Risk Factors

Factors determining the risks for projects to rewet and regenerate peatlands in Berlin according to nature targets.

Below the table, the risk factors are discussed individually.

Risk Factor


Nature Target

Eutrophic Peatland

Brown Moss Peatland

Sphagnum Dominated Bog


insufficient water supply

rewetting is not possible


release of phosphorus due to overflow (up to 40 cm)

reaching the nature target (medium-term) not at risk

disqualifies for reaching the nature target

probable limitations of chances to reach nature target


high degree of decomposition (depth) of the peat soil (> 20 cm)

reaching the nature target not at risk


Phosphorus (P) is a macro nutrient, which often plays a major role for the productivity of peatlands (Gelbrecht & Koppisch 2001). Undisturbed peatlands possess a higher capacity for P-retention than drained peatlands, but significant amounts of P of redox and pH-sensitive P fractions can be mobilized through rewetting, which may constitute the hazard of eutrophication through rewetting for the peatland itself or its natural waters and lakes. This particularly applies to peatlands that had previously been deeply drained and utilized for intensive agriculture, as an enrichment with P occurred here in the aerated horizons (Zak & Gelbrecht 2008b).

When the water regulation is controlled insufficiently in a peatland preservation project and causes lengthy phases of overflow to happen, this can result in irreversible eutrophication or polytrophication of the site. This correlation is relevant to the nature target, as they typically show a mesotrophic trophic status. If sufficient water regulation cannot be ensured, plans for a rewetting must be dismissed as a consequence, or the nature target should be adjusted to „eutrophic peatland“. In Berlin, permanent flat water lands on rewetted peatlands are very productive and the formation of organic-rich gyttja gradually transitions over to peat formation (Lietzengrabenniederung, Fließwiese Ruhleben, Wartenberger/Falkenberger Luch). Generally, raising the water level gradually is recommended in peatlands, in order to manage the hydrological effect during water affluent phases and prevent overflow. Furthermore, proceeding this way has been tested and proven also with respect to satisfying local neighbourhood interests (Luthardt mündl. Mitt. 2015).

In addition to greenhouse gases like carbon dioxide (CO2) or nitrous oxide (N2O), considerable amounts of nutrients are released through the mineralizatin of peat. As limiting factors of the peatland ecosystem, especially the macronutrients nitrogen (N) and phosphorus (P) contribute to site eutrophication and to a change in vegetation. In the process, less competitive moor plants, most frequently such that are rare and endangered, are replaced by reed grass with strong growth, grey willows or alder bushes. These often form dominant stocks in Berlin and hence contribute to an impoverishment of peatland habitat biodiversity.

The original trophic conditions can be restored through topsoil removal and uncovering of secondary decomposed peat, if the degree of decomposition or depth of trophic changes in the soil is relatively low. With an increasing depth or degree of decomposition, the technical realisation of topsoil removal becomes more difficult and the issue of the disposal of the soil matter more acute. Where topsoil removal is carried out on flat land, the removed material may well - circumstances permitting - be completely reused for backfilling ditches or trenches. And while successive restoration may well be achieved without topsoil removal with eutrophic peatlands and sphagnum bogs, the nature target of Brown Moss Peatland can only achieved when the semi-natural trophic status of the site is restored (Thormann & Landgraf 2010).

In Berlin, there is the added aspect of wet, mineral matter atop peat soils which affects peatlands. This benefits the development of brown moss vegetation, as the decomposed soil is covered up and usually not directly in the primary root zone; also, mineral substrates for replenishment have a comparatively low nutrient content. Therefore, i.e. with a view to nutrient ecology, no soil removal should be considered in these cases. Fen sites where the degree of decomposition of topsoils goes deeper than 20 cm, can only be developed towards the nature target of Eutrophic Peatland. For sphagnum bogs, topsoil removal should only be considered, where a eutrophic status has been determined for the site.