Biodiversity in Canadian Lakes and Rivers
- Trends in Freshwater Fish of Special Interest
- Trends in Hydrological Regimes
- Trends in River and Lake Ice Break-Up/Freeze-Up
- Trends in Habitat Loss and Fragmentation
- Trends in Pollutants in Lake and River Systems
- Future Climate Impacts on Lakes and Rivers
- Synthesis of Data
- Appendix 1
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Table of Contents
- Document Information
- Executive summary
- Trends in freshwater fish of special interest
- Trends in hydrological regimes
- Trends in river and lake ice break-up/freeze-up
- Trends in habitat loss and fragmentation
- Trends in pollutants in lake and river systems
- Future climate impacts on lakes and rivers
- Synthesis of data
- Appendix 1. Summary of ecozone+ trends in Indicators of Hydrologic Alteration (IHA) variables.
List of Figures
- Figure 1. Ecozones+ and major drainage basins designated by the Water Survey of Canada
- Figure 2. Water use stress worldwide
- Figure 3.Total number of at-risk freshwater and diadromous fish taxa for North American freshwater ecoregions found in Canada, 1979, 1989, and 2008.
- Figure 4. Commercial Atlantic salmon catches in the inner Bay of Fundy, from fishery districts in Albert and Westmorland counties, New Brunswick, 1875–1984.
- Figure 5. Reconstructed time series of wild coho salmon escapements, total escapements (wild + hatchery fish), and total returns (escapement + catch) for the interior Fraser River watershed, 1975–2011.
- Figure 6. Reconstructed time series of wild coho salmon escapements for the five Conservation Units (CUs) within the interior Fraser River watershed, 1975–2011.
- Figure 7. Juvenile production of white sturgeon, Nechako river populations, 1945–1990. Estimated based on age composition data collected from 1995–1999.
- Figure 8. Distribution of existing and historically gauged water monitoring stations across Canada: (a) natural lakes; (b) regulated lakes; (c) natural rivers; and (d) regulated rivers.
- Figure 9. Number of sites with hydrological records for regulated and natural lakes and rivers, 1800–2006.
- Figure 10. Frequency histogram for the total number of years of data at each hydrometric site.
- Figure 11. Map of stations with suitable hydrological data used in trend analyses and table summarizing the number of suitable stations by ecozone+.
- Figure 12. Summary of the total number of stations displaying significant (p<0.1) increasing and decreasing trends for each IHA variable, using data for hydrological years 1970–2005.
- Figure 13. Summary of the total number of stations displaying significant (p<0.1) increasing and decreasing trends for each IHA variable for the Atlantic Maritime, Taiga Plains, Boreal Shield, and Pacific Maritime ecozones+, using data for hydrological years 1970–2005.
- Figure 14. Summary of the total number of stations displaying significant (p<0.1) increasing and decreasing trends for each IHA variable for the Montane Cordillera and Newfoundland Boreal ecozones+, using data for hydrological years 1970–2005.
- Figure 15. Trends in long-term monthly runoff for RHBN stations using data for hydrological years 1970–2005.
- Figure 16. Trends in the magnitude of the 1-day, 3-day, 7-day, 30-day, and 90 day minimum runoff and in baseflow for RHBN stations using data for hydrological years 1970–2005.
- Figure 17. Map showing trends in 1- day minimum river flow in natural rivers across Canada, using data for hydrological years 1970–2005.
- Figure 18. Trends in the magnitude of the 1-day, 3-day, 7-day, 30-day, and 90 day maximum runoff for RHBN stations using data for hydrological years 1970–2005.
- Figure 19. Map showing trends in the 1-day maximum river flow in natural rivers across Canada, using data for hydrological years 1970–2005.
- Figure 20. Trends in date of annual 1-day minimum and 1-day maximum runoff for RHBN stations using data for hydrological years 1970–2005.
- Figure 21. Trends in the frequency and duration of low and high pulses for RHBN stations using data for hydrological years 1970–2005
- Figure 22. Map showing trends in the duration of low pulses for natural rivers across Canada, using data for hydrological years 1970–2005.
