MIV sampling
The benthic community was sampled during base flow with Hess samplers
(sampling area 0.045 m2, mesh size 500 µm,) 2 – 5 m
upstream of each drift net. At each sampling site, three benthic samples
were collected transect-wise (from the bank margin to the in-stream
area) along a flow velocity gradient to include taxa of different
current preferences (Figure 2a). Benthic samples in the HP reaches were
collected four times a day (before each HP scenario and at the end of
the day; Figure 2b), whereas they were taken twice a day (beginning and
end of the day) in the RF reaches.
Drifting MIV were collected at each sampling site with drift nets (frame
size 53 x 27 cm, mesh size 500 µm) fixed with thick rebars on both
sides. The long side of each net was placed on the riverbed. Samples in
the HP reaches were taken separately (nets exchanged) during base flow
(exposure time 60 min) and during each HP phase: up-ramping (UR), first
and second part of the peak (P1, P2; each 30 min) and down-ramping (DR;
Figure 2b). In the RF reaches, MIV drift was sampled for approximately
60 min, simultaneously with the induced peak flows in the HP reaches.
Stranding MIV were collected according to Tanno et al. (2016). Four flat
nets (net size 50 x 50 cm, mesh size 500 µm) were installed at each
sampling site nearby the drift nets on the dewatering area (temporally
wetted area, dry at base flow and wetted during peak flow; Figure 2a):
two nets directly at the waterline and two nets 1 m away from the
waterline and 0.5 m offset from the other nets. Ten stones of the
dominant grain size were placed on each flat net to increase roughness
and thus better mimic the substrate condition of the dewatering area.
Stranded MIV on the nets and on the stones were collected after each HP
scenario (Figure 2b). In the RF reaches, stranding was not assessed, due
to stable flow conditions.