The greenhouse gas balance of a drained fen peatland is mainly controlled by land-use rather than soil organic carbon content

Abstract

Abstract. Drained organic soils are considered as hotspots for greenhouse gas (GHG) emissions. Particularly arable lands and intensively used grasslands have been regarded as the main producers of carbon dioxide (CO2) and nitrous oxide (N2O). However, GHG balances of former peatlands and associated organic soils not considered as peatland according to the definition of the Intergovernmental Panel on Climate Change (IPCC) have not been investigated so far. Therefore, our study addressed the question to what extent the soil organic carbon (SOC) content affects the GHG release of drained organic soils under two different land-use types (arable land and intensively used grassland). Both land-use types were established on a mollic Gleysol (named Cmedium) as well as on a sapric Histosol (named Chigh). The two soil types significantly differed in their SOC contents in the topsoil (Cmedium: 9.4–10.9% SOC; Chigh: 16.1–17.2% SOC). We determined GHG fluxes (CO2, N2O and methane (CH4)) over a period of 2 years. The daily and annual net ecosystem exchange (NEE) of CO2 was determined with the closed dynamic chamber technique and by modeling the ecosystem respiration (RECO) and the gross primary production (GPP). N2O and CH4 were determined by the close chamber technique. Estimated NEE of CO2 significantly differed between the two land-use types with lower NEE values (−6 to 1707 g CO2–C m−2 yr−1) at the arable sites and higher values (1354 to 1823 g CO2–C m−2 yr−1) at the grassland sites. No effect on NEE was found regarding the SOC content. Significantly higher annual N2O exchange rates were observed at the arable sites (0.23–0.86 g N m−2 yr−1) compared to the grassland sites (0.12–0.31 g N m−2 yr−1). Furthermore, N2O fluxes from the Chigh sites significantly exceeded those of the Cmedium sites. CH4 fluxes were found to be close to zero at all plots. Estimated global warming potential, calculated for a time horizon of 100 years (GWP100) revealed a very high release of GHGs from all plots ranging from 1837 to 7095 g CO2 eq. m−2 yr−1. Calculated global warming potential (GWP) values did not differ between soil types and partly exceeded the IPCC default emission factors of the Tier 1 approach by far. However, despite being subject to high uncertainties, the results clearly highlight the importance to adjust the IPCC guidelines for organic soils not falling under the definition, to avoid a significant underestimation of GHG emissions in the corresponding sectors of the national climate reporting. Furthermore, the present results revealed that mainly the land-use including the management and not the SOC content is responsible for the height of GHG exchange from intensive farming on drained organic soils.

Divergent NEE balances from manual‐chamber CO2 fluxes linked to different measurement and gap‐filling strategies: A source for uncertainty of estimated terrestrial C sources and sinks?

“…Manual closed chambers (0.75 m × 0.75 m × 0.5 m) were used in non‐steady‐state flow‐through mode ( Livingston and Hutchinson , ) to estimate R ECO (opaque chambers) and NEE of CO 2 (transparent chambers). Chambers were constructed and instrumented as described by Drösler () and used in various previous studies ( e.g ., Elsgaard et al, ; Beetz et al, ; Leiber‐Sauheitl et al, ; Eickenscheidt et al, ; Hoffmann et al, ). CO 2 concentrations in the chamber headspace were determined with an infrared gas analyzer at 3‐s intervals (LI‐820, LI‐COR, USA) during a measurement period of 180 s after chamber deployment.…”

Dependence of spectral characteristics on parameters describing CO2 exchange between crop species and the atmosphere

“…For each measurement campaign, relationships between measured R eco and air and soil temperatures were found (Lloyd and Taylor, 1994) as well as between GEP and PARi (Michaelis-Menten, 1913). The protocols of data analysis and flux modelling applied were identical to those in Eickenscheidt et al (2015). The obtained relationships were used together with model CO 2 fluxes in the periods between the measurement campaigns.…”

Surface interpolation of environmental factors as tool for evaluation of the occurrence of high methane and nitrous oxide fluxes

“…Usually the occurrence of significant methane and nitrous oxide fluxes is much more variable compared to carbon dioxide (CO 2 ) and is rather event‐like. It is common that the majority of the fluxes of methane and nitrous oxide along the year are close to zero and only emissions from few periods determine the whole annual balance ( Koch et al, ; Beetz et al, ; Beyer et al, ; Eickenscheidt et al, ). This leads to a skewed distribution of flux values (Fig.…”