Hurricane cut size of this summer's Gulf ‘dead zone,’ but work remains for Iowa, other states

Hurricane Hanna cut the size of the Gulf of Mexico "dead zone," a stretch of water with low to no oxygen that kills fish and marine life, to its third-smallest in 34 years of surveys, scientists reported Tuesday.

The dead zone — attributable in part to agricultural runoff from states including Iowa —was about 2,116 square miles, said Nancy Rabalais, a professor at Louisiana State University, whose team measures the dead zone each year. 

The hurricane, which passed through the Gulf days prior to the survey, mixed the Gulf's water column, disrupting the hypoxic, or dead, zone, she said.

"This was well below the projected estimate, which was about four times" larger, Rabalais said in a call with reporters.

Rabalais said she expects the hypoxic zone to form again within a few days or weeks.

Alicia Vasto, the Iowa Environmental Council's water policy specialist, said the change won't be sustained. 

“The dead zone remains a significant problem in the Gulf and is still largely caused by agricultural pollution from the Midwest,” Vasto said. 

Runoff from Iowa and 31 other states contributes to the Gulf dead zone, which forms when excess nutrients drain into the Gulf from rivers and stimulate algal growth during the spring and summer. The algae eventually die, sink and decompose, depleting the water of oxygen. Fish and marine life must either move or die.

In June, scientists forecast a larger-than-average hypoxic zone of 6,700 square miles, based on high river flows and nutrient loads. The nitrate loads were about 2% above the long-term average in May, and phosphorus loads were about 25% above the long-term average, according to the National Oceanic and Atmospheric Administration.

The annual hypoxic zone size determination is a key metric used by the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force to measure progress toward achieving the five-year average target of 1,900 square miles or less by 2035.

Asked if farm states such as Iowa need regulations to cut nutrient losses, Iowa Agriculture Secretary Mike Naig said during the press conference Tuesday that meeting the goals of the state's Nutrient Reduction Strategy are "voluntary, but not optional."

The strategy, adopted in 2013, seeks to cut by 45% the nitrogen and phosphorus levels that leach from urban and rural areas in the state and flow down the Mississippi and Missouri rivers, contributing to the Gulf dead zone.

Under the strategy, cities, businesses and other point-sources with nitrogen and phosphorus discharge must meet nutrient reduction requirements. But nutrient losses from farms and other so-called non-point sources are not regulated.

"Models are models, and estimates are estimates," said Naig, the hypoxia task force co-chairman. "Even this measurement is a point in time. They're important pieces, but they don't tell the entire story.

"There is more work going on in states up and down the river than there has been before," he continued. "Certainly, when I look at the state of Iowa, I know we have more resources, more funding, more partnerships, more work being done."

A report on Iowa's nutrient reduction strategy in July says conservation practices have cut phosphorous losses by an estimated 18.5% from 2006-2010. Nitrogen levels, however, have climbed an estimated 5%.

"We believe to truly achieve lasting change — to create a culture of conservation, rather than a culture of regulation — we go and work with landowners, we go and work with cities and industries," Naig said. "But we know it will take a tremendous amount of time to do this work. It will take years of work."

Scientists said this year's dead zone is equivalent to 1.4 million acres of habitat potentially unavailable to fish and bottom-dwelling marine species.

Scientists at Louisiana State University and the Louisiana Universities Marine Consortium conducted the survey during a July 25-Aug. 1 research cruise.

Donnelle Eller covers agriculture, the environment and energy for the Register. Reach her at deller@registermedia.com or 515-284-8457. 

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