Benthic communities: multivariate analysis 
For diatoms, we applied the NMDS to community species abundances. Results are shown in Figure 6, where the 2020 samples outline an inner ellipsoid nested in a wider ellipsoid including the 2005 data. This distinction is confirmed by the PERMANOVA test which confirms a significant difference between the 2005 and the 2020 assemblages (F 1,22=2.692, p<0.05). Moreover, the analysis of multivariate homogeneity of group dispersions highlighted significant differences between the two sampling years (F1.22 = 8.953; p = 0.007). The 2005 communities showed a higher heterogeneity among sites in the taxonomic composition than the 2020 communities, as proved by a higher (and statistically significant) distance from the centroid in 2005, while 2020 sites appear more homogenous and therefore graphically closer to each other.
Fig6
The same analysis applied to macroinvertebrate communities (in this case, on presence-absence data) did not detect a significant difference between the two sampling years, with only a slightly higher distance from the centroid in the 2005 assemblages (graphic not shown).
Figures 7 and 8 report the results concerning LCBD and SCBD applied to diatom and macroinvertebrate data respectively. The two years did not show a significant difference in terms of LCBD (Figure 7a and Figure 8a). For this reason, Figures 7b,7c, 8b and 8c report the single LCBD and SCBD calculated for the most recent campaign.
Fig 7
Fig 8
A. minutissimum  and A. lineare  got the highest SCBD score in 2020 (0.08 for both species). The other species contributing most to ß-diversity were C. excisiformis, Achnanthidium thiennemanii, E. silesiacum  and Fragilaria pectinalis .
Concerning macroinvertebrates, S. montana  among others got the highest SCBD score, followed by several other taxa attaining similar scores (e.g. Blephariceridae, Elmidae, Nemoura  sp., Limoniidae). Chironomidae got by far the lowest score.
Regarding the contribution of sites to local diversity, sites displaying the highest LCBD in 2020 based on diatom community composition were Leviona, Roc and Gran Nomenon; Roc Entrelor, Savara and Campiglia according to macroinvertebrate data. Averaging the LCBD values obtained on the two communities, the sites that contribute most to local diversity are Roc, Entrelor and Leviona.