Coastal dead zones spread globally, study finds

In the latest sign of trouble in the planet's chemistry, the number of oxygen-starved "dead zones" in coastal waters around the world has roughly doubled every decade since the 1960s, killing fish, crabs and massive amounts of marine life at the base of the food chain, according to a study released on Aug. 14. Driving the trend are nitrogen and phosphorous from chemical agricultural fertilizers that reach coastal waters after flowing off farm fields and into streams and rivers, according to the study published in the journal Science. Nitrogen compounds from burning fossils fuels, particularly from power plants and cars, also are settling back to the ground and eventually wash into coastal waters, they said. This decade alone, the number of coastal dead zones has risen by about a third to 405 worldwide, with clusters on the coasts of the United States and Europe. Combined, they take up an area of at least 95,000 square miles. The biggest one measures about 30,000 square miles in the Baltic Sea, the researchers said. This is followed in size by one in the Gulf of Mexico starting at the mouth of the Mississippi River in the United States and one at the mouth of China's Yangtze River in the East China Sea. "It's not sort of a local or regional problem, which is how it was thought of in the past," Robert Diaz of the College of William and Mary's Virginia Institute of Marine Science said. "It is actually a global problem." "Most of it is agricultural-based, but there is a lot of industrial nitrogen in there, too, if you consider electric generation industrial," added Diaz, who tracked the proliferation of the dead zones along with Rutger Rosenberg of the University of Gothenburg in Sweden. The number of dead zones started to approximately double every 10 years starting in the 1960s, the researchers said. There were 301 such dead zones at the end of the 1990s, 132 at the end of the 1980s, 63 at the end of the 1970s and 39 at the end of the 1960s, Diaz said. The researchers said dead zones must be considered an important source of stress on marine ecosystems, ranking alongside over-fishing, habitat loss from human development and harmful algal blooms as global environmental problems. Dead zones are formed when excess nutrients, mostly nitrogen and phosphorus, enter coastal waters and help fertilize blooms of algae. When these tiny plants die and sink to the sea bottom, they provide a food source for bacteria, which consume dissolved oxygen from surrounding waters. As a result, there are large areas of sea floor with insufficient oxygen to support most marine life. Low oxygen, known as hypoxia, is in significant measure a downstream effect of chemical fertilizers used in agriculture. Air pollution, including smog from automobiles, is another factor. The nitrogen from the fertilizer and the pollution feeds the growth of algae in coastal waters, particularly during summer. "We're saying that hypoxia is now everywhere, it seems," Diaz said. "Human activities really screwed up oxygen conditions in our coastal areas." "Fish are the best at avoiding dead zones. When the oxygen starts to decline, they're smart -- they leave, they don't hang around. Crabs and shrimp are pretty good at getting away, too, as are lobsters," Diaz said. But slower-moving creatures on the sea floor often die, including worms, clams and small crustaceans. "These are the animals that are the fundamental food base for the commercial crabs, shrimp and fish that feed on the bottom," Diaz said. The study is the latest alarm sounded by scientists and environmentalists about deteriorating oceans and watersheds. Douglas N. Rader, chief ocean scientist for the Environmental Defense Fund, said the chaos in the planet's nitrogen cycle is not only creating dead zones but also inciting the spread of toxic organisms, such as the pfiesteria that has appeared in recent years in the Chesapeake. "The next big challenge, after global warming, is going to be addressing the massive upset of the world's nitrogen cycle," Rader said. Earlier this week, the Proceedings of the National Academy of Sciences published online a study warning of "mass extinction in the oceans with unknown ecological and evolutionary consequences." The author, Jeremy Jackson, a professor at the Scripps Institution of Oceanography, contends that global warming, overfishing, invasive species, habitat destruction and agricultural runoff are creating oceans crammed with algae and jellyfish -- a process he calls "the rise of slime." "We have utterly failed to appreciate the magnitude of the problem," Jackson said yesterday. "The oceans are out of sight and out of mind."