Authors: Malm Renöfält, Birgitta; Jansson, Roland;Widén, Åsa;

Riparian vegetation occupies the transition zone between aquatic and terrestrial ecosystems along rivers, and perform multiple important ecosystem services. In regulated river systems of northern Sweden, riparian vegetation has been reduced to a fraction of its former area, with concomitant losses in species richness, as a result of changes in the magnitude, frequency and timing of water-level variation. Based on the hydrologic niche requirements of riparian plants, we projected the consequences of introducing environmental flows to rehabilitate riparian vegetation abundance by (1) re-introducing more natural water-level variation in run-of-river impoundments, and (2) re-introducing spring flood events. We contrast these projections with assessments of the effectiveness of rehabilitating riparian vegetation by placing boulders in near-shore areas to reduce erosion caused by hydropeaking. We conclude that while environmental flows have the potential increasing the area of riparian vegetation in entire catchments, it comes with costs associated with reductions in hydropower production. Reducing erosion by placing boulders to protect riparian zones is an effective nature-based solution but has more limited scope in terms of the potential areas being restored.