Assessment of Bioenergy-Related Scenarios for the Boone River Watershed in North Central Iowa

Abstract

The Boone River Watershed (BRW) is an intensively cropped region dominated by corn and soybean production that covers over 237,000 ha in north central Iowa. The BRW is reflective of both current Iowa cropping trends and elevated levels of nutrient pollution in streams. Nitrate losses are of particular concern, much of which escapes the cropland via subsurface tiles that drain the predominantly flat landscapes that characterize the watershed. Concerns have emerged as to whether current trends towards more corn production in the watershed could result in greater nitrate and other nutrient losses to the BRW stream system. A modeling system been constructed for the watershed using the Soil and Water Assessment Tool (SWAT) model to address biofuel-related water quality and other relevant issues. The system has been configured for a broad suite of scenarios including several that are related to current and possible future bioenergy demands. The results of six scenarios are reported here that reflect current or near-future biofuel scenarios (varying levels of expanded corn production) and six that focus on expansion of perennial grasses, which represent future ligno-cellulosic biofuel crop production and/or simply introduction of more perennial species for reducing non-point source nutrient pollution. Expansion of continuous corn was predicted to result in sediment decreases of 2 to 11% and nitrate increases of 9 to 100%, relative to the baseline. The perennial grass scenarios resulted in sediment and nitrate loss decreases that ranged between 5 to 39% and 3 to 26%, respectively, as compared to the baseline.