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What have we learned from studying 20 years of fish community dynamics in large reservoirs? A multi-scale approach
- 6. Impede the movement of migratory species (fragmentation) Non-native species colonization (confounding) Impacts of drawdown (regulation)
- 8. 20y of data (before and after) Different stations types Water quality data Very little confounding factors
- 13. cc Management Ecology and foodweb Change in T° Energy demand profiles Precipitations
Editor's Notes
- If you were to redo the same study in future years, how do you think climate change would influence your study design ? What variables of your study are most vulnerable to climate change and would most likely affect the interpretation of results? Response of fish to water temperature Water availability in reservoirs (likely not an issue in Northern Québec) Profile – HE use - demand How would you discriminate measured impacts from the reservoir with those induced by climate change? Importance of reference sites
- To see what is happening at the population level over time following impoundment, I decided to revisit the Trophic surge hypothesis. The TSH makes predictions about how the increase in phosphorus loading from the leaching and decomposition of organic matter from newly flooded terrestrial areas would affect productivity in reservoirs How this can be translated biologically, During the surge, the large influx of allochthonous inorganic nutrients and organic detritus from the flooded area should translated quickly into high primary production The rapid expansion of littoral habitat from the inundated terrestrial area would create new ecological niches, and coupled with high primary production, should result in high zooplankton and benthos productivity. Increases in primary production and secondary consumers should lead to a peak in fish recruitment followed by an increase in adults a few years. After the surge, the reservoir should experience a trophic depression, when available nutrients and detritus stocks are exhausted. The non-equilibrium phase should be then followed by a new trophic equilibrium where the reservoir stabilizes toward a steady “lake-type” ecosystem (Grimard and Jones 1982). We evaluated the prevalence of a hump-shaped pattern (i.e., surge and then depression during the trophic non-equilibrium phase) in 40 recruitment and 109 adult fish time series that came from seven different reservoirs in boreal and temperate ecosystems. This analysis was perform at the global scale. To test if the TSH was supported by each individual time series, we compared the fit of the data to alternative scenarios corresponding to plausible general abundance patterns that could be observed for the period covering before impoundment, during reservoir filling and after impoundment. Specifically, we tested for the presence of 1) no pattern over time (flat line function), 2) a linear increasing pattern; 3) a linear decreasing pattern, 4) a non-linear decreasing trend (negative exponential function), 5-6) two non-linear increasing pattern (negative exponential and quadratic polynomial functions), 7-8) two hump-shaped patterns suggested to capture the whole trophic surge hypothesis (using either Ricker and negative quadratic polynomial functions; Table S1, Fig. S1).
- To see what is happening at the population level over time following impoundment, I decided to revisit the Trophic surge hypothesis. The TSH makes predictions about how the increase in phosphorus loading from the leaching and decomposition of organic matter from newly flooded terrestrial areas would affect productivity in reservoirs How this can be translated biologically, During the surge, the large influx of allochthonous inorganic nutrients and organic detritus from the flooded area should translated quickly into high primary production The rapid expansion of littoral habitat from the inundated terrestrial area would create new ecological niches, and coupled with high primary production, should result in high zooplankton and benthos productivity. Increases in primary production and secondary consumers should lead to a peak in fish recruitment followed by an increase in adults a few years. After the surge, the reservoir should experience a trophic depression, when available nutrients and detritus stocks are exhausted. The non-equilibrium phase should be then followed by a new trophic equilibrium where the reservoir stabilizes toward a steady “lake-type” ecosystem (Grimard and Jones 1982). We evaluated the prevalence of a hump-shaped pattern (i.e., surge and then depression during the trophic non-equilibrium phase) in 40 recruitment and 109 adult fish time series that came from seven different reservoirs in boreal and temperate ecosystems. This analysis was perform at the global scale. To test if the TSH was supported by each individual time series, we compared the fit of the data to alternative scenarios corresponding to plausible general abundance patterns that could be observed for the period covering before impoundment, during reservoir filling and after impoundment. Specifically, we tested for the presence of 1) no pattern over time (flat line function), 2) a linear increasing pattern; 3) a linear decreasing pattern, 4) a non-linear decreasing trend (negative exponential function), 5-6) two non-linear increasing pattern (negative exponential and quadratic polynomial functions), 7-8) two hump-shaped patterns suggested to capture the whole trophic surge hypothesis (using either Ricker and negative quadratic polynomial functions; Table S1, Fig. S1).
- If a time series support the TSH, we should statistically detect a hump-shaped pattern A hump-shaped trend was the predominant pattern identified across individual recruitment time series based on curve fitting
- To go a step further to undersand what can cause variability in our ability to detect the surge and on the duration and magnitude and extract generalities, we extracted 5 TSH metrics that could be used in a predictive framework. These TSH metrics were: 1) the occurrence of the TSH (i.e., detection of a hump-shaped pattern or not), 2) the duration of the trophic non-equilibrium phase in years (i.e., the time needed for abundance values to either come back to values comparable to pre-impoundment or to reach a stable state), 3) the duration of the surge in years (i.e., time needed to reach the peak in abundance from t0), 4-5) the magnitude of the peak in abundance in relation to t0BF and t0EF, and 5-6) the timing of the peak (i.e., year at which the peak occurred) in relation to t0BF and t0EF. We defined the duration of the trophic non-equilibrium and surge phases based on visual inspection of the time series whereas the magnitude of the peak was extracted by dividing the actual observed value at the peak for a given time series by the mean value of abundance before impoundment.
- 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
- I call it my local scale but the La Grande River hydroelectricity complex is as large as the New Brunswick and consist of 1, 3, 28
- 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.
- Measures descriptives
- Measures descriptives
- Measures descriptives