The influences of vegetation and peat properties on the hydrodynamic variability of a constructed fen, Fort McMurray, Alberta

Abstract

In Alberta’s Western Boreal Plain, oil sands mining strips overburden materials including vegetation and soils, leaving unnatural, undulating landforms where wetlands previously covered >50% of the landscape. Due to their complexity, the re-establishment of peatland ecosystems had not been tested prior to two fen reclamation projects on oil sands leases north of Fort McMurray. One of which, the Nikanotee Fen, was constructed using peat stripped as part of the mining process and placed in an engineered watershed designed to provide the requisite groundwater supply to support fen hydrological functions and vegetation. The unknown effects of disturbed, placed peat and vegetation treatments on the constructed fen’s soil water dynamics were studied from 2013 to 2015, the first three growing seasons post-construction. Water table, soil moisture (θ), pore water pressure (ψ), evapotranspiration (ET) and surface elevation were monitored in thirty-one study plots designed to test revegetation strategies, including control (bare peat), moss, seedling, mulched moss and mulched seedling treatments. Fifty-four peat samples were tested for a suite of hydrophysical parameters, including saturated and unsaturated hydraulic conductivity and soil-water retention. Plot water table positions fluctuated 36 cm below ground surface (bgs) despite a relatively small range in surface elevation between plots (~24 cm), where plots located at higher elevations had consistently lower and more variable water tables. Although average plot water tables all ranged within 5–7 cm bgs, θ, ψ and ET differed significantly between certain plot types (p < 0.05). The observed hydrology is partially affected by the heterogeneous peat properties across the fen, created by the salvage and placement methods of the peat, which significantly differed with location (p < 0.05). The variability in the hydrophysical properties and surface elevations, thus water table position, appear to mask the effects of vegetation and treatment type on plot hydrology, at least at this early stage of development. While significant increases in plot ψ and θ were observed from 2013 to 2015, further studies are required to track the effects of greater vegetation establishment and peat formation and elucidate the effects of different vegetation treatments.