Scaling Biogeochemical Processes to Quantify the Impacts Regional Scale Land-Use-Change in the Context of Bioenergy.

The Energy Independence and Security Act (EISA) of 2007 set in place a mandate to produce 36 billion gallons of renewable fuel per year, the majority of which non-cornstarch derived, by 2022.  As a result, land use has and will likely continue to undergo major shifts within regions such as the Mississippi River Basin (MRB).  Major questions concerning the impacts of this land-use-change on the cycling of carbon, nitrogen and water have emerged, with those related to changes water quality and quantity presenting a particular challenge.  Ecosystem models have evolved to be a powerful for predicting the impacts of such transitions and are critical in scaling field-based measurements.  Central to this scaling effort is the need to resolve a complex and interacting set of above and below ground processes which are sensitive to soil texture.   Soil texture is highly variable across the MRB, which will have major impacts associated with the inputs of carbon, nitrogen and water as well as their storage and cycling.  This presentation will explore the example of the impacts of soil texture on the prediction of water quality and quantity in the context of large scale adoption of cellulosic ethanol production under a range of EISA-motivated scenarios.  Modeling results from these scenarios produced with the agricultural version of the Integrated Biosphere Simulator (Agro-IBIS) and the Terrestrial Hydrology Model with Biogeochemistry (THMB) that indicate that some scenarios could significantly reduce the Gulf of Mexico Hypoxic zone associated with nitrate leaching in the MRB will be shown.  We will highlight a specific example related to the impact of sub-grid scale variability from field-based measurements on assessing model uncertainty.  The presentation will conclude with a discussion of the broader scale policy implications of model uncertainty and the potential role of improved soil texture datasets in reducing this uncertainty.