- Figure 23. Trends in the variability of runoff for RHBN stations using data for hydrological years, 1970–2005.
- Figure 24. Map showing trends in the number of hydrograph reversals in natural rivers across Canada, using data for hydrological years 1970–2005.
- Figure 25 Trends in lake ice break-up dates and spring temperature in Canada, 1966–1995.
- Figure 26. Map showing major water diversions and transfers in Canada and the United States.
- Figure 27. Number of dams (<10 m in height) completed each year in Canada, pre 1900–2005. Records for pre-1900 go back to 1830.
- Figure 28. Spatial distribution of dams (>10 m in height) grouped by year of completion, 1830–2005.
- Figure 29. Temporal distribution of dams (>10 m in height) by decade and ecozone+, pre-1900–2005.
- Figure 30. Number of water quality monitoring sites in each major ocean drainage basin with increasing, decreasing, and unchanged phosphorus levels between 1990 and 2006. Only sites with statistically significant results are shown (p<0.05).
- Figure 31. Median total phosphorus and B) dissolved phosphorus concentrations in the Bow River, 1975–2010.
- Figure 32. Trends in sulphate levels and acidity (pH) in lakes at five intensive monitoring sites in southeastern Canada, 1972 to 2008.
- Figure 33. Combined aquatic and terrestrial atmospheric deposition critical load index for Canada, 2008.
- Figure 34. Areas where the critical load has been exceeded in the Boreal Shield Ecozone+, 2009.
- Figure 35. Impact of acidification on Atlantic salmon, 1996
Figures 3 to 35
List of Tables
- Table 1. The number of lakes in each region of Canada by size category
- Table 2. Summary of published scientific papers exploring statistical trends in streamflow and runoff in Canadian rivers.
- Table 3. Description of flow regime components, their instream ecological impacts, and exemplar variables.
- Table 4. Ecologically relevant hydrological parameters used in the Indicators of Hydrologic Alteration (IHA) and their characteristics.
- Table 5. Trend results for the Indicators of Hydrologic Alteration (IHA) variables for 172 RHBN stations used in this analysis, using data for hydrological years 1970–2005.
- Table 6. Literature review summary of physical habitat changes and the direct and indirect effects on instream biodiversity and habitat availability in ice impacted rivers..
- Table 7. Summary of scientific studies quantifying trends in freeze-up for Canadian lakes and rivers using data up to and including the year 2000..
- Table 8. Summary of scientific studies quantifying trends in break-up for Canadian lakes and rivers using data up to and including the year 2002.
- Table 9. Trends in the alteration of freshwater systems worldwide, pre-1900 to 1996/98.
- Table 10. Summary of national trends from this analysis, literature analysis, and previous published scientific research. Trends derived for data from 1970 to 2005
- Table 11. Summary of hydrological trends by ecozone+, 1970–2005.
- Table 12. Summary of trends from this analysis, literature analysis, and previous published scientific research by ecozone+.
Tables 3 to 12
W.A. MonkReference Note  and D.J. Baird Reference Note ,Reference Note 
Canadian Biodiversity: Ecosystem Status and Trends 2010
Technical Thematic Report No. 19
Published by the Canadian Councils of Resource Ministers
Library and Archives Canada Cataloguing in Publication
Biodiversity in Canadian lakes and rivers.
Issued also in French under title:
Biodiversité dans les rivières et lacs du Canada.
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Monk, W.A. and Baird, D.J. 2014. Biodiversity in Canadian lakes and rivers. Canadian Biodiversity: Ecosystem Status and Trends 2010, Technical Thematic Report No. 19. Canadian Councils of Resource Ministers.Ottawa, ON. vi + 92 p.
© Her Majesty the Queen in Right of Canada, 2014
Aussi disponible en français
The Canadian Councils of Resource Ministers developed a Biodiversity Outcomes FrameworkFootnote1 in 2006 to focus conservation and restoration actions under the Canadian Biodiversity StrategyFootnote2 . Canadian Biodiversity: Ecosystem Status and Trends 2010Footnote3 was a first report under this framework. It assesses progress towards the framework's goal of "Healthy and Diverse Ecosystems" and the two desired conservation outcomes: i) productive, resilient, diverse ecosystems with the capacity to recover and adapt; and ii) damaged ecosystems restored.
