Hydrologic and Water Quality Assessment of Bioenergy Scenarios for the Boone River Watershed in North Central Iowa, U.S.

Abstract:

he 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. Phosphorus export to stream systems in the BRW is also a problem of considerable concern. Questions have emerged as to the possible impacts of adopting cellulosic biofuel production systems in Iowa watersheds such as the BRW, which would be developed as function of corn stover removed after harvest or via the introduction of perennial biofuel crops such as switchgrass and miscanthus. In response, a modeling system been constructed for the watershed using the Soil and Water Assessment Tool (SWAT) model to address biofuel-related water quality and related issues. The specific version of SWAT (SWAT version 2012; Release 615) that is being used in the study features recent modifications made to the source code that corrected inaccuracies in previous codes in regards to simulating removal of corn stover and also the growth of switchgrass and miscanthus. In addition, updated crop growth parameters that more accurately represent the biomass production potential of switchgrass and miscanthus varieties being grown in the U.S. Corn Belt region are being used in this SWAT modeling system. The results of several scenarios are reported here that reflect future cellulosic biofuel scenarios based on 20%, 30% or 50% removal levels of corn stover or widespread adoption of switchgrass and/or miscanthus across much or all of the BRW. Both hydrologic and pollutant loss (sediment, nitrogen and phosphorus) losses are reported for all of the simulated scenarios.