February 6, 2008
|Two new studies have shed light on some of the primary culprits in the degradation of the Gulf of Mexico and the Mississippi River. The information can be used immediately by journalists covering the issue, and is likely to influence long-term policy-making designed to reduce the problem.
It's been known for some time that one of the main culprits in the annual formation of the dead zone in the Gulf is nitrogen from the Mississippi River basin. Phosphorous has also been pegged recently as a major culprit.
A USGS study that was announced Jan. 29, 2008, provides significant new information on both substances. The team found that the great majority of nitrogen and phosphorous comes from just 9 of the 31 states in the basin: IL, IN, IA, MO, AR, TN, KY, OH, and MS. The biggest sources are corn and soybean crops, and manure from animals on open pasture. These pose the greatest threat when they are near larger rivers, and where there are no dams. Atmospheric deposition from sources such as power plants is also a significant source.
For journalists, it will be relatively easy to identify in the field the primary pollution sources, and see what the landowners and operators are doing. Nutrient loads on the Gulf also put a new light on the push to expand corn acreage for ethanol production.
A study published Jan. 24, 2008, in the journal Nature looks at other significant agricultural impacts on the Mississippi River basin. The Yale and Louisiana State Univ. researchers found that certain agricultural practices, such as liming, installation of tile drains below fields, and tilling methods, have substantially increased runoff volume and added carbon dioxide to the system, increasing water acidity. The study was based in part on data tucked away for half a century in a New Orleans attic.
The study is available here. A Jan. 23, 2008, press release is here.