The 22 recurring key findings that are presented in Canadian Biodiversity: Ecosystem Status and Trends 2010 emerged from synthesis and analysis of technical reports prepared as part of this project. Over 500 experts participated in the writing and review of these foundation documents. This report, Ecosystem status and trends report: biodiversity in Canadian lakes and rivers, is one of several reports prepared on the status and trends of national cross-cutting themes. It has been prepared and reviewed by experts in the field of study and reflects the views of its authors.
- R. Allen Curry
- Canadian Rivers Institute, University of New Brunswick
- Nancy Glozier
- Prairie and Northern Wildlife Research Centre, Environment Canada, Saskatoon
- Daniel L. Peters
- Water and Climate Impacts Research Centre, Environment Canada, University of Victoria
Data for the hydrological analyses were provided through Water Survey of Canada's HYDAT database. Additional geospatial data were accessed through Geogratis and Geobase. We also thank the reviewers of this report.
Ecological Classification System – Ecozones+
A slightly modified version of the Terrestrial Ecozones of Canada, described in the National Ecological Framework for Canada,Footnote4 provided the ecosystem-based units for all reports related to this project. Modifications from the original framework include: adjustments to terrestrial boundaries to reflect improvements from ground-truthing exercises; the combination of three Arctic ecozones into one; the use of two ecoprovinces – Western Interior Basin and Newfoundland Boreal; the addition of nine marine ecosystem-based units; and, the addition of the Great Lakes as a unit. This modified classification system is referred to as "ecozones+" throughout these reports to avoid confusion with the more familiar "ecozones" of the original framework.Footnote5
- Over 8,500 rivers and 2 million lakes cover almost 9% of Canada's total land area. Canada's watersheds flow into five major ocean drainage basins: the Arctic, Pacific, and Atlantic oceans; Hudson Bay; and the Gulf of Mexico, with almost three‑quarters of their volume flowing north into the Arctic Ocean and Hudson/James Bay.
- Within Canada, it remains challenging to assess status or trends in freshwater ecosystems and their biodiversity due to a lack of long-term, nationally consistent observational data. There have been positive moves to address this, for example through the development of a national aquatic biomonitoring network (CABIN).
- As a direct consequence of habitat loss, competition from alien invasive species, and overexploitation, the number of imperilled fish species in Canada has risen steadily from 12 in 1979 to 62 in 2008.
- It was not possible to determine national trends in lake levels for this report due to a lack of data. However, research in prairie lakes indicates an overall decline in lake levels in that region over the past 90 years as a result of reduced levels of precipitation consistent with predictions from climate warming models.
- Trends in ecologically important properties of river flows were analysed for the period 1970 to 2005 and results indicate a significant increase in their variability, together with regional trends in the magnitude of both short-term and longer-term minimum and maximum runoff.
- While few statistically significant trends in ice freeze-up or break-up were found, the majority of sites monitored demonstrated a tendency towards earlier break-up, and also an earlier date of the annual one-day maximum flow (often related to the spring freshet), which seems to correspond with an earlier arrival of the spring 0°C-isotherm date.
- Dam construction (>10 m in height) peaked between 1950 and 1980, and has since declined across Canada.
- From 1980 to 2006, sulphur dioxide emissions in Canada and the U.S. declined by about 45% and emissions of nitrogen oxides declined by about 19%. Although significant declines in lake sulphates followed closely behind the emission reductions, the response of lake acidity, measured by pH, has been slow and less widespread, due in part to declines in calcium which are also related to acid deposition.
- Beyond the Great Lakes region of Canada, there is a lack of data by which to assess long-term trends in contaminant levels in biota. One area of recent concern, the Canadian Arctic, exemplifies the problem of data scarcity, with localised patterns being reported in some studies, over time periods too short to properly observe trends.
