Restored peatlands under nitrogen pressure (PRINCESS)

The project PRINCESS (Restored fens in a nitrogen-rich environment) examines the effects of different ways of rewetting fens depending on the nitrogen saturation in the environment of these peatlands. The negative effects of the drainage of peatlands includes a significant reduction in biodiversity, decreased water and lost carbon storage, the release of greenhouse gases and a deterioration of water quality. At the same time, many European ecosystems are oversaturated with nitrogen. The restoration of peatlands must aim to eliminate these negative effects, but it is not necessarily possible to meet all of these goals equally well. The nitrogen saturation of the environment also determines the appropriate measures. At the same time it is necessary to give farmers the opportunity to generate an income. The project PRINCESS examines the effects of different ways of rewetting fens on biodiversity, greenhouse gas emissions, nitrate pollution of the groundwater, crop yield and welfare for society. This is examined in fens in the Netherlands, Germany and Poland. PRINCESS examines peatlands that have been rewetted to become wilderness, as well as extensively and intensively used rewetted peatlands. The project assumes that intensive use after rewetting achieves all goals except the restoration of biodiversity, that extensive use after rewetting, in comparison, restores biodiversity better, but does not secure the income for farmers as well and that wilderness achieves all goals except ensuring the income for farmers. These questions are being dealt with by a consortium of scientists from Germany, Austria, Belgium, Poland, Norway and Finland. The Austrian sub-project focuses on determining the greenhouse gas balance of peatlands. There, the sequestration and release of carbon dioxide, methane and nitrous oxide is investigated.

A growing number of studies highlight the benefits of rewetting drained peatlands to facilitate the practice of traditional forms of agriculture and forestry. The conversion of drained peatlands, back to "wet wilderness", is accepted as an effective method to decrease, or even reverse, their substantial net greenhouse gas (GHG) emissions - converting them back into net sinks of GHG. Peatland rewetting is seen as a potentially effective means toward achieving EU climate goals of net GHG emission reductions, but rewetting limits the practice of traditional agriculture and other typical economically productive land uses. Paludiculture (wet peat conserving land use) represents a possible solution, a balance between achieving lower GHG emissions, increased biodiversity and maintaining socio-economic benefits to land owners / managers and society. While the benefits of peatland rewetting and returning formerly drained peatlands to a state of "wet wilderness" are relatively well understood, it is uncertain to what extent, and under which conditions, paludiculture can maintain similar GHG emissions to "revitalized"/wet wilderness peatlands. To address this knowledge gap, we investigated how different intensities of paludiculture impact GHG emissions at a range of different fen (nutrient rich, groundwater fed, non-acidic) peatlands. Further, we investigated the factors influencing GHG emissions from the investigated paludiculture sites, as well as how the practice of paludiculture impacts carbon quality and quantity, and microbial community composition. We found that GHG fluxes, in particular methane (CH4), showed significant temporal (seasonal and diurnal) variability. Higher observed CH4 emissions at paludiculture sites were compensated by reductions in carbon dioxide (CO2) emissions, with little impact of very low nitrous oxide (N2O) emissions across all treatments. While the individual GHG fluxes (CO2, CH4, N2O) significantly differed between paludiculture intensity treatments, the total GHG flux (measured as CO2 equivalents, CO2eq) under all paludiculture treatments were statistically similar to that under wet-wilderness, irrespective of sampling country or dominant vegetation. Investigating the drivers of GHG emissions from the investigated sites, we found that the water table, soil temperature, soil compactness (bulk density), Carbon:Nitrogen ratio and phosphorous concentration were the most important predictors of GHG fluxes from paludiculture sites. The findings of our study furthers our current understanding of how different paludiculture practices may impact microbial communities, and influence GHG emissions from differently managed paludiculture sites. Overall, we highlight paludiculture as a potentially viable alternative to non-productive use of rewetted peatlands (wet-wilderness) in terms of GHG emission - with similar GHG emissions to re-vitalized peatlands, as well as offering socio-economic benefits to farmers / land owners and society. Further we highlight the importance of land management in maintaining low GHG emissions from rewetted peatlands, and show how past land management which impacts peat soil properties, acts as a strong control on current GHG emissions.