EDDY COVARIANCE AND BOWEN RATIO ESTIMATES OF WATER VAPOR AND CO_2 FLUXES OVER CRESTED WHEATGRASS

摘要

Recent studies of CO_2 exchange for various terrestrial ecosystems include a global network of sites called FLUXNET (Baldocchi et al., 2001). These sites use the eddy covariance approach. There is also a network in the US operated by the USDA estimating CO_2 fluxes with the Bowen Ratio technique (Svejcar et al., 1997). This approach is most valid for uniform surfaces, but may have problems in heterogeneous landscapes (Hipps et al., 1998). Since some sites are in regions not covered by FLUXNET, it would be valuable to integrate the two sets of data. However, consistency between the two approaches must be determined. We address this issue by comparing energy balance and CO_2 fluxes over crested wheatgrass (Agropyron desertorum) measured with Bowen Ratio (BR) and eddy covariance (EC) systems. The uniform nature of this community, makes it ideal to examine the agreement between the systems. The specific goals of this study are:1. Measure the energy, water, and CO_2 fluxes over crested wheatgrass from early spring to late fall with both a BR and EC system.2. Quantify energy balance closure for the EC system, and examine the effects of forcing the fluxes to match the available energy.3. Compare fluxes from the two systems, and examine how agreement varies with season and environmental conditions.