Pros and Cons of Strategies to Reduce Greenhouse Gas Emissions from Peatlands: Review of Possibilities

Abstract

Peatlands can become valuable resources and greenhouse gas sinks through the use of different management practices. Peatlands provide carbon sequestration; however, they are also among the greatest greenhouse gas emissions sources. The estimated annual carbon dioxide equivalent emissions from peat worldwide are 220 million tons. Novel strategies, methods, and technologies must be developed to enhance the sustainable use of peatlands and achieve climate targets by 2050, as set forth by the European Commission. There is no consensus in the scientific literature on which strategies included in the policy documents are more fruitful for reducing emissions. There are uncertainties and knowledge gaps in the literature that summarise the cons and benefits of each strategy regarding the potential of GHG emission reduction. Currently, peat is undervalued as a resource in the bioeconomy and innovation—a way that could save costs in peatland management. This review paper aims to analyse existing and potential strategies to minimise greenhouse gas emissions from peatlands. Studies show significant debates in the literature on whether the rewetting of peatlands and afforestation of previously drained peatlands can be defined as restoration. A more effective management of peatland restoration should involve combining restoration methods. The rewetting of peatlands should be realised in combination with top-soil removal to minimise methane emissions. The rewetting of peatlands should be used only in combination with revegetation after rewetting. One of the promising solutions for methane emission reduction could be paludiculture using sphagnum species. Products from paludiculture biomass can reduce GHG emissions and store long-term emissions in products. Paludiculture can also be the solution for further income for landowners and innovative products using the biomass of harvested paludiculture plants.

1. Introduction

Peat plays a vital role in peatland ecosystems for vegetation growth and habitats, ensuring biological diversity [1,2,3]. Peatlands are critical in climate regulation as carbon sinks [1,4,5,6,7,8,9]. Peatlands are the most significant natural terrestrial carbon sink, which can continuously attract carbon from the atmosphere over long periods [8,10,11]. While peatlands cover only 3% [12,13,14] of the area, they store 30% of the world’s carbon [8,9]. The resource’s quality has decreased [15,16,17,18], and peat is currently viewed more as an emission source [5,15,19,20]. Peatlands have to be managed sustainably, interrupting extensive peatland drainage and extraction [21]. It is estimated that more than half of the peatlands in Europe are lost [22]. The increase in population density and intensity of agricultural practices has driven the increased drainage of large European peatlands [23]. In Europe, 25% of peatlands are estimated to be degraded [23].

In Europe, peatlands can be found in wide areas in Eastern Europe, Central Europe, and Northern Europe. These regions include Ireland, the United Kingdom, Germany, Austria, The Netherlands, Poland, the Nordic countries, and all the Baltic states [24,25,26]. In Finland, more than 30% of the territory is covered with peatlands [12,17], but in Sweden, it is approximately 15% of the territory’s land surface [4]. In Iceland, peatlands cover ~9% of the total area [27], while in Norway, peatlands cover ~6% of the land territory [12].

About 12% of the peatland area has been drained and used for forestry and agriculture [28]. The water table is low at the drained peatland level; therefore, carbon dioxide (CO₂) emissions increase. In peatlands where drainage has been carried out, CO₂ is the main GHG emission [29]. It has been determined that drained peatland causes ~2% to 5% of the emissions of greenhouse gas (GHG) emissions and ~10% of CO₂ emissions in total [30]. Degraded peatlands produce large GHG emissions and greatly affect peatlands’ water-holding resistance [31].

Peat continues to be one of the main energy sources in Europe, for example, in Sweden and Finland [32]. The extensive drainage of peatlands for agricultural use, extraction as an energy source, and removal of all but a thin peat layer explain the decrease in peat quality [20,33]. It is predicted that in northern peatlands, GHG emissions from peatlands might increase in the following years because of global warming [34]. The European Union (EU) is rated as the third greatest carbon dioxide (CO₂) emitter of degraded peatlands after Russia and Indonesia [31], with annual GHG emissions of roughly 220 million megatons of CO₂ equivalents/year [35,36]. Some of the greatest CO₂ emissions in the EU from degraded peatlands are in Poland, Germany, and Finland [31].

The degraded peatlands used for agriculture are significant emission sources, emitting CO₂ and CH₄ into the atmosphere [37,38,39]. In their natural conditions, peatlands are also CH₄ emitters [40]. At the same time, natural peat bogs sequester CO₂ from the atmosphere and, thus, compensate for the emission of CH₄. The effect of N₂O on global warming is higher than that of CO₂ by an approximate factor of 265 [41,42,43]. Nitrous oxide (N₂O-N) emissions increase along with the increase in peat soil degradation. In the form of N₂O-N, EU peatlands release around 145 gigagrams of nitrogen per year [44,45]. The amounts of GHG emissions from peat are affected by the type of peat, the carbon-to-nitrogen ratio in the soil, hydrology, temperature, land use, and biodiversity [1,2,7,46].

In 2015, climate targets were set at the Paris Climate Conference (COP 21)—to reduce the GHG emissions in the EU by 40% by 2030 compared to 1990. The EU signed a binding agreement with states to act towards achieving these targets. To achieve these targets, the GHG emissions from peatlands must also be minimised [47]. Peat production in Europe is estimated to be twenty million tons annually [47]. If degraded peatlands are not restored in time, peatland ecosystems will be more fragile to carbon loss and could transform into dry forests, for example [48]. Peatlands’ restoration aims to restore their natural functions [49]. After the drainage, the peatland decomposes and releases carbon [50]. Peatland restoration promotes carbon sequestration and emissions of N₂O reduction [34].

Returning hydrologic changes similar to previous conditions before drainage is one of the goals of peatland restoration [50]. Peatland restoration can increase ecosystem resilience against extreme weather conditions, biodiversity, soil health improvement, and climate change mitigation [22]. It is estimated that a thoughtful extraction site restoration might transform peatlands into carbon sinks in approximately twenty years. Peatland rewetting and revegetation are currently some of the most widespread approaches [49]. However, these strategies have disadvantages [51,52,53]. Thus, other solutions must also be explored to minimise peatland GHG emissions. Some studies in the literature show that severe uncertainties and underwater rocks exist in connection with restoration using inundation, resulting in nutrient leakage and increased methane emission concentrations [51]. Previous studies show that, when comparing nearly pristine peatlands and peatlands after rewetting, there are some uncertainties regarding the impact of the rewetting and its efficiency over a long period [50].

According to previous studies, the part of climate scientists and decision-makers do not assign a sufficiently influential role to peatland management as an instrument for climate change mitigation in the future. Also, there is a lack of requirements for reporting the removal of GHG emissions from wetlands [51,53]. Although there are several peatland conservation policies for implementation in EU member states, there is a lack of mandatory requirements for governments [49]. Both policy documents and the scientific literature outline several strategies and methods to restore peatlands and reduce GHG emissions. However, there are some knowledge gaps and contradictive views on which strategies may be the most effective and appropriate [54,55]. Particularly, it is true for EU countries where peat is used for energy production [29,47,55,56,57]. Existing peatland strategies do not always solve issues regarding the restoration and management of peatland in sufficient detail [49].

Choosing proper peatland strategies and their effective realisation is crucial for reducing GHG emissions [54] and restoring peatland functions [48]. The selection of inappropriate peatland policies can have further adverse effects on peatlands, making them more vulnerable [49]. Among alternative approaches is the production of innovative peat-based products and materials if it is economically justified [57,58,59]. The potential of peat as a high-value natural resource has so far been undervalued [32,33].

Unlike other reviews, this review focuses on both the pros and cons of each peatland strategy and the alternative use of peat as a valuable resource for high-added products to reduce GHG emissions from peatlands, focusing on European peatlands.

