Macroinvertebrate metrics responses to morphological alteration in Italian rivers

The responses of river macroinvertebrates to hydromorphological alteration are often considered weak or unclear. It is therefore crucial to verify if and how existing invertebrate-based approaches can reveal the effects of hydromorphological modification. We analyzed the responses of benthic metrics to morphological impairment, with emphasis on the STAR_ICM index, legally required for macroinvertebrate-based ecological status assessment in Italy. A Principal Component Analysis (PCA) was run to condense information on morphological impairment. The major gradient (Component 1) expressed a combination of bank and channel modifications opposed to tree-related features indicating the presence of comparatively unmodified habitats. Jointly, habitat descriptors including Habitat Modification Score (HMS) derived from the application of a habitat survey method were calculated. Spearman rank correlations between biological metrics and morphological impairment indicators (PCA scores and HMS) were significant. A linear mixed-effects regression approach was applied to relate HMS and STAR_ICMi across a wide geographical context. HMS explained > 60% of STAR_ICMi variability, in the absence of apparent water pollution. Results demonstrated that morphological information resumed with habitat survey methods is meaningful for the biological community and that HMS can support the interpretation of ecological status across rivers' types and in different environmental settings.