The AQEM multimetric system for the southern Italian Apennines: assessing the impact of water quality and habitat degradation on pool macroinvertebrates in Mediterranean rivers

In accordance with the aims of the E. U. funded AQEM Project, an assessment system module based on aquatic macroinvertebrates was developed for small sized rivers in the southern Apennines (south Italy). Eleven stream sites, impacted to a greater or a lesser extent by organic pollution and/or habitat impairment and chosen to cover the whole degradation gradient present in the geographical area were sampled in three seasons. The samples were collected following a proportional, multihabitat procedure, afterwards considering separately the replicates collected in the depositional (pool) and transport (riffle) areas for the analysis. A PCA multivariate analysis was performed to extract the main axes of variation of the biological community, which resulted in the first axis being strongly correlated to ecological quality. The final assessment module is based on a multimetric system, structured by selecting the best metrics in simulating the first axis gradient. The system considers a total of 15 different metrics, mainly providing information concerning tolerance to pollution, taxa richness, habitat features and trophic structure of the community. In accordance with the WFD requirements, some of these metrics are based on abundance classes of taxa. Depositional and transport units, due to the observed dissimilarity in the structure of their benthic communities, were kept separate during the development of the assessment system to retain this potentially useful information and to clear interpretation of the results. Both 'riffle' and 'pool' invertebrate data showed clear differences in ecological quality between sites. Nevertheless, the final assessment module is based on the macroinvertebrates inhabiting depositional areas of rivers only, because the metrics for these river units showed a better performance than those examined for the transport river units. The application of the assessment module requires 10 replicates to be quantitatively collected, for a total area of 0.5 m(2). In terms of sampling and identification effort, the assessment module shows a good comparability with the standard Italian method presently in use and might thus be easily applied for river sites classification according to the Water Framework Directive in southern Italy. The site classification obtained with the proposed multimetric index shows a very good correspondence with the post-classification based on multivariate analysis.