Patterned fens of western Labrador and adjacent Quebec: phytosociology, water chemistry, landform features, and dynamics of surface patterns

Abstract

The landforms, vegetation, water chemistry, and stratigraphy of four patterned fens (aapamires) in western Labrador and adjacent Quebec are described in a study investigating the origin and characteristics of surface patterns on northern peatlands. Phytosociological analysis by the relevé approach, in conjunction with analysis by TWINSPAN, is used to describe 11 floristic noda. The vegetational patterns are largely controlled by depth to the water table. Mire landforms discussed in detail include ice-push ridges, flarks and pools, peat ridges, and mire-margin hummocks. Water chemistry is typical of minerotrophic conditions, with pH ranging from 4.4 to 6.7 and calcium concentrations from 20 to 430 μiequiv. L−1. The water chemistry, vegetation, and landforms on the mires are compared with other studies from Labrador and circumboreal regions. Stratigraphic results and field observations support the theory that surface patterns on the mire develop slowly through the interplay of biological and hydrological processes, specifically differential rate of peat accumulation controlled by vegetation type and depth to water table. Pool formation apparently involves four steps: (i) gradual differentiation of shallow flarks on previously undifferentiated mire surface; (ii) expansion and deepening of flarks and development of ridges due to differential peat accumulation; (iii) degradation of flark vegetation into mud bottoms and open-water pools; and (iv) coalescence, continued expansion, and deepening of open-water areas. Hydrological controls over the rate and extent of pool formation are discussed as a probable explanation of the geographical distribution of patterned mires.