Effects of altered atmospheric nutrient deposition from Alberta oil sands development on Sphagnum fuscum growth and C, N and S accumulation in peat

Abstract

Associated with the development of the oil sands resource in northern Alberta, Canada are elevated emissions of NOx and SOx from diesel-fueled vehicle and upgrader stack emissions. Ultimately these emissions are returned to regional terrestrial and aquatic ecosystems in the form of elevated atmospheric N and S deposition. About 30 % of the regional landscape is covered with peatlands, including ombrotrophic bogs that receive nutrient inputs solely from the atmosphere. From 2009 to 2014 we examined the effects of N and S deposition on Sphagnum fuscum growth and on recent net accumulation of C, N, and S in peat in six bogs, located between 11 and 251 km from the oil sands industrial center. Averaged across all sites and years, average deposition of NH4 +–N, NO3 −–N, DIN, SO4 2−–S, Ca2+, Mg2+, and ortho-P was 0.52, 0.64, 1.17, 7.70, 10.04, 3.29, and 0.15 kg ha−1 year−1. Deposition of NO3 −–N, DIN, SO4 2−–S, Ca2+, and Mg2+ decreased exponentially with distance from the industrial center. Averaged across all sites and years, vertical growth and NPP of S. fuscum was 16.6 ± 0.6 mm and 259 ± 9 g m−2 per growing season, increasing exponentially with proximity to the industrial center. Correlations suggested that climatic factors, and in particular late growing season precipitation and the growing season Aridity Index (potential evapotranspiration to precipitation ratio) may be more important than the chemistry of atmospheric deposition in affecting S. fuscum growth. Across all sites and years, net C, N, and S accumulation in peat over the most recent 25 years averaged 67, 1.29, and 0.30 g m−2 year−1 and increased with proximity to the industrial center. Over the past 25–50 years, net C, N, and S accumulation in peat was lower than in surface peat, with only net S accumulation exhibiting an increase with proximity to the industrial center. In a region where bogs have persisted on the landscape for millennia with low atmospheric deposition of elements, changing precipitation chemistry, and in particular elevated deposition of N, S, Ca and Mg, related to oil sands development is influencing bog function, as evidenced by S. fuscum growth and biogeochemical responses.