This review paper is structured as follows: first, it is crucial to understand existing restoration strategies and their pros and cons to find innovative solutions. It analyses whether and how peatland emissions change after implementing each strategy. Data on strategies and techniques from the literature are analysed to identify the most effective ones in GHG emission reduction from peatlands.

Peat processing methods to obtain high-added-value peat products and materials to sequester emissions in these products are reviewed in the closing section.

2. Materials and Methods

This review emphasises the significance of peatlands’ restoration in climate change mitigation, ecosystem services provision, and biodiversity conservation. The need for the sustainable management, restoration, and conservation of peatlands to preserve these valuable ecosystems and reduce GHG emissions is highlighted. Future research and integrated approaches are crucial to addressing peatland conservation and management challenges affecting climate change.

2.1. Framework for the Study

To identify and evaluate the potential approaches that could help reduce emissions when the source of the emissions is peat, the literature review consists of the following steps. The review first examines peatland restoration strategies and some risks associated with implementing these strategies. The review also examines peatland restoration alternatives and their advantages and disadvantages.

The final part of the review is focused on peat processing methods and potential solutions for peat as a valuable resource in various products and materials.

The framework of the study is shown in Figure 1.

2.2. Methodology for Qualitative Assessment

First, the research field was identified, along with the knowledge gap and research question in the scientific literature, aimed at addressing the critical challenge in Europe—the reduction of GHG emissions from peat.

Within the framework of the defined research question, the possibilities of reducing GHG emissions of existing and potential peatland strategies and their obstacles were investigated. There are deep-seated knowledge gaps and uncertainties regarding which restoration strategies are more effective and what kind of blind spots and risks may occur after implementing these strategies. Similarly, there is also a question of the kind of benefits that can be expected after introducing strategies. This includes research into existing and potential strategies and innovative solutions for storing emissions using peat. The selected well-known bibliographic databases for a comprehensive investigation of peat and peatland literature analysis (More than 160 literature sources in total) were Web of Science, SCOPUS, Science Direct, and Google Scholar.

Inclusions criteria for qualitative analysis:

A collection of the scientific literature and reports was reviewed, addressing the following questions:

• Methane, carbon dioxide, and nitrous emissions from peatlands;
• Strategies to reduce emissions from peatlands;
• Mitigation measures and degraded peatlands;
• Negative side effects of strategies related to emissions, biodiversity, and hydrology functions;
• Potential of peat use in high-added-value products.

After defining the main questions, appropriate keywords and their combinations to answer these questions were selected. Keywords of four distinct categories were chosen—(1) overview of the state-of-the-art peatlands, (2) emissions, (3) restoration and management strategies, (4) and peat use for materials and products—for a qualitative analysis of the scientific literature combined with the study of reports.

For the qualitative analysis, as many literature sources as possible were used, focusing on those published in the last five years and related to European peatlands.

Sources regarding tropical peatlands were not included in the analysis due to their specifics.

The main keywords used to answer the research question are listed in

Table 1. Summary of keywords used in the review paper.

Overview of State-of-the-Art	Emissions	Restoration and Management Strategies	Production of Materials and Products from Peat
Drained peatlands Drained peatlands in Europe Peatland protection Peatland management Sustainable management of peatlands Mitigation measures in degraded peatlands Peatland management scenarios Peat extraction in Europe Peat trade in Europe Energy and non-energy peat in Europe	Emissions from peatlands Methane, carbon dioxide, and nitrous emissions from peatlands Reduction of emissions Potential emission savings from peatlands Greenhouse gas fluxes from peatlands Carbon emission reduction Carbon storage C sequestration	Strategies to reduce emissions from peatlands GHG emission effects of rewetting drained peatlands Rewetting strategies, water table peatlands Methane emissions from rewetting Peatland conservation strategies Paludiculture Fire management in peatlands Afforestation strategies in peatlands Topsoil removal Slow rewetting	Energy peat, peat as fuel, non-energy peat Peat processing techniques, peat production Peat in biotechnology The potential of peat use High-added-value products Peat is a valued resource for products with added value After the use of peat Possibilities of peat use Peat utilisation options Biochar from peat Horticulture Peat as insulation material, insulation panels, building materials Biofuel from peat as raw material Composite materials from peat
Main literature sources:
[60,61,62,63,64,65,66,67,68,69,70]	[45,63,71,72,73,74,75,76]	[5,29,45,56,66,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91]	[6,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112]

.

3. Literature Review

3.1. Conservation and Restoration Policies and Strategies to Reduce Emissions from Peatlands and Their Side Effects

Increased attention is being paid to wetland ecosystems and their possibility of reducing GHG emissions and opportunities to improve the conditions of endangered peatlands [50]. Annual GHG emissions from drained peatlands are ~1.2–1.9 gigatons (Gt) CO₂ equivalent globally [105]. Annual GHG emissions from degraded and non-degraded European peatlands are reported to reach 582 megatons (Mt) of CO₂ equivalent [25].

For effective peatland restoration, it is necessary to consider both the hydrology of peatlands and species diversity and conservation. Peatland restoration is aimed at restoring degraded peatlands to their natural status and hydrological conditions, recovering their natural habitats, and, thus, increasing biodiversity [1,106,107,108,109].

3.1.1. Policies Related to Peatland Restoration

The Convention of Ramsar regulates wetland management policies internationally (since 1975) [53]. The Ramsar Convention is based on three principles: wetland smart usage, notification of the profound negative changes in wetlands, and provision of international cooperation regarding wetlands [54]. Despite the establishment of the Ramsar Convention, wetlands have been lost through drainage and degradation until today [54]. In the case of climate change mitigation policies, there are gaps in specific directions and rules in the Convention [54]. Some gaps arise concerning the defined wetland restoration aims and their generality regarding climate change mitigation [53]. There are some uncertainties in monitoring and evaluating the achievements of the farmer and landowner sides [54].

Within the scope of the Directive of Water Framework, the EU has considered the ecological conditions of wetlands. Still, the Water Framework Directive directly emphasises water quality conservation as a crucial element of sustainability [53]. In 2019, the Directive of Water Framework was revised, establishing that climate change mitigation solutions will be sought through developing guidelines and adaptation practices [53]. In 2019, the United Nations Environment Assembly, in cooperation with the Convention of Ramsar, promoted the establishment of a worldwide peatland inventory [50].

In the EU Biodiversity Strategy of the European Commission (revision 2020) [110], a vision for restoring nature in Europe, aimed at benefiting the environment, nature, and citizens, was set. Policies included in the strategy are aimed at preserving and restoring peatlands with an emphasis on the role of peat in carbon sequestration, as well as preserving valuable habitats for various species [21,110].

The United Nations’ Sustainable Development Program has been established to promote peatland management in Europe for 2030 [49]. In its framework, specifically the Peatland Restoration program for sustainable water resources, it aims to increase knowledge for more sustainable decision-making. Support for peatland restoration as a priority in peatland conservation is the main aim of the program. Realising strategies and management activities for peatlands, the program will encourage the biological diversity of the peatland ecosystem and maintain previous conditions before drainage. The benefits of this program are also related to the increased well-being of the peatland ecosystem, including peatland fauna and flora [110].

Globally predicted investments diverted to peatland restoration are approximately USD 19 billion yearly [64,112]. In the year 2020, the Government of Scotland committed to investing more than EUR 250 million in the next ten years for peatland restoration [113,114,115,116]. Costs for peatland restoration can be long-term and short-term. Costs can be divided into capital costs for restoration and staff costs, including workers and costs regarding peatland restoration experts [117].

