Impact of Drainage Ditch Construction and Subsequent Use on a Treed Bog Adjacent to a Peat Harvesting Operation, Southwestern Manitoba, Canada

Abstract

Manitoba has the most peatland by provincial area of any province in Canada, and contributes ~13% of Canada’s horticultural peatland production. Peat harvesting requires the lowering of the water table; this water is usually channeled to a fluvial system (e.g., a river) but in some cased must be actively pumped. In the case of the South Julius bog in Manitoba, the pumped discharge was through a treed bog. The trees in the bog on one side of the drainage ditch were dead, but on the other side were alive. This study investigated possible hydrological causes by instrumenting three transects of wells that ran perpendicular to the drainage ditch and extended 20 and 50 m into the bog on the dead and live side, respectively. Average water tables on the live side were 15 cm lower than the dead side. The dead side water levels were similar to a natural fen located adjacent to the treed bog. Construction of the drainage ditch yielded a >20 cm high berm that ran alongside the live side, functionally isolating the live side from the surplus water in the drainage ditch, maintaining the lower and healthier water table treed bog vegetation requires. We recommend that future drainage ditches be constructed in such a way that berms on both sides are made, functionally creating a canal to the fen, where the excess water can be more easily dealt with by the fen vegetation adapted to wetter average conditions.