A dynamic modelling assessment of the chemical response of soils and surface waters to changes in sulphur and nitrogen deposition in the Athabasca Oil Sands Region

The objective of this thesis was to assess historic and future change in catchment soil and surface water chemistry in response to changing atmospheric deposition of acid (S and N) in the Athabasca Oil Sands Region (AOSR), Alberta, through the development of new approaches for the application of a dynamic hydrogeochemical model (MAGIC: Model of Acidification of Groundwater in Catchments). Despite high emissions of acid precursors, S and N deposition is low relative to other industrial areas. Peatlands are prevalent in the study area and were found to retain large amounts of S, N and Cl-, while cation exchange with organic soils is also an important regulator of groundwater and precipitation inputs. Upland mineral soils have very low capacity to adsorb SO42-. In a MAGIC application at two intensively studied boreal lake catchments, model simulations indicated that there is little risk of surface water acidification (decrease in acid neutralizing capacity) owing to terrestrial retention of S and N, and large base cation inputs to the lakes. This work highlighted the need for independent modelling of the hydrochemistry of forest soils and a regional plot-scale application indicated that base saturation will exhibit only minor changes under projected future levels of elevated acid deposition. A bilateral regional application of MAGIC was used to model the chemical response of soils and lakes to acid deposition across a wide number (n = 50) of catchments considered acid-sensitive. Model simulations indicated that even with a doubling of S and N emissions, acidification impacts in the AOSR will be limited.