Explaining the groundwater salinity of hard-rock aquifers in semi-arid hinterlands using a multidisciplinary approach

ABSTRACT

Shallow crystalline groundwater in the semi-arid hinterland of Ceará is brackish or saline with mixed chloride or sodium chloride facies. Very few hydrochemical data are available for the area and the drivers behind this salinity are not clearly identified. In this study, extensive field data collection was performed to provide new information about the hydrogeological functioning and the salinization processes, through the implementation of piezometric, hydrogeochemical, isotopic (¹⁸O, ²H) and multitracer dating (¹⁴C, ³H, CFC, SF₆) monitoring. Piezometric and isotopic data evidence fast flow circulation processes and a high contribution of evaporated surface water to aquifer recharge. Multitracer dating shows the groundwater is essentially composed of seasonal vertical infiltration flows that mix with older waters stored in the aquifer. Chemical analyses suggest the groundwater, originally low mineralized, has become progressively saltier due to leaching of salts that were evapoconcentrated in either surface waters or the unsaturated zone during drier periods.

KEYWORDS:

• hydrogeology
• hardrock aquifers
• semi-arid climate
• salinization
• isotopes
• environmental tracers
• groundwater dating
• hydrochemistry
• Brazil

Editor A. Fiori; Associate Editor G. Jeelani

Editor A. Fiori; Associate Editor G. Jeelani

Acknowledgements

This work is part of the multidisciplinary French–Brazilian cooperation between IRD and FUNCEME, and was carried out in the frame of PhD research. The authors thank the FUNCEME for all the financial and technical support of the field work, as well as the FUNCAP for the scholarship provided. The authors also give credit to the LAMA, Condate Eau-OSUR, EMMAH and AETE-ISO laboratories for their analytical support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/02626667.2023.2253227.

Additional information

Funding

This work was supported by the Fundação Cearense de Apoio ao Desenvolvimento Científico e Tecnológico [MAPP153/2018].