Amazonian run‐of‐river dam reservoir impacts underestimated: Evidence from a before–after control–impact study of freshwater turtle nesting areas

Abstract

Hydropower dams are associated with adverse impacts on biodiversity, yet there remains a lack of robust scientific evidence documenting the magnitude of these impacts, particularly across highly biodiverse tropical waterways. Aquatic and semi‐aquatic vertebrates are disproportionately affected by human changes to aquatic environments and hydropower expansion is an increasing threat to the Endangered yellow‐spotted river turtle (Podocnemis unifilis) across its tropical South American range. Yellow‐spotted river turtle nesting areas were monitored as an indicator of dry season river level changes following run‐of‐river dam reservoir filling. A before–after control–impact (BACI) study design was used with multi‐year field campaigns monitoring turtle nesting areas upstream of the dam. The cause and extent of changes in nesting areas were established using generalized additive models. Nesting area density was evaluated in relation to time (before vs. after), treatment (control vs. impact), time–treatment interaction (BACI), distance to the dam and precipitation. The extent of changes was examined by comparing the remaining proportion of nesting areas after reservoir filling. Dam construction generated an immediate and apparently permanent dry season river‐level rise that extended more than 20 km beyond impact assessment limits. On average the density of nesting areas declined by 69% (from 0.48 to 0.15 per km) across 33 km of river directly affected by the dam. This loss was reflected in a significant BACI interaction. Nesting area density was not explained by seasonal precipitation. Monitoring of freshwater turtle nesting areas provided an effective means to quantify hydropower dam impacts across biodiverse yet rapidly changing waterways. The adverse impacts documented in this study should be preventable by mitigation actions including habitat creation and dry season flow regulation. Such measures are also likely to benefit multiple sandbar‐nesting species (including turtles, crocodiles and birds) in tropical rivers increasingly influenced by run‐of‐river dams.

Anthropogenic influences on the distribution of a threatened apex-predator around sustainable-use reserves following hydropower dam installation

“…1 ). The 59.1 km dam “reservoir” impact zone included approximately 39 km of reservoir and an additional 20 km where upstream river levels changed after dam construction ( Bárcenas-García et al, 2022a ; Norris, Michalski & Gibbs, 2018 ), together with relatively high levels of anthropogenic disturbance. The control zones included a 79.3 km “intermediate impact” zone not directly affected by the dam (>70 km upstream of the dam) but with an intermediate anthropogenic disturbance (including commercial fishing activity), and a 74.3 km “low impact” zone not directly affected by the dam (>70 km upstream of the dam) with low anthropogenic disturbance and no commercial fishing allowed ( Oliveira, Norris & Michalski, 2015 ).…”

“…Most work documenting biological responses to hydropower impacts focused on fishes in temperate regions ( Algera et al, 2020 ; Harper et al, 2020 ). Although some localized studies quantified hydropower dam impacts on vertebrates such as freshwater turtles ( Bárcenas-García et al, 2022a ) and dwarf caimans ( Paleosuchus palpebrosus and Paleosuchus trigonatus ) in the Brazilian Amazon, the majority focused on fishes, and adopted less robust study designs that limited the insight possible from the available scientific evidence ( Santos, Michalski & Norris, 2021 ). It is therefore unsurprising that to date, there has been no consensus on the effects of hydropower dams on giant otters, the world’s largest otter ( Groenendijk et al, 2021 ; Santos, Michalski & Norris, 2021 ).…”

Charapa Turtles (Podocnemis unifilis), an Opportunity to Improve Community Tourism and Contribute to Their Conservation in Yasuní National Park, Ecuador

“…Scopus and Web of Sciece 17 [23,24,35,[38][39][40][41][42][43][44][45][46][47][48][49][50][51] "Turismo", "Conservación", "Charapa" y "Ecuador" Redalyc and Scielo 2 [52,53] With respect to the second objective and to learn about perceptions, field visits were made to the Río Indillama community, where a meeting was held with the community president and the rest of the inhabitants. During the visits to the study area (Figure 2b), semistructured interviews (Table 2) were conducted, that is, open-ended questions directed to focal groups in the community (Figure 2a).…”

Impacts of dams on freshwater turtles: a global review to identify conservation solutions

“…river banks) may be at greater risk from flooding (Bodie, 2001), as is the case of species of the South American genus Podocnemis (Eisemberg et al, 2016;Gallego-García & Castaño-Mora, 2008;Norris et al, 2018a;Norris et al, 2020), genus Elseya in Austrailia (Espinoza et al, 2022), and of the North American Emydidae and Trionychidae (Pitt et al, 2021;Tornabene et al, 2018). Changes to a river's annual discharge cycle caused by dams can therefore reduce the availability of nesting areas (Bárcenas-García et al, 2022;Norris et al, 2018a;Tornabene et al, 2018), as well as the duration of low water levels, which may affect the behavior and nesting success of these species (Eisemberg et al, 2016;Espinoza et al, 2022;Tornabene et al, 2018).…”

“…In Brazil, the filling of a hydropower dam reservoir resulted in the flooding and loss of 3.9 hectares of nesting habitats and areas used by the yellow-spotted river turtle Podocnemis unifilis (Norris et al, 2018a). Besides Norris et al (2018a) and (Bárcenas-García et al, 2022) who applied before-after control-impact study design, no other study evaluated freshwater turtle nesting patterns with baseline monitoring previous to dam installation.…”