La elva leve : kaskade- effekter av restaurering av Bognelv

Numerous river processes regarded as problems by today’s society, such as flooding and erosion, are vital to many organisms depending upon unstable environments. Several rivers have been altered to safeguard settlements and agricultural land with negative ecological consequences; red listing of flood- and river dependent species and eco-sites, and severely reduced ecosystem services once provided by such rivers. Previous to the late 1900s, the River Bognelv appeared as a meandering river, a fact that the name states well, as Bognelv means “the curling river”. Following decades of channelization and straightening, the river was heavily changed, and its salmonid fish populations severely reduced. Fortunately, channels were only closed and not cultured, making a nearly full restoration possible. Early in the 21th century, an extensive restoration of Bognelv was initiated and the work is still in progress. A study in Bognelv in 2008 revealed that the density of Sea trout (Salmo trutta) increased compared to earlier records, concluding that re-opening of sidechannels and tributaries were the most positive restoration measures conducted for this species. In 2011, I conducted a new study of Bognelv, including sampling of macroinvertebrates and other environmental factors as well as humans. In light of the European Water Framework Directive, this study aimed to apply quantitative and qualitative sampling in a holistic approach towards the effects of river restoration. The effect on an entire ecosystem was studied, spanning from abiotic variables, through lower trophic levels of riparian vegetation and invertebrates, onto fish populations and finally, also the effects on us humans. Despite short recovery time, a tendency towards increased 0+ Sea trout density was found, coherent with increase in time since restoration. The results strongly indicate that sidechannels are important, also for the macroinvertebrates, though further structural improvements with in-flow are required if they are to function also during low-flow. Increasing tree density on the riverbank and construction of additional pools could further improve conditions for invertebrates and fish. Additional to an aesthetic demolition, interventions often diminish the social and ecosystem value provided to humans by rivers. Bognelv provided an opportunity to explore human aspects of river restoration in Norway, and specifically, the non- monetary benefits provided by rivers. Residents and non- residents were interviewed regarding their relationship to, and awareness of, the river Bognelv. The river was important for residents and non-residents, anglers and non-anglers, who seemed to appreciate the values of both active use, and a more intangible, yet potentially positive, non-use. The amount of fish in the river was important even to non-anglers who claimed that an increased fish density would not make them start fishing. Fish were appreciated as a sign of a “living river”, which seemed important to all groups. Other wildlife, especially birds, and the river’s importance for these species was emphasized