Macrophyte biological index for rivers (MBIR) application for an ecological assessment of walloon rivers, prelilminary investigations.

Samples were collected from 45 sites along the Walloon river network in 2007, in accordance with the Water Framework Directive (WFD, European Union, 2000), used to define the overall ecological status of rivers. Within each collected sample, macrophyte data were gathered at species level and the main water quality parameters were analyzed. This involved the use of two approaches: firstly, methods of ordination and classification (Principal Component Analysis and Multiple Factorial Analysis) and secondly, aquatic macrophyte community indexes.
The Macrophyte Biological Index for Rivers (MBIR) was used to define the ecological status of the macrophyte community in response to eutrophication pressure. Four trophic qualities were detected in all the monitored stations: 56% of the sites showed a good trophic quality, with the Ardennes region in the leading position and only 2% of the sites showed a poor trophic quality. A Multiple Factorial Analysis (MFA) made it possible to regroup the species according to their ecological affinities and to specify their indicator values in relation to some abiotic parameters. As a result, a rivers typology was outlined based on this analysis. The dendrogram of the Hierarchical Cluster Analysis (HCA) gave three clusters determined by active variables of each compartment that defined functional parts of the Walloon network: Chiloscyphus polyanthos (L.) Corda, Rhynchostegium riparioides(Hedw.)C.Jens., Fontinalis squamosa(Hedw) and Ranunculus penicillatus (Dum.)Bb. showed an oligotrophic status and low mineralization in the Ardennes (GI), while P. pectinatus(Linne), Cladophora glomerata(Linnaeus)proved to be found more often in eutrophicated waters in the Region limoneuse (GIII). Pellia endvifolia (Dicks.)Dum, Fissidens crassipes(Br.Eur);Cinclidotus riparius (Web. & Mohr.) appeared in the Condroz and Famenne, rivers characterized by a high concentration of nitrogen (N-35. NO3-) (GII).