INVESTIGATION OF SOIL-WATER PROPERTIES FOR RECLAIMED OIL SANDS, FIRE-DISTURBED, AND UNDISTURBED FORESTED SOILS IN NORTHERN ALBERTA, CANADA

Abstract

Oil Sands mining operations in Northern Alberta, Canada generate large areas that contain marginal soil conditions and must be overlaid with reclamation substrate. In order to expedite revegetation efforts, salvaged peat is often incorporated with mineral subsoil to compose a peat:mineral mix (PMM) to act as a soil cover. However, the soil water characteristics and physical properties of these covers are poorly understood for reclamation. Therefore, the objective of this study was to determine the soil physical properties and soil water characteristics of reclaimed covers compared to naturally disturbed sites (i.e. fire) and undisturbed reference sites. Soil samples were collected in the summer of 2012 and 2013 from three reclaimed PMM soil covers, one recently fire-disturbed natural site and one undisturbed reference site. Of all the nutrients analyzed, soil phosphorous (PO4-) concentrations were significantly lower in the reclaimed soils compared to the disturbed and undisturbed natural sites.

Near-saturated hydraulic conductivity (Kns) for water transmission through the soil were measured, along with soil water retention curves developed for describing moisture storage. Topsoil (0-20 cm) Kns measurements revealed no statistical difference between reclaimed and natural sites and extremely high variation was detected at all sites. Three different models for estimating Kns also revealed only minor differences between methods, although high variation within each site prevented conclusions on whether the mini-disc infiltrometer and associated Kns models was an appropriate tool for measuring hydraulic conductivity in peat-dominated reclaimed soils.

Soil water retention curves were developed by tension table and pressure plate methods on intact soil cores. Five soil hydraulic models – three unimodal and two bimodal - were fit to the retention curves and parameterized. Bimodal models showed a superior fit compared to the unimodal models at all three reclaimed and one undisturbed sites. Bimodal trends are typically associated with natural soils exhibiting a high degree of soil aggregation and associated heterogeneous pore structure. The fire-burnt site showed a unimodal trend possibly as the result of its sandy texture and lack of aggregation. These model fits suggest that a juvenile PMM have similar soil water storage characteristics to certain highly-structured natural soil as provided by its peat additions. Available water holding capacity was determined by both soil core and Land Capability Classification System methods. No differences were detected between techniques and a mesic soil moisture regime was predicted at all sites.

This study found that juvenile PMM soil covers exhibited similar soil-water characteristics to a well-aggregated, undisturbed forested soil after only a few years post-placement. These results establish a comparative baseline for future soil research on reclaimed tailing ponds, as well as provide the necessary soil-water relationships for watershed and/or regional scale hydrological modelling.