Water level, vegetation composition, and plant productivity explain greenhouse gas fluxes in temperate cutover fens after inundation
- 1Thünen Institute of Climate–Smart Agriculture, Braunschweig, Germany
- 2Institute for Landscape Biogeochemistry, ZALF e.V., Müncheberg, Germany
- 3Scientific and Practical Centre of the National Academy of Sciences of Belarus for Biological Resources, Minsk, Belarus
- 4Institute for Nature Management of the National Academy of Sciences of Belarus, Minsk, Belarus
- 5Institute of Botany and Landscape Ecology, Ernst-Moritz-Arndt University, Greifswald, Germany
- 6Michael Succow Foundation, Greifswald, Germany
- 7Institute of Soil Landscape Research, ZALF e.V., Müncheberg, Germany
Abstract. 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 Eriophorum angustifolium, Carex spp., Typha latifolia or Phragmites australis dependent on water depth. Reeds of Typha and Phragmites are reported as large sources of methane, but data on net CO2 uptake are contradictory for Typha and rare for Phragmites. 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.
All sites had negligible nitrous oxide exchange rates. Most sites were carbon sinks and small GHG sources. Methane emissions generally increased with net ecosystem CO2 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 CO2 eq. ha−1 yr−1. Eutrophic tall sedge – Typha latifolia reeds on newly formed floating mats were substantial net GHG emitters in the range of 25.1 to 39.1 t CO2 eq. ha−1 yr. They represent transient vegetation stages. Phragmites reeds ranged between −1.7 to 4.2 t CO2 eq. ha−1 yr−1 with an overall mean GHG emission of 1.3 t CO2 eq. ha−1 yr−1. The annual CO2 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.
Shallow flooding of cutover temperate fens is a suitable measure to arrive at low GHG emissions. Phragmites australis 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 – Typha latifolia reeds, did not exceed the typical range of GHG emissions from drained fen grasslands and the spatially dominant Phragmites australis reed emitted by far less GHG than drained fens.