The purpose of this section is to give the readers a general knowledge about peat bogs. Research and text are by Ms. Catherine ÉMOND, M.Sc. and biologist. Translation by Françoise de MONTIGNY-PELLETIER.
In the province of Quebec, peat bogs cover between 7 and 9% of the territory. These numbers are the equivalent of about 82 600 km2 and 106 200 km2 (Poulin and Pellerin, 2001).
In Canada, 1 700 000 km2 or 17% of the lands surface are covered by peat bogs (Gorham, 1990).
A peat bog is a wetland developing itself on a site poorly drained and where can be noted an accumulation of organic matters at least 40 cm thick (Warner and Rubec, 1997).
It is actually a system in which the production of vegetal matter is bigger than the quantity of decayed matter. The lack of oxygen, caused by water saturation and vegetation slow to decay, will generate a very poor rate of decomposition by bacteria and other micro-organisms. This unbalance process will induce, year after year, the formation of an organic soil thicker and thicker.
By the transformation of terrestrial and aquatic habitats into peat bogs. Peat appears when soil is filling a pool, a process called terrestrialization, and/or by paludification of a terrestrial site. Peat created by filling occurs in small pools, not deep, colonized by floating aquatic plants. This process will be accelerated if the water level gets lower allowing plants to gradually cover the whole pond’s surface.
Paludification is more common and has given birth to the wide peat bogs found in temperate, boreal and subarctic regions. It will occur in badly drained sites covered or not with plants, where the underground water-level is near the soil surface.
In such conditions, plants can invade the site and even spread over the peripheral grounds if the underground water table increases (see in Payette’s work, 2001).
Peat bogs are classified following two large types: ombrotrophic peat bogs, also named bogs,
and minerotrophic ones, or fens (Warner et Rubec, 1997).
Hydrology, water physico-chemistry and vegetation are the main factors characterizing the two types (Gorham et Janssens, 1992; Rydin et Jeglum, 2013). Water supply in minerotrophic peat bogs has minerogenic origins, it means that it comes from waters in contact with a mineral substratum on the catchment area. Fens are generally located at a lower level of the ground or right on a slope helping water run down to the peat bog. In addition to surface waters, water supply can be brought by underground springs (these peat bogs are named terrigenous). Fens can also be located along a stream (littogenous or riparian peat bogs).
The type of substratum, influencing the water content in mineral components and the power of water spreading into the peat bog will determine the peat bog richness. A peat bog fed by a water enriched with calcium and magnesium and having a pH over 5,5 will be considered rich. A peat bog with a water having low concentrations in minerals with a pH between 4,5 and 5,5 is considered as poor. Peat accumulation in a rich fen may diminish the hydrologic link with minerotrophic waters, transforming this rich fen into a poor one. This transition will be quickly done and will last from few years to few decades only. Vegetation is directly affected by the origin of water. A very wide diversity of specialized species will grow only in rich fens. Many types of mosses belonging to the brown mosses category will multiply in such bogs. Specific sphagnum species thrive only in rich fens. Plants of grass-leaved type from the sedge family will sometimes dominate on large surfaces. The vegetation in poor fens is similar to the one of bogs. Many species of sphagnum and heaths will colonize this kind of area. Progressively, with peat accumulation, the peat bog surface will elevate enough to allow vegetation to be free from minerogenic waters and this will create a doming of the surface and the birth of an ombrotrophic peat bog. This one gets water exclusively from precipitations. Mineral components being very limited in rain falls, these environments are very poor. The very acidic pH is between 3 and 4,5. Only the flora adapted to these difficult conditions may survive. For example, sphagnum, heaths and carnivorous plants thrive in abundance in bogs.
The answer is: both.
Let us look at the picture showing the pH scale.
On the left, the red rectangle indicates the acid characteristic while the blue rectangle, on the right, shows the alkaline one.
Following the synthesis done by Andersen, Rochefort and Landry (2001), generally, the water pH in ombrotrophic peat bogs goes from 2,8 to 5,4. The pH in minerotrophic peat bogs can reach as much as 8-8,5 in extreme cases.
Sphagnum are considered as engineers in their own ecosystem because they are contributing to their habitat modification in order to multiply.
Thanks to their strong cation exchange capacity (CEC) allowing them to exchange cations with the immediate environment, thanks also to their great productivity and their important capacity to accumulate water into the peat, they succeed in raising the peat bog surface and also the underground water table by capillarity and in releasing compounds (H+) that will acidify the environment (Gauthier, 2001; Payette, 2001).
