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Peatlands : carbon sinks

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Peatlands : carbon sinks

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  1. Comparison of carbon fluxes between different stages of regeneration in a harvested bog (Jura, France)E. Bortoluzzi1, D. Epron2, D. Gilbert1, A. Buttler1,21 University of Franche-Comté (France)2University Henri Poincaré, Nancy (France) 3 Swiss Federal Institute of Technology-EPFL, Swiss Federal Institute WSL, Lausanne (Switzerland)

  2. 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 (...)” Article 10b (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 (...)”

  3. Peatlands, carbon sinks ? Accumulation NEE NPP GP - Rv -Ru-FCH4 At which time in the regeneration process does the peatland again become a carbon sink? CO2 This is one of the problematic of the european project RECIPE (Reconciling commercial exploitation of peat with biodiversity in peatland ecosystems) CO2 CO2 CO2 Rtotal Rtotal CH4

  4. Objectives : • Establishment of a carbon balance for different stages of a regeneration process: • Bare peat • Recent regeneration with much Eriophorum angustifolium and few Sphagnum • Advanced regeneration with mainly Sphagnum. • Comparison of these balances with the vegetation diversity • Compartimentation of the fluxes for more precision in the balance

  5. In order to establish a carbon balance • Selection of the presented study site : a bog in the french Jura mountains, exploited until 1984

  6. In order to establish a carbon balance (2) • Setting of the site in a cut-over strip:

  7. 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.

  8. 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.

  9. In order to establish a carbon balance (5) • Leaf area index (LAI) for vascular plants : calculated with the measurement of the leave length and their density within the collars. Relation between leaf length (mm) and leaf area (mm2) for Eriophorum angustifolium Y=0,248X1,439 R2=0,953 • For Sphagnum and Polytrichum, measurement of the density only. • Surveys in April, July and October.

  10. 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)

  11. 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. 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.

  12. Field equipment Rain collector Light sensor Air temperature sensor T. sensor T. sensor Light sensor Chamber temperature Leaf area index Sphagnum humidity (analysis in Lab.) CO2 analyser CH4 chamber - 5 cm Water table level - 30 cm

  13. Results : daily variations of CO2 fluxes - Use of sigmaplot software - Model equation: NEE = GP - Rtot with GP = (GPM*I)/(K+I) with GPM = AT2+BT with Rtot = C*exp(D*T) -Parameters of entry : I : light intensity T : air temperature - Parameters determined by the software : K : half saturation light A et B : factors of adjustment of GPM function of airtemperature Q : factor of adjustment of Rtot function of air temperature

  14. Results : daily variations of CO2 fluxes (2) Recent regeneration Advanced regeneration sink NEE (micromoleCO2/m2/s) NEE measured source NEE simulated

  15. Results : comparison between regeneration stages NEE NEE (micromoleCO2/m2/s) sink source GP Fluxes between regeneration stages which are statistically different with non parametric testing (Kolmogorov Smirnov). GP(micromoleCO2/m2/s) advanced RTOT(micromoleCO2/m2/s) recent Bare peat Total Respiration

  16. Results : Rtot = f(temperature) Y=a*ebTair Y=a*ebT10cm Bare peat Bare peat R2=0.78 R2=0.90 Tair T10cm Recent and advanced Recent and advanced R2=0.65 R2=0.90 Tair T10cm

  17. Preliminary results for methane CH4 (ppm) Y= 1.4146x+1.0143 R2=0.99 Incubation time (hours)

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

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

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