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Impact of Dams on River Ecosystems
- 2. (Grill 2015, Winemiller 2016, Zarfl et al. 2014) The size of the represents the storage capacity of the reservoir From Grill et al. 2015
- 3. From Grill et al. 2015
- 4. Impact of the Yacyreta Dam on the Paraguay-Parana River (from “Images of change”, NASA) New lentic habitat Variation in water levels and flow far beyond natural amplitudes Changes in water temperature regime, sedimentation, nutrient cycling (Nilsson et al. 2005; Dudgeon et al. 2006; Poff et al. 2007; Vörösmarty et al. 2010)
- 5. (Stanford et al. 1996; Zohary and Ostrovsky 2011; Johnson et al. 2008; Liermann et al. 2012; Rahel 2000, 2002)
- 7. 1
- 8. 1 3
- 9. 1 3 28
Notes de l'éditeur
- Thanks everyone for taking the time to hear what I have to say about fish community dynamics in large reservoirs. What I will present you today are results from my postdoc at McGill University in collaboration with Hydro-Québec as an industrial partner through a Mitacs Elevate scholarship. In this postdoc, I am looking at the effects of river impoundment on fish community dynamics using a multi-scale approach. If you want to learn more about my research interests, I invite you to have a look at my webpage.
- One of the most important challenge we face as a society is the increase in energy demand worldwide (SEforALL 2016; US EIA 2016). In response to this demand, the construction of large dams to provide hydroelectricity experience an unprecedented boom in emerging economies (Zarfl et al. 2014; Grill et al. 2015; Winemiller et al. 2016) Hydroelectricity is presented as a being one of the most stable, reliable, clean and renewable energy source
- If we sur-impose the existing dams (in orange) over the dams under construction and planned projects, we can see that only arid or semi-arid regions are not affected by the presence of dams In number, 59% of river basins contain large dams today and with the planned and under construction dams, this number should raise to 75%
- Since flow is the major driver of ecological processes in rivers, the regulation and fragmentation caused by dams can impact ecosystems functions and biodiversity More specifically, dams regulated the river flow by transforming large rivers into storage reservoirs and thus creates new lentic habitats upstream of the dam Dams also generate variation in water levels far beyond natural amplitudes by imposing significant winter drawdown and by dampening spring flooding. Downstream of dams, seasonal and interannual streamflow magnitude and variability are generally reduced These hydrological modifications, and the ways in which reservoirs are managed, can change the water temperature regime and ice cover dynamics, can impact sedimentation processes and nutrient cycling and can change the general riverscape connectivity by fragmenting the fluvial network. Its why we need data upstream and downstream of the dam In this figure, we have aerial pictures of the Paraguay-Parana River before and after the construction of the Yacyreta Dam in 1985.
- These alterations will consequently favor the persistence of certain species over others by impeding the movement of migratory species, by modifying the quality, diversity, and distribution of habitats, and by increasing the susceptibility to non-native species colonization This should ultimately results in loss of biodiversity
- Using the La Grande Rivière hydroelectricity complex in Northern Québec, I investigate these three questions:
- Size of the New-Brunswick
- The fish community dataset collected by Hydro-Québec during the construction and first 20 years of operation of the La Grande hydroelectricity complex allows us to do the most thorough evaluation of impoundment on fish and is unique in many respects. First, we have data before impoundment on several stations. We have data on stations that are upstream, downstream, different habitats, over time… Second, quantify the trajectories of fish community over more than 20y in boreal reservoirs. Finally, this dataset represents a unique opportunity to measures the single effect of impoundment on fish community (not land use, fishing intensity, invasive species). – No strong confounding factors.
- No drastic change in diversity, richness and even evenness, but is there a change in fish assemblages? Maybe some species benefited from impoundment and other did not and this switch mask diversity patterns. To investigate that, and to look if some variables or set of variables are responsible of a potential change in fish assemblages, we used RDA and variation partitionning. The first matrix of interest Time since impoundment The advantage of using variation partitioning is that we can get information on shared variation between the different matrices.
- The average variation explained at the station level
- At the complex and reservoirs scales, spatial heterogeneity among sampling stations (and reservoirs) masked the effects of impoundment on fish assemblages Ecological filters Differentiation and “nestedness” – geography and isolation This is the reason why using several scales is important
- The effect of impoundment on species differed between upstream and downstream stations, and between reservoirs (SCBD values) Is there consistent patterns regarding which species are affected and in which directions? Using these spider web graphs, we can look at the combined effects of stations on turnover rate in species over time. A species that is more strongly affected will have a spike or a peak in its direction. The effect of impoundment on species differed between upstream and downstream stations, and between reservoirs. The really understand what is going on, we need to look at each reservoir separately. And we can add the direction of the change In several upstream stations, we observed a general change in assemblage from a catastomids dominated community before impoundment (longnose sucker and white sucker) toward a pike-coregonid dominated community (Northern pike, whitefish and cisco; Figs. ). This change seems to occurred within the first 5 years of impoundment (Fig. X). Change in community structure regarding change in species is less clear in downstream stations and seems to be reservoir specific.
- USEFULNESS: CIRAIG Environmental footprint – Lycle Cycle assessment – impact of hydro…