Characterization of groundwater in the Cariri (Ceara, Brazil) by environmental isotopes and electric conductivity

The Cariri region is the largest sedimentary basin in the state of Ceara, Brazil. Located in the southern portion of the state, it comprises the Araripe Plateau and the Cariri Valley on its northern foot. The region's groundwaters are being heavily exploited. Using electric conductivity (EC) and O-18, C-14 and H-3 data, we differentiate groundwaters from various origins. We identified three horizons of springs on the slope of the Plateau through their geologic environment and the EC of their waters. Groundwaters from wells in the Cariri Valley are classified according to the aquifers exploited as indicated by the drilling profiles. However, strong tectonic features and intense fracturing in the Valley produce a great many horizontal discontinuities, which result in a mixing of groundwaters from different aquifers. Mixing systems are described in terms of delta(18)O-C-14 and EC-C-14 linear trends.