Site Assessment
If not state otherwise, the text in this chapter is derived from: Convention on Wetlands. (2021). Global guidelines for peatland rewetting and restoration. Ramsar Technical Report No. 11. Gland, Switzerland: Secretariat of the Convention on Wetlands.
Peatland types
The first step in determining restoration goals, is to identify the specific site type that is being dealt with. Two main categories exist, bogs and fens. Bogs are peatlands that rely on atmospheric precipitation for their water supply, meaning they are not connected to the groundwater. This causes bogs to become nutrient poor and strongly acidic. Fens are peatlands that receive water from the ground, this water has been in contact with mineral soil or bedrock, leading to a more nutrient rich environment that can be weakly acidic or even alkaline. Not all peatlands fall neatly in these two categories, leading to transitional mires that share some characteristics of both peatland types.
Another factor that is important to determine before starting restoration efforts, is whether you are dealing with a horizontal or inclining mire. In a horizontal mire, the water table is levelled, and peat can form up to the water surface.
The water level can fluctuate horizontally depending on the hydrology in the surrounding area. This means that if the water does not rise, new peat cannot be formed. An inclining mire has a slightly angled water table. This causes horizontal water movement in the peatland that is obstructed by the dense vegetation, leading to a slowly increasing water table. This increasing water table constantly creates new space for peat formation. These inclining mires self-regulate but are also more susceptible to disturbance which can lead to rapid erosion.
A final step in determining the site type is the surrounding hydrology. Peatlands often depend on water supply form surrounding areas, and the peatland hydrology is often determined by the surrounding hydrology. It is important to know if surrounding water tables are stable or fluctuating, and if so to take the correct measures. The water quality of the surrounding water is also important. As certain mire specific vegetation relies on an acidic and oligotrophic environment, surrounding water from agricultural areas can easily disturb this balance. Buffer zones might be needed to protect the peatland from low-quality water as well as stabilize the local hydrology.
Degredation intensity
After determining the site type, the next step is to determine the level of degradation of the site. Sites that have minimal or minor degradation are sites that have lost some specific peatland vegetation, but where the hydrology is still mostly intact. In this case, disturbing cover material can be removed, and the lost vegetation reestablished through seeding, planting, or spontaneous reestablishment. Restoration efforts should begin in these sites since most can be gained with minimal effort.
Sites with modest degradation are areas that have been drained recently and can be restored relatively quickly by stopping drainage in the peatland and/or the surrounding area. In some cases, nutrient rich water from surrounding areas needs to be kept out of the peatland to assure reestablishment of the peatland vegetation.
Peatlands that have undergone major degradation, are peatlands that have undergone substantial changes to hydrology over a longer period leading to increased peat decomposition. Peatlands that have been used for peat extraction, leaving only strongly decomposed peat behind, also fall into this category. The peat has then lost much of its water-storage capabilities and these changes are largely irreversible or take multiple decades to restore.
In more than half of the degraded peatlands, degradation is caused by intensive agricultural use of drained peatlands. This form of degradation leads to a nutrient legacy in the soil due to peat mineralisation, use of fertilizers, and the input of airborne nutrients from cattle, industry, and traffic. This nutrient rich soil frustrates restoration efforts, as after rewetting a nutrient rich wetland emerges that will be dominated by competitive and fast-growing helophytes instead of the desired mire specific and peat forming vegetation. When rewetting a former agricultural area, two possible courses of action exist.
- The extremely nutrient rich top-soil layer can be removed before rewetting. This is a costly measure, especially since the best results are gained when at least 20 cm of soil is removed. The removal of top-soil also exposes a more porous soil layer, increasing the water retention potential and speeding op restoration efforts.
- The nutrients in the top soil can also be removed by phyto-extraction. In this case, the area will be temporarily used for paludiculture with species that rapidly take up nutrients such as cattail. By removing the biomass of these plants from the field, the nutrients are effectively removed from the area. This method takes more time, but also poses opportunities for farmers and landowners to have a transitional business plan.
RESTORATION GOALS
After the site type and its level of degradation have been determined, it is time to set restoration goals. The restoration goals should be ambitious but realistic and based on the actual potential for restoration. This potential depends on the level of degradation, the technical possibilities, but also the legal, economic, and societal constraints.
The restoration goals should cover a broad scope of ecosystem services such as carbon capture and GHG emissions, biodiversity, water retention, flood prevention, health benefits, and so on. Some of the goals set for these ecosystem services might conflict with each other, in this case a judgement should be made on which service carries more importance in the specific case. For more information on trade-offs between ecosystem services, see Annex III in Convention on Wetlands (2021).
Once the restoration goals have been identified, it is time to concretely formulate them. The methods that will be used for restoration should be formulated, tuned specifically to the goals that have been set. If there are conflicting goals, one of the goals should be prioritized and the other one, at least partially, let go. Finally, a monitoring plan should be set in motion to check whether the restoration efforts are having the desired effect. For more information, see the Peatland Monitoring chapter.