Introduction to Freshwater Wetlands

Wetlands

Wetlands are habitats that are either under water, or soaked with water part of the year. Freshwater wetlands include marshes, swamps, bogs and fens. 

Geography

Canada has about 1.29 million km2 of wetlands. This covers 13% of Canada's land. And this is about 25% of the wetlands in the world. 

25% of Canada's wetlands are in the Boreal Shield. 21% are in the Hudson Plains. 18% are in the Boreal Plains.

Did you know?

Almost 80% of the Hudson Plains is wetland. The Hudson Plains curve around Hudson Bay and James Bay. They include land in eastern Manitoba, northern Ontario and western Quebec.

There were once many wetlands all over Canada. But over time, wetlands are becoming more rare. In southern Ontario, 68% of the original wetlands have been converted from their natural state. They are now used for things like agriculture and housing. In southwestern Manitoba, only about 25% of the original wetlands in the ‘pothole’ region remain. The good news is that in the northern part of Canada, most of the wetlands are intact.

Chemistry

Just because an area is wet, doesn’t mean it’s a wetland. The amount of water in a wetland can change depending on temperature and precipitation. This means we need to look at other things to determine if an area is a wetland or not. One way is to examine the soil. 

Wetlands have hydric soils. These are soils that are fully saturated with water. Hydric soils are also anaerobic. This means they contain very little oxygen. 

The absence of oxygen means this soil has different colours and textures than aerobic soils. Aerobic soils have large amounts of a form of iron (Fe) that makes soil a yellow, orange or reddish colour. Anaerobic soils have a different form of iron. This gives the soil a gray colour.

The plants that grow in wetlands need to have special adaptations. These allow them to grow in low-oxygen conditions. Cattails and bulrushes have these adaptations. If you see cattails and bulrushes, this is a good indication that the area is a wetland.

Ecology

Wetlands are important to many animals. Some of these are familiar, like frogs. Some are less well-known. 

Every drop of water contains microscopic phytoplankton and zooplankton. These are important parts of the food chain. Phytoplankton are microscopic algae and diatoms that can create their own food. Zooplankton are microscopic animals that eat phytoplankton. 

The surface of the water and the wetland bottom are covered with insect eggs, larvae, and nymphs. Fish, amphibians, and reptiles depend on the habitat provided by wetlands. And many bird and mammal species use the water and its adjacent shores. 

Let’s look more closely at the different types of wetlands and some of the plants and animals found there.

Marshes

Marshes are permanently or regularly covered in standing or slowly-moving water. Marshes are rich in nutrients. 

They have many kinds of emergent vegetation. These are plants that grow up through the water. They include reeds, rushes, cattails and sedges. The roots of these plants are covered in water for most of the growing season. Marshes are the most productive type of wetlands. This means they produce more organic matter than other wetlands. 

Marshes are home to many protected species. These include the Bald Eagle, Sandhill Crane, Eastern Fox Snake and Fowler’s Toad. 

Swamps

Unlike marshes, swamps have trees and shrubs. Swamps may be flooded seasonally, or for long periods of time. Like marshes, swamps are also nutrient-rich and productive. 

Swamp plants include coniferous, or cone-bearing trees and deciduous trees. Swamps are most common in the southern part of Canada. Swamps are home to many protected species. These include the Eastern Prairie Fringed Orchid, Loggerhead Shrike, Red-shouldered Hawk and Blanding’s Turtle. 

Bogs

Bogs are also known as peat bogs. They are a kind of peatland. Peatlands are wetlands that contain peat. Peat is a build-up of partly-decayed plants. The top 30 to 50 cm of a peatland is made up of mosses and other living plants. Under that layer is the peat, which can be up to 10 metres deep! 

Did you know?

In some parts of the world, dried peat is harvested as a source of fuel!

In a peatland, the peat acts like a giant sponge. This makes it hard for water to drain through it. Poor drainage and decaying plant material makes bogs very acidic. The water in bogs only comes from precipitation. 

The high acidity and low oxygen in bogs makes it very difficult for plants to grow. This is why the biodiversity in peatlands is low. 

The main kinds of vegetation in bogs are sphagnum mosses. These are often called peat moss. Mosses are small, soft plants with small leaves. Mosses do not have roots. They absorb water through their leaves instead. 

Shrubs like heaths can also be found in bogs. Heaths have adaptations for living in acidic soil. Other bog plants include cotton grass, cranberry, bog laurel, leatherleaf, blueberry and Labrador tea. 

Carnivorous plants also live in peatlands. They include things like sundews, butterworts and pitcher plants. Carnivorous plants are interesting. They get the nutrients they need by catching and digesting small insects and spiders. They can do this using a sticky liquid or by trapping them in their leaves.

Did you know?

Peatlands cover over 1.1 million square kilometres, or about 12 percent of Canada. 

Bogs provide habitat for both migratory bird species and permanent residents. These include palm warblers, Lincoln’s sparrows, tree swallows and northern harriers. 

Some large mammals also live in peatlands. These include moose, white-tailed Deer, wood bison and caribou. Small mammals like bog lemmings, southern bog lemmings and Arctic shrews prefer bogs to other types of habitats.

Fens

Fens are a type of peatland. Unlike bogs, fens are fed by surface water and groundwater. This means the soil there is less acidic. Fens are not as low in nutrients as bogs, so they are more productive than bogs. 

The main kind of plant growing in fens are sedges. Trees like cedars, dwarf birches, black spruces, and tamarack can also be found there. 

Fens are more common in the northern part of Canada. Birds found in fens include Virginia rails, yellow warblers and swamp sparrows. Mammals include water shrews, star-nosed moles and muskrats. 

Did you know? 

In some parts of Canada, peatlands are called muskegs. This comes from the Cree word maskek and Ojibwe word mashkiig, meaning “grassy bog.”