Marginal land has been proposed to be a viable choice for biomass production to meet the biofuel development goal set by Energy Independence and Security Act (EISA). However, very little information is currently available for quantifying biomass production potential and impacts on hydrology and water quality. The objectives of this study were to: (1) quantify availability of marginal land in a typical agricultural watershed; (2) test whether the biomass feedstock produced from marginal land in the study watershed can support a hypothetical small bio-refinery with annual capacity of 50 million gallons of ethanol produced; and (3) evaluate the hydrological/water quality impacts of projected biomass production scenarios using Agricultural Policy/Environmental eXtender (APEX) model. In this study, the three types of marginal land were mapped in the St. Joseph River watershed. Yield of switchgrass and Miscanthus from both APEX simulation and literature were used to calculate total biomass produced from marginal land. Total bioethanol that potentially could be produced from biomass produced on marginal land in the watershed was calculated based on the marginal land area, biomass and bioethanol yield. The impacts on hydrology and water quality were evaluated using APEX model. The watershed contains 641 km2 of marginal land (23% of whole watershed area) that could potentially be used for biomass feedstock production. If all marginal lands are converted to switchgrass and Miscanthus production, 45 million gallon bioethanol could be produced from switchgrass and 57 million gallon bioethanol could be produced from Miscanthus according to simulated yield for these two perennial crops. This indicates that the biomass produced from marginal land in the watershed could not support an assumed medium size cellulosic biorefinery with annual production capacity of 50 million gallon by growing switchgrass, but could support that biorefinery by growing Miscanthus on marginal land defined in this study watershed. When land cover on marginal land was converted to switchgrass and Miscanthus, hydrologic and water quality would be impacted significantly (P<0.05) at the marginal land scale (evaluation conducted across all marginal fields), but the impact could be insignificant at watershed scale (evaluation conducted across all fields, including both marginal and non-marginal). Water yield would potentially decrease because of higher evapotranspiration (ET) rate from switchgrass and Miscanthus. Total ET loss for switchgrass is more than Miscanthus because of higher evaporation during non-growing season. Soil erosion would also be reduced because of lower C factor from switchgrass and Miscanthus. Both mineral and organic nitrogen and phosphorus were reduced because of the reduction of fertilization rate when cropland was converted to biomass production. However, the time for fertilization needs to be further investigated because nitrogen in both surface and subsurface flow tend to be increased during the early stage of growing season when grass and forest land are converted to switchgrass and Miscanthus. Generally, Miscanthus showed higher reduction in soil erosion than switchgrass and higher reduction in nutrient loss.
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