Nelson River
The Nelson River, located in central Manitoba, Canada, is a significant waterway that drains from Lake Winnipeg and flows approximately 400 miles (644 kilometers) into Hudson Bay. This river is integral to the region's ecology and hydrology, with a drainage basin that spans over 892,000 square miles (2.3 million square kilometers), impacting multiple Canadian provinces and several U.S. states. The river has historically been harnessed for hydroelectric power generation, leading to extensive damming and significant environmental changes, including rising water levels and shoreline erosion. These alterations have sparked controversy, particularly among First Nations communities and environmentalists, due to the disruption of local ecosystems and wildlife.
The Nelson River's surrounding environment features a sub-Arctic climate with cold winters and short summers, affecting the biodiversity in the area. It supports a variety of fish, birds, and mammals, although human activity has negatively impacted fish populations and the overall health of the ecosystem. Concerns regarding the increase in mercury levels in fish and decreased fisheries quality have emerged as notable issues. Additionally, ongoing climate change poses further threats to the river's ecological balance, with rising temperatures and changing precipitation patterns potentially exacerbating existing challenges. Efforts to mitigate these environmental impacts have been initiated, though their effectiveness remains limited. The Nelson River serves as a critical ecological and cultural resource, highlighting the complex interplay between natural systems and human influence.
Nelson River
- Category: Inland Aquatic Biomes.
- Geographic Location: North America.
- Summary: The ecosystem of Manitoba’s Nelson River has experienced environmental changes ranging from rising water levels to coastal erosion in the wake of hydroelectric development.
Spanning much of the central Canadian province of Manitoba, the Nelson River drains from Lake Winnipeg and runs a length of 400 miles (644 kilometers), with its mouth providing freshwater inflow to Hudson Bay. The river’s considerable volume and long drop have historically made it useful in hydroelectric generation, which has caused the river to be dammed repeatedly. This has led to controversy with First Nations (aboriginal Canadians) and concerns among environmentalists about the changes wrought on the region’s ecosystem. The river’s drainage basin affects a huge area, including four Canadian provinces and four American states.
Hydrology and Climate
The total length of the Nelson River, including the Saskatchewan River system, is about 1,600 miles (2,575 kilometers), and includes water from the Red, Grass, Burntwood, and Winnipeg Rivers, as well as from Lakes Cross, Sipwesk, Split, and Stephens. The Nelson River discharge rate is 84,000 cubic feet (2,379 cubic meters) per second. Its drainage basin of more than 892,000 square miles (2.3 million square kilometers) includes about 70,000 square miles (181,299 square kilometers) in the United States. This basin includes the Canadian provinces of Alberta, Saskatchewan, Manitoba, and Ontario; and the U.S. states of Montana, Minnesota, North Dakota, and South Dakota.
Located in an ecosystem characterized by a sub-Arctic climate, the region surrounding the Nelson River experiences short, cool summers and long, cold winters. Daily mean temperatures in January are minus 30 degrees F (minus 34 degrees C), while temperatures in July are in the range of 55–65 degrees F (13–18 degrees C). Annual precipitation averages 16–20 inches (406–508 millimeters), of which approximately one-third falls as snow.
Traditionally, the riverine nature of many of the lakes in the Nelson River region are high in nutrients. The area has an ion concentration much higher than that of the nearby Churchill River, with elevated levels of chloride, magnesium, sodium, sulphate, and suspended sediments. Scientists believe this characteristic is due to the Nelson River draining primarily through weathered, fine-grained prairie soils, while the Churchill primarily drains the granitic Canadian Shield.
Fauna and Flora
Algal biomass is lower in the cloudy Nelson River than in surrounding lakes. The benthic macroinvertebrate fauna is dominated by midge flies (chironomidae), worms (oligochaeta), and fingernail clams (sphaeriidae). The fish found in lakes along the Nelson River are typical of relatively shallow boreal Canadian lakes, and diversity of fish is low. A small number of cool-water benthivores (bottom-feeders) such as lake whitefish (Coregonus clupeaformis), white suckers (Catostomus commersoni), walleye (Stizostedion vitreum), and northern pike (Exos lucius) are common, as is sturgeon. Commercial and domestic fisheries are present, although sport fishing is rare due to limited access, and the cost of production has kept the area from being overfished.
