Greenhouse gas (GHG) emissions from rewetted peatlands:
studying influencing factors by
incubation experiments Maria Hahn-Schöfl
Definitions
• Peatland = all soils with organic layer > 30 cm and water saturation at least during part of the year
• Fen = peatland influenced by groundwater
• Bog = peatland influenced by rainwater (raised above groundwater influence)
• Mire = undisturbed peatland
• small area: peat cover = 3% of land area (7% in EU-25)
• storage of large amount of C: ~ 30% of soil C ~ 70% of atmospheric C
Importance of peatlands (worldwide)
• German peatlands = 3% of EU land area• total C stored ~ 1070 - 2400 Mio. t C• 80% of German peatlands are used in agriculture
( drainage changes in GHG fluxes)
Importance of German peatlands
-5000
0
5000
10000
15000
20000
25000
Finlan
d
Sweden
Norway
Belaru
s
United
King
dom
Germ
any
Poland
Irelan
d
Estonia
GH
G b
ala
nc
e [
Gg
CO
2-e
qu
]
(Drösler et al. 2008)
• drained peatlands emit 4.5% of the total German GHG emissions
• in EU-25: Germany is largest emitter of GHG from peatlands
Greenhouse gases (GHG) in peatlands
GHG balance is determined by
production and consumption of CO2, CH4 and N2O
Aerobic
Anaerobic
Production
Water table
Capillary fringe
ConsumptionSoil surface
CO2N2OCH4
Peat profile
organic substrate
Studying GHG fluxes in German peatlands
• Integrative project “Climate mitigation via peatland management” (2006-2010)
• financed by BMBF
TG2
TG1TG
3
TG4
TG5
TG6
• Aim:– Field measurements of GHG
fluxes on 6 German peatlands differing in management and water table position (over 2 years)
– Incubation experiments: to gain more knowledge on processes (manipulation of e.g. water table, radiation, temperature, substrate)
Parameter influencing the climate impact
of fen and bogs
-10
-100
010
1020
2030
3040
4050
5060
60
EF
-GW
P:t
_C
O2
-ae
qu
iv h
a-1
a-1
EF
-GW
P:t
_C
O2
-ae
qu
iv h
a-1
a-1
bmbf_nutzungskategorien_gesamtfluesse_20100626_for_tc.xls : (2)Original_ZRank 59 Eqn 2058 z=a+bx+cx^2+EXTRVALY(d,e,f)
r^2=0.71883037 DF Adj r^2=0.70276354 FitStdErr=8.3958029 Fstat=54.199324a=30.164878 b=5.7259477 c=-0.34967194 d=-31.485433 e=1.6308593 f=-22.002118
TH
G-B
ilanz
[ t C
O2
Äqu
iv.
ha-1
a-1
]
G
HG
ba
lan
ce [t
CO
2-e
qu. h
a-1 a
-1]
Mean water table [cm] C export
[t CO 2
-equ. h
a-1 a
-1 ]
Effect of substrate on GHG exchange
• Site „Zarnekow“ high CH4 emissions after rewetting why ?
• Incubation experiments without vegetation• Questions to be answered:
– What is the main substrate for microbial processes?
– What is the reason for high CH4 emissions ( high climate impact)?
– When after inundation do high CH4 emissions occur?
