Carbon-wise ways to use peat extraction sites after extraction
Combatting climate change and habitat loss have become concrete policy objectives in recent years, bringing new alternatives to the conventional forms of the after-use of peat extraction sites. Often there is still a layer of peat in former peat extraction sites, the carbon in which should be stored in the soil instead of being released into the atmosphere. Choosing carbon-wise forms of after-use for peatlands could at best preserve soil carbon storage and enhance carbon sequestration.
In many cases, wise use of the land after peat extraction also increases biodiversity. In the age of green transition, renewable energy production and solar parks in particular are seen as suitable use for peatlands.
In Finland, once peat extraction has ceased the peatland typically changes users, often changing owners as well. It is up to the landowner to decide what activities they want to use the land for. Traditionally, the most common forms of after-use have been afforestation and crop production. Bird and biodiversity wetlands have been established in the wettest areas.
Due to the transition of the peat production sector, many former peat production areas are currently being converted to after-use. The increasing number of sites released from peat extraction and the changing objectives have increased the need to examine the environmental impacts of after-use and to improve planning. There is a particular need for information right now.
The Ministry of Agriculture and Forestry’s Hiilestä kiinni (´Catch the Carbon`) programme’s after-use projects have provided information to meet this need. In the JälkiHiili project GTK investigated how best to select the most suitable form of after-use for the different parts of peatland. The project also compared the climate impacts of different forms of after-use.
Identifying the best options for after-use
The dryness or wetness of a specific area factor in the most when choosing the after-use of peatland. Wetness conditions are created by surface elevation of the area in relation to its surrounding area and by flows of water. Typically, three types of areas are found on peatland.
There are areas where the surface is well below its surroundings and keeping them dry is challenging, if not impossible. The most sensible choice is to rewet these areas.
The deepest parts form pools and wetlands, although embankments and dams should be reinforced to prevent flooding from carrying away the soil. The shallow water areas around the pools form a zone of sedge or common reeds. There may be areas that can be rewetted or restored on the edges of pools or on otherwise drained, flat parts of the site. Effective peatland restoration requires the creation of stable moisture conditions and the transplantation of bog vegetation, especially Sphagnum moss, to the site. This method, which is new to Finnish peatlands, is used in Canada and has also been studied and tested in Estonia.
Other parts of the site are so high in relation to their surroundings that it is not possible to rewet them, at least not without flooding the surrounding land. Under such conditions, land use that require dry conditions, such as forestry and agriculture, are suitable.
Often most parts of the peatland can be either rewetted or kept dry by modifying drainage and/or dykes. In such areas, the thickness of the peat layer determines the choice of best after-use. On sites with thin peat layer (less than 40 cm), almost all activities are suitable, but on parts of the field with thick peat layer, the type of after-use should be considered more carefully.
For example, in areas with thick peat layer the most popular after-use, afforestation, may not be economically viable. If the nutrients in the peat layer are not sufficient to grow a productive stand, the stand will require repeated fertilisation. At sites with thick peat layer, the importance of preserving peat carbon storage also increases. Peat decomposition and carbon dioxide emissions to the atmosphere are reduced by raising the water level close to the peat surface.
The open, vegetation-free former peat production sites are well suited for solar parks. A solar park can be established on a wide range of former peat extraction sites varying in peat thickness and moisture, as there are many different ways of constructing the park. However, especially in thick peat layer areas, it is worth considering the conservation of peat carbon storage, so that fossil fuel emissions are not replaced by carbon dioxide emissions from decomposing peat. If the water level in the solar park can be kept close to the peat surface, the climate effects of the park will be significantly better than with dry peat.
When planning land use of peatland located in an area of acid sulfate soils, the soil must remain saturated with water to prevent forming sulfuric acid. Therefore, the soil drainage depth should not be increased in these areas. Given this constraint, the landowner can decide what form of after-use they want, but the most preferable forms of use in acid sulfate soils are wetland construction or rewetting.
Planning for after-use requires current information on the characteristics of the former peat production area. The most important information is an up-to-date surface elevation model and the thickness of residual peat in different parts of the site.
However, the surface elevation model must be laser-scanned after ending peat extraction for the data to be current. If up-to-date data is not available, a surface elevation model can be commissioned using a UAV (unmanned aerial vehicle). Data on the thickness of the residual peat and its variation in different parts of the site should be requested from the peat producer when the site is handed over. The peat thickness can also be measured with a peat auger if data is not available. The surface elevation model and peat thickness data can be used to produce a combined model of peat thickness and rewetting potential, which provide a good indication of suitable after-uses.
Choice of after-use impacts climate
A single area of former peat production site typically has a range of characteristics and there are many subareas, each suited for several different uses. The climate impacts of different forms of after-use differ, so the choices matter.
Afforestation and restoration to bog vegetation dominated by Sphagnum moss are best forms of after-use for the climate. Traditional agriculture is the worst option. However, there are big differences between crops: grass is much better than cereals, and reed canary grass can be a good alternative. Solar power, wetlands, and the planting of vegetation fall somewhere in between in terms of climate impacts. The impacts of a solar park can be improved by reducing peat decomposition by raising the water level.
The Jälkihiili project presented the climate impacts of landowner choices in two peat production sites. The climate-warming effect of the traditional agriculture-afforestation-wetland option was 50 to 80 times higher than that of the climate-friendly options.
As landowners generally seek financial return on their land, it would benefit Finland’s climate goals to create incentives for landowners to choose the most climate-friendly options.
All the latest information in one place
The results of the Hiilestä kiinni wetland projects on the potential, planning, and impacts of peatland after-use have been summarised on the jointly produced website ‘Climate smart solutions for peatland after-use – A guide for landowners and wider planning`. The website provides information for landowners, planners, and authorities alike. It presents the steps for transforming former peat extraction sites for after-use and the impacts of different after-use options on the climate and the environment. It also provides information on the possibilities for after-use of peatlands as part of regional planning.
Text
Anna-Laine Petäjäkangas
Liisa Maanavilja, Senior Researcher
Oona Allonen, Researcher
Heikki Sutinen, Geologist
Mika Larronmaa, Geodata Planner
Tuija Vähäkuopus, Team Manager
Further information
(In Finnish) Ilmastoviisaat ratkaisut turvetuotantoalueiden jatkokäyttöön – Opas maanomistajalle ja laajempaan suunnitteluun (Climate-smart solutions for the after-use of peatland – A guide for landowners and wider planning)
Research report:
Laine-Petäjäkangas, A., Maanavilja, L., Allonen, O., Sutinen, H. & Vähäkuopus, T. 2023. Turvetuotannosta vapautuvien suonpohjien hiiliviisas jatkokäyttö. Summary (in English): Carbon-wise after-use of peat extraction sites. Geological Survey of Finland, Research Report 82/2023.
Project introduction:
Planning for the Carbon-Smart After-Use of Peatlands (Jälkihiili)
