https://hdl.handle.net/10388/18094

Sanchez Garces, M. E. (2026) Mountain Peatlands: Natural Laboratories for Understanding Climate Change Effects on Carbon Fluxes, Department of Geography and Planning, University of Saskatchewan https://hdl.handle.net/10388/18094

Mountain peatland ecosystems are relatively rare in the Canadian Rockies but ecologically and hydrologically significant. Their provision of ecohydrological benefits, which include flood prevention, erosion control, water regulation and support of specialized biodiversity that is adapted to high elevation and wet environments, position them as climate refugia which offer landscape heterogeneity to mountain environments. Mountain peatlands contribute to carbon sequestration, and their stability is strongly associated to high water table levels and cool environments, a characteristic that makes them particularly vulnerable to rising air temperatures and declining snowpack due to climate change. Despite their importance at landscape and catchment levels and their vulnerability to climate variations, mountain peatlands remain understudied. Knowledge gaps exist from their mapping and carbon accounting to ecological and functional processes such as thermal regimes, biogeochemistry, and resilience to climate variations. It becomes crucial to address these gaps as our global context is marked by rising greenhouse gas emissions, incidence of extreme weather events and water insecurity. This dissertation’s primary question is to understand how climate-driven temperature dynamics, from seasonal variability to extreme events, regulate carbon exchange in mountain peatlands, and what insights these responses reveal about their vulnerability to climate change. To achieve this, the influence of fluctuations in peat temperature on carbon flux dynamics were investigated by exploring the vulnerability of mountain peatlands at opposite ends of their Canadian Rockies elevational range to short-term and extreme climate changes. This Ph.D. project produced carbon emissions through field campaigns, data processing and conference travel, which was quantified and observed critically as part of the carbon cycle aligning research goals with the sustainability of the research process itself. It was found that peat temperature dynamics are shaped by various parameters including local microclimate, snowpack, surrounding landscape, and vegetation cover which vary largely across elevational gradients and can shape the vulnerability of mountain peatlands to climate change. During an unprecedented heatwave, the above-treeline site showed greater sensitivity in terms of proportional thermal diffusivity and radiation responsiveness than the lower-elevation montane site, despite having deeper snowpack and higher water table, two factors that are expected to provide greater thermal buffering. The timing of the heatwave (marked by snow presence and absence of vegetation at the high site) combined with the landscape surrounding both sites (rocky outcrops at the high site vs forested land in the low site) explained the differences in sensitivity. An experimental study revealed that emissions of both CO2 and CH4 are dominated not only by environmental conditions but also by intrinsic peat characteristics such as vegetation composition, peat bulk density and substrate lability. In this reciprocal peat transplant, peat from high elevation (cool and wet) was forced to drier and warmer temperatures and vice versa. This experiment showed that the peat that was forced to drier and warmer conditions showed no change in net ecosystem exchange but increased CH4 emissions. The increased CH4 emissions showed a rapid methanogenic response to warming and a dependence on peat structural characteristics that helped retain water to allow for anoxic conditions despite lowered water tables. Conversely, peat that was forced to wetter and cooler conditions showed increased uptake and no decrease in CH4 emissions despite cooling, indicating short-term resistance to changing conditions. Additionally, the predicted growing season cumulative values of CO2 and CH4 emissions underscored the impact of a lengthened growing season in shaping future carbon dynamics. In addition to understanding thermal responses to extreme events, this study observed the CO2 emission response of a montane peatland to regularly occurring transient events like chinook winds. Chinook winds, which cause dry and warm episodes that can increase winter temperatures by 20 °C, were shown to increase CO2 emissions during and after these events. The mechanisms for CO2 emissions varied seasonally from physical degassing during snowmelt to enhanced microbial activity in thawed peat layers. Finally, it was found that the carbon emissions from the entire research process of this dissertation (e.g. energy use, travel to sites and conferences, etc.) were 9.1 t CO2eq; this represents ~8.5% of the average Canadian’s annual emissions. These emissions were equivalent to ~30 days of carbon accumulation from a 0.74 km2 montane peatland, providing context to the emissions of the science-making process. It highlighted hotspots of emissions mainly through land and air travel to research sites and conferences. This exercise offered a replicable model for peatland researchers to develop plans that include environmentally conscious strategies that will allow C reduction in their research processes. Overall, the results of this research reveal that mountain peatlands do not respond to climate change in a simple manner and their responses challenge common assumptions about their thermal buffering capacity and carbon cycling stability, particularly under both transient climatic fluctuations and extreme events. This research contributes to literature by providing new insights into the vulnerability and resilience of mountain peatlands to climate change, overturning the assumption that all mountain peatlands might be equally buffered from extreme temperature events like heatwaves. In fact, the peat sensitivity to warming might depend on the timing of the heatwave, and the surrounding landscape of the peatland. Additionally, this study provides rare and high-resolution thermal baseline data for two sites including a remote high elevation peatland in the Canadian Rockies, filling a geographic gap in peatland science. This dissertation also provides key information on the resilience and resistance mechanisms of mountain peatlands to climate change by showing that, in some cases, responses to specific short-term climate changes are shaped by intrinsic peat characteristics over environmental conditions. The results present quantitative evidence that transient warming events like chinook winds can cause CO2 releases from mountain peatlands highlighting an emission pathway during the non-growing season that has not, to our knowledge, been reported in literature. Finally, by extending beyond peatland science and into the ethics of field-based research, this dissertation contributes by including a reflexive consideration of its own C impact and innovates by providing guiding questions aimed to lower C emissions in research projects.

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