A Geochemical Comparison of Three Large Edwards Aquifer Springs at Comal Springs, Texas

Comal Springs is a major multi-outlet Edwards aquifer spring system that supports many threatened or endangered federally-protected species. Climate change and rising demands for Edwards groundwater raise spring flow and water quality concerns. This research aims to assess spring system water chemistry and water quality and their interdependent controls by characterizing spring water chemistry over time. Understanding timescales over which water quality changes and the mechanisms behind those changes promotes effective groundwater management and protection, helping to ensure resource sustainability. Spring water hydrochemical data were collected from three orifices of the Comal Springs system, Spring 7, Spring 3, and Spring 1, over nineteen months. Results were evaluated using geochemical modeling, statistical analyses (one-way ANOVA and two-sample t-testing), simple mixing models, and water chemistry plots and constituent time-series. Results demonstrate the majority of spring flow from each orifice is sustained by a common Edwards aquifer deep artesian source and establish Springs 7 and 1 as spring system geochemical end-members, indicating Spring 3 is fed by sources that contribute flow to Springs 1 and 7. Sources that feed Spring 1 contribute slightly more to Spring 3 flow than Spring 7 sources do. Assessments indicate waters discharging from Spring 1 are affected by small inclusions of freshwater from a Glen Rose-Trinity aquifer or Trinity-like source and waters discharging from Spring 7 are characteristic of artesian baseflow chemistry. Study results also suggest regional recharge events and rising aquifer levels produce initial spring system pressure pulses that flush deep aquifer waters through spring system conduits.