Page 25 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

terrestrial and marine biosphere. During the decay of organic matter, C bound in this biomass can be converted to CH4 depending on environmental conditions. CH4 will eventually be oxidized back to CO2, either in terrestrial and aquatic zones, or in the atmosphere (Fig. 1.). It has been estimated that approximately 2% of CO2 fixed in the biosphere annually is released into the atmosphere as CH4 (Thauer et al. 2008).
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CH4
OM CO2
OM
Aerobic Mixed Anaerobic
Figure 1. Schematic overview of the microbial processes in the Earth’s carbon cycle. This diagram shows the autotrophic and heterotrophic processes. Arrows show microbial substrate conversion processes. OM: organic matter, CO2: carbon dioxide, CH4: methane. Picture adapted from Brock Biology of Microorganisms (Madigan et al. 2019).
1.1 Methane dynamics in the atmosphere
Methane is a major anthropogenic greenhouse gas (GHG), second only to CO2 (Myhre et al. 2013). Although atmospheric concentrations of CH4 are about 200 times lower than CO2, its global warming potential (GWP) is 28 over a 100-year time horizon and 84 over a 20-year time span in comparison with CO2 (Myhre et al. 2013). It is important to consider the time horizon because of the relatively short lifetime of CH4 in the atmosphere. Since the onset of the
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