Amazonian run-of-river dam reservoir impacts underestimated: Evidence from a Before-After Control-Impact study of freshwater turtle nesting areas

Barcenas-Garcia, A.; Michalski, F.; Gibbs, J. P.; Norris, D.

doi:10.1101/2021.07.29.454366

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bioRxiv · 10.1101/2021.07.29.454366

Amazonian run-of-river dam reservoir impacts underestimated: Evidence from a Before-After Control-Impact study of freshwater turtle nesting areas

Barcenas-Garcia, A.·Michalski, F.·Gibbs, J. P.·Norris, D.

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Abstract

O_LIConstruction of hydropower dams is associated with negative impacts on biodiversity, yet there remains a lack of robust scientific evidence documenting the magnitude of these impacts particularly across highly biodiverse tropical waterways. Hydropower expansion is an increasing threat to the Endangered yellow-spotted river turtle (Podocnemis unifilis) across its tropical South American range. C_LIO_LIYellow-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. C_LIO_LIThe cause and extent of changes in nesting areas were established using Generalized Additive Models. Nesting area density was evaluated in relation to: time (before versus after), treatment (control versus impact), time treatment interaction (BACI), distance to the dam and precipitation. The extent of changes was examined by comparing the proportion of nesting areas remaining during four years after reservoir filling. C_LIO_LIDam 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 69% (from 0.48 to 0.15 per km) across 33 km of river directly impacted by the dam. This loss was reflected in a significant BACI interaction. Nesting area density was not explained by seasonal precipitation. C_LIO_LIStandardized monitoring of freshwater turtle nesting areas provided an effective means to quantify impacts of hydropower developments across biodiverse yet rapidly changing waterways. The negative impacts documented in this study should be preventable by mitigation actions including habitat creation and dry season flow regulation. Such measures would also likely benefit multiple species elsewhere in tropical rivers increasingly impacted by run-of-river dams. C_LI

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Barcenas-Garcia, A., Michalski, F., Gibbs, J. P., Norris, D.. 2021-07-30. Amazonian run-of-river dam reservoir impacts underestimated: Evidence from a Before-After Control-Impact study of freshwater turtle nesting areas. https://doi.org/10.1101/2021.07.29.454366

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