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).