In order to achieve the aims of national peatland strategies, there is a crucial role for private finance. One of the most significant financial sources for peatland restoration and the realisation of strategies is the European Agricultural Fund for Rural Development and the EU Common Agricultural Policy and EU Life Program. One of the options for revenue from private investors is carbon finance. For the reduction of GHG emissions from peatlands, it is possible to obtain carbon certificates [31].

3.1.2. Peatland Management and Restoration Strategies

Peatland management can be realised in different ways, including reducing GHG emissions by maintaining wet conditions in peatlands, including paludiculture [36] and restoring degraded peatlands [36]. Several policy instruments can be applied to regulate European peatland management. For example, the Peatland Code [31,115] includes standards to evaluate GHG emissions from peatlands. Carbon labelling and certification, used successfully in France, can be mentioned among other policy instruments in peatland management. Regulations of peatlands [3,8] provide binding provisions and initiatives to engage landowners in peatland restoration and management. Restoration programmes for deteriorated peatlands include rewetting and revegetation in large areas [117].

Among several member states in the European Union, national strategies were developed for more effective peatland management in sectors [53]. Even though the specific aims defined in the national peatland strategies differ for each country, the main strategies are related to protection through sustainable management and the use of peatlands [31]. Peatland national strategies can significantly affect the increase in the sustainable use of peatland [31]. On the other hand, a shortage of peatland policies at the national level can hinder local climate change mitigation solutions [53]. Although the structure of national peatland strategy depends on country specifics, strategies should include insight into issues regarding peatland conservation and restoration, also including specific measures for sustainable peatland use [31].

National peatland strategies have already been developed and adapted, for example, in England, Finland, Irelan Austria, Germany, and Scotland [31]. In the context of drained peatlands, European countries like Finland, Germany, and Poland are the most significant CO₂ emitters. In the time period of 2011–2015, Ireland, Scotland, and Finland developed their national strategies, but strategies regarding peatland were implemented only in the years 2020 and 2021 [31]. In these places in Europe, the role of sustainable peatland management has increased in recent years [31].

England’s action plan regarding peatland conservation and restoration was issued in 2021 and aimed to move towards zero-emissions targets related to peatland restoration. According to the plan, the aim is to achieve appropriate peatland conditions for peatlands in the territory and move towards more sustainable peatland management by 2040 [31].

In 2021, Northern Ireland issued its national peatland strategy defining targets for 2040. The strategy focuses more on semi-natural peatland conservation measures, aiming to reach good conditions in 2040 for all semi-natural peatlands in Northern Ireland [31]. Austria and Germany developed their national peatland strategies in 2022. Austria’s strategy focuses on the conservation of peatlands, the achievement of a more sustainable use of peat, and less use of peat in horticulture. According to the strategy, support for carbon emission reduction development programmes is included in the national peatland strategy of Austria [31].

Germany’s national peatland strategy focuses on returning and conserving natural conditions in peatlands using a rewetting approach. Also, the strategy focuses on peatland use in paludiculture and the more sustainable further use of peat. The strategy aims to reduce 5 million tons of CO₂ from peatlands in Germany by 2030. One of the greatest steps defined for CO₂ emission reduction from peatland is to terminate the extraction of peat in Germany by 2040. Regarding strategy in the time period of 2027–2031, peat use in horticulture will also be gradually discontinued [31].

Various strategies and approaches are known to reduce GHG emissions, including the reduction of the intensity of agriculture, peatland afforestation and reforestation [73], and peatland rewetting [117,118]. Also, paludiculture methods have become more widely used in recent years [119]. Other restoration methods include, for example, restoring natural marsh vegetation or planting vegetation [40]. The existing emission mitigation strategies are shown in Figure 2.

(1)

Rewetting may cause nutrient leakage in peatlands

One of the most often used methods to raise groundwater levels is peatland rewetting. Peatland rewetting is performed in degraded and drained peatlands to restore hydrological conditions [29]. According to estimations, peatland rewetting is effective if the water table is 20–30 cm [29] below the peat surface throughout the year [29].

Technological solutions such as drainage blocking allow for water retention in previously drained peatlands. It gradually raises the groundwater level, hence restoring a hydrological regime similar to that before the artificial drainage of the peatlands [120].

Methods of peatland rewetting

The rewetting of peatlands using drainage blocking, small dam construction, and other methods is further described. Drain-blocking is a method used in rewetting peatlands, where the drainage areas of drained peatlands are blocked using technological structures, thus raising the water level. Ultimately, the drainage paths are blocked to prevent debris and trees from entering. Peat may settle within the dams and cause leakage. Therefore, the dams are recommended to be higher than the surrounding bog surface [12,121]. Another rewetting method to prevent CO₂ emissions from degraded peatlands is drainage blocking with small dam constructions. It is estimated that an annual CO₂ emission reduction of 1.4–1.6 million tonnes yearly can be achieved by rewetting a peatland forest area of 590 km² using small dams [122].

Pros and cons of peatland rewetting

Studies predict that by delaying or refusing to rewet, GHG emissions from degraded peatlands could reach 12 to 41% by the year 2100 [32,42,117]. Previous studies show that CO₂ emissions decrease after the rewetting of peatlands [123]. Peatland rewetting reduces emissions from peat mineralisation processes and reduces land subsidence [78,124,125]. The benefits of peat rewetting are not only related to the reduction of GHG emissions, but studies indicate that rewetting can also preserve and even increase biodiversity and restore ecosystem services because after rewetting, peatlands can be returned close to the state they were in before the drainage was performed and restore species’ habitats. Also, studies show that peat rewetting can improve the nutrient balance regulation in peat [124]. Peat rewetting can gradually reduce the overall global warming potential, reducing the emissions of GHG from the soil in the long term (100 years) [124].

Groundwater level

Although rewetting methods have several benefits, rewetting as a strategy for peatland restoration also has drawbacks [52]. During and after peat rewetting by drain-blocking or small dams, CO₂ emissions decrease, but the groundwater level rises, which can also change surface water levels, resulting in increased CH₄ emissions. Variability in the groundwater level and incomplete flooding may also affect the anticipated reduction of CO₂ emissions. For peatland rewetting to be successfully implemented and effective, the hydrological regime must be controlled, and no water level fluctuations are permitted; the water level must be sufficiently high and stable. Blocking runoff is considered the most economically feasible solution for small areas of agricultural land. However, in this case, it is more difficult to control the groundwater level [14,117].

Due to peat rewetting, the groundwater level must not be too low or too high. A low groundwater level will affect vegetation in the peatland, causing carbon emissions. A groundwater level that is too high will cause surface water to accumulate and form lakes. A groundwater level that is too high will cause surface water to accumulate, forming lakes that, in turn, also hinder vegetation growth and negatively affect biodiversity [52] in peat bogs [65]. Therefore, the groundwater level must be continuously monitored. One can also use peat or wood for drain-blocking or dam construction. However, there is less information about the efficiency of using such raw materials in peatland rewetting [81]. The amount of GHG emissions reduction after rewetting can differ regarding peatlands’ biological processes [5]. Also, emissions vary due to factors like vegetation, level and water table fluctuation, and land use history [5].

