Sensitivity Analysis of the Factors Influencing the Environmental Impact of Biofuel Production in the Upper Mississippi River Basin

The U.S. biofuel industry, namely the conversion of ethanol from corn, has increased the demand for corn as a result of government initiatives to increase alternative fuel productions to 35 billion gallons annually by 2017. Currently, a third of the corn crop grown nationally is used for ethanol production and this is expected to increase significantly in the foreseeable future. Growing corn traditionally requires high inputs of water and nutrients. The inevitable increase of environmental impacts resulting from increased corn production has been the focus of a US EPA-funded modeling study. The objective has been to identify the significant factors under various climate and management conditions that are most influential in controlling the environmental impacts. These factors can then serve as quantitative indicators to guide policy and management practices to minimize negative effects on the environment. This work focuses on the Upper Mississippi River Basin (UMRB), which is central to the nation's corn production. UMRB is one of the major sources of excess nutrient loadings into the Mississippi River and considered a leading contributor to the hypoxia problem in the Gulf of Mexico. The Soil and Water Assessment Tool (SWAT) model was applied to simulate the hydrologic and water quality impacts of increased corn production in the UMRB area. UMRB SWAT model sensitivity analyses were performed for a variety of different climate and management scenarios. The results indicate that changes in rainfall and temperature are the most influential factors for all hydrologic and nutrient outputs. When the management practice of removing corn stover (a process to yield more ethanol producing material) was incorporated in the model, it generally reduced the nutrient loss and increased erosion. Nutrient management practices did not produce large impacts or changes in nutrient loss at the basin scale.