This report provides an analysis of status and trends in freshwater biodiversity within Canada's lakes and rivers using a combination of: i) quantitative data; ii) qualitative data from a literature review; and iii) evidence from the peer-reviewed scientific literature. This report considers biodiversity in the broadest sense, focusing specifically on lake and river ecosystems. Its scope is limited, with no specific consideration of wetlands. The Great Lakes are reported on in the State of the Great Lakes Reports (for example, Environment Canada and U.S. Environmental Protection Agency, 2009) and Lake Winnipeg is covered in the Boreal Plains evidence for key findings summary and supplemental background information (ESTR Secretariat, 2014), so they are not included here. During the writing of the report, it became apparent that any conclusions drawn from the data would be necessarily limited due to a general lack of quantitative, nationally consistent, observational data for aquatic species in Canada. For this reason, proxies, for example habitat trends, have been employed to examine likely trends in biodiversity. These trends are also explored further within the context of the Ecozone+-specific reports that are part of the Ecosystem Status and Trends Report (ESTR). With this proviso, we attempt to explore key trends in lake and river ecosystems, with coverage of the following areas: i) fish species at risk; ii) hydrological regimes; iii) ice freeze-up and ice break-up; iv) habitat loss and fragmentation; v) contaminants, nutrients, and acidification; and vi) future climates. Finally, it should be noted that this report uses the Ecozone+ framework consistent with other reports produced in this series. This has implications for the assessment of trends in freshwater ecosystems, which do not follow Ecozone+ geographical boundaries.
Lakes and rivers in Canada
Canada has an area of 9,984,670 km2 of which 9,093,507 km2 are land and 891,163 km2 is water (The Atlas of Canada, 2004a). Canada's borders span a continental land mass and therefore contain a wide range of climates. This climatic diversity, coupled with large topographic variation and significant human modification of the environment, has strongly influenced Canada's hydrology (Meteorological Survey of Canada, 2003). Both local and regional climates are heavily influenced by the interaction of a westerly circulation, with natural topographic features which include vast mountain ranges, wide plains, and extensive river basins (Meteorological Survey of Canada, 2003; Bonsal and Shabbar, 2011). Annual precipitation varies from less than 100 mm in the dry regions of the Arctic Archipelago to more than 4,000 mm along the wetter parts of the Pacific coast (The Atlas of Canada, 2007a). Moving north from its southern border, the climate shifts from continental to subarctic to arctic. In addition, a secondary maritime influence in coastal regions affects both the west and east coast climates, while permafrost underlies about half of Canada's land area in the mid- to northern latitudes (The Atlas of Canada, 2004b).
Lakes and reservoirs provide a potentially important source of trend information as they reflect the influence of climate through changes in water levels and water quantity (Williamson et al., 2009). Canada is covered by over two million lakes, which together with rivers, cover almost 9% of the country (The Atlas of Canada, 2004a). There are more than 900,000 lakes larger than 0.1 km2, which together represent 37% of the total lake area of the world (Minns et al., 2008). This includes over 560 lakes which exceed 100 km2 in area (Table 1). The largest group, the Great Lakes, span the Canada–United States border, and contain 18% of the world's freshwater lake volume (The Atlas of Canada, 2007b). Strongly influenced by geological history, the majority of larger lakes are found within the Canadian Shield, the Interior Plains, and the St. Lawrence Lowlands, while glacial activity had a strong role in the formation of other lakes, for example Great Bear Lake, Great Slave Lake, Lake Athabasca, Lake Winnipeg, and the Great Lakes. Table 1 provides a summary of the distribution of lakes by size class across Canada.
|Region||Lake size (km2)|
|Lake size (km2)|
|Lake size (km2)|
|Lake size (km2)|
|Lake size (km2)|
|Lake size (km2)|
|Lake size (km2)|
Source: data from Environment Canada (1973) as reported in The Atlas of Canada (2008a)
Atlantic provinces = New Brunswick, Prince Edward Island, Nova Scotia, and Newfoundland and Labrador;
Prairie Provinces = Manitoba, Saskatchewan, and Alberta;
Territories = Nunavut, Northwest Territories, and Yukon Territory.
