Quantifying baseflow inputs to the San Pedro River : a geochemical approach

Abstract

The Upper San Pedro River Basin (Arizona, U.S.A.) contains one of the few remaining desert riparian areas in the Southwest. This study characterizes and quantifies the water sources that contribute to riparian groundwater and sustain river baseflow using a suite of geochemical tracers including stable and radioactive isotopes and anions. Results indicate that of the possible sources, basin groundwater from the west and local recharge of monsoon floodwaters are the most significant water sources to the riparian system. Using a simple two end-member mixing model, riparian groundwater varies from 10 to 90% basin groundwater whereas baseflow ranges from 0 to 55%; the percentage is well correlated with gaining (basin groundwater dominated) and losing reaches (monsoon dominated). These results highlight the importance of monsoon floodwater recharge as a water source for desert riparian systems, a fact that future water management decisions need to address.