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

Abstract

Abstract. Peatland restoration by inundation of drained areas can alter local greenhouse gas emissions as CO 2 and CH 4 . 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 CO 2 and CH 4 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 CO 2 and CH 4 production and emission.The position in the soil profile of the pre-existing drained peat substrate affected initial rates of anaerobic CO 2 production subsequent to flooding, with the uppermost peat layer producing the greatest specific rates of CO 2 evolution. CH 4 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 CO 2 (maximum of 412 mg C d −1 kg −1 C) and CH 4 production (788 mg C d −1 kg −1 C) were observed in a new sediment layer that accumulated over the 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 CO 2 (max. 28 mg C d −1 kg −1 C) and CH 4 (max. 34 mg C d −1 kg −1 C) production that were Correspondence to: M. Hahn-Schöfl (maria.hahn@yahoo.de) 10-20 times lower than for the new sediment layer and were comparable to those of a newly flooded upper peat layer. Lowest rates of anaerobic CO 2 and CH 4 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 CH 4 production, whereas peat without any fresh plant-derived material is relatively inert. Significant anaerobic CO 2 and CH 4 production in peat only occurs when some labile organic matter is available, e.g. from remaining roots or root exudates.

Nitrogen mineralization and gaseous nitrogen losses from waterlogged and drained organic soils in a black alder (&lt;i&gt;Alnus glutinosa&lt;/i&gt; (L.) Gaertn.) forest

“…Due to temporal pseudoreplication of time series data (N 2 O field measurements) and repeated measurements of vessels in the incubation experiment, we applied linear mixed effect models (Crawley 2007;Eickenscheidt et al, 2011;Hahn-Schöfl et al, 2011). For N 2 O field measurements we set up a basic model with site type as a fixed effect and the spatial replication (individual plot) nested in time as a random effect.…”

Effect of reed canary grass cultivation on greenhouse gas emission from peat soil at controlled rewetting

“…Plant roots release organic compounds to soil, which are easily available carbon sources to anaerobic microbial consortia eventually producing the precursors (acetate or H 2 / CO 2 ) for methanogenesis (Ström et al, 2003). Such fresh organic carbon is suggested to be an important substrate for methanogenesis as peat carbon is shown to be more recalcitrant to anaerobic decomposition (Tuittila et al, 2000;Hahn-Schöfl et al, 2011).…”

Large-scale regionalization of water table depth in peatlands optimized for greenhouse gas emission upscaling

“…This can be achieved by transforming WL into a transformed variable WL t , which shows a linear relationship with GHG emissions. The sensitivity of greenhouse gas emissions to water level has been analyzed in several laboratory and field experimental and monitoring studies (Berglund and Berglund, 2011;Drösler et al, 2011;Hahn-Schöfl et al, 2011;LeiberSauheitl et al, 2014;Moore and Roulet, 1993;Moore and Dalva, 1993;van den Akker et al, 2012). General trends are a strong increase of methane (CH 4 ) emissions for annual mean water levels of approximately > −0.1 m and an increase of CO 2 emissions for water levels < −0.1 m with a trend similar to a saturation function that levels out approximately between −0.4 and −0.8 m (Fig.…”