Origins And Residence Times Of Water Supporting O’Donnell Creek Cienega In Southeastern Arizona

Presenter: Adam Stratman1
Co-Author(s): Andrew Salywon
Advisor(s): Dr. Jen McIntosh
1Department of Hydrology and Atmospheric Sciences, University of Arizona

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Ciénegas are freshwater wetlands characterized by permanently saturated soils that are found in the arid Southwest. They provide habitat to many threatened and endangered plants and animals, and are a good indicator of their watershed’s health. Ciénega habitats are rare and have significantly declined because of several factors including headcutting and channelization of watercourses, water diversion, groundwater overdraft, and climate change. Different management strategies are needed to preserve the health of ciénegas depending on if the source of water supporting them is local recharge, basin groundwater, or a mixture of both. This project is focused on the O’Donnell Creek Ciénega (OCC) located within the foothills of the Canelo Hills in Southeastern Arizona. OCC is biologically diverse and provides critical habitat to several endangered species (including the orchid Spiranthes delitescens). Therefore, protecting and restoring this wetland will result in significant water quality and ecological benefits. Groundwater, surface water, and precipitation samples were collected over the 2021 winter and summer rainy seasons. Tritium in groundwater was predominantly below detection limits, indicating limited (local) diffuse basin recharge. The few samples with detectable tritium were lower than modern precipitation, indicating mixing with older groundwater. Groundwater radiocarbon results ranged from 29.9 to 88.8 pMC indicating that the groundwater supporting the ciénega’s watershed is up to ~5,700 years old, likely from mountain front recharge. Initial results suggest that the best practice for managing this wetland would involve a dual approach: utilizing land management practices that promote habitat restoration and through active management of groundwater resources.

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