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Winter/Spring 2008 Vol. 8 No. 1

Table of Contents


Fuel for Thought

Water Implications of Biofuels

Ever since the "going green" movement captured the American consciousness, corn-based ethanol has been at the forefront as a viable alternative energy choice. Its status was elevated further last year when the Bush administration called for the production of more ethanol -- 35 billion gallons by 2017, compared with 4.5 billion gallons in 2006. As more and more farmers begin to grow corn to keep up with ethanol demand, a central question for the nation is how this agricultural shift will impact water supplies and other resources. 

A National Research Council committee found that the surge would likely lead to adverse effects on local water sources and water quality if new practices are not put into use promptly. Expanding corn and other biofuel crops into regions with little agriculture, especially dry areas, could change current irrigation practices and greatly increase pressure on water resources, particularly limited or dwindling supplies. For example, large portions of the Ogallala aquifer -- which includes a highly agricultural area extending from west Texas into South Dakota and Wyoming -- have shown water-table declines of more than 100 feet. The report stresses that these reduced levels and unsustainable sources should be examined when determining future water-availability scenarios.

Although modest compared with the water needed to grow biofuel crops, water consumed at biorefineries during the ethanol production process could also diminish local water supplies, the report says. A biorefinery that produces 100 million gallons of ethanol a year would use the equivalent of the water supply for a town of about 5,000 people.

More crops also means increased use of fertilizers and pesticides, which would impact the water quality of groundwater, rivers, and coastal and offshore waters. Corn has higher application rates of both fertilizer and pesticides per acre than soybeans and mixed-species grassland biomass do. If farmers switch from growing other crops and plants to corn, larger amounts of soluble nitrogen could run off and migrate to drinking water wells, rivers, and streams. Nitrate and nitrite -- products of nitrogen fertilizers -- could impact human health considerably if their levels are not lowered to below drinking water standards before consumption.

Higher levels of nitrogen, as well as phosphorus, from fertilizers washing into streams could also lead to low-oxygen or hypoxic bodies of water, commonly known as "dead zones," which are lethal for most creatures. Such areas already cover vast parts of the Gulf of Mexico and Chesapeake Bay.

Streams and rivers could also suffer as a result of soil erosion; sediment both impairs water quality and carries pollutants. The amount of sediment erosion is directly related to land use -- the more intensive the use, the greater the erosion. Besides environmental impacts, high sedimentation rates bring financial consequences because they increase the cost of often-mandatory dredging for transportation and recreation.

Geneticist Ken Vogel, who is conducting breeding and genetics research on switchgrass to improve its biomass yield; switchgrass can yield almost twice as much ethanol as corn, photo by Brett Hampton, USDA Agricultural Research ServiceErosion could be minimized if perennial crops -- like switchgrass, poplars, or willows -- or prairie polyculture are used for biofuels instead of corn, the committee suggested, as these hold the soil and nutrients in place better than most row crops. Conservation tillage and leaving most or all of the cornstalks and cobs in the field after the grain has been harvested are additional ways soil erosion could be reduced.

Although the committee laid out numerous steps in its report that could help reduce these impending problems, it stated that fundamental knowledge gaps prevent making reliable assessments about how feedstocks other than corn could impact water resources. Other aspects of crop production may not be fully anticipated, or genetically modified, water-efficient crops could be developed, both of which could also influence future assessments.   -- Jennifer Walsh

Water Implications of Biofuels Production in the United States. Committee on Water Implications of Biofuels Production in the United States, Water Science and Technology Board, Division on Earth and Life Studies (2008, 88 pp.; ISBN 0-309-11361-X; available from the National Academies Press, tel. 1-800-624-6242; $21.00 plus $4.50 shipping for single copies).

The committee was chaired by Jerald L. Schnoor, Allen S. Henry Chair Professor, department of civil and environmental engineering, and co-director of the Center for Global and Regional Environmental Research, University of Iowa, Iowa City. The study was funded by the McKnight Foundation, Energy Foundation, National Science Foundation, U.S. Environmental Protection Agency, and National Research Council Day Fund.

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Copyright 2008 by the National Academy of Sciences