From:
Environmental Science and Technology Source: pubs.acs.org
Iowa farmer Steve Rash has just begun to harvest this year's corn. He planted half corn and half soybeans, just as he has for 30 years. And that makes Rash different. All around him, midwestern farmers are cashing in on golden ears. In fact, the U.S. Department of Agriculture (USDA) recently forecast (PDF: 886KB) the largest corn crop ever this year—13.3 billion bushels—to meet the nation's demand for ethanol-based fuel.
That has scientists and environmental advocates worried about the toll that expanding biofuel crops, such as corn, will have on land and water. Farmers planted an extra 14 million acres of corn this year—equal to an area more than half the size of Indiana. And more growth is coming: the U.S. ethanol sector will need 2.6 billion bushels per year (yr) by 2010—nearly 50% more than in 2005, according to USDA. The rush to farm more corn is a result of President Bush's call to produce 35 billion gallons (gal) of renewable and alternative fuel by 2017, or about 15% of all U.S. liquid transportation fuel.
Now, the National Academies' National Research Council (NRC), the top science review board in the U.S., has released a new report that fuels the concerns of environmentalists. The study, Water Implications of Biofuels Production in the United States, warns that if the U.S. continues to expand corn-based ethanol production without new environmental protection policies, "the increase in harm to water quality could be considerable." The results: more soil erosion, more pesticides and herbicides in waterways, more low-oxygen "dead zones" from fertilizer runoff, and more local shortages in water for drinking and irrigation.
For now, Rash is waiting to see whether corn ethanol will keep its front-runner status or will be replaced by other green fuels. "I'm not anti-ethanol, I'm just really cautious about the boom," he says, citing concerns about both the economic and environmental sustainability of corn ethanol. For one thing, he notes, traditional corn–soy rotation replenishes soil nutrients that could be stripped away by corn in the long run.
The environmental impacts of biofuel sources, such as corn and soy, have not been adequately factored into policy decisions that encourage biofuel production, according to the NRC report. "We wanted to look at the full life cycle of biofuel production and its impact," says Dara Entekhabi, a report coauthor and hydrologist at the Massachusetts Institute of Technology. Those impacts, he says, could include increases in water, fertilizer, and pesticide use; downstream effects on rivers and estuaries; increased soil erosion; and depletion of aquifers. "These are aspects that have not been carefully considered in assessing whether biofuels are the way to go in the U.S.," he adds.
The NRC Water Science and Technology Board initiated the report after board members brainstormed "the most immediate and high-priority water problems today," says Entekhabi, a board member. Six experts from various disciplines of science, engineering, and agricultural economics, chaired by ES&T's editor in chief, Jerald Schnoor of the University of Iowa, wrote the report after holding a workshop with 130 scientists and stakeholders. The board convened the workshop to speed up the report-writing process, in hopes of providing timely guidance for the U.S. farm and energy bills making their ways through Congress, Schnoor says.
Biofuels could be made "greener" than they are now, experts say. "We already know how to grow corn with less nutrient runoff," adds Nathanael Greene, a senior researcher at the environmental group Natural Resources Defense Council. The key, he says, is making policy choices that set goals not only for more gallons of biofuels but also for reducing water-quality impacts, whether from corn or other biofuel feedstocks. "We have to pursue biofuels because of the climate change imperative," he says. "But we don't want to trade off water pollution, and we don't have to."
Bigger dead zones?
One of the top water-quality concerns about biofuel crops, especially corn, is fertilizer use, the NRC writes. "Corn is such a leaky crop," says environmental scientist Don Scavia of the University of Michigan, referring to the large amounts of nitrogen from fertilizer that runs off cornfields. For one thing, he notes, corn farmers often use drain tiles, a kind of belowground "plumbing", to promote drainage. This drainage also helps flush fertilizer nitrogen from soil into ditches and nearby waters. Plus, corn requires more fertilizer per hectare than other biofuel feedstocks such as grasses, although the report notes that this amount is coming down because of recent advances in biotechnology.
In general, planting more corn should increase the amount of nitrogen that enters groundwater and streams, says Eugene Turner, an oceanographer at Louisiana State University. Others who study hypoxia, the low-oxygen condition resulting from excess nutrients, agree. But this effect is not entirely straightforward, notes Mark David, who is a biogeochemist at the University of Illinois and sits on a U.S. EPA panel studying hypoxia in the Gulf of Mexico. "Every year it's dependent on whether it rains or not," he says. Warmer, wetter conditions flush more nitrogen into waterways. Future climate change adds another layer of uncertainty, according to the NRC report, because major U.S. agricultural regions are projected to become warmer and wetter, but the climate also could be more variable.
The timing of fertilizer application is important, too. Farmers often apply fertilizer in the fall rather than the spring, because fall is drier (so equipment is less likely to compact the soil), less busy, and often brings lower fertilizer prices. Unfortunately, fall application also can give fertilizer more time to leak from soil before the growing season. Overall, increasing corn production by 18 million acres—foreseeable soon given this year's 14 million acre increase—could result in a 33% increase in annual nitrogen loss from soil, according to the latest draft (PDF: 3.1 MB) of the EPA panel's hypoxia report.
The corn boom is so recent, occurring mostly in the past year, that David says "no one can tell for sure yet" whether corn expansion has added to the dead zone in the Gulf of Mexico, which this year was the third-largest on record. But many scientists suspect a link. "The amount of nitrogen in the water in Iowa was at record levels this year," says Matt Rota, water program director for the Gulf Restoration Network, an advocacy group. These levels are so closely tied to hypoxia that Turner says "you almost have to prove it's not the case" that the corn boom contributed to this year's large dead zone.