Mammals found along the Nelson River include polar bear, woodland caribou, timber wolf, moose, and black bear. Birds that frequent the area include North American ruddy turnstones, semipalmated sandpiper, dunlin, and least sandpiper. Among the waterbirds are white-winged scoter, surf scoter, sandhill crane, Bonaparte’s gull, and bald eagles.
Vegetation in the river basin features tracts of grasses and willows interspersed with black spruce. The land behind the Nelson River estuary is boggy and has extensive expanses of stunted spruce.
Effects of Human Activity
Beginning in the mid-1950s, Manitoban power planners made the decision to build a series of hydroelectric generating stations on the northern part of the Nelson River. This process included constructing generating stations along the lower portions of the river at Kettle, Limestone, and Long Spruce, as well as the installation of a high-voltage direct-current transmission system to carry electricity to southern population centers. These changes diverted most of the flow of the Churchill River into that of the Nelson, causing certain ecological effects. Water levels of adjoining lakes reached 20-year highs shortly after the 1974 construction of a dam near Southern Indian Lake, raising its level by nearly 10 feet (3 meters).
Shoreline erosion rates and forms were altered by impoundment, especially since rising water levels swept over long-established granite beaches and began affecting land that was formerly permafrost. The change in water levels has caused shore erosion of nearly 30 feet (9 meters) per year in some areas, dramatically shifting the ecosystem. Sediment in the Nelson River, already high, has increased fivefold since the damming began.
The local flooding originally prompted increased crop production, due to the additions of organic matter and other nutrients, but subsequently this declined due to the depletion of the flooded organic matter. This caused a rapid response of macroinvertebrates in many of the reservoirs along the Nelson River. Zooplankton levels increased dramatically in some places, changes that coincided with the other effects of impoundment. Higher flow rates in certain areas of the Nelson River caused a decrease in measurable zooplankton levels elsewhere. Similarly, crustaceans responded in different ways to the damming of the river. Cyclopoid populations declined, while calanoids remained relatively stable.
Hydroelectric development had a negative effect on fisheries along the Nelson; the grade of the whitefish caught by commercial fisheries declined from export (A grade) to continental (B grade). Overall fish populations are down as well, and mercury levels in fish are up. Mitigation efforts have been undertaken to restore the Nelson River’s ecosystem, but with limited effectiveness to date.
Climate change may further stress the area in terms of lower runoff by earlier seasonal snowmelt from diminished snowfall, resulting from higher temperatures, which will have ripple effects throughout the ecosystem. Annual temperatures in the area of the Nelson River Basin have increased by 1.9 degrees C since 1984, creating greater variability in rainfall and droughts within the region. Further, sea levels are expected to rise which could lead to coastal flooding and erosion at the river's basin.
Bibliography
Bodaly, R. A., D. M. Rosenberg, M. N. Gaboury, R. E. Hecky, R. W. Newbury, and K. Patalas. “Ecological Effects of Hydroelectric Development in Northern Manitoba, Canada: The Churchill-Nelson River Diversion.” In Patrick J. Sheehan, Donald R. Miller, Gordon C. Butler, and Philippe Bourdeau, eds., Effects of Pollutants at the Ecosystem Level. New York: John Wiley & Sons, 1984.
Coward, H. and A. J. Weaver. Hard Choices: Climate Change in Canada. Waterloo, Canada: Wilfrid Laurier University Press, 2004.
Dmitrenko, Igor A., et al. "Storm-Driven Hydrography of Western Hudson Bay." Continental Shelf Research, vol. 277, 2021. DOI: 10.1016/j.csr.2021.104525. Accessed 18 Nov. 2024.
Kim, Su Jin; Masoud Asadzadeh, and Tricia A. Stadnyk. “Climate Change Impact on Water Supply and Hydropower Generation Potential in Northern Manitoba.” Journal of Hydrology: Regional Studies, vol. 41, 2022, doi.org/10.1016/j.ejrh.2022.101077. Accessed 18 Nov. 2024.
Minns, Charles K. “Factors Affecting Fish Species Richness in Ontario Lakes.” Transactions of the American Fisheries Society 118, no. 5 (1989).