One of our restoration methods, the demonstration action, is a new method in the field of river restoration and therefore the project has undertaken to follow up the effects of this action. The restoration work were made in 2010. Our reference sites in the follow-up studies are situated within the same river basin and has previously (2003-2005) been restored with best practice methods. Therefore we don’t compare with channelized streams (which presumably would provide clearer differences), but with a different restoration method.
Results from the follow-up studies of the demonstration actions:
The stream restoration has led to 24% slower streamflow and 13% wider streams in the demonstration streams after restoration compared to before. Streamflow and width were the same in the reference streams at both times. We got much more diverse stream flows after restoration in the demonstration streams compared to the reference streams which is a natural consequence of the increased complexity of these streams.
- Field inventory:
The follow-up studies were performed 2013-14. The demonstration reaches (restored in 2010) had slightly more species than the reference reaches (restored 2003-2005) but the result is slightly different between the sites. The following species were found frequently in our plots nearest to the watercourse: Molinia caerulea, Filipendula ulmaria, Viola palustris, Valeriana sambucifolia and Carex flava. Higher up in the riparian zone the vegetation changed and the most common species were Vaccinium vitis-idaea, Trientalis europaea, Linnaea borealis, Carex Vaginata, Maianthemum bifolium and Melica nutans.
Solidago virgaurea, Geranium sylvaticum, Rubus saxatilis and Vaccinium uliginosum were found in the whole riparian area, in both types of reaches.
In the plots near the watercourse in the demonstration sites there were more common to find species commonly found higher up in the riparian zone (Vaccinium vitis-idaea, Trientalis europaea, etc.), which is probably because the area was higher up from the water before the restoration.
- Planting of seeds:
There were more naturally occurring seedlings in the demonstration reaches in summer 2013 compared with the reference reaches, which is probably due to more seeds captured by trees and large boulders in the shore line in the demonstration reaches.
During the winter, the number of seedlings decreased a lot in the demonstration reaches but not to the same extent in the reference reaches, and therefore the difference in the number of seedlings in 2013 had disappeared in summer 2014. That more seedlings died in the demonstration reaches was probably due to higher soil moisture in those reaches and that soil moisture has a strong impact on the species ability to survive the winter.
Otter (like mink) occurred in most of the tributaries, and there was no difference between the number of traces in demonstration and reference reaches. The territories of these animals is bigger than the length of the investigated stretches, thereby a proper evaluation of the demonstration actions effects on otters is impossible.
- Number of fishes
The number of fishes was counted and the size and species were investigated by using electro fishing. Results showed that there were 7-424 fishes and 2-6 species per study area. Fish density per 100 m2 varied between 1,6 and 79,3 individuals. In total nine fish species were found in the sites: brown trout (Salmo trutta), brook trout (Salvelinus fontinalis), bullhead (Cottus gobio), minnow (Phoxinus phoxinus), grayling (Thymallus thymallus), northern pike (Esox lucius), roach (Rutilus rutilus), burbot (Lotalota L.) och perch (Perca fluviatilis).
Fish assemblages were strongly dominated by either brown trout or bullhead, together accounting for 80% of all individuals collected. No differences in fish abundance and biomass existed between demonstration and best practice sites. The measurements were probably done too close to the restoration work for effects to be seen.
– Spawning beds
To investigate if substrate size at spawning beds changes over time, pebbles from the top layer was randomly collected from the centre of each spawning bed in 2011 and 2013 respectively. Results showed that the median size of the substrate increased from 2011 to 2013 which indicates that the finer substrate fractions move downstream. The proportion of sand and fine material in the spawning beds did not differ between 2011 and in 2013.
In mid October 2013, egg incubators were placed in the spawning beds. The eggs came from wild anadromous brown trout captured at Stornorrfors power plant in Ume River. The incubators was buried under sand and gravel of mixed size fractions. The survival of the embryos, measured after 7 months when the incubators were taken up, was between 45-84 %, which is unusually high in these type of studies. We found no correlation between content of sand and fines and embryo survival. Our levels of fines and sand were probably low compared to many other studies and it suggests that the levels in the Vindel river area don’t affect the embryonic survival.