Water balance for Great Basin phreatophytes derived from eddy covariance, soil water, and water table measurements

This study was conducted in the Owens Valley, California to determine the relative contribution of groundwater and soil water to evapotranspiration (ET) from phreatophytic meadow and scrub plant communities. Groundwater uptake during the growing season was estimated from the difference between ET measured using eddy covariance, and the sum of soil water depletion, precipitation, and evaporation from the water table. Total ET during the growing season (March 26 to October 15) ranged from 53 to 646 mm among all sites and years. ET during winter was small, averaging approximately 40 mm. Estimates of evaporation from the water table based on soil properties and ET measurements at night both suggested this flux was a small component of the water balance. For alkali meadows with water table depths of 1–3 m, groundwater uptake accounted for 60–81% of ET. Shrub-dominated sites had lower cover and transpiration, and relied less on groundwater than meadows. Groundwater uptake was correlated with water table depth and leaf area index (r2 = 0.62 and 0.70, respectively) even though water table depth and vegetation cover were less correlated (r2 = 0.44). A slightly higher correlation was observed between groundwater uptake per unit leaf area and water table depth (r2 = 0.73). Annual ET results from this study could assist the management of groundwater pumping in areas of phreatophytic vegetation by improved accounting of the sources of ET as vegetation leaf area and water table depths vary.