Figure 1 - Study area with sampling sites

Figure 2- Boxplots of the indices derived from the RHS application in 2005 and 2020. The bottom and top of each box are the 25th and 75th percentiles, the line in the middle is the median, whiskers go from the end of the interquartile range to the furthest observation within 1.5 times the interquartile range. HQA = Habitat Quality Assessment HMS = Habitat Modification Score LRD= Lentic Lotic River Descriptor.

Figure 3 – Comparison between climatic data in the years 1999-2005 and 2014-2020. Maximum air temperature a) summer monthly data b) winter monthly data; c) average monthly rainfall (data source: Arpa Piemonte www.arpa.piemonte.it ). Errors bars are standard deviations.

Figure 4 – Comparison between 2005 and 2020 diatom community indices. Boxplots from d) to g) show the most common European diatom indices: IPS= Indice de Polluosensibilité Specifique (Coste, 1982); ICMi= Intercalibration Common Metric Index (Mancini and Sollazzo, 2009); TI= Trophic Index (Rott et al., 1999). Boxplot statistical limits as in Figure 2.

Figure 5 – Comparison between 2005 and 2020 macroinvertebrate community indices. IBE= Italian Biotic Index (Ghetti, 1997). Boxplot statistical limits as in Figure 2 BMWP, ASPT, IBE, N families, N taxa, N EPT families, % stenocious taxa

Figure 6 – Graphical result of the NMDS displaying samples based on the diatom matrix.

Figure 7 - Contribution to diatom community β-diversity. a) LCBD for 2005 and 2020; b) SCBD of each diatom species; c) LCBD of sampling sites. Species with SCBD<0.02 were not included. Boxplot statistical limits as in Figure 2. LCBD= Local Contribution to β Diversity; SCBD= Species Contribution to β Diversity.

Figure 8 - Contribution to macroinvertebrate community β-diversity. a) LCBD for 2005 and 2020; b) SCBD of each taxon; c) LCBD of sampling sites. Boxplot statistical limits as in Figure 2. LCBD= Local Contribution to β Diversity; SCBD= Species Contribution to β Diversity.