Geochemical characterization in karst basin tributaries of the San Franciscan depression: The Corrente River, western Bahia, NE-Brazil

• Three water-types in Corrente River (Brazil) hydrological basin were found.
• This water sources has been overexploited by the increase in agriculture.
• Seasonal behavior is different between major and trace and rare earth element.
• Three main mechanisms controlling dissolved elements are proposed.

Karst aquifers are important freshwater resources for the growing population in Brazil. The sandstones of Urucuia plateau and the limestone of Bambui Group constitute important aquifer systems in the western part of Bahia state. The Corrente River provides ∼30% of the total water flow of the São Francisco River and crosses karstified structures. Surface and groundwater samples were collected during the dry period, the beginning of the wet season, and the wet season. The main objective was to define sources and distribution of dissolved elements and to describe the geochemical processes that govern their mobility within the system. Water samples are classified into three groups, depending on the dominant weathering process. When carbonate dissolution governs, waters are bicarbonate–calcium-type; whereas when the atmospheric precipitation signal is present, the samples in siliciclastic terrain are more Cl− - Na+. Groundwaters reflect bicarbonate–mixed-type, with the highest dissolved concentrations. In contrast to the major elements, trace elements, including Rare Earth Elements (REE), show seasonal behavior: their concentrations increase with the beginning of the wet season, due to re-mobilization and release into the solution of adsorbed elements from the system and the atmospheric dust. The total dissolved REE concentration (800–7500 ng L−1) is one order of magnitude more concentrated in karsts than in siliciclastic rocks. Principal component analysis was performed, explaining >77% of the variance. First factor extracted (REE, Y, Th, Al, Fe) explain the washout and enhancement of atmospheric dust weathering throughout the beginning of the wet seasons. The second component comprises variables related to karsts lithology, representing calcite and dolomite dissolution.

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