Résumé:
Thermo-mineral springs are widely distributed across northeastern Algeria and
represent both a natural resource and a potential sector for therapeutic and tourism
development. These waters exhibit significant variability in temperature, discharge, and
chemical composition, reflecting heterogeneous hydrogeological conditions. This study
aims to characterize the regional variability of hydrothermal systems in Guelma, Souk
Ahras, Khenchela, and Tebessa, and to interpret groundwater circulation within the
framework of hierarchical flow systems. For the first time in this region, the conceptual
model of gravitational groundwater flow systems defined by József Tóth is applied to
interpret hydrothermal circulation patterns. The methodological approach combines
classical hydrogeological investigation with the gravitational flow system theory,
incorporating hydrochemical analyses, isotopic measurements of δ¹⁸O and δ²H,
characteristic ionic ratios, geothermometric estimations using Na/K, Na–Li, and
Na–K–Ca geothermometers, and multivariate statistical analyses (principal component
analysis and hierarchical cluster analysis). This integrated approach is used to identify
the factors controlling water composition, the origin of recharge, and circulation
pathways within hydrothermal units across a regional basin scale comprising
hierarchical groundwater systems. Results show water temperatures ranging from 18 °C
to 94.7 °C, and total mineralization varying from 424 mg/L in F6 (Khenchela) to 15,992
mg/L in S13 (Tebessa), reflecting contrasting circulation depths and degrees of
water–rock interaction. Three dominant hydrochemical facies: calcium bicarbonate,
calcium sulfate, and sodium chloride, which correspond to local, intermediate, and
regional flow systems within the hierarchical groundwater circulation framework.
Isotopic compositions confirm a meteoric origin for all thermal waters. Regionally, the
Guelma province forms a distinct hydrothermal domain characterized by higher
temperatures and specific mineralization patterns. Geochemical temperature
estimations indicate that S7 (Guelma) and S13 (Tebessa) exhibit ion ratios and
geothermometric signatures of chemically mature groundwater, suggesting prolonged
circulation and stable hydrochemical evolution. This integrated framework enhances the
understanding of hydrothermal processes and supports the sustainable development
and management of geothermal resources in northeastern Algeria.Keywords: Thermal
springs; Hydrochemistry; Stable isotope; Gravitational flow systems;
Regionalhydrogeology; Principal component analysis (PCA)
