Site-specific nutrient mass balances and critical loads for forests in Canada Shaun Watmough*, Julian Aherne, Rock Ouimet, Paul Arp, Ian Demerchant • Critical loads allow soils to acidify to the critical chemical criterion used in the SMB model. • Large parts of Canada currently receive acid deposition in excess of the critical load. • Are soils acidifying? • Do site specific critical loads compare with regional assessments? • The way ahead (Parks, Forest Health and Dynamic Modeling) *ERS Program, Trent University, Peterborough, ON. K9J 7B8 [email protected]
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Site-specific nutrient mass balances and critical loads for forests in Canada Shaun Watmough*, Julian Aherne, Rock Ouimet, Paul Arp, Ian Demerchant Critical.
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Site-specific nutrient mass balances and critical loads for forests in Canada
Shaun Watmough*, Julian Aherne, Rock Ouimet, Paul Arp, Ian Demerchant
• Critical loads allow soils to acidify to the critical chemical criterion used in the SMB model.
• Large parts of Canada currently receive acid deposition in excess of the critical load.
• Are soils acidifying?• Do site specific critical loads compare with
regional assessments?• The way ahead (Parks, Forest Health and
Dynamic Modeling)
*ERS Program, Trent University, Peterborough, ON. K9J 7B8 [email protected]
1. Are Soils Acidifying?
• Base Cation (and S and N) mass balances conducted for 21 sites in Canada, eastern United States and Europe.
Site Mass Balances: Contributing Authors:
Shaun A. Watmough, Julian Aherne, Christine Alewell, Paul Arp, Scott Bailey, Tom Clair, Peter Dillon, Louis Duchesne, Catherine Eimers, Ivan Fernandez, Neil Foster, Thorjorn Larssen, Eric Miller, Myron Mitchell, Stephen Page.
Funded by NERC
Mass Balances
• Mass Balance = Input – Output
• Inputs = deposition + (mineral weathering)
• Outputs = stream export
WeatheringSoil calcium
pool
Deposition
Soil leaching losses
Net forest uptake
The Sites:
Sulphate Deposition
0
10
20
30
40
50
60
ELA TL MH LL LC LT MP BB CP AB HB WF VL SH LH LG BK
Site
SO
4 (k
g/h
a)
*
Canada US Europe
Annual sulphate deposition (1990s) was between 7.3 and 28.4 kg/ha (excluding WF). No notable differences between Canada, US and Europe.
Nitrogen Deposition
02468
101214161820
ELA TL MH LL LC LT MP BB CP AB HB WF VL SH LH LG BK
Site
N (
kg
/ha
)
Ammonium
Nitrate
*Canada US Europe
Annual N deposition (1990s) was between 2.8 kg/ha and 13.7 kg/ha (excluding WF). Nitrogen deposition was generally higher at the European sites where a greater proportion of the annual N deposition was as NH4.
Calcium Deposition
Annual Ca deposition (1990s) was between 0.8 kg/ha and 4.2 kg/ha. Calcium deposition was highest at the eastern Canadian and central European sites.
0
1
2
3
4
5
6
ELA TL MH LL LC LT MP BB CP AB HB WF VL SH LH LG BK
Site
Ca
(k
g/h
a)
*
Canada US Europe
Sulphate export exceeds input at 18/21 sites:
WF
-100
-80
-60
-40
-20
0
20
0 20 40 60
SO4 deposition (kg/ha/yr)
De
po
sit
ion
-Ex
po
rt (
kg
/ha
/yr)
The majority of N is retained:
0
2
4
6
8
0 5 10 15 20
Inorganic N deposition (kg/ha/yr)
N-N
O3
ex
po
rt (
kg
/ha
/yr)
Between 31 and 100% of inorganic N input in deposition was retained across the study sites; median retention of 94%
Estimates of base cation weathering:
Site name Ca Mg K NaRawson NW (ELA) a 1.3 0.3 2.4 3.6Rawson NE (ELA) a 1.3 0.3 2.5 3.7Rawson E (ELA) a 1.5 0.3 2.7 4.4Turkey Lakes a 4.2 2.9 5.2 7.9Plastic (MUS-HAL) a 2.0 1.0 1.6 3.2Chub (MUS-HAL) a 5.0 3.3 2.5 3.5Harp (MUS-HAL) a 4.6 1.9 3.7 6.8Lac Laflamme a 13.9 3.6 2.1 7.1Lac Clair a 6.2 1.3 3.1 3.9Lac Tirasse a 5.4 1.6 0.6 2.5Bear Brook a 1.5 0.8 5.8 5.3Moose Pit a 3.3 2.0 1.8 2.1Cone Pond 1.2 1.1 1.1 3.0Arbutus a 5.6 4.1 6.0 5.5Hubbard Brook 2.1 2.5 1.2 5.1Whiteface 8.7 2.3 2.9 1.9Langtjern 6.0 1.0 5.6 1.3Birkenes 10.0 0.6 1.6 0.9
a Estimated using the PROFILE model (version 4.0; Warfvinge and Sverdrup 1992).
