2.1 Study sites
The Fusta (rotenone treated) and Drevja (control) water courses are situated in Northern Norway (Figure 1). The Fusta watercourse has a catchment area of 538 km2. The largest and lowermost lake of the catchment, Lake Fustvatnet (38 m a.s.l.), has a surface area of 11 km2 and a maximum depth of 68 m. Concentrations of total nitrogen and total phosphorus from water samples taken in August 2014 of 70 μg/L and <2 μg/L, respectively, indicate oligotrophic conditions. River Fusta, which is the outlet of Lake Fustvatnet, is 8.5 km long and drains to the sea. The river has a mean annual discharge of 34 m3 s-1.
The Drevja watercourse (untreated), which is bordering the Fusta watercourse, has a catchment area of 178 km2. Lake Drevvatn (47 m a.s.l.), the largest and lowermost lake in the catchment, has a surface area of 5 km2 and a maximum depth of 40 m. Concentrations of total nitrogen and phosphorus from water samples taken in August 2014 of 55 μg/L and <2 μg/L, respectively, indicate oligotrophic conditions. River Drevjaelva, which is the outlet of Lake Drevvatn is 17.7 km long and drains to the sea. The river has a mean annual discharge of 12 m3 s-1.
Both watercourses are surrounded by sparsely vegetated mountain areas, spruce dominated forests and scattered farmlands.