Greenhouse gas exchange of different fen paludicultures during establishment

Conventional agriculture on peatlands requires drainage, but this practice causes high emissions of the greenhouse gases (GHG) carbon dioxide (CO₂) and nitrous oxide (N₂O). Paludiculture is an option to mitigate these adverse environmental effects while maintaining productive land use. Whereas the GHG exchange of paludiculture on rewetted bog peat, i.e. Sphagnum farming, is relatively well examined, data on GHG emissions from fen paludicultures is still very scarce. As typical fen paludiculture species are aerenchymous plants, the release of methane (CH₄) is of particular interest when optimising the GHG balance of such systems. Topsoil removal is an option to reduce the CH₄ emissions upon rewetting but retaining a nutrient rich topsoil might foster the biomass growth.

In this project, Typha angustifolia, Typha latifolia, and Phragmites australis are grown at a fen peatland formerly used as grassland. Water levels will be kept at the surface or slightly above it. In parts of the newly created polder surrounded by a peat dam, the topsoil is removed. Four smaller sub-polders are installed to separate the effects of topsoil removal and water level. Here, the water levels can be adjusted independently from the main polder. Greenhouse gas exchange is measured for all three species with and without topsoil removal. Additionally, a reference grassland site close by and a site on the dam are included in the measurements. GHG measurements are carried out every two to four weeks on a campaign basis using manual chambers and a portable analyser for both CH₄ and CO₂. Here we present GHG balances of the first two years after planting the paludicultures.

Despite of imperfect water management during the first year after planting, all paludiculture species were both a net CO₂ and GHG sink regardless the topsoil treatment. During this period, fluctuating water levels resulted in low CH₄ emissions while N₂O emissions were of greater importance regarding the GHG balance. Due to more stable water levels in the second year, higher methane emissions are expected. Carbon export by the first biomass harvest will also be taken into account.