Mackenzie River - Ecology

Ecology

The Mackenzie River's watershed is considered one of the largest and most intact ecosystems in North America, especially in the north. Approximately 63% of the basin – 1,137,000 km2 (439,000 sq mi) – is covered by forest, mostly boreal, and wetlands comprise some 18% of the watershed – about 324,900 km2 (125,400 sq mi). More than 93% of the wooded areas in the watershed are virgin forest. There are fifty-three fish species in the basin, none of them endemic. Most of the aquatic species in the Mackenzie River are descendants of those of the Mississippi River and its tributaries. This anomaly is believed to have been caused by hydrologic connection of the two river systems during the Ice Ages by meltwater lakes and channels.

Fishes in the Mackenzie River proper include the northern pike, some minnows, and lake whitefish, and the river's shores are lined with sparse vegetation like dwarf birch and willows, as well as numerous peat bogs. Further south the tundra vegetation transitons to black spruce, aspen and poplar forest. Overall, the northern watershed is not very diverse ecologically, due to its cold climate – permafrost underlies about three-quarters of the watershed, reaching up to 100 m (330 ft) deep in the delta region – and meager to moderate rainfall, amounting to about 410 millimetres (16 in) over the basin as a whole. The southern half of the basin, in contrast, includes larger reaches of temperate and alpine forests as well as fertile floodplain and riparian habitat, but is actually home to fewer fish species due to large rapids on the Slave River preventing upstream migration of aquatic species.

Migratory birds use the two major deltas in the Mackenzie River basin – the Mackenzie Delta and the inland Peace-Athabasca Delta – as important resting and breeding areas. The latter is located at the convergence of four major North American migratory routes, or flyways. As recently as the mid-twentieth century, more than 400,000 birds passed through during the spring and up to a million in autumn. Some 215 bird species in total have been catalogued in the delta, including endangered species such as the whooping crane, peregrine falcon and bald eagle. Unfortunately, the construction of W.A.C. Bennett Dam on the Peace River has reduced the seasonal variations of water levels in the delta, causing damage to its ecosystems. Populations of migratory birds in the area have steadily declined since the 1960s.