2.2 | Study design
We performed the study using a Before-After-Control-Impact design (Josefsson et al., 2020). Rotenone was used in the Fusta watercourse to eradicate the invasive parasite Gyrodactylus salaris through exterminating its host populations of salmonid fish. Three rotenone treatments were conducted in the watercourse, with two treatments of the River Fusta (August 2011 and 2012) and one subsequent treatment of the upstream Lake Fustvatnet (October 2012), causing the downstream River Fusta to be treated a third time. The neighboring Drevja watercourse was used as a control site (Figure 1). Sampling was conducted at two lotic and three lentic sampling stations in each watercourse during the autumn from 2011 to 2016, as well as one spring sampling in June 2013, eight months after the lake treatment. Sampling started in August 2011 before the first rotenone treatment and ended in Autumn 2016. An overview of times of sampling and rotenone treatments is given in Table 1.
Figure 1
Riverine stations were situated in riffle areas dominated by cobbles (particle size of 64-256 mm) and pebbles (particle size 4-64 mm) and with scattered patches of river moss and alga. Two of the stations in each lake were situated in exposed areas were pebbles (particle size of 4-64 mm) dominated the substrate. One of the stations in each lake was situated in sheltered areas with a substrate dominated by finer inorganic and organic substrate (particle size < 2mm) and with little or no aquatic vegetation.
Table 1.