Of the 25 largest rivers in North America ranked by annual discharge, 14 flow completely or partly within Canada (Benke and Cushing, 2005). Canadian rivers flow into five major ocean drainage basins: the Arctic, Pacific, and Atlantic oceans; Hudson Bay; and the Gulf of Mexico. However, almost three-quarters of the rivers in Canada, making up almost half (47.9%) of the total annual discharge, flow north into the Arctic Ocean or into Hudson/James Bay (Déry and Wood, 2005). Most rivers in Canada show pronounced seasonal variation in runoff, and the majority of high flows are driven by spring snowmelt. Secondary flow variation arises from seasonal rainfall patterns, while glacial meltwater sustains flow in mountainous regions. For most unmodified rivers, low flows generally occur in late summer, arising from reduced precipitation and high evaporation, or in late winter, as precipitation accumulates in the form of ice and snow.
Monitoring national hydrological trends is accomplished by summarizing data collected from hydrometric gauging stations, through the Water Survey of Canada's extensive hydrometric network (but see also Shrubsole, 2000). Extended site-specific hydrological time series have also been developed using palaeo-environmental data to allow longer-term analysis of the impacts of a changing climate. For example, a recent study by Wolfe et al., (2008) extracted a long time series of water levels over the past thousand years for the upper Mackenzie River system using this approach. Using palaeo-environmental data from the Peace-Athabasca Delta, water levels for Lake Athabasca appeared to directly reflect overall water availability. Their results demonstrated that lake water levels showed systematic fluctuations over time, reflecting a maximum glacier extent during the Little Ice Age (1700s to 1900s) and a glacial minimum during the comparatively warm 11th century (Wolfe , 2008). In this context, recent hydrological trends suggest a trend towards lower water levels as high elevation snow and glacier contributions continue to decline. Shifts in the shape and timing of the annual hydrographs were also suggested to reflect a greater variability in the spring freshet during the Medieval period, a delayed spring freshet during the Little Ice Age, and a delayed spring freshet throughout the 20th century (Wolfe et al., 2008).
An increasing number of human activities currently pose threats to Canada's rivers (see examples in Environment Canada, 2001; Environment Canada, 2004). These include dams for flood control or hydropower (for example, Poff et al., 2007), irrigation and municipal water use (for example, Fitzhugh and Richter, 2004), chemical contamination (for example, Wan et al., 2006; Smith et al., 2007; Bordeleau et al., 2008), and the spread of invasive alien species (for example, Boyer et al., 2008). All of these threats are likely to be further exacerbated by the pervasive effects of climate warming, through the need to alter national infrastructure to adapt to a changing climate. Hydrological systems are naturally dynamic (Milly et al., 2008), as can be seen, for example, in the variation in permafrost levels driving changes in the hydrological landscape of the north (Vallee and Payette, 2007). Given this changing baseline, detecting additional effects as a result of global climate change is challenging (for example, Rand et al., 2006). However, it is obvious that both natural and anthropogenic activities can significantly alter water quality and quantity and thus influence habitat diversity (for example, Charron et al., 2008). As a component of biodiversity, habitat diversity strongly influences other biodiversity attributes, such as species or genetic diversity. Therefore, in the absence of any historical data arising from strategic monitoring of species and/or genetic diversity, an examination of how habitat itself is changing through time can be used as a surrogate. Nevertheless, we acknowledge that the systematic, strategic collection of monitoring data on the remaining components of biological diversity, currently lacking for freshwater ecosystems in Canada, is required to address these questions directly.
Linking lake and river systems with Ecozones+
This report focuses on river and lake ecosystems across Canada. Watershed boundaries are commonly used as the basis for analyses of freshwater ecosystems as they represent drainage networks of connected systems. A watershed can be defined as the land area that topographically drains surface water to a particular point of interest (for example, a river, stream, or lake). The main criteria for defining a watershed are topography and the presence of a water body. An ecozone is defined based on a different set of criteria which includes climate, plants, soils, landforms, animals, and water features, and therefore implies taking into account biodiversity. From Figure 1, it is clear that the watershed boundaries (as defined by the Environment Canada, 2006c) and the terrestrial ecozone+ delineations used in ESTR are not spatially contiguous. Within a drainage basin, there will be variations in habitats and communities along natural longitudinal gradients. This report is structured by ecozone+ but it is important to realize that an activity within a specific ecozone+ within a drainage basin will be influenced by upstream ecological processes in contiguous ecozones+.
