ISODRIP, a model to transfer the δ18O signal of precipitation to drip water — implementation of the model for Eagle Cave (central Spain)

David Domínguez-Villar*, Kristina Krklec, Ian Boomer, Ian J. Fairchild

*Corresponding author for this work

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The isotope signature of cave waters provides an excellent opportunity to better understand the recharge in karst regions and the complexity of drainage systems in the vadose zone. We have developed a cave isotope hydrological model (ISODRIP) that requires entering basic hydrometeorological information and a precipitation δ18O record to simulate the discharge and δ18O signals of different drip sites. The model includes four different modules to simulate various flow route regimes: continuous and discontinuous drips under diffuse or preferential flows. We use precipitation and cave water δ18O records that were obtained in Eagle Cave (central Spain) during a 5-year period to test our model and to better understand the dynamics of karst aquifers. Eagle Cave waters do not record evaporation. The δ18O signals do not have seasonality, although they record intra-annual and inter-annual variability. Additionally, cave water δ18O signal falls within the range of the annual average weighted isotope composition of precipitation. Well-mixed cave waters, that characterize diffuse flows, record 1‰ δ18O variability, whereas partially-mixed waters, that flow along preferential drainage routes, have up to 3‰ δ18O variability. The results suggest that precipitation takes on average 15 months to reach the cave through the diffuse flow network, whereas under preferential flow the transit time is highly variable depending on the previous condition of the system. ISODRIP includes a soil layer above the vadose zone that controls large recharge events, together with direct recharge components that bypass the soil layer enabling at least some recharge all year round. Thus, the simulations reproduce the observed lack of seasonal bias in the cave water δ18O composition in relation to the average weighted isotope composition of precipitation. This research highlights the importance of understanding recharge dynamics and the configuration of particular drips sites to properly interpret speleothem δ18O records.

Original languageEnglish
Article number149188
JournalScience of the Total Environment
Early online date22 Jul 2021
Publication statusPublished - 25 Nov 2021

Bibliographical note

Funding Information:
The research leading to these results has received funding from the European Community under a Marie Curie Intra-European Fellowship of the Seventh Framework Programme FP7/2007–2013 (grant agreement n° 219891 ; PROCAVET project). This research received funds from the project “Inter-comparison of karst denudation measurement methods” (KADEME) ( IP-2018-01-7080 ) financed by Croatian Science Foundation . We thank the suggestion of four anonymous reviewers that improved the original version of this manuscript.


  • Cave drip water
  • Karst hydrology
  • Oxygen isotopes
  • Simulation
  • Transfer function

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution


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