Abstract
Groundwater resources are facing increasing pressure especially in semi-arid regions where they often represent the main freshwater resource to sustain human needs. Several aquifers in the Mediterranean basin suffer from salinization and quality degradation. This study provides an assessment of Grombalia coastal aquifer (Tunisia) based on multidisciplinary approach that combines chemical and isotopic (δ2H, δ18O, 3H, 14C and δ13C) methods to characterize the relation between groundwater quality variation and aquifer recharge. The results indicate that total dissolved solids exceed 1000 mg/L in the most of samples excepting the recharge area. In addition to water–rock interaction, evaporation and nitrate pollution contributing to groundwater mineralization, the reverse cation exchange process constitute an important mechanism controlling groundwater mineralization with enhancing risk of saltwater intrusion. Environmental isotope tracers reveal that groundwater is evolving within an open system to close system. A significant component of recent water that is recharging Grombalia aquifer system is confirmed by applying correction models based on the δ13C values and 14C activities and tritium contents. However, this recharge, which is mainly associated to the return flow of irrigation water, contributes to the groundwater salinization, especially for the shallow aquifer.
Highlights
In arid and semi-arid regions worldwide, local populations mainly rely on groundwater resources to sustain domestic, industrial and agricultural needs [1,2,3]
Many natural factors contribute to groundwater mineralization: (i) the source of recharge water and its chemical composition; (ii) the lithological and hydrological characteristics of the aquifer matrix; (iii) groundwater residence time; and (iv) the chemical processes occurring within the aquifer
The relationship among carbon-14 activities, total dissolved solids (TDS), nitrate values and δ13 C confirmed that mineralization processes in the Grombalia shallow aquifer are related to the infiltration of recent poor-quality water rather than to water–rock interaction, whose consequences depends on the residence time
Summary
In arid and semi-arid regions worldwide, local populations mainly rely on groundwater resources to sustain domestic, industrial and agricultural needs [1,2,3] Despite their vital role, aquifers are exposed to multiple pressures resulting in over-exploitation, quality degradation and salinization [1,4,5]. Understanding the processes and factors controlling the temporal dynamic of the chemical groundwater composition is essential to guide decision-makers towards a rational and more sustainable management of these resources To this end, this work presents the results of an integrated assessment performed in the Cap Bon peninsula, and in particular in the Grombalia aquifer, the most important agricultural area in this region. The findings of this study will be very useful to improve management strategies to protect scarce groundwater resources in the region, as well as to deepen the knowledge on the status of coastal aquifers in the Mediterranean basin
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