Human actions can have serious ecological impacts, even those meant to solve environmental problems and increase sustainability. Take the policy-driven boom in corn-ethanol in the United States: while intended to increase energy security and reduce carbon emissions, this action may increase the size of the low oxygen ‘dead zone’ in the northern Gulf of Mexico.
Nitrogen Pollution from Fertilizer in the Mississippi River Causes the Dead Zone in the Gulf of Mexico
The dead zone is caused by the influx of excess nitrogen delivered by the Mississippi River, which largely originates from agricultural fertilizers. It has serious impacts on the Gulf’s coastal ecosystem and the commercial fisheries it supports. This is a long-recognized problem; the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force has a goal to shrink the dead zone by reducing river nitrogen export levels by 45%.
Biofuels like Corn-Ethanol are Intended to Increase Energy Security and Reduce Carbon Emissions
Rising energy costs and environmental concerns have led a number of countries to create energy policies that promote the production of biofuels to both increase energy security and reduce carbon emissions. Recent U.S. Energy Policy set a domestic production target of biofuels at 15-36 billion gallons of ethanol and biodiesel biofuels per year by 2022.
To stimulate the industry growth necessary to enable reaching this target in only 17 years, the U.S. government introduced subsidies, which triggered a ‘biofuels boom’, which focused on corn-based ethanol because corn was easy to obtain and use for ethanol ‘feedstock’. The increased demand drove corn prices up, encouraging U.S. farmers to increase corn production. In 2007, for example, U.S. farmers planted more corn on more land than in the previous 60 years.
Growing More Corn in the Midwest for Ethanol Increases Nitrogen Export by the Mississippi River
However, growing corn requires lots of nitrogen fertilizer and corn production in the American Midwest already contributes significantly to the nitrogen exported to the Gulf of Mexico by the Mississippi River. Furthermore, most of the increased corn production in 2007 occurred within the northern Mississippi River watershed. Thus, the Energy Policy ethanol goals directly conflict with the Task Force’s goal of reducing nitrogen export.
Recent science confirms this conflict. In a large-scale ecosystem modeling analysis, scientists Simon Donner and Christopher Kucharik showed that expanded corn-ethanol production in the Midwest would increase nitrogen export by the Mississippi River above current levels(S. Donner and C. Kucharik, 2008, 'Corn-based ethanol production compromises goal of reducing nitrogen export by the Mississippi River', Proceedings of the National Academy of Sciences, 105(11), pages 4513 to 4518).
This result held for several land use/corn production scenarios that met the 2022 biofuels goal. In fact, only a scenario of intense and probably unrealistic mitigation was able to meet both the Energy Policy ethanol target and Task Force nitrogen reduction target.
Using an Ecosystem Model to Identify Environmental Trade-offs
This unexpected trade-off between energy security and lower carbon emissions on the one hand and a healthier coastal ecosystem on the other exemplifies the challenge of crafting environmental policy that broadly supports sustainability. It also emphasizes the need to look widely for unexpected conflicts during policy development. The ecosystem modeling approach taken by Donner and Kucharik is an excellent example of how this can be done.
