Avaliação espaço-temporal dos efeitos da inundação de habitats sobre a diversidade taxonômica e funcional de anuros em uma hidrelétrica a fio d’água na Amazônia, Brasil.

Abstract

The Brazilian Amazon has approximately 90% (~ 95 MW) of untapped energy potential and there are future projects by government planning agencies to build over 200 new hydroelectric dams in the region. Although hydroelectric dams have been promoted as “cleaner” sources of energy, damming rivers interrupts river continuity and causes the flooding of adjacent riverine and terrestrial ecosystems. Flooding of the lowlands causes changes in species abundance and composition, particularly in species directly associated with the flooded gradients. For a better understanding of the environmental impacts of hydroelectric dams on wild species, it is advisable to assess impacts before and after reservoir flooding. The fauna surveys associated with the environmental impact assessments for the Santo Antônio hydroelectric dam in Rondônia are among the most intensive, well-planned, and long-term surveys ever conducted in Brazil. It is a hydroelectric plant with bulb type turbines which require less water and produce a small reservoir size (271 km2). The overall objective of this thesis was to evaluate the spatial and temporal effects of the flooding of the Santo Antônio HPP reservoir, upper Madeira River, Rondônia, integrating data on anuran species sampled in areas that would be flooded and not flooded before the construction of the hydroelectric dam with data collected in areas not flooded after the damming of the river. We used the Herpetofauna Monitoring database collected between 2010 and 2017 in which data were collected 2 years before, in areas subsequently flooded by the hydroelectric dam (pre-flooded stage) and not flooded (pre-not flooded), with intervals just after filling (post 1) and 4 years after filling (post 2). The thesis consists of two chapters that evaluate different aspects of the temporal and spatial effects of dam filling on the taxonomic and functional composition of anurans. A total of 120 species of anurans were recorded throughout the monitoring, including occasional records. In Chapter 1 the filling of the hydroelectric dam had little effect on the number of species, but altered their abundance. The frog composition in the areas permanently flooded by the damming of the river was not reestablished in the remaining areas and 6% of the species were no longer recorded. In the non-flooded areas, there were also changes in species composition over time, with a gain of species in 82% of the plots sampled, especially in those located near the new Madeira River bank. This increase in the number of species in the remaining areas may be a response to the flooding of low-lying areas, because after the reservoir was filled, the anurans may have moved to nearby areas, increasing the number of species recorded. This occurs during the period of community restructuring after a disturbance, where some populations may decrease while others occupy the new environments. In chapter 2, we sampled 58 plots before the flood (2010-2011), 19 of which were flooded after the creation of the reservoir. For the pre-flood period we categorized the data into 19 flooded and 39 non-flooded plots. These were sampled again two years after the dam was established. With the flooding of the lowlands, there was a loss of diversity and functional uniqueness of the anuran assemblages. The functional composition of the flooded area was distinct from the non-flooded area. Flooding did not result in the complete elimination of any trait or combination of traits from the anuran assemblages. The differences in functional diversity of Amazonian anuran assemblages were largely due to baseline environmental differences between seasonally inundated and non-inundated areas. Functional traits linked to reproductive strategies, such as egg deposition and larval development, help to understand community-wide responses of anurans to temporal changes caused by run-of-the-river dams. The results of this thesis showed that the effects of the damming of the Madeira River by the Santo Antonio Hydroelectric Plant were rapid, observed in the first two years after the reservoir flooding. The anuran assemblages of the floodplain forests were the most impacted by the formation of the reservoir and were not incorporated into the remaining non-flooded areas after the dam construction. The implementation of the reservoir did not reduce the number of anuran species, but there were changes in functional and taxonomic composition with an overall decrease in abundance after the reservoir flooding. Understanding effects on biodiversity requires long-term studies, and in the case of large-scale infrastructure projects, these studies should begin well before dam construction so that natural fluctuations in species can also be documented. As new hydroelectric dams are planned for the Amazon, we recommend the adoption of legislation for hydroelectric dams that incorporates the creation of protected areas with special attention to the types of vegetation permanently suppressed. Thus, our results show the need for protection of floodplain forests affected by hydroelectric dams.