Wednesday, October 25, 2006

A rise in the number of dead zones

The latest count of hypoxic or "dead" zones in coastal oceans around the world is up to almost 200, according to scientists at a recent UN Environment Program meeting in Beijing.

As I've mentioned before, these areas of low oxygen are usually caused by excess loading of nutrients by nitrogen (from things like fertilizer). The nutrients cause lots of algae to grow, and when the algae dies and decomposes, much of the oxygen in the water at the bottom is consumed. The lack of oxygen makes life difficult for fish and other organisms living in the deep waters near the coast.

The "dead zone" in the Gulf of Mexico near the mouth of the Mississippi River is one of the best known examples. Robert Diaz from the College of William and Mary, who has published surveys of the world's hypoxic zones in the past, reports that hypoxia is now common in Fosu Lagoon, Ghana; the Pearl River Estuary and the Changjiang River, China; the Elefsis Bay, Aegean Sea, Greece; Paracas Bay, Peru; Mondego River, Portugal; Montevideo Bay, Uruguay and the Western Indian Shelf.

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