From Time, Coastal Dead Zones Are Growing
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 150 to 200.
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.
The best way to prevent this from happening would be to reduce the amount of nitrogen introduced into the ocean. The technology already exists to do that. If, for example, farmers in the upper part of the U.S. were given a financial incentive to plant crops like winter wheat, rather than leaving their fields fallow after the fall harvest, 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.
No comments:
Post a Comment