Abstract

Within a small geographic area near Bromide Oklahoma U.S.A., seven springs discharge brackish water from a carbonate aquifer. The discharged spring water flows along individual spring runs allowing the study of the spatial and temporal variations in the chemistry of the waters. While the overall characterization of the Na-Cl spring waters does not change spatially or temporally, the chemistry of the water discharged at the individual springs ranged from fresh (9.6 ± 0.8 mmol L–1 Cl–) to slightly brackish (142.3 ± 6.4 mmol L–1 Cl–). The largest spatial variation in water compositions occurred in October 2010 when the Cl–1 concentration ranged from 20.78 mmol L–1 at Mary Mac spring to 137.8 mmol L–1 at Ekie spring. The largest temporal change was 110 to 138 mmol L–1 noted at Ekie Spring. The observed spatial and temporal variations are hypothesized to result from the mixing of two hydrologic systems. Deep flow paths deliver different amounts of basinal brine to individual springs (spatial variation), whereas shallow flow paths deliver different amounts of freshwater to individual springs seasonally (temporal variation).

Along the spring runs, the decreasing concentration of dissolved CO2 is driven by outgassing to the atmosphere. The concentration of dissolved H2S also decreased along the spring runs due to oxidization within the water along the spring runs and possibly due to outgassing into the atmosphere. The concentration of dissolved oxygen increased from near zero at the spring orifices to nearly 5 mgL–1 as oxygen from the atmosphere entered the oxygen-poor spring waters. As expected, along the spring runs, the concentrations of dissolved oxygen and H2S showed a breakpoint; upstream of which H2S was present and dissolved oxygen was absent and downstream of which H2S was absent and dissolved oxygen was present.