Bog plant/lichen tissue nitrogen and sulfur concentrations as indicators of emissions from oil sands development in Alberta, Canada

Abstract

Increasing gaseous emissions of nitrogen (N) and sulfur (S) associated with oil sands development in northern Alberta (Canada) has led to changing regional wet and dry N and S deposition regimes. We assessed the potential for using bog plant/lichen tissue chemistry (N and S concentrations, C:N and C:S ratios, in 10 plant/lichen species) to monitor changing atmospheric N and S deposition through sampling at five bog sites, 3–6 times per growing season from 2009 to 2016. During this 8-year period, oil sands N emissions steadily increased, while S emissions steadily decreased. We examined the following: (1) whether each species showed changes in tissue chemistry with increasing distance from the Syncrude and Suncor upgrader stacks (the two largest point sources of N and S emissions); (2) whether tissue chemistry changed over the 8 year period in ways that were consistent with increasing N and decreasing S emissions from oil sands facilities; and (3) whether tissue chemistry was correlated with growing season wet deposition of NH4+-N, NO3−-N, or SO42−-S. Based on these criteria, the best biomonitors of a changing N deposition regime were Evernia mesomorpha, Sphagnum fuscum, and Vaccinium oxycoccos. The best biomonitors of a changing S deposition regime were Evernia mesomorpha, Cladonia mitis, Sphagnum fuscum, Sphagnum capillifolium, Vaccinium oxycoccos, and Picea mariana. Changing N and S deposition regimes in the oil sands region appear to be influencing N and S cycling in what once were pristine ombrotrophic bogs, to the extent that these bogs may effectively monitor future spatial and temporal patterns of deposition.

Is bog water chemistry affected by increasing N and S deposition from oil sands development in Northern Alberta, Canada?

“…A one-time synoptic sampling of 19 bogs distributed across a 3,255 km 2 area centered on the midpoint between the Syncrude and Suncor stacks revealed significant correlations of bog porewater SO 4 Annual net primary production (NPP) of Sphagnum fuscum across 6 bogs, 5 of which are the same as bogs used in the present study, was 259 ± 9 g dry mass m −2 year −1 (Wieder et al, 2016b). At these bogs, S concentrations in S. fuscum capitula ranged from 1.13 to 1.83 mg g −1 and decreased with increasing distance from the oil sands industrial center (Wieder et al, 2021). Therefore, the annual quantity of S taken up through NPP of S. fuscum would be 2.9-4.7 kg ha −1 year −1 .…”

“…Six of the sites are ombrotrophic bogs, with acidic porewaters (Table 1), a nearly continuous cover of Sphagnum mosses (S. fuscum and S. capillifolium on hummocks, S. angustifolium in hollows), and an abundance of Rhododendron groenlandicum, Vaccinium oxycoccos, and Vaccinium vitis-idaea. Porewater at the top of the water table at the Mildred site has a circumneutral pH, although the site has ombrogenous hummocks dominated by S. fuscum and/or S. capillifolium, and a species composition similar to bogs (Vitt et al, 2020;Wieder et al, 2021). Recognizing the unique nature of the Mildred site, we will refer to all sites as bogs.…”

“…Oil sands development in northern Alberta has grown markedly since 1967 when the first oil sands mine began operations. Annual emissions of gaseous nitrogen oxides (expressed as NO 2 ) from upgrader stacks and dieselfueled mine fleets have increased over time, reaching about 98,000 metric tonnes in 2019; gaseous SO 2 emissions peaked in 2009 at about 120,000 metric tonnes and decreased markedly to about 49,000 metric tonnes in 2014, flattening out at about 45,000 metric tonnes through 2019 (updated from Davidson & Spink, 2018;Wieder et al, 2021;Tables S1, S2). These emissions have led to wet and dry N and S deposition that is highest nearest to the oil sands industrial center and decreases with distance (Edgerton et al, 2020;Fenn et al, 2015;Hsu et al, 2016;Wieder et al, 2016a, b).…”

“…Increasing N, and to a lesser extent S, deposition has the potential to affect bog ecosystem structure and function (Bobbink & Hettelingh, 2011;Wieder et al, 2016aWieder et al, , b, 2019Wieder et al, , 2021Vitt et al, 2020). Ultimately, when N or S inputs in atmospheric deposition exceed the retention capacity of Sphagnum mosses at the bog surface, N and S can move downward into the peat profile (Lamers et al, 2000).…”

Selecting Biomonitors of Atmospheric Nitrogen Deposition: Guidelines for Practitioners and Decision Makers

“…The nitrogen content of woody plants also responded to the rate of dry deposition. In particular, their nitrogen content increases with the proximity to highways or industries [59,66,68,69].…”