Greenhouse gas GHG emissions from rewetted peatlands studying

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

Importance of peatlands (worldwide) • 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 German peatlands a to ni Es la nd Ire nd an y Po la G er m do m Ki ng ru s U ni te d Be la or w ay n N ed e Sw Fi nl an d GHG balance [Gg CO 2 -equ] • 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) 25000 • drained peatlands emit 4. 5% of the total 20000 15000 German GHG 10000 emissions 5000 • in EU-25: Germany 0 is largest emitter of -5000 GHG from peatlands (Drösler et al. 2008)

Greenhouse gases (GHG) in peatlands GHG balance is determined by production and consumption of CO 2, CH 4 and N 2 O Peat profile Consumption Production Soil surface Aerobic CH 4 Capillary fringe Anaerobic N 2 O CO 2 organic substrate Water table

Studying GHG fluxes in German peatlands • Integrative project “Climate mitigation via peatland management” (2006 -2010) TG 3 TG 1 • financed by BMBF • Aim: TG 2 TG 4 – 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) TG 5 TG 6

GHG balance [t CO 2 -equ. ha-1 a-1] Parameter influencing the climate impact of fen and bogs -1 ] -1 a q h u. Mea n wa ter ta ble [ cm] C ex rt o p [ O C t -e 2 a

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 prior to rewetting / inundation (2004) • 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

Sampling site inundation (04/2005) 08/2008 prior to rewetting / inundation (2004) inundation (11/2005) inundation (06/2006) 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)

Incubation & parameter measured long incubation short incubation sampling prior rewetting post rewetting substrates incubated duration peat from different soil depths upper peat layer only / differing (upper, middle, lower peat in the amount of fresh plant litter layer) or roots present (organic sediment, peat with roots, peat only) long (363 days) short (53 days) conditions constant temperature, no light, water-saturated conditions measurement CO 2 und CH 4 emissions from substrate surface analysis of pore water chemistry

Results: short incubation

Results: long 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

Management options to avoid high CH 4 emissions CO 2, CH 4, N 2 O Renaturation: flooded Permanendly flooded Renaturation: flooded slightly drained Renaturation: flooded Alternation of dry and flooded periods

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?

Sampling site extensively managed meadow (sedges) intensively managed meadow (grass) • 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 Net ecosystem exchange (NEE) water level -5 cm intensively managed extensively managed water level raised stepwise (-30 +5 cm) temperature level 23°C PAR = 915 µmol m-2 s-1

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

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

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

Results: N 2 O emissions intensively managed N 2 O flux [mg C m-2 h-1] extensively managed Incubation period [days] 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 (Rref, E 0, 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, Ro. Ma, Spec. Lab, students, diploma student Jan Heinichen …. Angelika Thuille: supervision of experiment, evaluation and analysis of CH 4 / N 2 O data Annette Freibauer: Ph. D 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

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

Vegetation development in peat cores