Carbon dioxide (CO₂)

Based on the literature, it is estimated that CO₂ emissions will reduce after the water table level increases [29]. It is estimated that increasing the water table level by about 10 cm can reduce emissions of three tons of CO₂ equivalent ha⁻¹ yearly [30]. Some studies suggest that rewetting peatlands and restoring the hydrological conditions using dams or drainage blocking can reduce CO₂ emissions by 70%, and rewetting peatlands can reduce or even stop carbon loss [45]. As previously mentioned, GHG emissions after rewetting can vary, from strong sinks of ~8 tons of CO₂ equivalent ha annually to 0.71 tons of CO₂ equivalent ha annually [5]. For large emissions sources, it could be even 25 to 53 tons of CO₂ equivalent ha annually [5]. Studies in 2023 [29] showed that rewetting drained peatlands can reduce CO₂ emissions by 1.343 ± 0.36 Mg CO₂ -C ha⁻¹ year ⁻¹ [29]. For the EU, peatland mitigation potential through rewetting is estimated to be ~51–54 megatons of CO₂ equivalents annually [36]. The European Commission estimated that interrupting peat extraction would be possible to achieve an emission reduction of ~9 megatons CO₂ equivalent annually [5]. According to studies, rewetting can reduce annual CO₂ emissions in forested peatlands by as much as 15.4 tons of CO₂ equivalent per hectare, 25% lower than emissions before forested peatland rewetting [29]. If the rewetting of degraded grasses is carried out on peat soils, it is estimated that it is possible to reduce emissions by 20 tons of CO₂ equivalent per hectare annually. The rewetting of cultivated crops can reduce CO₂ emissions by even 30 tons of CO₂ equivalent ha⁻¹ annually. There is a reported annual reduction in GHG 773 tons CO₂ equivalent for a rewetted peatland in northeastern Germany [126]. From 1990 to 2019, roughly 150 hectares of drained organic soils were rewetted on forest land in Sweden. The cumulative decrease in emissions was 9.5 kilotons over two decades, but the factual numbers could be higher [127]. It is estimated that rewetting all organic soils in Denmark will result in a reduction of CO₂ emissions of about 4.1 million tons [127].

Methane (CH₄) emissions

Determinants of CH₄ emissions in naturally formed peatlands include the pH level of vegetation and soil, hydrological regime, and groundwater depth [40,125]. As a result of the increase in water table level due to rewetting, methane forms a more potent greenhouse gas than CO₂ [49]. The radiation efficiency of CH₄ is substantially larger than that of CO₂ [125]. In drained peatlands, CH₄ emissions are low if the water level is less than 20 cm below the surface [39]. Rewetting may increase the CH₄ emissions and cause the input of nutrients in the short term [39]. Peatlands, after rewetting and sequestering CO₂, may emit up to 46% more CH₄ [25,40].

The uncertainty in the scientific literature regarding emissions from rewetted peatlands is significant [29,45,83]. The 2014 Intergovernmental Panel on Climate Change (IPCC) Wetlands Supplement excluded emissions from rewetted drainage ditches. After rewetting, ditch systems or networks of plugged or backfilled canals are left open, and the rise in the water table results in CH₄ emissions [128]. Few studies have shown that CH₄ emissions from peatlands in northern regions have been rewetted for more than ten years [106]. For this reason, changes in GHG emissions from these peatlands remain to be discovered. After peatland rewetting, litter decomposes faster, which may raise CH₄ emissions for up to 30 years [37,112]. One of the latest studies has shown that drained peatland rewetting can cause an increase in CH₄ emissions of 0.033 ± 0.003 Mg CH₄-C ha⁻¹ on average after rewetting yearly [29]. CH₄ emissions could be reduced through diverse vegetation growth [37,40,112].

Nitrous oxide (N₂O)

Where drainage has been previously performed, peatlands can act as a potent or insignificant N₂O emission source. This depends on land use and geographical location [39]. Natural peatlands usually emit low amounts of N₂O. Rewetting has often been proposed to reduce GHG emissions from drained peatlands. An assumption made by the IPCC is that undrained and rewetted peatlands do not emit N₂O. It is based on research results that saturated and undrained peatlands emit nitrous oxide in minimal amounts [129].

During the rewetting of drained peatlands, the production of N₂O and, thus, its emissions may increase in the short term [39]. Vastly degraded peat with a high nutrient availability contributes to increased nitrification and denitrification [39]. Studies on changes in nitrous oxide emissions after rewetting are fewer for degraded peatlands. Comparative studies have been conducted on the N₂O emissions of rewetted and naturally formed peatlands. According to the estimations, emissions from nutrient-poor peatlands are 0.08 m⁻² a⁻¹, and from nutrient-rich peatlands, they are 0.05 m⁻² a⁻¹. Peat rewetting effectively reduces N₂O emissions in drained peatlands, and it has been believed that by rewetting, it is possible to achieve emissions close to the state of natural peatlands, producing from 0.022 to 0.191 m⁻² a⁻¹ annually [129]. If the water level throughout the year approaches the surface, the emissions are minimal or even non-existent. If the water level annually is 10 to 30 cm below the soil surface [29], both aerobic and anaerobic conditions are maintained on top of the soil, and nitrification and denitrification produce N₂O. Thus, with this water level, peatland rewetting can create N₂O-N emissions [29,45,72,125]. In the literature, rewetting is considered the most effective approach to decreasing N₂O emissions from degraded peatlands. An estimated reduction in N₂O emissions by ~70% in the next 30 years has been reported [45], and all degraded peatlands in Europe are rewetted—an essential step towards climate goals [11,129].

Rewetting less degraded peatlands first would give an estimated 30% reduction in emissions. It is important to understand the processes generating each GHG separately. However, there is also a need to assess the total emissions of multiple GHGs objectively. The cumulative N₂O, CO₂, and CH₄ emissions after peat rewetting should be evaluated because these gases accumulate in the atmosphere, but the duration of their residence there is different [11].

Nutrients and dissolved organic carbon (DOC).

The drainage of peatlands results in nutrient accumulation in the upper layer of the peat. Therefore, rewetted peatlands can be phosphate and ammonium nutrient sources. Regarding nitrate, rewetted peatlands can be a sink of nutrients [39]. It has been confirmed that the drainage of peatlands causes increased concentrations and fluxes of dissolved organic carbon (DOC) in streams and rivers [130]. Rewetting of peatlands in temperate and boreal regions can positively affect the DOC concentrations in freshwater [130]. Despite this positive effect, peat rewetting may cause nutrient leakage in the short term [39] and phosphate ion (PO₄^3-) mobilisation, which may lead to further eutrophication due to the input of nutrients. There are a few contradicting studies that claim that peat rewetting increases DOC concentrations in waterbodies and promotes an increase in CH₄ emissions [39].

Rewetting is not suitable for all cases of peatlands. The prospects of peat rewetting are influenced by the location of the peat and the need to maintain a regularly high level of water. Rewetting after peat cutting could be a sustainable strategy, as rewetting is often more straightforward when the peat is removed [117,121].

In the short term, rewetting may have negative consequences, such as degraded water quality in downstream areas or aggravating GHG emissions [106,117,131]. Rewetting is also reported to cause slight changes in the chemical composition of the peat. The quality and chemical composition of the water used for rewetting affects the efficiency of the rewetting of peatlands [55,71]. When water with high phosphorus concentrations is used for peat rewetting, nutrient leakage and eutrophication risks will increase [70,71]. It is possible to use salt water, brackish water, or freshwater from rivers or groundwater [39].

Peatland management requires striking a balance between CO₂ emissions from drained peatlands and CH₄ emissions from rewetted peatlands. Before deciding, it is important to consider both the radiative properties and longevity in the atmosphere of CO₂ and CH₄. CO₂ is a weaker GHG with a longer lifetime, while CH₄ is a potent GHG with a short residence time in the atmosphere [62]. Despite the environmental gains from peat rewetting, the cultivation of crops (not wet-adapted) and conventional agriculture, in general [20], is hardly possible due to the high water level. The lands nearby are also not functional for agricultural practice [20,117,127].

