Effects of Canopy-Deposition Interaction On H+ Supply to Soils In Pinus Banksiana and Populus Tremuloides Ecosystems In the Athabasca Oil Sands Region of Alberta, Canada.

Soil acidification in forest ecosystems is of concern in the Athabasca oil sands region (AOSR), the largest area for open-pit oil sands mining in Alberta, Canada, due to acid emission and its subsequent deposition. This research was conducted to quantify H⁺ deposition in forest soils in AOSR and to determine sources of H⁺ deposition in different forest stands. We evaluated bulk precipitation, interception deposition (ID), canopy leaching (CL), and canopy uptake (CU) of H⁺ in throughfall in jack pine (Pinus banksiana) and trembling aspen (aspen, Populus tremuloides) stands in two watersheds (NE7 and SM8) in AOSR between 2006 and 2009. Bulk precipitation of H⁺ was 47.1 mol_c ha^-1 yr^-1 in NE7 and 117.2 mol_c ha^-1 yr^-1 in SM8. The major anion and cation of bulk deposition was SO₄^2- and Ca²⁺, respectively. The pH of throughfall in jack pine stands was generally lower than that of bulk precipitation while the reverse was true in aspen stands. Greater H⁺ supply in jack pine than that in aspen stands was caused by the greater ID of SO₄^2-, greater organic acid release, and less CU of H⁺ by jack pine canopy. The ID of H⁺ ranged from 127.8 to 148.2 mol_c ha^-1 yr^-1 in jack pine and from 61.3 to 135.7 mol_c ha^-1 yr^-1 in aspen in NE7 and from 158.3 to 176.9 mol_c ha^-1 yr^-1 in jack pine and from 41.1 to 134.2 mol_c ha^-1 yr^-1 in aspen in SM8. The CL of H⁺ by organic acids ranged from 127.1 to 128.7 mol_c ha^-1 yr^-1 in jack pine and from 0 to 6.0 mol_c ha^-1 yr^-1 in aspen. In conclusion, significant amounts of acid materials are being deposited in AOSR and canopy interception was a major process of atmospheric deposition. Jack pine stands may be exposed to a greater risk of soil acidification than aspen stands due to the greater acid deposition and organic acid production.