Peatland Resource Centre

What are Peatlands?
Peatlands, often termed muskeg, differ from non-peat forming wetlands by a combination of interrelated hydrologic, chemical, and biotic factors that results in a decrease in decomposition relative to plant production allowing for the accumulation of peat. Peatlands represent an important terrestrial carbon sink, with an estimated 450 Pg currently stored (Gorham 1991) or 25% or the world's terrestrial carbon (Woodwell and Houghton 1991). The amount of carbon stored in peatlands is roughly equivalent to 3/4 of the total amount of global atmospheric carbon.

Wetland Classification and Ecology
A wetland is any land saturated with water long enough to promote wetland or aquatic processes as indicated by poorly drained soils, hydrophytic vegetation, and various kinds of biological activity that are adapted to a wet environment (NWWG 1988). The environmental processes that control wetland development form hydrologic, chemical, and biotic gradients and commonly have strong cross-correlations. These interrelated gradients are represented by five wetland classes, of which three are non-peat forming wetlands generally having < 40 cm of accumulated organics and two are peatlands with > 40 cm of accumulated organics. Non-peat forming wetlands are subdivided into 1) shallow open water, 2) marsh, and 3) swamp; whereas peatlands can be subdivided into 1) fen and 2) bog (Figure 1). This primary wetland subdivision forms the foundation for defining Alberta's wetlands (Alberta Vegetation Inventory 1997) and Alberta?s wetland policy (AWRC 1993).

Shallow Open Waters are non-peat forming wetlands that are characterized by aquatic processes confined to less than 2 m depth at midsummer. These wetlands have submergent to floating vegetation and form a transition to truly aquatic ecosystems. The chemistry of this wetland class is variable and does not distinguish it from the remaining four wetland classes, and floristic composition is dependent on chemical conditions.

Marshes
Marshes are open, non-peat forming wetlands that are dominated by sedges (Cyperaceae) and other monocots. Marshes are characterized by seasonal water level fluctuations, relatively high amounts of water flow, and are influenced by ground and surface waters. As a result, concentrations of nitrogen and phosphorus are high, leading to abundant vascular plant production; however, peat accumulation is limited by high decomposition rates. Mosses are generally lacking or not abundant as they do not compete well with rapid vascular plant growth and do not tolerate large fluctuations in seasonal water levels. As with shallow open waters, chemical differences in marshes strongly influence their floristic composition. Alkaline marshes (dominated by calcium and bicarbonate) are dominated by Carex, Scirpus, and Typha, whereas saline marshes (dominated by sodium and sulfate) are largely occupied by Salicornia and Scirpus.

Swamps
Swamps are forested, wooded or shrubby non-peaty wetlands. Swamps and marshes have a poorly developed bryophyte layer that results from strong seasonal water level fluctuations and high vascular plant production. Peat accumulation is limited in swamps as decomposition rates are high. Vegetatively swamps are quite diverse and in Alberta may be composed of some combination of Larix laricina, Picea mariana, Betula, and Salix.

Peatlands
Peatlands, often termed muskeg, differ from non-peat forming wetlands by a combination of interrelated hydrologic, chemical, and biotic factors that results in a decrease in decomposition relative to plant production allowing for the accumulation of peat. Peatlands represent an important terrestrial carbon sink, with an estimated 450 Pg currently stored (Gorham 1991) or 25% or the world's terrestrial carbon (Woodwell and Houghton 1991). The amount of carbon stored in peatlands is roughly equivalent to 3/4 of the total amount of global atmospheric carbon.

The initiation of peat accumulation is related to stabilization of seasonal water levels and restriction of water flow through a wetland, in conjunction with leaching of salts from the mineral substrate allows for the establishment and development of a moss layer. The stabilization of regional water tables appears to have been an important component in the successional change from prairie marshes to boreal fens in the western interior of Canada over the past 10,000 years (Zoltai and Vitt 1990).

The establishment of a moss layer results in the accumulation and maintenance of nutrients in a nonavailable form, reducing vascular plant production. Stabilized water levels, anaerobic conditions, and decreased nutrient availability lead to a substantial decrease in decomposition rates, that results in the development of peat accumulating ecosystems (Vitt and Kuhry 1992). As peat accumulates, surface vegetation can become isolated from the underlying substrate, coupled with biologic and chemical processes this can lead to acidification and oligotrophication. Alberta peatlands are classified into geogenous fens and ombrogenous bogs, each with distinctive indicator species, acidity, alkalinity, and base cation content (Figure 1).

Fens
Fens are geogenous ecosystems that are affected by mineral soil waters (ground and/or surface) that may be relatively rich in mineral elements. Fens can be subdivided on the basis of hydrology into: soligenous and largely influenced by flowing surface water; topogenous and largely influenced by stagnant ground water; or limnogeneous and largely influenced by associated lakes and ponds. All three fen types have water levels at or near the peat surface. Soligenous fens commonly have discrete patterns of open pools (flarks) alternating with elongate, shrubby to wooded ridges (strings) oriented perpendicular to the direction of surface water flow. These patterned fens may be either acidic or basic. Topogenous, limnogenous, and some soligenous fens are nonpatterned. Fens can be open and dominated by Carex, Scirpus, and Eriophorum; shrubby and dominated by Betula and Salix; or wooded to forested dominated by some combination of Picea mariana, Larix laricina, Betula, and Salix..

Originally based on criteria derived from vegetation, fens have in the past been subdivided on the basis of the number of indicator species. Poor fens are low in indicator species, while extreme-rich fens are high in indicator species; moderate-rich fens are intermediate. This gradient of indicator species correlates with a chemical gradient (Sj?rs 1952). Poor fens are acid (pH 4.5-5.5), poor in base cations and have no or little alkalinity. They are dominated by oligotrophic and mesotrophic species of Sphagnum. Moderate-rich fens have slightly acid to neutral pH (5.5-7.0) and have low to moderate alkalinity with a ground layer of brown mosses namely: Drepanocladus, Brachythecium, Calliergonella, and low abundances of mesotrophic species of Sphagnum. Extreme-rich fens have basic pH (above 7.0), high concentrations of base cations, and high alkalinity. They are characterized by species of Drepanocladus, Scorpidium, and Campylium and may contain marl deposits.

Bogs
Bogs are ombrogenous peatlands that receive their surface water only from precipitation and have low water flow. The water table is generally 40-60 cm below the peat surface. For these reasons bogs are acidic ecosystems with pH below 4.5; they are poor in base cations, and have no alkalinity. Bogs are dominated by oligotrophic species of Sphagnum; feather mosses: Pleurozium schreberi and Hylocomium splendens; and lichens of Cladonia and Cladina. They may be open, wooded or forested with trees limited to Picea mariana. As a result of the low thermal conductivity of dry Sphagnum, bogs have lower surface water temperatures then other surrounding organic and nonorganic soils. Permafrost is consequently restricted to bogs at its southern limit, where it forms peat plateaus and palsas (Vitt et al. 1994).