Efeitos de estratégias sustentáveis em uma hidrelétrica na comunidade de aves aquáticas ao longo de 14 anos

Abstract

Reservoirs of hydroelectric power plants, built for the production of renewable energy, are part of the reality of many Brazilian municipalities. However, these enterprises promote profound changes in river morphology, converting lotic environments into lentic systems, in addition to causing the suppression of riparian vegetation. Such alterations to the original ecosystem typically affect aquatic bird communities through a strong replacement of specialists by generalists, without necessarily reducing total species richness in some ecosystem types, but with marked changes in community composition and increased functional dissimilarity. Because assessments of the impacts of hydroelectric construction on aquatic bird communities remain scarce, this study evaluated the water-dependent avifauna at the Anhanguera Small Hydropower Plant (northeastern São Paulo State, Brazil) over a 14year period, starting one year before reservoir filling and the implementation of restoration actions. Our objective was to quantify avifaunal responses to reservoir filling—associated with an increase in water surface area from approximately 0.3 to 2.05 km²—and to riparian forest restoration, in which dry biomass increased from 1100.15 kg/m² to 2,296.31 kg/100 m² in the remnant forest, and from 0.304 kg/100 m² to 1,773.117 kg/100 m² in the restored area. In both restored areas and forest remnants, we assessed: (i) species richness and composition; (ii) taxonomic β-diversity (Jaccard index); (iii) functional richness (FRic); (iv) functional redundancy (FRed); and (v) functional β-diversity and its decomposition into nestedness and turnover components. Over the study period, species richness increased linearly in both areas, with a higher rate of increase in the restored area than in the forest remnant. Taxonomic β-diversity increased in both areas, more intensely in the restored site and particularly during the first two years after reservoir filling. Cluster analyses of species composition revealed distinct temporal trajectories, with greater dissimilarity amplitude in the restoredarea (up to 0.68) compared to the forest remnant (up to 0.34). Functionally, FRic increased linearly in both areas, at a higher rate in the restored site, whereas FRed remained stable, showing only a transient peak immediately after reservoir filling. Functional β-diversity increased over time in both areas but was dominated by the nestedness component (with turnover ≈ 0), indicating the cumulative addition of functional groups rather than functional replacement. Our results revealed an initial colonization by aquatic predators, followed—after canopy densification and increased structural complexity of riparian vegetation—by an increase in forest dependent species that use perches and have lower body mass. We conclude that the conversion of aquatic environments from lotic to lentic systems, combined with riparian forest restoration, simultaneously promoted taxonomic diversity and expansion of the functional hyperspace of the avifauna, with important implications for aquatic ecosystem functioning. Thus, although hydroelectric development generally tends to cause negative impacts on aquatic bird communities, our results clearly demonstrate that, in already degraded ecosystems, reservoir implementation can contribute to the conservation of these species when combined with the preservation of river margins, remnant forest fragments, and active riparian forest restoration, constituting a more sustainable development strategy. From a management perspective, the preservation of riverbanks and the continuous development of riparian forests are key to sustaining functional expansion and may, in the medium to long term, lead to increased functional redundancy and ecosystem resilience.