Ocean "Dead Zones" Increasing: 400 Oxygen-Deprived Areas Now Exist

mississippi delta gulf of mexico satellite photo

image: NASA

Every year the topic of the dead zone in the Gulf of Mexico seems to pop up on TreeHugger—most recently in a report which links expanded corn production to the increasing size of the zone. New research shows that it's not just in the Gulf that ocean dead zones are expanding but throughout the world.

Dead Zones Have Doubled Every 10 Years Since 1960s
According to the study, the number of marine dead zones—areas which are periodically or permanently starved of oxygen—has doubled every 10 years since the 1960s, with those along coastlines increasing in size and intensity. Currently there are about 400 coastal areas, with a combined area larger than the size of Oregon, with such poor water quality, with so little oxygen that only microbes can survive in it. Fish and crustaceans must flee the area or die.

marine dead zones map image

Map showing partial number of current marine dead zones: Dr Robert Diaz/NASA
Fertilizer Run-Off, Sewage Worsen the Problem
The reason for the increase? The predictable culprit of human activity.

The New York Times describes what is happening:

Nitrogen from agricultural runoff and sewage stimulates the growth of photosynthetic plankton on the surface of coastal waters. As the organisms decay and sink to the bottom, they are decomposed by microbes that consume large amounts of dissolved oxygen. Most animals that live at the bottom of the coastal ocean cannot survive as oxygen levels drop.

how marine dead zones happen image

image: US DEP
Stop the Runoff and the Dead Zones Could Recover
And steps that can be done the address the problem:
Robert W. Howarth, a professor of ecology and environmental biology at Cornell, said that methods to reduce nitrogen-rich runoff exist, including planting winter rye or winter wheat in cornfields during the off-season so the spring rains do not cause the chemicals to leach into waterways. [TH note: You could also decrease the amount of fertilizer used...]

Nevertheless, most experts agree that the changes needed to reverse the trend are dramatic. For example, scientists estimate that cutting the Gulf of Mexico's dead zone by a third would require a 45 percent decrease in nitrogen-rich runoff from the Mississippi River watershed, which extends into the croplands of the upper midwest.

Want to know more? NASA has a pretty good overview of the issue of marine dead zones.

via :: The New York Times
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