Abstract. Estimates of potential harmful effects on ecosystems in the Canadian provinces of Alberta and Saskatchewan due to acidifying deposition were calculated, using a 1-year simulation of a high-resolution implementation of the Global Environmental Multiscale-Modelling Air-quality and Chemistry (GEM-MACH) model, and estimates of aquatic and terrestrial ecosystem critical loads. The model simulation was evaluated against two different sources of deposition data: total deposition in precipitation and total deposition to snowpack in the vicinity of the Athabasca oil sands. The model captured much of the variability of observed ions in wet deposition in precipitation (observed versus model sulfur, nitrogen and base cation R2 values of 0.90, 0.76 and 0.72, respectively), while being biased high for sulfur deposition, and low for nitrogen and base cations (slopes 2.2, 0.89 and 0.40, respectively). Aircraft-based estimates of fugitive dust emissions, shown to be a factor of 10 higher than reported to national emissions inventories (Zhang et al., 2018), were used to estimate the impact of increased levels of fugitive dust on model results. Model comparisons to open snowpack observations were shown to be biased high, but in reasonable agreement for sulfur deposition when observations were corrected to account for throughfall in needleleaf forests. The model–observation relationships for precipitation deposition data, along with the expected effects of increased (unreported) base cation emissions, were used to provide a simple observation-based correction to model deposition fields. Base cation deposition was estimated using published observations of base cation fractions in surface-collected particles (Wang et al., 2015).Both original and observation-corrected model estimates of sulfur, nitrogen, and base cation deposition were used in conjunction with critical load data created using the NEG-ECP (2001) and CLRTAP (2017) methods for calculating critical loads, using variations on the Simple Mass Balance model for terrestrial ecosystems, and the Steady State Water Chemistry and First-order Acidity Balance models for aquatic ecosystems. Potential ecosystem damage was predicted within each of the regions represented by the ecosystem critical load datasets used here, using a combination of 2011 and 2013 emissions inventories. The spatial extent of the regions in exceedance of critical loads varied between 1  ×  104 and 3.3  ×  105 km2, for the more conservative observation-corrected estimates of deposition, with the variation dependent on the ecosystem and critical load calculation methodology. The larger estimates (for aquatic ecosystems) represent a substantial fraction of the area of the provinces examined.Base cation deposition was shown to be sufficiently high in the region to have a neutralizing effect on acidifying deposition, and the use of the aircraft and precipitation observation-based corrections to base cation deposition resulted in reasonable agreement with snowpack data collected in the oil sands area. However, critical load exceedances calculated using both observations and observation-corrected deposition suggest that the neutralization effect is limited in spatial extent, decreasing rapidly with distance from emissions sources, due to the rapid deposition of emitted primary dust particles as a function of their size. We strongly recommend the use of observation-based correction of model-simulated deposition in estimating critical load exceedances, in future work.

Abstract.Estimates of potential harmful effects to ecosystems in the Canadian provinces of Alberta and Saskatchewan due to acidifying deposition were calculated, using a one year simulation of a high resolution implementation of the Global Environmental Multiscale -Modelling Air-quality and Chemistry (GEM-MACH) model, and estimates of aquatic and terrestrial ecosystem critical loads. The model simulation was evaluated against two different sources of deposition data; 20 total deposition in precipitation and total deposition to snowpack in the vicinity of the Athabasca oil sands. The model captured much of the variability of observed ions in wet deposition in precipitation (observed versus model sulphur, nitrogen and base cation R 2 values of 0.90, 0.76 and 0.72, respectively), while being biased high for sulphur deposition, and low for nitrogen and base cations (slopes 2.2, 0.89 and 0.40, respectively). Aircraft-observation-based estimates of fugitive dust emissions, shown to be a factor of ten higher than reported values (Zhang et al.., 2017), were used to estimate the impact of 25 increased levels of fugitive dust on model results. Model comparisons to open snowpack observations were shown to be biased high, but in reasonable agreement for sulphur deposition when observations were corrected to account for throughfall in needleleaf forests. The model-observation relationships for precipitation deposition data, along with the expected effects of increased (unreported) base cation emissions, were used to provide a simple observation-based correction to model deposition fields. Base cation deposition was estimated using published observations of base cation fractions in surface 30 collected particles .Both original and observation-corrected model estimates of sulphur, nitrogen and base cation deposition were used in conjunction with critical load data created using the NEG-ECP (2001) and CLRTAP (2004, 2016, 2017) Base cation deposition was shown to have a neutralizing effect on acidifying deposition, and the use of the aircraft and precipitation observation-based corrections to base cation deposition resulted in reasonable agreement with snowpack data collected in the oil sands area. However, critical load exceedances calculated using both observations and observationcorrected deposition suggest that the neutralization effect is limited in spatial extent, decreasing rapidly with distance from 10 emissions sources, due to the rapid deposition of emitted primary particles dust particles as a function of their size.

We used zooplankton communities as indicators to evaluate the potential influence of acidifying-eutrophying emissions from the Athabasca oil sands region (AOSR) on 244 downwind lakes in northwest Saskatchewan. The impacts of regional environmental change on zooplankton communities are determined by responses of resident species to altered local environmental conditions as well as changes in composition due to dispersal processes. To test and quantify the relative importance of these individual processes, we conducted ordination analyses, spatial modeling, and variation partitioning. Local environmental factors were the dominant determinants of community structure, including two major environmental gradients susceptible to atmospheric emissions (i.e., acid-base status and productivity). Spatial structuring of these factors induced similar spatial structures in zooplankton distribution across the region. However, disentangling any impacts of the AOSR on these environment-spatial-species relationships from the underlying natural variability was precluded by unavailability of baseline data. Nevertheless, as our findings indicate that dispersal of zooplankton was not strongly limiting across this broad geographic region, zooplankton indicators can be crucial to detect future environmental changes in lakes across northwest Saskatchewan.Résumé : Nous avons utilisé les communautés de zooplancton comme indicateurs pour évaluer l'influence potentielle des émissions acidifiantes-eutrophisantes issues de la région des sables bitumineux de l'Athabasca (RSBA) sur 244 lacs du nord-ouest de la Saskatchewan situés en aval du vent. Les impacts des modifications régionales de l'environnement sur les communautés de zooplancton sont déterminés par les réactions des espèces résidentes à la modification des conditions ambiantes locales, ainsi que par les modifications de la composition découlant de processus de dispersion. Pour valider et quantifier l'importance relative de ces différents processus, nous avons utilisé des analyses d'ordination, la modélisation spatiale et le partitionnement de la variation. Les facteurs environnementaux locaux étaient les principaux déterminants de la structure des communautés, notamment deux importants gradients environnementaux sensibles aux émissions atmosphériques, à savoir le statut acidobasique et la productivité. La structuration spatiale de ces facteurs induisait des structures spatiales semblables dans la répartition du zooplancton dans la région. Toutefois, étant donné l'absence de données de référence, il été impossible de distinguer les incidences de la RSBA sur ces relations environnement-emplacement-espèces de la variabilité naturelle sous-jacente. Cela dit, puisque nos résultats indiquent que la dispersion du zooplancton n'était par fortement limitative dans cette grande région géographique, les indicateurs zooplanctoniques peuvent jouer un rôle clé dans la détection de modifications futures de conditions ambiantes dans les lacs du nord-ouest de la Saskatchewan. [Traduit par la Rédaction]

Converging evidence suggests that freshwater systems play an important role in the carbon cycles at both regional and global scales. In addition, there are serious concerns that ongoing and future changes to the environment could alter these dynamics. This is particularly important in the boreal forest biome, which contains a very high density of lakes. In this review, we synthesize the current state of research to provide a critical overview of (i) the role of boreal lakes as emitters versus sinks of carbon, (ii) their contribution to the regional carbon balance, (iii) knowledge gaps that may inhibit an accurate evaluation of the role of boreal lakes in a landscape context, and (iv) impacts of environmental perturbations on carbon dynamics in boreal lakes. Several recent studies indicate that boreal lakes are actively processing, emitting, and storing carbon rather than being passive transport conduits. Yet, generalizing the role of lake ecosystems for the overall carbon balance of the boreal forest biome is challenging because of the scarcity of studies on lake carbon budgets in a landscape context that can capture the potential temporal and spatial variability and uncertainties associated with the available estimates of carbon pools and fluxes. Further, environmental perturbations, such as climate change, acidic deposition, and nutrient enrichment, likely affect both carbon export to lakes and in-lake carbon processing in boreal regions. Predicting their overall impacts on lake carbon budgets is particularly difficult, not only because individual environmental stressors likely affect multiple processes involved in carbon cycling, but also because often multiple stressors act synergistically or antagonistically at the landscape level. Accordingly, long-term, system-wide approaches are required to accurately evaluate the importance of lakes for boreal carbon budgets in a changing environment.

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