Peatland management impacts on carbon/climate regulation - international evidence

transcript

Assessing GHG Emissions from peatlands

using vegetation as a proxy

John Couwenberg

Peatlands contain a lot of carbon

Tollund Man, Denmark

Kalimantan, Indonesia

drainage mobilises carbon: CO2 (und N2O) emissions

Peenetal, Germany

rewetting to reduce emissions

Quantifying GHG fluxes:

• direct flux measurements (chambers, micrometeorol.)

– combined with indicators / proxies (cf. IPCC)

• CO2 flux also assessed via stock-change approach

– standard approach for e.g. forest, mineral soil)

– not practicable for organic soils

organic soil fluxes are based on direct measurement

Measuring over small areas: closed chamber method

For all three GHG (CH4, CO2, N2O)

Measuring over large areas: eddy covariance

Mainly used for CO2, but also for CH4 and N2O

Measurements need to be frequent, long term, intensive

Wide variety of site parameters influencing emissions

…peatland types, peat types, spatial heterogeneity,

land use, former land use, abiotic conditions, vegetation…

Measuring is complicated, time consuming, expensive

Measure pilot sites, develop proxies

Meta-analysis: water level main single explanatory variable

CO2 emissions from temperate European peatlands

Field measurements: WL is a good proxy

mean annual water level (cm)

after Couwenberg et al. (2011)

-140 -120 -100 -80 -60 -40 -20 0 20 40

r2 = 0.68, p < 0.01

-140 -120 -100 -80 -60 -40 -20 0 20 40

r2 = 0.68, p < 0.01

CO2 emissions from temperate European peatlands

Subsidence based emissions: WL is a good proxy

after Couwenberg et al. (2011): ● direct flux, ● site specific subsidence

N2O emissions from temperate European peatlands

Direct flux measurements: WL is a good proxy

Couwenberg et al. (2011), bog sites, fen sites without fertilizer application, fen sites with fertilizer

application; x treed sites.

-100 -80 -60 -40 -20 0 20 40 60

-100 -80 -60 -40 -20 0 20 40

CH4 emissions from temperate European peatlands

Direct flux measurements (annual flux): WL is a good proxy

Couwenberg et al. (2011)

CH4 emissions from tropical and boreal peatlands

Direct flux measurements (hourly flux): WL is a good proxy

Tropical; Temperate; ∆ Boreal

-100 -80 -60 -40 -20 0 20

water level [cm]

-100 -80 -60 -40 -20 0 20

wood peat SE Asia

• many and frequent data necessary

• measure a lot (e.g. automatic logger)

• modeling using weather data (calibrate, monitor)

• WL not yet measurable using remote sensing

• particularly for CH4 high uncertainty remains

Proxy: Water level

-100 -80 -60 -40 -20 0 20 40

WL is not a quantitatively precise proxy

-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0

Direct flux measurements (annual flux): WL + vegetation

Couwenberg et al. (2011), sites with aerenchymous shunt species; sites with open vegetation without

shunt species; x treed sites.

r2 = 0.76, p < 0.01

Direct flux measurements (annual flux): vegetation

After Drösler (2005)

0 500 1000 1500 2000 2500

aerenchymous leaves (n m-2)

Emissions strongly related to water level

Vegetation strongly related to water level

Emissions also related to vegetation

Use vegetation as indicator for emissions!

Vegetation as indicator of emissions

• Integration of site parameters

• Quick

• Easy

• Cheap

• Reliable … ?

Greenhouse Gas Emission Site Types (GESTs)

advantages

• relationship to long-term water level

• relationship to other relevant site conditions

(nutrient status, pH, land use, …)

• influences fluxes itself

(substrate quality, aerenchyma)

• can be mapped on relevant scale (1:2,500 – 1:10,000)

• can be mapped using remote sensing (good for €)

Proxy: Vegetation

disadvantages

• slow reaction to changing site conditions

• must be calibrated for different climate and

phytogeographic regions

• not suitable when not there (e.g. ‘black deserts’)

Proxy: Vegetation

Towards GESTs: Vegetation-forms

Integration of flora and environment

- Species groups

- Presence and absence as indicator

site factor gradient

species groups

site factor classes

subunits 1

Water level class long-term median water level (cm)

wet season dry season

7+ upper sublitoral +250 to +140 +250 to +140

6+ lower eulitoral +150 to +10 +140 to +0

5+ wet (upper eulitoral) +10 to -5 +0 to -10

4+ very moist -5 to -15 -10 to -20

3+ moist -15 to -35 -20 to -45

2+ moderately moist -35 to -70 -45 to -85

2- moderately dry Water supply deficiency: < 60 l/m²

3- dry Water supply deficiency: 60–100 l/m²

4- very dry Water supply deficiency: 100–140 l/m²

5- extremely dry Water supply deficiency: > 140 l/m²

Water level classes (Wasserstufen)

GESTs:

Greenhouse gas Emission Site Types

Assessing rewetting

• N2O fluxes from drained peatlands very erratic

• N2O fluxes from rewetted peatlands negligible

• N2O fluxes can only decline upon rewetting

• reduction cannot be quantified

• disregard N2O: conservative estimate of reductions

Ostrovskoje: GESTs

A: 2009

B: 2039 Baseline

C: 2039 Wiedervernässung

A: 7343 t CO2-eq / J

B: 7933 t CO2-eq / J

C: 3779 t CO2-eq / J

Rewetting

• hydrologic analysis necessary:

which sub-area will become how wet ?

• CH4 emissions may become very high

• but unlikely higher than previous CO2 emissions

Complication: methane spike after rewetting

plants not adapted to wet conditions will die off

labile carbon pool anoxic conditions methane

direct flux measurements rare or lacking

avoid: remove plants, possibly even enriched upper soil

Complication: nutrient enriched soils

Large methane fluxes may persist (how long ?)

2005 2006 2007

kg CH4 ha-1 a-1 2521 4934 2376

Augustin & Chojnicki, 2008

additional problem: litter import

Peatlands contain a lot of carbon

Tollund Man, Denmark

peatlands are much more than just carbon…

avoid one-dimensional approach to rewetting

• biodiversity

• water retention

• nutrient retention

• local cooling

• tourism

• production (paludicultures)

and make it wet !

Peatland management impacts on carbon/climate regulation - international evidence

Education