The world is getting familiar with the carbon cycle and how pumping carbon that's been buried for millions of years into the atmosphere causes some global problems. Well, get ready to learn about nitrogen.
Like carbon, the nitrogen cycle is all out of whack. In this case, the origins are similar. Instead of burning petroleum or coal, nitrogen comes from natural gas transformed into ammonia fertilizer and used to grow crops; what doesn't absorb into the soil runs off into streams, which flow into rivers, which flow to the ocean, where the nitrogen fuels "dead zones" – areas where nitrogen (and phosphorus) fertilizes so much algae growth that it absorbs enough oxygen to make the water inhospitable to fish and other marine life. Jellyfish are about the only thing that thrives in these conditions; corals certainly do not.
There are other causes of dead zones; human sewage, inadequately treated, is another, as is the fallout from burning fossil fuels and certain industrial processes. Dead zones, which start as "eutrophic" zones (that is, over-rich with fertilizers), and end up as "hypoxic" areas (that is, short of oxygen), often shrink and grow with the seasons.
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The World Resources Institute recently mapped the world's dead zones and found a whopping 415 eutrophic zones, including 169 that are known to be hypoxic and another 169 that probably are. The researchers believe the number is much higher, since only the United States and the European Union do an adequate job of counting and reporting problem coastal areas. China and other fast-growing Asian economies are likely polluting their coasts, but the problem hasn't been documented, the researchers say.
As the map shows, a mere 13 eutrophic zones are in recovery – a particularly sorry tally considering scientists have long known the causes and have long since identified solutions to the problem. The Chesapeake Bay and Gulf of Mexico are two examples close to home of systems whose dead zones are well documented, but not greatly improved, even despite millions of taxpayer dollars being spent on the problem. (The Gulf of Mexico dead zone threatened to grow bigger than ever in 2007, as farmers buoyed by ethanol subsidies planted a near-record crop of corn, leading to a flood of fertilizer down the Mississippi.)
"Our findings highlight the dramatic growth of areas receiving the endflows of nitrogen and phosphorus created by agriculture, increasing industry, fossil fuel combustion, and population growth," Mindy Selman, one of the researchers, wrote. "More than 1,000 scientists estimated, in the Millennium Ecosystem Assessment, that, as a result of human activities over the past 50 years, the flux of nitrogen has doubled over natural values while the flux of phosphorus has tripled."
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