Dynamic of macro-algae populations in large rivers: application in Dordogne and Garonne rivers, 2001-2004.
Dynamique des macro-algues en grands cours d'eau : application à la Dordogne et à la Garonne, 2001-2004.
Résumé
In the ECOBAG program (Environment, ECOlogy and ECOnomy of the Adour-Garonne Basin) the present survey concerns the dynamics of the macro-algae on eight reference stations of two rivers, the Dordogne and the Garonne, 2001 - 2004 period. It also tries to evaluate the impact of discontinuities on these biological processions and their main discriminative parameters. The specific richness and algal coverings vary a lot within these stations. The stations of the Dordogne are more vegetalized by macro-algae than the stations of the Garonne. The genus Cladophora is very present on the whole stations of the two rivers but seems to show a preference for the stations including a substratum constituted of pebbles. Two species of Rhodophyceae represent each one more specifically a station: Lemanea sp. and Thorea hispida. The genus Oedogonium and Hildenbrandia are found more particularly on stations comprising a strong proportion of pebbles. The stations, with bed rock domination, are less vegetalized and diversified; they present however, in addition to Cladophora, Cyanobacteria at the end of the summery season. The application of various statistical tests didn't permit to demonstrate that discontinuities presented direct influences on the macro-algae of the reference stations of the survey. The use of Hierarchical Ascending Clustering and Principal Component Analyses permitted to identify 3 groups of stations and to specify the main features of it. Some logistical regressions permitted to distinguish the main determining parameters of the presence of the filamentous algae.