Drösler, M.

Hommeltenberg, J.

Mauder, M.

Schmid, H.P.

Steinbrecher, R.

Schmid, H. P.

KITopen

KIT – Universität des Landes Baden-Württemberg undnationales Forschungszentrum in der Helmholtz-GemeinschaftNatural and Drained Temperate Bog-Forest Ecosystems: Carbon Sink or Carbon Source?Standorte:Janina Hommeltenberg1), Rainer Steinbrecher1), Matthias Drösler2), Matthias Mauder1), Hans Peter Schmid1), 1) Karlsruhe Institute of Technology KIT, Institute of Meteorology and Climate Research IMK-IFU, Garmisch-Partenkirchen2) University of Applied Sciences Weihenstephan-Triesdorf, Chair of Vegetation-Ecology, Freisingjanina.hommeltenberg@kit.eduIntroductionGenerally drained peatlands are considered as CO2 sources and naturalpeatlands as CO2 sinks. However, to date sound greenhouse gas emissionfactors of peatland forests of the temperate climate zone are still rare.This study aims to shed more light on the GHG exchange of peatland forests inthe temperate, pre-alpine region of southern Germany. Therefore, we compareddirectly the CO2 exchange of a natural bog-pine forest (Schechenfilz) and of abog drained for forestry (Mooseurach), by eddy covariance measurements overtwo annual cycles (July 2010 to June 2012). In addition, the CH4 exchange isstudied at the natural site since summer 2012, to account for all relevantgreenhouse gases. Both sites are separated only by a few kilometers, thusweather conditions and peat-formation history are the same, and differences inthe GHG exchange are mainly attributable to differences in land use, land usehistory and management.Differences and similarities in the CO2 budgets and of the component fluxesrespiration (Reco) and gross primary production (GPP) have been determined.Furthermore, most relevant driving factors for methane fluxes at the natural sitemust be identified and finally it must be examined whether methane emissionsoffset the expected radiative cooling effect, caused by CO2 uptake.Furthermore, for meaningful carbon budgets of drained and managed peat-forest sites the total carbon accumulation of the trees as well as the carbon lossfrom the peat in the same time frame have to be taken into account.Conclusion• Two years of eddy covariance measurements indicate larger CO2 uptakeat the drained site However, respiration rates are two times larger at the drained site At the natural site the CO2 balance is more robust than at the drained site• In the long-term perspective:carbon losses from the drained soil are three times stronger than thecarbon uptake of the trees over a period of 50 yearsStudy sitescFig.1 a) Aerial image of the peatland forests Schechenfilz and Mooseurach, source: Google Earth; b) Distribution of peatland in Germany (grey-shaded) and location of the study sites of the project „organic soils“; c) measurement tower at the drained spruceforest Mooseurach and d) measurement towers at the natural bog-pine forest at the Schechenfilz site.Lake StarnbergSeeshaupt Königsdorf10 kmcMooseurach:drainedNorway spruce (~50 years)Canopy height: 21 mLeaf area index (LAI): 5.9Peat thickness: ~ 3.4 mMeasurement height: 30 mbMooseurachSchechenfilzadSchechenfilz:near-naturalBog-pine (differ in age)Canopy height: 2 mLeaf area index (LAI): 2.3Peat thickness: ~ 5.1 mMeasurement height: 6 mCarbon dioxide exchange Methane exchange at the natural site Schechenfilz• CO2 uptake at the drained site is 2.5to 4 times larger than at the naturalbog site: -130 ±41 and -300 ±74 g C m-2a-1vs. -53 ±28 and -73 ±38 g C m-2 a-1Fig . 2 Annual sums of GPP, Reco, NEE at a) Schechenfilz  and b) Mooseurach.But:• measurements are just a „snapshot“of two years• Estimated carbon accumulation ofthe spruces in the last 50 yearsis 86 t C ha-1 (biometric estimation)• Roughly estimated carbon loss ofthe peat is 244 t C ha-1at the drainedsite in the same timeFig. 3 Comparison of annual CO2 exchange from July 2010-June 2014 at a) Schechenfilz and from July 2010 to June 2012 at b) Mooseurach.Schechenfilz Similar CO2 uptake in four years Robust behaviorMooseurach High variability, strong influence of environmental drivers More sensitiveFig. 5 Annual cumulative NEE, CH4 and GWP exchange and the daily sum of methane exchange from July 2012-June 2014.• Mean daily methaneexchange correlates wellwith soil temperature,except for water tabledrawdown events• The natural bog-pine siteis a weak but robust CO2sink, but a minor source ofCH4 Neutral global warmingpotential (GWP) balanceof the 100-yr time horizon(-50 and+32 g [CO2-eq.] m-2a-1)• Extraordinary water tabledrawdown has a strongimpact on the carbon andGWP balance To compensate the former carbon loss, the spruces have to fix carbon for another100 years at the current rate• Considering a realistic life cycle of a spruce forest (60 to 100 years), the drainedspruce forest site is a greenhouse gas (GHG) source• At the natural site methane exchange correlates best with soil temperature, exceptduring an extraordinary dry period of six weeks• Currently, in terms of its global warming potential (GWP), the natural bog-pine sitecould be considered as neutral, while the drained site is a significant GHG sinkFig. 4 Mean daily methane exchange vs. mean daily air temperature, soil temper-ature, water level, PPFD and GPP. Red dots mark CH4 fluxes at low water tables.c

Natural and drained temperate bog-forest ecosystems: Carbon sink or carbon source?

https://publikationen.bibliothek.kit.edu/220098736/3816752

Natural and drained temperate bog-forest ecosystems: Carbon sink or carbon source?

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