21st March 2014. A new paper published in Nature has shed light on the subject of the temperature dependence of methane fluxes measured across three different scales: cultures of methanogens, laboratory sediment incubations, and field measurements. The meta-analysis considered wetlands (such as peat bogs), aquatic systems (such as lakes and rivers), and rice-paddy fields.
The analysis showed that the temperature dependence for the three different ecosystems was indistinguishable, with an average activation energy of 0.96 eV. Furthermore, temperature dependence at the ecosystem scale was statistically identical to that of cultured methanogens (1.1 eV) and sediment incubations (0.93 eV). The authors therefore suggest that the ecosystem-scale seasonal temperature dependence of methane fluxes is driven primarily by the methanogenic community.
Lead author, Dr Yvon-Durocher said: “This is important because biological methane fluxes are a major component of global methane emissions, but there is uncertainty about their magnitude and the factors that regulate them. This hinders our ability to predict the response of this key component of the carbon cycle to global warming. Our research provides scientists with an important clue about the mechanisms that may control the response of methane emissions from ecosystems to global warming.”
This similarity in temperature dependence across scales and ecosystems has important ramifications, as discussed by the paper. For instance, the calculated temperature dependence of methane emissions is higher than that of carbon dioxide fluxes from both respiration (0.65 eV) and photosynthesis (0.3 eV). The authors investigated the implications of this difference in activation energy in relation to a warming climate. They found that the contribution of methane fluxes to total carbon emissions increased at elevated temperatures. As methane is an extremely potent greenhouse gas, this finding suggests that positive feedbacks between climate change and the carbon cycle could be stimulated in future. However, substantial variation existed in the temperature dependence of methane fluxes at the ecosystem scale, and the authors hypothesise that other factors such as water table depth, methanotrophy, substrate supply and microbial community structure could constrain changes on methane emissions in the long-term.
Dr Yvon-Durocher, from the Environment and Sustainability Institute (ESI) at the University of Exeter’s Penryn Campus in Cornwall, added: “The discovery that methane fluxes are much more responsive to temperature than the processes that produce and consume carbon dioxide highlights another mechanism by which the global carbon cycle may serve to accelerate rather than mitigate future climate change. However more research, using our results as a platform for refining Earth system models, is required to fully explore the consequences of our findings for future levels of climate change”.
Reference – Yvon-Durocher, G., Allen, A.P., Bastviken, D., Conrad, R., Gudasz, C., St-Pierre, A., Thanh-Duc, N., del Giorgio, P.A. 2014. Methane fluxes show consistent temperature dependence across microbial to ecosystem scales. Nature, doi:10.1038/nature13164
Photograph – a Welsh peatland on the island of Anglesey. Mike Peacock.