The National Research Council’s new report discussed the impact of biofuels of today and tomorrow on water supply and pollution.
From the Executive Summary (pictures and graphs from elsewhere):
President Bush has called for production of 35 billion gallons of ethanol annually by 2017, which, if achieved, would comprise about 15 percent of U.S. liquid transportation fuels.
USDA estimates of corn use
This goal is almost certain to result in a major increase in corn production, at least until marketable future alternatives are developed…Corn generally uses less water than soybeans and cotton in the Pacific and Mountain regions, but the reverse is true in the Northern and Southern Plains, and the crops use about the same amount of water in the North Central and Eastern regions.
In some areas of the country, water resources already are significantly stressed. For example, large portions of the Ogallala (or High Plains) aquifer, which extends from west Texas up into South Dakota and Wyoming, show water table declines of over 100 feet. Deterioration in water quality may further reduce available supplies. Increased biofuels production adds pressure to the water management challenges the nation already faces.
The Ogallala aquifer is the largest aquifer in North America.
Water Quality Impacts
Fertilizer use results in increased nutrients, nitrogen and to a lesser extent phosphorous, in groundwater and surface runoff.
Excess nitrogen in the Mississippi River system is known to be a major cause of the oxygen-starved “dead zone” in the Gulf of Mexico, in which many forms of marine life cannot survive. The Chesapeake Bay and other coastal waterbodies also suffer from hypoxia (low dissolved oxygen levels) caused by nutrient pollution. Over the past 40 years, the volume of the Chesapeake Bay’s hypoxic zone has more than tripled. Many inland lakes also are oxygen-starved, more typically due to excess levels of phosphorous….Of the potential feedstocks, the greatest application rates of both fertilizer and pesticides per hectare are for corn. Per unit of energy gained, biodiesel requires just 2 percent of the N and 8 percent of the P needed for corn ethanol. Pesticide use differs similarly. Low-input, high-diversity prairie biomass and other native species would also compare favorably relative to corn using this metric.
Dead zone expanding, and expected to reach 8,500 square miles this year.
Greater use of marginal land, except for native grasses, could increase soil loss and pollutant transport. Corn requires much more fertilizer — 50 time as much nitrogen and 12 times as much phosphorous as for biodiesel, and pesticide than other fuel sources. Low-input, high-diversity prairie biomass and other native species also do much better than corn.
Reducing Water Impacts through Agricultural Practices
There are many agricultural practices and technologies that, if employed, can increase yield while reducing the impact of crops on water resources. Many of these technologies have already been developed and applied to various crops, especially corn, and they could be applied to cellulosic feedstocks. Technologies include a variety of water-conserving irrigation techniques, soil erosion prevention techniques, fertilizer efficiency techniques, and precision agriculture tools that take into account site-specific soil pH (acidity, alkalinity), soil moisture, soil depth, and other measures. Best Management Practices (BMPs) are a set of established methods that can be employed to reduce the negative environmental impacts of farming.
Such practices can make a large, positive environmental impact. For example, in 1985, incentives were put in place to encourage adoption of conservation tillage practices. According to data from the National Resources Inventory (NRI), maintained by the Natural Resources Conservation Service, overall annual cropland erosion fell from 3.06 billion tons in 1982 to about 1.75 billion tons in 2003, a reduction of over 40 percent (http://www.nrcs.usda.gov/TECHNICAL/NRI/).
In addition, biotechnologies are being pursued that optimize grain production when the grain is used for biofuel. These technologies could help reduce water impacts by significantly increasing the plants’ efficiency in using nitrogen, drought and water-logging tolerance, and other desirable characteristics.
Soil erosion decreased 43%.
The water impact of biorefineries will be less overall, but locally it could be large.
A biorefinery that produces 100 million gallons of ethanol per year would use the equivalent of the water supply for a town of about 5,000 people…use of water is declining as ethanol producers increasingly incorporate water recycling and develop new methods of converting feedstocks to fuels that increase energy yields while reducing water use.
In 2006, 4.9 billion gallons of ethanol supplied 2.4% of US fuels on an energy basis (about 1.5 gallons of ethanol provides the same energy as 1 gallon of gasoline). 100 million gallons of ethanol would supply enough fuel for 29 such towns.
Key Policy Considerations
Subsidy policies have driven dramatic expansion of corn ethanol production.
From a water quality perspective, it is vitally important
to pursue policies that prevent an increase in total loadings of nutrients, pesticides, and sediments to waterways. It may even be possible to design policies in such a way to reduce loadings across the agricultural sector, for example, those that support the production of feedstocks with lower inputs of nutrients.
Cellulosic feedstocks, which have a lower expected impact on water quality in most cases (with the exception of the excessive removal of corn stover from fields without conservation tillage), could be an important alternative to pursue, keeping in mind that there are many uncertainties regarding the large-scale production of these crops….
Biofuels production is developing within the context of shifting options and goals related to U.S. energy production. There are several factors to be considered with regard to biofuels production that are outside the scope of this report but warrant consideration. Those factors include: energy return on energy invested including consideration of production of pesticides and fertilizer, running farm machinery and irrigating, harvesting and transporting the crop; the overall “carbon footprint” of biofuels from when the seed is planted to when the fuel is produced; and the “food vs. fuel” concern with the possibility that increased economic incentives could prompt farmers worldwide to grow crops for biofuel production instead of food production.
Though biofuels are a marginal additional stress on water supplies in the US today, they have probably already affected Gulf hypoxia. The anticipated increase in biofuels over the next decade could lead to problems of water supply and pollution in the absence of policies.