Mass balances including
weathering:
-40
-30
-20
-10
0
10
ELA
-NW
ELA
-NE
ELA
-E
TL
MH
-PC
MH
-CB
M/H
-HP
LL
LC
LT
MP
BB
CP
AB
HB
WF
VL
SH
LH
LG
BK
Annual C
a e
xport
(kg
/ha/y
r)
Canada US Europe
Calcium
Magnesium
Annual Ca and Mg losses represent appreciable proportions of the current exchangeable soil Ca and Mg pools, although losses at some of the sites likely occur from weathering reactions beneath the rooting zone. There is also considerable uncertainty associated with mineral weathering estimates.
Ca and Mg export exceeded inputs at 14/18 and 10/18 sites respectively:
-4
-3
-2
-1
0
1
2E
LA
-NW
EL
A-N
E
EL
A-E
TL
MH
-PC
MH
-CB
M/H
-HP
LL
LC
LT
MP
BB
CP
AB
HB
WF
VL
SH
LH
LG
BK
An
nu
al M
g e
xpo
rt (
kg/h
a/y
r)
Canada US Europe
Mass balances including
weathering:
-2
0
2
4
6
8
EL
A-N
WE
LA
-NE
EL
A-E
TL
MH
-PC
MH
-CB
M/H
-HP
LL
LC
LT
MP
BB
CP
AB
HB
WF
VL
SH
LH
LG
BK
An
nu
al
K e
xp
ort
(k
g/h
a/y
r)
Canada US Europe
Sodium
Potassium
-15
-10
-5
0
5
EL
A-N
WE
LA
-NE
EL
A-E
TL
MH
-PC
MH
-CB
M/H
-HP
LL
LC
LT
MP
BB
CP
AB
HB
WF
VL
SH
LH
LG
BK
An
nu
al
Na
ex
po
rt (
kg
/ha
/yr)
Canada US Europe
Inclusion of mineral weathering balances K and Na budgets (i.e. deposition + weathering ≥ export) at 16/18 and 10/18 sites, respectively:
Conclusions
• Mass Balance Studies indicated that base cation losses are occurring at the majority of sites.
• Sulphate export generally exceeds sulphate deposition (is it all dry deposition?)
• Losses are occurring despite the fact that 31 -100 % of the N is currently retained (not the assumption of the SMB model)
How do site specific critical load estimates compare?
< 250250–500500–750750–1000> 1000
Critical loads (eq ha–1 yr–1)
What are the critical loads for Parks?
• An example with the Kawartha Highlands Park in Ontario (The First Steps).
< 250250–500500–750750–1000> 1000
Critical loads (eq ha–1 yr–1)
Forest health plotSurvey lake
Pencil lake (3337)
Bottle lake (833)
Cavendish lake (McGinnis) (1265)
Litte horse shoe lake (5675)
Loon call lake (1162)
> 400 (EXC)100–400 (EXC)0–100 (EXC)-100–0 (no EXC)< -100 (no EXC)
Exceedance (eq ha–1 yr–1)
Forest health plot
The Next Steps• More Detailed Site Specific Data (MOE
Plots, MNR Plots, CWS, Surface Water Chemistry).
• Ground-Truth Maps.• Target Sampling.• Link to Forest (Ecosystem) Health.• Dynamic Approach (combining surface
water/soil data).• Include Disturbance in Dynamic Scenarios.
0.5
1.0
1.5
2.0EPA (2000)Husar (1994), Lefohn et al. (1999) Kaminski (2002)
Observed ForecastHistoric reconstruction
50
67
83
100
117
133
150
0
5
10
15
20
25
30
35
1850 1875 1900 1925 1950 1975 2000 2025 2050
Med
ian
lake
AN
C (
µm
ol c
L–1)
Sul
pha
te d
epos
ition
sca
le f
acto
r
Median soil base satu
ration (%)
Deposition
Soil base saturation continues to decline, despite large reductions
Lake ANC (acid neutralizing capacity) increases in response to reduced deposition, but will start to slowly decline again as soil base saturation decreases