Hydropower is favored by energy strategists, as it is considered to be predictable and can have approximately 90% water-to-wire conversion efficiency. Brazil is unique in that approximately 80% of its electricity already comes from hydropower, and Brazil's energy planners continue to favor hydropower over environmentally-friendly alternatives like wind- and solar energy because they perceive dams as the least expensive and most reliable option. Unfortunately, their decision-making typically considers only financial expenses, ignoring non-financial costs such as biodiversity loss and the impacts dams have on local human populations.
Like many other tropical countries, Brazil has the option of supplying all additional power without resorting to the exploitation of environmentally-damaging energy sources. The use of wind- and solar technologies results in relatively insignificant impacts on biological communities.
Dams convert turbulent river into still water. This seriously impacts flow regimes, temperature regimes, and sediment transport. This shift from fast-flowing to still waters favors generalist- or invasive species over specialist species that require fast-flowing rivers and exposed rocky islets, and this eventually results in significant losses of regional biodiversity. Dam operations are designed to optimize energy production and do not consider the ecological needs of organisms within these habitats. The presence of dams eliminates the natural cycle of flood pulses, which in turn eliminates environmental triggers necessary for the onset of fish spawning, various insect activities, and fruit production in flooded forests. Dams inhibit both downriver sediment flow and the migration of organisms up- and downstream. The loss of nutrient connectivity is likely to be most ecologically-damaging downstream of Andean-Amazonian dams, whose rivers supply most of the sediment, nutrients, and organic matter to the main stem of the Amazon River, affecting marine processes thousands of kilometers away.
Fish are the most discussed casualties of dam activities. Changes in water depths, water discharge, and sediment deposition patterns in reservoirs and dam tailwaters remove niches for many species, and dams themselves fragment populations, as they are an impediment to fish migration to spawning- or feeding grounds. Large dam reservoirs often vastly increase the extent of freshwater environments, but these typically provide low-quality habitat for aquatic organisms. Amazonian freshwater organisms are severely under-inventoried, as 30-40% of the region's freshwater fish remain undescribed. The Amazon harbors over 2500 fish species. Approximately 80% of these species are endemic to the region, many of which have extremely small range sizes. Looking solely at the Belo Monte Dam on Brazil's Xingu River, at least 44 fish species (approximately 10% of the fish species occurring in this river basin) are considered endemic, and many of these are at risk of extinction by the construction of this dam. Furthermore, the loss of migratory fish and invertebrates will impact nutrient transport, resulting in losses for local fisheries.
Knowledge of migratory behavoir for most species is very poorly documented. Only recently was the mass-migration of juvenile pencil catfish (Trichomycterus barbouri) documented. It is likely that the construction of dams will put an end to other spectacular migratory events before they are known to us.
Scientists very recently described a new river dolphin, the Araguaian boto (Inia araguaiaensis) from the Araguaia River basin in the south-eastern region of the Brazilian Amazon. It is most-likely that this species will be moved straight onto the global Red List. Indeed, populations of river dolphins in this region are the most threatened in Amazonia.
Species requiring rocky islets in rivers are particularly threatened. Without a change in current plans regarding dam construction, there is a foreseeable near-complete loss of this rare habitat type in most river stretches within the Brazilian and Guiana Shields. These rocky islets are required habitat for many species that require fast-flowing waters, such as a large group of river weeds (Podostemaceae), as well as armored catfish such as the zebra pleco (Hypancistrus zebra). Furthermore, these rocky outcrops are the primary breeding habitat for some bats (Nyctinomops) and the black-collared swallow (Atticora melanoleuca). Dam construction, and the subsequent changes in upstream and downstream habitats, will further endanger these river island-dependent species that will lose significant portions of their already-small ranges. Ironically, many of the species threatened by dams in Amazonian Brazil are strictly protected by Brazilian law from unlicensed harvesting, while Brazilian law simultaneously allows for the complete loss of these species due to dam-building projects.
Indirect effects of dam-construction projects will add to the profound impact on regional biodiversity. For example, once construction contracts end, the suddenly-unemployed workers often join others in resorting to exploitation activities such as illegal deforestation. Brazil's Belo Monte Dam project is expected to lead to an additional loss of 4000-5000 square kilometers of forest by 2031, on top of the forest-loss that is expected from "legal" activities associated with the construction project. The loss of vegetation will result in drier climates, reducing river discharge. Dam projects in the southern and eastern part of the Amazon Basin are already situated within the Amazon's "Arc of Deforestation", a vast area of agressively-expanding agriculture practice. The resulting increased potential for forest fires, and subsequent far-reaching biodiversity loss, further strengthens the negative impact of dam-building on a substantial portion the Amazon Basin's aquatic- and terrestrial biota.
Aside from reducing energy consumption, reducing dependence on hydropower by investing in wind- and solar power and other ecologically-friendly alternatives will immensely benefit natural communities, including indigenous and non-indigenous human communities. Plans to build new dams in Amazonia will inevitably calalyze further losses of aquatic- and terrestrial biological communities, and (both directly and indirectly) threaten many range-restricted species with extinction.
LINK to Lees et al.'s 2016 article in Biodiversity and Conservation.
