| Summary: | Prior to oil sands extraction, mineral soil from local boreal forest is salvaged and stored, together with additional peat obtained from local peatlands, for future reclamation use. The ability of reclaimed soils to stabilize carbon is an important indicator of soil functioning and successful reclamation. The objective of this research was to compare total soil carbon and the distribution of carbon in chemically and physically protected pools between three reclaimed vegetation treatments, and naturally fire-disturbed boreal forest sites. Twenty sites that were reclaimed or disturbed 20 – 40 years ago were chosen, and the top 10 cm of mineral soil was sampled. Density and size fractionation was used to separate soil organic carbon (SOC) into unprotected light fraction C, physically protected C, and chemically protected C. Aggregate size distribution, microbial biomass C, root biomass, and exchangeable cation concentrations were also measured. Reclaimed sites had three times more total SOC than natural sites and similar or greater SOC in physically and chemically protected pools. However, reclaimed sites were also estimated to have reached carbon saturation in chemically protected C pools, and half of the total SOC on average was unprotected, compared to 9 % unprotected C at natural sites. Accumulation of SOC in unprotected pools and C saturation in chemically protected pools at reclaimed sites suggest that further incorporation of SOC into chemically protected pools may be limited, possibly by soil texture (< 3% clay). Almost one third of reclaimed soil C was old, biochemically resistant C, compared to only 10 % at natural sites, and is probably peat that is persisting in reclaimed soils. Within reclaimed vegetation types, grassland sites had the greatest physically and chemically protected C, while deciduous sites had the greatest unprotected C, despite both vegetation types having similar total SOC content. Coniferous sites had the lowest total SOC content, but tended to have more physically and chemically protected C than deciduous sites, and may ultimately surpass grasslands if C accumulation rates continue to increase at these sites. === Forestry, Faculty of === Graduate
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