Proc. Natl Acad. Sci. USA 105, 4513–4518 (2008)

Credit: NASA

Efforts to reduce US greenhouse gas emissions by increasing the production of corn-based biofuels could contribute to an already worsening 'dead zone' in the Gulf of Mexico, finds a new study. Covering an area some 20,000 square kilometres most summers, the Gulf dead zone is characterized by low oxygen levels and is partly caused by nitrogen runoff from farms in the midwest.

Simon Donner of the University of British Columbia, Canada, and Christopher Kucharik of the University of Wisconsin used nutrient-cycling and land-use models to look at how growing more corn for ethanol production would alter nitrogen flow from the Mississippi and Atchafalaya Rivers into the Gulf. Their results suggest that a bill currently before the US Senate, which recommends producing 15 to 36 billion gallons of renewable fuels by 2022, would boost nitrogen runoff by 10 to 34 percent.

This would jeopardize an existing goal of reducing the dead zone to less than 5,000 square kilometres to preserve Gulf coast fisheries. The researchers warn that reaching this target would require fewer, not more, nitrogen-heavy corn fields, which could be achieved only through a radical shift in the American diet and in agricultural land-use practices.