Spatial variability of cave-air carbon dioxide and methane concentrations and isotopic compositions in a semi-arid karst environment

  • L. K. McDonough
  • C. P. Iverach
  • S. Beckmann
  • M. Manefield
  • G. C. Rau
  • A. Baker
  • B. F. J. Kelly
Original Article


There is insufficient information on the movement of air in karst environments to constrain the uncertainty associated with quantifying sources and sinks of methane (CH4) and carbon dioxide (CO2) within caves for global carbon accounting. We analysed cave-air samples for their CO2 and CH4 concentrations ([CO2] and [CH4]) and carbon isotopic compositions from sampling campaigns in winter (August 2014) and summer (February 2015) at numerous heights and locations throughout Gaden and Cathedral caves, in a semi-arid environment, Wellington Caves, NSW, Australia. Ventilation is the dominant control on cave-air CO2 and CH4, with the highest cave-air CO2 concentrations ([CO2]cave) occurring in summer, in association with the lowest cave-air CH4 concentrations ([CH4]cave). Analyses show that the cave-air CO2 has both atmospheric and soil sources. Soil air and cave air in both caves undergo methanogenesis and methanotrophy, but we identify cave-specific differences in cave-air CH4 and CO2. [CH4]cave in Cathedral Cave shows an inverse relationship to [CO2]cave, particularly in areas separated from the main cave passage. In contrast, Gaden Cave has near-atmospheric [CH4]cave and isotopic ratios present at all locations sampled in winter. Where no ventilation is occurring in summer, [CH4]cave in Gaden Cave decreases, but remains reasonably high compared to Cathedral Cave. Our research shows adjacent caves vary in their ability to act as a net sink for CH4, and highlights the need for further studies before global generalisations can be made about the carbon budget of karst environments.


Karst Methane sink Semi-arid Carbon dioxide Caves Isotopic ratio 



Completion of this study was supported by the NCGRT. Cave survey data were provided by Phil Maynard, Ian Cooper, Kevin Moore, Greg Ryan and Kier Vaughan-Taylor. Thanks go to Wellington Caves’ staff and Mike Augee, for providing accommodation and access to the site. We also thank the NCRIS Infrastructure program for funding the purchase of the Picarro systems. Thank you to Lewis Adler from the Bioanalytical Mass Spectrometry Facility at UNSW, Australia for analysing the δ13C values for thinly bedded and massive limestone samples from Wellington. Assistance in the collection of samples and analysis of samples by Justin Snyder is also appreciated.

Supplementary material

12665_2016_5497_MOESM1_ESM.doc (2.8 mb)
Supplementary material 1 (DOC 2832 kb)


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Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  • L. K. McDonough
    • 1
    • 2
  • C. P. Iverach
    • 2
  • S. Beckmann
    • 3
  • M. Manefield
    • 3
    • 4
  • G. C. Rau
    • 2
  • A. Baker
    • 2
  • B. F. J. Kelly
    • 2
  1. 1.School of Biological, Earth and Environmental SciencesUNSW AustraliaSydneyAustralia
  2. 2.Connected Waters Initiative Research CentreUNSW AustraliaSydneyAustralia
  3. 3.School of Biotechnology and Biomolecular SciencesUNSW AustraliaSydneyAustralia
  4. 4.Urban Water System EngineeringTUMMunichGermany

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