Estimating phreatophyte evapotranspiration from Diel groundwater fluctuations in the middle Rio Grande Bosque

Professional Project submitted in partial fulfillment of the requirements for the degree of Master of Water Resources, Water Resources Program, University of New Mexico.Throughout the Southwest, non-native phreatophytes such as saltcedar have rapidly replaced native cottonwoods along river corridors. The USDA Forest Service (USFS)Fuels Reduction Study (FRS) is an effort to quantify the effects of the removal of non-native riparian vegetation on multiple parameters of riparian ecology, including groundwater variation over time. Here, 8 years of measurements from 12 wells at 5 research sites in the Middle Rio Grande riparian corridor (bosque) of Albuquerque area are considered. Of these research sites, 4 were cleared of non-native vegetation, 2 experienced wild fires, and 1 was a control. This professional project quantified the connection between river flow and groundwater level at each well using ordinary least squares (OLS) regression of groundwater level onto river flow. Groundwater at each well was strongly influenced by river flow. Pronounced hysteresis and inter-well variability were observed. Phreatophyte consumption of groundwater via evapotranspiration (ET) constitutes a significant use of available water resources in arid riparian ecosystems. Phreatophyte-induced diel groundwater fluctuations in unconfined, shallow aquifers have been used to estimate well-specific ET since the introduction of the White method in 1932 (White, 1932). This professional project estimated well-specific ET from diel groundwater fluctuations using the White method. Modest reductions in ET were observed following treatment, and cessation in ET was observed immediately following wildfire. White method ET from 4 wells at one site was compared with on-site eddy covariance ET estimates. Despite the high variance of the White method, estimates from the two methods match closely when averaged over long time periods