Lower Mackenzie



ID

105

Author(s)

Mary Burridge and Nicholas Mandrak


Countries

Canada

Major Habitat Type

Polar freshwaters

Drainages flowing into

All drainages in this ecoregion drain into the Arctic Ocean.


Main rivers to other water bodies

The Mackenzie River system (4241 km long) is the largest river in North America after the Mississippi. It begins in shallow swamps and mudbanks in the west arm of Great Slave Lake. Some of the river’s larger tributaries include the Liard, Redstone, Keele and North Nahanni rivers from the west. The Great Bear River (Central Arctic Coastal [106] ecoregion) enters from the east over a shallow gravel bar. The Arctic Red River enters the Mackenzie from the east below Great Bear River, and at Point Separation the massive Mackenzie Delta begins. The Liard River (1115 km long) rises in the Pelly Mountains of the Rockies, then flows through heavily forested land to the Mackenzie River. The major tributaries of the Liard include the South Nahanni, Petitot, and Fort Nelson rivers. Great Slave Lake is the largest lake in this ecoregion. The southern and eastern shores of the lake cut into the granite of the Canadian Shield and the northern and western shores lie in the Barren Lands of the NWT. Great Slave Lake has many rivers and streams falling over the edge of the Canadian Shield, including the Yellowknife, Snare, Emile, Beaulieu, Snowdrift, Taltson, and Hay (Upper Mackenzie [104] ecoregion). The Anderson River (692 km long) is isolated from the Mackenzie River drainage and originates in a group of lakes north of Great Bear Lake. It empties into the Beaufort Sea, just east of the Mackenzie Delta.



Description

Boundaries

This ecoregion occurs in northeastern British Columbia, northern Saskatchewan and the Northwest Territories (NWT). It includes the Mackenzie River and the rivers flowing into it primarily north and west of Great Slave Lake.

Topography

The topography of this ecoregion is, in large part, characterized by the Mackenzie River. The Mackenzie River delta consists of alluvial channels, estuarine deposits, and innumerable lakes. Glaciation has resulted in flat to rolling moraine and marine deposits. Further inland, broad lowlands and plateaus are incised by the Mackenzie and its tributaries. The bedrock is sedimentary, and the topography is flat to gently rolling. Further to the south, the bedrock is often covered with glacial deposits. Alpine and valley glaciers are present. The Mackenzie River Plain, lying between the Mackenzie and Franklin mountains, extends north as a broad, rolling area from the boreal forest along the east side of the Mackenzie River. The Northern Alberta Uplands are found in this ecoregion, and span the border with British Columbia and Northwest Territories. To the east, broad, sloping terrain of crystalline Archean rocks cause numerous small lakes and eskers to form in the lowlands that drain into Great Slave Lake.

Freshwater habitats

The Mackenzie River is the single most outstanding aquatic feature in this ecoregion. Its delta is almost 80 km wide and is a vast marsh divided into three navigable channels with a maze of streams, lakes and ponds. Upstream from the delta the river flows between limestone cliffs causing the water to be fast and turbulent. In other areas it widens and slows to create weedy channels, sandbars and islands. Smaller rivers, such as the Liard, Redstone and Keele, cut through narrow canyons creating rapids and whirlpools. The Liard River has a hot springs.

Great Bear, Great Slave, Lake Athabasca and a chain of lakes between them are remnants of a single postglacial pool. The largest and deepest of these is Great Slave Lake (614 m deep), which is cold and is frozen eight months of the year. There are many low-lying wetlands in this ecoregion.

Terrestrial habitats

The northern coastal plains support shrubby tundra vegetation such as dwarf birch (Betula sp.), willow (Salix spp.), northern Labrador tea (Dryas spp.), alder and sedges along the Mackenzie Delta. Wetland vegetation, including sedges and grasses with small peat bogs, is common. This ecoregion also includes the tundra-boreal transition zone. Further south, open stands of black spruce (Picea mariana) may also occur. In warmer upland and foothill areas, mixed-wood forests of white and black spruce (P. glauca), lodgepole pine (Pinus contorta), tamarack (Larix laricina), white birch (Betula spp.), quaking aspen (Populus tremuloides) and balsam poplar (P. balsamifera) occur and grow to greater heights along the Mackenzie River and its larger tributaries. In some low elevation and mid-slope areas, paper birch (B. papyrifera) occurs extensively.

Description of endemic fishes

There are no known endemic fish species within this ecoregion.

Other noteworthy fishes

A form of lake chub (Couesius plumbeus) is known to occur in the Liard Hot Springs and is thought to represent a distinct subspecies; however, it has not been formally described.

Ecological phenomena

Several species in this ecoregion exhibit anadromy including the chars (Salvelinus spp.) and whitefishes (Coregonus, Stenodus spp.). The Lower Mackenzie River Islands Bird Sanctuary (270 km long) is the staging ground for large numbers of shorebirds including the snow goose (Chen caerulescens), tundra swan (Cygnus columbianus), and black brant (Branta bernicla nigricans). More than 5,000 beluga whales (Delphinapterus leucas) calve in the Mackenzie River delta.

Justification for delineation

The ecoregions of Canada were identified based on the faunal similarity of 166 major watersheds based on a cluster analysis of freshwater fish occurrences in these watersheds. The Lower Mackenzie ecoregion includes the very large Mackenzie River watershed and other smaller watersheds that drain directly into the western Arctic Ocean. The fish fauna of the Mackenzie watershed is a mix of fishes from the northwestern Beringian refugium and southern Mississippian refugium; whereas, the fauna of the smaller watersheds is depauperate as a result of their remoteness and northern location.

Level of taxonomic exploration

Fair / Poor


References

  • McPhail, J. D. a. R. C. (1992) \A foundation for conservation: the nature and origin of the freshwater fish fauna of British Columbia\ Field Museum, Department of Zoology, University of British Columbia..
  • Abell, R.,Olson, D.,Dinerstein, E.,Hurley, P. T.,Diggs, J. T.,Eichbaum, W.,Walters, S.,Wettengel, W.,Allnutt, T.,Loucks, C. J.;Hedao, P. (2000). "Freshwater ecoregions of North America" Washington, D.C.: Island Press.
  • Eswg (1995) \A national ecological framework for Canada\ Ottawa/Hull, Ontario, 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..
  • Lindsey, C. C. and McPhail, J. D. (1986). "Zoogeography of fishes of the Yukon and Mackenzie basins" H. C.H and E. O. Wiley (Ed.) Zoogeography of the freshwater fishes of North America ( pp. 639–674 ) New York, NY USA: Wiley Interscience.
  • Ricketts, T. H.,E. Dinerstein,D.M Olson;C.J. Loucks (1999). "Terrestrial ecoregions of North America: A conservation assessment" Washington, D.C.: World Wildlife Fund.
  • Rowe, J. S. (1972) \Forest Regions of Canada\ Ottawa. Canadian Forest Service, Department of Environment..
  • Scott, W. B. and Crossman, E. J. (1998). "Freshwater fishes of Canada" Fisheries Research Board of Canada Bulletin 184 pp. 966 + xvii..