HR: 0830h
AN: A31C-0042    [PDF]
TI: Surface flux processes and evolution of characteristic eddy scales above a young Middle Rio Grande forest
AU: * Cleverly, J R
EM: cleverly@sevilleta.unm.edu
AF: Department of Biology, University of New Mexico, Albuquerque, NM 87131-1091 United States
AU: Thibault, J R
EM: jrtebo@sevilleta.unm.edu
AF: Department of Biology, University of New Mexico, Albuquerque, NM 87131-1091 United States
AU: Slusher, M
EM: cheepnis@sevilleta.unm.edu
AF: Department of Biology, University of New Mexico, Albuquerque, NM 87131-1091 United States
AU: Hipps, L
EM: larry@claret.agsci.usu.edu
AF: Plant, Soils, and Biometeorology Department, Utah State University 4820 University Blvd, Logan, UT 84322 United States
AU: Prueger, J
EM: Prueger@nstl.gov
AF: USDA National Soil Tilth Laboratory, Iowa State University 2150 Pammel Dr, Ames, IA 50011 United States
AU: Dahm, C N
EM: cdahm@sevilleta.unm.edu
AF: Department of Biology, University of New Mexico, Albuquerque, NM 87131-1091 United States
AB: The extended drought throughout the Southwest has brought water budgets and policy decisions into public purview. It is often presumed that riparian restoration, i.e. removal of non-native species, presents a water salvage panacea. The cost of such operations can be prohibitive, making reliable estimates of phreatophytic ET a crucial piece of information. This study has taken a long-term approach to monitoring ET water flux from a variety of these forests. ET monitoring towers have been established at 5 sites along the Middle Rio Grande -- 2 over mature cottonwood forests, 2 over mature saltcedar forests, and 1 over a young mixed stand of Russian olive and willow. Because there is yet no infallible method for determining ET fluxes, eddy covariance technology provides the best method for evaluating those processes in the surface layer by provided data directly into surface layer similarity relationships. ET, energy, and carbon flux were measured during the 2003 growing season from towers using the 3-dimensional sonic eddy covariance (3SEC) method. Scalar flux sensors included a 3-D sonic anemometer, Krypton hygrometer, 12.7 $\mu$m type E fine wire thermocouple (Campbell Scientific, Inc), and LI-7500 open-path IRGA (Licor, Inc). An averaging period of 30 min was chosen based as a period of low cospectral density. The following corrections were applied to these fluxes: coordinate rotation; correction of frequency-specific signal attenuation due to instrument separation, instrument line averaging, and signal path length (Massman 2000 \& 2001); krypton hygrometer calibration as a function of humidity; oxygen contribution to the krypton hygrometer signal; and flux effects on measured densities (Webb et al 1980). These corrections reduced the closure error by 5 percent. Closure was then forced using the measured Bowen Ratio as the weighting factor. Measured ET, along with leaf area index, was reduced as much as 35 percent during the prolonged drought in the southwestern U.S. At the end of the season, younger cottonwood, willow, and Russian olive forests were developing severe chlorosis ($<$ 100 mg m${^-2}$ at some locations), and ET rates fell from 8.5 mm day$^{-1}$ to 4.4 mm day$^{-1}$ due to a record-breaking hot July. Evaluation of the 10-Hz raw data from the 3SEC system was performed using cospectral and wavelet time series analyses. Of particular interest are the low frequency harmonics between the turbulent scales and the spectral gap. Correlation of intermittent flux variations with variations in net radiation preceding summer monsoon precipitation illustrates the relative roles of vegetative homeostasis and advection in explaining remaining closure error following turbulence corrections. This time series analysis of physical turbulent Monin-Obukhov scales and surface fluxes illustrates the frequency-temporal relationships between surface processes, stomatal control, and mesoscale forcing events.
DE: 0315 Biosphere/atmosphere interactions
DE: 1818 Evapotranspiration
DE: 1851 Plant ecology
DE: 3307 Boundary layer processes
DE: 3322 Land/atmosphere interactions
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting