Hydrochemistry and Nitrate Pollution of Groundwater in the Alluvial Aquifer of the Eastern Mitidja (Algeria)

Abstract

The study carried out in the eastern Mitidja (Algeria) using groundwater chemistry data is aimed at clarifying the geochemical behavior of the alluvial groundwater as well as assessing the degree of nitrate contamination. The aquifer is characterized by a heterogeneous lithology marked by alternating levels of alluvium, gravel, sand and clay. The chemical facies encountered are: Na - Cl type with 52.7%, Mixed Ca - Mg - Cl type with 29.1%, Mixed Ca - Na - HCO3 type with 9.1% and Ca – HCO3 type with 9.1%. The interpretation of the analytical data shows that water mineralization is controlled by many ions Na+, SO42-, Cl-, Ca2+ and HCO3-. The Gibbs diagram suggests that weathering rock is the determining factor in the current chemical composition of groundwater. Agricultural activity is the main source of groundwater contamination by nitrates. Most of the water points tested have NO3 values very close to the critical threshold of 50 mg/l, the world health organization (WHO) drinking water reference value. By comparing this with the "human affected value" of 13 mg/l, 95% of the analyzed waters are considered contaminated. This water degradation is linked to the widespread use of nitrogen fertilizers, agricultural practices and increasing urbanization.