Modelling boreal lake catchment response to anthropogenic acid deposition

A dynamic hydrogeochemical model of water acidification (MAGIC: Model of Acidification of Groundwater in Catchments) was applied to two catchments with contrasting hydrological influences in the Athabasca Oil Sands Region of Alberta to predict catchment response to elevated levels of acidic deposition. Key processes that determine catchment response to atmospheric deposition, including groundwater base cation inputs and retention of sulphur (S) in peatland complexes were parameterized in the model. Although deposition of S and nitrogen (N) in the region has increased over the last 40 years, levels are low at the study sites relative to impacted areas of eastern North America. Model forecasts for the period 2005–2100 were run under constant 2005 deposition levels (base case) and at acid deposition double this level. Simulated past and future soil base saturation was constant over the course of the 200 year (1900–2100) modelled period. At the lake with high charge balance acid neutralizing capacity (ANCCB), where large base cation sources dominate lake chemistry, little change in surface water chemistry was predicted under either forecast scenario. Under the double acid forecast scenario at the low ANCCB lake, simulated lake ANCCB decreased in response to elevated S deposition, but the magnitude of decrease was comparable to the range in observational data. The simulations suggest limited risk of acidification, primarily due to S retention in the catchments, but the potential for drought-induced episodic depression of ANCCB may be important on this landscape.