LAUSR

Abstract Study region: Loja Basin, Ecuador. Loja city is mainly supplied by surface water and solely few places in the city make use of groundwater. For sustainable handling and consumption; development of groundwater inventories, determination of physical and chemical characteristics and the analysis of modifying phenomena and contaminating sources that may affect these waters, is vital. Chemical analyzes were performed on groundwater samples from Loja basin and with all these data, through the use of bivariate diagrams (TDS vs Na/(Na + Ca), TDS vs Cl/(Cl + HCO3), Mg/Na vs Ca/Na and HCO3/Na vs Ca/Na), determine the hydrochemical processes that control the composition of groundwater. New hydrological insights for the region: In Loja basin, the rock-water interaction determines; mostly, the composition of groundwater. The predominant ion in most of these waters was HCO3- followed by Cl-. Ions such as sulfate, bicarbonate, calcium and gypsum come from the weathering of calcite, dolomite and gypsum (Ca + Mg vs. HCO3, SO42- = r2 = 0.93). Silicate weathering also generates an input of calcium, magnesium and sodium to groundwater. Local increases in the K+ and NO3− levels of some sampling points cannot be justified by the interaction with the basin's geological materials so these variations may probably be influenced by anthropic factors such as: domestic wastewater contamination, application of fertilizers and garbage accumulation contiguous to the places where the water emerge. Springs were more affected by anthropogenic activity.