Performance of a constructed fen peatland: Reclamation of oil sands landscapes
Abstract
Wetlands cover >60% of the landscape in the Athabasca oils sands development region. These are predominantly fen peatlands, that rely to varying extent on base-rich surface- and/or ground-water derived from adjacent mineral lands. Large areas of peatland are removed by surface stripping to access the bitumen. Reclamation of post-mined landscapes to peatland has not previously been attempted. Groundwater modeling was used to guide design choices on the optimal geometry, placement (layering) and hydraulic properties of locally available materials; these include processed tailings sand, as well peat and forest soils from newly developed lease areas. The constructed system comprises a ~3 ha fen with 2 m of peat and an adjacent upland specifically designed to supply the requisite water to maintain suitable hydrological conditions. The upland is primarily tailings sand covered by a forest soil. The constructed fen/upland system was set within a ~30 ha basin that was reclaimed using standard techniques and materials, and supplements water inputs to the designed system. Both fen and upland were placed at water contents well below equilibrium levels, so there was concern about the wetland function during the years following construction. However, in its first year following construction (2013), a higher than normal snowpack flooded the system, but by surface inflow rather than seepage from the upland. Ground-ice in the fen limited the general infiltration and percolation of meltwater into the peat, although fortuitously a localized recharge pipe developed through thermal erosion and substantially recharged the fen. Water was redistributed beneath the fen through a highly permeable sublayer (petroleum coke) designed for this purpose, and created artesian pressures. Backflow into the upland also resulted, although much of the upland remains well below design water contents. Modification of the upland soils by plowing, and development of local recharge basins, is expected to improve upland function. Water quality issues related to the transport of residual process water in the tailings sand are part of the design. Initially these are less problematic than sediment entering the fen due to the overland flow caused by the large snowmelt and several extreme rainfall events that have occurred. The modifications to the upland, and a suite of sediment-trapping geotextile logs, will reduce the sediment issue. Monitoring continues.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.H11J1271P
- Keywords:
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- 0497 BIOGEOSCIENCES Wetlands;
- 1843 HYDROLOGY Land/atmosphere interactions