Abstract
AbstractWe present the first spatially resolved wetland δ13C(CH4) source signature map based on data characterizing wetland ecosystems and demonstrate good agreement with wetland signatures derived from atmospheric observations. The source signature map resolves a latitudinal difference of ~10‰ between northern high‐latitude (mean −67.8‰) and tropical (mean −56.7‰) wetlands and shows significant regional variations on top of the latitudinal gradient. We assess the errors in inverse modeling studies aiming to separate CH4 sources and sinks by comparing atmospheric δ13C(CH4) derived using our spatially resolved map against the common assumption of globally uniform wetland δ13C(CH4) signature. We find a larger interhemispheric gradient, a larger high‐latitude seasonal cycle, and smaller trend over the period 2000–2012. The implication is that erroneous CH4 fluxes would be derived to compensate for the biases imposed by not utilizing spatially resolved signatures for the largest source of CH4 emissions. These biases are significant when compared to the size of observed signals.
Highlights
Methane (CH4) is the second most important greenhouse gas after carbon dioxide and is emitted from a variety of natural and anthropogenic sources (Saunois et al, 2016)
We present the first spatially resolved wetland δ13C(CH4) source signature map based on data characterizing wetland ecosystems and demonstrate good agreement with wetland signatures derived from atmospheric observations
We evaluate the map against independent observations of regional wetland δ13C(CH4) signatures inferred from Keeling plots of atmospheric observations
Summary
Methane (CH4) is the second most important greenhouse gas after carbon dioxide and is emitted from a variety of natural and anthropogenic sources (Saunois et al, 2016). Measurements of δ13C(CH4) are useful for source attribution because fossil fuel, and biological CH4 sources have distinctive signatures and sink process partition 13CH4 and 12CH4 to different extents Accurate characterization of these isotopic “fingerprints” coupled with observations of atmospheric CH4 and δ13C(CH4) enables the diagnosis of drivers of variability in the growth rate of atmospheric CH4. Differences in primary δ13C(CH4) compositions (Bellisario et al, 1999; Hornibrook & Bowes, 2007) coupled with predictable distributions of methanogenic pathways (Hornibrook, 2000) and gas transport processes (Chanton, 2005) yield CH4 emissions with distinctly different δ13C(CH4) values in ombrotrophic bogs (À74.9 ± 9.8‰, n = 42) and minerotrophic fens (À64.8 ± 4.0‰, n = 38) These values are means and standard deviations from a compilation of field-based chamber studies of δ13C(CH4) flux to the atmosphere (Hornibrook, 2009). We develop a wetland δ13C(CH4) source signature map based on current understanding of key biogeochemical distinctions between wetland types and the source signatures associated with those types as discussed above
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