How do functional riparian groups from northern Sweden respond to hydropeaking? : Short-term indoors study on germination, mortality and performance of Swedish riparian species from different species groups subjected to water treatments mimicking hydropea

Abstract: With the ever increasing reliance on hydropower in the world, it is important that its effects on riparian vegetation is well understood. This study aimed to explore the effects of different forms of hydropeaking, which results from the rapid and frequent opening and closure of hydroturbines, on different species groups of riparian species native to northern Sweden. Thirteen riparian species belonging to three different species groups, forbs, graminoids and woody species, were subjected to three different watering treatments simulating water stress, rapid fluctuation and prolonged flooding, which often correspond to different hydropeaking conditions. A fourth treatment maintained individuals under controlled conditions and simulated a non-regulated stream. The treatments were carried out over seven weeks. The results showed that the treatments affect the three tested species groups differently. Woody species responded to all treatments with lower germination, higher mortality and lower root elongation, while forbs and graminoids responded to flooding and fluctuation with increased germination but higher mortality and lower root elongation. Fluctuation and flooding had in general positive effects on germination and short term growth but also increased mortality, particularly fluctuation. There were no significant results regarding change in number of leaves for any treatment or species group. As this study only covered seven weeks it can only account for short-term trends, but it still provides interesting information about general expected trends for a wide variety of species native to northern Sweden and belonging to the main three species groups. Such information is key for river management.