39-5 Natural tracers differentiate the behavior of the karstic aquifers that supply Grand Canyon’s water during baseflow and snowmelt conditions

Session: Understanding Karst Hydrology and Karst Aquifers Using Innovative Tracers and Other Technologies

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Abstract:

High-elevation karstic aquifers fed by snowmelt are integral to supplying water for arid regions. The Grand Canyon’s regional deep (> 1,000 m) R aquifer has been under-studied regarding understanding the dynamics and differences between base-flow and snow-melt flow conditions. It is hypothesized that natural tracers collected from the water of Roaring Springs, the main water source of Grand Canyon National Park’s Transcanyon Waterline, will differentiate snow-melt and base-flow conditions. An automatic water sampler stationed at the bottom of the Grand Canyon near Roaring Springs collected daily stable isotopes of ¹⁸O and deuterium samples before, during, and after snowmelt in 2024 and 2025. A data logger inside Roaring Springs has collected a continuous record of temperature and pressure since 2013 and specific conductance since 2023. Natural tracers describe shifts in the flow regimes of water through the regional aquifer and identify differences between base-flow and snow-melt conditions. The peaks in discharge resulting from snowmelt reaching the logger at Roaring Springs correlate with the timing of more negative isotopic values from samples collected at the automatic water sampler. The peaks in discharge at a large, shallow, surficial C aquifer spring on the North Rim called Robber’s Roost are one day prior to snow-melt peaks at Roaring Springs. Snowmelt flows laterally from the North Rim to Roaring Springs where water is discharged from the Redwall-Muav aquifer thousands of meters below. These data delineate the time of recharge of snowmelt to the C and R aquifers. They can also enable Grand Canyon National Park to better understand the timing and magnitude of recharge to a major part of its water supply as they plan for a future where there will be less water available to provide to residents, visitors, and ecosystems.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10466

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