4.1 Influence of sampling time and position on community
composition
Our results indicated that differences in community composition were
caused by seasonality but not sampling position, which matched our
expectations despite positional compositional differences occurring in
other studies examining fish and macroinvertebrates (e.g. Berger et al.,
2020; Macher & Leese, 2017; Thalinger et al., 2021). High similarity
among sampling positions likely occurred due to the complete mixing of
eDNA in the water body, with smaller compositional differences occurring
by replication, the three water samples taken within the sampling site,
and not by systematic differences between positions (Macher et al.,
2021). The stream sampled in our study had a water depth <1 m
and sampling positions were less then 10 m apart with a mostly turbulent
flow, all of which can reduce community heterogeneity (see Shogren et
al., 2017; Fremier et al., 2019 for further discussions). As we sampled
only one location in a single temperate stream, it is not possible to
derive general predictions from our results regarding eDNA detection
probability of macroinvertebrates between different sampling positions
in other streams and regions. As a next step, it would be of interest to
systematically compare sampling position differences among divergent
stream types.
Temporal beta-diversity shifted in a seasonally cyclical and gradual
pattern, which was primarily driven by turnover, with turnover and
nestedness both returning to the same level after one year. The
potential of eDNA in detecting seasonal shifts in community composition
has been already shown for marine environments (Jensen et al., 2022; Liu
et al., 2022) but not for freshwater.