Crop management strategies key to healthy Gulf and planet

Terra Daily: Improved management of crops and perennials could go a long way toward alleviating the problem of hypoxia, which claims thousands of fish, shrimp and shellfish in the Gulf of Mexico each spring. An assessment by a team led by Virginia Dale of Oak Ridge National Laboratory's Environmental Sciences Division concludes that low oxygen levels in water, or hypoxia, causes problems throughout the ecosystem. The death zone, scientifically documented in the Gulf since 1985, has consistently covered about 6,000 square miles, usually off the coast of Louisiana west of the Mississippi River's mouth.

The problem is caused in part by fertilizer run-off from agricultural activities in the Mississippi basin, which drains about 48 percent of the U.S. land. These nutrients combined with stratification caused by warm freshwater from the Mississippi and Atchafalaya rivers running into the colder saltwater of the Gulf sets up the deadly process. Algae grows, then dies and sinks to the bottom, where it decomposes, using up oxygen in the process.

"The oxygen-depleted water at the bottom is not replenished because of the lack of circulation," Dale said. "The more water that flows into the Gulf and the more nutrients in the water, the worse the hypoxia becomes."

While scientists initially believed nitrogen was the major culprit, the assessment team for the Science Advisory Board of the Environmental Protection Agency realized that phosphorus also plays a significant role. The team is recommending a 45 percent reduction in phosphorus and nitrogen from the 1980-1996 average flux during the spring (April, May and June) on a five-year running average….

The delta of the Atchafalaya River on the Gulf of Mexico. View is upriver to the northwest. Photo by Arthur Belala, U.S. Army Corps of Engineers, Wikimedia Commons