Figure 2: Comparison of the three sampling positions. Left:
Venn diagram for the different combinations of sampling positions. For
each combination read proportion in relation to overall
macroinvertebrate reads is given in percent, numbers of species shown in
brackets. Right: species richness over time for each sampling position.
Points represent pure species numbers, solid lines represent the fitted
values of the GAM.
Additionally, the NMDS analysis showed no differences in species or OTU
beta-diversity between sampling positions based on ANOSIM tests
(p-value: 0.7371/0.7079) (Figure S5 & S6). Based on these results,
samples from the different sampling positions were merged for each
sampling day and subsequent analyses focused on sampling time and
seasonal differences. NMDS analysis for the merged samples revealed a
strong impact of sampling season on community structure (Figure 3 &
S7). Summer and winter samples were separated on the first axis, spring
and autumn samples on the second axis, producing a cyclic temporal
beta-diversity pattern resembling a “seasonal clock”. When temporal
beta-diversity was partitioned into turnover and nestedness, turnover
was the driving factor for change in beta-diversity while nestedness was
of less importance (Figure S8). Over the year, turnover increased over
the winter samples and decreased again in summer with nestedness showing
the opposite trend, reaching its highest value in summer 2018 (Figure
S8).