Advertisement

The CO2 Dynamics in the Continuum Atmosphere-Soil-Epikarst and Its Impact on the Karstification Potential of Water: A Case Study of the Lascaux Cave Site (Montignac, France)

  • Nicolas HouillonEmail author
  • Roland Lastennet
  • Alain Denis
  • Philippe Malaurent
Conference paper
Part of the Advances in Karst Science book series (AKS)

Abstract

The aim of this work was to understand the dynamics of CO2 in the atmosphere-soil-epikarst continuum of the Lascaux Cave site and to evaluate its impact on the hydrogeochemical signal of epikarstic waters. For these purposes, PCO2, \(\updelta^{13} {\text{C}}_{{{\text{CO}}_{2} }}\) and associated hydroclimatic parameters were recorded at different depths in soil and epikarst. In parallel, hydrogeochemistry of an epikarstic emergence (SAS1 spring) located in the entrance of the cave (6 m depth) was studied. PCO2 recorded in the soils underlines the seasonality and different levels of biogenic production according to the pedological facies and the physicochemical properties (higher in the calcisol than in the brunisol). CO2 efflux measurements show a seasonal evolution with maximum value (25 g m−2 d−1) in summer and minimum in winter (6 g m−2 d−1). It decreases during rain events because of the soil moisture increases which limits CO2 diffusivity. In the same way, seasonal processes of CO2 accumulation (winter and spring) and CO2 emission to the atmosphere (summer and autumn) are observed under the effect of soil moisture seasonal variations. These processes explain the very variable CO2 concentrations (0.6–6%) and \(\updelta^{13} {\text{C}}_{{{\text{CO}}_{2} }}\) values (−22.1 to −24.5‰) in the superficial epikarst (0–3 m depth). This CO2 accumulation explains the presence of higher CO2 contents in the epikarst than in the main production area: the soil. At deeper level exists a differentiated CO2 stock slightly variable (4–6%) with stable \(\updelta^{13} {\text{C}}_{{{\text{CO}}_{2} }}\) values from −22.7 to −21.7‰. Inter-annual variability of CO2 contents is influenced by the synchronicity or not of intense production and high soil moisture. A conceptual scheme of CO2 cycle is produced as a conclusion. The comparison with the evolution of water chemistry at the epikarstic emergence brings elements for understanding the acquisition of the karstification potential. Indeed, the seasonal evolution of the calcic carbonated mineralization of water is very well explained by the evolution of the CO2 contents in the epikarst (PCO2 at saturation with respect to calcite similar to the PCO2 of the air of the epikarst). In addition, the presence of two different CO2 compartments in the epikarst makes it possible to explain the variability of the chemical marking of water at the outlet depending on the flow conditions (transmissible and capacitive zones).

Keywords

Carbon dioxide Continuous monitoring Epikarst Hydrogeochemistry Lascaux 

Notes

Acknowledgements

The authors wish to thank the DRAC Nouvelle Aquitaine for its funding and support. This work benefits from scientific discussion within the Karst National Observatory Network.

References

  1. Atkinson, T. C. (1977). Carbon Dioxide in the Atmosphere of the unsaturated Zone: an important control of groundwater hardness in limestones. Journal of hydrology 35, 111–23.CrossRefGoogle Scholar
  2. Bruxelles L., Camus H., Sirieix C., Poulenard J., Perrin J. (2014). Etude des contextes géologique, géomorphologique et pédologique de la Grotte de Lascaux. Synthèse des rapports d’étude, 64 p.Google Scholar
  3. Houillon N., Lastennet R., Denis A., Malaurent P., Minvielle S., Peyraube N. (2017). Assessing cave internal aerology in understanding carbon dioxide (CO2) dynamics: implications on calcite mass variation on the wall of Lascaux cave (France), Environmental Earth Sciences, Vol 76, 19 p.Google Scholar
  4. Maier M., Shack-Kirchner H., Hildebrand E.E., Schindler D. (2011). Soil CO2 efflux vs soil respiration: implications for flux models. Agricultural and forest meteorology, Vol 151, 1723–1730.CrossRefGoogle Scholar
  5. Mattey, D.P., T.C. Atkinson, J.A. Barker, R. Fisher, J.-P. Latin, R. Durrell, et M. Ainsworth (2016). Carbon Dioxide, Ground Air and Carbon Cycling in Gibraltar Karst». Geochimica et Cosmochimica Acta, Vol 184, 88–113.CrossRefGoogle Scholar
  6. Peyraube N., Lastennet R., Denis A. (2012). Geochemical evolution of groundwater in the unsaturated zone of a karstic massif using the PCO2-Sic relationship. Journal of Hydrology, Vol 430–431, 13–24.CrossRefGoogle Scholar

Copyright information

© Springer Nature Switzerland AG 2020

Authors and Affiliations

  • Nicolas Houillon
    • 1
    Email author
  • Roland Lastennet
    • 1
  • Alain Denis
    • 1
  • Philippe Malaurent
    • 1
  1. 1.Laboratory I2M (UMR 5295), University of BordeauxPessac CedexFrance

Personalised recommendations