Lakes and Rivers

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Status and trends of stream flows

Most rivers in Canada show pronounced seasonal variation in flows. Minimum annual flow occurs in late summer when precipitation is low and evaporation is high, and in late winter when precipitation is frozen in ice and snow. Minimum flows can limit the availability of specific aquatic habitats and also influence water temperatures and dissolved oxygen levels. For example, a decrease in minimum flow can affect the quantity and temperature of water for late-spawning fish and increase thermal stress and exposure to predation for all fish.

In a study of 172 sites in naturally flowing rivers, the lowest annual flow increased between 1970 to 2005 at 13% of the sites. These sites were generally in the northern Montane Cordillera, Boreal Cordillera, Taiga Plains, Taiga Shield, and Arctic ecozones+. Twenty–eight percent of the sites had decreases in minimum flow, generally in the southern Pacific Maritime, southern Montane Cordillera, Boreal Shield, Mixedwood Plains, Atlantic Maritime, and Newfoundland Boreal ecozones+. Twelve percent of the sites, mostly in eastern Canada, Great Lakes, and the North, had later minimum flows, while 9%, mostly in the South and along the western coast, had earlier minimum flows.2

Trends in minimum river flow in natural rivers
1970 to 2005
Map: trends in minimum river flow in natural rivers. Click for graphic description (new window).
Long Description for Trends in minimum river flow in natural rivers

This map of Canada with ecozone+ boundaries shows trends in minimum river flow for 172 natural (unregulated) rivers from 1970 to 2005. The lowest annual flow increased significantly over this period at 13% of the sites. These sites were predominantly in the northern Montane Cordillera, Boreal Cordillera, Taiga Plains, Taiga Shield, and Arctic ecozones+. Twenty-eight percent of the sites had significant decreases in minimum flow, generally in the southern Pacific Maritime, southern Montane Cordillera, Boreal Shield, Mixedwood Plains, Atlantic Maritime, and Newfoundland Boreal ecozones+.

 

Source: Monk et al., 20102

Maximum annual flow, or spring freshet, generally occurs in late spring and in early summer and is driven by snow melt and seasonal rainstorms. A change in maximum flow can affect species with life cycles synchronized to the spring freshet and the rich foods provided by flood plains.

Almost 20% of the sites showed a decrease in maximum flow. These sites were distributed across almost all ecozones+. About 5% showed an increase in maximum flow, mostly in the Atlantic Maritime Ecozone+. Maximum flow occurred earlier at about 10% of the sites and later at about 8% of the sites.2

Trends in maximum river flow in natural rivers
1970 to 2005
Map: trends in maximum river flow in natural rivers. Click for graphic description (new window).
Long Description for Trends in maximum river flow in natural rivers

This map of Canada with ecozone+ boundaries shows trends in maximum annual river flow for natural (unregulated) rivers from 1970 to 2005. Almost 20% of the sites showed a significant decrease in maximum flow. These sites were distributed across almost all ecozones+. About 5% of rivers showed an increase in maximum flow, mostly in the Atlantic Maritimes, but also in the Taiga Shield and the Montane Cordillera.

 

Source: Monk et al., 20102

Summer flow of four rivers in the Prairie Provinces

Percent loss, 1985 to 2001
Four graphs showing the summer flow in four Prairie rivers. Click for graphic description (new window).
Long Description for Summer flow of four rivers in the Prairie Provinces

This graphic contains line graphs displaying summer flow trends for four prairie rivers over scales of decades. Flow values are plotted as the percent of the flow at start of timeline for each of the four rivers. The graphs each show annual fluctuations overlain by a trend line. The overall trends show reduction in summer flow in each of the rivers. The trends for the four rivers are described in the point form in the text below the graph.

 

Source: adapted from Schindler and Donahue, 20064

The average flow of prairie rivers has been declining over the past 50 to 100 years, including:

  • 20% reduction from 1958 to 2003 – 33% since 1970 – for the Athabasca River at Fort McMurray, Alberta;
  • 42% reduction from 1915 to 2003 for the Peace River, near the town of Peace River, Alberta;
  • 57% reduction from 1912 to 2003 for the Oldman River at Lethbridge, Alberta;
  • 84% reduction from 1912 to 2003 for the South Saskatchewan River at Saskatoon, Saskatchewan.4

Reduced flows like these can impact biodiversity in many ways, including reducing habitat availability, not meeting the minimum flow requirements for aquatic species, and increasing summer temperatures.5

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Water levels

  Photo: an example of closed-basin lakes in southern Saskatchewan © dreamstime.com/Andre Nantel
  An example of closed-basin lakes in southern Saskatchewan

Water levels in prairie closed-basin lakes

1910 to 2006
Eight graphs showing water levels in prairie closed-basin lakes. Click for graphic description (new window).
Long Description for Water levels in prairie closed-basin lakes

This series of 8 line graphs displays changes in water levels in prairie closed-basin lakes from as early as 1910 to 2006. Dashed lines connecting widely separated data points indicate possible trends for years without data. All lakes experienced overall declines in water levels with the exception of Waldsea Lake.

