Small hydropower dams in Brazil threaten marine biodiversity

small hydropower dams in brazil, food security
© Ondřej Prosický

The University of Washington found that small hydropower dams in Brazil are potentially damaging river connectivity and marine biodiversity – what’s going on?

Their findings suggest that small hydropower plants are relatively responsible for river fragmentation than large hydropower plants, because where they are built and how many of them exist.

This source of energy impacts food security and financial security, for certain communities that have depended on the way a river flows for hundreds of years. The same thing can be seen in the subtle shifting of the Tropical Rain Belt – which is expected to change how agriculture works across several countries, and leave Indigenous people without reliable crops. It is also happening where land-grabbing deals are being made, with foreign companies taking control of ancient grounds – in moves that were found by scientists to leave locals without reliable food security.

“The cumulative impacts of many small hydropower dams have long been ignored; instead, focus has been on them in isolation, resulting in claims that their impacts are small,” said co-author Julian Olden, a UW professor of aquatic and fishery sciences.

The landscape of hydropower power in Brazil

According to the Associação Brasileira de Distribuidores de Energia Elétrica (ABRADEE), there are currently 201 hydroelectric power stations in the country. Brazil uses hydroelectric power for around 70% of their electricity consumption, whereas the world average is roughly 16%.

The development of small hydropower dams is widespread throughout Brazil and elsewhere in the world, significantly overshadowing large hydropower projects. The existence of these smaller dams is a response to growing security needs, which makes sense in a country that is so capable of using renewable energy.

Dams limit how migratory fish move along river networks and they isolate critical habitats, which can then contribute to local extinctions, population declines and collapses of fishery stocks. This makes migratory fish species some of the most vulnerable organisms to hydropower development in the tropics.

The further expansion of small dams basically threatens many of the remaining free-flowing rivers and biodiverse tropical regions of the world. And why is it so crucial that fish can migrate freely? Because that is the process on which millions of peoples’ livelihoods depend.

Some communities get hit harder than others by fish losses

Many fish species impacted by fragmentation are of high ecological and socioeconomic importance – with some communities feeling the impact far more than others. For example, some small hydropower dams have been linked to the decline of fish stocks that are relied on heavily by Brazil’s Indigenous groups, because fish are no longer reliably migrating through their historic range.

Another concern cited by the authors is that small hydropower dams greatly outnumber large hydropower dams, but their combined energy output is much less. In Brazil, small hydropower plants only account for only 7% of total generation capacity even though they represent more than 85% of hydropower plants in the country.

Scientists say river fragmentation will increase by 21%

The collective impacts of Brazil’s rapidly growing small hydropower development on river fragmentation and migratory fish species is extensive.

Right now, it shows no signs of lessening as the planned construction of new dams continue. It is projected that river fragmentation will increase by 21% in the future, and two-thirds of the 191 migratory species assessed in the study occupy river basins that will experience greater connectivity losses.

The research team want improved strategic planning of hydropower development with environmentally informed criteria to decrease the potential ecological impact.

“We were motivated by the hope that society could be smarter about new dam constructions in the future,” said Olden.

“The study demonstrates that with careful planning, Brazil can meet future energy production needs with only modest impacts on river fragmentation and migratory fishes.”

Read the full study here.


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