Groundwater salinity in a semi-arid region of central-eastern Tunisia: insights from multivariate statistical techniques and geostatistical modelling

This study aims to investigate the hydrochemical behaviour of a shallow aquifer of a semi-arid environment in central-eastern Tunisia. It is based on a combined approach of multivariate statistical tools and a geostatistical analysis. The analysis of 49 groundwater samples underlined the heterogeneity between water classes. The factor analysis and the analysis of principal components highlighted that the deterioration of the groundwater quality results essentially from natural factors, such as rock weathering, and marginally from associated anthropogenic factors, in most cases, with artificial groundwater recharge from water irrigation at the soil surface. The natural factors are clearly associated with chloride, sodium and sulphate, and they are responsible for the water quality class with a salinity higher than 6 g/L. The anthropogenic factors are characterized by calcium and potassium ions. Based on the variograms obtained for the vector of both factors, their spatial interpolation by kriging showed that the high values of vector 1 (the natural factors) were recorded near the sabkha Sidi El Hani, indicating a rock-water interaction. However, vector 2 is high in the central part of the Ouled Chamekh plain, likely due to the water irrigation of agricultural soils.