Canada's major river systems encompass a wide variety of habitats and ecosystems. They include endemic species, as well as a diverse range of hydrological and climatic characteristics. Characterized by high runoff, draining westward into the Pacific Ocean through the Pacific drainage basin, the majority of coastal Pacific rivers have their headwaters at high elevation across a series of mountain ranges with considerable topographic relief throughout their catchments (Richardson and Milner, 2005). For example, the Fraser River is the fifth longest river system in Canada, flowing 1,400 km from its headwaters in Mount Robson Provincial Park, through both the Montane Cordillera and Pacific Maritime ecozones+, to its mouth at Vancouver on the Pacific coast (Abell et al., 2000; Burridge and Mandrak, 2009a). Rivers within the Montane Cordillera, Boreal Cordillera, and Pacific Maritime ecozones+ exhibit high annual runoff, both westward to coastal areas and eastward to the Prairies Ecozone+ in the south and the Boreal Plains and Taiga Plains ecozones+ to the north (Environment Canada, 2010a). Runoff within montane coastal rivers often exceeds 3,000 mm per year while within the drier prairies it can average under 200 mm annually (Environment Canada, 2010a). Classified as temperate upland freshwater habitat, the Nelson River drainage basin has several large rivers including the Churchill, Nelson, and Saskatchewan rivers, and many interconnected lakes (Abell et al., 2000). For example, over a total distance exceeding 3,000 km before discharging into Hudson Bay, the Nelson River covers more than 1 million km2 of the interior of North America--892,300 km2 in Canada and 180,000 km2 in the United States (Rosenberg et al., 2005). The habitat within this region includes slow, meandering rivers flowing through wide, interconnected valleys. Here freshwater fish species diversity is low, with a number of introduced species thought to be responsible for the decline of several native species.
Moving east to the Great Lakes, annual runoff ranges from 100 mm in the northwest, to 800 mm in the southeast, to over 1,000 mm along the Atlantic Maritime coast (Environment Canada, 2010a). The greatest diversity of freshwater fish species in Canada is found in the Great Lakes and southern Hudson Bay areas with 87 freshwater species recorded, including 18 diadromous fish species within the main stem of the St. Lawrence River alone (Thorp et al., 2005). As an example, the Mixedwood Plains Ecozone+ is an area of extensive wetlands within the populated area of southern Ontario and southern Quebec. The climate in this area is strongly influenced by the Great Lakes causing a continental to modified continental climate. Numerous streams, rivers and lakes, springs, spring ponds, and wetland areas are found within and near this Ecozone+ with annual runoff ranging from 200 mm in the southwest to over 600 mm at the northeastern end of the Ecozone+ (Thorp et al., 2005; Environment Canada, 2010a). However, this area has historically been strongly influenced by urbanization, including several large cities (Abell et al., 2000; World Wildlife Fund and The Nature Conservancy, 2008a). Surrounded by the Canadian Shield, the extensive wetlands of the Hudson Plains Ecozone+ drain northward to Hudson and James bays.
