peatland management impacts on carbon/climate regulation - international evidence
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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)
t C
O2·h
a-1
·y-1
after Couwenberg et al. (2011)
-10
0
10
20
30
40
50
60
70
-140 -120 -100 -80 -60 -40 -20 0 20 40
r2 = 0.68, p < 0.01
-10
0
10
20
30
40
50
60
70
-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
mean annual water level (cm)
t C
O2·h
a-1
·y-1
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.
0
20
40
60
80
100
-100 -80 -60 -40 -20 0 20 40 60
mean annual water level (cm)
kg
N2O
·ha
-1·y
-1
0
100
200
300
400
500
600
-100 -80 -60 -40 -20 0 20 40
mean annual water level (cm)
kg
CH
4·h
a-1
·y-1
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
Couwenberg et al. (2010)
Tropical; Temperate; ∆ Boreal
0
1
2
3
CH
4 e
mis
sio
n [
mg
m-2
h-1
]
-0,5
0
5
10
15
-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
0
100
200
300
400
500
600
-100 -80 -60 -40 -20 0 20 40
mean annual water level (cm)
kg
CH
4·h
a-1
·y-1
CH4 emissions from temperate European peatlands
WL is not a quantitatively precise proxy
Couwenberg et al. (2011)
0
100
200
300
400
500
600
-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0
mean annual water level (cm)
kg
CH
4·h
a-1
·y-1
CH4 emissions from temperate European peatlands
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
CH4 emissions from temperate European peatlands
Direct flux measurements (annual flux): vegetation
After Drösler (2005)
0
100
200
300
400
500
600
700
800
0 500 1000 1500 2000 2500
aerenchymous leaves (n m-2)
kg
CH
4·h
a-1
·y-1
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
1 2
2
3 4 5
1 2
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 !
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