Atmospheric Nitrogen Deposition On Reclaimed Soils In the Athabasca Oil Sands Region.

Atmospheric nitrogen (N) deposition is of global concern and is a potential source of pollution in the Athabasca oil sands region (AOSR). Nitrogen enters the atmosphere during bitumen upgrading and is deposited in terrestrial ecosystems through dry and wet deposition. It has been estimated that N deposition levels in the mine footprint are much higher than in surrounding non-industrialized areas but to date, relatively little data exist on the actual levels of N deposition. Nitrogen deposition can cause N saturation, which results in increased soil N availability, increased plant productivity, and ultimately shifts in plant community composition. The objective of this study is to quantify atmospheric N deposition on reclaimed soils and to trace N through soil and plant pools to determine its impact on land reclamation. Data has been collected since 2008 (n=20) encompassing two stand types, jack pine (Pinus banksiana Lamb.) and aspen (Populus tremuloides Michx.), and three density classes (0-30, 31-65 and 66-100%). Wet deposition and soil N availability were both collected with ionic exchange resins. Results indicate that significant amounts of N were deposited on reclaimed soils. Average wet deposition in aspen was 12.9±7.6 kg N ha^-1 yr^-1, while in jack pine it was 15.6±13.0 kg N ha^-1 yr^-1. Estimated total N deposition in aspen was 20.2±11.9 kg N ha^-1 yr^-1, and was 24.3±20.0 kg N ha^-1 yr^-1 in jack pine. In all cases, there were strong seasonal differences in N deposition and soil N availability among density classes and stand types. Differences in atmospheric nitrogen deposition rates were driven mainly by % canopy cover, and distance to closest stack.  As indicated by preliminary results, ¹⁵N natural abundance in wet deposition was 4.5±8.3 ‰ for δ¹⁵NH₄⁺  and -5.5±5.8 ‰ for δ¹⁵NO₃^- in aspen; and 5.6±6.0 ‰  for δ¹⁵NH₄⁺ and -7.1±4.3 ‰ for δ¹⁵NO₃^- in pine (n=12).