The restoration of rewetted peatlands to their original conditions may not happen instantly; it may take decades. This is especially true for peatlands in temperate climate areas due to substantial disturbance and prolonged drainage. These peatlands are predominantly fed by groundwater, and oxidation occurs during drainage, altering the peat’s physical properties. The changes include increased bulk density, decreased porosity, hydraulic conductivity, and storage capacity. These changes, in turn, lead to more substantial fluctuations in groundwater levels. The effects of peatland rewetting have been studied in the field. Among the main gains from rewetting is a substantial decrease in soil subsidence [125], which prevents carbon mineralisation in deep soil [78].

Farmers and landowners receive carbon certificates as financial compensation mechanisms for peat rewetting on their lands, for reducing CO₂ emissions per hectare per year after rewetting. Monitoring and reliable measurements are needed to establish emission reductions accurately so that landowners can be compensated [116,132,133].

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Revegetation of peatlands

In addition to peatland rewetting, revegetation can be an appropriate measure in peatland restoration [50]. After peat rewetting, revegetation is the next stage to restore the peatland to its initial condition regarding species diversity. Restoring vegetation is also essential to reducing GHG emissions [1,134]. Planting vascular plants after rewetting can have a positive effect on the reduction of increased CH₄ emissions, promoting pumping out CH₄ [50]. Scientists have estimated that active revegetation can be a promising solution for introducing sphagnums and lowering CH₄ emissions after rewetting [50]. In some studies, it is estimated that rewetting should be combined with revegetation methods after rewetting to reduce CH₄ emissions, and without appropriate revegetation, it is complicated to gain emission reduction [50].

Revegetation can improve carbon sequestration, while in peatlands without a sufficient vegetation layer, soil carbon is reduced; there are also soil erosion risks. Revegetation directly impacts whether peatland rewetting will be considered sufficiently effective in the long term [1,134]. Restoring vegetation is critical for peat formation processes, and it is possible to restore degraded peatlands [7,134]. Peatland-typical plants are used in revegetation [3,134]. In peatlands, where the hydrological regime and vascular plants have been restored, the soil accumulates higher amounts of carbon and organic matter, characteristic of peat soils [7].

Other hydrological regime restoration methods are described in the scientific literature, which are discussed less than peat rewetting with drain-blocking or dam constructions. These methods rely on the slow rewetting [51] or top-soil removal of peatlands before rewetting [70,87,88]. When the water table in a peatland is raised over a more extended period, the risk of rising phosphorus concentrations, nutrient leakage, and CH₄ emissions is reduced. In the slow rewetting process, the water table is gradually raised, leading to a partial saturation of the degraded soil layer, which reduces phosphorus mobilisation [51].

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Topsoil removal of peatlands.

To reduce the risks of nutrient leakage and restore nutrient-poor conditions, it is possible to remove the top layer of soil before peat rewetting [39]. This practice is called top-soil removal. After peat extraction, nutrients are most released in pre-drained peatlands and bogs [117,135]. Top-soil removal methods increase the effectiveness of peat rewetting and reduce GHG emissions. In peatland regeneration and GHG emission reduction plans, top-soil removal is recommended to reduce nutrient release, mobilisation, and CH₄ emissions that form after rewetting by first removing the eutrophic topsoil and promoting peat regeneration [70,89].

The wider use of the method is restricted by high investments and a lack of knowledge. Removing the topsoil before peat rewetting decreases nitrogen and phosphorus levels, reduces the risk of eutrophication and algal blooms, and diminishes DOC, CH₄, and CO₂ emissions. Studies have estimated that by removing the nutrient-rich topsoil in agricultural lands before rewetting, the risk of eutrophication decreases by 80 to 90%, DOC losses by 60%, and CH₄ emissions by 99% [70]. The estimated global warming potential is reduced by 50–70% by first performing top-soil removal [70]. The removed topsoil can be used in agriculture against land subsidence. In general, top-soil removal can contribute to the soil’s carbon balance and enhance peatlands’ rewetting efficiency [70,89].

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Afforestation of peatlands

In the literature, another method of peat restoration is the afforestation of peatlands. It is an efficient way to store atmospheric CO₂. Studies have shown that afforestation can reduce emissions, reduce net sinks, and increase tree biomass. CO₂ is absorbed and sequestered through afforestation in wood biomass grown in degraded peatlands. The afforestation of degraded peatlands can also improve ecosystem resilience [136,137]. It is estimated that if the afforestation of previously drained agricultural lands is completed, it is possible to reduce the annual CO₂ emissions by 7.8–9.8 tons of CO₂ equivalent/hectare [127].

EU member states prefer a vast peatland afforestation of drained and degraded peatlands, insisting that afforestation without rewetting can be considered restoration based on the Nature Restoration Law [. However, some studies indicate that only the afforestation of degraded peatlands is insufficient to restore the peatland ecosystem, return the wetland species, restore habitats, and return biodiversity to the original state [37,86]. To restore deteriorated peatlands, the hydrological regime must first be recovered [86]. The drained and degraded peatlands emit CO₂, and CO₂ storage in trees after afforestation does not entirely compensate for these emissions [46,138].

Growing trees in degraded peatlands causes tree transpiration and lowers the water table [106]. Fire is a risk in peatlands after afforestation. Forest fires have increased in boreal regions due to climate change. Fires in reforested peatlands cause carbon loss. Reforestation also impacts nutrient release and water storage capacity [46]. CO₂ uptake exceeds CH₄ losses, resulting in a net CO₂ equivalent reduction in the longer period [139]. Studies have demonstrated that net carbon emissions from peatland reforestation exceed the emissions the planted trees absorb. In Scotland, afforestation on shallow peat and mineral soils with minimal disruption has increased carbon storage. Afforestation is not a common method in Scotland to restore peatlands due to scientifically indicated risks and alternative methods being investigated [12,139].

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Paludiculture

The paludiculture method implies land-use change, from degraded pre-drained peatlands to cultivating plants typical in peatlands in wet conditions. In recent years, paludiculture has become an increasingly used method to reduce GHG emissions from peatlands [119,140]. In paludiculture, plants that tolerate wet conditions are grown. The constant hydrological conditions and cultivated wetland plants reduce peat oxidation and CO₂ emissions [141]. Paludiculture strategies are classified into two categories—deliberately cultivated plants such as Cattail (Typha) or sphagnum moss, which are planted and harvested. The second category is moisture-resistant plants that seed naturally, for example, reeds, which are harvested after a certain period [25]. The cultivated plant biomass is a suitable bioresource for sustainable energy production. The paludiculture approach can reduce N₂O and CO₂ emissions [119,142,143,144]. Besides reducing emissions, the peatland quality is improved as peatland-native plant species are planted and cultivated, and farmers and landowners gain financially from cultivating and harvesting the plants [143].

In paludiculture, farmers and landowners use the land, but after rewetting, the land is not suitable for growing crops. Paludiculture allows for growing and harvesting moisture-resistant plants and using the harvest to produce energy or innovative products and materials [45,119]. Similarly to peat rewetting, the plants used in paludiculture need a high water table that does not change throughout the year, contributing to CO₂ emission reduction [25]. Areas proper for paludiculture, mire, shallow lakes, or wet forests can be formed after the rewetting of peatlands [34].

Cultivating paludiculture crops in peatlands can be considered carbon farming on organic soils. Carbon farming implies agricultural practices that increase the rate at which CO₂ is captured from the atmosphere and converted to soil organic matter. Carbon farming in paludiculture can reduce peatland GHG emissions [84,144]. Emission and emission reduction from paludiculture can be hard to evaluate because of the diversity of the wetlands plants that can be used in paludiculture practices. In shallow lakes, CO₂ emissions might be low to moderate [11].

Paludiculture practices and paludiculture-based products can positively affect emissions reduction from traditionally used energy-intensive products and the storage of carbon in these products [5]. The harvested biomass may serve as a resource to produce high-added-value products [25].

