Word: deadly
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Dates: during 2000-2009
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Over the past two or three decades, scientists have noticed with growing alarm that vast stretches of coastal waters are turning into dead zones - patches of seabed so depleted of oxygen that few creatures, if any, can survive there. In 2004, the United Nations Environment Program (UNEP) took stock of the phenomenon - which is caused in large part by agricultural runoff - and pronounced it one of the biggest environmental problems of the 21st century. Two years later it noted that the number of identified dead zones, some of which cover thousands of square miles, had climbed from...
Predictably, things have gotten worse since then. Robert Diaz, an ecologist at the College of William and Mary in Virginia who helped UNEP with its numbers, reports in the current issue of the journal Science that today there are more than 400 known dead zones along coastlines around the world, covering roughly 95,000 sq. mi. of seabed. Some of the dead zones that Diaz and his Swedish co-author identify in their review have been around for some time, but have only recently been studied. Many others appear to be new. About 8% of them, mainly those...
...breeding grounds and nurseries for many valuable species. Biologists haven't been able to figure out how much oxygen depletion alone contributes to the decline of teetering fisheries - the question is hotly debated in marine-science circles these days - but few experts would disagree that an increase in dead zones can only be a detriment...
...Dead zones are created when excess nitrogen and other pollutants in ocean water promote large blooms of algae and phytoplankton on the surface. The nitrogen gets there in a couple of ways: through river water filled with fertilizer from farm runoff and from air polluted with tailpipe and smokestack emissions. When the algae die and sink to the ocean floor, bacteria there break them down, while consuming pretty much all of the available oxygen in the water. The bacteria also proliferate wildly, taking over the ecosystem and exacerbating the oxygen depletion. If conditions like strong currents, which are common...
...says marine ecologist Robert Howarth of Cornell University, much of the nitrogenous fertilizer that would normally get washed into waterways by spring thaws could instead be absorbed into winter grain crops. Measures of this sort, if uniformly implemented, could all but eliminate the Gulf of Mexico's famously ballooning dead zone...