site-specific nutrient mass balances and critical loads for forests in canada shaun watmough*,...

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 swatmough@trentu.ca

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

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Forest health monitoring plots

exceedance > 100exceedance 0–100no exceedance 0–100no exceedance > 100

Exeedance (eq ha –1 yr –1)

y = 0.015x + 8.1614

R2 = 0.295

0

5

10

15

20

25

30

35

0 100 200 300 400 500 600 700 800 900

Exceedance (molc ha–1)

y = 0.0189x + 7.8257

R2 = 0.4315

1989

5 sites were mis-classified (yellow dots on the previous slide)– soil data indicated high weathering potential

Regression excluding 5 sites

Relationship between exceedance of the critical load and forest health

Many factors may be responsible for poor crown condition

R2 = 0.49; p< 0.001

0

0.2

0.4

0.6

0.8

1

1.2

0 0.1 0.2 0.3 0.4 0.5 0.6

Foliar Mg (%)

Fol

iar

K (

%)

critical foliar K limit

Forests are not at steady state and disturbances such as harvesting or

fire must be considered.

The Ca dynamics of Fire

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

1970 1975 1980 1985 1990 1995 2000

Year

Ca

(m

g l-1

)

0

2

4

6

8

10

12

14

SO

4 (m

g l-1

)

Ca

SO4

Fire in 1980

Effect of forest fire on stream Ca and SO4 concentration at Rawson lake (NW basin; S. Page, unpublished data)

Conclusions

• General agreement with regional maps and site specific data.

• Maps may be used to highlight potentially sensitive areas (target sampling).

• Mass balance estimates at 18 sites indicate that soils are acidifying at the majority of sites, despite the fact that N is currently retained.

• Dynamic models have much potential, but require more data and the issue of uncertainty with respect to N and disturbance remains.

• Link to forest health?