This post will provide an overview on the general impacts that hydroelectricity has on the environment, narrowing the scope also to a case study on Canada, and how Canada is coping with the environmental effects.
Greenhouse Gases
Even though a hydroelectric plant produces no greenhouse gases, they can have an impact on the greenhouse effect. When a reservoir is filled and vegetation is submerged, methane and carbon dioxide can be produced as the vegetation decomposes. It has been proposed that as the size of the lake associated with the flooding due to a hydroelectric scheme increases, so does the amount of CO2 equivalent emissions. In fact, The Canadian Hydropower Association estimates that hydropower in Canada generates about 15,000 tonnes or less of carbon-dioxide equivalent for each gigawatt-hour of electricity produced. The amount of the carbon (contained in biological material) that is converted to methane increases with the size of the lake. However, this decreases as the output of the hydro-scheme and its lifetime increases. Over a period of a hundred years, methane has a warming effect twenty-one times that of CO2.
Although greenhouse gas emissions from reservoirs are small compared with emissions from other energy sources, studies are being conducted to better understand the source of emissions and to identify solutions. One option being used is clearing vegetation before an area is flooded.
Water
Some hydro facilities divert or store water to produce electricity, later discharging it back to the watershed. Although water is returned to its natural setting, this “in-stream” use of water has environmental impacts. Reservoirs can significantly change river use and habitat downstream. For example, they can:
- change water flow rates
- block fish migration
- disturb fish habitat
- expose riverbeds to erosion
Not all impacts, however, are negative. Reservoirs, for example, provide habitat for lake fish and nesting and feeding areas for migratory birds and waterfowl. In addition, they are used for recreation.
Fish and aquatic habitat
The need to protect fish and aquatic habitat is increasingly important. In inland regions of Canada, conserving local fish and their habitat is also becoming an issue, as a wide range of human activities put stress on regional ecosystems, including rivers and streams. In the case of hydroelectric generation, some fish species and aquatic habitats can be adversely affected through the creation of barriers and the modification of water flows.
Hydro operations affect fish and river ecosystems in different ways:
- dams can block salmon and other migratory fish species from reaching upstream spawning and rearing grounds.
- fish can be injured if they are drawn through water intakes or turbines.
- dams raise and lower water levels to meet changing electricity demand, causing fluctuations that are different from those naturally occurring in rivers and lakes. This can have harmful consequences: Low flows can contribute to the loss of fish habitat, while high flows may prevent fish migration or spawning. Wetlands are also sensitive to fluctuations since they depend on seasonal water flows such as spring flooding to maintain their ecosystems.
- dams can change the temperature and chemical balance of rivers and streams. For example, when river flow slows due to a dam, colder, denser oxygen-depleted water sinks to the bottom. If the water released to produce electricity is from the lower levels, the oxygen-depleted water can change habitat downstream.
In some cases, dams provide positive benefits to fish. Because the water stays longer in reservoirs, it becomes rich in zooplankton produced by decomposing organic matter. Slower-moving waters also attract fish such as trout that thrive in lake environments. Reservoirs can provide minimum flows in rivers, even in dry summers.
Hydro-operators in the Canadian Centre of Energy use a set of internal operating and reporting rules (called an environmental management system) to reduce their daily impacts on fish and their habitat. They also identify and monitor their impacts on fish throughout their hydro systems, and work to identify solutions. Hydro plants have facilities that direct fish around, over or through the dam. Examples include fish ladders (a series of pools arranged like steps that allow fish to pass upstream over a dam), fishways (channels that take fish over the dam) and screens that guide fish away from turbines, spillways and canals. Fish ladders help salmon and other migratory fish to swim upstream around dams to reach their spawning grounds. Hydro operators protect fish spawning habitats from disruptions by adjusting the timing and volume of water discharges from hydro facilities.
Slower-moving water in reservoirs can trap nutrients important to fish survival downstream. In these cases, hydro operators sometimes use fertilization programs to maintain food production and sustain healthy fish populations. Companies adopt new practices that improve hydro operations while reducing environmental impacts. One example involves replacing conventional greasing mechanisms at hydro stations to prevent the discharge of grease into the environment. Where dams affect river flows and fish habitat, industry invests in projects to restore or enhance the aquatic environment — for example, stocking streams and lakes with fish, rebuilding fish spawning areas and planting trees and grasses along shorelines.
