KEY FINDING 3. High loss of wetlands has occurred in southern Canada; loss and degradation continue due to a wide range of stressors. Some wetlands have been or are being restored.
Wetlands are land saturated with water all or most of the time, as indicated by poorly drained soils and vegetation and biological activity adapted to wet environments.1, 2 They are of two types, organic (peatlands) and mineral, and are classified in five categories: bogs and fens, which are both peatlands; marshes and shallow water, which are both mineral; and swamps, which can be either.1 Canada has approximately 1.5 million km2 of wetlands.1, 3 This represents about 16% of Canada's land mass and approximately one quarter of the world's remaining wetlands.1 Thirty–seven of Canada's wetlands, an area covering almost 131,000 km2, have been designated as wetlands of international importance.4 This key finding discusses freshwater wetlands – estuaries, salt marshes, and other marine coastal wetlands are discussed in Coastal Biome.
Wetlands are important as one of Earth's most productive ecosystems, supporting a disproportionately high number of species,5 including species at risk and significant numbers of migratory birds, fish, amphibians, a wide diversity of plants, and many other species. Wetlands provide essential services such as controlling floods, recharging groundwater and maintaining stream flows, filtering sediments and pollutants, cycling nutrients, stabilizing shorelines and reducing erosion, and sequestering carbon.
Despite the importance of wetlands, a comprehensive national inventory or monitoring program does not exist.6 The most comprehensive data are for the Prairies and southern Ontario. Most studies examining wetland loss are small, localized, old, and vary in scale. Although results find high variability of loss and degradation across the landscape and across time, evidence shows that wetland conversion was rapid from settlement through the early 1900s in many parts of southern Canada, largely as a result of conversion for agriculture.7 In 1991, it was estimated that the total wetland loss for Canada since the 1800s was 200,000 km2.8
Recent studies indicate that although there is an increase of wetlands in some areas, loss continues in many parts of Canada from land conversion, water level control, including flooding from hydroelectric development, and climate change.9-13 In addition to direct loss, wetlands continue to be degraded, fragmented, and to suffer a loss of function due to hydrological alteration, development, pollution, invasive species, recreation, grazing, management of adjacent land, and climate change.5
Wetlands near large urban centres are particularly at risk and have suffered severe losses. It has been estimated that less than 0.2% of Canada’s wetlands fall within 40 km of urban centres,14 and that 80 to 98% of wetlands in or adjacent to major urban centres have been lost.