Karst Research at LH2

Established karstification models describe the dissolution of limestone or dolomite primarily as a result of CO₂ dissolved in flowing water. Processes such as mixing corrosion and nonlinear dissolution kinetics can effectively explain the formation of larger cavities, as they are based on the transport of CO₂ with moving water. To date, the uptake of CO₂ in stagnant or very slowly moving water has scarcely been discussed in the karst literature in the context of karstification mechanisms. However, laboratory experiments, field studies, and numerical simulations have now shown that even fresh, standing karst water (for instance, after a major rainfall event) can take up significant amounts of CO₂ relatively quickly through density-driven diffusive-convective dissolution, thereby contributing to further rock corrosion potential (Class et al., 2020; Class et al., 2021; Class et al., 2023; Keim & Class, 2025). In this process, the dynamics of CO₂ in cave air play a decisive role as the driving force for dissolution. A sound understanding of seasonal CO₂ production, its transport in both water and air, and its storage in rock and water is therefore crucial for assessing and quantifying the dissolution process in stagnant karst water.

The motivation for the ongoing research arises from ideas and long-term experience of cavers from the Laichingen Cave Association and their network. The term “Nerochytic Speleogenesis” was coined here to describe the process that highlights the density-driven “autonomous” mobility of CO₂ in both cave air and water (Scherzer et al., 2017; Scherzer et al., 2020).

The Swabian Alb is characterized by what is known as the Green Karst. A soil layer generates CO₂, and the vadose zone extends to depths of up to 200 m. More than 2,500 caves are known in the region. At the margins of the upland, karst springs emerge from spring caves, and the karstification process continues to this day. The subsurface consists mainly of massive, unbedded limestone. The history of karst development can be roughly reconstructed from river and landscape evolution.

The Laichingen Tiefenhöhle has served as a long-term CO₂ monitoring site since 2021 (Class et al., 2023). Meanwhile, the dissolution of CO₂ in an artificial water column has also been experimentally observed (Class et al., 2021). Since 2025, radon has additionally been measured alongside CO₂ to use the differing dynamics of the two gases to infer transport and storage processes.
 

In addition to laboratory experiments (Class et al., 2020; Strauch et al., 2025), we are conducting a long-term monitoring campaign in the Laichingen Tiefenhöhle (see above). Numerical simulations play a key role, complemented by machine learning methods. Current research investigates the dissolution dynamics of CO₂ in water (e.g., Keim & Class, 2025) and quantifies limestone dissolution kinetics as a function of CO₂ concentration in water. Reactive transport models are being developed for this purpose (Weiss et al., 2025; Strauch et al., 2025).
 

• Helmholtz-Zentrum Potsdam
• Höhlen- und Heimatverein Laichingen e.V. 
• Collaborative Research Centre 1313, Vision Topic "Calcite"
   

• EXC 2075: Coupled flow, transport, and geochemical processes in fractures/fissures with a focus on geothermal and karstic systems
• Experimental and numerical investigations on density-driven dissolution of CO2 and related carbonate dissolution in karst water
• SFB 1313, C04: Pore-scale and REV-scale approaches to biological and chemical pore-space alteration in porous media
• EXC 2075, PN 1-5: Numerical simulations and process analysis of CO2 enrichment in the vadose zone and at the gas-water interface of karstic systems
• SFB 1313, CX6: GAS-REACT: GAS interchange and REACTive processes in coupled subsurface/atmosphere systems(HE 9610/CL 190))
   

• Scherzer, H.; Class, H.; Weishaupt, K.; Sauerborn, T.; Trötschler, O. (2017). Nerochytische Speläogenese: Konvektiver Vertikaltransport von gelöstem CO₂ – Ein Antrieb für Verkarstung in der phreatischen Zone im Bedeckten Karst. Laichinger Höhlenfreund, 52, 29–35.
• Scherzer, H.; Class, H.; Bürkle, P. (2020). Nerochytische Speläogenese - Versenkung von CO₂ aus der vadosen Zone in das Kastwasser der phreatischen Zone: Stand der Forschung 2020. Laichinger Höhlenfreund, 55, 3-20.
  Weitere Informationen zu dieser Publikation.
• Class H.; Weishaupt K.; Trötschler, O. (2020). Experimental and simulation study on validating a numerical model for CO₂ density-driven dissolution in water. Water, 12, 738
  https://doi.org/10.3390/w12030738
• Class, H., Bürkle, P., Sauerborn, T., Trötschler, O., Strauch, B., & Zimmer, M. (2021). On the role of density‐driven dissolution of CO₂ in phreatic karst systems. Water Resources Research. American Geophysical Union (AGU). https://doi.org/10.1029/2021wr030912
• Class, H., Keim, L., Schirmer, L., Strauch, B., Wendel, K., & Zimmer, M. (2023). Seasonal dynamics of gaseous CO₂ concentrations in a karst cave correspond with aqueos concentrations in a stagnant water column. Geosciences, 13 (2), 51.
  https://doi.org/10.3390/geosciences13020051 
• Keim, L., Joao, R., Class, H. (2024). CO₂ in Höhlenluft und an der Grenzfläche von Luft und Karstwasser – Messungen, Dateninterpretation, Modellierungskonzepte. Laichinger Höhlenfreund.
  PDF of the publication.
• Keim, L., & Class, H. (2025). Rayleigh Invariance Allows the Estimation of Effective CO₂ Fluxes Due To Convective Dissolution Into Water-Filled Fractures. Water Resources Research, 61, Article 2.
  https://doi.org/10.1029/2024WR037778
• Strauch, B., Zimmer, M., Wendel, K., Keim, L., Class, H. (2025). Measuring carbonate dissolution rates under well-controlled conditions for reactive CO₂-water flow in a large lab-scale karst fracture imitate. MethodsX. 2025 Mar 19;14:103271.
  https://doi.org/10.1016/j.mex.2025.103271
• Weiss, F. J., Keim, L., Wendel, K., Class, H. (2025). Implementation Pitfalls for Carbonate Mineral Dissolution -- a Technical Note. Pre-print submitted to Applied Geochemistry, available on arXiv.org.
  https://doi.org/10.48550/arXiv.2501.05225
   

• Südwestpresse on 25th May 2021
• Schwäbische Zeitung on 8th June 2021
• SWR Baden-Württemberg: Radio broadcast from 14th June 2021
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• SimTech Magazin vom 23. Mai 2025