Yukon River
The Yukon River is the fifth-longest river in North America and is recognized as the continent's longest free-flowing river. Originating near Whitehorse in British Columbia, it stretches approximately 1,988 miles (3,200 kilometers) to the Yukon delta and the Bering Sea in Alaska. The river passes through diverse ecosystems, including boreal forests and tundra, and supports a variety of flora and fauna, including iconic fish species like Arctic grayling and chinook salmon. The river's hydrology is significantly influenced by seasonal and annual variations in temperature and precipitation, with climate change posing a growing threat to its ecosystems and hydrological patterns.
The Yukon River basin is home to around 125,000 people, primarily concentrated in Whitehorse and Fairbanks. Human activities, such as oil and gas exploration, mining, and climate change, have significantly impacted the river's health and biodiversity, leading to pollution, habitat fragmentation, and declining salmon populations. Notably, recent years have seen historic lows in salmon runs, prompting fishing restrictions to protect these species. As the region faces ongoing environmental challenges, understanding the Yukon's ecology and human impact remains crucial for conservation efforts.
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Yukon River
Category: Inland Aquatic Biomes.
Geographic Location: North America.
Summary: The fifth-longest river in North America is being threatened by oil exploration.
The Yukon River is the fifth-longest river in North America, and is considered to be the longest free-flowing river on the continent. Only one dam has been constructed on the river. Yukon, in the Gwich’in language, means great river. The Yukon River begins near Whitehorse, British Columbia, and flows for about 1,988 miles (3,200 kilometers) to the Yukon delta and the Bering Sea in Alaska. The Yukon River lies in the largest freshwater ecoregion in North America, which includes all but the southern portion of Alaska and several other rivers draining into the Bering and Beaufort seas.
Major rivers draining into the Yukon include the Teslin, Big Salmon, Nordenskiold, Pelly, White, Stewart, and Klondike. The Yukon basin is formed as the river flows through Alaska; the population of the entire Yukon River basin is about 125,000, mostly concentrated in Whitehorse on the upper Yukon River and Fairbanks, Alaska, on the lower stretch.
The Yukon basin lies in the continental climate zone, characterized by cool summers, cold winters, and low annual precipitation. The basin includes several terrestrial ecoregions: the Yukon Interior Dry Forests in the upper part, the Interior Yukon-Alaska Alpine Tundra in the middle basin, the Interior Alaska-Yukon Lowland Taiga in the northern part, and the Beringia Lowland Tundra in the lower part. The landscape of the basin is natural tundra and boreal forest.
The headwaters of the Yukon collect in Teslin, Atlin, Tagish, and Bennett Lakes in the northwestern corner of British Columbia. From Whitehorse to Dawson City, the Yukon receives water from large tributaries, and then flows into the Yukon Flats area, which is currently protected as the Yukon Flats National Wildlife Refuge Area. Flowing out of the flats, the river crosses the Trans-Alaskan Pipeline and flows west through the Nulato Hills along the west coast of Alaska. There, the Tanana, Innoko, and Koyukuk Rivers join the Yukon, forming the Yukon Delta. This delta is similar in topography to the Mississippi River Delta—but is twice as large.
Like that of many northern rivers, the hydrology of the Yukon River is influenced by a combination of seasonal and annual variations in temperature and precipitation, and their effect on the supply of glacial meltwater and the distribution of permafrost. The mean annual discharge of the Yukon is 223,895 cubic feet (6,340 cubic meters) per second, which is the sixth-largest in North America. Because of the cold environment, evapotranspiration is relatively low, and annual runoff is a high fraction of precipitation. The strong influence of temperature on runoff indicates that climate change will influence the overall function and seasonal dynamics in the future.
Flora and Fauna
Common trees in the Yukon River biome include the white and black spruce, alpine fir, lodgepole pine, balsam poplar, white birch, and green alder in the boreal forests; the higher-elevation areas feature shrubs and sedges. The area holds rich floral diversity, with many species still being discovered. Wetlands and grasslands spread across great expanses between hilly zones.
