3.2 Mero- vs hololimnic
There was a significant relationship between sampling day and overall
merolimnic species richness (F = 4.419, p-value = 0.005, ndf = 3.59, ddf
= 27.41, R-sq. (adj.) = 0.538), but not OTU richness, which was also
true for the most species-rich merolimnic taxon Diptera (species
richness: F = 3.231, p-value = 0.021, ndf = 3.649, ddf = 27.351, R-sq.
(adj.) = 0.369). For merolimnic, most species were detected in spring
(115),) and lowest richness was detected in summer (60) (Figure S13), as
well as for the most species-rich merolimnic subgroup Diptera (spring:
95 species; summer: 50 species) (Figure S14). While the detection of
merolimnic subgroups Ephemeroptera, Plecoptera and Trichoptera species
richness was unaffected by sampling day, it had an effect on the
detection of OTU richness (E: Chi-squared = 39.11, p-value =
<0.001, ndf = 7.27, ddf = 23.73, R-sq. (adj.) = 0.433; P:
Chi-squared = 21.01, p-value = 0.005, ndf = 6.156, ddf = 24.844, R-sq.
(adj.) = 0.781; T: Chi-squared = 20.11, p-value = 0.002, ndf = 4.636,
ddf = 26.364, R-sq. (adj.) = 0.738). For Ephemeroptera, most OTUs were
detected in autumn (15) and in late spring (20). In contrast, the
detected Plecoptera and Trichoptera OTU richness was highest from
December to March (10) and January to March (20) respectively (Figure
S15). Lowest richness for all EPT were detected in summer (E: 6, P: 1,
T: 6).
Sampling day had an effect on the detection of overall hololimnic
species richness (Chi-squared = 32.28, p-value = <0.001, ndf =
5.498, ddf = 25.502, R-sq. (adj.) = 0.439) but not OTU richness. Most
hololimnic species were detected between autumn and spring with
relatively stable numbers inbetween (30) (Figure S16). The detection of
the most abundant hololimnic taxon, Annelida, was influenced by sampling
day for both species (Chi-squared = 20.56, p-value = 0.004, ndf = 5.392,
ddf = 25.608, R-sq. (adj.) = 0.444) and OTU richness (Chi-squared =
2.534, p-value = 0.043, ndf = 5.243, ddf = 25.757, R-sq. (adj.) = 0.51)
with the highest richness detected in autumn (species: 20/OTUs: 50) and
a constant decline afterwards (summer: 5/10) (Figure S17 and S18). The
number of detected species and OTUs for the second most abundant
hololimnic taxon, Coleoptera, was not affected by sampling day.
Temperature had no effect on the detection of species nor OTU richness
for any of the tested groups. Higher discharge negatively affected the
detection of Ephemeroptera and overall hololimnic and Annelida species
(E: Chi-squared = 4.213, p-value = 0.04, ndf = 1, ddf = 28.292, R-sq.
(adj.) = 0.384; hololimnic: Chi-squared = 6.639, p-value = 0.01, ndf =
1, ddf = 25.502, R-sq. (adj.) = 0.439; Annelida: Chi-squared = 6.182,
p-value = 0.013, ndf = 1, ddf = 25.608, R-sq. (adj.) = 0.444) (see
Figures S11, S10 and S12). Per 10 m³/s increase in discharge
Ephemeroptera lost 1 species, hololimnic taxa 5 species and Annelida 3
species.