Effect of landscape position on carbon and water fluxes from tallgrass prairie

John Norman participated in the well-known FIFE experiments on the tallgrass prairie near Manhattan, Kansas. Many of Dr. Norman's contributions on measuring and modeling carbon fluxes during FIFE continue to affect research on this important ecosystem. The need to scale tower and chamber measurements to larger watershed and pasture scales is still an important research question. This is a challenging issue in the tallgrass prairie where the convoluted landscape causes significant variations in soil moisture and primary productivity. A network of eddy covariance towers and a large aperture scintillometer were used to evaluate the effect of landscape position on CO2, H2O, and energy fluxes. Results showed that net carbon exchange at lowland landscape positions was 15 % greater than at the upland locations over the growing season (May to October). Water vapor fluxes were 5 % greater at the lowland over the same period. Measurements of soil respiration using a Norman-inspired flux chamber showed significant spatial variation across the landscape and evidence of temporal stability. Data suggest that using flux towers on upland positions only could result in significant bias of watershed scale carbon fluxes. However, temporal stability coupled with remotely sensed information should make it feasible to use measurements at few key locations on the landscape to estimate fluxes over larger areas.