Hydroelectric Power: Pollution Paradox And Its Impact

Hydroelectric power has long been considered a clean and renewable energy source. However, recent studies have revealed that the construction and operation of hydroelectric plants can cause significant environmental damage and contribute to global warming. The flooding of land for reservoirs leads to the release of greenhouse gases, particularly methane and carbon dioxide, as vegetation and soil decompose underwater. The impact of these emissions varies depending on the size and location of the reservoir, with some acting as carbon sinks and others emitting more greenhouse gases than fossil fuels. Additionally, hydroelectric facilities can have negative consequences for aquatic ecosystems, including the disruption of river flow, the injury and death of fish and other organisms, and the cultivation of excess algae and aquatic weeds. While hydroelectric power offers benefits in the long term, the near-term warming effects of methane emissions and carbon dioxide releases from newly flooded reservoirs cannot be ignored.

Hydropower's methane emissions are as high as Canada's

Hydropower has long been considered a "clean" energy source and a low-carbon alternative to electricity generation by fossil fuels. However, recent studies have brought to light the fact that the hydropower industry's methane emissions are as high as Canada's. This has prompted a re-evaluation of the wisdom of relying on hydropower to replace fossil fuels.

The high methane emissions from hydropower are primarily due to the decomposition of organic matter in reservoirs. When land is flooded to create a reservoir, the vegetation and soil in that area start to decompose and release both carbon dioxide and methane. The release of these greenhouse gases is highest in the first 10 to 20 years after reservoir impoundment and then decreases over time. The size of the reservoir and the nature of the land that was flooded also play a significant role in the amount of emissions produced.

The challenge in accurately measuring emissions from reservoirs is due to the varying reservoir features and meteorological characteristics. The water levels in hydropower dams are constantly manipulated to make electricity, which also affects the amount of emissions released into the atmosphere. As water levels decline, the hydrostatic pressure on submerged soils decreases, allowing gas bubbles to escape. Sometimes the methane in these bubbles is absorbed by the water column, but other times it reaches the air.

While some hydropower reservoirs act as carbon sinks, absorbing more carbon through photosynthesis than they emit through decomposition, others have carbon footprints equal to or greater than fossil fuels. The International Hydropower Association (IHA) estimates that if hydropower was replaced with coal for electricity generation, more than 4 billion metric tonnes of additional greenhouse gases would be emitted annually. Despite this, the hydropower industry's high methane emissions have led to concerns about its environmental impact and the need for better control and reduction of these emissions.

Hydropower facilities can negatively impact aquatic ecosystems

Hydropower facilities can have a detrimental impact on aquatic ecosystems in several ways. Firstly, the construction and operation of dams and reservoirs can obstruct fish migration, affecting both individual fish and disrupting the entire food chain. Fish and other organisms can also be injured or killed by turbine blades, despite the existence of methods to minimise this impact, such as fish ladders and intake screens.

Secondly, the water in reservoirs is typically more stagnant than normal river water, leading to higher levels of sediments and nutrients. This can result in excessive growth of algae and aquatic weeds, which then crowd out other plant and animal life in the river. The water in reservoirs is also usually colder and has lower levels of dissolved oxygen than normal river water. When this water is released, it can negatively impact downstream plants and animals, although this can be mitigated to some extent by aerating turbines and multi-level water intakes.

Thirdly, the flooding of land to create reservoirs can lead to the decomposition of vegetation and soil, releasing carbon dioxide and methane. This can contribute to global warming and impact the climate, with some hydropower reservoirs having a larger carbon footprint than fossil fuels in the short term. The size of this impact depends on various factors, including the size and location of the reservoir, and the nature of the land that was flooded.

Finally, the physical presence of dams and reservoirs can change the environment over a much larger area than just the reservoir itself. This can include changes to natural water temperatures, water chemistry, river flow, and silt loads, all of which can have negative effects on native plants and animals in and around the river. Additionally, reservoirs may cover important natural areas, agricultural land, or archaeological sites, further impacting the surrounding ecosystem.

Hydropower dams can cause the extinction and near-extinction of species

Hydropower dams can have detrimental effects on the environment, and they have been linked to the extinction and near-extinction of several species. The construction of dams can cause immediate loss of habitat and species, and also result in a "significant future biological cost". This phenomenon has been termed "extinction debt" by researchers.

Islands, in particular, undergo a sustained loss of species year on year after dam construction. A study found that islands have 35% fewer species than nearby mainland sites on average, with one South American bird community suffering an 87% loss of species. The loss of species is not limited to birds, but also includes insects, spiders, and other arthropods.

Dams can obstruct fish migration, as they block natural pathways between feeding and spawning grounds. This interruption in their life cycles can limit their ability to reproduce. For example, salmonids in North America were mostly wiped out by dams, and the Chinese paddlefish became extinct due to the construction of dams on the Yangtze River. Hydropower turbines can also kill and injure fish that pass through them.

The flooding of terrestrial habitats caused by dam construction can also lead to extensive habitat loss and degradation, triggering biodiversity loss. This has been observed in the habitats of jaguars and tigers, with 164 dams intersecting the jaguar range and 421 dams in the tiger range. As a result, these species face the risk of extinction.

In addition to the direct impacts on species, dams can also change natural water temperatures, water chemistry, river flow characteristics, and silt loads. These changes can have negative effects on native plants and animals in and around the river. Therefore, it is crucial to carefully consider the potential environmental impacts of hydropower dams and take steps to minimize their negative effects on species and their habitats.

Hydropower reservoirs can act as carbon sinks

Hydropower is often considered a clean and renewable energy source, but the construction and operation of hydroelectric power plants can still contribute to pollution and environmental degradation. One of the main ways that hydropower reservoirs can act as carbon sinks is by sequestering carbon dioxide (CO2) through the absorption and storage of carbon by the reservoir's ecosystem.

When a hydropower reservoir is created by flooding a valley or river

Hydropower plants emit carbon dioxide during installation and dismantling

Hydropower is a widely available, reliable, and renewable energy source. It is considered a low-carbon alternative to fossil fuels for electricity generation. However, the creation of reservoirs during the installation and dismantling of hydropower plants can result in the emission of carbon dioxide and other greenhouse gases.

When reservoirs are constructed for hydropower plants, they alter the natural dynamics of carbon emission and storage in river systems. The flooding of vegetation and soil in these areas leads to their decomposition, releasing carbon dioxide and methane. The depth and shape of the reservoir, sunlight exposure, and wind speed all influence the rate at which these gases are produced and released into the atmosphere.

The impact of these emissions varies depending on the specific conditions of the reservoir. In some instances, reservoirs can act as carbon sinks, absorbing more carbon through aquatic organisms' photosynthesis than they emit through decomposition. However, in other cases, particularly in tropical regions, reservoirs have been found to produce significant greenhouse gas emissions, with over 100 facilities worldwide having emissions that cause more warming than fossil fuels.

The size of the reservoir also matters. Large reservoirs, such as the Balbina hydroelectric plant in Brazil, can flood vast areas, resulting in high carbon dioxide emissions and significant environmental impacts. On the other hand, small run-of-the-river plants emit lower amounts of carbon dioxide equivalent per kilowatt-hour.

While hydropower plants do emit carbon dioxide during installation and dismantling, the overall lifecycle emissions of hydropower are generally lower than those of fossil fuels. Independent research suggests that the use of hydropower has helped avoid more than 100 billion tonnes of carbon dioxide in the past 50 years. Additionally, the long lifespan of hydropower assets means that emissions associated with construction can be spread out over a much longer period compared to shorter-lived technologies.

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