Deconstruction of the drainage of moor soils. The agricultural use of drained moor soils must be stopped or converted to paludiculture.
Moors are landscapes in which dead, only partially decomposed plant rests have accumulated as "peat" due to permanent water saturation of the soil. Because the plant rests consist of 50-60% carbon, moors contain the highest concentration of carbon of all terrestrial ecosystems. The vast majority of Germany's moors are now drained - with increasingly obvious negative consequences. Drainage causes oxygen to enter the soil, the peat is microbially decomposed, large amounts of greenhouse gases (GHG; CO2 and N2O) and nutrients are released and the moor loses 1-2 cm of height every year, leading to increasing drainage costs, flood risks and ultimately land loss.
There are three main ways in which climate-friendly bog management can save greenhouse gas (GHG) emissions or even fix carbon in the soil:
- Avoiding carbon losses (avoidance): By rewetting, i.e. closing existing drainage systems, GHG emissions from drained moors are greatly reduced.
- Binding & using carbon (biofuels/bioresources): If, after rewetting, the growing biomass is used to replace fossil raw materials and energy sources, an additional reduction in emissions is achieved compared to abandonment of use. This reduction can amount to 4-10 t CO 2 eq. per ha and year (Dahms et al. 2017).
- Carbon capture & storage (carbon capture & storage): Through rewetting, moorlands can grow again and permanently fix part of the produced biomass as peat. The annual sink capacity is not high (about one t CO 2 eq. per ha and year), but certainly - in the absence of alternative, long-term effective sinks - significant
The 17,800 km² of drained, mainly agriculturally used peatlands in Germany produce 51 million tonnes of CO2 eq., or 5.7 % of total German greenhouse gas emissions. Meadows and pastures on drained moors emit 29 tons per hectare per year, arable land even 37 tons.³ This could be saved if the moor soil drainage was reduced. In this way, 20-30 tons of CO2-eq. per hectare could be saved annually.¹² Re-wetted moor areas emit hardly any CO2 and nitrous oxide. Although methane emissions can occur, methane is much more short-lived in the atmosphere than other gases and contributes much less to long-term warming.
Rapid rewetting (between 2020 and 2040; rewet all, start now) leads to faster netto-emission-reductions and a significantly lower warming effect triggered by peatlands than rewetting that only takes place between 2050 and 2070 (rewet all, start later).
Fig. 2.1 Default values for annual greenhouse gas emissions from peat soils in Germany (in tonnes of CO 2 equivalents per hectare) for various forms of use (according to Joosten et al. 2016, based on values of the Intergovernmental Panel on Climate Change IPCC)
Projected radiative forcing (mW/m 2 ) and temperature effect of greenhouse gas emissions from peatlands worldwide in the period 2000-2100¹¹. The total human-made radiative forcing in the period 1750 to 2011 was 2.3 W/m2 net (i.e. after deduction of cooling effects) (IPCC AR5).
While CO2 emissions are immediately reduced sharply as the water level rises to the surface, emissions of CH-4 (methane) increase. In the first few years after rewetting, it is often even higher than in natural moors, especially when they are flooded. Since CH4 has 34 times the global warming potential of CO2, the climate impact of a rewetted moor is often slightly negative. However, the negative climate impact is considerably reduced compared to the previous drained state (Joosten et al. 2016). As soon as after 5-10 years a closed, at best peat-forming vegetation cover has formed, the emissions of a rewetted moor are similar to those of a natural moor (Fig. 2.1).
The following measures reduce the CH4 emissions caused by rewetting:
- Removal of above-ground biomass before rewetting;
- Removal of 5-10 cm of topsoil before rewetting to remove the underground biomass and reduce the nutrient availability in the soil;
- Avoidance of overflow and open water areas (also in ditches);
- Use of water that is as low in nutrients as possible;
- Gradual, stepwise raising of the water level;
- Facilitation of plant species typical of the bog.
Moor climate protection¹² as nature-based solution is:
- Tried and tested (federal states such as Mecklenburg-Western Pomerania can quantify the savings achieved)
- Cost-efficient (with one-off planning and construction costs of around 4000 euros per hectare, 20-30 tonnes of CO2 eq. per hectare could be saved annually)
- Synergetic (through water and nutrient retention, flood protection, landscape cooling and promotion of biodiversity
- Area-neutral (in the case of paludiculture) or area-favourable (in the case of abandonment of use)
A transformation path¹² for the future climate-friendly management of peatlands should be developed today, with clear goals (net zero emissions, which can only be achieved by additional C-regulation) and milestones, which will give all actors long-term planning security. We propose the following transformation path:
- Forest: 50% of drained forest should be rewetted by 2030, an additional 25% by 2040 and the remaining 25% by 2050;
- Arable land: phasing out arable land use on peaty soils by 2030, conversion of arable land into grassland with substantially raised water levels (see grassland) or paludiculture;
- Grassland: water level increase on all grassland up to ≤ 30 cm below ground and on at least 200,000 ha (15 %) in pasture by 2030. Stop support for increased drainage
- Raising water levels in arable land to 60% of total grassland by 2040 and to 100% of the area by 2050
- peat extraction: phasing out peat extraction and consumption and replacing all peat with renewable alternatives by 2030;
- other wetlands (unused areas): achieving net zero emissions (CO2) by 2030;
- settlements: Re-wetting of two thirds of the settlement area on drained peatlands by 2050.
The following instruments and measures can be used to achieve the objectives:
- Stopping agricultural subsidies for arable land on drained moor soils from 2021, phasing out arable land use on moor
- Recognition of paludiculture as agriculture and inclusion in agricultural subsidies, investment programmes and climate protection area premium
- Stop the drainage of all federally owned bog areas by 2030 and establish paludiculture demonstration farms
Development trajectories and intermediate targets for the area shares of the individual land use categories on peat soils in the LULUCF sector according to the transformation path 2050.
Dry = deeply drained (peat-consuming); Moist = slightly drained (water pond ~30 cm below ground level, peat-consuming); Wet = water pond in ground level (peat-conserving).
³Standard values of the IPCC, Joosten, H. et al. (2016) The role of peatlands in climate regulation. In: Peatland restoration and
ecosystem services: Science, policy and practice. (ed. by A. Bonn et al.), 63-76. Cambridge: Cambridge University Press/British
¹¹Günther et al. (2019) Prompt rewetting of drained peatlands reduces climate warming despite methane emissions:
¹²Abel, S., Barthelmes, A., Gaudig, G., Joosten, H., Nordt, A. & Peters, J. (2019) Climate protection on peaty soils - possible solutions
and best practice examples. Greifswald Moor Centrum publication series 03/2019 (self-published, ISSN 2627-910X), 84 p.