Changing Nutrient Cycles Across the Boreal Forest Landscape in the Athabasca Oil Sands.

Changing nutrient cycles across the boreal forest landscape in the Athabasca oil sands

Brad Pinno¹, Evelyne Thiffault² and Christian Bégin³

¹Natural Resources Canada, Canadian Forest Service, Edmonton, Alberta, Canada

²Natural Resources Canada, Canadian Forest Service, Sainte-Foy, Québec, Canada

³Natural Resources Canada, Geological Survey of Canada, Québec, Québec, Canada

The boreal forest of northern Alberta has recently undergone changes in ecosystem nutrient cycles, at least in part due to increased atmospheric deposition from the industrial developments associated with the Athabasca oil sands. Estimates of atmospheric deposition range from greater than 6 kg N and 6 kg S ha^-1 year^-1 (with some estimates of up to 50 kg N) close to the industrial developments to less than 2 kg N and S in unaffected areas. These rates are expected to rise into the future given the increase in mining activity in the area. We examined mineral soil and foliar characteristics from jack pine forests growing on sandy soils across the landscape at different distances (10 – 200 km) from the industrial developments. These dry, sandy site types are characterized by a very tight nutrient cycle but are thought to be the most vulnerable to changing environmental conditions due to their inherently low buffering capacity and low nutrient availability. Across the landscape, mineral soil total nitrogen increased from 0.01% to 0.03% with decreasing distance to developments while the ratio of exchangeable base to acid cations increased from 0.1 to 0.4 with distance. Foliar nitrogen concentrations increased from 1.0% to 1.3% moving towards the developments. Foliar base cation concentrations showed a similar pattern while foliar sulphur was only increased at the sites closest to the developments and foliar phosphorus increased with distance resulting in potential N:P nutrient imbalances at the closest sites. The overall result is a nutrient cycle which is clearly impacted closer to industrial developments relative to the undisturbed forest. In terms of land management, sites reclaimed post-mining are likely to experience nutrient regimes substantially different from previous forests with a larger share of nitrogen and base cations derived from atmospheric deposition rather than from internal nutrient cycling within the ecosystem.