Study location and study setup
Our study was located in the boreal region of northern Sweden in two catchments of similar size (~350 km2): Hjuksån and Bjurbäcken (ån and bäcken both mean ‘stream’/ ‘creek’), both of which are tributaries of the free-flowing Vindel River that in turn flows into the Ume River ~30 km upstream of its outlet in the Baltic Sea (Figure 2). In addition to glaciation shaping the catchment through numerous mainstem lakes and large amounts of coarse glacial sediment, the landscape is divided into two regions—above and below the former highest coast-line (FHC). The FHC divides areas that have been only affected by glaciation and contains undisturbed glacial sediment from areas that have been under sea level after glaciation and affected by deltaic processes and subsequently uplifted by post-glacial isostatic rebound (Fredén, 1994). Hjuksån catchment (64° 25’N, 19° 45’E, alt. 245 m) is located nearly entirely below the FHC, whereas Bjurbäcken (65° 6’N, 18° 4’E, alt. 320 m) is completely above the FHC. The upland vegetation in the study area is dominated by boreal forest with Scots pine (Pinus sylvestris ) and Norway spruce (Picea abies ) and the riparian vegetation is dominated by deciduous trees, tall herb, and graminoid communities.
We started collecting geomorphic and ecological data directly downstream of the furthest upstream lake, encompassing 18 process domain reaches in Bjurbäcken and 20 process domain reaches in Hjuksån catchment. Geomorphic data were collected along the entire mainstem channel of Bjurbäcken and Hjuksån, starting below the upstream lake, to the tributary junction with the Vindel River. Riparian vegetation data were collected starting at the same point and ~18 km downstream in Bjurbäcken and ~9 km downstream in Hjuksån.