SUSTAINABILITY SCIENCE
Corn-based ethanol production compromises goal of reducing nitrogen export by the Mississippi River
*Department of Geography, University of British Columbia, 1984 West Mall, Vancouver, BC, Canada V6T 1Z2; and
Center for Sustainability and the Global Environment, Nelson Institute for Environmental Studies, University of Wisconsin, 1710 University Avenue, Madison, WI 53726
Edited by Robert Howarth, Cornell University, Ithaca, NY, and accepted by the Editorial Board January 21, 2008 (received for review September 1, 2007)
Abstract
Corn cultivation in the United States is expected to increase to meet demand for ethanol. Nitrogen leaching from fertilized corn fields to the Mississippi–Atchafalaya River system is a primary cause of the bottom-water hypoxia that develops on the continental shelf of the northern Gulf of Mexico each summer. In this study, we combine agricultural land use scenarios with physically based models of terrestrial and aquatic nitrogen to examine the effect of present and future expansion of corn-based ethanol production on nitrogen export by the Mississippi and Atchafalaya Rivers to the Gulf of Mexico. The results show that the increase in corn cultivation required to meet the goal of 15–36 billion gallons of renewable fuels by the year 2022 suggested by a recent U.S. Senate energy policy would increase the annual average flux of dissolved inorganic nitrogen (DIN) export by the Mississippi and Atchafalaya Rivers by 10–34%. Generating 15 billion gallons of corn-based ethanol by the year 2022 will increase the odds that annual DIN export exceeds the target set for reducing hypoxia in the Gulf of Mexico to >95%. Examination of extreme mitigation options shows that expanding corn-based ethanol production would make the already difficult challenges of reducing nitrogen export to the Gulf of Mexico and the extent of hypoxia practically impossible without large shifts in food production and agricultural management.
Gulf of Mexico | hypoxia | nitrogen cycling | biofuels | agriculture
Author contributions: S.D.D. designed research; S.D.D. and C.J.K. performed research; S.D.D. contributed new reagents/analytic tools; S.D.D. and C.J.K. analyzed data; and S.D.D. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. R.H. is a guest editor invited by the Editorial Board.
To whom correspondence should be addressed. E-mail: simon.donner{at}ubc.ca
© 2008 by The National Academy of Sciences of the USA
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