By Keith Magill | Houma Today
August 2, 2017

“We will never reach the action plan’s goal of 1,950 square miles until more serious actions are taken to reduce the loss of Midwest fertilizers into the Mississippi River system,” one researcher says.

Shrinking the annual Gulf of Mexico dead zone to the size of Delaware will require a 59 percent reduction in the amount of fertilizer runoff flowing down the Mississippi River, a new study says.

The area of low to no oxygen off Louisiana and Texas, which kills fish and other marine life that fail or are unable to move out of the area, spans 8,776 square miles, about the size of New Jersey, the National Oceanic and Atmospheric Administration said in a separate report today.

It is the largest measured since dead zone mapping began 1985, said the NOAA team, led by Nancy Rabalais, a researcher at the Louisiana Universities Marine Consortium’s research center in Cocodrie.

The dead zone is caused by runoff from Midwest farms and cattle pastures that flows down the Mississippi River, scientists say. The pollution, which scientists refer to as “nutrients,” stimulates an overgrowth of algae, which sinks and decomposes, depleting the Gulf waters of oxygen.

The new study, co-authored by LSU scientists, used four computer models to see what it would take to reach the longstanding but elusive goal of cutting the dead zone’s size by more than two-thirds.


“The bottom line is that we will never reach the action plan’s goal of 1,950 square miles until more serious actions are taken to reduce the loss of Midwest fertilizers into the Mississippi River system,” University of Michigan aquatic ecologist Don Scavia, the study’s lead author, said today in a news release.

Published this week in the Proceedings of the National Academy of Sciences, the study concludes that while the goal is still attainable, reaching it will require bold new approaches applied on a large scale in upstream agricultural areas.

“By synthesizing information from multiple sources and computer models, we have developed the most accurate predictions of the dead zone, which is located in one of the most economically and environmentally important bodies of water for our country — the Gulf of Mexico,” said co-author R. Eugene Turner, LSU Boyd Professor in the Department of Oceanography and Coastal Sciences.


The researchers note that little progress has been made in reducing either the nitrogen levels in the rivers that empty into the Gulf or the size of the dead zone itself.

In February 2015, the Mississippi River-Gulf of Mexico Watershed Nutrient Task Force, a coalition of federal, state and tribal agencies, pushed to 2035 the goal of reducing the dead zone to 1,950 square miles.

The most recent five-year average is 5,410 square miles.

The task force also agreed on an interim target of a 20 percent reduction in the amount of nitrogen by 2025.

River concentrations of the nitrogen compound nitrate have not declined since the 1980s, though federal taxpayers have spent more than $28 billion in the 20 Mississippi Basin states since 1995 to reduce the pollution, the researchers said.


“Clearly, something more or something different is needed,” Scavia and his colleagues wrote. “It matters little if the load-reduction target is 30 percent, 45 percent or 59 percent if insufficient resources are in place to make even modest reductions.”

The study’s recommendations to reduce pollution levels include:

  • Change fertilizer application rates.
  • Use cover crops that prevent runoff or fast-growing crops to prevent soil erosion.
  • Improve pollution management,
  • Pursue alternatives to corn-based biofuels, which produce some of the nitrogen runoff.
A 20 percent nitrogen reduction would produce an 18 percent drop in dead zone size over the long term, though it may not have a measurable effect in the next five to 10 years, the study says.

Nitrogen has been considered the main problem, but reducing both it and phosphorus stands the best chance of working, the researchers say.


The 59 percent nitrogen reduction needed to shrink the dead zone to the size of Delaware is larger than the 45 percent cut called for in the Gulf Task Force’s action plan. It is also higher than recommendations made for other U.S. dead zones, including those in Lake Erie and Chesapeake Bay.

Scavia and his colleagues say the new study marks the first time multiple models have been combined to develop a consensus estimate of how a dead zone will respond to fertilizer reductions.

Co-authors are R. Eugene Turner of LSU, Isabella Bertani of the University of Michigan, Daniel Obenour and Alexey Katin of North Carolina State University, and David Forrest of William & Mary College.

The work was supported in part by grants from NOAA and the University of Michigan’s Graham Sustainability Institute.