The vast peatlands of the Hudson Bay Lowlands (HBL) are globally important carbon stores and are considered to be significantly at risk from climate change. Changes in peatland biogeochemical processes in this region could have major consequences for global climate regulation and yet our understanding of the mechanisms controlling these processes is limited. Peatlands are often described as self-regulating systems, maintaining long-term stability due to feedbacks between biological and hydrological processes. It is not certain if there are limits to this self-regulating behaviour, and particularly whether shifts in ecosystem state are likely (due to loss of resilience) under future climate change scenarios.
Here we compare a pristine peatland and a drained peatland site (water table ~ 1.5m below hummock surface) in the HBL to understand ecosystem structure and function in current climate conditions and a future climate scenario (drier conditions). Plots were selected to represent the dominant vegetation and microform (e.g. hummocks, pools) types at each site. Over two summer field campaigns (2013, 2014), we measured carbon dioxide and methane fluxes, nutrient availability, vegetation composition, water table and soil moisture at each plot. In summer 2015 we also took shallow peat cores (~40cm) for chemical analyses.
Our results suggest that although consistently low summer water levels are changing peatland structure and function, these changes may not be large enough to result in a shift in ecosystem state due to feedbacks among vegetation and hydrology at the microform scale. We found statistically significant differences in gross primary productivity (GPP), maximum photosynthesis (PSNmax), and ecosystem respiration (ER) but this was limited to certain vegetation-microform types. For example, GPP and PSNmax were significantly lower (p<0.0001) for sphagnum-spruce hummocks at the drained peatland site compared to the pristine site, and ER was significantly higher (p<0.0001) for sphagnum pools at the drained site compared to the pristine site. However, in some cases the opposite trend was observed (e.g. higher ER for sphagnum-spruce hummocks at the pristine site). Furthermore, analysis of total soluble phenolics and enzyme activity (phenol oxidases), both proposed to be important factors for carbon loss from peatland ecosystems in future drier conditions (e.g. Fenner and Freeman, 2011), revealed no significant difference between the two sites.
Our results highlight the importance of vegetation-hydrology feedbacks controlling carbon dynamics within peatland ecosystems, and lead us to question the proposed mechanisms for significant carbon loss due to climate change in one of the world’s largest peatlands.