Unlike vascular plants that take water and minerals with the help of their roots, bryophytes (among them sphagnum and brown mosses) do not have vascular tissues to transport water and nutrients. It is the CEC that allows them to get the necessary nutrients (Clymo et Hayward, 1982).
Floral diversity found in peat bogs is associated with:
► mounds and hollow grounds models where each species has its own preferences in pH and humidity (Andrus, Wagner, Titus, 1983; Clymo et Hayward, 1982; Vitt et al., 1975),
► gradient between centre and peat bogs edges where trees are sometimes more numerous (Gauthier et Grandtner, 1975 ; W. H. Damman et Dowhan, 1981),
► richness gradient in indicatory species related to minerotrophic or ombrotrophic peat bogs,
► and climatic gradient between regions where are located peat bogs (continental and maritime) (Vittet Slack, 1984 ; Gignac et al., 1991 ; Gignac, 1992).
Micro-organisms involved in the decomposition process need most of the time oxygen, nutrients and a pH close to neutrality in order to function efficiently. As the underground water table under peat bogs is near the surface and because these bogs are poor in nutrients and are rather acid, it becomes logical that the decomposition will be mainly slow. These micro-organisms are fungus specialized in decomposing the matter. They are named saprobes.
First, peat bogs are the home for a very specific biodiversity. They are often considered as «boreal islands» within a temperate region. Although this species diversity found in peat bogs is not too high, it is typical to the peat bogs and still contributes to raise the regional biodiversity where they exist.
Secondly, they also can be used as paleo-ecological archives as their decomposition rate remains very weak. Debris stuck into peat are preserved for thousands of years. In northern Europ, naturally mummified humans since the Iron Age (around 2050 to 2800 years before now) have been studied thanks to their conservation conditions in peat (Glob, 1966). As for vegetal remains like pollens, seeds and charcoal, that will be preserved in peat bogs and will give researchers precious clues about past times.
Macrofossils (vegetal and animal) and microfossils (pollen seeds and thecamibes) can then be used to reconstitute environmental conditions prevailing since the ice retreating and about as much the regional climate and perturbations (fires, insects) as the history of the peat bog (Bhiry et Filion, 2001). Thirdly, we may add that peat has the capacity to filter contaminants possibly carried by the wind and surface waters. These surface waters come from precipitations, fogs and melting snow and are absorbed by peat, that allowing the formation of clean water supply. Finally, peat bogs are storing great amounts of carbon (carbon sequestration). Normally, plants would capture carbon dioxide (CO 2) with the help of photosynthesis all along their life, but will release it when decomposing.
As mentioned before, the high water table level in peat bogs will result in a lack of oxygen in the ground, for that reason and because of their acidity and a low availability of nutrients found in them, the micro-organisms involved in decomposition will not be able to work as efficiently as they would in well-aired and nutritious ground conditions. Carbon of which plants are made then is kept inside peat bogs instead of being released in the atmosphere and contributing to the planet warming. In conclusion, peat, it is carbon! Scientists estimate that peat bogs have stocked between 50 et 150 kg/m2 of carbon since the last glaciation (Gorham, 1991 ; Ovenden, 1990 ; Vitt et al., 2000). At the world scale, wetlands are stocking about one third of all the carbon in grounds. But, draining associated to peat extraction (as for natural draining) will diminish the quantity of stocked carbon when eliminating vegetation and will release CO 2 when lowering the underground water table, that helping decomposition but contributing on the other hand to the reduction of the ecological role of peat bogs (Glenn, Heyes,et Moore, 1993).
Andersen, R., Rochefort, L., et Landry, J. (2011). La chimie des tourbières du Québec : une synthèse de 30 années de données. Le Naturaliste Canadien, 135(1), 5–14.
Bhiry, N., et Filion, L. (2001). Analyse des macrorestes végétaux. In L. P. de l’Université Laval (Ed.), Écologie des tourbières du Québec-Labrador (pp. 259–273).Québec.
Clymo, R. S., et Hayward, P. M. (1982). The ecology of Sphagnum. In C. & Hall (Ed.), Bryophyte Ecology (p. 229–289). London.
Coupal, B., et Lalancette, J. (1976). The treatment of waste waters with peat moss. Water Research, 10, 1071–1076.
