Soil acidification has been of concern in the oil sands region in Alberta due to increased acid deposition. Using the canopy budget model, and accounting for H⁺ canopy leaching by organic acids, we determined sources and sinks of H⁺ in throughfall in jack pine (Pinus banksiana) and trembling aspen (Populus tremuloides) stands in two watersheds from 2006 to 2009. In pine stands, H⁺ deposition was greater in throughfall than in bulk precipitation while the opposite was true in aspen stands. The annual H⁺ interception deposition was 148.8–193.8 and 49.7–70.0molcha⁻¹ in pine and aspen stands, respectively; while the annual H⁺ canopy leaching was 127.1–128.7 and 0.0–6.0molcha⁻¹, respectively. The greater H⁺ supply in pine stands was caused by greater interception deposition of SO₄ ²⁻ and organic acids released from the pine canopy. Such findings have significant implications for establishing critical loads for various ecosystems in the oil sands region.

Atmospheric deposition in the Athabasca Oil Sands Region decreased exponentially with distance from the industrial center. Throughfall deposition (kg ha−1 yr−1) of NH4–N (.8–14.7) was double that of NO3–N (.3–6.7), while SO4–S ranged from 2.5 to 23.7. Gaseous pollutants (NO2, HNO3, NH3, SO2) are important drivers of atmospheric deposition but weak correlations between gaseous pollutants and deposition suggest that particulate deposition is also important. The deposition (eq ha−1) of base cations (Ca + Mg + Na) across the sampling network was highly similar to N + S deposition, suggesting that acidic deposition is neutralized by base cation deposition and that eutrophication impacts from excess N may be of greater concern than acidification. Emissions from a large forest fire in summer 2011 were most prominently reflected in increased concentrations of HNO3 and throughfall deposition of SO4–S at some sites. Deposition of NO3–N also increased as did NH4–N deposition to a lesser degree.

Elevated emissions of nitrogen oxides (NOx) in the Athabasca Oil Sands Region, Alberta and higher foliar nitrogen (N) concentrations in jack pine (Pinus banksiana) needles close to major emission sources has led to concerns that the surrounding boreal forest may become N-saturated. Despite these concerns, N deposition and impacts on upland forests in the region is poorly quantified. The objective of this study was to characterize N cycling in five plots representing the two dominant upland forest types (jack pine and trembling aspen, Populus tremuloides) close (<30 km) to the largest mining operations in the region, during a 2-year period. Despite the high level of NOx emissions, bulk throughfall and deposition measured at both study sites were surprisingly very low (<2 kg N ha−1 year−1). Internal N cycling was much greater in aspen stands; annual N input in litterfall was ten times greater, and net N mineralization rates were two to five times greater than in jack pine stands. Nitrogen use efficiency (NUE) was much greater in jack pine when calculated based on N litterfall indices, but not when N pools in biomass were considered. Despite differences in internal cycling among forest types, nitrate leaching from mineral soil in both forest types was negligible (<0.1 kg N ha−1 year−1) and patterns of 15N in roots, foliage, and mineral soil were typical of N-limited ecosystems, and both sites show no evidence of N saturation.

In Canada, low-grade ore mines generate large amounts of mineral waste, such as mine tailings. To control erosion of the fine-grained tailings particles as quickly as possible, it is common practice for the mining industry to revegetate the mine tailings with agronomic herbaceous plants. However, it is unclear whether this practice is consequential to the natural establishment of boreal species. The first objective of this study was to evaluate which families of agronomic herbaceous plants (legumes or grasses) result in the most favorable physical and chemical soil properties for the establishment of boreal species. The second objective was to determine the effect of the agronomic herbaceous plants on the growth and foliar nutrient concentration on three indigenous boreal forest seedlings; jack pine (Pinus banksiana Lambert), tamarack (Larix laricina Du Roi), paper birch (Betula papyrifera Marshall), and a willow cultivar (Salix miyabeana Seemen). In 2013, a 1-ha in situ experimental surface of mine tailings was set up on the gold mine site in Malartic, Abitibi-Témiscamingue, Quebec. The experimental site was subdivided into three blocks, each further divided in 5 plots. Each plot was randomly seeded as follows: 100% grass, 100% legumes, a mixture of both, topsoil, and a control (tailings only, no seeding). In the 2015 spring season, thirty seedlings of the three boreal tree species and cuttings of the willow cultivars were planted in each treatment plot. Seedling height and root biomass were measured at the end of the 2016 growing season. Soil sample analyses indicated significant differences for bulk density, wilting point, and organic matter content between the topsoil and the different agronomic herbaceous and control treatments; however, no significant differences were found between the different herbaceous treatments and the control for soil pH, bulk density, wilting point, macroporosity, and organic matter content. The mortality rate of jack pine, tamarack, and paper birch seedlings was higher in the control plots compared to all other treatments. Root biomass and height of the willow cultivar were significantly higher in the legumes compared with topsoil treatment. Among the four pioneer tree seedlings studied, this research indicates that the combination of the willow cultivar with the legumes treatment produces the best seedling growth and survival in the highly abiotic and stressful environments inherent to mine tailings.