The push to ramp up biofuel production may reduce oil imports, but it's likely to come at a high environmental cost: It will boost the size of the Gulf of Mexico's dead zone, a huge swath so depleted of oxygen that almost nothing can live there, according to a new analysis.
The gulf's dead zone is already a major environmental problem. First spotted in 1971, it now spans 14,600 square kilometers, or 1,460,000 hectares, a region larger than Connecticut. It is triggered every spring and summer when nutrient-rich water flows from the Mississippi and Atchafalaya Rivers into the Gulf of Mexico. The nutrients, including nitrogen and phosphorus, come primarily from fertilizer washed off of farms throughout the Midwest. They trigger blooms of algae that then die and are eaten by bacteria. The bacteria use up most of the water's dissolved oxygen, killing fish, shrimp, crabs, and other organisms.
The U.S. federal government and agencies from several states in the Mississippi River Basin have established efforts to reduce nutrient flows into the Gulf of Mexico in hopes of limiting the size of the dead zone to 500,000 hectares, about one-third of its current size. But in 2007, Congress passed the Energy Independence and Security Act (EISA) that aims to reduce oil imports by backing the production of 36 billion gallons of biofuels by 2022. Of that, 15 billion gallons is slated to come from corn ethanol and the rest from cellulosic ethanol and other "advanced biofuels" that require less energy and fertilizer inputs.
Last year, researchers reported that if 15 billion gallons or more of biofuels per year came from corn ethanol, the result would be a large spike in nutrients hitting the Gulf of Mexico. For the current study, Michael Griffin, a microbiologist at Carnegie Mellon University in Pittsburgh, Pennsylvania, and colleagues asked how the gulf would fare if more fuels came from cellulosic feedstocks, which typically require only about one-fourth of the fertilizer that corn does.
They found that even if all the biofuels came from cellulosics, the amount of nitrates in the water would be only about 20% lower than if 15 billion gallons came from corn ethanol. But in both scenarios, the nitrogen emissions into the gulf would be higher than today's levels, and thus would be expected to increase the size of the gulf's dead zone.
The new work, reported in the 1 October issue of Environmental Science & Technology, underscores just how difficult it will be to reverse the growing dead zone in the Gulf of Mexico, says Simon Donner, a climate scientist and ecologist at the University of British Columbia, Vancouver, in Canada: "Something that was already difficult, the biofuels mandate will make practically impossible."