Hypoxia (environmental): oxygen depletion, a reduced concentration of dissolved oxygen in a water body leading to stress and death in aquatic organisms
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.
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.
The map (click for the larger version):
According to the WRI:
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.
It appears to be part of a broader policy release, due in February. They’ve written a couple of things (in 2003) about the problem on a more localised scale. Globally, I’m looking forward to seeing their ideas about funding conservation and replacing incomes (since agriculture usually pumps the nitrogen into these areas – not for nothing am I Australian). In a world with increasing food prices, I can’t imagine pressure easing from agricultural intensity naturally.