PRINCESS

Background

Europe faces three major environmental challenges: greenhouse gas (GHG) emissions, nitrogen (N) pollution, and biodiversity loss. Peatlands can play a vital role in addressing these challenges. Drained peatlands in the EU emit ~200 Mt CO₂eq a^-1 (app. 5% of total EU emissions), mainly from conventional agriculture on drained peat soils (144 Mt CO₂eq a^-1). The latter make up only 2.5% of the total agricultural area but produce 25% of the total agricultural GHG emissions in the EU (incl. methane from enteric fermentation and nitrous oxide from fertilization), with an even larger contribution in peatland-rich countries, e.g. Finland (62%), Poland (42%), and Germany (37%, based on NIR 2019 data).

Drained, agriculturally used peatlands in the EU are – through peat mineralization – also an annual source of 1-5 Mt of NO₃ (own estimates based on NIR 2019), with substantial impact on ground and surface water quality, drinking water provision, and biodiversity. Typical peatland biodiversity, in particular that of groundwater-fed fens in temperate Europe, has been devastated by drainage. Consequently, all relevant EU policy objectives include rewetting of drained peatlands as an essential ecosystem-based solution to avoid peatland GHG emissions, reinstall carbon sequestration, reduce nitrogen mineralization, enhance nitrogen removal, and/or restore peatland-specific biodiversity.

Project goals & content

PRINCESS is the first project to categorise and evaluate the effects of alternative land use options after peatland rewetting on key EU environmental policies: (1) as a measure to halt biodiversity loss, (2) as a nature-based solution for mitigating and adapting to climate change, and (3) as a management tool to reduce nitrate release and, thus, eutrophication. PRINCESS investigates the interaction of the two main important global change drivers and attempts to take advantage of the coupling between the C and N cycles to maximise benefits from rewetting peatlands.

Our focus on interactions of peatland rewetting with N loads denotes the knowledge gap concerning the overall behaviour of N as a result of peatland rewetting, compared to the relatively well-studied behaviour of phosphorous (P) in rewetted peatlands. In an integrated and novel approach, PRINCESS examines the direct and indirect consequences of nitrogen loads on biodiversity, GHG emission, nitrate release, and biomass yield of rewetted peatlands. PRINCESS focuses on biodiversity of plants, microbes and selected fen mire-specific fauna, takes a functional perspective, and assesses above- and below-ground productivity. While evaluating landscape-scale solutions for key environmental problems, particular attention is paid to synergies and trade-offs between climate and biodiversity goals and to tipping points indicating when switching from one land use option to another would shift the optimum between policy objectives.

To achieve these objectives, PRINCESS will

• focus on the peatlands which are the largest sources of GHG and affected most by nitrogen loads, i.e. temperate fens. Results, however, are relevant across drained-and-to-be-rewetted peatlands in the temperate and boreal zones.
• bring together complementary skills from six peatland-rich countries, including those with little (FI, NO, PL) and strong peatland degradation and N loading (AT, BE, DE), the latter being also front-running in rewetting and paludicultures
• analyse crucial processes under highly controlled conditions in the laboratory and in mesocosms, test them under more realistic conditions in the field, and model and upscale them to catchment and EU scale
• use these different scales of study to maximize internal (sound interpretation of causal effects) and external (their relevance) validity
• apply the most advanced techniques and methods from biogeochemistry, microbial ecology, plant ecology, socioeconomic modeling on and across scales, using measurable and quantifiable indicators.

PRINCESS will provide vital scientific information for agricultural land use policies for peatlands in the EU by evaluating which land use option after rewetting complies best - under high nitrogen loads - with key policy objectives such as healthy ecosystems, climate change mitigation and adaptation, clean water, fair income to farmers, or, taken together, a greener and more sustainable Europe.