Assessment of the impacts of biofuel crops on the carbon, water, and nitrogen cycles in Central Illinois Marcelo Zeri, Andrew VanLoocke, George Hickman, Carl Bernacchi Energy Biosciences Institute, University of Illinois, Urbana, IL Introduction Eddy covariance measurements of carbon and energy fluxes are performed in Central Illinois over four crops that can be used for cellulosic biofuel production. The objective of this work is to assess the long term environmental impacts of each crop on the carbon and water cycles at this site. The species planted are Corn (Zea Mays), Miscanthus (Miscanthus x giganteus), Switchgrass (Panicum virgatum) and a selection of prairie varieties. The plots were established in the spring of Future activities The measurements will continue for the next 10 years. During this time the collected data will be used to test the effects of different management practices on yields and efficiencies on biomass conversion for each species, as well as to validate carbon cycle models. Additionally, measurements of methane (CH 4 ) and nitrous oxide (N 2 O) will be performed on the next growing season by the use of a tunable diode laser analyzer. For the short term the quality of the data will be compared to fetch and footprint conditions and the uncertainty in the annual sums of NEE will be calculated. Additional information can be found online at References: Foken, T., M. Göckede, M. Mauder, L. Mahrt, B. D. Amiro, and J. W. Munger. "Postfield data quality control." In Handbook of micrometeorology: a guide for surface flux measurement and analysis., edited by X. Lee, W. J. Massman, and B. Law, Dordrecht: Kluwer Academic Publishers, 2004, pp 181–208. Reichstein, M., et al. "On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm." Global Change Biology 11, 9: (2005) 1424–1439. Measurements The measurements are made using a RM Young sonic anemometer and a LICOR Open Path analyzer installed at 4 m. The fluxes are later processed using Alteddy (Jan Elbers, This software includes all the necessary corrections and generates also the quality flags for each half hour (Foken et al., 2004). The gaps in the time series of CO 2 -flux and latent (LE) and sensible heat fluxes (H) were later filled according to Reichstein et al. (2005). The fluxes of CO 2, H, and LE for a period at the end of August are shown below (left). Maize had the highest uptake of carbon (negative values), while Miscanthus, Switchgrass and Prairie had lower but comparable values. Sensible and latent heat fluxes had similar diurnal cycles. The energy balance closure was calculated for Prairie during a period of 10 days at the end of August (below, right). The closure was of ~80%, in agreement with the values commonly reported. Annual sums of Net Ecosystem Exchange Preliminary results for the annual sums of Net Ecosystem Exchange (NEE) are shown below. Maize had the highest annual uptake (-278 gCm -2 y -1 ) and the highest ratio of Gross Primary Productivity over ecosystem respiration, GPP/R eco, (1.32). Miscanthus was a source of carbon due to the fact that 2008 was the establishment year and the vegetation cover was still sparse. It is expected that the uptake increases over the next growing seasons. Prairie and Switchgrass were comparable in the annual uptake and on the ratio of GPP/R eco.