Despite the fact that the Canadian Wetland Classification System is optimized to classify wetlands in Canada, wetlands all over the world can be classified using it. The system recognizes that wetlands can be classified according to their mineral levels and organic contents.

1) Mineral-rich Wetlands refer to wetland environments that contain a high level of minerals. The mineral level is important to a wetland because minerals determine the types of plants that grow there. A certain level of minerals, such as phosphorus, potassium and calcium, is needed for all plants to grow and to remain healthy. The minerals in these environments usually come from the water. Seawater and groundwater, which contribute water to mineral wetlands, also supply minerals for these ecosystems.

Organic Wetlands are so-named because their soils are covered with organic materials. This organic material is called peat. Consequently, organic wetlands are also called peatlands. In the Canadian Wetland Classification System, peatlands are defined as environments that contain at least 40 centimetres of peat accumulated in the soil. Peat is a brown/dark brown organic substance that results from the accumulation of dead plants. A number of plants, namely sedges, grasses, shrubs, trees, or mosses can form peat. Peat formed mainly by wood material is called woody peat; peat consisting principally of Sphagnum mosses is called Sphagnum peat.

In addition to classifying wetlands according to their mineral and organic levels, the system is structured with three hierarchical levels: class, form and type. Wetlands are classified into different classes, forms, and types according to many criteria. Some examples of these criteria are their surface type, shapes and sizes, and the characteristics of water on the wetlands. The five classes are: marshes, swamps, shallow water, fens and bogs.

Canadian Wetland Classification System by forms.

1) Marshes  

Marshes are periodically inundated by standing or slow-moving water. The easiest way to identify a marsh is to observe the water levels. The water levels in marshes usually fluctuate considerably. The pattern in which it fluctuates can be seasonal or diurnal. That means that if the water levels change in cycles that last roughly a day or a season, the wetland is a marsh. Mudflats are the most common examples of marshes. Flooding by tidal water occurs regularly in mudflats. They therefore display diurnally fluctuating water levels. All marshes are mineral-rich wetlands. Most marshes are flooded by seawater, though some are flooded by freshwater. Sedges and grasses commonly occur there. In some marshes, fast-growing mangroves grow. Peat is uncommon in marshes. In the rare exception of organic marshes, peat, usually formed by partly decomposed sedges and grasses, constitutes only a very thin layer.

Like marshes, swamps are also flooded. The main difference between swamps and marshes is that the water level does not fluctuate as regularly. The water source of a typical swamp consists mostly of mineral-rich groundwater and water from streams, rivers and lakes. Seawater usually does not contribute water to swamps. The water levels are usually at or close to the surface. The vegetation cover of swamps is characterized by dense deciduous trees. Coniferous trees, shrubs, herbs and mosses can also be found in some swamps. Peat is uncommon in swamps, and occurs only in thin layers.

Shallow Water is a class of wetland that is difficult to identify at times. It may or may not have fluctuating water levels. Because seawater, groundwater, melted ice, and freshwater are possible sources of water to this class of wetland, its mineral levels vary. Characteristic vegetation ranges widely among different sub-types. The only thing that distinguishes the Shallow Water class is that 75% or more of the surface area of these wetlands is occupied by mid-summer open water. Shallow water wetlands are distinguished from deep water by mid-summer water depth of 2 metres or less. Peat sometimes occurs in shallow water

2) Fens

Fens are mineral-rich peatlands. A typical fen receives significant amounts of mineral-rich groundwater. Grasses, reeds, and brown mosses characterize fens. As their name implies, bog mosses do not grow in fens. Trees can grow in fens, although they usually form only a sparse canopy cover. Trees do not grow as densely as in marshes. Peat is always found in fens. The thickness of the peat found in fens is less than that in bogs. Depending on the subtype, the thickness of peat found in fens ranges from 0.5 to 2 metres.

Bogs are mineral-poor peatlands. Bogs have only one major source of water: precipitation. Rainwater has very few minerals in it. Nutrient levels are also low in precipitation. Peat is always found in bogs, where it is generally thicker than in fens. Sphagnum peat characterizes peat in bogs’ soils. Other forms of peat, such as woody peat, and sedge peat, are common in bogs. A bog’s natural suitability to the formation of a thick peat layer relates to the interaction between the hydrology, the soil conditions, microorganism activities, and most importantly a very special plant – Sphagnum moss. 

People in different parts of the world call bogs by different names. Muskegs and moors describe similar environments to bogs. To avoid confusion, these terms are generally avoided in scientific reports.

Many wetlands are complex combinations of different kinds of wetlands described in the Canadian Wetland Classification System. For example, a wetland can be a wetland complex, consisting of a bog in the middle, a fen at the edge, and some shallow water around it. Wetlands can be classified by the locations at which they are found, as in the US Geological Survey Classification System.

So, what is a bog?

[> Joho Guide to Burns Bog]