Hydrochemical Characterization, Source Identification, and Irrigation Water Quality Assessment in the Voghji River Catchment Area, Southern Armenia

Water quality is a fundamental parameter for assessing the suitability of surface waters. Likewise, the hydrochemical behavior is critically important to understand for rivers used in irrigation. This study aims to evaluate and characterize the surface water quality of the Voghji River catchment basin for irrigation, as it reveals the hydrochemical origins in the catchment basin. Nine key parameters, including EC, Cl−, SO42−, Ca2+, Mg2+, Na+, K+, CO32−, and HCO3−, were measured at seven sampling points in July and September 2017. The ion concentration patterns in July followed the sequence: Ca2+ > Na+ > K+ > Mg2+ and HCO3− > SO42− > Cl− > CO32−, while in September, they were Ca2+ > Na+ > Mg2+ > K+ and HCO3− > SO42− > Cl− > CO32−. The sequences were almost similar between the two months, with minor differences in cation distribution, particularly between Mg2+ and K+. Overall, Ca2+ and HCO3− were the dominant ions in the studied surface water samples. The concentrations of K+, Na+, Mg2+, Ca2+, Cl−, SO42−, and HCO3− were found to be well below the FAO irrigation water standards, indicating that the waters of the Voghji River and its tributaries (Achanan, Vachagan, and Geghi) were generally safe for irrigation. However, the FAO threshold value was exceeded only for CO32− in the Vachagan River in Kapan Town. The chemical analysis of surface waters in the Voghji River catchment basin revealed dominant Ca2+-HCO3− and mixed Ca2+-K+-SO42−-Cl− facies, with key geochemical processes including carbonate and gypsum dissolution, silicate weathering, and cation exchange. Ionic correlations indicated that Na+ and Cl− sources were influenced by both natural (e.g., halite dissolution, weathering) and anthropogenic inputs, while Ca2+ and Mg2+ primarily originated from carbonate dissolution. The Gibbs diagram suggested that rock–water interactions were the primary natural mechanism controlling the water chemistry, with evaporation also playing a significant role. Various indices, including the Kelly index, magnesium adsorption ratio, sodium percentage, sodium adsorption ratio, permeability index, potential salinity, residual sodium carbonate, soluble sodium percentage, and irrigation water quality index, were applied, along with US Salinity Laboratory diagram and Wilcox diagram, to further assess the irrigation suitability. Most indices confirmed the suitability of the waters for irrigation; however, the Achanan River near the mouth and the Voghji River downstream of Kapan Town exhibited moderate salinity levels, underscoring the need for water management to prevent potential soil degradation.