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Fens

What is a fen?

Fens are peatlands with over 40 cm of accumulated peat that is primarily composed of sedge and brown moss plant materials. This is an important distinction from bogs, as it can point to a system which receives more varied water sources (e.g. groundwater), and fens are typically more nutrient rich than bogs. Fens can also look very different because of how they receive water compared to bogs. Some fens may be treed and look like bogs, while others may have water channels lined with sedges. Vegetation characteristics vary based on the wetness of a site – sedges dominate at wetter sites, shrubs (e.g. willow and alder) at drier sites.

Diagram of a fen

Types of wetlands

Canada’s wetlands can be broadly categorized into two types: organic and mineral. Within these categories, they are further grouped into five classes: bog, fen, swamp, marsh, and shallow water wetlands.

Organic wetlands

Organic wetlands are known as peatlands (or muskeg) and include bogs and fens and sometimes swamps. These wetlands have accumulated 40 cm or more of organic material (peat).

Bogs

Bogs

Bogs are peatlands with over 40 cm of accumulated peat, averaging 3 to 5 m, and with some exceptional cases reporting up to 10 m.

Fens

Fens

Fens are peatlands with over 40 cm of accumulated peat that is primarily composed of sedge and brown moss plant materials.

Mineral wetlands

Mineral wetlands include swamps, marshes and shallow water. Mineral wetlands are characterized by saturated (wet) soils resulting in gleying (blue-grey colour) and mottling (red or brown mottles). There may be some organic material (peat) accumulation, but it is a thin layer less than 40 cm thick.

Marshes

Marshes

Marshes are mineral wetlands with areas of shallow water that tend to fluctuate (change up and down), daily, seasonally or even annually.

Swamps

Swamps

Swamps, sometimes called thickets, are dominated by either trees or tall shrubs.

Shallow water wetlands

Shallow water wetlands

Shallow water wetlands (that may also be called ponds, shallow lakes, oxbows and sloughs), are a distinct class of mineral wetlands.

Salt marshes

Salt marshes

Salt marshes are tidal wetlands typically found in the upper intertidal zone between mean sea level and high tide, where salt- and flood-tolerant vegetation can grow.