Moving further east towards the Atlantic coast, runoff continues to increase significantly, varying from 600 mm annually in the western part of the Atlantic Maritime Ecozone+ to over 2,000 mm along the Atlantic coast (Burridge and Mandrak, 2009b; Burridge and Mandrak, 2009c; Burridge and Mandrak, 2009d; Environment Canada, 2010a). Flowing through extensive forest cover with numerous inland waters towards the Atlantic Ocean (Cunjak and Newbury, 2005), the Saint John is the largest river system within the Atlantic Maritime Ecozone+ (Burridge and Mandrak, 2009c). Within this Ecozone+, several rivers, including the St. Croix and the Upper Restigouche rivers in New Brunswick and the Hillsborough and Three Rivers systems in Prince Edward Island, are designated as Canadian Heritage Rivers (Burridge and Mandrak, 2009b; Burridge and Mandrak, 2009c). In addition, this Ecozone+ has several small lakes with the largest being GrandLake in New Brunswick. The freshwater fish diversity within the Atlantic Maritime Ecozone+ is relatively low and is dominated by freshwater fishes with some salt‑water tolerance, for example sturgeons (Acipenserspp.), American eels (Anguilla rostrata), killifishes (Fundulus spp.), and smelts (Osmeridae). In addition, there are important nesting sites for osprey (Pandion haliaetus) and ring-necked duck (Aythya collaris) (Burridge and Mandrak, 2009b; Burridge and Mandrak, 2009c; Burridge and Mandrak, 2009d).
The Newfoundland Boreal Ecozone+ exists in a maritime climate with low freshwater fish diversity. The Main and Bay du Nord rivers are Canadian Heritage Rivers (Burridge and Mandrak, 2009b). Many of the freshwater fish species are saltwater-tolerant and exhibit diadromy, for example the shad (Alosa spp.) and the Atlantic salmon (Salmo salar). The main rivers draining the Ecozone+ include the Exploits, Gander, Humber, and Main, with many glacial finger lakes also being characteristic of this region (Burridge and Mandrak, 2009b).
Few data on runoff are available for the Northern Arctic portion of the Arctic Ecozone+, which is characterized by very low precipitation (100 to 200 mm annually) (Environment Canada, 2010a). Even less is known concerning runoff from the glaciated, mountainous Arctic Cordillera portion of the Arctic Ecozone+. This latter region encompasses the Arctic drainage basin in addition to part of the Northern Quebec and Labrador drainage area. The diversity of freshwater fish species is among the lowest in North America, with no known endemic species (Abell et al., 2000; World Wildlife Fund and The Nature Conservancy, 2008a).
With the seventh largest basin in North America, encompassing an area of 839,200 km2 (Bailey, 2005), the Yukon River area is characterized by a mixture of sub-arctic and tundra conditions, draining part of Alaska, the Boreal Cordillera, and Taiga Cordillera ecozones+, and also a small part of the Pacific Maritime Ecozone+. In addition to being one of the most important salmon‑bearing rivers in the world, the "Thirty Mile Section" of the Yukon River has been designated a Canadian Heritage River (Abell et al., 2000; World Wildlife Fund and The Nature Conservancy, 2008a). With no known endemic freshwater fish species and only 30 recorded fish species, fish diversity is relatively low (Bailey, 2005).
The Mackenzie River flows through Canada's largest river basin, draining nearly 1.8 million km2 (20%) of Canada's land area (Culp et al., 2005). The system includes a number of other important systems, including the Athabasca, Peace, Liard, Slave, Arctic Red, and Peel rivers before flowing into the Mackenzie Delta (The Atlas of Canada, 2008a; The Atlas of Canada, 2008b). In addition, the system has two major inland deltas (the Peace-Athabasca and the Slave) as well as three very large lakes (Athabasca, Great Slave, and Great Bear) (Culp et al., 2005). The Mackenzie system supports 34 fish species on the main stem, with 52 species occurring throughout the basin (Culp et al., 2005).
Broader implications for aquatic biodiversity
River flow and lake level regimes are driven by climate and basin controls, and vary considerably over space and time. Such hydrological regimes are determined in part by lake or river dimensions, but are also influenced by factors including geology and topography (Poff et al., 1997). Local environmental conditions determine rates of change and other aspects of flow variability, including seasonal flow patterns and the timing, frequency, predictability, and duration of extreme events such as floods and droughts (Richter et al., 1996; Poff et al., 1997). The resulting hydrological regimes directly affect river and lake ecosystem characteristics, including the physical nature of lake habitats and river channels, sediment regimes, and prevailing water quality conditions which, in turn, drive the key aquatic ecosystem processes. Hydrological variability influences the structure of aquatic habitats and the composition of ecological communities, including plankton, plants, benthic macroinvertebrates (for example, Monk et al., 2008), and vertebrates, including fish, amphibians, reptiles, birds, and mammals.
