SCIENCE IN THE NEWS in VOA Special English.
I'm Bob Doughty.
I'm Faith Lapidus. This week, we will
tell about two studies. Both involve
the world's oceans. One study examined
the health of coastal waters for fish and other sea life. The other study examined the quality of air
in coastal cities.
A recent study has raised serious
questions about the health of the world's coastal waters. Coastal waters are important feeding grounds
for fish and other sea life. But the
waters of many coastal areas are being starved of oxygen. The result is that increasingly large areas
of ocean are becoming "dead zones" with almost no sea life.
Diaz was the lead writer of the study.
He says historically good fishing areas are becoming dead zones. Mister Diaz is a professor at the Virginia
Institute of Marine Science at the College of William and Mary. He worked with Rutger Rosenberg of the
University of Gothenburg in Sweden.
Their study appeared last month in Science, a publication of the
American Association for the Advancement of Science.
scientists found that an increasing amount of chemical nutrients have been
entering coastal waters. The nutrients
are mainly nitrogen and phosphorus.
They come from crop fertilizers and wastewater that pollute streams and
rivers, which flow to the sea.
can also come from the atmosphere.
Agriculture, the burning of fossil fuels and natural processes can
produce nitrogen compounds. For
example, nitrous oxide is a gas linked to climate change. Nitrogen then enters the ocean through
rainfall and other atmospheric processes.
Mister Diaz says one fourth of the nitrogen affecting coastal areas
comes from the atmosphere.
nutrients cause an explosion in populations of phytoplankton, small organisms
that use light to make food.
Phytoplankton create oxygen on their own. But as they die, they sink to bottom waters where bacteria break
down the organisms.
The bacteria use up oxygen in the
water. This creates areas at the bottom
of coastal waters that have little or no dissolved oxygen. Fish, crabs and other sea life cannot live
in water that lacks oxygen. They must
either move to more oxygenated waters or die.
Sometimes the oxygen level in the water
drops so quickly that it kills all sea life.
Professor Diaz tells VOA this happened near the coast of New York in
nineteen seventy-six. The damage to the
coastal fishing industry was estimated at five hundred million dollars.
The study shows that the problem of
oxygen-poor water or hypoxia is growing every year. Professor Diaz began studying dead zones in the nineteen
eighties. He has found that the number
of dead zones around the world has doubled every ten years since the nineteen
study found more than four hundred dead zones around the world. They affect more than two hundred forty-five
thousand square kilometers of ocean.
zones are generally seasonal. They
increase in size during the warm summer months when there is more light for
phytoplankton and algae. But after
becoming dead zones, it is very difficult for coastal waters to regain good
levels of oxygen. Some areas, such as
parts of the Baltic Sea, have become permanent dead zones.
Gulf of Mexico has a huge dead zone extending from the mouth of the Mississippi
River. It has doubled in size in the
past twenty years to about twenty-two thousand square kilometers. Hypoxic waters in the Gulf threaten an
important shrimp and crab fishing industry.
Close to Washington, D.C., up to forty
percent of the bottom waters of the Chesapeake Bay become a dead zone in the
world's largest dead zone is in the Baltic Sea. Professor Diaz says about half of the Baltic dead zone contains
no oxygen. This creates another
problem. Different bacteria live in
water that completely lacks dissolved oxygen.
They are known as anaerobic bacteria because they do not need oxygen to
live. Some of these bacteria produce
poisonous hydrogen sulfide gas.
Diaz and Rosenberg say no other environmental problem facing coastal waters has
changed so much over such a short period of time. They say the only way to reduce dead zones is to keep fertilizers
on the land and out of the sea. They
say it is important that scientists and farmers work together to find ways to
reach this goal.
You are listening to SCIENCE IN THE
NEWS, a program in VOA Special English.
With Faith Lapidus, I'm Bob Doughty in Washington.
cities are often considered good places to live. When many people think of such cities, they think of healthful,
fresh air from the sea. But scientists
at the University of California at San Diego found that this idea can be far
A report on the subject recently was
published in Proceedings of the National Academy of Sciences. University of California Professor Mark
Thiemens led the research team.
His team's report blames ships that release dirty smoke by burning
low-cost, high-sulfur fuel. The report
says both ships at sea and those using their engines in port to produce
electricity are to blame.
researchers worked at the Scripps Institution of Oceanography in La Jolla,
California. They directly measured
smoke released from the smokestack of a ship. They also tested air at the end
of the Scripps Pier. The area is just
north of San Diego, which is both a major city and port. The Scripps Pier is also close to waters
with heavy shipping traffic and the city of Los Angeles. Los Angeles has the third largest port in
sulfate is produced when a ship burns fuel called bunker oil. Bunker oil
contains a large amount of sulfur. Most
sulfur released by ships burning bunker oil is a gaseous pollutant -- sulfur
dioxide. After a time, sulfur dioxide
becomes sulfate in the atmosphere. The
researchers say this primary sulfate may be only a small part of what ships
The researchers found that ship smoke
could cause up to forty-four percent of the sulfate particulates found in
coastal California's atmosphere. They
say the levels rose to nearly fifty percent on days when ships burning high
sulfur fuel in the nearby ports were a major influence.
Professor Thiemens said no one had really
expected that ships would be responsible for so many particulates. He said the extremely small particles are
especially threatening. They measure
only one and one half microns in size.
A micron is one millionth of a meter.
researchers say the particulates can travel long distances because they stay in
the atmosphere longer than other pollutants.
Professor Thiemens noted that the air of Los Angeles influenced air
quality in San Diego. That distance is
almost one hundred eighty kilometers.
sulfur particulates also can threaten human health. When people breathe, the particulates stay in their lungs. Other scientists have said that up to sixty
thousand people around the world die each year from dirty ship smoke.
Dominguez was a lead writer of the report.
He developed a chemical test that showed differences between ship smoke
and gases from trucks, cars and other causes.
The researchers also used another test that let them identify sulfur
molecules in the atmosphere. Professor
Thiemens had developed that method earlier.
Other pollutants from ships include
nitrogen oxide and carbon dioxides.
Earlier this year, a United Nations report said gases from ships
produce more than one billion tons of carbon dioxide every year. Ships are not governed under the Kyoto
Protocol, the agreement that establishes limits for gases linked to climate
change. But international rules
requiring ship fuels that burn cleanly are to become effective in twenty
The state of California has already
approved new fuel requirements. They
are to begin next July. All tankers,
supply and passenger ships will have to use cleaner-burning fuels within forty
kilometers of the coast.
SCIENCE IN THE NEWS program was written by Mario Ritter and Jerilyn
Watson. Our producer was Brianna
Blake. I'm Faith Lapidus.
And I'm Bob Doughty.
Read and listen to our programs at voaspecialenglish.com. Join us again at this time next week for more news about
science in Special English on the Voice of America.