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5 December 2013 11:26 am ,
Vol. 342 ,
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Dawn of the Dead Zones
26 October 2006 (All day)
The number of oxygen-starved "dead zones" in global marine waters has jumped by more than a third in the last 2 years, according to a United Nations Environment Programme (UNEP) report released last week. The latest figures reveal some 200 dead zones worldwide, up from 149 since 2004. The affected waters are robbed of fish, oysters, sea grasses, and other marine life, damaging food supplies for millions of people worldwide, the report warns.
Dead zones form when microscopic marine plants called phytoplankton explode in number. When the phytoplankton die, bacteria feast on them and consume vast amounts of dissolved oxygen. The resulting oxygen depletion--or hypoxia--kills fish, oysters, sea grasses, and other marine life. Although phytoplankton are the backbone of marine food chains and their populations naturally wax and wane, abnormally large "blooms" have been on the rise since the 1970s. According to the UNEP report, this has been due to skyrocketing marine levels of nutrients such as phosphorus and nitrogen from fertilizers, sewage, animal wastes, and other sources.
Marine biologist Robert Diaz of the Virginia Institute of Marine Sciences in Williamsburg compiled much of the findings on dead zones from exhaustive reviews of scientific journals around the world. Better scientific reporting in recent years likely accounts for some of the apparent increase in the phenomenon, he says; "however, there's no mistaking the consistent upward trend over the last 50 years." It is difficult to estimate the total area affected worldwide, but he believes the total is "on the order of" 300,000 square kilometers. About 80% of the zones occur every summer and autumn, he says. Some, such as the Baltic Sea's 80,000-square-kilometer zone, even persist year-round.
The situation may well worsen. The UNEP report projects that the volume of nitrogen alone dumped by rivers into the oceans will climb 14% by 2030, compared to mid-1990s levels. However, not all dead zones are linked to human activities, says paleoceanographer Kjell Nordberg of Göteborg University in Sweden. His historical and geological studies indicate that natural changes in climate and ocean conditions have caused oxygen depletion in some North Sea estuaries and fjords. Not all hope is lost, however. In some areas where sewage discharge and agricultural practices are implicated, regulations to curb the impacts have helped improve oxygen levels over the last few years, Nordberg says.