WESTAR Council
Understanding the Critical Loads Approach
Denver, November 15-16, 2005
Using Critical Loads to Protect
Canadian Ecosystems from Damage
due to Acid Deposition
Kerri Timoffee*
Environment Canada Transboundary Air Issues Branch, Ottawa
(* plus a many others, e.g., Silvina Carou, Dean Jeffries,
Mike Moran, C.-H. Ro, R.J. Vet)
Outline
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Post-2000 Acid Rain Strategy
How we got there
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Current status
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Scientific evidence of impacts, basis for 1982 deposition targets
& decision process
control programs and anticipated ecological benefits
2004 Canadian Acid Deposition Science Assessment
Current situation with respect to critical loads
Next Steps
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Forecasting the future
Where to next
Canada’s current policy instrument is the 1998
Canada-Wide Acid Rain Strategy for Post-2000
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Signed by all Federal/Provincial/Territorial Energy
and Environment Ministers
Main elements
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Reduce acidifying emissions in eastern Canada and the
United States
Prevent pollution and keep clean areas clean
Maintain an adequate science and monitoring program
Report annually
Long term goal is to reduce acid deposition to
below critical loads across Canada
Early scientific evidence for
ecological impacts in Canada
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acidic lakes, damage to terrestrial vegetation
near smelters, Gorham and Gordon, 1960
acidification damage in cottage country far from
local emission sources, Dillon et al, 1977
decrease in number and variety of fish species in
lakes and rivers of Ontario and the Atlantic
provinces, BRCG, 1979
Canada realised that controlling acid deposition
would require an effects-based program
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Large but local sources
Worlds’ tallest
“superstack” was built
Air quality standard
addresses local air
pollution problem
missed the problem of
damage downwind &
cumulative exposures
Sulphate loadings and observed effects as
basis for defining deposition targets
Area
I.L.W.A.S. Project,
Adirondacks
Southern Norway
Loading (Kg/Ha*Yr)
40
20-40
Observations
Acidified lakes in the area
Acid lakes, fish populations lost
Hubbard Brook, New
Hampshire
Muskoka-Haliburton,
Ontario
Algoma
35
Acid lakes in the area
30
20
pH depression, evidence of
biological damage
Acidic headwater lakes
Nova Scotia
20
Acidified Rivers
Minnesota Boundary
Waters
ELA, Northeastern
Ontario
14
Some pH depression, no
biological effects reported
10
No apparent detrimental effects
observed in 10 yrs of study
Canada adopted a critical load to
protect aquatic ecosystems in 1982
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aquatic evidence was sufficient
forest damage was, and still is, controversial
experimental cause-effect evidence of the chemical
processes and sequence of biological changes as
acidification progressed
targeted wet sulphate deposition
In 1982, Canada proposed a critical load of 20
kg/ha/yr to protect all but the most sensitive areas
In 1983 New England Governors and Eastern Canadian
Premiers endorsed the 20kg/ha/yr target.
