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Ecoregion Description


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Species Richness


# of Endemic Species


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105: Lower Mackenzie

Major Habitat Type:

polar freshwaters

Author:

Mary Burridge and Nicholas Mandrak

Countries:

Canada

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.

Drainages flowing into:

All drainages in this ecoregion drain into the Arctic Ocean.

Main rivers or 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.

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.

Climate:

As one moves upstream along the Mackenzie River, climate varies from continental Arctic conditions around the delta to continental conditions towards Great Slave Lake. Winters are generally long and very cold, with short, cool summers. The delta is underlain by thick, continuous permafrost, and experiences less precipitation than areas further south.

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.

Fish Fauna:

This fish fauna is a mix of secondary freshwater fishes such as the Pacific salmons (Oncorhynchus spp.), chars (Salvelinus spp.) and whitefishes (Coregonus, Prosopium, Stenodus spp.), and a variety of primary freshwater fishes (e.g. northern pike (Esox lucius), minnows (Cyprinidae), suckers (Catostomidae)). The primary freshwater species are indicative of the Mackenzie River as a post-Wisconsinan dispersal corridor between the Beringian and Mississippian Wisconsinan refugia.

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.

Evolutionary phenomena:

None known

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/sources:

Abell, R., Olson, D., et al. (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.,McPhail, J. D. (1986)"Zoogeography of fishes of the Yukon and Mackenzie basins" In C.H, H.;Wiley, E.O. (Ed.). Zoogeography of the freshwater fishes of North America. (pp. 639–674) New York, NY USA: Wiley Interscience.

McPhail, J. D. and R. Carveth (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..

Ricketts, Taylor H. Dinerstein Eric Olson David M. Loucks Colby J. (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.,Crossman, E. J. (1998). "Freshwater fishes of Canada" Fisheries Research Board of Canada Bulletin 184 966 + xvii..

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