In the search for renewable fuel alternatives, biofuels have gained strong political momentum. In the last decade, extensive mandates, policies, and subsidies have been adopted to foster the development of a biofuels industry in the United States. The Biofuels Initiative in the Mississippi Delta resulted in a 47-percent decrease in cotton acreage with a concurrent 288-percent increase in corn acreage in 2007. Because corn uses 80 percent more water for irrigation than cotton, and more nitrogen fertilizer is recommended for corn cultivation than for cotton, this widespread shift in crop type has implications for water quantity and water quality in the Delta. Increased water use for corn is accelerating water-level declines in the Mississippi River Valley alluvial aquifer at a time when conservation is being encouraged because of concerns about sustainability of the groundwater resource. Results from a mathematical model calibrated to existing conditions in the Delta indicate that increased fertilizer application on corn also likely will increase the extent of nitrate-nitrogen movement into the alluvial aquifer. Preliminary estimates based on surface-water modeling results indicate that higher application rates of nitrogen increase the nitrogen exported from the Yazoo River Basin to the Mississippi River by about 7 percent. Thus, the shift from cotton to corn may further contribute to hypoxic (low dissolved oxygen) conditions in the Gulf of Mexico.
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Unintended consequences of biofuels production?The effects of large-scale crop conversion on water quality and quantity
U.S. Geological Survey
Mississippi Water Science Center
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Welch, H.L., Green, C.T., and Coupe, R.H., 2009. The fate and transport of nitrate through the unsaturated zone at a site in northwestern Mississippi in Geological Society of America 2009 Annual Meeting, Proceedings: Geological Society of America Abstracts with Programs, volume 41, number 7, p. 29. Green, C.T., Welch, H., and Coupe, R., 2009. Multi-tracer analysis of vertical nitrate fluxes in the Mississippi River Valley alluvial aquifer, in Eos Transactions of the American Geophysical Union, 90 (52), Fall meeting, Abstract H31C-0799.