Paludiculture lowers CO₂ emissions compared to agriculture, and emissions can also be reduced through carbon storage in products [5,84]. Paludiculture products can replace products that create high carbon emissions [5]. Reed substrate application in agricultural lands can reduce the emissions and store GHG. Greenhouse gases are stored in various products obtained from paludiculture biomass [83]. It is estimated that reed substrate and insulation boards from cattail positively impact GHG emission reduction, compared to land use for agriculture. Reed substrate is ~3 tons of CO₂ equivalent ha⁻¹, and for cattail (Typha) insulation boards, they are ~6 tons of CO₂ equivalent ha⁻¹ average [5]. For Reed, the CH₄ emission reduction potential is influenced by the level or water table. According to studies, for the achievement of a larger potential for emissions reduction, greater control of emissions in paludiculture should be carried out [5].

Cattail (Typha latifola or Typha angustifola), canary grasses, or sweet grasses are examples of plants [82] that are deliberately grown in paludiculture. The applications of harvested paludiculture biomass include insulation and sound insulation panels as building materials and other materials for the construction industry and the energy sector [57]. It is estimated that berries, especially cranberries, are also proper for restoring and capturing carbon using paludiculture practices [34]. Further research is needed to investigate paludiculture and its potential to reduce CO₂ and other GHG emissions in peatlands, as there are knowledge gaps and uncertainties in the scientific literature [5].

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Peatland management to prevent fire

Forest and peatland fires create large carbon emissions, and degraded peatlands are particularly at risk [85,145,146]. Peatlands where the drainage has been performed before are more vulnerable to wildfire risks [34]. Afforested peatlands, where drainage had previously been performed, are especially seriously exposed to wildfire risks because of their more frequent periods of drought [34].

It is estimated that vast boreal peatlands are exposed to wildfire risk. During boreal peatland wildfires in the combustion process, carbon fluxes are released in the amount of ~85 kg m⁻² [30]. Boreal peatland’s intensive use as a gas or an oil may increase drainage speed and wildfire risks in peatlands [30]. Boreal peatland wildfires can result in a 10% increase in carbon emissions in previously drained peatlands [30].

Early warning systems, controlled burning, and the construction of firebreaks are among the fire prevention measures in peatlands [85,145,146]. Controlled burning is an efficient measure, but knowing how to contain fire is critical. After controlled burning, vegetation in peatlands grows and develops, increasing the carbon sequestration ability [76,141,145].

Reducing emissions from peatlands requires new management methods, innovative technological solutions, and instructions to farmers and landowners [141]. To monitor and prevent peatland fires, firefighting stations may be located near degraded peatlands to allow for acting in the case of fire in the shortest possible time. The firefighting department’s role is not only to prevent and extinguish fires but also to cooperate with the local authorities and advise landowners on the best peatland management practices [1,74,118,147,148].

3.2. Peat Processing Technologies and Peat Applications

To reduce peat emissions in Europe, effective restoration measures and, together with scientists and industry representatives, investigating how peat is a valuable resource for producing higher-added-value materials and products are needed. Storing carbon in products reduces emissions from peatlands [12,67,95,125].

3.2.1. Technologies and Technological Processes in Peat Processing

Peat can serve as a replacement for fossil-based resources. The potential applications of peat biomass include using it as a raw material for building materials, in the food industry, and even as pharmaceutical products. Only a limited perspective can be found in the scientific literature on how peat can be processed for use in innovative products and materials as the key component or additive [57,117,149]. Peat can be used for energy production through gasification, direct combustion to produce electricity, or methane production [150]. Direct combustion for power production is a simple method for converting biomass energy into electrical energy. The process involves converting chemical energy into steam and then using this steam to rotate the turbine and generate power [150].

Gaseous and liquid substances are transformed at high and elevated temperatures in the gasification process. The thermochemical processes include drying, pyrolysis, combustion, cracking, and reduction. Biomass is converted into gaseous biofuels. It is a more complicated method than direct combustion [150].

Peat methane utilisation is a processing method for use with methane fuels, converting biogenic gas into electricity. The actual collection of CH₄ from peatlands is meant here [150].

Processing techniques for energy peat are summarised in Figure 3.

In Finland, 3–5% is used as a fuel resource [150]. However, peat is also used as a raw material in agriculture and livestock farming [150]. In northern Europe, peatlands are often transformed into grasslands, which can be used for dairy and livestock farming. In recent years, the bioeconomy has become a possible solution for the more sustainable use of peatlands [36,46,126]. The use of peat for energy purposes is evaluated with the lowest added value [33]. Developing technologies that can convert biomass into liquid biofuels, such as hydrothermal liquefaction, pyrolysis, and gasification, is an active area of research. Volatile organic compounds and carbon found in peat biomass can be converted into liquid biofuel [102,151].

Using different methods, peat can produce thermal insulation and raw materials in various construction materials substrates, and pharmaceutical products [152,153,154,155,156]. Also, an agro-industrial resource, peat, has a high but not fully used potential [57,58]. The following section discusses technologies and processing processes for producing non-energy peat materials and products. Before peat can be used as a raw material in products or materials, peat must undergo chemical and thermal treatment processes [55,98,102]. Various methods can be applied to process non-energy peat, such as extraction, pyrolysis, hydrolysis, thermal dissolution, and chemical modification [95,150]. Peat hydrolysis allows for the extraction of biologically active compounds from organic matter. Peat wax with valuable properties can be obtained for industry and medicinal applications. Pyrolysis produces liquid fuel, coke, and fuel gas [95,150]. The processing methods of non-energy peat are shown in Figure 4.

3.2.2. The Potential of High Added Value of Peat Products and Materials

After the literature review regarding peat processing methods, a further investigation of opportunities for peat’s industrial use in high-added-value products is required. Biomass from paludiculture can be used for innovative product production that might positively affect GHG emission reduction, partly replacing existing products that generate higher emissions [5].

• Building materials

Peat’s possibilities have been proven in the building sector, where peat soil composite materials can be used as raw materials or additives. Peat soil can be a promising additive in construction materials, strengthening the durability of masonry blocks to meet necessary building standards. It is possible to improve building materials’ characteristics, including insulation properties, using peat as an additive or producing the products themselves [99,152,153,154,155,156]. In building materials, cement has often been used with high-lying peat, moistening peat with water first. Then, after the peat is wholly saturated with water, calcium oxide, which can be obtained by calcining limestone, is added to the peat [154]. The search for alternative and innovative thermal insulation solutions in renovation has been more common recently, including using peat as a raw material or additive in thermal insulation panels [57,93,155,156].

In Finland, research has been conducted on peat moss use as an effective insulation solution in buildings. It is also possible to use lowland peat as a raw material to produce thermal insulation materials. Thermal insulation materials using peat consist of peat binders, additives, and components for creating a framework [94,156]. It has been found that thermally treated fen peat, also known as black peat, can be mixed with gypsum and tar, which can then be used to produce thermal insulation materials [33,157].

There are examples of successful models in which the raw materials for creating heat insulation panels are wood in combination with peat, and the peat serves as a binder. Using peat as a binder makes it possible to produce sound-absorbing panels, whereas several models use natural fibres. These panels, made from natural resources, compete with synthetic materials [99,152].

If the thermal conductivity of a thermal insulation material is to be assessed, thermal insulation materials where peat is used can be compared to mineral wool on the market. It is estimated that the coefficient of thermal conductivity of peat moss material is 0.35 mW/mK [100], which is significantly lower than other insulation materials. In the panel production process, resin strengthens the thermal insulation panels [99,100].

