Doyle, Geoffrey (USDA-ARS, Grazinglands Research Laboratory, 7207 W. Cheyenne, El Reno, OK, 73036; Phone: 4052625291; Fax: 4052620133; Email:


Direct Comparison Of Two Systems For The Measurement Of Carbon, Water And Energy Fluxes In Tallgrass Prairie


G.L. Doyle *, W. Dugas, H. Mayeux


Micrometrological literature reflects a lack of extensive research on grassland mass and energy flux, and there remains a lacks of a standard method/measurements system. The objective of this study was to compare mass and energy fluxes of sensible heat flux density (H), latent heat flux density (LE) and carbon dioxide (CO2) from CSI-manufactured Eddy Covariance (EC) and Bowen Ratio/Energy Balance (BREB) instrumentation. The study site was a tallgrass prairie located in central Oklahoma, with above ground biomass of 8 Mg ha-1, and mean annual precipitation of 840 mm y-1. Results from co-located EC and BREB units over more than 36 month period indicated that both systems demonstrated similar seasonal patterns, yet the EC measured 30% lower values for H and LE when compared to the BREB. The sum of EC H and LE fluxes were 20-70% less than what was required to close energy balance. On days with flux greater than 0, BREB CO2flux was 2 - 10% more positive (more loss) when compared to the EC. The tallgrass prairie site typically was a source of CO2for up to 8 months each year, and a sink during the other 4 months - where the uptake rates were sufficiently high enough to produce average annual uptake. Average daily CO2 flux for the entire period was approximately -0.4 g CO<sub>2</sub> m-2 d-1small sink).