Rivers
The temporal species turnover appeared to co-vary in the treated and untreated river, especially for abundance data (Figure 2). The exception was the period after the lake rotenone treatment in October 2012 to summer 2013 where benthic invertebrate abundances of the rotenone treated River Fusta changed significantly (Figure 2a, Appendix 1), mainly due to losses (Figure 2b). For presence-absence data, there was a significant dissimilarity of species occurrences in the treated river from immediately after the lake treatment in October 2012 until August 2015 (Figure 2d, Appendix 2). The species loss-rate of the treated river was at its highest from October 2012 to June 2013 (Figure 2e) and gain-rate at its highest from June 2013 to August 2013 (Figure 2f, Appendix 2). No significant changes in abundance or species occurrence were found in the untreated river (Figure 2a, b, Appendix 1 and 2).
Figure 2
The total abundance of benthic invertebrates reflects the temporal turnover indices (Figure 3a). There were no clear short-term effects on the total abundance or the abundance on most taxa following the two rotenone treatments of River Fusta (Figure 3). As an exception, the abundance of Plecoptera decreased strongly in the treated river immediately after the first and second river treatment (89% and 92%, respectively), whereas the changes were smaller in the untreated river (+17% and -37%, respectively) (figure 3c).
Figure 3
In contrast, there was a marked increase in the abundance of taxa observed in samples from both the treated and the untreated river in October 2012, followed by a pronounced decline in the treated river in June 2013 (Figure 3a). However, the observed response in total abundance masks distinct differences in response to the lake rotenone treatment of riverine benthic invertebrate taxa.
The abundance of Ephemeroptera in the treated river decreased shortly after the two river treatments (Figure 2b). This was also found in the untreated river after the first river treatment. The Ephemeroptera Baetis rhodani and Baetis sp. decreased in the treated river after both treatments, and in the untreated river after the first treatment. Abundances of all taxa from the rivers not presented in the figures are listed in Appendix 3. For other Ephemeroptera, like Heptagenia dalecarlica and Ephemerellasp., the abundance in both rivers was relatively high shortly after the river treatments. Immediately after the lake treatment in October 2012,B. rhodani was the only Ephemeroptera with reduced abundance and was not recorded in the treated river. In June 2013, eight months after the lake treatment, there was a dramatic decline in the Ephemeroptera abundance in the treated river (Figure 3b) with only a few specimens present of Siphlonurus sp., B. rhodani and H. dalecarlica . However, a decline was also found in the untreated river, but here most taxa were present in June 2013. In the subsequent years, the Ephemeroptera abundances in the treated river increased, mainlyB. rhodani and H. dalecarlica . A similar increase occurred in untreated river, in addition to an increase in B. muticus.
There was a strong decrease in the abundance of Plecoptera in the treated river after both river treatments, whereas there was an increase in the untreated river. Taxa with reduced abundances includedDiura sp., Isoperla sp. and Leuctra sp. Shortly after the lake treatment in October 2012, the abundance of Plecoptera in the treated river decreased with 95% compared to September 2012 (Figure 3c), and only three specimens of the genus Nemoura were recorded. Most taxa were present in the untreated river and with a relatively high abundance of Amphinemura borealis , Diura sp. andIsoperla sp. In June 2013, eight months after the lake treatment, no Plecoptera were detected in the treated river, while at the same time there was an average of more than 200 specimens of Plecoptera in the untreated river (Figure 3c). Contrary to the river treatments, were the negative effect were minor, Trichoptera abundances decreased in the treated river immediately after the lake treatment but did not change in the untreated river (Figure 3d). Eight months after the lake treatment in June 2013, there was a dramatic decrease (99%) in the abundance of Trichoptera in the treated river, and only a few specimens ofRhyacophila nubila , Hydropsychidae sp. andMicrasema sp. were present. A corresponding but smaller decline (41%) was observed in the untreated river.
Both rivers had high abundance of Chironomidae shortly after the lake treatment (Figure 3e). The abundance of Chironomidae co-varied considerably among rivers. The abundance of Oligochaeta in the treated river decreased shortly after the first river treatment and increased subsequent to the second river treatment and the lake treatment (Figure 3f). In June 2013, eight months after the lake treatment, the abundance of Oligochaeta was at its minimum in the treated river.
There was a low abundance of Hydrachnidia in the treated river and the taxon was absent in 2013 (Appendix 3). In the untreated river, Hydrachnidia was recorded in all sampling occasions and with the highest abundances after the treatments. The abundance of the riffle beetles (Elmidae) decreased in the treated river following the treatment. In the untreated River Drevjaelva, the taxon also decreased in abundance, albeit at a much lower rate than in the treated River Fusta.