Water Implications of Biofuels Production in the United States
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October 2007 Water Implications of Biofuels Production in the United States National interests in greater energy independence, concurrent with favorable mar- ket 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. This report examines some of the key issues and identifies opportunities for shaping policies that help to protect water resources. iofuels—fuels derived from biological materials—are likely Bto play a key role in America’s energy future. In 2007, President Bush called for U.S. production of ethanol to reach 35 billion gallons per year by 2017, which would displace 15 percent of the nation’s projected annual gasoline use. By 2030, the administration aims to increase that production to 60 billion gallons per year. Recent increases in oil prices in conjunction with subsidy policies have led to production based on discussions at the collo- a dramatic expansion in corn ethanol production quium, written submissions of participants, the and high interest in further expansion over the peer-reviewed literature, and the best profes- next decade. sional judgments of the committee. Increased use of biofuels offers many ben- efits, such as a decreased reliance on foreign oil, Types of Biofuels but it also presents some challenges. Among Currently, the main biofuel in the United the challenges that may not have received ap- States is ethanol derived from corn kernels. Corn- propriate attention are the effects of biofuel de- based ethanol is made by converting the starch in velopment on water and related land resources. corn kernels to sugars and then converting those Growing and processing biofuel crops to meet sugars into ethanol. Ethanol derived from sor- America’s energy needs will alter how the na- ghum and biodiesel derived from soybeans com- tion’s water resources are used. However, the prise a very small fraction of U.S. biofuels. Other water implications of biofuels production are potential sources of materials for use in biofuels complex, difficult to monitor, and will vary include field crops such as soy; short-rotation greatly by region. woody crops such as poplar and willow; animal To help illuminate these issues, the Na- fats, vegetable oils, and recycled greases; peren- tional Research Council held a colloquium on nial grasses, such as switchgrass; agricultural July 12, 2007 in Washington, DC to facilitate and forestry residues such as manure and cellu- discussion among representatives from federal losic waste; aquatic products such as algae and and state government, non-governmental orga- seaweed; and municipal waste such as sewage nizations, academia, and industry. This report sludge or solid waste. Different biofuel sources examines the water implications of biofuels have unique implications for water resources. One of the most potentially significant new biofu- Water Use for Biorefineries els on the horizon is “cellulosic ethanol,” derived from All biofuel facilities require water to convert bio- fibrous material such as wheat straw, native grasses, and logical materials into fuel. The amount of water used forest trimmings. Because of technological limitations, in the biorefining process is modest compared to the cellulosic ethanol can currently be produced only at pilot water used for growing the plants used to produce and commercial demonstration-scales; however, produc- ethanol; however, because water use in biorefineries is tion of cellulosic ethanol is expected to begin commer- concentrated into a smaller area, such facilities effects cially within the next decade. can be substantial locally. A biorefinery that produces 100 million gallons of ethanol per year, for example, Implications for Water Supply would use the equivalent of the water supply for a town Water is an increasingly precious resource used of about 5,000 people. Ethanol producers are increas- for many critical purposes; in some areas of the coun- ingly incorporating water recycling and use-reduction try, water resources are already significantly stressed. measures in order to maximize energy yields while re- For example, large portions of the Ogallala (or High ducing water use. Plains) aquifer, which extends from west Texas up into South Dakota and Wyoming, show water table declines Implications for Water Quality of over 100 feet since about the 1940s. Increased bio- Shifting agricultural practices to incorporate fuels production will likely add pressure to the water more biofuel crops will affect water quality as well as management challenges the nation already faces as bio- water quantity. Converting pastures or woodlands into fuels drive changing agricultural practices, increased cornfields, for example, may exacerbate problems as- corn production, and growth in the number of biore- sociated with fertilizer runoff and soil erosion. fineries. Water Use for Irrigation Fertilizer Runoff and Nutrient Pollution Whether or not biofuel crops will require more For most crops, it is standard agricultural practice or less water will depend on what crop is being sub- to apply fertilizers such as nitrogen and phosphorus, as stituted and where it is being grown. Corn generally well as pesticides, which include herbicides and insec- uses less water than soybeans in the Pacific and Moun- ticides. However, these chemicals can wash into bodies tain regions, but the reverse is true in the Northern and of water and affect water quality. For example, excess Southern Plains. Therefore, farmers switching from nitrogen washing into the Mississippi River is known soybeans to corn will need more water in some regions to be a cause of the oxygen-starved “dead zone” in the and less water in others. As this example demonstrates, Gulf of Mexico, in which marine life cannot survive. there are many uncertainties in estimating the overall Different crops require different amounts of fer- net impacts of biofuel crops on our water resources. tilizers. One metric that can be used to compare wa- Another important consideration is how biofuel ter quality impacts of various crops are the inputs of production might drive the expansion of agricul- ture into regions that currently support little ag- Fuel Feedstock U.S. Production in 2006 riculture. Expansion of agricultural lands, espe- cially into dry western areas, has the potential to Ethanol Corn 4.9 billion gallons dramatically affect water availability. Sorghum < 100 million gallons The report concludes that in the next 5 to Cane sugar No production (600 million 10 years, increased agricultural production for gallons imported) biofuels will probably not alter the national- Cellulose No production (one demon- aggregate view of water use. However, there are stration plant in Canada) likely to be significant regional and local impacts Biodiesel Soybean oil Approximately 90 million where water resources are already stressed. gallons Depending on what crops are grown, where the crops are grown, and whether there is an increase Other vegetable oils < 10 million gallons in overall agricultural production, significant Recycled grease <10 million gallons acceleration of biofuels production could cause Cellulose No production much greater water quantity problems than are U.S. production of different types of biofuels in 2006. currently experienced. SOURCE U.S. Congressional Research Service. fertilizers and pesticides per unit of the net energy gain captured in a biofuel. Of the potential bio- fuel crops, the greatest application rates of both fertilizer and pesti- cides per acre are for corn. Per unit of energy gained, biodiesel requires a small fraction of the ni- trogen and phosphorous used for corn-based ethanol. All else being equal, converting other crops or non-crop plants to corn will likely lead to much higher application rates of nitrogen. However, there are many management practices that can improve the efficiency of fertilizer application and how it is used by plants. For example, recent ad- vances in biotechnology have in- creased yields of corn per unit of Existing and planned ethanol facilities (2007) and their estimated total water applied nitrogen and phosphorous. use mapped with the principal bedrock aquifers of the United States and total water use in year 2000. SOURCE: Janice Ward, U.S. Geological Survey. Soil Erosion and Sedimentation Sedimentation occurs when Reducing Water Impacts through Agricul- soil erodes from land and washes down into surface tural Practices water bodies. Sediments impair water quality and also There are many agricultural practices and tech- carry agricultural and other pollutants. The amount of nologies that can simultaneously increase crop yields sediment eroding from agricultural areas is directly while reducing impacts on water resources. These tech- related to land use—the more intensive the use, the nologies include a variety of water-conserving irriga- greater the erosion. For example, more sediment erodes tion techniques, erosion prevention techniques, fertiliz- from row crop fields, such as corn, than from pastures er efficiency techniques, and precision agriculture tools or woodlands. that take into account site-specific soil pH (acidity/al- One of the most likely causes of increased erosion kilinity), moisture, and other measures. Such practices in the near term may be withdrawal of lands from the can have a large, positive environmental impact. U.S.