Using water stable isotopes and tritium to characterize the age and travel paths of the Santa Cruz headwaters
Fernanda Munari, Jennifer C. McIntosh
Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ
The San Rafael Valley is a geologically complex region in southern Arizona which contains the headwaters of the Santa Cruz River. This valley is also one of the last untouched grasslands in the U.S., serving as a critical wildlife corridor at the Mexico border. Despite its ecological and hydrologic importance, previous studies in this region have only focused on basic water quality characterization. This region faces numerous issues such as drought and groundwater extraction from nearby mining operations and installment of the border wall, making further characterization of this basin important. Our study employs the use of water stable isotopes and age tracers to understand recharge sources, flow paths, and residence times across the San Rafael Valley. To quantify origin and travel paths of surface water and groundwater in the valley, the isotopic values of oxygen-18 (δ18O) and deuterium (δ2H) were measured for each sample. These isotope measurements will be compared to precipitation data and results from previous nearby studies. Tritium (3H) concentrations were also measured to estimate the age of water samples and approximate groundwater residence times and flow paths. The combination of all studied parameters can be used to build a more complete conceptualization of recharge zones and surface water-groundwater interactions in the study area. Comprehensive studies such as these are paramount to the sustainable management of this ecosystem which is a vital resource for southern Arizona and Mexico.