Water Quality Investigation of Agua Caliente Spring Martha Conklin & Roger Bales University of Arizona Background on Agua Caliente Science questions & hypotheses Results of initial investigations

Agua Caliente, a county park, starts as a small spring, an oasis in the semi-arid Sonoran Desert

Observations Perennial spring Flow rate varies throughout the year Water temperature at source is not very sensitive to air temperature

Research Questions Why does it flow all year? Where does the water come from? Why is it warm at its source?

Data Sources A GLOBE school, Fort Lowell Elementary in Tucson, AZ, has been making measurements at 2 sites at Aqua Caliente Water agency data are available from several groundwater wells within a few km of the site

Agua Caliente Temperatures Air Temp. ºC Water Temp. ºC Pond 1 entrance Pond 1 island GLOBE data, Ft. Lowell Elementary

Hypothesis Accepted explanation: The water comes from a higher elevation. It follows a deep flow path and a fracture in the bedrock allows it to surface. Our hypothesis: The water source must be a mixture of deep ground water and shallow recharge.

Approach Locate existing data sources Develop a sampling plan to test our hypothesis, i.e. determine if the water composition and temperature vary with flow rate.

Chemical Comparison Parameter Deep well a Aqua Caliente b Shallow well a Electrical conductivity Alkalinity, mg/L pH R. Kalin Ph.D dissertation, 1998 GLOBE data, Ft. Lowell Elementary a b

Detailed Chemical Analyses Constituent, mg/L Deep well a Aqua Caliente b Shallow well a Ca Mg Na SO Cl NO R. Kalin Ph.D dissertation, 1998 Recent analyses, UA HWR a b

Conclusions The composition does not match other deep ground water; it appears to be a mix of shallow and deep ground water. Seasonal changes are important; time series data are needed to understand seasonal cycles

Proposed Weekly Measurements Conductivity, pH and alkalinity (GLOBE) Flow rate of spring Water chemistry: Ca 2+, Mg 2+, Na +, Cl -, SO 4 2-, NO 3 -

Footnote on GLOBE Data Very useful for starting the investigation Good supplemental source for continuing longer-term investigations