The vast oxygen-starved dead zone in the northern Gulf of Mexico shrunk by more than half its typical size this year, but scientists see nothing to celebrate.
The dead zone -- an area so low in oxygen that it hosts almost no life -- still spanned 3,000 square miles when measurements were taken last week.
In comparison, a coalition of state and federal agencies wants to see the dead zone shrink to a five-year average of 2,000 square miles by 2015. That average now is about 6,000 square miles, with 2009 included.
"The size this year seems to be a little bit smaller, but clearly there is still a lot to be concerned about," said Suzanne Schwartz, acting director of the Office of Wetlands, Oceans and Watersheds for the Environmental Protection Agency. "The dead zone continues to be a problem locally, regionally and nationally."
Since 2001, when goals were first set to reduce the dead zone and curb nutrient pollution in the Mississippi River by 45 percent, virtually no progress has been made. For the past three years, record amounts of nutrient pollution -- the primary driver behind the dead zone -- have entered the Gulf of Mexico through the Mississippi.
Only weather variables have kept the zone from approaching its record size of approximately 8,900 square miles in 2002, scientists said.
Schwartz said the federal government is increasing efforts to combat the dead zone, focusing attention on nutrient pollution and considering stricter enforcement of water quality standards through the Clean Water Act.
The push could lead to heightened nutrient pollution reduction efforts in Florida and elsewhere.
The Mississippi River drains roughly 41 percent of the continental U.S., encompassing 1.2 million square miles of cities and farmland.
An average of about 1.7 million tons of nutrients, mostly from fertilizer runoff, enters the Gulf yearly, according to the National Oceanic and Atmospheric Administration.
Nutrients feed plants, but also algae, which eventually dies and drops to the ocean floor. Decaying algae sucks oxygen from the water, suffocating animals that cannot escape.
NOAA considers the dead zone a major threat to the Gulf's $2.8 billion recreational and commercial fishing industries.
The smaller dead zone this year is "just a little blip on the long-term data that we have," said Nancy Rabalais, a lead scientist for the Louisiana Universities Marine Consortium, which collaborates with NOAA to track the dead zone's size.
"The fact that it's smaller might make people tend to think the problem has gone away, we're making a difference. Whereas this smaller size doesn't really indicate that because there really hasn't been much movement to cut the nutrients in the river," Rabalais said.
Mississippi nutrient pollution was so high in May and June that forecasters, sponsored by NOAA, predicted the dead zone would reach up to 8,500 square miles.
But river flows plummeted in July and a series of odd weather events, including stronger than normal winds, foiled predictions. Wind helps circulate water, bringing fresh oxygen to depleted areas.
Where the dead zone did occur, however, it was more severe. Depletion stretched from the sea floor to near the surface, where scientists found crabs, shrimp, eels and other bottom-dwellers swimming.
Similar episodes of oxygen depletion occur on a smaller scale in Southwest Florida, particularly in Charlotte Harbor and Tampa Bay.
"Both of them are related to excessive nutrients in freshwater runoff," said Rick Bartleson, research scientist with the Sanibel-Captiva Conservation Foundation.
Low oxygen events in parts of Charlotte Harbor date to at least the 1990s, Bartleson said. Massive algal blooms off the coast here also have led to widespread areas of depleted oxygen, especially during red tides.
Recently, low oxygen killed scores of clams in the Caloosahatchee River.
In Tampa Bay, recurrent algal blooms have formed two years in a row.
"It's becoming more of a concern to bay managers," said Ed Sherwood, program scientist with the Tampa Bay Estuary Program.
Donald Boesch, president of the University of Maryland Center for Environmental Studies, said standards need to be set along the Mississippi so that changes occur on state, local and regional scales.
"There's a need to move beyond the denial phase we've often gone through," Boesch said. "We need to recognize the compelling science and use our best strategies."