Changes of the CO2 and CH4 production potential of rewetted fens in the perspective of temporal vegetation shifts

[摘要] Rewetting of long-term drained fens often results in the formation ofeutrophic shallow lakes with an average water depth of less than 1 m. Thisis accompanied by a fast vegetation shift from cultivated grasses viasubmerged hydrophytes to helophytes. As a result of rapid plant dying anddecomposition, these systems are highly dynamic wetlands characterised by ahigh mobilisation of nutrients and elevated emissions of CO₂ andCH₄. However, the impact of specific plant species on these phenomena isnot clear. Therefore we investigated the CO₂ and CH₄ production dueto the subaqueous decomposition of shoot biomass of five selected plantspecies which represent different rewetting stages (Phalarisarundinacea, Ceratophyllum demersum, Typha latifolia,Phragmites australis and Carex riparia) during a 154 daymesocosm study. Beside continuous gas flux measurements, we performed bulkchemical analysis of plant tissue, including carbon, nitrogen, phosphorusand plant polymer dynamics. Plant-specific mass losses after 154 days rangedfrom 25% (P. australis) to 64% (C. demersum).Substantial differences were found for the CH₄ production with highestvalues from decomposing C. demersum (0.4 g CH₄ kg⁻¹ dry massday) that were about 70 times higher than CH₄ production from C.riparia. Thus, we found a strong divergence between mass loss of the litterand methane production during decomposition. If C. demersum as ahydrophyte is included in the statistical analysis solely nutrient contents(nitrogen and phosphorus) explain varying greenhouse gas production of the differentplant species while lignin and polyphenols demonstrate no significant impactat all. Taking data of annual biomass production as important carbon sourcefor methanogens into account, high CH₄ emissions can be expected to lastseveral decades as long as inundated and nutrient-rich conditions prevail.Different restoration measures like water level control, biomass extractionand top soil removal are discussed in the context of mitigation of CH₄emissions from rewetted fens.

[学科分类] 地球化学与岩石