Modeling Soil Acidification in the Athabasca Oil Sands Region, Alberta, Canada

Abstract

Industrial activities have proliferated across Canada's Athabasca Oil Sands Region in recent years, stimulating concerns over the impact of atmospheric sulfur dioxide (SO2) emissions on acid-sensitive terrain. Upland jack pine forests have been identified as possibly the most sensitive ecosystem in the region but despite high emissions of SO2, sulfur (S) deposition is relatively low across much of the region. The response of forest soils at 11 locations that exhibit low estimated weathering rates (< 10 mmol(c) x m(-2) x yr(-1)) was simulated for the period 1900-2100 using a dynamic hydrogeochemical model assuming no change or doubling of S deposition. The model predicted minimal impact on soil base saturation (BS), but a decline in soil solution base cation (BC) to aluminum (Al) ratio (BC:Al). The regional effects-based emissions management framework uses modeled changes in these two parameters relative to site-specific chemical thresholds to trigger actions to reduce S emissions. Modeled changes in BS are insufficient to invoke a response. Under base case conditions, modeled BC:Al reaches the chemical threshold at two and three sites within 15 and 30 years, respectively. Under conditions of double S deposition, seven sites are simulated to reach the threshold within 30 years. Nonetheless, the chemical thresholds are stringent relative to critical chemical criteria used elsewhere and the impacts of acidic deposition in the region are anticipated to be limited.