Hydrological Feedbacks in Northern Peatlands 2: Peat Depth as a Control on Peatland Resilience

As climate change increasingly threatens the northern peatland net carbon sequestration function, there is a pressing need to better understand the limits of ecohydrological regulatory mechanisms. This is especially urgent for shallow peatlands (< 40‐cm average peat depth), which consistently experience water stress with greater intensity, frequency and duration than deep peatlands and may represent sentinels for climate change. In this ‘part 2’ paper, we review the peatland hydrological feedbacks originally proposed a decade prior in Hydrological Feedbacks in Northern Peatlands ‘part 1’ (Waddington et al. 2015) to investigate the strength of feedback mechanisms as a function of peat depth. We show that in some hydrogeomorphic and hydroclimatic settings there are differences in hydrophysical properties and vegetation cover between shallow and deep peatlands. These structural characteristics influence the strength of the fast (i.e., function on a timescale of seconds to days) hydrological feedbacks (moss surface resistance and albedo, transmissivity, peat deformation and specific yield). In contrast, the slow feedbacks (i.e., operating on the scale of months to decades) related to vegetation community change and peat decomposition directly impact peatland physical characteristics (patterns and composition of vegetation, bulk density, etc.). We discuss how the vulnerability of shallow peatlands arises from the interactions between regulatory (negative) and destabilizing (positive) ecohydrological feedbacks.