KARST SPRING PROCESSES AND STORAGE IMPLICATIONS IN HIGH ELEVATION, SEMI-ARID SOUTHWESTERN UNITED STATES

Karst springs and aquifers are significant resources globally yet continue to be poorly understood because of their heterogeneity in porosity and response to climate variability. In semi-arid, mountainous regions where total precipitation and groundwater recharge rates will likely decline due to climate change, improved understandings of karst groundwater recharge processes are imperative to plan for future hydrologic responses. The Colorado Plateau is a high-elevation, heavily dissected region of over 2,000 m thickness of sedimentary rock units containing multiple layered karst aquifers. This is the first study to use hydrograph analyses on springs in the uppermost regional Coconino aquifer (C aquifer) of the southern Colorado Plateau in Arizona to detail karst aquifer response to recharge. Coupled hydrograph and stable isotope (δ¹⁸O and δ²H) analyses document seasonal recharge as well as groundwater mixing and storage processes in the C aquifer. A critical relationship between seasonal snowpack timing and duration of ephemeral spring discharge indicates seasonal buffering and attenuation to drought. Event-scale hydrograph analyses show rapid hydrologic responses to precipitation in two ephemeral karst spring systems and quick drainage without extended seasonal snowmelt contribution. As climate change intensifies throughout the Southwestern United States and other drought-ridden areas of the world, aquifer and spring ecosystem conditions will significantly worsen without mitigation measures. The recharge and groundwater flow processes demonstrated in this study of a complex karst system support informed water resource decision-making on the southern Colorado Plateau and other climate-sensitive regions around the world.