Assessment of groundwater hydrochemical properties and irrigation water quality using GIS in the Tolga Region, South-East Algeria

Groundwater is the primary water source in arid and semi-arid regions due to the scarcity of surface resources and irregular rainfall. making the assessment of its quality essential to ensure sustainable use in agriculture. Despite the importance of groundwater for irrigation, previous studies have not applied an integrated approach combining hydrochemical sample classification according to Gibbs diagrams, calculation of the Irrigation Water Quality Index (IWQI) for each category and spatial analysis using Geographic Information Systems (GIS). This study aimed to assess groundwater quality for irrigation and analyze the spatial variability of the IWQI in the Tolga region, southeastern Algeria, using hydrochemical analysis and geostatistical modeling. Samples were classified into two main types: rock-affected and evaporation-affected with dominant hydrochemical processes identified using Gibbs diagrams. IWQI classification results indicated that rock-affected samples fall within low and moderate restriction classes, whereas evaporation-affected samples are categorized into high and severe restriction classes, highlighting the crucial role of evaporation in determining irrigation water suitability and its direct impact on operational constraints. Spatial distribution maps revealed a clear northwest–southeast gradient in IWQI values for rock-affected samples associated with geological formations, while evaporation-affected samples showed a simpler pattern with only two main zones. The results confirm that the spatial variability of groundwater quality is primarily influenced by geological factors and evaporation processes, emphasizing the importance of integrating hydrochemical analysis with GIS to understand water distribution and support sustainable management of agricultural resources.