Comparison of carbon fluxes between different stages of regeneration in a harvested bog (Jura, France)

E. Bortoluzzi1, D. Epron2, D. Gilbert1, A. Buttler1,2

1 University of Franche-Comté (France) 2University Henri Poincaré, Nancy (France)

3 Swiss Federal Institute of Technology-EPFL, Swiss Federal Institute WSL, Lausanne (Switzerland)

Peatlands : carbon sinks

A considerable stake in the actual context, as illustrated by these extracts of the Kyoto Protocol (1992)

Article 7 ”1. Each Party (...) shall incorporate in its annual inventory of anthropogenic emissions by sources and removals by sinks of greenhouse gases (...)”

(ii) ”Parties (...) contribute to addressing climate change and its adverse impacts, including the abatement of increases in greenhouse gas emissions, and enhancement of and removals by sinks (...)”

Article 10b

Peatlands, carbon sinks ?

Rtotal

CO2CO2

CH4CH4

GP - Rv - Ru - FCH4

NPPNPP

NEENEE

Accumulation

CO2

CO2

Rtotal

At which time in the regeneration process does the peatland again become

a carbon sink?

This is one of the problematic of the

european project RECIPE (Reconciling commercial exploitation of peat with biodiversity in peatland

ecosystems)

CO2CO2

Objectives :

• Establishment of a carbon balance for different stages of a regeneration process:1. Bare peat2. Recent regeneration with much Eriophorum angustifolium

and few Sphagnum3. Advanced regeneration with mainly Sphagnum.

• Comparison of these balances with the vegetation diversity

• Compartimentation of the fluxes for more precision in the balance

In order to establish a carbon balance

• Selection of the presented study site : a bog in the french Jura mountains, exploited until 1984

• Setting of the site in a cut-over strip:

In order to establish a carbon balance (2)

In order to establish a carbon balance (3)

• Recording permanently the local climate factors :– Light intensity– Air temperature, peat

temperature (depth of 5 cm and 30 cm)

– Rain events.

In order to establish a carbon balance (4)

• Fluctuation of ground water table• Estimation of Sphagnum humidity with a visual index:

1 : Sphagnum completely dessicated

…to

6 : Sphagnum inundated.

Collar, 30 cm of diameter.

In order to establish a carbon balance (5)

• Leaf area index (LAI) for vascular plants :

0

500

1000

1500

2000

2500

3000

0 100 200 300 400 500 600

Relation between leaf length (mm) and leaf area (mm2) for Eriophorum angustifolium

Y=0,248X1,439

R2=0,953

calculated with the measurement of the leave length and their density within the collars.

• For Sphagnum and Polytrichum, measurement of the density only.• Surveys in April, July and October.

In order to establish a carbon balance (6)

• Measurements : once a week under light saturation and darkness (except when snow) for CO2 with a infrared gas analyser ( CIRAS1,PPsystems)

• Every month for CH4 (incubation in a dark closed chamber and analysis in the laboratory with a micro GC CP 4900, Varian)

In order to establish a carbon balance (7)

• Measurement of the net primary production :– for Sphagnum and Polytrichum using the cranked wire

method (growth in length) and the density– for vascular plants using the density

and the correlation

between leaf length

and biomass.

0

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0,09

0,1

0 50 100 150 200 250 300 350 400

Relation between leaf length (mm) and dry biomass (g) for Carex nigra

Y=4e-0,6 X1,7124

R2=0,95

• Estimation of vegetation diversity on 1m2 around each collar.

Field equipment

Light sensor

Rain collector

Air temperature sensor

CH4

chamber

T. sensor

T. sensor

- 5 cm

- 30 cm

Chamber temperature

CO2

analyser(analysis in Lab.)

Light sensor

Leaf area index

Sphagnum humidity

Water table level

Results : daily variations of CO2 fluxes

- Use of sigmaplot software

- Model equation:

NEE = GP - RtotNEE = GP - Rtot with GP = (GPM*I)/(K+I) with GP = (GPM*I)/(K+I)

with GPM = ATwith GPM = AT22+BT+BT with Rtot = C*exp(D*T)with Rtot = C*exp(D*T)

- Parameters of entry : I : light intensityT : air temperature

- Parameters determined by the software :K : half saturation lightA et B : factors of adjustment of GPM function of air temperatureQ : factor of adjustment of Rtot function of air temperature

Results : daily variations of CO2 fluxes (2)

-5

-4

-3

-2

-1

0

1

2

3

0 200 400 600 800 1000 1200

20/05/2004 R2=0.88 recent regeneration 26/04/2005 R2=0.97advanced regeneration

Parameter Value StdErr Parameter Value StdErr

K 1.92E+02 3.13E+01 K 1.38E+02 2.84E+01

A -4.92E-03 1.15E-03 A -6.38E-03 1.96E-03

B 2.97E-01 3.69E-02 B 3.99E-01 5.98E-02

C 9.36E-01 6.91E-02 C 9.87E-01 3.65E-02

D 3.55E-02 3.31E-03 D 4.90E-02 1.82E-03

Topt 3.01E+01   Topt 3.13E+01  

GPM25 4.34E+00   GPM25 5.98E+00  

R25 2.27E+00   R25 3.36E+00  

Q1O 1.43   Q1O 1.63  

Recent regeneration

-4

-3

-2

-1

0

1

2

3

0 200 400 600 800 1000 1200

Advanced regeneration

NE

E (

mic

rom

oleC

O2/

m2 /

s)

sink

sourceNEE measured

NEE simulated

Results : comparison between regeneration stages

-1

0

1

2

3

4

5

05/11/2003 25/12/2003 13/02/2004 03/04/2004 23/05/2004

0

1

2

3

4

5

6

7

5/11/03 25/12/03 13/2/04 3/4/04 23/5/04

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

5/11/03 25/12/03 13/2/04 3/4/04 23/5/04

NEE

Total Respiration

GP

NE

E (

mic

rom

ole

CO

2/m

2/s

)G

P(m

icro

mol

eCO

2/m

2/s

)R

TO

T(m

icro

mo

leC

O2/m

2/s

)

Fluxes between regeneration stages which are statistically different with non parametric testing (Kolmogorov Smirnov).

advancedrecent

Bare peat

sink

source

Results : Rtot = f(temperature)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 10 15 20 25 30 35

0

0.5

1

1.5

2

2.5

3

3.5

0 5 10 15 20 25 30 35

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 10 15 20

0

1

2

3

4

5

6

7

0 2 4 6 8 10 12 14 16

R2=0.78

R2=0.90R2=0.65

R2=0.90

Y=a*ebT10cm Y=a*ebTair

T10cm

T10cm

Tair

Tair

Bare peat Bare peat

Recent and advanced Recent and advanced

Preliminary results for methane

  CH4 flux (nmol m-2 s-1)

Bare peat 3.14

Recent regeneration 20.17

Advanced regeneration 0.086

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0 1 2 3 4 5 6 7 8

Y= 1.4146x+1.0143R2=0.99

CH4 (ppm)

Incubation time (hours)

Conclusion and perspectives :

1) Preliminary results show that CO2 fluxes between regeneration stages are significantly different, with a trend to higher gas exchanges in the advanced situation.

3) The data set which will be collected over the year will allow us to compare the carbon balance of the different regeneration stages with their net primary production and the related vegetation diversity.

2) The summer data should be particularly interesting with the impact of Sphagnum dessication on the photosynthesis.

We acknowledge the contribution and the help of our colleagues from the RECIPE project