GROUNDWATER DISCHARGE BY PHREATOPHYTE SHRUBS IN THE GREAT-BASIN AS RELATED TO DEPTH TO GROUNDWATER

An equation describing the mean daily discharge of groundwater by transpiration from phreatophyte shrubs as a function of plant density, leaf area index, and depth to groundwater was developed using an energy combination model calibrated with energy fluxes calculated from micrometeorological data. The energy combination model partitions the energy budget between the soil and canopy permitting plant transpiration to be separated from evaporation from the soil. The shrubs include greasewood, rabbitbrush, shadscale, and sagebrush. Converting a daily groundwater discharge rate calculated by the equation to an annual rate requires an estimate of the number of days the plants used only groundwater. Rates used during previous studies in the Great Basin range from 0.030 to 0.152 m yr(-1) rates calculated with the equation developed during this study range from 0.024 to 0.308 m yr(-1) for the reported field conditions. Annual rates estimated in this study differ from the estimated annual rates used in previous studies by factors ranging from 0.8 to 5.0.