Lakes and Rivers
An example of closed-basin lakes in southern Saskatchewan
Water levels in prairie closed-basin lakes
In the Prairies, a combination of glaciation and dry climate has resulted in numerous closed-basin saline lakes, that drain internally, rarely spilling runoff. These lakes are sensitive to climate, with water levels and salinity driven by precipitation on the lake, local runoff to the lake, and evaporation off the lake.6 Aquatic communities within these closed-basin lakes are sensitive to chemical changes that can be a result of changes in water levels. For example, water levels affect salinity and the diversity of aquatic species declines as salinity increases. When salinities reach extremely high values, species diversity becomes very low.7
From 1910 to 2006, water levels in 16 representative closed-basin lakes showed an overall pattern of decline by 4 to 10 metres.6 Declines can be explained in part by climate,6 including increases in spring temperatures, for example from 1950 to 2007,8 potentially resulting in increased evaporation rates and declining stream runoff9 to the lakes. However, climate variables alone cannot explain the declines, for example no significant change was evident in precipitation or in an index of drought severity, from 1950 to 2007.8 Other contributing factors that reduce surface runoff to the lakes include land use changes, such as dams, ditches, wetland drainage, and dugouts, and changes in agricultural use and practices,6 such as the decline in summer fallow,10 increase in conservation till, and continuous cropping.6
Loss of variability in Great Lakes water levels
Diverse and varied plant communities inhabiting Great Lakes wetlands are dependent on the high seasonal and year-to-year variability in water levels found naturally,18 in, for example lakes Huron and Michigan, which are unregulated. Natural water levels are affected by precipitation, evaporation from the lake surface, inflow from upstream, and outflow to the downstream lakes.
Water levels are also affected by direct regulation as well as dredging, control structures, dams, canals, and diversions.19 The regulation of water levels in Lake Superior since 1914 and in Lake Ontario since about 1960 has reduced the variability of water levels. In Lake Ontario, this has adversely affected coastal wetland ecosystems, reduced plant species diversity, and altered habitat values for many animals that depend wholly or partly on wetlands to thrive.18, 20 As water shortages become more common in the southern U.S., there may be pressure for water diversions from the Great Lakes, which could, if allowed, result in further impacts on biodiversity.
The Thousand Islands, Ontario
- Date Modified: