16 years of river restoration : effects of restoration measures on macroinvertebrates and salmonids in Bognelv, Northern Norway

• Main Authors: Kivle, Dina Emilie Norum, Schmitz, Sunniva Buvarp
• Other Authors: Haugen, Thrond Oddvar, Colman, Jonathan Edward
• Format: Master Thesis
• Language: English
• Published: Norwegian University of Life Sciences, Ås 2022
• Subjects: Arctic; Alta; Norway; Bognelv; Arctic charr; Atlantic salmon; Finnmark; Northern Norway; Salmo salar; Salvelinus alpinus
• Online Access: https://hdl.handle.net/11250/3005030

Lotic ecosystems worldwide are being degraded by human activities, with severe consequences for stream biota. River restoration has gained momentum over the last decade, but many projects lack the long-term monitoring needed to efficiently evaluate restoration outcomes. One river restoration project operating with a long-term perspective is the project in Bognelv in northern Norway. The river was channelized and secured against erosion and flooding between 1930 and 1990, with a resulting decline in fish stocks of Atlantic salmon (Salmo salar), brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus). Restoration began in 2006 and is now going on its 16th year, the latest measures being conducted in 2019. This thesis is the eighth study investigating effects of river restoration on stream biota in Bognelv. Earlier studies show that Atlantic salmon and brown trout have responded well to the restoration measures, while Arctic charr have been absent from studies since 2013. Macroinvertebrates have been sampled in 2015, 2019 and 2021, to better understand how the restoration process affects the river biota. In August and September 2021, we registered environmental variables and conducted electrofishing and kick-sampling in Bognelv. We followed the study design of earlier studies with a total of 56 stations spread from the lower to the middle stretches of the river. Our analysis focused on three main effects; type of restoration measure, time since last restoration measure, and distance from estuary. Only one Atlantic salmon was caught during electrofishing, and was therefore excluded from analysis. Due to unusual small body sizes and the resulting impaired catchability, 0+ for brown trout were difficult to sample in 2021 and were also excluded from our analyses. Our results show a sharp decline in brown trout densities from previous years for the age classes included in our analyses, but an increase in macroinvertebrate abundance. The effect of type of restoration measure on macroinvertebrate diversity was ...