3.2 Mero- vs hololimnic
Sampling day affected the detection of overall merolimnic species richness (F = 4.419, p-value = 0.005, ndf = 3.59, ddf = 27.41), 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). 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; P: Chi-squared = 21.01, p-value = 0.005, ndf = 6.156, ddf = 24.844; T: Chi-squared = 20.11, p-value = 0.002, ndf = 4.636, ddf = 26.364). 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 numbers 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) 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) and OTU richness (Chi-squared = 2.534, p-value = 0.043, ndf = 5.243, ddf = 25.757) 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; hololimnic: Chi-squared = 6.639, p-value = 0.01, ndf = 1, ddf = 25.502; Annelida: Chi-squared = 6.182, p-value = 0.013, ndf = 1, ddf = 25.608) (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.