Environmental conditions
We estimated the number of dry/ponded and flowing days at each
intermittent site, using photo trap cameras, taking twice-daily picture
of the river channel. From these pictures we determined the flow
permanence (FP; proportion of days flowing during the study period) and
the total duration of flowing days during each sampling campaign at each
site. We also calculated spatial variables representing site
connectivity using geographic information system analyses and digitized
network maps that included information on the permanence regime of each
reach (i.e. intermittent vs. perennial), based on long-term observations
(Datry 2012, Gauthier et al. 2020). To estimate the site location within
the network we calculate the distance to the source (DS). We measured
distances to the nearest perennial site for intermittent reaches. To
estimate upstream connectivity; i.e. the amount of perennial reaches
potentially serving as colonization source, we calculated the length,
and the percentage of all perennial reaches upstream (%UC) from each
site (see e.g. Sarremejane et al. 2017). For graphical representation
and analyses, sites were sometimes divided into flow regime categories:
perennial (FP = 1; n=10) and intermittent (FP < 1; n=10) and
into network location categories: headwaters (DS < 10km, n=14)
and mainstem (DS > 10km, n=6).
We also measured a set of environmental variables at each site and in
each season. When water was present, pH, conductivity and oxygen
concentrations instream were measured using a multiprobe (Hach) and
total dissolved nitrogen and soluble reactive phosphorus (SRP) were
measured from filtered water samples in the laboratory. Dissolved
nitrogen was determined in a TOC-Analyzer with Nitrogen-Analyzer
(Shimadzu) and soluble reactive phosphorous (SRP) was determined with
the molybdate blue reaction (spectrophotometer U-3900H, Hitachi). Flow
velocity was determined using a flowmeter at 10 to 30 (depending on
channel width) random locations at each reach. The wetted width was
averaged across 10 transects. Instream bryophyte and substrate (bedrock,
boulders, cobbles, gravel and sand) cover was determined visually.
Riparian soil and instream sediment samples were dried (70⁰C) and burnt
(550⁰C) to ashes in the laboratory to determine moisture and organic
matter content, respectively. In summer, we estimated canopy cover in
the instream and in the riparian area at each site, using a vertical
tube (15 cm diameter) at 10 random locations. We also identified all
ligneous plants located in the riparian area (<5m from the
stream) and estimated their relative density and the total tree richness
at each site. Temperature was recorded hourly for the duration of the
study instream and in the riparian area using iButton dataloggers (Maxim
Integrated Products, USA). Site altitude above sea level was also
determined from a digitized elevation model.