HR: 1330h
AN: B52A-1030    [PDF]
TI: Ecosystem Scale Fluxes of Water and Carbon in Semiarid Grassland and Shrubland
AU: * Kurc, S A
EM: kurc@colorado.edu
AF: University of Colorado Department of Geological Sciences, 2200 Colorado Ave., Boulder, CO 80309-0399 United States
AU: Small, E E
EM: eric.small@colorado.edu
AF: University of Colorado Department of Geological Sciences, 2200 Colorado Ave., Boulder, CO 80309-0399 United States
AB: To understand how woody encroachment into grassland influences water and carbon cycling in semiarid environments, we measure ecosystem-scale water and carbon fluxes and identify factors that control variability of the fluxes. Flux measurements are made using both the Bowen ratio and eddy covariance methods, accompanied by measurements of soil moisture and radiation. We present data from both a grassland site and a shrubland site, situated within 2 km of each other at the Sevilleta LTER site in central NM. The study includes data from three summer monsoon seasons, the time of year when rainfall and evapotranspiration (ET) are greatest and both grasses and shrubs are active. Midday available energy is higher at the grassland than at the shrubland by about 20 percent, or 80 Wm-2. At both sites, evaporative fraction (EF, the fraction of available energy partitioned to latent heating) is strongly correlated with surface soil moisture. However, the sensitivity of EF to surface soil moisture is about 30 percent lower at the grassland site. The differences in available energy and EF offset each other, yielding (1) remarkably similar time series of ET and (2) an identical relationship between ET and water content at the two sites. Decreases in soil moisture, EF, and ET are rapid at both sites, about 2-3 days. In contrast, variability in net ecosystem exchange of carbon has both a fast and slow response component. Short bursts of respiration occur after most rainfall events, whereas periods of net assimilation last for several weeks but only follow intervals with substantial rainfall.
DE: 0400 Biogeosciences
DE: 1800 HYDROLOGY
DE: 1809 Desertification
DE: 1818 Evapotranspiration
DE: 1878 Water/energy interactions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting