Key finding overview
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.
This key finding is divided into five sections:
- Key finding overview (this page)
- Change in extent of wetlands
- Status of peatlands
- Peace–Athabasca Delta
- Health of Great Lakes wetlands
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.
Status and trends
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.
Change in extent of wetlands
Wetland loss in the Prairies
The millions of small wetlands of the Canadian and U.S. prairies are the most productive waterfowl habitat in the world, supporting 50 to 88% of the North American breeding populations of several species.20-22 Availability and condition of wetlands are primary factors determining the number and diversity of these waterfowl. Although these factors are influenced greatly by climate variation,22 land use change is also important.
As land was settled and converted to agriculture, extensive areas of wetlands were drained. No comprehensive data on historical loss exist, however analysis of localized studies in the Canadian Prairies shows high variability12, 23-25 with loss estimates between settlement and the 1990s of 40 to 71%.12, 24, 26, 27 Despite conservation efforts over the past several decades, wetland loss and degradation continue, largely as a result of intensification of agriculture.25, 28 Between 1985 and 2001, 6% of wetland basins were lost, representing 5% of the total estimated wetland area. In addition, estimates of wetland area suffering a loss of function due to factors such as partial drainage were about 6% annually.12 An analysis of agricultural impact and recovery of wetlands between 1985 and 2005 found the edges of wetlands were impacted more than wetland basins. Although the rate of impact for edges declined over the period, the rate of recovery was slower, indicating an increasing overall impact. The percent of edges impacted ranged between 82 and 97% in 1985, depending upon location, and stabilized in the early 1990s at between 90 and 95%.28
Up to 90% of prairie wetlands are estimated to be smaller than 1 ha.12 Research indicates that, overall, smaller wetlands support a greater number of waterfowl than larger ones.29 These small wetlands are also suffering the greatest losses. From 1985 to 2001, the average size of wetland basins lost was 0.2 ha, with 77% smaller than 2.6 ha.12 Between 1985 and 2005, shallow seasonal wetlands in agricultural fields had the highest rate of impact and slowest recovery rates relative to other wetland types.28
Wetland loss in southern Ontario
Prior to European settlement, southern Ontario had approximately 20,266 km2 of wetlands. By 2002, 72% had been converted to other uses. This represents a decrease in the proportion of wetland cover on the landscape from 25 to 7%.11 Historically, the highest concentrations of wetlands were found in southwestern and eastern Ontario. These areas are also where the most severe losses have occurred. For example, prior to settlement, 83% of Essex County, at the tip of southwestern Ontario, was wetland but by 2002 this was reduced to less than 2%.11, 30 From 1967 to 1982, conversion of wetlands for agriculture accounted for 85% of the losses.30 Urban development and associated transportation infrastructure were significant factors in the areas surrounding southeastern Lake Ontario.11
Most wetland conversion happened in the 19th and early 20th centuries (68% of wetlands were converted prior to 1967).30 Nevertheless, despite wetland gains in some areas, overall net loss continues. While the estimated extent of wetlands larger than 10 ha remained relatively stable between 1967 and 1982, from 1982 to 2002 an additional 3.5% of pre–settlement wetlands were lost – an average of 3.5 km2 per year. These estimates are conservative since Great Lakes coastal wetlands and wetlands smaller than 10 ha were not included in the analyses.11
Change in extent of wetlands along the St. Lawrence River
Over 60 km2 of riparian habitat along the St. Lawrence River was modified from 1945 to 1984.51 Most changes occurred prior to the mid–1970s and were a result of draining and filling of open waters and wetlands for housing, roads, and agriculture. Losses near major urban centres were the greatest,49, 51 for example, 83% of Montreal's wetlands were lost by 1976.52 Construction of water control structures, including dams and the St. Lawrence Seaway (1954–1958), was also responsible for change in the late 1950s,49 while urbanization was more important after that time.52
Since the 1970s, the overall extent of wetlands has increased, although there is variability depending upon the type and location of the wetland.51 While wetland loss continues due to urbanization, particularly in the Montreal and Lac Saint–Pierre areas, restoration efforts and reduced water levels have resulted in a 2.7% net gain of marshes and swamps between 1990 and 2002.51 Gains were mainly in the fluvial, upper, and lower estuaries and occurred mainly at the expense of open water. Declining water levels in the 1990s may have accelerated the drying trend in some areas,51, 53 transforming low marshes to high marshes and swamps that are dominated by invasive plant species. Water levels are influenced by a number of factors, including water control structures, flow from the Great Lakes and the Ottawa River, and climate change, particularly in the estuary and Gulf of St. Lawrence.49, 51
Exotic wetland plants now comprise 14% of vascular plants in St. Lawrence River wetlands.54 Their expansion can be attributed to shoreline alteration, excavation of the navigation channel, and water level regulation, which have reduced the magnitude of floods, decreased circulation in shallow littoral areas, and reduced the efficiency of the river to flush nutrients from sediments and to uproot robust emergent vegetation.55
Old Crow Flats
Designated as a wetland of international importance,4 Old Crow Flats is a large, undeveloped complex (over 6,000 km2) of more than 2,000 lakes and wetlands formed by thawed permafrost. It provides continentally significant habitat for up to half a million breeding and moulting waterbirds.57, 58 The overall surface area of water decreased by 13 km2 (3.5%) from 1951 to 2001, with greatest overall decreases found in large and very large lakes. Ponds increased in extent by 7% from 1951 to 1972, and decreased by 8.5% between 1972 and 2001. Changes are attributed to a mix of interacting processes with some lakes forming or expanding, and some suddenly draining due to collapse of permafrost – along with an overall drying trend due to increased evaporation from hotter summers in recent years.56
Change in extent of wetlands in the south Okanagan and lower Similkameen valleys, B.C.
Wetlands occupy a small portion of the Western Interior Basin due to the region's climate, soil, and topographic features.2, 88 Nevertheless, they play a crucial ecological role particularly because wetlands in arid areas support more species than other ecosystems.88, 89 Wetlands of the southern interior of B.C. support many species at risk. Most wetlands in this area are located in valley bottoms where development is also concentrated and wetland loss has been extensive since European settlement mainly due to conversion for agriculture and more recently for urban development.87, 90 Between 1800 and 2005, specific wetland communities suffered different degrees of loss, including, 92% of shrubby water birch/red–osier dogwood riparian wetlands, 63% of black cottonwood–red osier dogwood riparian wetlands, and 41% of cattail marshes from the south Okanagan and lower Similkameen valleys.87 Wetlands continue to be lost and degraded by urbanization, intensive agriculture, and, in some areas, heavy recreational use.87, 91, 92 In addition, invasive species and climate change pose serious threats.
St. Lawrence River wetland
Status of peatlands
Canada has about 1.1 million km2 of peatlands, which represents about 12% of its land area74 and the majority of its total wetland area.75 Ninety–seven percent occur in the boreal and subarctic regions.74 In addition to their significance to biodiversity, Canadian peatlands, which are wetlands that have accumulated more than 40 cm of organic soil,2, 76 are important globally as carbon stores.77-79 Although it is estimated that 90% of Canada's peatlands remain intact in terms of total area,13 comprehensive data do not exist. Some example estimates of peatland loss through direct human activity include:
- 9,000 km2 flooded for hydroelectric development throughout Canada between 1960 and 2000;13, 80
- 250 km2 drained for forestry in the Boreal Shield between 1980 and 2000;80
- 240 km2 drained for horticultural peat across Canada by 2007, including a 56% increase in area under active extraction from 1990 to 2007;81
- 237 km2 disturbed by oil sands mining in Alberta by mid–2009;82
- 110 km2 converted to agriculture in Quebec prior to 2001.83
Approximately 60% of the peatlands in Canada, particularly those in Hudson/James Bay lowlands, Mackenzie River Basin, and parts of northern Alberta and Manitoba, lie within areas expected to be severely affected by climate change.74, 84 Climate change is already affecting northern peatlands through permafrost thaw and other changes in hydrology. These impacts show rapid changes with lake expansion in some areas, shrinkage or disappearance in others,85 including the replacement of forests in some areas by wet sedge meadows, bogs, and ponds and lakes86 (see Ice Across Biomes). Climate change may also result in changes to the carbon balance of Canada's extensive peatlands.74
The Peace–Athabasca Delta, covering over 5,000 km2, is one of the largest inland freshwater deltas in the world. Made up of two large central lakes and over 1,000 small lakes and wetlands,59 it is of international importance for waterbirds, bison, and fish.4 The delta's dynamics are driven largely by short– and long–term fluctuations in water levels, including occasional spring floods caused by ice jams60, 61 and summer open–water floods, with intervals of drying between flood events.62 Studies have found recent ice–jam and flood frequency to be within the range of historical variability and intervals.63-65 Nevertheless, although the delta has experienced several major ice–jam and open–water flooding episodes since the 1940s,66 the most recent occurring in 1997,60, 64 landscape analyses have found a significant overall drying trend from 1945 to 2001 in which wet communities declined in extent while dry communities increased.63, 67
Determining the cause of landscape change is difficult because the delta is constantly changing – driven by climate, hydrology, and deltaic processes, all of which are variable and influenced by natural and anthropogenic factors.63, 65, 66 Influences over the past 45 years include:60, 62, 66, 68-72
- a warmer, drier climate;
- the prevention of a natural change in the course of the Athabasca River in 1972 and the natural occurrence of a channel breakthrough in 1982;
- flow regulation, including the construction of the Bennett Dam on the Peace River in 1968, and subsequent weirs on outflow channels built in 1975–76 in response to concerns about changes in connected lake levels;
- land use changes and development, including forestry, agriculture, and oil sands extraction;
- growing water uses; and
- cultural changes.
A projected reduction in ice–jam flood frequency over the next century due to climate change may result in further drying,73 and additional upstream development may add additional stress to the delta's ecosystem.
Mamawi Creek, Peace–Athabasca Delta
Health of Great Lakes wetlands
Covering over 700 km2, wetlands along the shores of the Great Lakes, their connecting channels, and tributaries provide critical habitat for wildlife, including birds, mammals, fish, amphibians, reptiles, and a diversity of plants. They have suffered extensive loss and degradation over the past 200 years30, 31 and many have been greatly affected by pollution.32, 33 It is estimated that, by 1984, 35% of wetlands along the Canadian shores of lakes Erie, Ontario, and St. Clair had been lost,34 with greatest losses, 73 to 100% by 1979, occurring between Toronto and the Niagara River.35 Most conversion occurred from the late 19th to early 20th centuries when large wetlands were dredged for shipping and filled for industrial and urban development.36 Loss and degradation continue due to shoreline alteration, water level control, nutrient and sediment loading, invasive non–native species, dredging, and industrial, agricultural, and residential development.36-41 Upstream land practices also have an impact, particularly through run–off from agricultural lands and impervious surfaces.42-44
Recent surveys show that the health of wetlands is variable across the basin.40 Water Quality Index scores, one method of monitoring wetland health, indicate that for Canada, the lower Great Lakes, especially the western end of lakes Ontario and Erie, which are most heavily impacted by urbanization and agriculture, suffer the most degradation. Comparatively few sites in Canada in Georgian Bay, Lake Huron, and Lake Superior are degraded.45-48
- Date Modified: