Nitrogen fertilizers expand Gulf "dead zone," make streams unsafe for swimming, drinking

The "dead zone" in the Gulf of Mexico, caused mainly by use of nitrogen fertilizers, has reached near-record size and would be bigger than ever if Hurricane Dolly hadn't stirred up the water, Joel Achenbach reports in The Washington Post. As the Post chart shows, the zone has grown in four of the last five years.

Achenbach, the author of Why Things Are (1991), explains that nitrogren spurs "the growth of algae. Animals called zooplankton eat the algae, excreting pellets that sink to the bottom like tiny stones. This organic matter decays in a process that depletes the water of oxygen," killing or driving away fish. "The hypoxia tends to go away after October as cooler weather slows algae growth and storms mix the waters. Even so, there's a "legacy" from year to year, said Eugene Turner, a professor of coastal ecology at Louisiana State University who makes annual predictions of the size of the dead zone. Not all organic matter on the bottom decays in any given year."

Turner told Achenbach that the whole Mississippi River watershed, including the Ohio and Missouri rivers (which are larger than the Mississippi where they join), is affected by increased use of nitrogen, mainly by corn farmers seeking high prices driven by ethanol. Achenbach wrotes, "About half the streams and rivers in the watershed are unsafe for swimming, drinking, recreational contact or use as drinking water, Turner said." (Read more)