Spatial and temporal impacts of acid disposition in the Oil Sands Region: estimating time-to-effects for soils and freshwaters using dynamic simulation models

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Recent industrial activity in the Oil Sands Region of north-eastern Alberta has led to increased emissions of sulphur and nitrogen oxides with the potential to acidify surrounding acid-sensitive ecosystems (forests and lakes). Acidification of soils can lead to increased leaching of base cations and the mobilisation of potentially toxic elements such as aluminium and other trace metals. In acid-sensitive regions, the gradual acidification of soils will ultimately cause surface waters to acidify as the soils buffering capacity diminishes. However, consideration of time-scale in the acidification process is of vital importance, particularly when industrial activities only have a finite lifespan. Estimating the 'time-to-effects' for acid-sensitive ecosystems is extremely important in the Alberta Oil Sands Region where acid emissions are predicted to remain elevated for several decades. The objective of this research programme is to use dynamic acidification models to identify whether critical chemical limits (indicators of adverse impacts) for soil and freshwaters in the region will be exceeded under various future emission scenarios. The principal task will focus on estimating 'time-to-effects' for ecosystems that receive acid deposition in excess of their critical load; supported by a number of related tasks including a dynamic model comparison study and a detailed evaluation of mineral weathering estimates. Relating the critical chemical limits used in acidification models to biological effects in aquatic ecosystems will also be addressed through field studies. In addition, a detailed regional critical load assessment of acid sensitive soils and freshwaters will be carried out, focusing on uncertainties associated with nitrogen dynamics and critical chemical limits to ensure that dynamic models are applied to the areas most at risk from acid emissions.  Results from this research will be communicated to stakeholders and used to help formulate emission control strategies for the Alberta Oil Sands Region to prevent negative effects on aquatic and terrestrial ecosystems.