Identification of dominant hydrogeochemical processes for groundwaters in the Algerian Sahara supported by inverse modeling of chemical and isotopic data

Abstract

Abstract. Unpublished chemical and isotopic data taken in November 1992 from the three major Saharan aquifers, namely the Continental Intercalaire (CI), the Complexe Terminal (CT) and the phreatic aquifer (Phr), were integrated with original samples in order to chemically and isotopically characterize the largest Saharan aquifer system and investigate the processes through which groundwaters acquire their mineralization. Instead of classical Debye-Hückel extended law, a specific interaction theory (SIT) model, recently incorporated in PHREEQC 3.0, was used. Inverse modeling of hydrochemical data constrained by isotopic data was used here to quantitatively assess the influence of geochemical processes: at depth, the dissolution of salts from the geological formations during upward leakage without evaporation explains the transitions from CI to CT and to a first end member, a cluster of Phr (cluster I); near the surface, the dissolution of salts from sabkhas by rainwater explains another cluster of Phr (cluster II). In every case, secondary precipitation of calcite occurs during dissolution. All Phr waters result from the mixing of these two clusters together with calcite precipitation and ion exchange processes. These processes are quantitatively assessed by the PHREEQC model. Globally, gypsum dissolution and calcite precipitation were found to act as a carbon sink.

Assessment of groundwater vulnerability to pollution in an Arid environment

“…The Continental Terminal, a continental formation composed primarily of sands deposited and solidified in The hydrographic network of the Ouargla basin is sparse and consists of a fossil wadi called Wadi Mya and two functional wadis called Wadi N'sa and Wadi M'zab. All these wadis have a temporary flow (Slimani et al 2017).…”

The Integrated Use of Heavy-Metal Pollution Indices and the Assessment of Metallic Health Risks in the Phreatic Groundwater Aquifer—The Case of the Oued Souf Valley in Algeria

“…In an effort to evaluate the situation, very few studies have been conducted to assess the physicochemical quality of the phreatic aquifer for drinking and irrigation use, and the impact of direct discharge of wastewater and drainage waters into the phreatic aquifer of Oued Souf, as well as its influence on the degradation of the phreatic groundwater quality using hydrogeochemical, geographic information system (GIS), and isotopic ap-proaches [30][31][32][33][34]. No study has been conducted to assess heavy-metal contamination in the phreatic groundwater aquifer under its illegal utilization for irrigation and industry.…”

Assessment of Complex Terminal Groundwater Aquifer for Different Use of Oued Souf Valley (Algeria) Using Multivariate Statistical Methods, Geostatistical Modeling, and Water Quality Index

“…Northern Sahara of Algeria has been the subject of research in several studies, that have mainly highlighted on the geological and hydrogeological contexts of their aquifers, in reconnaissance of the northern Sahara aquifer system [7][8][9][10][11][12][13]. In addition to geological and hydrogeological studies, various studies undertaken over the past thirty plus years have shown that the groundwater's quality of this region is characterized by excessive total mineralization, most often associated with high hardness and high fluoride concentrations, which often exceed the guide values recommended by the World Health Organization (WHO) and values of Algerian limits using conventional methods hydro-chemically, statistically, and even using isotopic methods [14][15][16][17][18][19][20][21][22][23]. Other studies focused on the treatment of these groundwaters using different techniques, such as lime precipitation and electrocoagulation using bipolar aluminum electrodes and activated natural materials [24][25][26].…”