Pollution washing off farms in nine states is creating a vast "dead zone" in the Gulf of Mexico, federal scientists said in a new report.
The U.S. Geological Survey report links excessive nitrogen and phosphorus in the northern gulf to Arkansas, Illinois, Indiana, Iowa, Kentucky, Mississippi, Missouri, Ohio and Tennessee.
The nine states make up a third of the 31-state Mississippi River drainage area but contribute more than 75 percent of the nutrient runoff, the report says. Corn and soybean farming was identified as the source of most of the pollution.
The runoff has overfertilized the northern gulf, spurring the growth of excessive quantities of algae and creating a vast swath of water with low levels of dissolved oxygen known as the "dead zone." Low oxygen can smother marine life.
The USGS report is the second this month to link farms in the Mississippi River Basin to problems in the Gulf of Mexico. A study this month in the journal Nature linked farm runoff to the damage of coral formations.
In that report, Yale University and Louisiana State University researchers found that farms have changed the chemistry of the river and gulf by pumping more carbon dioxide into the river over the past 50 years. Carbon dioxide from the farms has made the Mississippi River and the ocean more acidic, which in turn disrupts coral growth.
"It's like the discovery of a new large river being piped out of the Corn Belt," said Yale's Pete Raymond, the study's lead author.
The USGS study used geospatial modeling and tracked 66 percent of the gulf's nitrogen to crops, mostly corn and soybeans. Atmospheric conditions contribute 16 percent of nitrogen and animal grazing and manure are responsible for 5 percent, the report says. Managing manure
But the researchers found that manure, especially from unconfined animals, is a bigger problem with phosphorous than previously thought. Efforts to improve manure management has focused mostly on large confined feeding operations. The USGS study found that animal manure on pasture or range lands was responsible for 37 percent of phosphorous pollution. Corn and soybean cultivation generated 43 percent of the phosphorous, according to the study.
U.S. EPA's scientific advisory board recommended that state and federal officials set reduction targets of at least 45 percent for nitrogen and phosphorous in an effort to shrink the dead zone in half by 2015. A joint federal-state task force is in the process of evaluating the recommendations.
Michelle Perez of Environmental Working Group, an advocacy organization, said the study points to the need for greater investment in farm bill conservation programs, to help farmers improve crop and nutrient management. Crops like corn and soybeans are benefitting from new renewable fuels mandates and some federal farm subsidy programs.
"A good start would be the implementation of a mandatory and comprehensive nutrient management plan that would require all commodity crop subsidy recipients to lower their nutrient pollution while optimizing production," Perez said.E&E News PM
