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Biodiversity in Canadian Lakes and Rivers

Future Climate Impacts on Lakes and Rivers

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Water resources in North America are already over-allocated in many regions and, therefore, are highly susceptible to future change., Bates et al. (2008) discussed the impacts of changes to the timing, volume, quality, and spatial distribution of freshwater resources in North America expected with increased rates of warming. Precipitation in Canada is forecast to increase in the range of +20% for the annual mean and +30% for winter under the highest emissions scenario in addition to widespread increases in extreme precipitation events (Bates et al., 2008). For example, the projected increases in precipitation, earlier and more severe spring flooding, and increased duration of summer drought periods in British Columbia will affect streamflow and, in turn, fish survival. The Intergovernmental Panel on Climate Change (2007) synthesized scientific studies using data between 1970 and 2004 to explore changes in physical (such as snow, ice, frozen ground, hydrology, and coastal processes) and biological (terrestrial, marine, and freshwater) systems in relation to changing surface temperatures  on all continents, including North America (Intergovernmental Panel on Climate Change, 2007). Of the North American studies reviewed, 334 of 355 (94%) data series exploring physical systems and  419 of 455 (92%) data series exploring biological systems could be attributed to warming (Intergovernmental Panel on Climate Change, 2007). Future climate change is very likely to have both direct and indirect effects on aquatic community structure and function within lake and river ecosystems in Canada.

Future climate change will affect the volume and timing of precipitation and evaporation in addition to causing increased variability in precipitation type. These changes will affect the hydrological regimes of rivers in addition to lake levels (Bates et al., 2008). Regional variations in response are forecast with large-scale relative changes in annual runoff for the period 2090 to 2099 relative to 1980 to 1999. For the majority of northern latitude areas in Canada, there is a projected 20 to 40% increase in runoff. The remainder of Canada, with the exception of the Prairies, is projected to experience a 5 to 20% increase (Milly et al., 2005). Biological effects of climate-related warming have already been observed, for example shifts in species composition, abundance, productivity, and phenological shifts (for example, fish migration). Increases in water temperatures and precipitation, in addition to longer periods of low flows, will cause significant effects in lake and river systems through increases in sediment levels, runoff levels, and thermal pollution. Aquatic communities will be affected by changes in water levels and temperatures; for example, cold-water salmonid species are predicted to be negatively affected while warm-water species will likely benefit (for example, Eaton and Scheller, 1996; Wrona et al., 2006).

Under climate warming scenarios, snow and ice cover will continue to decline, particularly in spring and summer (Bates et al., 2008). Using satellite images over the 1966 to 2005 period, Bates et al. (2008) reported that snow cover in the Northern Hemisphere has decreased in every month, with the exception of November and December. Under future climate warming, widespread reductions in snow cover are forecast, in addition to increases in thaw depth over much of the permafrost regions as a result of increased air temperatures (Bates et al., 2008). However, despite the reductions in lake and river ice cover, the effect may be less severe in large northward-flowing rivers because of reduced regional contrasts in south-to-north temperature and hydrological gradients (Bates et al., 2008). Lake and river ice regimes will continue to change under future climates, for example the length of ice cover will continue to decrease. Any future changes in climate could affect aquatic morphology and therefore the ice regime, in both a direct and indirect manner. For example, longer term changes in lake water levels could affect the ice regime of tributary rivers (Beltaos and Burrell, 2003).

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