Lateral expansion of northern peatlands calls into question a 1,055 GtC estimate of carbon storage

“Both the size of the peatland carbon pool and its development over time are poorly constrained1. In a recent analysis, Nichols and Peteet2 proposed that the northern peatland carbon store is 1,055 GtC, two to three times higher than previously thought3. We argue that such a large figure is inconsistent with measured peat depth and physical properties. The 1,055 GtC estimate was produced using an incorrect assumption of how peatlands expand, a methodology that is vulnerable to outliers, and using a dataset that lacks the necessary reproducibility and context for quality control. Underpinning the time-history approach used by Nichols and Peteet2 is the assumption that peatlands expand linearly in time after initiation. Thus the increase in peatland area is proportional
to the summed frequency of peat initiation1. This assumption has been repeatedly called into question1,4 and runs contrary to the overwhelming majority of evidence available from the literature4–8, spanning a considerable number of peatlands across a diverse range of regions. Notably, the assumption that lateral expansion rates are linear is untenable as the literature points to nonlinear, initially restricted, lateral peatland expansion being the rule rather than
the exception. The reason for restricted lateral expansion rates is that the underlying and surrounding topography strongly controls peatland lateral expansion5,6,8. Even a relatively shallow slope (0.5%) may halt lateral expansion entirely6. After deglaciation, peat predominantly initiated in hollows and steep-sided basins9. In a practical sense this means that peat formation was often constrained, with little to no lateral growth for a long period of time. This was demonstrated as early as 1923 for a Swedish peatland10, for example. Importantly, neglecting the influence of topography will result in a systematic
bias towards the earlier expansion of peatlands, hence an overestimate of the peatland carbon stock. Notably, in studies that have directly investigated peatland expansion rather than initiation, lateral expansion is consistently most rapid in the mid-Holocene4,11, even though initiation may have been much earlier.”

(Citaat: Ratcliffe, J.L., Peng, H., Nijp, J.J.,et al. – Lateral expansion of northern peatlands calls into question a 1,055 GtC estimate of carbon storage – Nature Geoscience (2021) 14)