Because of the extreme climate, the overall diversity of invertebrates is low in the Yukon basin. Few species of mollusks, clams, or snails have been reported. Diptera (true flies), mayflies, and stoneflies dominate the insect community in the basin.
Similarly, only 30 fish species have been reported in the Yukon River. Two fish, the Arctic grayling and the Alaska blackfish, are considered to be the icons of the Yukon River. The Arctic grayling is found throughout the river, and the Alaska blackfish is common in weedy areas in the lower part of the river.
In addition, several ecologically and culturally important salmonids—lake trout, dolly varden, and chinook salmon—are found in the Yukon River. Other notable fish species are the endemic (found only here) Arctic lamprey, as well as such regionally-distributed types as wintering spawning burbot, Bering cisco, whitefish, chum salmon, coho salmon, northern pike, and rainbow trout.
Some of the keystone terrestrial fauna in the Yukon are bald eagle, beaver, muskrat, brown and black bear, and moose.
Effects of Human Activity
Recently in its evolutionary history, the Yukon River basin has been a part of a transportation route to the south for oil and gas. Hydrocarbon fuel exploration in Alaska began in the mid-1950s, before statehood in 1959. In the mid-1960s, a major oil discovery on the north slope of Alaska led to the construction in 1977 of the Trans-Alaskan Pipeline, which runs through the Yukon River basin. Additional oil exploration has been conducted on the northern slope of Alaska and in and around the Arctic National Wildlife Refuge. The ongoing gold mining and oil exploration activities of the region have directly affected the Yukon River basin.
Major effects include direct pollution of lower streams from mining activities, loss and fragmentation of wildlife habitat, disruption of water flow, and secondary ecological degradation from oil exploration and infrastructure. However, the effects can worsen still from mining, oil exploration, forestry, dams, and climate change. Climate change has significant effects on the hydrology and ecosystems of the river, as these are largely controlled by seasonal temperature regimes. Warmer temperatures can change the hydrological patterns regulated by autumn freezes and spring melts. In particular, climate change has led to increased ice jam floods, which damage surrounding areas and bring more contaminants into the river.
The effects of climate change have also had a negative impact on the Yukon River’s salmon population. The chinook salmon run in 2020 was considered to be so weak, it did not replenish the salmon population on the Canadian portion of the river. That year’s chum salmon run was also the lowest ever recorded. The low salmon populations prompted both Alaskan and Canadian authorities to halt sport salmon fishing on portions of the river in 2020. The warmer temperatures are also thawing the region’s permafrost and increasing the release of mercury that is naturally found in the soil. A 2020 study published in the journal Nature Communications found that if the problem continues, mercury levels in the river will top federal safety guideline levels by 2050.
Bibliography
Benke, Arthur C. and Colbert E. Cushing. Rivers of North America. New York: Elsevier Academic Press, 2005.
"Climate Warming Leads to Changes in River Ice across the Yukon Territory." A&B, 28 Feb. 2017, arcticjournal.ca/health-science/science/climate-warming-leads-to-changes-in-river-ice-across-the-yukon-territory/. Accessed 31 July 2018.
Environment Yukon. “Yukon Plants.” Government of Yukon. http://www.env.gov.yk.ca/wildlifebiodiversity/plants.php.
Northern Climate ExChange. Yukon Climate Change Indicators and Key Findings 2015. Yukon College, 2016. Yukon College, www.yukoncollege.yk.ca/sites/default/files/inline-files/Indicator‗Report‗Final‗web.pdf.
Roland, Carl, Mary Beth Cook, Amy Larsen, and Claudia Rector. Results of an Inventory of Vascular Plants of Yukon-Charley Rivers National Preserve. Fairbanks: Central Alaska Network, National Park Service, 2004.
Rosen, Yereth. "Yukon River, Beset by Salmon Woes and Mercury Threats, Signals Broader Arctic Climate Change." Arctic Today, 29 Sept. 2020, www.arctictoday.com/yukon-river-beset-by-salmon-woes-and-mercury-threats-signals-broader-arctic-climate-change/. Accessed 8 Aug. 2022.