Abstract

Mountain catchments are critical sources of water. Particularly in semiarid regions, where precipitation is exceeded by potential evapotranspiration, mountain catchments are important water reservoirs for the population settled in the nearby lowlands. This study investigates the spatio-temporal variability of water stable isotopes and hydrochemical properties in the semiarid Huaco catchment, located in the Sierras Pampeanas of the Andean foreland in Northwestern Argentina. Stream water samples were collected across four sub-catchments along an altitudinal gradient. The results indicate that electrical conductivity and chloride concentrations increase downstream (from 148.1 to 307.2 ?S cm?1 for the former and from 17.7 to 46.4 ppm for the latter) while water stable isotopic composition (?18O and ?2H) remain uniform across the altitudinal gradient (with averages of ?5.1 ‰ and ?24 ‰, respectively). These spatial variations are indicative of increasing evaporative concentration with decreasing altitude, also exhibiting decreasing streamflow with decreasing altitude. Moreover, water is diluted (with TDS up to 175 mg L?1), alkaline (pH = 8.2–8.5), and transitions from bicarbonate-mixed to bicarbonate-sodium types downstream. Within the year 2022, major ions showed slight seasonal variation. Conversely, water stable isotopes remained constant within the temporal scale. This suggests groundwater as a uniform source feeding streamflow. Additionally, concentration-streamflow relationships of electrical conductivity and chloride suggest predominantly chemostatic behavior, highlighting limited variability in solute concentrations despite changes in streamflow. This integrative isotopic, hydrochemical, and hydrometric approach provides insights into the hydrological dynamics in this semiarid mountain catchment, improving the understanding of hydrological processes in these environments. © 2025 Elsevier Ltd