Effect of overpumping and irrigation stress on hydrochemistry and hydrodynamics of a Saharan oasis groundwater system

ABSTRACT

Stepwise hydrochemical and isotope-based methodology was adopted to identify mineralization processes, assess the impact of resources overexploitation and flood irrigation, and conceptualize groundwater hydrodynamics in the Djérid aquifer system, Tunisia. The study demonstrates that the main processes controlling groundwater geochemistry are dissolution of evaporates and phosphate-bearing rocks, cation exchange, mixing between high and low TDS end-members, and irrigation return flow. Interpretation of isotope data demonstrates that the deep aquifer was mostly recharged by late Pleistocene palaeowater, while the shallow aquifer is entirely recharged by return flow. The intermediate aquifer groundwater is actually a mixing of early to middle Holocene palaeowater, late Pleistocene deep aquifer palaeowater and return flow waters. The established conceptual model shows that deep and shallow groundwater leakages into the intermediate aquifer are enhanced by the presence of deep faults, the high hydraulic head of the deep aquifer, the overexploitation of the intermediate aquifer, and the long-term flood irrigation.

KEYWORDS:

• hydrochemistry
• environmental isotopes
• water–rock interaction
• return flow
• mixing
• conceptual model

Editor R. Woods Associate editor E. Rozos

Editor R. Woods Associate editor E. Rozos

Disclosure statement

No potential conflict of interest was reported by the authors.