Each graph is described in the following set of points:

  1. In Muriel Lake, water level declined approximately 3 metres from 1967 to 2006.
  2. In Little Fish Lake, water level declined approximately 6 metres from 1939 to 2004.
  3. In Manito Lake, water level declined approximately 7 metres from 1919 to 2006
  4. In Redberry Lake, water level declined 9 metres from 1918 to 2006. Four data points are marked as records that were recovered by means of air photos or survey notes.
  5. In Waldsea Lake, water level increased approximately 4.5 metres from 1964 to 2006.
  6. In Big Quill Lake, water level declined approximately 3 metres from 1919 to 2006.
  7. In Oro Lake, water level was measured using three data points from air photos or survey notes and three samples. Water levels increased approximately 3 metres from 1947 to 1981, and then declined approximately 2 metres by 2006.
  8. In Kenosee Lake, water level declined approximately 6 metres from 1938 to 2006. Four of the data points are based on records from air photos or survey notes.

 

Source: adapted from van der Kamp et al., 20086

 

Locator map for graph of prairie closed-basin lakes. Click for graphic description (new window).
Long Description for Southern Saskatchewan and southeastern Alberta

Two maps show the location of the lakes included in the study across southern Saskatchewan and southeastern Alberta.

 

 

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

Metres, 1918 to 2007
Three graphs: water levels in the Great Lakes. Click for graphic description (new window).
Long Description for Loss of variability in Great Lakes water levels

This graphic consists of line graphs showing trends in water level variability in the five Great Lakes from 1918 to 2007. Water levels are plotted as metres in relation to a lake reference point. All lakes displayed seasonal fluctuations, but the patterns of year-to-year variation differed among lakes. Lake Erie, Lake Michigan, and Lake Huron all showed strong year-to-year fluctuations over the period from 1918 to 2007. Lake Ontario displayed this pattern of strong year-to-year fluctuation from 1918 until 1960, from which point fluctuations were predominantly seasonal. Lake Superior showed little year-to-year variability over the period of record.

 

Note: Metres are in relation to the International Great Lakes Datum (IGLD), 1985, which is a lake reference level adjusted every 25 to 30 years to account for movement of the Earth's crust.
Source: adapted from Environment Canada and U.S. Environmental Protection Agency, 200917

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.

Photo: the Thousand Islands © Environment Canada
The Thousand Islands, Ontario

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Change in freshwater discharge into the Arctic and North Atlantic

1964 to 2003
Map: freshwater discharge into the Arctic and North Atlantic. Click for graphic description (new window).
Long Description for Change in freshwater discharge into the Arctic and North Atlantic

This graphic consists of a bar chart and an associated map. The bar chart displays the percent change in freshwater discharge into the Arctic and North Atlantic from 1964 to 2003. The associated map displays the five watersheds draining into these northern ocean regions. The map also shows locations of major river mouths and indicates, by means of symbols, whether the discharge decreased or increased during the study period. Percent changes in freshwater discharge are shown on the bar chart, by drainage basin. These are: 1) discharge to the Labrador Sea decreased by 10.6%; 2) discharge to eastern Hudson Bay decreased by 11%; 3) discharge to western Hudson Bay decreased by 13%; 4) discharge to the Arctic Ocean increased by 2%; and 5) discharge to Bering Strait decreased by 4.8%. The total decrease in freshwater discharge from 1964 to 2003 was 10%.

 

Note: Red triangles indicate a decrease in flow; green triangles indicate an increase in flow. The size of the triangle indicates the magnitude of change.
Source: adapted from Déry and Wood, 200511
Percent change
1964 to 2003
Graph: change in freshwater discharge into the Arctic and North Atlantic. Click for graphic description (new window).
Long Description for Percent change

This graphic consists of a bar chart and an associated map. The bar chart displays the percent change in freshwater discharge into the Arctic and North Atlantic from 1964 to 2003. The associated map displays the five watersheds draining into these northern ocean regions. The map also shows locations of major river mouths and indicates, by means of symbols, whether the discharge decreased or increased during the study period. Percent changes in freshwater discharge are shown on the bar chart, by drainage basin. These are: 1) discharge to the Labrador Sea decreased by 10.6%; 2) discharge to eastern Hudson Bay decreased by 11%; 3) discharge to western Hudson Bay decreased by 13%; 4) discharge to the Arctic Ocean increased by 2%; and 5) discharge to Bering Strait decreased by 4.8%. The total decrease in freshwater discharge from 1964 to 2003 was 10%.

 

Source: adapted from Déry and Wood, 200511

 

Freshwater discharge from Canadian rivers into the Arctic and North Atlantic Oceans has decreased by about 10% over the past 40 years. This has been attributed to a decrease in precipitation over the same period.11, 12 In spite of this, an overall 5.3% increase in river discharge to the Arctic Ocean has been documented. The net increase is due to significant increases in annual discharge from the six largest Eurasian rivers.13, 14 Freshwater discharge to northern seas can influence ocean processes that, in turn, influence the population dynamics of marine species.

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