Estimates of exceedances of critical loads for acidifying deposition in Alberta and Saskatchewan
<p>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 Chemistr...
Main Authors: | , , , , , , , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2018-07-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/18/9897/2018/acp-18-9897-2018.pdf |
Summary: | <p>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 <i>R</i><sup>2</sup> 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).</p><p>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  ×  10<sup>4</sup> and
3.3  ×  10<sup>5</sup> km<sup>2</sup>, 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.</p><p>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.</p> |
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ISSN: | 1680-7316 1680-7324 |