PARENT SESSION
Oral Session 10: Physiology I: Temperature, Light, and Growth.
Presiding: C Knight
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room C 123.
The role of soilmoisture as a control on surface energy fluxes at a Bahia grass (Paspalum notatum) pasture in central Florida.
Bracho, Rosvel*,1, Sumner, David2, Powell, Thomas3, Hinkle, C.Ross4, Drake, Bert3, 1 National Research Council, Washington, DC2 U.S. Geological Survey, Altamonte Springs, FL.3 Smithsonian Environmental Research Center, Edgewater, MD.4 Dynamac Corporation, Kennedy Space Center, FL
ABSTRACT- Continuous eddy covariance measurements (June 2000 − Feb. 2004) were used to characterize seasonal and annual variability of latent (LE) and sensible heat (H) fluxes over a pasture in Central Florida. Maximum evapotranspiration (ET) rates were > 5.0 mm d-1 and occurred during the summer seasons. Soil water content (SWC) tracked the precipitation pattern and varied between 0.065 and 0.5 m3 m-3, affecting the energy partitioning. Bowen ratio (H/LE) was below 1 at high SWC, but increased sharply to above 2 when SWC decreased below a critical value of 0.15 m3 m-3. The Priestley-Taylor coefficient (LE/LEeq) was calculated to compare observed evapotranspiration to an expected, equilibrium evapotranspiration rate. LE/LEeq was also affected by the SWC, reaching an average of 0.95 and 0.4, above and below the critical value in SWC, respectively. LE/LEeq was strongly correlated with the surface conductance (gs), and reached a value of 1 when gs was approximately 15 mm s-1 during the wetter periods. The decoupling coefficient (
) reached values over 0.5 during periods of high SWC and leaf area and ranged between 0.15 and 0.3 during the driest periods, indicating that LE is strongly controlled by gs at low SWC. The relative sensitivity of LE to changes in gs was high (0.81) at low SWC and low (0.55) at high SWC. These results indicate that a strong vegetative control on LE is imposed through gs at low SWC. During times of high SWC, LE is largely controlled by the available energy.
Key words: Priestley-Taylor, Omega, Soil water content, Surface conductance