The name of the problem is hypoxia. Since 1972, scientists have reported areas in the Gulf where seawater contains less than 2 parts per million of dissolved oxygen. Such hypoxic areas cannot support most marine life, and have thus earned the nickname "dead zones."

Oxygen depletion in sea water occurs when an overabundance of nutrients, most notably nitrogen, phosphorus and carbon, promote the rapid growth and decomposition of algae and phytoplankton. The phenomenon, called "eutrophication," is a natural process, but it has been greatly accelerated by human activity. Scientists call this people-driven form of the process "anthropogenic eutrophication."

In the Gulf of Mexico, as in other oceans and lakes around the world, anthropogenic eutrophication has caused the formation of hypoxic areas from which mobile organisms, such as fish, crabs and shrimp, are forced to flee. Creatures that can't escape either die or grow weaker, depending on how low the oxygen level drops and for how long.

Nancy Rabalais, a professor and the executive director of the Louisiana Universities Marine Consortium, has studied hypoxia in the Gulf of Mexico for 21 years. She says hypoxia has not caused any catastrophic losses in fisheries resources in the northern Gulf -- yet.

"We do have an impaired habitat; we do have evidence of shifts in fisheries," Rabalais says. "But as stated, we have not seen a catastrophic loss."

Still, she expects losses to occur if hypoxic conditions continue to worsen. That's because other marine ecosystems that have experienced dead zones, such as the Baltic and Black Seas, have witnessed steep declines in ecologically and commercially important species.

The size of the Gulf's dead zone varies widely from year to year, depending mostly on how much water flows down the Mississippi River. Years with high rainfall generally create large dead zones, while drought years create smaller ones. In both 2001 and 2002, the hypoxic area in the Gulf grew to encompass an area larger than the state of New Jersey.

The Environmental Protection Agency has created an "action plan" aimed at controlling hypoxia in the northern Gulf of Mexico. Part of the plan includes research by universities and the USDA's Agricultural Research Service (ARS). At MU, investigators have begun their effort by working to establish a contamination timeline, chiefly by examining levels of nitrogen in the Gulf's sediment record.

To almost no one's surprise, the record indicates an overall increase in nitrate loads since the 1950s, an increase that corresponds to a rise in levels of nitrogen fertilizer used on Midwestern farm fields. It has been during this post-1950 nitrate-usage surge that the hypoxic zone has grown alarmingly large.

Back at Mark Nuelle's cornfield, the MU and USDA team doesn't need reminding about the scale of the Gulf crisis. But they also understand the farmer's perspective.

"There isn't a farmer out there who hasn't heard that nitrogen can be a problem, and yet they know they have to apply nitrogen to make money," says Newell Kitchen, a soil scientist with the USDA-ARS. "There's no other management that has a greater impact on the amount of grain you put in the bin."

Applying only as much nitrogen fertilizer as the corn can use would allow farmers to maximize yield and profit while minimizing levels of nitrogen running off their fields after harvest. But it's easier said than done, explains Scharf.

Published by the Office of Research.

©2006 Curators of the University of Missouri. Click here to contact the editor.