Rates, pathways and drivers for peatland development in the Hudson Bay Lowlands, northern Ontario, Canada

1 The Hudson Bay Lowlands have been rising isostatically for the past 7000 years, creating a regional chronosequence as new land emerges from the sea. Rates of uplift are most rapid in the eastern portion of the lowlands near the lower Albany River study area. 2 The stratigraphy of three raised bogs was investigated to determine rates and pathways of peatland development in the Albany River region. The bogs are distributed evenly along the regional chronosequence from the oldest site at Oldman (5980 ± 100 BP) to progressively younger sites at Albany River (4810 ± 70) and Belec Lake (3960 ± 60). 3 Each bog had the same stratigraphic sequence, beginning with a basal tidal marsh assemblage that was rapidly replaced by a Larix-dominated swamp forest, followed by a Picea-forested bog, and ultimately a non-forested bog. The bog-fen boundary is marked by the disappearance of fen indicators, dominance of bog-forming Sphagna, and a sharp decline in nitrogen. Each of these successional stages was associated with different rates of vertical growth. 4 The rate of successional change was more rapid at the younger sites, and their vertical growth curve was more curvilinear. The formation of a raised bog, for example, was 1.3 times more rapid at Albany River and 5.5 times more rapid at Belec Lake than at Oldman. Belec Lake reached its ultimate successional stage first, although it was the last site to emerge from the sea. 5 The differential rate of isostatic uplift across this region rather than climate was the principal environmental driver for peatland development. The faster rate of uplift on the lower reaches of the drainage basin continues to reduce the regional slope, impede drainage and shift river channels, continually altering the local hydrogeological setting. 6 Groundwater flow simulations based on the Dupuit equation show that the growth of these raised bogs was probably constrained by their local hydrogeological setting. Bog formation was first induced by the creation of interfluvial divides between headwardly eroding streams or shifting river channels, and further bog growth was ultimately constrained by the width of the interfluve and the depth of river incision. The Belec Lake bog was the first to approach its limiting height because its narrow interfluve could only support a low water-table mound. 7 Although peatland succession largely followed the same conservative pathway at each site, both the pace and direction of these pathways were set by geological processes, which are probably the decisive drivers for the evolution of this large peat basin.