Combined geophysical and geochemical approaches to understand groundwater salinization processes in Sminja aquifer, northeast of Tunisia

• Published in: Arabian journal of geosciences Vol. 15; no. 24
• Main Authors: Mejri, Sabrine, Chkirbene, Anis, Chabaane, Achref, Gabtni, Hakim, Tsujimura, Maki, Mlayah, Ammar
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01-12-2022; Springer Nature B.V
• Subjects: Agricultural practices; Aquifers; Distribution; Earth and Environmental Science; Earth science; Earth Sciences; Electrical resistivity; Evaporation; Geoelectricity; Geology; Global Changes and Groundwater Responses; Groundwater; Groundwater data; Groundwater recharge; Ion exchange; Isotopes; Meteoric water; Original Paper; Saline water; Salinity; Salinity effects; Salinization; Spatial distribution; Stable isotopes; Water Quality; Water-bearing formations; Tunisia; Geochemical data; Groundwater salinization; VES; Sminja aquifer
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-022-11031-3

An integrated geological, hydrochemical, and geoelectrical investigation of groundwater occurrence in Sminja plain, Zaghouan prefecture (northeast of Tunisia). In this area, groundwater is the principal source of agriculture practices. Groundwater salinity has increased sustainably from 6 gl
−1
in 1985 to 13 gl
−1
in 2015. Geoelectrical data obtained from field measurements (vertical electrical sounding (VES)) using a Schlumberger array at 16 locations are used to delineate different water-bearing formations and the configuration of the interface between them. The spatial distribution of the resistivities shows a clear decrease in their values toward the central part of the plain. Pseudo-2D sections calibrated with boring data show that low resistivities (< 10 Ω.m) – which reflect the interface between saline and fresh groundwater – are found in depths ranging between 10 and 70 m. Also, to predict salinity variations at different depths, we use a coherent correlation between electrical resistivity and the salinity of the aquifer. In order to appreciate the spatial distribution of the salinity, an inventorying data of groundwater salinity is mapped. According to the salinity maps, the east, the center, and the southeastern of the aquifer are characterized by high salinity water. More than natural effects (rock-water interaction and ion exchange reaction), the high groundwater salinity anomaly observed in Sminja plain was explained by intensive agricultural activities and uncontrolled groundwater extraction. Thus, stable isotope results show that most of the samples are presenting enrichment in heavy isotopes which highlight the occurrence of the evaporation process of meteoric water prior to groundwater recharge. These methods provided reliable results for identifying the subsurface geology and delineating the saline water plume in Sminja plain.