Abstract
River flow regulation, fragmentation, and changes in water quality caused by dams have varying effects on aquatic biodiversity and ecosystem functions, but are not clearly resolved in boreal ecosystems. We adopted a multiscale approach to quantify fish community trajectories over 20 years using a network of sites spread across four reservoirs in two hydroelectricity complexes in northern Quebec, where other anthropogenic factors have been negligible. Across three spatial scales, we found little evidence of directional temporal trends in diversity relative to reference sites. Using beta-diversity analyses, we also detected a high degree of stability in fish composition over time and space at the complex and reservoir scales. However, changes in species assemblage following impoundment were detected at the scale of the sampling station. At this scale, we found that some species consistently benefited (coregonids and pikes) from impoundment, whereas others were detrimentally affected (suckers and one salmonid). Overall, we conclude that examining different scales is key when trying to understand the impacts of humans on biodiversity and in formulating management recommendations.
Highlights
In response to increased demand for energy, many large dams are currently in operation, or are being constructed to provide hydroelectricity (Grill et al 2015; Winemiller et al 2016).Dams transform large rivers into large reservoirs, affecting numerous important physical, chemical and biological processes (Ward & Stanford 1995; Friedl & Wüest 2002)
When station categories were added in the model (i.e., U vs. D, or Upstream river (UR), upstream lake (UL) vs. D), richness marginally decreased over time (Models 2 and 3; Table S6)
By using a network of sites with minimal confounding factors, and by conducting our analyses at three spatial scales, we have provided strong empirical evidence that impounding large rivers in these boreal ecosystems did not affect diversity, but resulted in a clear shift in fish assemblages
Summary
In response to increased demand for energy, many large dams are currently in operation, or are being constructed to provide hydroelectricity (Grill et al 2015; Winemiller et al 2016).Dams transform large rivers into large reservoirs, affecting numerous important physical, chemical and biological processes (Ward & Stanford 1995; Friedl & Wüest 2002). Agostinho 2015), and alter the natural hydrological regime of the ecosystem (i.e., discharge and water levels) upstream and downstream of the dam (Kroger 1973; Poff et al 2007). These modifications are susceptible to affect the overall biodiversity and ecosystem functions (Rosenberg, McCully & Pringle 2000; Vörösmarty et al 2010; Liermann et al 2012). This deficiency is surprising considering that hydroelectricity is a major source of energy in some Nordic countries (e.g., Norway: 96% of domestic electricity generation, Iceland: 70%, Canada: 58% and province of Québec in Canada: 95%; IEA 2016)
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