The Hydrology of a “Spontaneously” Re-vegetated Vacuum-harvested Peatland, Eastern Manitoba

English Abstract:

Peatlands cover over 38% of Manitoba’s land area and represent an important component of the natural landscape. Nearly 13% of Canada’s horticultural peat is produced in Manitoba in the southeastern part of the province. Vacuum harvesting requires the removal of all surficial vegetation and ditches to drain the peatland, lowering the water table. A consequence is that vacuumed harvested sites do not re-vegetate themselves naturally; active restoration efforts in eastern Quebec have been largely successful, though with considerable trial and error to get the ecohydrological processes correct.

The Moss Spur peatland was a large (~3 km diameter) domed bog, harvested from the 1940s and was abandoned in the early 1990s. With little intervention, the natural re-vegetation of the site has been remarkable, with over 90% wetland vegetation coverage and Sphagnum hummocks in a few locations, something that has not occurred naturally in Quebec. Preliminarily results suggest that the success of the re-vegetation is due to groundwater discharge under the site, which contradicts the ombrogenous requirement of bog hydrology. In areas with regeneration indicative of bogs (e.g., Sphagnum), hydraulic gradients of groundwater discharge averaged 0.02; in areas with more fen vegetation hydraulic gradients averaged 0.002; and in areas with no re-vegetation, hydraulic gradients averaged -0.1 (groundwater recharge). It is speculated that these groundwater flow reversals are occurring due to the lowered hydraulic head in the now abandoned former bog. This has been observed in other Western Boreal Plain peatlands in times of extreme drought, and thus peat harvesting may act as a surrogate extreme drought which causes groundwater flow reversals in large peatlands. Supporting this as a mechanism that aids restoration is that Moss Spur’s hydrogeomorphic setting is quite different than Quebec sites, as eastern boreal shield peatlands are more typically situated on a thin veneer of sediment over bedrock, thus precluding regional groundwater exchanges.