To detect possible changes in the habitat quality of the Gran Paradiso rivers from 2005 to 2020, we applied the RHS method to evaluate their hydro-morphological status and we measured the main chemical water parameters. In Figure 2 we reported the boxplots of the three indices derived from the RHS application on the 12 river stretches.
FIG2
For all three indices the difference between the two years is not significant (Wilcoxon Signed Test p>0.05). The median value of HQA is slightly lower in 2020, whereas HMS remains almost the same and the LRD highlights an even more lotic character in 2020. Overall, from 2005 to 2020 the hydro-morphology of the examined stretches did not highlight any evident change. Analyzing the individual sites, Leviona has suffered some deterioration in the HQA, while Valnontey is the site that has improved the most. In terms of HMS, Forzo, Roc and Nampio indicate the most marked increases in morphological alterations while Entrelor, Vaudaletta and Noaschetta are the most improved.
Concerning the physical and chemical water parameters, Table 1 reports the summary for the two years.
TAB1
The only significant differences concern nitrate, which increased in the 2020 survey, and pH, which showed a decrease (Wilcoxon Signed Test p<0.05 for both parameters). A slight yet not significant increase regards also SRP and conductivity.