The unspoken truth about impacted rivers: Consequences and implications of barriers for conservation of freshwater fish
To serve the expanding land, water and energy needs of a growing human population, rivers have been altered extensively over the last centuries to build hydropower stations, weirs and reservoirs mainly for electricity, water security and irrigation, making freshwater the most threatened of ecosystem...
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| Format: | Book |
| Language: | English |
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Technical University of Denmark
2020
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| Online Access: | https://orbit.dtu.dk/en/publications/d0336212-067d-4c9c-bee2-f644288f3847 https://backend.orbit.dtu.dk/ws/files/204995861/200121_PhD_thesis_Kim_Birnie_Gauvin_print_version_002_.pdf |
| Summary: | To serve the expanding land, water and energy needs of a growing human population, rivers have been altered extensively over the last centuries to build hydropower stations, weirs and reservoirs mainly for electricity, water security and irrigation, making freshwater the most threatened of ecosystems. Barriers come in many shapes and sizes, though most have had devastating effects on freshwater ecosystems by destroying habitats and critical spawning areas, hindering and delaying downstream and upstream passage for moving fish as well as leading to death and/or extinction for a range of species. While these effects have been investigated widely, there has been a focus on 1) large barriers, 2) the upstream passage of highly synchronized migratory species, 3) engineered solutions rather than removal, and 4) the effects at a local scale rather than catchment scale. As such, this thesis focuses on all of the ‘unspoken’ truths about barriers. In the first manuscript ( MS I ), the loss of rheophilic habitat caused by barriers is highlighted. Stretches of river characterized by gravel-substrate, high-gradient, fast-flowing and highlyoxygenated water are inundated due to barriers, leading to slow-moving water and sedimentation, thus removing the most suitable habitat for salmonid spawning and early development. Using examples from catchments in Denmark, we demonstrate that multiple barriers have cumulative effects in terms of vertical and horizontal habitat loss, causing between 21 and 40% habitat loss. This habitat is crucial for many rheophilic species such as brown trout ( Salmo trutta ) and Atlantic salmon ( Salmo salar ). While both species are strong swimmers and are typically considered as highly synchronized migrants, recent evidence suggest that anadromous brown trout are highly variable in their migration timing. As such, migration timing was investigated in the second manuscript ( MS II ), where the assumption that all juvenile trout leave in the spring is questioned. Our findings suggest that trout also ... |
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