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The acequias de careo are ancestral water channels excavated during the early Al-Andalus period (8th-10th centuries), which are used to recharge aquifers in the watersheds of the Sierra Nevada mountain range (Southeastern Spain). The water channels are maintained by local communities, and their main function is collecting snowmelt, but also runoff from rainfall from the headwaters of river basins and distributing it throughout the upper parts of the slopes. This method of aquifer artificial recharge extends the availability of water resources in the lowlands of the river basins during the dry season when there is almost no precipitation and water demand is higher. This study investigates the contribution of the careo channels in the watershed of Bérchules concerning the total aquifer recharge during the 2014-2015 hydrological year. Several channels were gauged, and the runoff data were compared with those obtained from a semi-distributed hydrological model applied to the same hydrological basin. The natural infiltration of meteoric waters accounted for 52% of the total recharge, while the remaining 48% corresponded to water transported and infiltrated by the careo channels. In other words, the careo recharge system enhances by 92% the natural recharge to the aquifer. Our results demonstrate the importance of this ancestral and efficient channel system for recharging slope aquifers developed in hard rocks. The acequias de careo are nature-based solutions for increasing water resources availability that have contributed to a prosperous life in the Sierra Nevada. Its long history (>1200 years) suggests that the system has remarkable resilience properties, which have allowed adaptation and permance for centuries in drastically changing climatic and socioeconomic conditions. This recharge system could also be applied to -or inspire similar adaptation measures in- semi-arid mountain areas around the world where it may help in mitigating climate change effects., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

In the arid area of northern Chile, groundwater resources in the Andean formations are essential for native populations, ecological services, mining, and other human activities. Validated conceptual hydrogeological models are required for current and future water and land management. This work aims to explain the processes controlling the origin and distribution of recharge and groundwater composition in the Andean Precordillera and Altiplano of the Tarapacá Region of northern Chile, using major solutes in spring, river, and well water, and the stable and radioactive isotopes of water oxygen, hydrogen, and dissolved inorganic carbon. The waters are mainly of the Na-Ca-SO 4 type. Processes controlling the chemical evolution of waters are atmospheric dust contribution, evapo-concentration, and enhanced volcanic rock weathering, as well as halite dissolution in some locations. The isotopic composition of Precordillera eastern flank water samples follows an evaporation line, while those in the western flank, in the Altiplano, follow a line that is parallel to the local meteoric line, suggesting unsaturated zone evaporation processes of infiltrated rainfall. δ 13 C DIC contents (-2 to -27‰) indicate mixing processes, volcanic CO 2 in the Altiplano, and calcite dissolution in some sectors. In the western depression, the only recharge is due to water infiltration in creek channels. In the highland areas, 5-25% of precipitation produces recharge. The estimated groundwater renewal time in the Precordillera was 3-14 kyr. The piezometric elevation in the Precordillera due to low-permeability intrusive rocks and local recharge prevents the east-west groundwater transfer from the Altiplano to the western depression and explains why the volcanic CO 2 in the Altiplano basins is not observed on the western flank. These results provide new insights for the evolution of water quality in volcanic aquifers in arid environments and provide considerations for estimating groundwater residence times using radiocarbon in areas influenced by volcanic CO 2 ., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The objective of this work is to characterize the impact of climate change in the karst aquifer of the Port del Comte Massif (PCM). Six regional climate models (RCMs) from CLYM'PY Project are used to analyse the magnitude and trends of changes on precipitation and temperature (RCP4.5 and RCP8.5 scenarios) and how these changes propagate through the hydrogeological system as groundwater resources availability and the associated water isotopic content. The study uses the RCMs climate change forcings as input data to a combination of (1) a semi-distributed hydrological model for simulating the hydrodynamical response of the aquifer, and (2) a lumped parameter model for simulating the isotopic content in groundwater at the outlet of the aquifer. A mean decrease of 2.6% and 1.9% in yearly precipitation and a mean increase of 1.9 and 3.1 °C in average temperature is expected in PCM at the end of the 21st century in the RCP4.5 and RCP8.5 scenarios, respectively. This climate signal entering the hydrogeological system results in a mean decrease in recharge of 3.9% and 0.5% from rainfall and of 59.3% and 76.1% from snowmelt, and a decrease of 7.6% and 4.5% in total system discharge, but also generates an isotopic enrichment in groundwater discharge (δ 18 O GW ) of 0.50‰ and 0.84‰, respectively. Moreover, from a long-term (2010-2100) perspective, the mean trend in δ 18 O GW is 0.7‰/100 yr and 1.2‰/100 yr for RCP4.5 and RCP8.5, respectively, resulting in easily measurable annual lapse rates with the current analytical methods., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The Ordesa and Monte Perdido National Park, located in the Southern Pyrenees, constitutes the highest karst system in Western Europe. No previous studies regarding its geochemical and isotopic groundwater characterization are available in this area. This work presents the results of field and sampling campaigns carried out between July 2007 and September 2013. The groundwater presents high calcium bicarbonate contents due to the occurrence of upper Cretaceous and lower Paleocene-Eocene carbonate materials in the studied area. Other relevant processes include dissolution of anhydrite and/or gypsum and incongruent dissolution of Mg-limestone and dolomite. The water stable isotopes (δ(18)O, δ(2)H) show that the oceanic fronts from the Atlantic Ocean are responsible for the high levels of precipitation. In autumn, winter, and spring, a deuterium excess is found in the recharge water, which could be related to local atmospheric transport of low-altitude snow sublimation vapour and its later condensation on the snow surface at higher altitude, where recharge is mostly produced. The recharge zones are mainly between 2500m and 3200ma.s.l. The tritium content of the water suggests short groundwater transit times. The isotopic composition of dissolved sulphate points to the existence of regional fluxes mixed with local discharge in some of the springs. This work highlights the major role played by the altitude difference between the recharge and discharge zones in controlling the chemistry and the vertical variability of the isotopic composition in high-altitude karst aquifers., (Copyright © 2014 Elsevier B.V. All rights reserved.)