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

Abstract

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 CO 2 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 CO 2 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 CO 2 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 CO 2 eq. ha −1 yr. They represent transient vegetation stages. Phragmites reeds ranged between −1.7 to 4.2 t CO 2 eq. ha −1 yr −1 with an overall mean GHG emission of 1.3 t CO 2 eq. ha −1 yr −1 . The annual CO 2 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.

Methane and Nitrous Oxide Emission Fluxes Along Water Level Gradients in Littoral Zones of Constructed Surface Water Bodies in a Rewetted Extracted Peatland in Sweden

“…A combination of wetland plant cover and high water level, but also non-inundation and high soil temperature, enhanced CH 4 emissions. This is in line with other studies for rewetted fens (e.g., [41]), shallow lakes [81], and rewetted peat extraction sites [45]. The higher CH 4 fluxes observed with increasing temperature for the Carex spp.-Typha latifolia community were associated with a steep slope in the linear mixed model function (Figure 3a,b).…”

“…Those tendencies are in line with the general understanding of N 2 O emergence in soils, where soil moisture is a major driver of N 2 O emissions [33,94]. Concerning the order of magnitude of the N2O emission fluxes from the non-inundated shore of the littoral zone, their overall level is not higher than on nutrient-rich temperate extracted fens after inundation [41] or from a cultivated fen peat [95]. All fluxes from the open water were below detection limit.…”

“…Further, the transition from extracted peatland to wetland ecosystem may reduce the overall climate warming impact due to C sequestration (peat). Graminoids such as Calamagrostis canescens, Poa trivialis, and Concerning the order of magnitude of the N 2 O emission fluxes from the non-inundated shore of the littoral zone, their overall level is not higher than on nutrient-rich temperate extracted fens after inundation [41] or from a cultivated fen peat [95]. All fluxes from the open water were below detection limit.…”

Impact of groundwater regimes on water balance components of a site with a shallow water table

“…, ; Mettrop, Rutte, Kooijman, & Lamers, ; Minke et al . , ; Richert, Dietrich, Koppisch, & Roth, ). Different target water levels depending on the development goals of the sites are one of the main reasons why shallow water table sites are often the centre of conflicts between different interest groups, especially between farmers and nature protection groups.…”

“…A model study by Grimaldi, Orellana, and Daly (2015) emphasized that different plants with different root depths have various effects on evapotranspiration, create different drops in the water table and groundwater depletion, which is additionally affected by varying soil types. The restoration of former agriculturally utilized areas by rewetting, especially, leads to a change in the plant communities and has to be considered in the development of water management strategies Minke et al, 2016;Richert et al, 2000;Zak et al, 2015;Zerbe et al, 2013).…”