Expert Report

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National interests in greater energy independence, concurrent with favorable market forces, have driven increased production of corn-based ethanol in the United States and research into the next generation of biofuels. The trend is changing the national agricultural landscape and has raised concerns about potential impacts on the nation's water resources. To help illuminate these issues, the National Research Council held a colloquium on July 12, 2007 in Washington, DC. This report, based in part on discussions at the colloquium, concludes that if projected future increases in use of corn for ethanol production do occur, the increase in harm to water quality could be considerable from the increases in fertilizer use, pesticide use, and soil erosion associated with growing crops such as corn. Water supply problems could also develop, both from the water needed to grow biofuels crops and water used at ethanol processing plants, especially in regions where water supplies are already overdrawn. The production of "cellulosic ethanol," derived from fibrous material such as wheat straw, native grasses, and forest trimmings is expected to have less water quality impact but cannot yet be produced on a commerical scale. To move toward a goal of reducing water impacts of biofuels, a policy bridge will likely be needed to encourage growth of new technologies, best agricultural practices, and the development of traditional and cellulosic crops that require less water and fertilizer and are optimized for fuel production.

Key Messages

  • Currently, biofuels are a marginal additional stress on water supplies at the regional to local scale.
  • Expansion of corn on marginal lands or soils that do not hold nutrients can increase loads of both nutrients and sediments.
  • Future expansions of biofuels may need to look to perennial crops, like switchgrass, poplars/willows, or prairie polyculture, which will hold the soil and nutrients in place.
  • Growing biofuel crops in areas requiring additional irrigation water from already depleted aquifers is a major concern.
  • If not addressed through policy and technology development, this effect could accelerate as biofuels expand to 15 percent of domestic usage to meet President Bush's 2017 goal, or to 30 percent of domestic fuel usage as proposed by President Bush as the ultimate goal.
  • If projected future increases in the use of corn for ethanol production do occur, the increase in harm to water quality could be considerable.
  • Policies that better support agricultural best practices could help maintain or even reduce water quality impacts.
  • Policies which conserve water and prevent the unsustainable withdrawal of water from depleted aquifers could also be formulated.
  • The extent of Gulf hypoxia in 2007 is among the three largest mapped to date, and the amount of N applied to the land is also at or near its highest level.
  • The growth of biofuels in the United States has probably already affected water quality because of the large amount of N and P required to produce corn.
  • To move toward a goal of reducing water impacts of biofuels, a policy bridge will likely be needed to encourage development of new technologies that support cellulosic fuel production and develop both traditional and cellulosic feedstocks that require less water and fertilizer and are optimized for fuel production.