"We found that meeting the ethanol production targets set for the year 2022 in the Energy Policy will increase nitrogen levels in the Mississippi by 10-34%," Simon Donner of the University of British Columbia told environmentalresearchweb. "This will make the already difficult challenge of reducing the 'dead zone' practically impossible."
The US Energy Bill sets a target of 36 billion gallons of renewable fuels by 2022; 15 billion gallons of this can be produced from corn starch. More than 80% of total US corn and soybean acreage is grown in the Mississippi-Atchafalaya river basin, which covers 3.2 million km2.
When nitrogen from agricultural fertilizers enters the ocean via this river system it boosts the growth of phytoplankton. As these organisms die, they accumulate at the bottom of the ocean, where their decomposition can lower the oxygen concentration to dangerous levels. This hypoxia creates a "dead zone", killing marine organisms such as crabs, fish, anemones and sea stars. The result has serious implications not only for ecosystems but also for the fishing industry.
In recent years the dead zone in the Gulf of Mexico has been more than 20,000 km2 in size. The Mississippi Basin/Gulf of Mexico Task Force hopes to reduce the zone to less than 5000 km2 but recent research indicates this could need a reduction in nitrogen export of up to 55%.
"However, the new US Energy Policy calls for a huge increase in the production of ethanol from corn," said Donner. "If the US pursues this biofuels strategy, there is little hope for reducing the dead zone. The only way to meet the corn ethanol goals and shrink the dead zone to an acceptable size will be to dramatically reduce the non-ethanol uses of corn. That means less animal feed: the US will face a choice between using corn to fuel animals, and using corn to fuel cars."
Donner and Chris Kucharik from the University of Wisconsin, US, used an agricultural version of the Integrated Biosphere Simulator (IBIS) – a process-based dynamic ecosystem model – and the Terrestrial Hydrology Model with Biogeochemistry (THMB) to simulate the effects of increased corn production on nitrogen export to the Gulf of Mexico. Nitrogen export depends not only on land use and land cover but also on annual variability in rainfall and river discharge.
"Even with reductions in other uses of corn, the construction of efficient riparian [river-side] wetlands adjacent to fertilized croplands and the implementation of on-farm nitrogen management practices will be necessary to achieve the large reduction in nitrogen loading required," write the researchers in a paper in PNAS. "A massive national wetland restoration project, on the order of 22,000 km2 of wetlands and/or widespread adoptions of efficient nitrogen management practices, like a change in diet and meat production, would not be trivial to implement."
Now Donner is looking at what the conflict between demand for meat and demand for biofuels means for nutrient pollution and greenhouse gas emissions.