The industry funds research activities by governments and conservation organizations that increase our knowledge about local fish species and the impacts of hydro operations on the aquatic environment. The topics of these studies are wide-ranging — everything from fish productivity to mercury levels in fish to turbine designs that are safer for fish to programs to restore healthy river ecosystems. The industry works closely with governments to create strategies and policies that protect fish and aquatic habitat. In 2002, for example, the Canadian Electricity Association entered an agreement with the Canadian Department of Fisheries and Oceans to work in partnership on initiatives to better protect fish and fish habitat resources associated with electricity generation in Canada.
Mercury
Mercury is a toxic element that enters the environment from natural processes (such as volcanic eruptions, vapor from oceans and the weathering of soils and rocks) and industrial activities (such as metal smelting, waste incineration, coal-fueled power plants).
Higher than normal levels of mercury can be found in fish inhabiting newly created hydro reservoirs. This mercury has a dual origin: part of it is released when soils and rocks, which naturally contain mercury, are flooded; the other part originates from the flooding of topsoil where mercury has accumulated from atmospheric emissions from industrial activities.
The creation of reservoirs frees the mercury trapped in soils and rocks. Bacteria then transform this relatively inert toxic mercury into a biologically more active form (methyl mercury), which penetrates the food chain and especially accumulates in the fatty tissue of predatory fish (such as northern pike, walleye, lake trout).
Well-established monitoring and mitigation procedures are in place to avoid health risks from mercury accumulation. Utilities and governments have carried out extensive research on mercury for many years. Recent studies have included monitoring of mercury content in fish in reservoirs, the impact of river flows on fish mercury levels and research on mitigation measures to reduce the mercury content of fish in new reservoirs. Industry and government studies suggest that the effect of flooding vegetation on mercury levels gradually decreases over time, with mercury levels returning to values similar to those measured in fish in surrounding natural lakes. This occurs after 10 to 30 years, depending on the fish species.
Land
Some of the most visible impacts of building and operating hydro projects affect the land. During construction, trees are cleared and roads are built. This can increase human access and hunting in fragile wildlife habitat areas.
If dams are constructed, there is generally a loss of forests and wildlife habitat. The land area disturbed or covered varies, depending on the type and size of the project.
One of the largest hydro systems ever built in Canada was the first phase of the James Bay Project in Quebec. Requiring major diversions of water, the project’s reservoirs cover an area equivalent to three times the size of Prince Edward Island. The project affected some 10,000 Aboriginal people.
Industry strives to manage these impacts through careful planning and operation of their facilities. Working with regulators, hydro developers assess new projects for potential environmental impacts, including local land use and wildlife areas, and identify different options. They also consult with local communities to identify ways to protect the environment, ensure access to hunting, fishing and trapping and preserve important cultural and recreational resources.
After completion, companies follow up by monitoring their projects to assess environmental impacts, including changes to wildlife and their habitat. If impacts cannot be avoided, they sometimes restore disturbed lands by planting trees and vegetation.
Biodiversity
With construction and operation of hydro facilities come changes to the different birds, animals, fish and plants populating an area. Dams can reduce biodiversity by making spawning habitat inaccessible to some fish species. Nesting, forage and cover along rivers and streams can be temporarily or permanently lost. Large reservoirs can block the traditional migration of animals along or across rivers.
These changes result in unsuitable habitat for some species. But in some cases, hydro plants and reservoirs can help wildlife habitat, supporting fish populations, especially those attracted to slower-moving waters, and providing resting and feeding points for geese and other migratory birds and waterfowl. Reservoirs can increase the shoreline of an original lake or river, expanding wildlife habitat for some animal species. Industry studies show that animals such as caribou seek out reservoirs in northern Quebec for feeding on banks and islands in the winter months.
In the initial years of their development, projects modify wildlife habitat. Hydro companies strive to reduce these impacts by careful planning and operation of facilities. For example, in Quebec, some hydro dams have been built on river sites not accessible to migratory fish.
The industry also implements measures to enhance wildlife habitat, including
- providing fish ladders
- rebuilding fish spawning habitat
- stocking streams and lakes with fish
- planting trees and grasses along shorelines
- creating wildlife preserves near reservoirs
To better understand industry’s impact on wildlife and their habitat, hydro companies fund wildlife research projects by government and conservation organizations.
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