Climate variability has direct and indirect effects on aquatic communities by influencing the timing, duration, magnitude, and flashiness of runoff, by altering the water temperature regime and water chemistry, and by driving geomorphological change. In addition, the availability of local resources, including the provision of dispersal opportunities, the maintenance of habitat heterogeneity and connectivity, the degree of biotic interactions, and the overall genetic capacity and adaptive potential together determine the degree of species richness, biodiversity, range, and distribution of species, within the limitations of current knowledge (see Wrona et al., 2005 for examples in Arctic systems).
One of the major obstacles to understanding and managing the relationships between hydrological variability and the structure and biodiversity of aquatic communities is the lack of appropriate coupled standardized, large-scale data collected over the long term. Often long-term biodiversity data is only available at local scales. Drawing on data from Abell et al., (2000) and Scott and Crossman (1998), Abell et al. (2008) identified 21 freshwater ecoregions in Canada based on the faunal similarity of 166 secondary watersheds obtained through a cluster analysis of freshwater fish occurrences within these watersheds. The study classified Canada's freshwater ecoregions into six different habitat types: i) large lakes, for example the Great Lakes; ii) large river deltas, for example the Upper Mackenzie; iii) polar freshwaters, for example the Arctic coastal region; iv) temperate floodplain rivers and wetlands, for example the St. Lawrence; v) temperate coastal rivers, for example the Pacific drainage region; and vi) temperate upland rivers, for example the Upper Saskatchewan. Their analyses demonstrated that the diversity of freshwater fish species is relatively low in Canada, with the exception of the Great Lakes region. The associated website provides additional information from their study (see hosted by World Wildlife Fund and The Nature Conservancy, 2008a). One of the analyses attempted to quantify water stress on lake and river systems, with the authors concluding that Canada's lakes and rivers were generally under minimal stress (Figure 2). However, it should be noted that, in this case, the water stress index was related to water use by human activity, and ecosystem requirements were not factored into the analysis. Attempts to overlay the Ecozones+ show that there are potential hydrological impacts in some of the freshwater systems in the Boreal Shield, Boreal Plains, Prairies, and Mixedwood Plains Ecozones+, which had 30 to 50% of their land cover converted for human useFootnote6 (World Wildlife Fund and The Nature Conservancy, 2008b).
- Footnote 1
Environment Canada. 2006. Biodiversity outcomes framework for Canada, Canadian Councils of Resource Ministers. Ottawa, ON. 8 p
- Footnote 2
Federal-Provincial-Territorial Biodiversity Working Group. 1995. Canadian biodiversity strategy: Canada's response to the Convention on Biological Diversity, Environment Canada, Biodiversity Convention Office. Ottawa, ON. 86 p.
- Footnote 3
Federal, Provincial and Territorial Governments of Canada. 2010. Canadian biodiversity: ecosystem status and trends 2010, Canadian Councils of Resource Ministers. Ottawa, ON. vi + 142 p.
- Footnote 4
Ecological Stratification Working Group. 1995. A national ecological framework for Canada. Agriculture and Agri-Food Canada, Research Branch, Centre for Land and Biological Resources Research and Environment Canada, State of the Environment Directorate, Ecozone Analysis Branch. Ottawa/Hull, ON. 125 p. Report and national map at 1:7 500 000 scale.
- Footnote 5
Rankin, R., M. Austin and J. Rice. 2011. Ecological classification system for the ecosystem status and trends report. Canadian Biodiversity: Ecosystem Status and Trends 2010, Technical Thematic Report No. 1., Canadian Councils of Resource Ministers. Ottawa, ON.
- Footnote 6
Converted lands are cultivated and managed areas, cropland mosaics, and artificial surfaces and associated areas. The analysis of converted lands is provided by freshwater ecoregions. The ecozones+ which encompass those freshwater ecoregions are identified in the text.
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