Eddy Covariance Measurements of CO2 and Energy Fluxes Above Mountain Grasslands in the Austrian Alps: Challenges and Results

Fluxes of CO2 and energy have been measured over several differently managed mountain grasslands in the Austrian Alps over the past seven years. Here we discuss the challenges associated with the application of the eddy covariance method in complex mountainous terrain and show how these flux measurements can be validated using a multiple-constraints approach. It is shown that defensible eddy covariance flux measurements over low-statured mountain grasslands are possible even in complex terrain as long as the measurement height is low enough to remain within the shallow equilibrium layer where the wind field exhibits characteristics akin to level terrain and rigorous quality control is exercised. Differences in ecosystem-atmosphere exchange of CO2 and energy between sites are related to gradients in land use and climate caused by differences in elevation. It is shown that elevation-mediated changes in climate, in particular the length of the vegetation period, and land use, in particular the cutting frequency, have an opposing influence on the carbon cycling of mountain grasslands, resulting in similar net carbon balances irrespective of elevation.