Influence Of Seasonal Precipitation Amounts On Stream Water Source Contributions
Presenter: Jeffrey Switzer1
Co-Author(s): Justin Headley
Advisor(s): Dr. Jennifer C. McIntosh
1Department of Hydrology and Atmospheric Sciences, University of Arizona
The intermittent and perennial stretches of Cienega Creek and Davidson Canyon, designated as Arizona Outstanding Waters are two of a few remaining perennial streams in southern Arizona. These streams provide critical riparian habitat and groundwater recharge to the Tucson Basin metropolitan area. The streams are supported by groundwater and seasonal precipitation. Streamflow over the past 16 years has steadily decreased from ongoing drought conditions; a leading reason for this study. The changes in flow also are dependent on the previous year’s rainfall. Whether the streams have more overland flow or more groundwater flow is important, as it can determine the magnitude of the changes on the stream felt by climate change or groundwater extraction. Water from both streams was collected as grab samples during baseflow conditions and by automated samplers (ISCOs1) during storm events. Water samples were analyzed for electrical conductivity, pH, major ion chemistry, and water isotopes (18O, 2H, 3H) to assess contribution percentages of precipitation and groundwater to stream flow. A comparison of EC and alkalinity of streamflow, groundwater and precipitation was conducted for the years of 2020, 2021, and 2022. The alkalinity for the 2021 stream data in the monsoon season started at 2 meq/L and eventually rose to 8 meq/L while the 2022 monsoon season started at 6 meq/L and stayed there. The EC for 2021 started at 400 μs/cm and rose to between 1800-800 μs/cm and 2022 stayed around 1400 μs/cm the entire season. This also shows the magnitude of the previous year’s precipitation on the following year’s streamflow.