Question

Hydroelectric schemes provide one of the least polluting ways of generating power. Nevertheless, they have a number of negative effects on natural systems. What are they?

Short answer

Hydroelectric schemes can displace wildlife, alter water ecosystems, change sediment transport, and produce methane emissions.

Step-by-step solution

Understanding Hydroelectric Schemes

Hydroelectric schemes generate electricity by harnessing the energy of flowing water, typically by constructing a dam on a river that creates a reservoir.

Environmental Displacement

The construction of a dam and reservoir can lead to the displacement of communities and wildlife habitats. It often results in the submergence of large areas of land, impacting ecosystems and the species that inhabit them.

Altered Water Ecosystems

Damming rivers can change the natural flow of water bodies, impacting aquatic life by altering habitats and migration patterns of fish and other aquatic organisms.

Changes in Sediment Transport

Dams can trap sediments that would naturally flow down the river. This can lead to sediment buildup in the reservoir and reduced sediment downstream, affecting riverine and coastal ecosystems.

Methane Emissions

Decaying organic material in a flooded reservoir can produce methane, a potent greenhouse gas, which contributes to climate change.

Consideration of Alternatives

While acknowledging these negative effects, it's important to weigh them against potential alternatives, to find a balanced approach to energy generation.

Key concepts

Environmental Impact

Hydroelectric power may seem like a green energy source at first glance, but its environmental impact is more complex. When a dam is constructed, it often leads to significant changes in the local environment. For starters, large areas of land may be submerged, leading to the displacement of communities and destruction of habitats.
Building these large-scale projects can also affect the local climate and impact agriculture by altering temperatures and humidity levels.
Another key point is that constructing and maintaining these dams requires a lot of resources and energy, which can contribute to pollution itself. Thus, even though hydroelectric power reduces reliance on fossil fuels, it still poses environmental challenges that need to be carefully managed.

Ecosystems

Ecosystems are intricately balanced environments that can be drastically disturbed by hydroelectric projects. When water is blocked by a dam, the natural flow is interrupted, and this can have severe consequences on the local flora and fauna.
Aquatic ecosystems are particularly vulnerable because the obstruction can prevent fish and other organisms from migrating, disrupting breeding and feeding patterns. Moreover, changes in water temperature and quality can lead to a decline in certain species that are not adaptable to new conditions.

• Altered fish migration routes
• Changes in water quality
• Loss of biodiversity

The effects spread beyond the aquatic ecosystems, impacting land animals too, as they lose water sources and habitat spaces.

Sediment Transport

Sediment transport is a crucial natural process that maintains river and coastal ecosystems. Dams interrupt this natural flow of sediments, causing several downstream effects.
When sediments are trapped in reservoirs, it means that less sediment is available downstream, which can lead to erosion of riverbeds and banks. This can further result in the destruction of habitats for various species, including both plants and animals.
Moreover, reduced sediment flow affects agricultural lands that rely on the nutrient-rich sands and soils carried by the river. On the flip side, sediment buildup in a reservoir can reduce the lifespan of the dam due to the accumulation and eventual clogging of the outlets.

Greenhouse Gas Emissions

Although hydroelectric power is primarily seen as a clean energy source, it is not entirely free of greenhouse gas emissions. When land is flooded to create reservoirs, plants and other organic matter in the soil decompose anaerobically (without oxygen), which produces methane, a potent greenhouse gas.
While not as high as emissions from fossil fuels, the methane released from reservoirs is significant enough to contribute to climate change.

• Production of methane from decaying plants
• Potential carbon dioxide emissions from dam construction

Recognizing these emissions is vital to make informed decisions about energy policies and to weigh them against the benefits they offer in reducing dependency on fossil fuels.