of 162 in the 1980s, 87 in the 1970s, and 49 in the 1960s. He has also found scientific reports of dead zones in the 1910s, when there were four.

The new study tallies 405 dead zones in coastal waters worldwide, affecting an area of 95,000 square miles, about the size of New Zealand, though Prof Diaz says that this is an underestimate. "The real number is likely much larger."

Earth's largest dead zone is to be found in the Baltic Sea and experiences hypoxia all year-round.

The largest dead zone in the United States is located at the mouth of the Mississippi river, covers more than 8,500 square miles, roughly the size of New Jersey.

In the Pacific, the biggest zones are around China and Japan, covering more than 7,700 square miles.

Dead zones in the UK tend to be small, he said.

At one time the Mersey estuary dead zone covered about 10 square miles, but now through management efforts the dead zone is gone and the estuary has recovered.

Dead zones occur when excess nutrients, primarily nitrogen and phosphorus, enter coastal waters and help fertilise blooms of algae, a process called eutrophication. Major nutrient sources include fertilisers and the burning of fossil fuels.

The result is an increase of nutrients in the water - usually nitrogen or phosphorus - that triggers a frenzy of action from microscopic organisms.

First phytoplankton take up the nutrients and produce organic matter than eventually sinks to the bottom and dies. There bacteria consume the organic matter and use up the oxygen as they do so.

Prof Diaz began studying dead zones in the mid-1980s after seeing their effect on bottom life in a tributary of Chesapeake Bay near Baltimore. "Dead zones were once rare. Now they're commonplace. There are more of them in more places."

The key to reducing dead zones is "to keep fertilisers on the land and out of the sea."

Prof Diaz says that goal is shared by farmers concerned with the high cost of buying and applying nitrogen to their crops.

"They certainly don't want to see their dollars flowing off their fields into the bay," says Prof Diaz. "Scientists and farmers need to continue working together to develop farming methods that minimise the transfer of nutrients from land to sea."

No species has been wiped out by hypoxia because species have wider ranges than the dead zones, but if there is continued expansion, a wipe out could happen, he said.

"There have been mass mortalities that have wiped out local populations, example of fisheries species mortalities that have had economic consequences," he said.

Examples of local extinctions include Norway Lobster in Kattegat Sweden-Denmark; cockles in Baie de Somme France; stomatopods in Tokyo Bay, clams in New York and oysters in Mobile Bay, United States.