Hydrochemical and isotopic characterization of a complex aquifer system

A methodology was developed and applied to the Tindouf basin (south-western Algeria) to understand the hydrogeology of a complex aquifer system with a limited number of data, to identify the favorable areas for the design and building of new wells, and to know whether there is still current recharge of these aquifers. The principal components analysis (PCA), diagram of deuterium versus oxygen-18, and equilibrium diagrams Mg/Na and Ca/Na were the techniques used to combine different datasets in order to identify chemical and isotopic groups, which were in turn used to define the groundwater flow paths. In addition, on the basis of thermodynamic equilibrium, it is possible to define the chemical evolution of the Tindouf basin aquifer. The results of this study are consistent with the generally accepted hydrogeological conceptual model. The combination of the different methods made possible to define and and to characterise the main groundwater flow paths from their sources to the discharge zones. These flow paths are defined by water categories, which are represented by salinity and groundwater origin. This approach can be used to analyze aquifers characterized by a lack of data and can also be useful for studying other complex groundwater basins

Fuzzy analytical hierarchy process for groundwater potential mapping in a Mediterranean catchment: the case of the Medjerda catchment in northeast Algeria

In this study, groundwater potential was mapped for a Mediterranean catchment using remote sensing techniques, geographical information systems (GIS), and the fuzzy analytical hierarchy (FAHP) process. Seven environmental factors were considered to influence groundwater potential, including soil type, lithology, precipitation, land use/cover, slope, lineament density, and drainage density. A FAHP method was implemented to calculate the weight of each factor and each class in the groundwater potential. The FAHP confusion matrix was established by eliciting opinions of local experts on factors that drive groundwater potential in this area. A weighted overlay was made in Arc-GIS™ for producing the final groundwater potential map. Three groundwater potential classes were considered (low, moderate, strong). Areas of very high potential represent 107.09 km2 (8%) of the total surface of the basin and are located in alluvial and calcareous formations of a high density of lineament and in areas with a low slope which promotes rapid infiltration. About 1022.124 km2 (71%) of the surface of the sub-catchment is characterized by a moderate to strong potential, while the remainder 305.945 km2 (21%) is characterized by a low potential. The results of the classification are validated by establishing the receiver operating characteristic (ROC) curve using 61 data from the wells located in the study area. The area under curve (AUC) yields 75.5% demonstrating the effectiveness of the method in identifying groundwater potential areas

Assessment of Groundwater Pollution Vulnerability, Hazard and Risk in a Semi-Arid Region

The Mio-plio-quaternary aquifer of the Djelfa Syncline is part of a region in Algeria which is characterized by the lack of surface water resources and located in a semi-arid climate. Since alluvial aquifers, and among them our aquifer, are the most vulnerable because of thier direct exposure to the pollution caused by the infiltrated pollutants, this work focused on the assessement of groundwater pollution vulnerability, hazard and risk. Thus, several methods were used; for this purpose, such as the DRASTIC and WQI methods mapped using a GIS. The results obtained clearly show a low to moderate vulnerability. The DRASTIC model and its validation based on the correlation with WQI revealed a low correlation ($WQ_I$vs $D_I$ : 0.221). Since the vulnerability model does not match with the groundwater quality, pollution risk was assessed by combining vulnerabilty and hazard (i.e, water quality). The risk map illustrated three levels ranging from low to high risk. This map should be helpful in decision making and groundwater management through avoiding high risk areas

Multi-tracer approach to understand nitrate contamination and groundwater-surface water interactions in the Mediterranean coastal area of Guerbes-Senhadja, Algeria

Implementing sustainable groundwater resources management in coastal areas is challenging due to the negative impacts of anthropogenic stressors and various interactions between groundwater and surface water. This study focuses on nitrate contamination and transport via groundwater-surface water exchange in a Mediterranean coastal area (Guerbes-Senhadja region, Algeria) that is heavily affected by anthropogenic activities. A multi-tracer approach, integrating hydrogeochemical and isotopic tracers (δ2HH2O, δ18OH2O, 3H, δ15NNO3 and δ18ONO3), is combined with a Bayesian isotope mixing model (MixSIAR) to (i) elucidate the nitrate sources and their apportionments in water systems, and (ii) describe potential interactions between groundwater and surface water. Results from nitrate isotopic composition and the MixSIAR model show that nitrate concentrations mainly originate from sewage and manure sources. Nitrate derived from the sewage is attributed to urban and rural wastewater discharge, whereas nitrate derived from the manure is related to animal manure used to fertilise agricultural areas. High apportionments of nitrate-based atmospheric precipitation are identified in groundwater and surface water; a finding that is specific to this study. The multi-origin stresses combined with evidence of interactions between surface water and groundwater contribute to negatively impacting large parts of the study coastal area. The outcomes of this study are expected to contribute to sustainable management of coastal ecosystems by drawing more attention towards groundwater use and protection. Furthermore, this study may improve scientists' ability to predict the behavior of anthropogenically impacted coastal ecosystems and help decision-makers elsewhere to prepare suitable environmental strategies for other coastal ecosystems currently undergoing an early stage of groundwater resources deterioration