Every year, excess fertilizers and animal manure flow down the Mississippi River and empties into the Gulf of Mexico, leaving an increasingly large swath of the gulf completely lifeless.


The Gulf's "Dead Zone," as it's commonly known, is largely the result of excess fertilizer use; as the NOAA website on the gulf hypoxic zone puts it, "Nutrient over-enrichment from anthropogenic sources is one of the major stresses impacting coastal ecosystems." When too much fertilizer and animal waste flow off of farm and ranch lands, it adds too much nitrogen and phosphorus to the water, which depletes oxygen, results in algae blooms, and drives off fish, shrimp and other aquatic life.

In addition to killing off massive amounts of sea life, the Gulf's dead zone has crippled fishing industries for long stretches of the summer in Louisiana and eastern Texas. Last year, the NOAA predicted the largest-ever dead zone, at 8,800 square miles about the size of New Jersey.

But a new report from the U.S. Geological Survey has pinpointed the regions that are responsible for releasing the most phosphorus and nitrogen into the Mississippi River basin.

The report, available at http://water.usgs.gov, follows on an earlier report that narrowed the culprits for 70 percent of the pollution leading to the dead zone to nine states: Illinois, Iowa, Indiana, Missouri, Arkansas, Kentucky, Tennessee, Ohio and Mississippi.

From the report:

Almost all of the top 150 watersheds are in the Corn Belt or near the Mississippi River, with the highest yields of TN [total nitrogen] being in northern Illinois and central Indiana and highest yields of TP [total phosphorus] being from watersheds along the Mississippi River, and in northern Kentucky, and distributed through Missouri, Illinois, and Indiana. [...] Therefore, if one were interested in placing management efforts only in a specified number of the highest contributing watersheds, the watersheds to place efforts could be readily identified.

The cause of the problem: top nitrogen-polluting regions. (Click for big)

The cause of the problem: top phosphorus-polluting regions. (Click for big)

A coalition of environmental groups are taking the report as a call to action: now that the federal government can pinpoint the causes of the problem, it should focus efforts on effective solutions.

"Currently, federal Farm Bill conservation dollars are not targeted to where the pollution is generated. This new report should help states focus their pollution reduction efforts in the top ranked watersheds and on the most cost-effective practices," Michelle Perez, Senior Agriculture Analyst for the Environmental Working Group, said in a statement. "A targeted approach to farm conservation programs will help demonstrate to taxpayers that states are trying to use their resources wisely and get the biggest bang for the buck."

In addition to educating farmers or smart use of fertilizers, possible solutions that could be put to work on the issue include restoring or rebuilding wetlands that can filter excess nutrients from farm runoff, or creating riparian zones of vegetation that parallel waterways and serve much the same filtering function.

In January 2008, two researchers cited a boost in corn ethanol production as another driver of the dead zone. Large-scale corn production is highly fertilizer-intensive, and as a result the USGS researchers' finding that Corn Belt states rank in the top 150 sources for phosphorus and nitrogen pollution comes as little surprise.

In related news, the EPA yesterday announced three grants to Iowa State University researchers that would focus specifically on reducing pollutant runoff into the Mississippi River.