Groundwater discharge by evapotranspiration, Dixie Valley, west-central Nevada, March 2009-September 2011

Abstract

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Evaluating Micrometeorological Estimates of Groundwater Discharge from Great Basin Desert Playas

“…Rates specific to phreatophytic shrubs were established using measured biomass‐to‐discharge relations determined from lysimeter measurements made in Winnemucca, Nevada (Robinson and Waananen ). Modern estimates of ET g rates typically are made using the Bowen ratio energy budget (BREB, Laczniak et al ; Reiner et al ) or eddy‐covariance (EC, Moreo et al ; Garcia et al ) micrometeorological techniques.…”

“…ET g rates in areas of phreatophytic vegetation have been measured using modern micrometeorological methods (BREB and EC) relatively accurately in many parts of the Basin and Range physiographic province. Phreatophytic vegetation ET g rates range from 0.05 to 1.3 m/year depending on factors such as vegetation type and density (Laczniak et al ; Reiner et al ; Welch et al ; Garcia et al ). However, despite significant effort, making accurate measurements of the low ET g rates occurring on desert playas remains difficult.…”

“…ET g rates are computed as: total ET minus precipitation minus surface water inflows. Precipitation measurements have a measurement error of 2% (Garcia et al ). Surface water inflows that inundate playa sediments are a confounding factor that introduces uncertainty into estimated total ET and playa ET g rates.…”

“…Kampf et al () examined playa evaporation rates at the Salar de Atacama in Chile and found that EC measurements could only constrain evaporation rates to within 0.04 m/year, and that some measured evaporation rates were less than this margin of uncertainty. In Dixie Valley, Nevada, Garcia et al () also computed a total ET uncertainty threshold of about 0.04 m/year, based on random error analyses of micrometeorological data obtained using the EC method. The Dixie Valley study reported mean playa ET g rates (total ET minus precipitation and surface water inflows) of 0.02 ± 0.023 m/year for bare‐soil playa (BSP) and 0.011 ± 0.02 m/year for salt‐encrusted playa (SEP), where these mean playa ET g rates are within the probable measurement error.…”

“…The Dixie Valley study reported mean playa ET g rates (total ET minus precipitation and surface water inflows) of 0.02 ± 0.023 m/year for bare‐soil playa (BSP) and 0.011 ± 0.02 m/year for salt‐encrusted playa (SEP), where these mean playa ET g rates are within the probable measurement error. Garcia et al () attribute low playa ET g rates to low‐permeability clay sediments and to surface and pore‐scale salt crusts observed on the playa, which restrict the movement and release of groundwater from the playa surface compared to vegetated sites with coarser salt‐free sediments near the edge of the valley floor. The conclusion to be drawn from previous studies is that best attempts to constrain ET g from desert playas have resulted in reported ET g rates that are: (1) within the measurement error and (2) only are constrained by the uncertainty threshold.…”