Stima della qualità degli ambienti fluviali in aree urbane attraverso l’uso di bioindicatori ai fini della costituzione di corridoi ecologici. Caso di studio: fiume Aniene

Estimating the environmental river quality in urban areas using bioindicators to restore ecological corridors. Case study: Aniene river Rosalba Tamburro Abstract The present thesis aimed first to compare the application of a broad set of indicators founded on the plant and animal components of the river ecosystem with the scientific purpose to evaluate the goodness of the indices, their possible correlations, and their limits. Second, the study was conducted to assess the Aniene environmental quality inside Rome to provide fundamental knowledge on river quality useful for making proposals improving the urban ecological corridor. The investigation was focused on the riparian vegetation, the river ecological state and his functionality inside Rome, from the Great Ring Road to the confluence with the Tiber river. Twenty sampling sites were selected where vegetation survey was carried out and inside them other seven sites were chosen to conduct studies on macrobenthic (RQE_STAR_ICMi) and macrophyte (IBMR) communities. Physical-chemical parameters of water were carried out too. Finally, the Fluvial Functionality Index (IFF) was applied to establish a broader environmental value of the river that enclosed the urban pressure too. All these investigations were carried out from April 2014 to October 2016. The floristic composition was analysed by means of transects comprising both water and riparian belts. Two bioindication models based on the plant species were applied to assess the habitat quality. They are represented by Ellenberg indicators and Hemeroby index for the evaluation of anthropogenic disturbance. The floristic matrix of 245 species X 104 relevès was subjected to multivariate statistical analysis for a first data exploration through Cluster Analysis (CA) and Principal Component Analysis (PCA). To identify and analyse the existence of the ecological gradients a bivariate Pearson correlation test was performed between the significative coordinates of the PCA and the 7 indicators set (Ellenberg and Hemeroby). The Pearson correlation analysis also was performed to verify the possible correspondence between the vegetation and the other indices and between them. Chemical analysis revealed a very poor percentage of water saturation of Oxygen concentration showing a lower water quality resulting from domestic, agricultural and factories pollutants. The most significant correlations between the indices of Ellenberg and Hemeroby is the one existing between indicators of luminosity and Hemeroby whose increase is accompanied by degradation of forest vegetation rearing towards more heliophilous conditions. These conditions seem to favour the continental indicators, when the mitigation effects of the shrub and the ocean species that accompany the riparian forests decrease. IBMR and emerobia calculated on the same list of species used for the calculation of the IBMR, are correlated by showing a parallel trend. The correlation of the IBMR with H calculated on the 25 species of the IBMR list and not with the total H, calculated on the whole set of species detected by Phytosociological detection, shows the limits of this European index which does not entirely correspond to the local flora. Especially about the quota of Mediterranean species that are missing or are underestimated in the databases currently available. The RQE_STAR_ICMi was inversely correlated with ecological disturbance conditions meaning that when Hemeroby decreases the macroinvertebrates presence rises. The index of macroinvertebrates, on the other hand, had the same low values on all sites, indicating that the water quality everywhere was polluted. This finding confirms what in previous studies had already been demonstrated: the quality of water expressed by the macrobenthic community may not coincide with that expressed by the plant community. This identifies a different behaviour of fauna and flora compared to ecological factors. The Nutrient indicators (N) of Ellenberg were also correlated to NO3 confirming that domestic and agricultural pollutants contaminated the water. Among the contaminants sodium and magnesium appear to be significantly related to the IBMR RQE. The work carried out identifies the need to use more indicators to identify the ecological state of the watercourses considering overall existing gradients and temporal variations, especially of macrophyte and spondal vegetation, that are most sensitive to environmental variables. It also identifies the need to consider faunistic data separately from floristic ones as the response to environmental variables is different. Finally, the investigation carried out on vegetation shows a fair resumption of near-natural formations to Populus nigra and Ulmus minor, which, though very fragmented, support the hope of reconstituting a wider riparian forest that can act as an ecological corridor in the urban area. The IFF has highlighted in detail the most compromised tracts that need riverway restoration. These results show that Mediterranean rivers, characterized by wide and well drained basins with dense and deep waters, develop a limited macrophyte diversity, while a self-purification function is surely exerted by the riparian vegetation, which is instead removed. Therefore, it would be more appropriate to include the IFF, Ellenberg and Hemeroby indices to make the assessment of the ecological quality of the watercourse more reliable.