The paleoecology of a peatland complex in continental western Canada

Abstract

The development of the present day vegetation, water chemistry, and landform features of a peatland complex in northeastern Alberta, Canada, was studied through analyses of macrofossils, peat stratigraphy, and inferred profiles. The Mariana Lakes peatland (55°54′N, 112°04′W) contains two geographical areas and four landform features (open lake basin, closed lake basin, water tracks, and forested Sphagnum islands). The surface vegetation was classified using TWINSPAN into four vegetation groups: (i) shrubby, open forest of Salix pedicellaris and Carex paupercula, (ii) closed Picea mariana forest, (iii) Sphagnum lawns of Sphagnum fallax, and (iv) Sphagnum carpets of Sphagnum subsecundum and Menyanthes trifoliata. Within the peatland complex, surface water chemistry ranges from a pH of 3.6 to 6.3, reduced conductivity of 0 to 232 μS, calcium content of 1.1–15.6 mg/L, and magnesium content of 0.6–2.8 mg/L. Peat macrofossils analyzed quantitatively were arranged (by TWINSPAN) into six macrofossil assemblages and were correlated to peat calcium content. Inferred pH profiles derived from linear regression transformations, and inferred-moisture profiles derived from a weighted moisture index, describe natural acidification and water levels. The mean initial inferred pH was at 5.6 ± 0.2, and mean initial inferred moisture indexed at 3.1 ± 0.2. Mean present day inferred pH is 4.9 ± 0.7, and mean moisture is 2.8 ± 0.6. Organic deposition at Mariana Lakes began about 8200 years BP in the closed lake basin. Filling-in of the lake basin produced a floating mat that upon enclosure developed into a poor fen. Paludification of the upper fen began about 6000 years BP, subsequent to terrestrialization in the lake basin, and progressed in a downslope direction. By 2960 years ago the entire drainage path was paludified.