Document: AND-3-59-26

Ecosystem level energy balance over a high-elevation subalpine forest.

TURNIPSEED, A.A.* and R.K.MONSON

University of Colorado, Boulder, CO 80309 ¹

Abstract:
The amount of energy moving in and out of an ecosystem has a direct impact on carbon cycling since it is one of the primary driving forces behind transpiration and respiratory processes. Since photosynthetic carbon uptake is largely limited by stomatal conductance and stomatal conductance is controlled by water availability, the partitioning between sensible and latent heat flux can be a good indicator of photosynthetic ability. Furthermore, closure of the surface energy budget (E_in ~ E_out) provides strong support for the validity of other measured fluxes, primarily CO₂. At the Niwot Ridge Ameriflux tower site, we have been investigating the energy balance within a high-elevation (z = 3020 m) subalpine forest since November of 1998. This particular site provides several challenges due to complicated topography and meteorology. Eddy covariance fluxes of sensible (H) and latent (E) heat, coupled with measurements of net radiation (R_net), soil heat flux (G), and heat storage (S), provide a detailed picture of the energy balance. Typical values of the daytime energy balnce ({H + E + G + S}/R_net) are ~ 0.8. This value is consistent with others reported over forested ecosystems. This value is independent of season and wind direction. Due to the complexity of the site, near closure of the surface energy budget lends confidence to all of our measured fluxes (such as CO₂). We also observe strong seasonal trends in the Bowen ratio (H/E) with values ranging between 1-2 in the summer and as high as 6 in the winter. These values correlate well with measured CO₂ fluxes on both seasonal and weekly basis, showing a clear connection between energy partitioning towards latent heat and carbon uptake in this ecosystem.

Keywords: Energy Balance Carbon Uptake Latent Heat

This abstract is being presented at: 10:30 AM in session:
CARBON STORAGE