Every spring and summer, a "dead zone" of oxygen-poor waters the size of Massachusetts forms in the Gulf of Mexico. Fish, crab and shrimp catches decrease in these hypoxic waters, which lose oxygen due to massive algal blooms triggered by fertilizer runoff.

The zone has existed for at least 50 years, and the Environmental Protection Agency has set goals to shrink this massive zone. Recent federal mandates to grow more biofuels in the agricultural region that drains into the Mississippi River basin promise to hinder those efforts, according to a new report.

Researchers from the Carnegie Mellon University in Pittsburgh concluded that "meeting the biofuel goals set forth [by the federal government] will likely increase the occurrence of hypoxia ... regardless of the selection of crops."

Some biofuel advocates had suggested that growing switchgrass and other biofuel crops that need less fertilizer than corn and soybeans would help reduce the nitrate pollution. The scientists said the change to more cellulose-based crops could cut nitrate runoff by as much as 20 percent, but that is not enough to meet EPA runoff targets intended to reduce the size of the dead zone.

The scientists advocate aggressive nutrient management that includes wetland construction, vegetative buffers, tillage management and precision fertilizer application.

"Only when all the nitrogen runoff associated with the production of corn, soy, and switchgrass is reduced will the EPA goal be met," the study said. The report will appear in the October issue of the journal Environmental Science and Technology.

Jim Dawson reports for Inside Science News Service, which is supported by the American Institute of Physics, a not-for-profit publisher of scientific journals.