Mire Development, Pool Formation and Landscape Processes on Patterned Fens in Dalarna, Central Sweden

Abstract

(1) Mire development and pool formation were examined stratigraphically on patterned fens in Dalarna, central Sweden. The palaeoecological study was complemented by mapping of the surface and substratum topography, description of modern landforms, analysis of the water chemistry and diatom flora, and phytosociological study of the vegetation. (2) Forty-three releves are organized into seven noda, which separate along a moisture gradient. The major landforms include mire-margin hummocks, pine islands, ridges, flarks, mud bottoms, and open-water pools. (3) Peat cores along a 900-m transect from the base to the top of one fen slope show that the mire developed through upslope paludification. Basal radiocarbon dates decrease sequentially from 9040 + 80 years B.P. at the base of the slope to 1640 + 50 years B.P. at a point 100 m from the top of the fen. Buried forest soils and stumps of Pinus sylvestris at the base of the peat indicate that forest communities were replaced by sedge fen. (4) Pools and ridges develop through gradual differentiation of the mire surface some thousands of years following mire initiation. The basal 2 m of peat beneath a flark and adjoining ridge are identical until this differentiation began. (5) Deep pools are underlain by more than 1 m of algal gyttja, which grades downward into peat detritus and then peat. Radiocarbon-dated profiles indicate that pools initially deepen through peat degradation before the deposition of algal sediment starts. (6) The surface patterning is dynamic. The total pool area on the mire increases with time and the size, shape and orientation of individual pools may change. Pools expand through gradual submergence of marginal areas as well as through coalescence. Pool drainage may occur through coalescence of pools at different elevations, through ridge erosion, and through subsurface piping. (7) The overall development of the mires involves progressive diversification on two scales. The regional landscape increases in complexity and landform diversity as mires form and replace forest communities. On the mires, local diversification involves the development and alteration of surface features through time.