Scavia, who designs models of nutrients' effect on the dead zone, helped to develop EPA's hypoxia plan in the 1990s. That plan has failed to meet its goal of reducing the size of the dead zone. "Conservation and environmental aspects of the action plan were trampled on the way to $3- and $4-a-bushel corn," he writes in a new commentary for the research organization Resources for the Future.
Scavia and others note that federal soil conservation programs, as well as EPA's hypoxia plan, focus on voluntary best management practices for farmers to reduce environmental impacts, rather than stricter performance standards. In part, this is because it's difficult to monitor runoff from individual farms to demonstrate compliance with standards. Scavia argues that this monitoring is possible if programs require states to conduct watershed-scale monitoring and representative sampling.
Chemicals and water
Fertilizer isn't the only potential problem. According to the NRC report, more pesticides are applied per hectare of corn than with other biofuel plants, such as soy or mixed-species perennial grasses. The report also notes that atrazine, a common herbicide used on corn, can wash into streams.
But an emphasis on atrazine would be misplaced, explains Robert Gilliom, director of the U.S. Geological Survey's National Water-Quality Assessment program. When USDA released enormous corn acreage projections this spring, Gilliom's team rushed to project increases in atrazine. But looking at the best available pesticide use data from industry, the team was surprised. Atrazine use remained level through 2006, but "glyphosate use has gone up dramatically," he says. One reason, according to Gilliom, is that corn farmers are switching from atrazine to glyphosate, sold under the trade name RoundUp, and are planting "RoundUp Ready" corn engineered to survive the herbicide while weeds die.
Glyphosate use has shot up from about 1–2 million pounds (lb) applied to corn and soy in the early to mid-1990s to 13 million lb in 2005. Gilliom says his team would like to keep a closer eye on glyphosate entering into streams, but "it's kind of a budget buster." Because it costs about $300 to analyze one water sample for glyphosate, the group has little data on where it ends up.
Underlying these issues is another problem—soil erosion, which accounts for up to half of the 1.5 billion metric tons of sediment dumped into U.S. waterways each year, carrying nutrients and farm chemicals. The USDA Conservation Reserve Program pays farmers to keep 34 million acres—much of it highly erodible—out of use. But land is in high demand to grow more corn, and USDA is expected to decide this fall whether to allow farmers to cancel contracts early, pulling up to 2.5 million acres out of the program to ease shortages. In addition, corn is considered poor for soil conservation, because it lacks the spreading roots that help perennial grasses hold soil. Tilling adds to that problem by loosening soil, but farmers argue that tilling is needed for seeds to germinate, or sprout, well.
Water use is another concern as corn expands into dry regions, like Texas, that require heavy irrigation. NRC predicts these impacts will be localized but potentially severe in some places. Ethanol production facilities can be water hogs, the report notes, using 3–5 gal of water for every gallon of fuel produced. This means an ethanol facility making 100 million gal/yr uses about 400 million gal of water—equivalent to water use by a small town of 10,000 people.
Again, farming practices could influence how strongly biofuel production exacerbates water supply shortages. For example, Márta Birkás, an agronomist at Szent István University (Hungary), recently presented a study at a farming conference in Budapest that shows that using corn stalks as cogeneration fuel to run biofuel facilities is worsening a drought in Hungary by removing cover and soil organic matter that would hold moisture in soil.
Right ways and wrong ways
The future of biofuels may not lie with corn, and the NRC report suggests that policies should promote the development of cellulosic biofuels from grasses or wood waste. Perennial prairie grasses, like switchgrass, hold great promise if done right, asserts Richard Cruse, an agronomist at Iowa State University and the director of the Iowa Water Center. These plants produce less erosion, because they root well and aren't tilled, and they need no or little fertilizer, he says. But if cropped in monoculture, he cautions, even they could have pest problems that require chemical inputs.
However, USDA's latest report on cellulosic ethanol sends a message to farmers that there is little hope for a boom on the horizon. Granting that cellulosic fuel holds "some longer-term promise," the report maintains that "much research is needed to make it commercially economical." And even that target is a drop in the bucket compared with the 140 billion gal of gasoline that Americans burn every year and the 6 billion gal of ethanol already produced every year from corn.
The NRC report suggests policies that could spur cellulosic development, or at least reduce harmful impacts from corn. For one thing, the farm subsidy system has to change, says report coauthor and Purdue University agricultural economist Otto Doering. "What's been driving the boom expansion has been the 53 cent subsidy for ethanol, and cheap corn," he says. Now, the subsidy is critical to allow ethanol producers to turn a profit, because the price of corn is going up with rising demand, and the price of ethanol is dropping as a supply glut overwhelms the specialized trucks, trains, and barges available to distribute it.
The report suggests a variable subsidy for ethanol, a tactic that has been taken up by Sen. Richard Lugar (R-IN). A sliding scale based on profitability would reduce taxpayer burden and discourage overexpansion funded on subsidies. Plus, the subsidy could be tied to performance standards that require environmental stewardship. Although the plan doesn't have strong support in Congress yet, the EU's European Council is working to define biofuel sustainability requirements, such as CO
2 savings, as part of its plan to increase biofuels to 10% of transportation use by 2020. Furthermore, Doering says, "There's an elephant standing in the corner of the room that no one's willing to tackle, and that's the potential for conservation—using less fuel in the first place."
—ERIKA ENGELHAUP
