Organic sediment formed during inundation of a degraded fen grassland emits large fluxes of CH<sub>4</sub> and CO<sub>2</sub>

Abstract

Peatland restoration by inundation of drained areas can alter local greenhouse gas emissions by altering rates of CO₂ and CH₄ emissions. Factors that can influence these emissions include the quality and amount of substrates available for anaerobic degradation processes and the sources and availability of electron acceptors. In order to learn about possible sources of high CO₂ and CH₄ emissions from a rewetted degraded fen grassland, we performed incubation experiments that tested the effects of fresh plant litter in the flooded peats on pore water chemistry and CO₂ and CH₄ production and emission. <br><br> The position in the soil profile of the pre-existing drained peat substrate affected initial rates of anaerobic CO₂ production subsequent to flooding, with the uppermost peat layer producing the greatest specific rates of CO₂ evolution. CH₄ production rates depended on the availability of electron acceptors and was significant only when sulfate concentrations were reduced in the pore waters. Very high specific rates of both CO₂ (maximum of 412 mg C d⁻¹ kg⁻¹ C) and CH₄ production (788 mg C d⁻¹ kg⁻¹ C) were observed in a new sediment layer that accumulated over 2.5 years since the site was flooded. This new sediment layer was characterized by overall low C content, but represented a mixture of sand and relatively easily decomposable plant litter from reed canary grass killed by flooding. Samples that excluded this new sediment layer but included intact roots remaining from flooded grasses had specific rates of CO₂ (max. 28 mg C d⁻¹ kg⁻¹ C) and CH₄ (max. 34 mg C d⁻¹ kg⁻¹ C) production that were 10–20 times lower, and were comparable to those of newly flooded upper peat layer. Lowest rates of anaerobic CO₂ and CH₄ production (range of 4–8 mg C d⁻¹ kg⁻¹ C and <1 mg C d⁻¹ kg⁻¹ C) were observed when all fresh organic matter sources (plant litter and roots) were excluded. In conclusion, the presence of fresh organic substrates such as plant and root litter originating from plants killed by inundation has a high potential for CH₄ production, whereas peat without any fresh plant-derived material is relatively inert. Anaerobic CO₂ and CH₄ production in peat only occurs when some labile organic matter is available, e.g. from remaining roots or root exudates

Variation of energy and carbon fluxes from a restored temperate freshwater wetland and implications for carbon market verification protocols

“…Despite the high carbon peat soils found on Twitchell Island, they attributed the lower initial fluxes to the lack of labile fresh plant material, but that in subsequent years the incorporation of rice straw was suggested to increase labile carbon and resultant CH 4 emissions [ Knox et al , ; Hatala et al , ]. Lower CH 4 production was also observed after initial inundation of a degraded fen grassland in NE Germany [ Hahn‐Schofl et al , ]. Here lower values were attributed to the competition between methanogens and iron‐ or sulfate‐reducing bacteria and/or continued aerobic conditions in the upper peat soil layers.…”

Top soil removal reduces water pollution from phosphorus and dissolved organic matter and lowers methane emissions from rewetted peatlands

“…The HD-peat DOM pool is apparently much less available for further processing, at least by methanogenic organisms, than in the detritus mud layer (Hahn-Schoefl et al, 2011).…”

“…Top soil removal (TSR), usually in combination with rewetting, has been proposed as a measure for restoring the nutrient-poor conditions in peatlands (Klimkowska, Van Diggelen, Bakker, & Grootjans, 2007;Patzelt, Wild, & Pfadenhauer, 2001) while mitigating the risk of eutrophication and elevated releases of methane (Hahn-Schoefl et al, 2011;Rasran, Vogt, & Jensen, 2007;Zak, Meyer, et al, 2017). TSR can, however, be a very cost-intensive operation and while there is evidence supporting an accelerated recovery of target vegetation communities following TSR (Klimkowska et al, 2007;Patzelt et al, 2001), little is known regarding how this measure influences the mobilization of P, dissolved organic matter (DOM) and greenhouse gases (GHG) after rewetting of TSR areas.…”

“…This mud layer can increase by 1-2 cm per year (Cabezas, Pallasch, Schoenfelder, Gelbrecht, & Zak, 2014) and consists mainly of detritus from partly decomposed plant biomass (aquatic plants and helophytes). This mud has been considered to be a "hot layer" of carbon turnover (Hahn-Schoefl et al, 2011).…”

“…through chamber system combined with automated gas analysis equipment was used as described in detail byHahn-Schoefl et al (2011).Briefly, a constant air flow of 6 × 10 −3 m 3 /hr (ambient air) was adjusted in the open headspace of the mesocosms. CO 2 and CH 4 emissions from the columns were calculated by measuring ambient air concentrations and concentrations in the air flowing through the headspace of the mesocosms using an infrared multigasmonitor (Typ INNOVA 1312 from INNOVA AirTech Instruments, Ballerup, Denmark).…”