Peat moss has potential use in the thermal insulation boards used in construction, with lower thermal conductivity in comparison to other materials [100]. Mats and moss slabs with a 100 kg/m³ density are estimated to have a thermal conductivity of 0.04 W/mK [100]. Peat moss is estimated to absorb ~30 times its weight in water before it becomes saturated [100]. Insulation panels made from peat moss possess better mechanical properties than wood panels. Peat moss panels are denser in comparison to other materials. Peat moss boards that contain tannin are comparable to cotton, and wet-processed peat moss boards have a higher water absorption than dry-processed [100].

3D-printed houses.

Peat mixture as an innovative solution in the building sector has emerged in recent years in Europe. Peat use in construction materials is more common in Norway, where peat is used in building new houses or renovating. Peat’s use in producing 3D-printing technologies as a construction material has been investigated in Estonia [156,157,158]. Geokar peat blocks are made using peat processed into a paste combined with straw or sawdust, which can be used to construct thermal insulation panels. Peat blocks can even be used for up to 75 years. It is estimated that using peat blocks in the building sector can reduce energy consumption. Architects have increasingly used biopositive materials in renovation and eco-building. Another possibility for peat use in construction is fibreboard made from agricultural residues and peat moss. Fibreboard using peat moss was evaluated as an effective and practical solution among the other insulation materials [156,158].

Peat has been successfully used as an effective thermal insulation material with high thermal properties. Peat’s thermal conductivity as an insulation material is from 0.037 to 0.08 W/m/K) [158]. Peat also has attractive antibacterial properties for use in construction materials [158].

A new type of peat composite building material was developed, allowing for the three-dimensional printing of entire house structures (walls, floors, ceilings, etc.). Peat can be used as a filler to improve materials’ thermal properties. The test samples were 3D-printed using a novel printing apparatus. The print head was a nozzle that conveyed a moist peat–ash mixture with compressed air [158]. In existing 3D printing technologies, concrete fibre clay has been used, but in test samples, a mixture of peat, silica, ash, and water was used for printing. The samples were kept at room temperature and 100% relative humidity [158]. Currently, the vast majority of production is focused on either planting substrates or using the product as fuel for heating purposes. It is possible to utilise peat as a building material, including for the 3D printing of whole buildings and for creating panels that provide thermal and acoustic insulation. Peat composite materials and their use as construction materials have been evaluated for their potential to reduce CO₂ emissions from peat [158].

• Biocomposites from peat

Peat composite materials in blocks or pellets are estimated to have potential in design and construction. The possibility of using peat is presented in the production of biological adhesives, where peat is a binder. For peat to be used as a biological binder, it must first be treated using hydro cavitation [159]. Biodegradable polymers should also be added to composite materials. Composite materials can be used both in construction and as a material for furniture production [160].

• Packaging

Research shows that it is possible to use peat as an ingredient in biodegradable packaging, also promoting carbon sequestration. These packaging materials are an alternative solution to traditional plastics from fossil materials, reducing GHG emissions. Studies have shown a promising efficiency for peat as a raw material in packaging production. It has been investigated that it is possible to use peat as a raw material in producing biodegradable containers and films, thus offering the opportunity to use biological materials instead of traditional fossil materials. Such materials are rated as highly resistant to moisture and rotting risks [30,94,95].

• Sorbents

It is possible to produce biosorbents from peat. Sorbents can be made from unprocessed peat. Biochar, where peat is used as a raw material, can serve as an alternative solution to chemical sorbents. Using biochar produced from peat positively affects carbon sequestration and water retention and improves soil fertility. Peat has been assessed as having a high potential for environmental remediation [161]. Using peat and producing activated carbon to purify liquid or gaseous media from pollution is also possible. The processing methods used are heat treatment and chemical modification. During the pyrolysis of peat, volatile organic compounds and moisture are separated, forming a denser carbon content. After removing organic compounds, the structure is porous, and biochar can provide better sorption. Decomposed peat can produce solid sorbents used to purify water from heavy metals, wastewater, and radioactive compounds [146,147,162]. The use of peat moss in biochar production has proven the possibility of removing higher concentrations of heavy metals from polluted water—with peat biochar, it was possible to remove more than 80% of lead and almost 40% of cadmium compounds from polluted water. Due to its porous structure and hydrophobicity, peat can be used as a sorbent to separate crude oil from water. Peat biosorbents are both a cost-effective solution, and biologically produced sorbents have been used more in recent years to remove crude oil in marine compared to chemical sorbents [146,147,162].

Activated carbon can also be used in the food industry, as well as in the pharmaceutical field. The possibilities of using activated carbon are also highly appreciated in the chemical industry, as it can be used to produce synthetic fibres. Compared to synthetic fibres, peat fibres are rated at lower costs. A low ash content characterises peat, and it is, therefore, evaluated as promising to produce activated carbon as a sorbent [162].

• Filtration systems

The possibility of peat has been assessed for use in water filtration systems and municipal wastewater treatment. Peat is suitable for water treatment because of its porosity and filtering properties, essential for removing pollution from water. Peat is used as activated carbon or as a peat filter. With a peat filter or activated carbon, it is possible to purify water from heavy metals and organic compounds [163]. Peat moss can be used as a raw material to produce activated carbon. Activated carbon can be widely used in soil and water purification from organic and inorganic pollution sources [6].

• Medicine and cosmetics

The possibilities of using peat are still being studied in pharmaceuticals and medicine. The use of peat in physiotherapy has been estimated as a potential application due to its heat capacity because of its decomposition state. Other uses include natural steroid formulations that use peat or anti-wrinkle products with peat ingredients. The selection of proper preparations requires research and the selection of raw materials, as the preparations must have a certain chemical composition and organic and mineral compounds [6,162].

• Use of Humic acids

It is possible to dye paper with peat humic acids, reducing the release of hazardous compounds into wastewater that the dyed paper would otherwise cause. Studies have indicated that peat humic acids can be used as additives to influence the structure and properties of lubricants. Peat can be converted into humic acids and used to mix and process rubber. Humic acids have a wide range of uses: possible additives, antioxidants, pigment dispersants, and colourants [33].

• Remediation of degraded soils

The potential for using peat has been assessed directly for the economically beneficial restoration of degraded soils. Peat material is used as a solution in rehabilitation processes. The use of peat to restore degraded soils is also called bioremediation. During this, peat separates oil and other polluting substances from soils, for example. In bioremediation, the absorbed oils are transformed into water and CO₂ using peat [14,33].

The applications of peat based on the literature mentioned above are shown in Figure 5.

4. Discussion

An analysis of the methods of peatland restoration shows that biochemical trade-offs do not often need to be sufficiently considered. This is mainly due to the lack of long-term ecosystem-level monitoring of CH₄ in northern peatlands. Plant species composition, depth of water table, or soil pH are not sufficiently taken into account [40,125]. To reduce GHG emissions from peatlands, attention must be paid to agricultural lands where drainage has occurred. These degraded peatland restoration strategies are related to the improvement of landowner and farmer knowledge about the effects of drainage, peatland rewetting afforestation of peatlands, and the impacts on peatland hydrology and climate change [63,71,117]. Increased concentrations of DOC in water bodies are often associated with peatland drainage and degraded peatlands. Naturally formed northern peatlands are estimated to be a significant source of GHG emissions due to their constant wet conditions [40,164].

In a study [29], it was estimated that in the first four years after rewetting, CH₄ emissions increased by ~0.033 ± 0.003 Mg CH₄/ha⁻¹ yearly [29]. To evaluate the effect of rewetting, a prolonged period should be considered. Often, there are arguments that increased CH₄ emissions after rewetting will decrease after a brief period. In the case of a lack of water table control after rewetting, GHG emissions could remain high for a long period [5]. Some studies [11] even estimated that more than 30 years after rewetting, the average yearly emissions of CH₄ are approximately twice as high as before the extraction of peatland [11].

The effect on nutrient flow and GHG emissions using brackish water for rewetting is still uncertain compared to freshwater [39]. Regarding coastal peatlands, a study [39] estimated that using brackish water for rewetting can have smaller CH₄ emissions compared to rewetting where freshwater is used [39]. Peatland rewetting impacts nutrient mobilisation and eutrophication in nearby water bodies and releases an essential amount of CH₄. Similarly, peat saturated with water promotes nitrate attraction [39]. Studies [39] have shown that rewetting previously drained coastal peatlands can be a GHG emission source in the first year. Regarding coastal peatlands, it is estimated that rewetting can result in unmonitored inputs of nutrients in nearby water in the short term [39]. After the peatlands’ rewetting, the peat bulk’s density could remain high. Therefore, because of rewetting, new biotopes like eutrophicated lakes can form on the degraded soil [12,52].

According to the literature sources, there is still some uncertainty regarding the DOC concentration level after peatland rewetting [29]. Some studies have shown no effects on DOC concentrations after peatland rewetting, or the effect is vague [29]. For a successful restoration strategy and mobilisation, it is vital to assess CH₄ fluxes. It is estimated that rewetting might reduce net CO₂ emissions in reforested sites by ~15.4 Mg CO₂ equivalent ha⁻¹ annually, a 25% reduction in the total [29]. Monitoring should be improved to ensure control over the nutrient release in nearby water bodies near peatlands. The monitoring of vegetation and hydrology should be simultaneously evaluated [51]. Monitoring should be conducted before and after peatland restoration [51]. Several methods can be used in peatland monitoring, including spatial analysis, aerial and drone photos, and a combination of vegetation, hydrology, and GHG emission measurements [50].

Brackish water use for peatland rewetting can reduce GHG emissions. It is also estimated that the reduction of CH₄ emissions after rewetting can be achieved by using fresh water for rewetting [29]. Reducing CH₄ emissions from rewetting and restoring the balance of the carbon topsoil removal can be used to avoid additional nutrient release. Removing the topsoil before rewetting can reduce eutrophication by 80–95% and DOC mobilisation by 60% [70]. Using topsoil removal, it is possible to reduce CH₄ emissions by 99% in comparison to emissions without topsoil removal [40,70].

It is estimated that the rewetting of peatland in combination with paludiculture using sphagnum farming [34] can have a positive impact on climate change mitigation [125]. Recent studies have shown that among restoration methods, the highest rate of sequestration of CO₂ > 1000 kg carbon ha⁻¹ y⁻¹ is from paludiculture practices [34]. According to recent studies, peatland restoration should include a hydrology restoration regime. On the other hand, afforestation should not be defined as restoration [34,86]. According to the literature, some sustainable land practices might reduce peat loss, including zero tillage in agriculture and cover cropping on fields [30]. Cover cropping combined with a higher water table may result in the reduction of GHG emissions and reduce nutrient inputs. However, there is essential indeterminacy regarding the long-term effect of cover cropping on peatlands [30]. In Finland, several solutions are used, including increasing vegetation, reducing soil tillage, avoiding peatland cutting, and converting land into paludiculture or peat forests [127]. Zero tillage combined with increasing water table seasonally could reduce GHG emissions [30]. This contradicts studies that determined that these practices might have the minimum effect on reducing GHG emissions [30].

To promote sustainable peatland management, peatland national strategies based on peatland conservation and promotion of the achievement towards sustainable development goals are crucial, which is not only in countries with great peatland areas [31]. In recent years, several European countries have developed their national peatland strategies, and other countries that still need to develop their strategies can gain common knowledge from other strategies [31]. For the establishment of national strategies, the absence of proper data can be an issue for correct evaluations [31].

According to earlier scientific studies, there is potential and necessity for improvements regarding peatland restoration strategies and methods [50]. Some of the recommendations are related to the opportunity to combine ecological and hydrological methods in peatland restoration [18,50].

National peatland policy aims should be more precise and specific, linking requirements with international principles in peatland restoration [50]. Peatland restoration success is affected by the gaps in restoration targets, a lack of detail, and the inability to determine the measurability of the results of the defined goals [50]. Peatland restoration can be negatively affected by policies that are too generic without specific, measurable outcomes regarding the quality of water [49]. Recommendations based on previous studies implementing more precise protocols for measuring data [49].

To select the right instrument among the substantial number of policies, one must consider environmental and socioeconomic factors, as well as landowner rights [112,116,127] Landowners and farmers can implement publicly available best practices in peatland management even if specific government regulations are not established [53]. Previous studies show that there is still a gap in knowledge regarding the estimation of carbon sequestration and storage possibilities among policymakers and ecosystem managers [50,53].

According to previous studies, on the path to sustainability, it is crucial to investigate innovative practices in peatland management [53].

5. Conclusions

There are a lot of uncertainties regarding GHG emission reduction in the long term. The success of rewetting should be evaluated over a longer period; some studies even argue that there is no decrease in CH₄ emissions after 30 years of rewetting. To gain successful results of rewetting and achieve emission mitigation, both methods—rewetting and revegetation—should be combined, especially for peat extraction sites, to be defined as restoration. According to studies, rewetting is a water table rise and cannot be defined as restoration. After rewetting, revegetation should be performed by introducing sphagnum species that can pump out methane that increases after rewetting and causes faster peat accumulation.

Recent studies argue that the afforestation of peatlands should not be considered as restoration. Also, drained and afforested peatlands, especially in boreal zones, are more vulnerable to wildfire risks, generating a great amount of GHG emissions from wildfires.

For sustainable peatland management, proper strategies and methods are required to reduce the degradation of peatlands. To advance peatland management, more involvement of landowners and local communities in the decision-making process is required, enhancing knowledge of peatland’s role in reducing GHG emissions. Industries and scientists should be allowed to promote more innovations and alternative solutions in peatland management. Strategies should also include more active interactions between organisations, industry, scientists, government, and landowners for sustainable peatland restoration and the creation of innovative solutions. Part of peatland management is continuous research promotion to encourage the production of new technologies and products where peat is used as a valuable raw material.

Coherent policy and peat use as an energy resource, not as a commercially usable resource, are some of the drawbacks in peatland management. One of the solutions for better and more effective management of peatland restoration should be to use a greater combination of restoration methods. For example, the rewetting of peatlands should be realised in combination with topsoil removal before rewetting and revegetation after rewetting. After rewetting, one of the promising solutions for methane emission reduction could be paludiculture using sphagnum species. Paludiculture can also be the solution for further income for landowners and new innovative product development using biomass of harvested paludiculture plants.

This review confirms that peat products and materials can compete with similar products in the market because of their unique properties. Peat products can replace some products where fossil materials are used. Peat, as a resource, has a wide range of applications in industry, from agriculture and construction to pharmaceuticals and medicine. Future peatland management strategies should consider alternatives to peat treatment, storage, and technological solutions to produce high-value-added peat products and materials that sequester carbon in the environment in production processes. The materials obtained from peat can also be used as a component in biodegradable packages, biosorbents, and filtering materials for water purification, and in bioremediation for the purification of contaminated soils. It is possible to obtain humic acids from peat, widely used in industry as dyes, air filtration systems, and batteries. Using peat in the bioeconomy can reduce the losses caused by peatland management and emission and also provide new innovative options for mitigating and managing the effects of climate change and achieving climate goals. Therefore, exploring alternative and novel strategies to reduce CO₂ emissions from peatlands, improve peat processing, and develop new, commercially viable peat-based products is critical.