Changes of the CO<sub>2</sub> and CH<sub>4</sub> production potential of rewetted fens in the perspective of temporal vegetation shifts

Abstract

Abstract. Rewetting of long-term drained fens often results in the formation of eutrophic shallow lakes with an average water depth of less than 1 m. This is accompanied by a fast vegetation shift from cultivated grasses via submerged hydrophytes to helophytes. As a result of rapid plant dying and decomposition, these systems are highly-dynamic wetlands characterised by a high mobilisation of nutrients and elevated emissions of CO2 and CH4. However, the impact of specific plant species on these phenomena is not clear. Therefore we investigated the CO2 and CH4 production due to the subaqueous decomposition of shoot biomass of five selected plant species which represent different rewetting stages (Phalaris arundinacea, Ceratophyllum demersum, Typha latifolia, Phragmites australis, and Carex riparia) during a 154 day mesocosm study. Beside continuous gas flux measurements, we performed bulk chemical analysis of plant tissue, including carbon, nitrogen, phosphorus, and plant polymer dynamics. Plant specific mass losses after 154 days ranged from 25 (P. australis) to 64% (C. demersum). Substantial differences were found for the CH4 production with highest values from decomposing C. demersum (0.4 g CH4 kg−1 dry mass day) that were about 70 times higher than CH4 production from C. riparia. Thus, we found a strong divergence between mass loss of the litter and methane production during decomposition. If C. demersum as a hydrophyte is included in the statistical analysis solely nutrient contents (nitrogen and phosphorus) explain varying GHG production of the different plant species while lignin and polyphenols demonstrate no significant impact at all. Taking data of annual biomass production as important carbon source for methanogens into account, high CH4 emissions can be expected to last several decades as long as inundated and nutrient-rich conditions prevail. Different restoration measures like water level control, biomass extraction and top soil removal are discussed in the context of mitigation of CH4 emissions from rewetted fens.

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

“…While bog ecosystems benefit from high water tables as Sphagnum mosses are able to follow the water level and even raise it themselves, in fens this would not happen. Flooded plant litter will provide carbon and nitrogen and cause even higher emissions ( Hahn‐Schöfl et al., ; Hahn et al, ; Zak et al, ).…”

Carbon emission along a eutrophication gradient in temperate riverine wetlands: effect of primary productivity and plant community composition

“…Another possible explanation is the capacity of vascular plants with floating leaves to transport oxygen through their stems and roots, which favours CH 4 oxidation (Sand-Jensen, Prahl & Stokholm, 1982;Smits et al, 1990;Ribaudo et al, 2012). Lastly, the higher variability in diffusive CH 4 emissions above floating vascular plants could be related to the differences among species in CH 4 transport efficiency, CH 4 oxidation and/or production of substrates for methanogens (Sch€ utz et al, 1991;Kankaala et al, 2003a;Zak et al, 2015). Lastly, the higher variability in diffusive CH 4 emissions above floating vascular plants could be related to the differences among species in CH 4 transport efficiency, CH 4 oxidation and/or production of substrates for methanogens (Sch€ utz et al, 1991;Kankaala et al, 2003a;Zak et al, 2015).…”