Habitat compensation on natural fish routes
Many rivers have been impacted by hydropower developments. As a result many organisms can no longer move freely through watercourses to lakes and oceans. Naturalistic fish passages built to approximate natural streams enable most fish species to pass such obstacles.
Fish passages that approximate natural streams have often been shown to be better than technical fish passages since they allow more fish species to pass. Naturalistic designs may also provide a habitat for other aquatic plants and animals.
In connection with the building of Fortum’s new hydropower plant in Eldforsen in the Västerdal River, a naturalistic fish passage was built that connects the hydropower dam to the old river channel. The goal was not just to construct a functional fish passage, but also to compensate for the biodiversity loss often incurred when watercourses are regulated. The passage has therefore been called the bio channel.
The bio channel has been designed to include three different special stretches with different environments: deep sections where the water runs slowly, looping sections with banks that are sometimes overflown and narrow channels separated by islands. These special stretches are separated by straight sections with rough substrate reminiscent of traditional fish ladders. Efforts were made to recreate the bottom substrates, water movements, flows and gradients found in natural watercourses so that as many aquatic organisms as possible can use the bio channel. Attention has also been paid to the surrounding terrestrial environment, as it serves as an important nutrient source and buffer zone for the aquatic environment. Shore vegetation plays an important role in maintaining biodiversity in natural watercourses and also provides protection and shade.
The main objective of the first two years of the project (2010–2012) was to investigate the colonisation of species in and along the bio channel and to see how the species composition changes over time. We studied the families of bottom fauna that colonised the different habitats in the bio channel and found that the specially designed fish passage with its extra habitat types may support greater biodiversity than a naturalistic fish passages. The family composition also seemed to approximate that found in natural watercourses in the area.
By comparing the different environments in the fish passage in which different bottom fauna families thrive, we found that the specially designed fish passage with its extra habitat types may support greater biodiversity and may therefore compensate for the habitats that were destroyed during the construction of the power plant.
When the new hydropower plant was built in Eldforsen, the rapids between the plants in Eldforsen and Hummelforsen were dammed and the habitat of the endangered freshwater pearl mussel disappeared. Between 2014 and 2016 we will therefore investigate whether the bio channel can serve as habitat for the freshwater pearl mussels and trout, its host fish. The bio channel includes sections with running water and gravel substrates that suit freshwater pearl mussels, as well as sections with shallower water and deadwood that suits small trout. This is important: the freshwater pearl mussel depends on trout during the first part of its life.
Gustafsson, S., Osterling, M., Skurdal, J., Schneider, L.D., Calles, O. 2013. Macroinvertebrate colonization of a nature-like fishway: The effects of adding habitat heterogeneity. Ecological Engineering. 61, 345-353