It’s the nitrogen, stupid

August 04, 2005

editorial page

The dead zone in the Gulf of Mexico this summer is smaller than last year, but the credit goes to weather conditions, not human efforts to reduce nutrient pollution, so it’s hardly cause for celebration.
Marine scientist Nancy Rabalais, who measures the area every year, found that the area of low oxygen covered 4,564 square miles last month. That compares with 5,800 square miles last year, which was considered an average-sized dead zone.
Dr. Rabalais attributes this year’s decline to reduced flow from the Mississippi and Atchafalaya rivers in May and June and a series of tropical storms and hurricanes that mixed oxygen into deeper water.
We can’t count on weather to stir the pot every year, though. Even though this dead zone is smaller than average, it’s more than twice as large as the national goal, which calls for an average dead zone of 1,930 square miles by the year 2015.
Reaching that goal is going to be impossible if Midwestern farm states continue to drag their feet on voluntary reductions in the use of nitrogen fertilizer — the main culprit behind the dead zone.
The same fertilizer that makes grain grow in the nation’s heartland drains into the Mississippi River as runoff and eventually enters the Gulf, where it triggers bumper crops of algae. As the algae die and decompose, oxygen is depleted in lower, saltier layers of the Gulf, repelling fish and shrimp and killing bottom-dwelling organisms.
Nitrogen’s role in this phenomenon is indisputable, given the wealth of peer-reviewed research that shows the link. But farm interests recently have been trying to shift the blame to phosphorus, and that has slowed efforts to reduce fertilizer use.
Such delay tactics must stop. An Environmental Protection Agency study looked at phosphorus and found that it plays only a small role, and nitrogen is the main problem. That should end attempts to turn phosphorus into the red herring of the dead zone.
Dr. Rabalais summed it up well: "We can keep measuring it year after year, but if we still allow nitrogen to flow off the land and the concentration is not going down, it’s not going to make a difference."