| Summary: | Riparian vegetation is one of the most complex and abundant ecosystems in the world and it provides important ecosystem services. These services are affected by electricity production from hydropower dams. Hydropower accounts for 16% of the global electricity production and almost 50% in Sweden. One effect of hydropower is sub-daily fluctuations of water level caused by the turbines being turned on and off according to electricity demand. This is referred to as hydropeaking and has largely unknown effects on the fluvial ecosystem, and especially on the riparian vegetation. No studies have been made on the effects of hydropeaking on riparian vegetation. In this study, three native plants (Carex acuta, Betula pubescens and Salix phylicifolia x myrsinifolia) and one non-native plant (Helianthus annuus) were used as indicators (i.e., phytometers) for the effects of hydropeaking along two rivers from northern Sweden; one used for hydropower production and the other free flowing. From each of the four species, seedlings of two sizes and seeds were transplanted into five different river reaches and bank elevations along a hydropeaking gradient from none to high hydropeaking intensity. C. acuta and S. phylicifolia x myrsinifolia showed significant positive relationships to the hydropeaking gradient, likely due to their natural high tolerance to frequent inundation events. Therefore, they are suitable for restoration of river shores along reaches affected by hydropeaking. In contrast, B. pubescens was negatively related to the hydropeaking gradient, losing leaves and biomass with increasing hydropeaking intensities. It turned out to be the most sensitive species among the ones used in the experiment making it suitable as an indicator. H. annuus showed no response and therefore did not serve as impact indicator or for restoration. Germination for all native species was significantly lower along the reaches affected by hydropeaking which indicates a strong connection between hydropeaking and germination. These findings ...
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