Water level, vegetation composition, and plant productivity explain greenhouse gas fluxes in temperate cutover fens after inundation

摘要

Peat extraction leaves a land surface with a strong relief of deep cutover areas and higher ridges. Rewetting inundates the deep parts, while less deeply extracted zones remain at or above the water level. In temperate fens the flooded areas are colonized by helophytes such as iEriophorum angustifolium/i, iCarex/i spp., iTypha latifolia/i or iPhragmites australis/i dependent on water depth. Reeds of iTypha/i and iPhragmites/i are reported as large sources of methane, but data on net COsub2/sub uptake are contradictory for iTypha/i and rare for iPhragmites/i. Here, we analyze the effect of vegetation, water level and nutrient conditions on greenhouse gas (GHG) emissions for representative vegetation types along water level gradients at two rewetted cutover fens (mesotrophic and eutrophic) in Belarus. Greenhouse gas emissions were measured campaign-wise with manual chambers every 2 to 4 weeks for 2 years and interpolated by modelling. brbr All sites had negligible nitrous oxide exchange rates. Most sites were carbon sinks and small GHG sources. Methane emissions generally increased with net ecosystem COsub2/sub uptake. Mesotrophic small sedge reeds with water table around the land surface were small GHG sources in the range of 2.3 to 4.2?t?COsub2/sub?eq.?hasup?1/sup?yrsup?1/sup. Eutrophic tall sedge – iTypha latifolia/i reeds on newly formed floating mats were substantial net GHG emitters in the range of 25.1 to 39.1?t?COsub2/sub?eq.?hasup?1/sup?yr. They represent transient vegetation stages. iPhragmites/i reeds ranged between ?1.7 to 4.2?t?COsub2/sub?eq.?hasup?1/sup?yrsup?1/sup with an overall mean GHG emission of 1.3?t?COsub2/sub?eq.?hasup?1/sup?yrsup?1/sup. The annual COsub2/sub balance was best explained by vegetation biomass, which includes the role of vegetation composition and species. Methane emissions were obviously driven by biological activity of vegetation and soil organisms. brbr Shallow flooding of cutover temperate fens is a suitable measure to arrive at low GHG emissions. iPhragmites australis/i establishment should be promoted in deeper flooded areas and will lead to moderate, but variable GHG emissions or even occasional sinks. The risk of large GHG emissions is higher for eutrophic than mesotrophic peatlands. Nevertheless, flooding of eutrophic temperate fens still represents a safe GHG mitigation option because even the hotspot of our study, the floating tall sedge – iTypha latifolia/i reeds, did not exceed the typical range of GHG emissions from drained fen grasslands and the spatially dominant iPhragmites australis/i reed emitted by far less GHG than drained fens.