Damman, A. W. H. (1986). Hydrology, development, and biogeochemistry of ombrogenous peat bogs with special reference to nutrient relocation in a western Newfoundland bog. Canadian Journal of Botany, 64 (2), 384–394. Doi:10.1139/b 86-055
Damman, W. H., et Dowhan, J. J. (1981). Vegetation and habitat conditions in Western Head Bog, a southern Nova Scotian plateau bog. Canadian Journal of Botany, 59, 1343–1359.
Gauthier, R. (2001). Les sphaignes. In L. P. de l’Université Laval (Ed.), Écologie des tourbières du Québec-Labrador (2ème ed. 2005, pp. 91–128). Québec.
Gauthier, R., et Grandtner, M. M. (1975). Étude phytosociologique des tourbières du Bas-Saint-Laurent, Québec. Naturaliste Canadien, 102, 109–153.
Gignac, L Dennis, Vitt, D. H., Zoltap, S. C., et Bayley, S. E. (1991). Bryophyte response surfaces along climatic, chemical , and physical gradients in peatlands of western Canada. Nova Hedwigia, 53(1-2), 27–71.
Gignac, L.D. (1992). Niche structure, resource partitioning, and species interactions of mire bryophytes relative to climatic and ecological gradients in Western Canada. American Bryological and Lichenological Society, 95(4), 406–418.
Glaser, P. H. (1987). The ecology of patterned boreal peatlands of northern Minnesota : A community profile. Biological Report, 85(June).
Glenn, S., Heyes, A., et Moore, T. (1993). Carbon dioxide and methan fluxes from drained peat soils, Southern Quebec. Global Biogeochemical cycles, 7(2), 247–257.
Golb,P.V. (1966). Les hommes des tourbières, Paris, Fayard, coll. «Résurrection du passé», 152 p.
Gorham, E. (1990). Biotic empoverishment in northern peatlands. Dans The earth in transition : patherns and processes of biotic impoverishment. Edited byG.M. Woodwell. Cambridge University Press. New York. p. 65-98.
Gorham, E. (1991). Northern peatlands: Role in the carbon cycle and probable responses to climatic warming. Ecological Applications, 1(2), 182–195.
Gravelle, D. V., et Landreville, E. (1980). Caractérisation de la tourbe pour le traitement des eaux usées d’abattoirs. The Canadian Journal of Chemical Engineering, 58 (April), 235–240.
Kivinen, E., et Pakarinen, P. (1981). Geographical distribution of peat ressources and major peatland complex types in the world. Annales Academiae Scientiarum Fennicae A III, 132, 1–28.
Lafrance, C., Lessard, P., et Buelna, G. (1996). Évaluation de la filtration sur tourbe et compost pour le traitement de l’effluent d’une usine de compostage de résidus verts. Canadian Journal of Civil engineering, 1050, 1041–1050.
Ovenden, L. (1990). Peat accumulation in northern wetlands. Quaternary Research, 33, 377–386.
Pakarinen, P. (1995). Classification of boreal mires in Finland and Scandinavia: A review. Vegetatio, 118, 29–38.
Payette, S. (2001). Principaux types de tourbières. Dans Écologie des tourbières du Québec-Labrador (2ème édition), Les Presses de l’Université Laval (Ed.). Québec. p. 39–89.
Poulin, M. et Pellerin S. (2001). La conservation. Dans Écologie des tourbières du Québec-Labrador (2ème édition), Les Presses de l’Université Laval (Ed.). Québec. p. 505-518.
Viraraghavan, T. et Rana, S. M. (1991). Treatment of septic tank effluent in a peat filter. International Journal of Environmental Studies, 37(3), 213–224. doi:10.1080/00207239108710632
Vitt, D.H., Crum, H. et Snider, J. A. (1975). The vertical zonation of Sphagnum species in hummock-hollow complexes in northern Michigan. Michigan Botanist, 14(4), 190–200.
Vitt, Dale H, Halsey, L. a, Bauer, I. E., et Campbell, C. (2000). Spatial and temporal trends in carbon storage of peatlands of continental western Canada through the Holocene. Canadian Journal of Earth Sciences, 37(5), 683–693. Doi:10.1139/e99-097
Vitt, Dale H, et Slack, N. G. (1984). Niche diversification of Sphagnum relative to environmental factors in northern Minnesota peatlands. Canadian Journal of Botany, 62, 1409–1430.
Wells, E. D., et Zoltai, S. C. (1985). The Canadian system of wetland classification and its application to circumboreal wetlands. Aquilo Series Botanica, 21, 45–52.