The influence of peat volume change and vegetation on the hydrology of a kettle-hole wetland in Southern Ontario, Canada

Abstract

Links between local hydrology and vegetation type exist in wetlands, yet it is unclear what role peat volume change plays in these interactions. We measured peat volume change and hydraulic conductivity (Kfield) at three contrasting sites located on the quaking vegetation mat of a kettle-hole peatland in southern Ontario. The three sites had visibly different plant communities and were named, according to their dominant vegetation, Sedge (Carex spp.), Typha (Typha angustifolia) and Carr (Cornus stolonifera). Peat was also collected for laboratory studies of peat volume change, vertical (Kv) and horizontal (Kh) hydraulic conductivity and the effect of compression on hydraulic conductivity (Kc).In the field, the water table rose throughout the study period, resulting in swelling of the peat. Peat volume change above the -100 cm layer was 11.2%, 6.0% and 3.8% at the Sedge, Typha, and Carr sites respectively. In laboratory samples, a falling water table caused compression of the peat below the structured surface mat, and relative peat volume change between the sites followed the same pattern as in the field. Kfield, Kv and Kh generally decreased with depth from ca. 10-2 to 10-6 cm s-1. In the surface layers (0 to -50cm) K trended Carr>Typha>Sedge, whereas the reverse trend was observed in deeper peat. Artificial compression affected K only in the uppermost layers (0 to -15cm). The decline in Kc with compression also trended Sedge>Typha>Carr. Differences in peat volume change and K are probably related to differences in vegetation and soil structure, and may be important for maintaining suitable growing conditions within each community.