Great Slave Lake ecosystem

• Category: Inland Aquatic Biomes.
• Geographic Location: North America.
• Summary: Great Slave Lake, among the deepest and northernmost North American lakes, supports a largely unspoiled habitat range that is, however, under pressure from global warming.

Great Slave Lake, ensconced in the boreal forest and undulating tundra of Canada's Northwest Territories, is the deepest lake in the continent, plumbed to a depth of 2,015 feet (614 meters). Except for the remnant (and some ongoing) contamination from mining on its northern shore and disruption from logging and road construction, Great Slave Lake anchors an almost pristine series of habitats, with intact forests, wetlands, shrublands, and tundra surrounding its clean, often ice-covered waters.

Contrary to popular belief, the lake's name has nothing to do with slavery; it was named for the Slavey North American Indians, a group that inhabited the region when it was discovered by Europeans. Located in the sub-Arctic, Great Slave Lake is at least partly frozen for as much as eight months each year. In winter, the ice is thick enough for ice roads crossing the lake to support tractor-trailers transporting goods and fuel to the communities and mines on the north shore.

Lake Formation

During the last ice age, two huge freshwater lakes formed from the ice melting off the leading edge of the Laurentide Ice Sheet in North America. Both formed about 12,000 years ago, and lasted for a few thousand years before draining into the lakes we know today. The larger Lake Agassiz changed continually in shape and size until the ice sheet retreated fully, leaving the modern lakes Winnipeg, Manitoba, and Winnipegosis behind. The other, Lake McConnell, reached its greatest extent 10,000 years ago. As the ice front retreated to the northeast, three daughter lakes remained behind. Great Bear Lake, Great Slave Lake, and Lake Athabasca have remained relatively unchanged.

Great Slave Lake has a very large drainage basin, about 375,000 square miles (975,000 square kilometers); in turn, it is a direct tributary source that is integral to the vast Mackenzie River catchment. Water exits at the shallow, marshy westernmost point of Great Slave Lake via the Mackenzie River, traveling north past Great Bear Lake to empty into the Arctic Ocean.

The Slave and Hay Rivers are the main tributaries feeding the Great Slave Lake, with the Slave River providing at least three-fourths of the incoming water. A tremendous sediment load is delivered through the Slave River Delta, in the southern area of the lake, greatly undercutting the water clarity at its southwestern end in spring and summer. The Hay, too, flows in from the south. The eastern arm of the lake is much deeper and clearer, and contains many islands.

Located about 320 miles (512 kilometers) south of the Arctic Circle, the lake straddles two distinct ecoregions: boreal forest and tundra. The summers are short and cool, with long hours of daylight. The long, cold winters have limited sunlight hours.

Flora and Fauna

The western shore of Great Slave Lake is covered with boreal forests, or taiga, containing aspen, spruce, and balsam fir. This is an area of alternating plateau and plains that overlaps with the Muskwa-Slave Lake Forests ecoregion. Wetlands and bogs here spread over one-fourth of the area.

A diverse and nearly intact wildlife system inhabits the boreal forest. Woodland caribou, moose, black and grizzly bear, wolf, lynx, deer, and elk all migrate naturally throughout the area. Given the remoteness, climate, and low human population of the basin, more than 75 percent of the biome remains intact. This is despite some logging operations and the construction of the Mackenzie Valley highway and pipeline corridors.

The northern and eastern shores of the Great Slave Lake transition into tundra. The Canadian Shield, among the oldest bedrock on the planet at more than four billion years old, underlies terrain here that is either flat or low rolling hills, with many bedrock outcrops. The land appears to be barren, but is rich in minerals. Vegetation consists of sparse, stunted stands of black spruce and tamarack, with ground cover of dwarf birch, shrubs, cottongrass, lichens, and moss. The combination of forests and tundra in this ecoregion results in a significant overlap of animal species, notably woodland and barren-ground caribou, along with the wolves that hunt them. Most of this ecoregion is intact, with the greatest fragmentation occurring in the western portion, where both permanent and seasonal roads have been created to support mining operations.

Effects of Human Activity

The First Nations Dene population was the principal Indigenous group in the Great Slave region; the Dene have inhabited the Great Slave Lake for thousands of years. Approximately 28,000 people live in the Great Slave subbasin in the twenty-first century. Twenty-two communities inhabit the area, mostly in small towns and hamlets; the largest community is Yellowknife, situated on the north shore of Great Slave Lake, with a population of more than 20,300. Other communities include the Hay River, Behchokǫ̀, Fort Resolution, Łutselk'e, Hay River Reserve, Dettah, and Ndilǫ.

The fur trade brought the first European settlers and dominated the economy until gold deposits were discovered on the northern shore in 1896. By the 1930s, bush aircraft made travel far easier, and in 1934, visible gold was found along the shores of Yellowknife Bay. That finding led to the establishment of Yellowknife near the outlet of the Yellowknife River; the settlement quickly became a boom town and eventually grew to become the capital of the territory. The name refers to a local Dene people once known as the Copper Indians or the Yellowknife Indians, who traded tools made from copper deposits found near the Arctic Coast.

Over the years, numerous mines were developed within the basin for a variety of minerals, including zinc and lead. By 2003, only two operating gold mines remained in Yellowknife. As capital of the territory, the town's purpose shifted to government services. However, the discovery of diamonds north of Yellowknife in the 1990s revived an interest mining. Later, the largest diamond ever found in North America was mined in this area.

Environmental Threats

Despite the region's reputation as one of the most pristine lake environments in the world, the residents of Yellowknife cannot drink the water. Drinking water must be drawn from a well up the Yellowknife River. Predictably, the mining legacy is a factor. Beginning in the 1940s, gold was extracted from ore by a process called roasting. This released arsenic trioxide and sulfur dioxide into the air. Pollution-control processes were belatedly added to the procedure, but contamination still proceeded. Roasting was discontinued in 1999, but 238,000 tons (215,910 metric tons) of highly toxic, water-soluble arsenic dust is stored in underground chambers close to Great Slave Lake. The Canadian government and the mine owners are working to evaluate strategies for managing waste and protecting the environment.

Global climate change, with average temperature increases in Arctic areas occurring faster than worldwide averages, is affecting the biological structure of the Great Slave Lake biome. According to a study published in 2021 funded by NASA, increased water temperature in the Great Slave Lake and other large lakes has caused an increase in nutrients. This led to an algal abundance, which has reduced water clarity and harmed some fish species. Additionally, the algal growth caused a change in the dominant algae species, impacting the food supply for many fish.

The warm water has also reduced ice cover and induced earlier annual ice breakups. This change is significant for the local ecosystems and people who rely on the winter’s solid ice roads for transportation. Flooding, erosion, unpredictable water levels and flow patterns, and erratic precipitation have also caused significant concern for the lake and the nearby communities.

Bibliography

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