Isotope hydrology in California: Tools for tracking water for storage and ecosystem functioning

Groundwater provides 40% of the water used in California for public supply and agriculture, and this figure is higher in drought years. Understanding surface and groundwater connections is central to storing groundwater for municipal use and supporting ecosystems but very difficult to measure. In this talk, I will present my isotope hydrogeology research to track where water comes from and how long it has been in the subsurface, using stable isotopes as source “fingerprints” and radioactive isotopes as “timers”.

In Livermore Valley, imported water from the California aqueduct system is isotopically distinct from local basins. I will show how this distinction enables me to track the infiltration of applied surface water into the groundwater system to evaluate the efficacy of sustainability planning and to understand how these efforts also support groundwater dependent ecosystems. I then use novel short-term isotope tracers to quantify the contributions of different water years to groundwater wells, calculating recharge rates for use in regional flow models. This analysis shows where and when recharge has been most effective.

Lastly, I will discuss how this water security research can be expanded to other priority sites such as the Central Valley and beyond, using machine learning and working directly with resource managers.