Modelling environmental change impacts on peat accumulation in northern peatlands

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Peatlands are ecosystems that accumulate a significant amount of organic matter in their soils (peat) because they are constantly water-saturated. Decomposition rates are greatly reduced in waterlogged conditions, so litter accumulates faster than it decomposes. Peat can accumulate for thousands of years and reach several meters in height. Peatlands cover only about 3% of the global land surface, but in Canada they cover significant portions of the landscape (~12 %), especially in the northern lowlands and in zones where the soil is permanently frozen (permafrost). **Peatlands are responsible for many ecosystem services, including providing habitats to wildlife and regulating water quality. They also have an important role in the climate system, as peat is composed of approximately 50% of carbon (dry weight). They therefore store a significant quantity of carbon globally, equivalent to the amount of carbon currently found in the atmosphere. As peatlands are located in areas undergoing rapid changes, including widespread climate warming and infrastructure development, the ecosystem services they provide might be significantly modified in the next few decades. These changes in ecosystem services may impact the environment and livelihood of the Canadians living in the North and further affect the stability of the global climatic system. **My research is focused on the impact that climate change will have on the climate regulating function of northern peatlands. My overall goal is to answer the following two questions: how is climate affecting the vegetation composition, internal processes and carbon accumulation of northern peatlands; and how will future changes in climate, permafrost, regional hydrology and nutrient availability affect their carbon balance? **I address these questions using two main research tools. I use the unique property that peatlands have to record and conserve thousands of years of ecological and climatic changes to reconstruct changes in peat accumulation. I relate peat accumulation variations to environmental changes such as permafrost thaw, or variations in nutrient availability. This work will be done in three different sites located in contrasting regions (Northwest Territories, Eastern Ontario in Canada; Northern Sweden). I also use computer simulations to synthesize what I learned from the reconstructions and to project what might happen to peat accumulation over the next decades and centuries. For this research, I will expand an already existing simple peat accumulation simulation model to include permafrost and nutrient-related processes.**I expect the results of my research to significantly improve the understanding of the factors governing long-term accumulation of peat, and therefore, to better understand the future role of peatlands in the climate system. This will in turn allow a better forecasting of future environmental changes in the North.