Abstract
The enormous biodiversity of tropical freshwater combined with a considerable increase in the construction of reservoirs urges to understand the ecological effects caused by damming. Using rarely available data obtained before (one year) and after (four years) the filling of a hydroelectric plant on the Teles Pires River (Amazon River basin), the effects on abundance, biomass, and diversity of the fish assemblage were evaluated using two complementary approaches: a BACI (before-after-control-impact) design with mixed models and analyses of covariance. Significant Before-After × Control-Impact interactions in abundance, biomass, and species richness were observed, with decreases of abundance and species richness and more stable biomass after filling. Some abundant species, such as Jupiaba polylepis, Jupiaba acanthogaster, Knodus cf. heteresthes, and Moenkhausia lepidura among others, declined in abundance or disappeared from the impact sites. However, temporal and particularly spatial variation independent of damming explained more variation in all the response variables analyzed, including species composition, and analyses of covariance demonstrated general negative trends irrespective of damming. This study illustrates the usefulness of BACI designs to assess the effects of damming but also that other statistical approaches are complementary, given the difficulty of identifying control sites and the short length of most ecological time series. The results also suggest that preserving tributaries upstream of reservoirs and natural regimes of spatial and temporal environmental variation might help to mitigate the impacts of damming in tropical ecosystems.
Highlights
Freshwater ecosystems cover only 0.8% of the Earth’s surface but harbor enormous biodiversity, with about 12% of the species known and one-third of all vertebrate species (Garcia-Moreno et al, 2014; Flitcroft et al, 2019)
Species accumulation curves (Fig. S1) showed that: i) a sampling campaign tended to capture about 20% of the total number of species observed in a site along the whole 5-year study period (21–29 out of 104–139 species), the differences in spe cies richness among sites did not depend on sampling effort; ii) the total observed richness per site varied from 107 species to 139 species; and iii) extrapolated richness was lowest in impact sites 1, 2 and 3, because in them species richness saturated with sampling effort more than in control sites
The BA × CI interaction, which is the main test of interest in a BACI design, was only significant for catch per unit effort (CPUE), biomass per unit of effort (BPUE), and observed richness, indicating that the differences among control and impact sites changed after filling the reservoir (Table 1)
Summary
Freshwater ecosystems cover only 0.8% of the Earth’s surface but harbor enormous biodiversity, with about 12% of the species known and one-third of all vertebrate species (Garcia-Moreno et al, 2014; Flitcroft et al, 2019). Despite that there are still long free-flowing rivers in the Amazon basin (Grill et al, 2019), there is a growing trend towards the con struction of reservoirs, as in many tropical, less impacted rivers (e.g. Congo and Mekong) (Latrubesse et al, 2017; Tundisi, 2018; Winemiller et al, 2016; Zarfl et al, 2015). Reservoirs are thought to provide so cioeconomic development of these regions through for instance elec tricity production, water supply, and flood control, long-term costs are often underestimated (Latrubesse et al, 2017; Stone, 2011; Tundisi, 2018; Winemiller et al, 2016). There are more than 415 dams in operation or under con struction in the Amazon basin and over 334 planned or proposed (Winemiller et al, 2016; Anderson et al, 2018)
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