Differential Effects of High Atmospheric N and S Deposition on Bog Plant/Lichen Tissue and Porewater Chemistry across the Athabasca Oil Sands Region

Abstract

Oil extraction and development activities in the Athabasca Oil Sands Region of northern Alberta, Canada, release NO_x, SO_x, and NH_y to the atmosphere, ultimately resulting in increasing N and S inputs to surrounding ecosystems through atmospheric deposition. Peatlands are a major feature of the northern Alberta landscape, with bogs covering 6-10% of the land area, and fens covering 21-53%. Bulk deposition of NH₄⁺-N, NO₃^--N, dissolved inorganic N (DIN), and SO₄^2--S, was quantified using ion-exchange resin collectors deployed at 23 locations, over 1-6 years. The results reveal maximum N and S deposition of 9.3 and 12.0 kg ha^-1 yr^-1, respectively, near the oil sands industrial center (the midpoint between the Syncrude and Suncor upgrader stacks), decreasing with distance to a background deposition of 0.9 and 1.1 kg ha^-1 yr^-1, respectively. To assess potential influences of high N and S deposition on bogs, we quantified N and S concentrations in tissues of two Sphagnum species, two lichen species, and four vascular plant species, as well as surface porewater concentrations of H⁺, NH₄⁺-N, NO₃^--N, SO₄^2--S and dissolved organic N in 19 ombrotrophic bogs, distributed across a 3255 km² sampling area surrounding the oil sands industrial center. The two lichen species (Evernia mesomorpha and Cladonia mitis), two vascular plant species (Rhododendron groenlandicum and Picea mariana), and to a lesser extent one moss (Sphagnum fuscum), showed patterns of tissue N and S concentrations that were (1) highest near the oil sands industrial center and (2) positively correlated with bulk deposition of N or S. Concentrations of porewater H⁺ and SO₄^2--S, but not of NH₄⁺-N, NO₃^--N, DIN, or dissolved inorganic N, also were higher near the oil sands industrial center than at more distant locations. The oil sands region of northern Alberta is remote, with few roads, posing challenges to the monitoring of oil sands-related N and S deposition. Quantification of N and S concentrations in bog plant/lichen tissues and porewaters may serve as a monitoring tool to assess both the local intensity and the spatial extent of bulk N and S deposition, and as harbingers of potential shifts in ecosystem structure and function.