Fig. 4. Ternary plot of periphyton compositions illustrating that most sites and transects are dominated by diatoms and/or chrysophytes. Colors highlight the dominance in all subsamples (transects). Each circle corresponds to a composite transect sample (each consisting of 7 single measurements). Shades of grey illustrate sample density in the respective corner(s), most samples are dominated by diatoms/chrysophytes.
The biomass of diatoms and chrysophytes was significantly negatively linked with glaciation (2nd order polynomial model, R²=42, p<0.001, Fig. 5 B), with biomass doubling when glacier-cover lowers from 30% to 0.5%. Pigment-group A was also negatively related to glacier-cover (R²=0.25, p<0.001), but biomass remained low (<3.2 mg cm-2; Fig. 5 A). In contrast, the biomass of pigment-group C was positively related to the glacier-cover in a catchment, but remained <2.5 mg cm-2 (=8 to 22% of total periphyton biomass, 95%-CI) across all study streams. The composition and the contribution of different groups did not differ significantly among different summer months (Fig. 5).
The estimated diatom biomass was related to the palmitoleic acid (16:1n-7) content, a diatom-related fatty acid (F=8.1, p=0.01, R²=0.4, Fig. 6).