Targeted Cuts Can Ease Gulf Dead Zone

Nine of the 31 states in the Mississippi River Basin contribute 75% of the two nutrients linked to the biological dead zone in the northern Gulf of Mexico, researchers reported last week. Those states are Illinois, Iowa, Indiana, Missouri, Arkansas, Kentucky, Tennessee, Ohio, and Mississippi, which together make up only a third of the Mississippi River drainage area, U.S. Geological Survey scientists found (Environ. Sci. Technol. 2008, 42, 822). Corn and soybean cultivation is the largest contributor of nitrogen discharged into the gulf from the Mississippi, they reported. The largest source of phosphorus is animal manure on pastures and rangelands. The USGS scientists said the most efficient way to curb the amount of nutrients carried to the gulf is to focus reduction efforts on sources such as agricultural fields located near large rivers or small streams that flow quickly. When the nutrients reach the gulf, they feed blooms of algae. The microscopic plants eventually die, decompose, and form the dead zone, a huge area of water with low levels of oxygen off the coasts of Louisiana and Texas.