Combining MLR and PLS‐SEM to Identify Hydrochemical Drivers of Groundwater Salinization in a Semi‐Arid Region of Central Tunisia

ABSTRACT

Groundwater salinization is a major cause of groundwater quality degradation in semi‐arid regions, primarily driven by evaporation and water–rock interaction. To better understand these processes, this study investigates the hydrochemical controls on groundwater mineralization in the Oued El Hjal basin (central Tunisia), where the mean total dissolved solids (TDS) concentration reaches 3111 mg/L, exceeding the World Health Organization (WHO) drinking water guideline. A combined multiple linear regression (MLR) and partial least squares structural equation modelling (PLS‐SEM) approach, supported by saturation indices and Piper and Gibbs diagrams, was applied to identify the main salinization drivers. MLR identified Cl ⁻ , SO ₄ ²⁻ , Na ⁺ , Ca ²⁺ and Mg ²⁺ as the principal contributors to TDS variability. PLS‐SEM confirmed strong associations with TDS, with Cl ⁻ showing the highest standardized effect ( β  = 0.954), followed by Mg ²⁺ , Ca ²⁺ , Na ⁺ and SO ₄ ²⁻ , indicating dominant evaporite dissolution. Saturation indices confirmed active halite and gypsum dissolution, while Piper and Gibbs diagrams classified groundwater as Ca–Mg–Cl–SO ₄ type, governed by rock–water interaction and evaporative concentration. Nitrate exceeded WHO guidelines but was not significantly associated with mineralization. This integrated framework supports groundwater salinity assessment and irrigation water management in semi‐arid aquifers.