Évaluation de la qualité des eaux de surface à l'aide de techniques statistiques multivariées et de méthodes hydrochimiques : étude de cas de l'oued El Hatab (Centre de la Tunisie).

Multivariate statistical techniques, and hydrochemical tracers of surface water of wadi Hatab watershed, central Tunisia, are used to assess the surface water quality for drinking and irrigation purposes. Then, in this context, it is fundamental to identify the sources of water pollution in this basin which represents a good example of anthropized and exploited basin in semi-arid region.

Stream chemistry was monitored in 28 sampling sitesThe projection of major ions on the Piper diagram reveals a variability of water chemical facies. It indicates that water mineralization is primarily governed by sodium, magnesium and calcium for cations and sulphates and chloride for anions. Surface water salinity ranged between 0.364 g/l to 29.173 g/l, and exceeds the WHO standard of salinity for 82% of stations. This variation is explained by domestic and industrial discharges in watershed and by the proximity of a salt-water source draining evaporitic formations. With naturally occurring mineralization, an anthropogenic mineralization is observed which is linked to domestic discharges, untreated industrial activities including paper mill discharges, and poorly controlled agricultural practices.

Several water quality parameters were applied for drinking and irrigation purposes. Water quality index (WQI) values indicate that 75% of surface water quality are not suitable for drinking usage. According to Percent Sodium (%Na), Residual Sodium Carbonate (RSC), the electrical conductivity (EC) and Wilcox classification, 85% of surface water samples are suitable for agricultural irrigation activities. Based on Sodium Adsorption Ratio (SAR) and USSL classification, it appears that only 47 % of water samples, mostly locared in the western part of the watershed, are suitable for irrigation use and almost 53 % of these samples are “good” or “permissible”.

This study demonstrated the impact of several processes on surface water resource. The dataset revealed that water physiochemical properties are mainly controlled by regional lithological features, but the nature of the discharges that are dumped there significantly changes it. In this respect, this research provides insights for sustainable water management. Generally, this study suggests the need and feasibility of multivariate statistics and hydrochemical techniques to evaluate chemical water quality and to determine the origin of water pollution.