Collaborative Research: Tracing the fate, age, and ecohydrologic significance of rock moisture

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Increased frequency and severity of drought is amplifying the importance of understanding where forests source water. Where soil water is unavailable, woody plants commonly access water stored in the underlying fractures and pores of weathered bedrock (rock moisture). However, in contrast to the soil mantle, little is known about water stored in bedrock and how accessible it may be to plants. Better tools for fingerprinting how different species access rock moisture are needed to understand how shifts in precipitation could impact local water resources. This experiment tracks water flow through soil, bedrock, and trees via isotopic tracers to document how forest water use influences of groundwater recharge and stream flow, especially during drought. New tools for tracing water will be evaluated and communicated to students and early career scientists, so that these tools can be widely applied to better understand the fate of water resources under changing climate.The research is conducted at an intensively characterized and monitored hillslope in a Northern Californian old-growth forest. Experimental results will provide direct, isotopic evidence for when and where trees source water during the dry season and how their water uptake impacts groundwater recharge and streamflow. The study overcomes previous challenges with tracing rock moisture by leveraging the unique capability to trace water through unsaturated, fractured bedrock using specialized sampling infrastructure. Labeled water will be injected into the bedrock at the start of the dry season. That labeled water will be tracked through the subsurface-plant-atmosphere continuum in the dry and wet seasons that follow. The project will also estimate water age and transit time of water pools by measuring concentrations of short-lived naturally occurring radio-isotopes. Estimated transit times from labeled water and radio-isotopes will be used independently to evaluate the fate of rock moisture and its ecohydrologic significance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.