Absence of visitors during lockdown reveals natural variation in carbon dioxide level in the Glowworm Cave, Waitomo, New Zealand

Authors

David J. Merritt, The University of Queensland, AustraliaFollow
Chris Hendy Dr, University of Waikato, Hamilton, New ZealandFollow
Shannon Corkill Ms, Tourism Holdings Limited, Waitomo, New ZealandFollow

Highlights

• We assess the natural microclimate of the cave over 60 days with no visitation
• Visitors increased the cave temperature but the effect was short-lived due to cave ventilation
• During lockdown, the usual daily increase in carbon dioxide due to visitors was absent
• The partial pressure of carbon dioxide level naturally lies above the external atmospheric levels
• Rain and flood events led to increases in carbon dioxide partial pressure

Abstract

Waitomo Glowworm Cave is a highly visited cave where the highlight is viewing the bioluminescence display of a large colony of glowworms. Anthropogenic carbon dioxide build-up in the cave is prevented by management of chimney-effect ventilation aided by a network of microclimate sensors. A cave door prevents ventilationunder drying conditions and promotes it when necessary to clear CO₂ and when inflowing air has high relative humidity. A COVID-19-related nationwide “lockdown” in New Zealand from March 2020 resulted in neither staff nor visitors being present in the cave for 60 days, and provided an opportunity to assess the natural microclimate of the cave, especially the natural variation in partial pressure of carbon dioxide (_pCO₂). In addition, comparison to the previous year showed that the presence of people in the cave increased the cave temperatures but the effect was short-lived due to cave ventilation. During the period of lockdown, the daily increase of carbon dioxide partial pressure (_pCO₂) due to visitors was absent. When the cave door remained sealed, _pCO₂ varied and tended to lie at levels above that of the external atmosphere (410 ppm). Notably, rain events raised _pCO₂ by up to 200 ppm (v/v), which appeared to be sourced from both stream water and drip water. These natural CO₂ sources rarely reached the levels associated with cave visitation. The results support current management practices that use door control to enhance cave ventilation when people are in the cave or when natural conditions (high stream levels and high drip-water levels) promote CO₂ outgassing into the cave. Suppressing ventilation outside of those times reduces the risk of introducing dry air that could desiccate the glowworms.

DOI

https://doi.org/10.5038/1827-806X.51.2.2435

Creative Commons License

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.

Recommended Citation

Merritt, D.J., Hendy, C.H., Corkill, S., 2022. Absence of visitors during lockdown reveals natural variation in carbon dioxide in the Glowworm Cave, Waitomo, New Zealand. International Journal of Speleology, 51(2), 133-139. https://doi.org/10.5038/1827-806X.51.2.2435