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 ~ Mio. t C 80% of German peatlands are used in agriculture (  drainage  changes in GHG fluxes) Importance of German peatlands Finland Sweden Norway Belarus United Kingdom Germany Poland Ireland Estonia GHG balance [Gg CO 2 -equ] (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 CO 2, CH 4 and N 2 O Aerobic Anaerobic Production Water table Capillary fringe Consumption Soil surface CO 2 N2ON2OCH 4 Peat profile organic substrate

Studying GHG fluxes in German peatlands Integrative project “Climate mitigation via peatland management” ( ) financed by BMBF TG2 TG1 TG 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 GHG balance [t CO 2 -equ. ha -1 a -1 ] Mean water table [cm] C export [t CO 2 -equ. ha -1 a -1 ]

Effect of substrate on GHG exchange Site „Zarnekow“  high CH 4 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 CH 4 emissions (  high climate impact)? –When after inundation do high CH 4 emissions occur? Hypothesis: –Litter from recently died-off plants causes high CH 4 emissions

Sampling site Fen: Polder Zarnekow (Mecklenburg-Vorpommern) Drainage in 18 th century, use as grassland (extensive in 19 th, intensive in 20 th century) rewetting in Oct 2004  inundation prior to rewetting / inundation (2004)

Sampling site Vegetation: dominated by reed canary grass (Phalaris arundinacea)  died off during 1 st year after rewetting/inundation  during 2 nd 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 CO 2 und CH 4 emissions from substrate surface  analysis of pore water chemistry

Results: short incubation

Results: long incubation

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 CO 2 and CH 4 emissions peat (without any fresh litter): low potential upper peat layer (peat with C from rhizodeposition): slow, continuous emission of CO 2 ; retarded start of methanogenesis (>150 days) What is the reason for high CH 4 emissions? vegetation is not adapted to inundation  died off  accumulation of plant litter  high potential for CH 4 production When after inundation do high CH 4 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 CO 2, CH 4, N 2 O Renaturation: flooded Renaturation: flooded Permanendly flooded Alternation of dry and flooded periods Management options to avoid high CH 4 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 CO 2 exchange affected by changing water level? At which water level do significant CH 4 emissions start? Does a dynamic water level reduce CH 4 emissions? Trade-off between N 2 O and CH 4 emissions at dynamic water level (gradient oxic/anoxic  ideal conditions for denitrification) –How could potentially high CH 4 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

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) CO 2 exchange CH 4 and N 2 O emissions Radiation (PAR) Air temperature Soil temperature

Results: CO 2 exchange temperature level 23°C PAR = 915 µmol m -2 s -1 water level raised stepwise (-30  +5 cm) Net ecosystem exchange (NEE) extensively managed intensively managed water level -5 cm

Results: CO 2 exchange temperature level 23°C PAR = 915 µmol m -2 s -1 water level raised stepwise (-30  +5 cm) Gross primary production (GPP) intensively managed extensively managed Ecosystem respiration (R eco ) water level +5 cm

Results: CH 4 emissions extensively managedintensively managed Incubation period [days] CH 4 flux [mg C m -2 h -1 ] water level raised stepwise (-30  +5 cm)

Results: CH 4 emissions water level in cycles (-30  +5 cm) intensively managed CH 4 flux [mg C m -2 h -1 ] Incubation period [days]

Results: N 2 O emissions extensively managedintensively managed Incubation period [days] N 2 O flux [mg C m -2 h -1 ] water level raised stepwise (-30  +5 cm)

Conclusions How is the GHG exchange affected by water level change? CO 2 Stepwise raising the water level: continuous decrease of ecosystem respiration and gross primary production CH 4 Emissions increase exponentially at a water level of -5 cm Significantly lower methane emissions when flooding periods are interrupted by short dry periods N 2 O In general: very low emissions (also at dynamic water level!)

Conclusions How could potentially high CH 4 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 (R ref, E 0, GP max, 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 CH 4 / N 2 O data Annette Freibauer: PhD supervisor Gerhard Schöfl: support in preparation, evaluation and analysis of CO 2 data

Thank you for your attention !

CO 2 data: modelling parameter extensive intensive extensive

Results: Redox potential in 5 soil depths 5 cm 10 cm soil depth 15 cm 20 cm 30 cm

Vegetation development in peat cores