• Hypothesis: – Litter from recently died-off plants causes high CH4
emissions
Sampling site
• Fen: Polder Zarnekow (Mecklenburg-Vorpommern)• Drainage in 18th century, use as grassland (extensive in 19th,
intensive in 20th century)• rewetting in Oct 2004 inundation
prior to rewetting / inundation (2004)
Sampling site
Vegetation: dominated by reed canary grass (Phalaris arundinacea) died off during 1st year after rewetting/inundation during 2nd year: high nutrient concentrations growth of water plants
(Ceratophyllum, Lemna sp.) died off formation of organic sediment layer (= plant litter + sand)
prior to rewetting / inundation (2004)inundation (04/2005) inundation (11/2005)
inundation (06/2006)
08/2008
short (53 days)long (363 days)duration
constant temperature, no light, water-saturated conditionsconditions
upper peat layer only / differing in the amount of fresh plant litter or roots present (organic sediment, peat with roots, peat only)
peat from different soil depths (upper, middle, lower peat layer)
substrates incubated
post rewettingprior rewettingsampling
short incubation
long incubation
Incubation & parameter measured
measurement CO2 und CH4 emissions from substrate surface
analysis of pore water chemistry
Results: short incubation
CO2
Incubation duration [days]
0 10 20 30 40 50
[mg
C d
-1 k
g-1
C]
0
100
200
300
400
organic sedimentpeat with rootspeat only
CH4
Incubation duration [days]
0 10 20 30 40 50[m
g C
d-1
kg-1
C]
0
200
400
600
800
Results: long incubation
CO2
Incubation duration [days]0 100 200 300
[mg
C d
-1 k
g-1 C
]
0
50
100
150
200
250
upper peat layermiddle peat layerlower peat layerorganic sedimentpeat with rootspeat only
CH4
Incubation duration [days]
0 100 200 300[m
g C
d-1
kg-1
C]
0
50
100
150
200
250
Results: long incubation
CO2
Incubation duration [days]
0 100 200 300
[mg
C d
-1 k
g-1 C
]
0
10
20
30
upper peat layermiddle peat layerlower peat layerpeat with rootspeat only
CH4
Incubation duration [days]
0 100 200 300[m
g C
d-1
kg-1
C]
0
20
40
60
concentration of sulfate in the pore water
Incubation duration [days]
0 100 200 300
Su
lfat
[mM
]
0
2
4
6
8
10
upper peat layermiddle peat layerlower peat layer
modified from Zak & Gelbrecht (2008)
Conclusions
• What is the main substrate for microbial processes? organic sediment (mix of sand + fresh plant litter) substrate for microbial degradation high CO2 and CH4 emissionspeat (without any fresh litter): low potentialupper peat layer (peat with C from rhizodeposition): slow, continuous emission of CO2; retarded start of methanogenesis (>150 days)
• What is the reason for high CH4 emissions?vegetation is not adapted to inundation died off accumulation of plant litter high potential for CH4 production
• When after inundation do high CH4 emissions occur?upper peat layer: rewetting event reaching anaerobiosis (>150 days)organic sediment: immediately (already anaerobic)peat with roots: ~ 3 weeks
Renaturation: flooded
slightly drained
CO2, CH4, N2O
Renaturation: flooded
Renaturation: flooded
Permanendly flooded Alternation of dry and flooded periods
Management options to avoid high CH4 emissions
Effect of water level on GHG exchange
• Incubation experiments of peat cores with vegetation
• Questions to be answered:– How is the GHG exchange affected by water level
change?How is CO2 exchange affected by changing water level?
At which water level do significant CH4 emissions start? Does a dynamic water level reduce CH4 emissions?
Trade-off between N2O and CH4 emissions at dynamic water level (gradient oxic/anoxic ideal conditions for denitrification)
– How could potentially high CH4 emissions be reduced after rewetting?
extensively managed meadow (sedges)
intensively managed meadow (grass)
Sampling site
• Fen: Freisinger Moos (Bayern)• drained; use in agriculture
– extensively managed meadow (sedges)– intensively managed meadow (grass)
• Sampling of intact peat cores with vegetation
Incubation in the climate chamber
PA
R [
µm
ol m
-2 s
-1]
0
500
1000
1500
2000
Air
tem
p [°
C]
10
15
20
25
Time of day [hour]
0.00 4.00 8.00 12.00 16.00 20.00 0.00
Soi
l tem
p at
-2
cm [
°C]
10
15
20
25in climate chamberat sampling site
Parameter measured
• Water level:• rising in steps: - 30 -20 -10 -5 0 (for 1 month)
+5 cm (for 3 months)• in 4 cycles: 1 week dry (-30 cm) 6 weeks flooding (+5
cm)
• CO2 exchange
• CH4 and N2O emissions
• Radiation (PAR)• Air temperature• Soil temperature
Results: CO2 exchange
temperature level 23°CPAR = 915 µmol m-2 s-1water level raised stepwise (-30 +5 cm)
Net ecosystem exchange (NEE)
extensively managed
intensively managed
water level -5 cm
Results: CO2 exchange
temperature level 23°CPAR = 915 µmol m-2 s-1water level raised stepwise (-30 +5 cm)
Gross primary production (GPP)
intensively managed
extensively managed
Ecosystem respiration (Reco)
water level +5 cm
Results: CH4 emissions
Extensive Wiese
Inkubationsdauer [Tage]
0 50 100 150 200 250
CH
4 F
luss
[m
g C
m-2
h-1
]
0
10
20
30
40
23 °C13 °C19 °C
Intensive Wiese
0 50 100 150 200 250
-30 -20 -10 -5 0 +5 -30 -20 -10 -5 0 +5
extensively managed intensively managed
Incubation period [days]
CH
4 flu
x [m
g C
m-2 h
-1]
water level raised stepwise (-30 +5 cm)
Results: CH4 emissions
water level in cycles (-30 +5 cm)
Intensive Wiese - Wasserstand in Zyklen
Inkubationsdauer [Tage]
0 50 100 150 200
CH
4 F
luss
[m
g C
m-2
h-1
]
0
1
2
3 18°C13°C
intensively managed
CH
4 flu
x [m
g C
m-2 h
-1]
Incubation period [days]
Results: N2O emissions
Extensive Wiese
Inkubationsdauer [Tage]0 50 100 150 200 250
N2O
Flu
ss [
mg
N m
-2 h
-1]
0.00
0.05
0.10
0.15
0.20
23 °C19 °C13 °C
-30 -20 -10 -5 0 +5
Intensive Wiese
0 50 100 150 200 250
-30 -20 -10 -5 0 +5
extensively managed intensively managed
Incubation period [days]
N2O
flu
x [m
g C
m-2 h
-1]
water level raised stepwise (-30 +5 cm)
Conclusions
How is the GHG exchange affected by water level change?
