A multidisciplinary approach for sustainable groundwater management in a semi-arid region: A case study in Zaghouan region (northern Tunisia)

The global water crisis, amplified by climate change, illustrates the pressing need for sustainable groundwater management, especially in semi-arid regions where water resources are under severe depletion.

In Zaghouan region of northern Tunisia, groundwater overexploitation, degradation of water quality (notably due to nitrate pollution and salinization), and the effects of climatic change are all threats to human livelihoods and ecosystems. Groundwater is the region's main source of water, provide drinking water, they are also essential for agricultural and socioeconomic development. However, insufficient surface water supply, harsh weather conditions, and high evaporation rates are all factors that compromise its long-term sustainability.

This study relies on a multidisciplinary approach, integrating geology, lithostratigraphy, hydrology, hydrogeology, and environmental tracers (major ions, noble gases, and isotopes: δ¹⁸O, δ²H, ³H, ¹⁴C, δ¹³C, δ¹⁸O-NO₃, and δ¹⁵N-NO₃) to investigate the dynamics of three key aquifers: the Jurassic limestones of Djebel Zaghouan and the Mio-Plio-Quaternary aquifers of the Sminja and Oued Rmel plains.

Groundwater samples were taken during three major campaigns: (1) October-November 2023, concentrating on major ions, stable isotopes, and tritium; (2) February-June 2024, targeting noble gases and radiocarbon (¹⁴C/¹³C); and (3) November 2024, assessing major ions, organic contaminants and nitrate isotopes. Preliminary findings shows that waters are classified into three types based on their chemical facies (sodium chloride, calcium sulfate chloride, and a mix between these two endmembers). Some of the samples exhibit chloride concentrations up to 8 g/l and sulfate concentrations up to 5 g/l. Furthermore, nitrate contamination is present in 25% of samples, and five samples exceed 100 mg/l.).

Occurrence of organic contaminants testifies to the general degradation of water resources quality caused by wastewater and the use of pesticides in the agricultural sector.

Stable isotope analysis identifies two different groundwater groups. The first group is isotopically aligned with local precipitation, indicating direct recharge processes. It is found mostly in deep and shallow wells in all aquifers. The second group shows isotopic signatures indicative of evaporation. It is found in shallow wells (depth < 20m). Most samples have tritium values above 0.5 TU, indicating that the aquifers have been recently recharged. Ongoing noble gas analyses will refine recharge estimates, including the determination of groundwater age using T-He.

This research advances our knowledge of semi-arid groundwater flow patterns and offers practical advice for integrated groundwater management.  The case study of the Zaghouan region offers valuable insights that can effectively address the challenges posed by climate change and human impact.