The Structure and Function of Peatlands in the Hudson Bay Lowlands – Comparing a Pristine and a Hydrologically Impacted Peatland Site

Climate change is considered to pose a significant risk to the vast and varied peatlands of the Hudson Bay Lowlands (HBL). Changes in peatland biogeochemical processes in this region could have major consequences for global greenhouse gas exchange and climate regulation, and yet there are still many gaps and uncertainties in our knowledge of these processes. In particular, our understanding of the mechanisms controlling the structure (vegetation and water table) and function (carbon flux) of these systems is limited. Various theories and models of peatland development have been proposed, including those that describe peatlands as self-regulating systems where long-term stability is maintained by feedback between biological and hydrological processes. There is limited field data however to support the different development theories and to validate proposed feedback mechanisms. Understanding how peatlands are controlled by internal and external forces is also particularly important when considering possible ecosystem shifts due to climate change.

Here we compare data from a pristine peatland and a drained peatland site in the HBL to understand peatland structure and function in current climate conditions and a future climate scenario (drier conditions). We measured carbon dioxide and methane fluxes using closed chambers at 51 collar locations (12 collars at the hydrologically impacted site, 39 collars at the pristine peatland site - triplicates at both study sites) representing a total of 13 vegetation communities and different peatland microforms (hummocks, ridges, hollows and pools). Continuous hydrological measurements and vegetation surveys were also completed.

These results suggest that peatland structure and function in the HBL must be explained by a combination of peatland development mechanisms and that these mechanisms are dependent on the variable hydroecological setting of peatland areas. We suggest that the drained peatland site may represent an alternative ecosystem state as indicated by considerably low water levels (2013 annual average water table depths of 129 cm for hummocks and 68 cm for pools), declining cover of healthy peatland vegetation (particularly Sphagnum moss) and lower CH₄ fluxes.