Bog Development and Landform Dynamics in Central Sweden and South-Eastern Labrador, Canada

Abstract

(1) Stratigraphic analysis, detailed surveying, and radiocarbon dating were used to document the development of Hammarmossen, a raised mire in central Sweden, and to contrast the structure, development, and dynamics of landforms there with those on Gilbert bog in south-eastern Labrador, Canada. (2) A series of basal radiocarbon dates from transects of peat cores across Hammarmossen shows that peat started to accumulate approximately 5500 years B.P. and spread radially across a glacial outwash plain throughout the late Holocene. The implications of this pattern of development for models of bog hydrology and growth and for interpretations of the process of paludification, e.g. by Malmstrom, are discussed. (3) On both Swedish and Labrador mires the distribution, shape and development of open-water pools are closely controlled by the topography of the peat surface. The largest and deepest pools occur on the flattest surfaces, where water outflow is slow. Pool development results from hydrological controls on relative rates of peat accumulation in hummocks and hollows. (4) Pools were initiated throughout the last 4000 years of bog development. On Hammarmossen a deep layer of algal gyttja partly fills the pools, whereas on Labrador bogs algal sediment is absent, and the pool floors are degrading peat and peat detritus. This contrast in stratigraphy of bog pools in Sweden and Labrador follows a similar pattern for pools on minerotrophic mires (fens) in the two areas. (5) Once formed, pools undergo similar dynamics in the two regions. Pool depth increases as peat accumulation on hummocks exceeds sedimentation in pools. Lateral expansion of pools occurs through marginal flooding, controlled by differential rates of accumulation and by the breakdown of peat ridges separating adjacent pools. Pools may be drained through surface erosion or through subsurface piping. Erosion of the bog from the mire margin towards the centre may gradually fragment the peat mass. Under very wet conditions raised bogs are inherently unstable systems on which water-dominated landforms increase through time until stream erosion gradually dissects the mire.