Estimating the sensitivity of forest soils to acid deposition in the Athabasca Oil Sands Region, Alberta

The Athabasca Oil Sandy Region of northern Alberta is home to the largest source S emission hi Canada, and some of the surrounding upland forests are located on acid-sensitive soils The relative sensitivity of these ecosystems to acidic deposition is largely dependent upon the numeral weathering rate. Weathering rates were evaluated across a range of soils (n = 43) typical of the region using a soil texture approximation (STA) and the PROFILE model. The STA was recalibrated Jar use in the region. and the weathering rates calculated with this method were used to calculate steady-state critical loads of acidity at 333 sites using the Simple Mass Balance (SMB) Model and a critical chemical criterion for molar base cation (Ca2+, Mg2+, K+) to aluminium ratio of 10. Soils are dominated by quart. with quantities of weatherable minerals, and consequently weathering rates are among the lowest in Canada (Median = 11.5 meq m(-2) y(-1)), resulting in very low critical loads. Atmospheric. acid (S and N) deposition varies considerably across the region. hut in general is much lower than impacted areas of central Canada. Under conditions of complete N retention. 34% oldie sites receive acid deposition in excess of their critical load; if all N deposition is leached, 62% of the sites are currently exceeded. Acid-sensitive soils in the region are at risk of acidifying due to pressures from industrialization associated with extraction of fossil fuels.