Gulf of Mexico’s dead zone is smaller in size, not impact: An editorial

By Editorial page staff, The Times-Picayune
31 July 2012

Scientists say the dead zone off Louisiana’s coast this summer is one of the smallest since mapping began 27 years ago, but that’s not cause for celebration.



The area of low oxygen didn’t shrink this year because of success in reducing nutrient pollution that enters the Gulf from the Mississippi and Atchafalaya rivers. Instead, the size owes to record drought conditions throughout much of the watershed.

The dead zone is 2,889 square miles this year — a bit larger than the state of Delaware — compared to a five-year average of 5,695 square miles. But the fact that the zone is smaller during a drought is just further proof that nutrient pollution, mainly from agriculture, is the cause of the low oxygen conditions.

Nitrogen and phosphorus that run off from farmland enter the Mississippi and eventually the Gulf, where the nutrients cause massive algae blooms. When the algae die and decay, oxygen is depleted. The resulting hypoxia kills bottom-dwelling marine life and causes others, like fish, to avoid the areas where oxygen is low.

Water levels in the Mississippi and Atchafalaya rivers was nearly half that of normal conditions, and the nutrient load was 56 percent lower than average, according to the U.S. Geological Survey.

"The issue of nutrient overload, of both nitrogen and phosphorus, remains a critical issue for the health of water bodies within the Mississippi River Basin and in the northern Gulf of Mexico,” according to the Louisiana Universities Marine Consortium, which just concluded a mapping cruise of the Gulf last week.

"Efforts should continue in full force to reduce nutrient loads,” the report said.

Unfortunately, those efforts to reduce nutrients have been voluntary and obviously not very effective. The Gulf of Mexico/Mississippi River Watershed Nutrient Task Force has set a goal of keeping the dead zone at about 1,930 square miles. But even though this year’s dead zone is the fourth-smallest on record, it still exceeds that target. And some years, the dead zone has been much larger. In 2002, for example, it measured 8,400 square miles.

Scientists also noted that there was patchy distribution of hypoxia across the Gulf this summer — different from anything previously observed. That’s puzzling, and researchers need to figure out what’s going on.

But as for the dead zone itself, the cause is obviously fertilizer use, and meaningful attempts to reduce nutrient runoff are long overdue.