Hydrochemical and Isotope Evidence of Groundwater Contamination of Cultivated Fields of Semi-Arid Environments in Tunisia

Abstract

This present study, which uses geochemical and isotope hydrological approaches, attempts to provide appropriate scientific information about the dominant geochemical processes that influence groundwater chemical composition in a semi-arid region of cultivated field. Therefore, particular emphasis has been placed on (1) the evolution of solute concentrations within the hydrological system as well as in the vadose zone, (2) the contribution of anthropogenic processes to the groundwater contamination, and (3) the estimation of groundwater recharge deriving from return flow of irrigation water. It has been demonstrated that the excess of irrigation waters has significantly influenced the rate of groundwater recharge. The annual amount of groundwater recharge related to the irrigation practices is approximately 100 mm. Modification of the geochemical characteristics of the Zeroud aquifer groundwater is caused by water-rock interaction, including both the dissolution of evaporate and the cation exchange process. However, anthropogenic processes related to the return flow of irrigation waters have led to extremely high nitrate concentrations and flushing of solutes, such as chloride, sulfate, sodium, and calcium. The isotopic signature provides evidence of groundwater contamination. Indeed, the relatively enriched stable isotope concentrations and low tritium concentrations highlight the important contribution of irrigation waters to the local groundwater recharge, particularly in the Menzel Mhiri agricultural area.