Coupled geochemical modeling and multivariate statistical analysis approach for the assessment of groundwater quality in irrigated areas: A study from North Eastern of Tunisia

Abstract

The evaluation of groundwater quality is crucial for water resources management in arid and semi-arid regions, particularly in irrigated area where groundwater chemistry can be modified by variety of natural and anthropogenic factors. This study aims to investigate the origin of water quality variation and the major geochemical processes controlling the groundwater evolution in the shallow aquifer of Takelsa, northeastern of Tunisia. The combined use of geochemical modeling and multivariate statistical analysis such as Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) indicates several major influences, including the lithology of the aquifer system and anthropogenic inputs. Saturation indices, PCO2 and hypothetical salt combinations in integration with various mapping and graphical method identified water-rock interaction reactions through dissolution and cation exchange reactions as a major factor. This process, controlling groundwater quality, explains 54.2% of the total variance and prevails mainly in southern part of the basin. Furthermore, the excessive use of composite chemical fertilizer was identified as a second factor with 14.3% of the total variance. This anthropogenic factor causes a change of chemical pattern of groundwater samples by an inversion of cation exchange reaction and an increase of nitrate contents in 84% of the wells located in the irrigated area of the basin.