• CO2
Stepwise raising the water level: continuous decrease of ecosystem respiration and gross primary production
• CH4
Emissions increase exponentially at a water level of -5 cmSignificantly lower methane emissions when flooding
periods are interrupted by short dry periods• N2O
In general: very low emissions (also at dynamic water level!)
Conclusions
How could potentially high CH4 emissions be reduced after rewetting? risk of high emissions is due to waterlogged conditions and the simultaneous presence substrate for decomposition processes
• no permanent flooding when easily degradable dead organic matter is present or freshly produced by plants – interupt flooding by short dry periods– hold water level at – 10 cm in summer
• avoid accumulation of organic substrate– avoid dying off of present plants (water level)– facilitate colonization by adapted plant
species (e.g. Typha sp., reeds or sedges)– remove fresh plant litter (organic sediment)
Outlook: comparison lab - field
• Comparison of modelling parameter (Rref, E0, GPmax, alpha) work in progress
• Ongoing manipulation experiment in Freisinger Moos by TUM (effect of water level and temperature)
Acknowledgements
Experiments without vegetation: co-operation with ZALF and IGB (Dominik Zak, Jörg Gelbrecht, Jürgen Augustin, Merten Minke)
Incubation of peat cores with vegetation in the climate chamber: technical support by mechanics and electronic workshop, central field instrumentation facility, RoMa, SpecLab, students, diploma student Jan Heinichen ….
Angelika Thuille: supervision of experiment, evaluation and analysis of CH4 / N2O data
Annette Freibauer: PhD supervisor
Gerhard Schöfl: support in preparation, evaluation and analysis of CO2 data
Thank you for your attention !
CO2 data: modelling parameter
Comparison sedges / grass (GPmax and alpha at boTemp2)
GP
max
[mg
C m
-2 h
-1]
-4000
-3000
-2000
-1000
Incubation period [days]
0 50 100 150 200 250
alph
a
-0,3
-0,2
-0,1
sedgesgrass
-30 -20 -10 -5 0 +5 cm
a)
b)
extensive
intensive
Comparison sedges / grass (Rref and E0 at boTemp2)
Rre
f [m
g C
m-2
h-1
]
200
400
600
800
sedgesgrass
Incubation period [days]
0 50 100 150 200 250
E0
[K]
0
200
400
600
-30 -20 -10 -5 0 +5 cm
a)
b)
intensive
extensive
Results: Redox potential in 5 soil
depths
Intensive meadow
Time [Day of experiment]
0 50 100 150 200 250
-600
-400
-200
0
200
400
600
800
1000
Time [Day of experiment]
0 50 100 150 200 250
-600
-400
-200
0
200
400
600
800
1000
Time [Day of experiment]
0 50 100 150 200 250
-600
-400
-200
0
200
400
600
800
1000
Extensive meadow
Time [Day of experiment]
0 50 100 150 200 250
Red
ox
pot
entia
l [m
V]
-600
-400
-200
0
200
400
600
800
1000
Time [Day of experiment]
0 50 100 150 200 250
Red
ox
pot
entia
l [m
V]
-600
-400
-200
0
200
400
600
800
1000
Time [Day of experiment]
0 50 100 150 200 250
Red
ox
pot
entia
l [m
V]
-600
-400
-200
0
200
400
600
800
1000
-30 -20 -10 -5 0 +5 -30 -20 -10 -5 0 +5
-30 -20 -10 -5 0 +5 -30 -20 -10 -5 0 +5
-30 -20 -10 -5 0 +5 -30 -20 -10 -5 0 +5
5 cm
10 cm
soil depth
15 cm
20 cm
30 cm
Vegetation development in peat cores