Go with the flow - can environmental flows save us? : A study of the flow patterns in Bredforsen and possibilities for the future

Abstract: Freshwater systems have, during human history, endured large-scale impacts. According to the water framework directive, measures must be developed to create a better environment for species in, and connected to, freshwater systems. Hydropower plants has caused loss of natural disturbance (e.g., floodings). Using already collected data from vegetation inventory in the riparian zone, probable distribution curves were created to find flooding requirements of different plant species, and linear regression analyses were run to see if hours of flooding and elevation above sea level had an effect on species richness and vegetation cover in the riparian zone. A model of Bredforsen 3 was conducted by using modelled values obtained from Vattenfall AB, with the aim to answer the following questions: How is riparian vegetation in mixed alluvial forests in reaches affected by static minimum flow levels structured according to flow dynamics? What would the zonation of riparian vegetation look like in an unregulated situation? How can minimum flow in Bredforsen be designed to better match the flooding regime similar to a natural riparian vegetation? Species richness showed to be dependent on elevation. Furthermore, significant results for species richness and vegetation cover both showed to be dependent on hours of flooding in the riparian zone for two of the three inventoried areas. In the alluvial forest, Picea abies, was not affected by hours of flooding. This might be caused by a low number of replicates available in Bredforsen of P. abies. In contrast, Quercus robur did show a significance towards hours of flooding and a vague negative trend for trees with high inundation distributed on lower elevations, though, it seems more parameters are affecting its distribution. The probable species distribution curves revealed the riparian zone in Bredforsen lack the clear vegetative zones visible along unregulated rivers. However, the model created for Bredforsen 3, following the assumptions of Ström et al. (2012) showed that today two vegetative zones, are apparent in Bredforsen 3 (amphibian zone and upland vegetation). With the modelled flow, a third zone (riparian forest) could appear. Because Bredforsen is a Natura 2000 reserve, the minimum flow needs alteration to mimic a relatively natural flow, which could lead to all vegetative zones to develop (amphibian zone, graminoids, willow shrubs, riparian forest, and upland vegetation). This could be achieved by using the spill water from Söderfors and time the release of spill to natural flow events. The model made from Bredforsen 3 indicates that this could cause positive changes in the riparian zone where a more natural distribution of vegetative zones is in place, meaning that species distribution returns to previous distribution patterns and would help disturbance dependent species.