Environmental Impacts of Using Annual Crops for Biofuel.

As first generation feedstocks, annual cropping systems have been the initial focus for unintended environmental impacts of the US bioenergy agenda. These early assessments had a myopic focus on carbon (C) and C accounting including greenhouse gas (GHG) emissions and C sequestration irrespective of the significant, existing research infrastructure dedicated to understanding and mitigating intensive annual crop production impacts on water quality. However, current bioenergy agendas now recognize the importance of nitrogen and a myriad of ecosystem services (ES) with water quality and quantity a prominent target. The purpose of this talk is to review critical challenges encountered when extending bioenergy environmental assessments to water quality and use-efficiency even for well-studied, familiar agroecosystems. First and foremost, current life cycle assessment/analyses (LCA) – the tool of choice for system comparisons – are not programmed to encompass water footprints or quality and there is scant data with which to calibrate and verify any expanded LCA platform. While candidate annual bioenergy crops including maize are well-studied when compared to all second generation, perennial systems, the emphasis has been almost exclusively on productivity in the context of a single environmental outcome (e.g. nitrate loss to surface/ground water). Yet, the few studies of multiple environmental outcomes suggest ES exist in tension and managements targeted at improving one ES may unknowingly have a negative impact on other ES. For example, manure managements designed to reduce nitrate losses to water have been documented to increase GHG emission from maize production. A second major challenge concerns differences in the spatial scale of impact for air and water ES. Unlike GHG emissions which contribute globally, water quality impacts are experienced locally or regionally and the exact location of the nutrient or sediment loss is important to understanding the extent of the impact. Thus, while both GHG and water quality impacts depend on the type of crop, amount and type of fertilizer, soil type, etc., regionalizing a water quality impact requires additional, complex hydrological modeling. Secondary water quality impacts of using annual crops for bioenergy such as land use change are even less understood and, for the present time, can be characterized as theoretical; general supply/demand aspects of water quantity have been entirely ignored although projected climate change scenarios identify water quantity as the most important determinant of system viability. Converting such theoretical characterizations to meaningful, quantitative accountings will require unprecedented unification of air and water research agendas and subsequent investment in long-term agroecosystem studies.