| Summary: | In this study I investigate how the biodiversity of vascular plants differs between three slow flowing parts of the stream Juktån in northern Sweden where hydropower has impacted the flow regime and thus the conditions for riparian vegetation. The hypothesis was that species richness would increase with the distance from the hydropower plant due to increasing naturalness of the flow regime. Species richness was investigated since it is a fundamental and important function for the maintenance and quality of ecosystems (Naiman and Décamps 1997). Juktån, where data for the study was collected, receives a static minimum flow of barely 12 % of the yearly natural medium flow released from the hydropower station into the channel (Wisaeus 2014). The minimum flow follows the variation set by the hydropower which deviates from natural seasonal flow variation, which is essential for the germination, growth, and reproduction of many plant species (Poff et al. 1997). The investigation includes a comparison between species richness and richness of 4 functional groups among the three study locations. In addition, analysis of the relationship between environmental variables such as position on the riparian zone (height) and substrate composition were performed. Sikselet that was the slow flowing reach closest to the hydropower station had the highest species richness while Bredselet further downstream had the lowest species richness with Långselet having intermediate species richness. One reason for the pattern in species richness could be that seeds get trapped in weirs located between Sikselet and Långselet. In that case, reintroducing a natural flow regime may not suffice to increase species richness.
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