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(A Canadian Perspective)
"Water is also a critical, limiting factor in the existence and distribution of our natural ecosystems.”
Wetlands, important natural modifiers of water quality, are highly sensitive to climate change. As water flows through a wetland, contaminants such as metals, nutrients and sulphates are often filtered out. Lower water table levels, however, decrease the assimilative and purification abilities of wetlands. Drier conditions have also been associated with acid pulses (which can cause fish kills) and the formation of highly toxic methyl-mercury. In the Canadian Prairies, wetlands (sloughs) are of tremendous hydrological importance, and provide vital habitat for birds and aquatic species. The persistence of these wetlands depends on a complex interaction between climate, geology
and land use patterns, and their extent is controlled by the balance between water inputs and outputs. The greatest impact of future climate change on Prairie wetland coverage would result from changes in winter snowfall, whereas changes in evaporation would have a smaller impact. Coastal wetlands of the Great Lakes are likely to suffer from decreased lake water levels and from shifts in surface-water and groundwater flow patterns.
River ecosystems are also an important component of the Canadian landscape. Their sensitivity to climate change is influenced by the characteristics of the river and its location. Northern rivers may be impacted by permafrost degradation and changes in
flood regimes. Ice-jam flooding is a key dynamic of the Peace–Athabasca Delta in northern Alberta, particularly for rejuvenation of riverside ecosystems. A decrease in ice-jam flooding due to climate change would significantly impact this ecologically sensitive
region. In southern Canada, seasonal shifts in flow regimes projected for rivers could have major ecological impacts, including loss of habitat, species extinction, and increased water contamination. Drainage basins containing large lakes or glaciers are generally less sensitive to changes in climate, at least in the short term, as these features help
buffer the impacts of climate change.
Forests cover almost half of Canada’s landmass and are important regulators of the hydrological cycle. Changes in forest extent and distribution, due to climate change or other factors, impact the storage and flow of water. An increase in forest disturbances,
such as fires and insect defoliation, would also affect the ability of the forest to store and filter water. The impacts of climate change on forest ecosystems are covered in greater detail in the forestry chapter.
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