Peat soils are formed from partially decomposed plant material under anaerobic water saturated conditions. They are found in peatlands (also called bogs or mires). Peatlands cover about 3% of the earth’s land mass; they are found in the temperate (Northern Europe and America) and tropical regions (South East Asia, South America, South Africa and the Caribbean) 1.
Peat soils are classified as histosols. These are soils high in organic matter content. Peat formation is influenced by moisture and temperature. In highly saturated anaerobic soils, decomposition of plant material by micro organisms is slowed down, resulting in high carbon accumulation. In colder climates decomposition of plant material by micro organisms is slowed down leading to quicker peat formation. The carbon content of peat soils makes peatland a major storage of carbon on the earth surface. This is why its importance in fighting climate change can never be overemphasized.
Some economic benefits of peatlands
Peatlands bring enormous economic benefits to regions where they are found.
1. Peat is extracted for use as horticultural compost. It is highly sought after in commercial horticulture because of its high water retaining ability and flow of air.1
2. Peat is used for fuel to generate electricity. It is also sold as briquettes for heating homes in cold climatic regions.
3. Peatlands are drained and used for agricultural purposes (pasture and crop production) and forestry.
Peat use for forestry and agriculture are beneficial but it alters the natural peatland hydrology. This causes oxidation of stored carbon therefore declining its organic matter content. During peat extraction, peat is drained and dried before storage or transportation for sale. These processes reduce the water content and encourage microbial decomposition of organic matter. The result of this is the release of greenhouse gasses such as CO2 and N2O.3, 4
Consequences of peat disturbance
Apart from greenhouse gas emission, peatland disturbance brings a number of other changes:
1. Drainage of peatland causes decline in biodiversity because its natural hydrological habitat is disturbed. Peatlands provide habitation for diverse species of meadow birds, animals, vegetation and insects.
2. Peat oxidation can lead to release of dissolved organic matter and peat particles into surface waters.
3. Peat oxidation can lead to the loss of a historical heritage. Peat soils have the ability to store human remains or ancient artefacts for thousands of years; since they have very minimal microbial decomposition. A good example of this is the 4000 year old body of a man found in peat from Cashel-Central Ireland.
4. Peat soils drained for agricultural purposes are more vulnerable to wind and water erosion when the topsoil is severely dry.
5. Drainage of peatland can lead to peat fires which destroy forestland and habitation and further increase the emission of CO2 to the atmosphere.
Although the above listed are negative consequences of peat disturbance, it is good to acknowledge that when peat soils are drained for use in agriculture, decomposition of organic matter is accelerated leading to the mineralization of nitrogen (a vital nutrient for plant growth). This in fact is a good thing. You can learn more about this from the nitrogen cycle.
Peatland conservation and restoration
1. Conserve wet peatlands: This approach is preventive and avoids the expensive cost of restoring peatlands to their natural hydrological state. This is simply putting a stop to the drainage of peatlands. There is no need for soil restoration projects if efforts are made to keep the soil in its natural state. People in surrounding communities must be educated on the benefits of conserving the peatland natural ecosystem.
2. Use of paludiculture: This method also maintains the wetness of peatlands. Paludiculture involves the cultivation of biomass crops on peatlands without disturbing the peat natural hydrology or ecosystem. There is no drainage of the peatland involved. It has multiple benefits; it reduces peat oxidation, greenhouse gas emission and at the same time supplies biomass used for combustion. It also serves as a source of food for neighbouring communities as some edible crops grow on the wetland. Examples of edible crops in paludiculture are wild rice -Zizania aquatica (also called floating rice), wild edible berries (blue berries, black currant, black raspberries) and sweet grass Hierochloe odorata. Paludiculture is practiced in Europe (Russia and Belarus) North America and Asia (Indonesia and Malaysia).
3. Re-wetting and restoration: In re-wetting effort is made to restore the soil back to its natural hydrological, anaerobic state by raising the water table level to the land surface. Re-wetting reduces CO2 and N2O emissions but increases the emission of CH4 (which is released naturally in undisturbed peatlands).4,6 Under anaerobic conditions decomposition of plant material by micro organism is slow but still in action. Decomposition of organic material under this condition is carried out by methanogenic Archaea (a methane producing micro organism).4
Bibliography and Further Reading
1. Puustjärvi V (1973) Physical properties of peat used in horticulture. ISHS Acta Horticulturae 37: I Symposium on Artificial Media in Horticulture.
2. Renou-Wilson et al. (2011) Bogland – sustainable management of peatlands in Ireland. STRIVE Report No 75. Environmental Protection Agency, Johnstown Castle, Co. Wexford, p. 157.
3. Byrne et al. (2004) EU peatlands: Current carbon stocks and trace gas fluxes. Retrieved from: https://scholars.unh.edu/earthsci_facpub/
4. Couwenberg J. (2011) Greenhouse gas emissions from managed peat soils: is the IPCC reporting guidance realistic. Retrieved from: https://www.mires-and-peat.net.
5. Wichtmann et al. (2016) Paludiculture – productive use of wet peatlands Climate protection – biodiversity – regional economic benefits. Schweizerbart Science Publishers, Stuttgart, p. 272.
6. Couwenberg J (2009) Methane emissions from peat soils (organic soils, histosols) Facts, MRV-ability, emission factors. UN-FCCC meetings in Bonn. Wetlands International Ede. www.wetlands.org.