Quantifying Groundwater Contribution To Streamflow In Cienega Creek During The 2021 North American Monsoon

Presenter: Justin Headley1
Co-Author(s): -
Advisor(s): Dr. Jennifer McIntosh
1Department of Hydrology and Atmospheric Sciences, University of Arizona

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The year-round streamflow of Cienega Creek has created a unique riparian area in the otherwise semi-arid southeastern corner of Arizona. This region typically receives an average of 12 inches of rainfall per year, roughly divided between the winter and summer seasons. In the winter, low-intensity rainfall, produced by frontal systems, can persist for several days at a time. During the summer, the region receives short-lived but intense downpours of precipitation, produced by monsoonal thunderstorms. Previous studies of Cienega Creek’s hydrogeochemistry have shown that its perennial streamflow is maintained by contributions from groundwater aquifers during the dry seasons of fall and spring. This study investigated the temporal hydrogeochemical changes that occurred in Cienega Creek’s surface water during nine precipitation events in the summer monsoon season of 2021. Automatic sampling machines were coupled with pressure transducers to take water samples at incremental changes in stream depth. Time-phased analysis of water alkalinity, major dissolved ions, and stable isotopes showed that rainwater made a significant contribution to streamflow in the beginning of a precipitation event. However, after the initial surge of precipitation runoff subsided, the stream’s chemical signature increasingly resembled local groundwater, signaling a rapid return of aquifer-fed baseflow. These results suggest that regardless of season, Cienega Creek and its riparian areas depend heavily on groundwater, and if greater demand were placed on the aquifer (e.g., through mining or urban development), there could be long-lasting negative impacts on the ecosystem.

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