Valdivielso et al. (2026) Isotopic characterization and recharge dynamics of Karst aquifers in a mediterranean basin

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2026
• Date: 2026-02-03
• Authors: Sonia Valdivielso, Marta Turull, Sergio Carrero, Benjamín Crisóstomo, Deby Jurado, Joan Botey i Bassols, Cèlia Riera, Sergi Díez
• DOI: 10.1016/j.ejrh.2026.103209

Research Groups

• MAiMA Group, Applied Mineralogy, Geochemistry and Hydrogeology—MAGH, Department of Mineralogy, Petrology and Applied Geology, Faculty of Earth Sciences, University of Barcelona (UB), Barcelona, Spain
• Institute of Environmental Assessment and Water Research (IDAEA), CSIC, Barcelona, Spain
• Department of Civil and Environmental Engineering, Technical University of Catalonia (UPC), Barcelona, Spain

Short Summary

This study characterizes the isotopic composition of precipitation, surface water, and groundwater in the headwaters of the Llobregat River, Spain, to understand hydrological processes in karst aquifers. It identifies dominant winter recharge from high elevations and the influence of air mass origin on isotopic signatures, supporting improved water resource management.

Objective

• Advance the understanding of isotopic processes in karst hydrological systems by characterizing the isotopic composition of precipitation and its controlling factors, and by identifying the origin and recharge zones of surface water and groundwater.

Study Configuration

• Spatial Scale: Headwater of the Llobregat River, Spain, specifically the upper basin of the Llobregat and Cardener rivers (733 km²), located on the southern slope of the Cadí-Moixeró Natural Park. This includes the Cadí, Moixeró, Tossa d′Alp, Puigllançada, and Pedraforca mountain ranges.
• Temporal Scale: Water samples collected between April 2024 and February 2025. Meteorological data from 2024. Hydrological, hydrochemical, and isotopic data from 2020 to 2024 (ACA) and 2015 to 2023 (Herms J.I., 2022). Backward trajectory analysis for precipitation events between April 6, 2024, and February 17, 2025.

Methodology and Data

• Models used: HYSPLIT model v.4 (Hybrid Single-Particle Lagrangian Integrated Trajectory Model), PySPLIT (Python-based tool for HYSPLIT), Ordinary Least Squares Regression (OLSR), Principal Component Analysis (PCA).
• Data sources:
  • Water samples: 115 samples (precipitation, surface water, groundwater from 15 springs and 4 piezometers) collected from 30 sites.
  • Isotopic analysis: δ¹⁸O and δ²H using LCRDS system.
  • Meteorological data: Precipitation, air temperature, relative humidity, atmospheric pressure, and global solar radiation from Meteorological Service of Catalonia (SMC) automatic stations.
  • Hydrological/Hydrochemical data: Daily surface water flow, monthly chemical composition and physicochemical parameters, and monthly piezometric levels from Catalan Water Agency (ACA).
  • Existing isotopic data: 71 isotopic analyses of precipitation from the Port del Comte sector (Herms J.I., 2022).
  • Geological/Hydrogeological data: Geological maps (1:25,000 scale) from the Cartographic and Geological Institute of Catalonia (ICGC).
  • Reanalysis data: Reanalysis Pressure data files (RP) from NCEP/NCAR for HYSPLIT model input.

Main Results

• An isotopic gradient linked to atmospheric humidity conditions was identified, showing greater isotopic enrichment under drier conditions (enhanced sub-cloud evaporation) and depletion under more humid conditions (minimal sub-cloud evaporation).
• Deuterium excess (D-excess) variability is controlled by thermodynamic processes and air-mass origin, with higher D-excess in colder precipitation and lower D-excess in warmer precipitation.
• The Local Meteoric Water Line (LMWL) for the upper Llobregat River basin was calculated as δ²H = 7.34δ¹⁸O + 8.14.
• Moisture sources contributing to precipitation were identified as the Atlantic Ocean (44%), Mediterranean Sea (24%), France (18%), and the Cantabrian Sea (14%).
• Precipitation isotopic signatures vary with moisture origin: French air masses (D-excess: 6.5–14 ‰), Atlantic air masses (D-excess: 10.5–13 ‰, mean ~12 ‰), and Mediterranean moisture (highest D-excess: ~15 ‰).
• Groundwater and surface water isotopic signatures indicate dominant winter recharge occurring above 1800 m a.s.l., consistent with regional topography and the highly karstified structure of the Moixeró massif.
• The preservation of seasonal isotopic signals in groundwater suggests short residence times and rapid recharge responses in karst aquifers.
• A revised Isotopic Altitude Line (IAL) was calculated as Altitude = -271.79*δ¹⁸O – 667.9, suggesting recharge from altitudes above 1200 m a.s.l., with significant contributions from above 1800 m a.s.l.

Contributions

• Advances the understanding of hydrological and hydrogeological processes in fractured and karstified carbonate massifs in a Mediterranean basin by providing a comprehensive isotopic characterization.
• Addresses key knowledge gaps regarding groundwater systems in the headwaters of the Llobregat River, including precipitation moisture sources, recharge areas, and groundwater circulation, extending beyond previously studied sub-basins.
• Integrates stable isotope data with backward trajectory analysis and multivariate statistical methods to delineate recharge zones and flow paths within complex karst systems.
• Provides robust scientific evidence to support improved water resource management and sustainable consumption strategies in mountain karst environments, particularly in the context of climate change.
• Emphasizes the high sensitivity of alpine karst systems to climatic variability and underscores the necessity for continuous isotopic monitoring.

Funding

• "Agencia Estatal de Investigación" from the Spanish Ministry of Science and Innovation
• IDAEA-CSIC, a Centre of Excellence Severo Ochoa (CEX2018–000794-S)
• SINERGIA-IDAEA project "Development of new passive samplers for the characterization of groundwater in the Llobregat Springs (SENTINEL)"
• Juan de la Cierva Program (JDC2023–051090) funded by MICIU/AEI/10.13039/501100011033 and by SE+ (for S. Valdivielso)
• Ramon y Cajal Program (RYC2023–04523-I) (for S. Carrero)

Citation

@article{Valdivielso2026Isotopic,
  author = {Valdivielso, Sonia and Turull, Marta and Carrero, Sergio and Crisóstomo, Benjamín and Jurado, Deby and Bassols, Joan Botey i and Riera, Cèlia and Díez, Sergi},
  title = {Isotopic characterization and recharge dynamics of Karst aquifers in a mediterranean basin},
  journal = {Journal of Hydrology Regional Studies},
  year = {2026},
  doi = {10.1016/j.ejrh.2026.103209},
  url = {https://doi.org/10.1016/j.ejrh.2026.103209}
}