Geochemical assessment of water quality and its suitability for agricultural use in the Djedra wadi subwatershed, northeast Algeria

Abstract

The superficial water of Djedra wadi was the subject of a feasibility study relating to a dam under construction to store water to meet the increasing needs imposed by various uses. This water, however, is loaded with minerals resulting from the leaching of rocks composed essentially of outcropped carbonates and evaporates. Therefore, the aim of this study was to interpret and evaluate the mineralization of this water and to characterize its suitability for agricultural use. To this end, we measured some physicochemical parameters. Electrical conductivity and salinity were measured in situ using a commercial multi-parameter portable meter. Some water samples were then analyzed in the laboratory to determine the following chemical parameters: calcium, magnesium, sodium, potassium, bicarbonates, chlorides, and sulfates. These data were used to construct a repartition map of the electrical conductivity and salinity, to determine the hydrochemical facies using Piper and Stiff diagrams, and to identify the (un)suitability of water for irrigation using Richard and Wilcox representations. The results show that the electrical conductivity and salinity increase downstream of the watershed. The conductivity values do not exceed 990 µS/cm for the El Hammam watercourse but they exceed 2200 µS/cm for the El Akiba watercourse. With regard to the hydrochemical facies, the water upstream indicates a sodium chloride facies, whereas downstream it indicates a calcium bicarbonate facies for El Hammam and calcium sulfate facies for El Akiba and Djedra. The results also show that the downstream water is considered unsuitable for irrigation in most crops and most soils. However, monitoring of the water mineralization allows one to use them for the irrigation of salt-tolerant and resistant plants on well-drained soils, but this requires the installation of a unit to record salt concentrations daily. The implementation of an ecological purification system appropriate to the climate of the region studied, by afforestation of reeds on the slopes downstream, allows the absorption of mineral salts contained in the water.