Effects of canopy–deposition interaction on H+ supply to soils in Pinus banksiana and Populus tremuloides ecosystems in the Athabasca oil sands region in Alberta, Canada

Soil acidification has been of concern in the oil sands region in Alberta due to increased acid deposition. Using the canopy budget model, and accounting for H+ canopy leaching by organic acids, we determined sources and sinks of H+ in throughfall in jack pine (Pinus banksiana) and trembling aspen (Populus tremuloides) stands in two watersheds from 2006 to 2009. In pine stands, H+ deposition was greater in throughfall than in bulk precipitation while the opposite was true in aspen stands. The annual H+ interception deposition was 148.8–193.8 and 49.7–70.0 molc ha−1 in pine and aspen stands, respectively; while the annual H+ canopy leaching was 127.1–128.7 and 0.0–6.0 molc ha−1, respectively. The greater H+ supply in pine stands was caused by greater interception deposition of SO42− and organic acids released from the pine canopy. Such findings have significant implications for establishing critical loads for various ecosystems in the oil sands region.

► We monitored acid deposition in the oil sands region of Alberta over three years.
► A modified canopy budget model was developed to evaluate H+ budget as the first such attempt in western Canada.
► The H+ supply by organic acid leaching from jack pine canopy was a significant source of H+.
► This has implications for establishing critical loads for acid deposition for watersheds in the region.