Drivers of Holocene Carbon Uptake and Release in Peatlands of the Hudson Bay Lowlands, Canada

Northern peatlands are a key component of the terrestrial carbon cycle, acting as both a source and sink of carbon. Therefore, to predict impacts from anthropogenic climate change and create effective land management policies, constraining how environmental factors impact peatland carbon fluxes is critical, especially in peatland-rich regions such as the Hudson Bay Lowlands (HBL), Canada. This thesis aims to understand how local-scale factors impacted Holocene carbon uptake and release in the HBL using paleoecological and geochemical analyses of radiocarbon-dated peat cores. Paleoecological analyses of a site on the southern HBL margin demonstrate that landscape position controls local hydrology and can subsequently limit Holocene carbon accumulation rates (CARs). This record also demonstrates a summer bias in temperature and validates pH reconstructions from lipid biomarker proxies. Paired treed fen and bog sites from the western HBL margin show markedly high carbon masses owing to deep peat accumulation with old initiation ages. Mean testate amoeba trait values reflect hydrology and food web structure and are also influenced by vegetation shifts and peatland type. Further, mixotrophic taxa are not related to higher millennial-scale CARs, suggesting a minor role for their primary production in long-term carbon storage. The above records were synthesized with other hydrological records derived from testate amoebae across the HBL to reconstruct paleo-methane fluxes via a linear regression model developed from modern relationships between methane fluxes and water table depths. Land availability controlled by glacial isostatic adjustment was an important control on Holocene emissions when fluxes were scaled to regional emissions. The combined hydrological reconstructions also suggest that peatlands were drier under warmer Middle Holocene conditions. A charcoal record collected from the western HBL margin supports drier conditions, as warmer Middle Holocene conditions were related to higher fire frequency. Although higher fire frequency did not have a significant impact on millennial-scale CARs, carbon loss from combustion was potentially doubled, which has implications for atmospheric carbon budgets. Overall, this thesis advances our understanding of the complex interplay between climate and local processes in long-term carbon dynamics that is of fundamental importance for conservation priorities and constraining future carbon emissions.

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