Observed response of soil O2 concentration to leaked CO2 from an engineered CO2 leakage experiment

The response of soil O2 concentration to artificially released CO2 was investigated during an engineered surface CO2 leakage experiment at a research facility at Bozeman, Montana, USA in the summer of 2010. Results show that (1) when there is no CO2 leakage, generation of CO2 at the research site was primarily due to oxidation of organic matter, soil O2 concentration is correlated negatively with soil CO2 concentration and soil moisture and positively with soil temperature. This represents the site's intrinsic relationship of soil O2 concentration with other soil environmental factors under natural conditions. (2) When there is CO2 leakage, soil O2 concentration is negatively associated with soil CO2 concentration, and positively associated with soil moisture and soil temperature. The observation that the dependence of soil O2 concentration on soil moisture is reversed from negative to positive when there is a CO2 leakage should be useful for CO2 leakage verification. Anomalous changes of soil gas composition at a CO2 sequestration site may provide important and direct signatures of CO2 leakage and important information of its impact on the environment, especially O2 dependent soil respiration processes, which may be compromised with elevated CO2 and reduced O2 concentrations.