Projected impact of reducing SO2 emissions on
the amount of wet sulphate deposited annually
Wet sulphate deposition (approx. kg/ha/yr)
Estimated effects of reducing SO2 emissions by
Area
Now
50% in
Canada
100% in
Canada
50% in Canada
50% in US
Muskoka’s
29-35
24-30
20-26
13-19
Quebec City
27-35
23-31
19-27
15-23
Central Nova
Scotia
17-23
16-22
14-20
15-20
Adirondacks
29-37
26-34
23-31
13-21
Vermont/New
Hampshire
20-30
17-27
15-25
10-20
Emission Reduction Control Programs
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1984 Sulphur Protocol
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1985 Eastern Canada Acid Rain Program
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30% reduction in SO2 emissions
national cap of 3.2 million tonnes beginning in 1993
no particular environmental limit
plan to reduce total national emissions by 30% over the
next ten years, about 50% of the emissions in Eastern
Canada
Goal to protect moderately sensitive aquatic ecosystems
Committed to further science
1991 Canada-US Air Quality Agreement reiterated
the national cap
Reporting indicated that both countries
would meet their targets for emission
reductions, so the expectation was for
ecosystems to improve
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Expectation that aquatic and terrestrial
ecosystems would recover significantly
Perhaps restore the most sensitive aquatic
ecosystems
Canada developed new critical loads
to fully protect all surface waters
20 <
16 <
<=20
10 <
<=16
8<
<=12
<=8
Critical load values (kg/ha/yr) of sulphate in precipitation
Even with full implementation of Canadian and US
programs, almost 800,000 km2 in southeastern Canada
would still receive harmful levels of acid deposition
Area of eastern Canada expected to receive wet SO4 deposition above
critical loads (in kilograms per hectare per year) in 2010, without further
controls beyond provisions in the 1991 Canada-US Air Quality Agreement
These critical loads and exceedance estimates
were accepted by the scientific and
political communities as the basis for developing
the Post-2000 Acid Rain Strategy
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Strategies goal is to achieve sulphate deposition levels
that do not exceed “critical loads”
Scenario modelling predicted the changes in critical load
exceedances resulting from further reductions in SO2
emissions in eastern Canada as well as the US
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25% cut in SO2 emissions → 34% reduction in area receiving
harmful levels
50% cut in SO2 emissions → 72% reduction
75% cut
→ virtually all of eastern Canada would
be protected from acid deposition
Current Status - Time Series
CAPMoN and CASTNet Networks
Current status - Changes in nssSO4=
Wet Deposition Patterns
1980-1984 Mean nssSO4= Wet Deposition (Kg/Ha/Yr)
1996-2001 Mean nssSO4= Wet Deposition (Kg/Ha/Yr)
Aquatic CLs
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5th percentile value for all lakes located within a grid square
Index map shows which model produced the grid value
1983 target load (20 kg/ha/yr) covered by lowest four classes
21% of eastern grid squares in lowest CL category
Area of Eastern Canada at Risk
from Acid Deposition
0.5 million km2
1.8 million km2
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New science considers both sulphate and nitrate deposition and
aquatic and terrestrial ecosystems.
Aquatic “N-leaching” Exceedances
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95th exceedance value for all lakes within a grid square
Current situation (note both positive and negative exceedance classes)
Largest (orange) exceedances occur in southern NS/NB and ON
Positive exceedance even occur in NW ON (but none in west)
Forecasting the Future
Annual Effective Acidity Wet Deposition
(combined annual SO4 and NO3 wet deposition)
keq/ha/yr
“First generation” Can-US SO2 and
NOX emissions reductions
keq/ha/yr
Most realistic Can-US SO2 and NOX
emissions reductions
Implementation of current (e.g. Post-2000 Strategy) and proposed (e.g. U.S.
Clear Skies) legislation is predicted to reduce the effective acidity of wet
deposition by at least 30% over much of eastern North America by 2020.
Forecasting the Future
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Implementation of current (e.g. Post-2000 Strategy) and proposed
(e.g. U.S. Clear Skies) legislation, will reduce but not eliminate acid
damage in eastern Canada.
Draft
Aquatic
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Draft
Terrestrial
It is estimated that a further reduction in SO2 of ~75% will be required
from Canada and the U.S. beyond those agreed to in the CanadaU.S. Air Quality Agreement to end acid rain.
Where to Next
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New critical loads and preliminary exceedance
estimates
Adjust our control control actions
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Further domestic cuts
Decrease TB flows
Increase effort at KCAC/PP
Monitor and report on ecological benefits
Summary
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Concept of working towards reducing deposition
to below critical loads has long been central to
Canada’s SO2 management program
There are still many regions of eastern Canada
(and perhaps even small parts of western
Canada) where present-day deposition levels
exceed aquatic critical loads
Developing critical loads is an iterative process
Challenges
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Concern that any sulphur dioxide control program
would require large, and possibly expensive,
reductions
Region of
Concern:
Where
Ecosystem
Effects
Likely Occur
(contains ~800000
water bodies)
Environment Canada (1988)
Contact information
Kerri Timoffee
Manager, Acid Rain Program
Transboundary Air Issues Branch
Environment Canada
Rm 1118, 351 St Joseph Blvd
Gatineau, Quebec K1A 0H3
Email: kerri.timoffee@ec.gc.ca
Telephone: (819) 994-9564
Fax: (819) 953-8963