Investigation of Bimodal Soil-Water Retention Properties of Reclaimed Oil Sands, Fire-Disturbed and Undisturbed Forested Soils in Northern Alberta, Canada.

Oil Sands mining operations in Northern Alberta, Canada often incorporate salvaged peat material with mineral subsoil to construct a peat:mineral mix (PMM) soil cover. Understanding the soil-water relationships of these novel soils is critical for projecting ecosystem trajectories, as well as hydrologic modelling efforts. It has been suggested that the organic components of PMMs may impart bimodal characteristics to its soil water retention curves. The objective of this study was to examine the soil-water retention characteristics of reclaimed PMM covers compared to naturally-disturbed sites (i.e. forest fire) and undisturbed, well-structured reference sites. Three juvenile reclaimed soils (two from a reclaimed tailings pond and one overburden dump), one juvenile burned soil, and one undisturbed forested soil were selected and 144 cm³ intact cores (n=5) were sampled from 7 cm and 55 cm depths. Soil water retention curves were developed by tension table and pressure plate methods on the intact soil cores. Five soil hydraulic models – three unimodal and two bimodal - were fit to the retention curves and parameterized. At the 7 cm depth, bimodal models showed a superior fit compared to the unimodal models at both the reclaimed and undisturbed forested sites. Bimodal trends are typically associated with dual pore structure in well-aggregated soils, which the PMMs may be imitating through its residual plant structure. The fire-burnt site lacked bimodal trends at this depth possibly as the result of its sandy texture and lack of aggregation, although fire effects cannot be disregarded. All five soils exhibited a typical unimodal trend at the 55 cm depth. These model fits suggest that juvenile PMMs have similar soil-water characteristics to certain highly-structured natural soils.