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