Conférence Internationale de Limnologie d'Expression Française (CILEF 5) - Namur, July 7th-11th, 1997.

Poster in French : Biomonitoring potentialities of the river Garonne chironomid (Diptera) populations. Garcia XF, Gendron JM, Laville H.

Abstract

The Chironomid populations of the higher and average course (255 km) of the river Garonne (578 km) were studied using pupal skin collections.

Two collections (June, September 1994) in 8 stations of the higher course (1100 m to 320 m) and three collections (March, May, July 1996) in 12 stations of the average course (270 m with 60 m) were carried out.

24 500 exuvies were sorted and 126 species or taxa identified.

The analysis of these populations highlighted 4 typological zones and their corresponding biocenosis among the 55 most frequent species (>1% at least in one station), as well as the modifications of their structures to the downstream of the two principal polluting points - effluents of paper mill of St Gaudens, km 84, in the rhithral, and domestic and industrial wastes of Toulouse, km 174, in the upper-potamal.

The Chironomid index (Ich) of Eulin et al. (1993) modified from Bazerque et al. (1989) reflects the reduction in the water quality of the Garonne to the downstream of these two polluting points.

The knowledge of the specific richness only does not appear a sufficient reference to appreciate the impact of deteriorations of the river. It must be combined with an analysis of the structure of the communities which appreciates the appearance or the disappearance of bioindicators which one knows the level of polluo-tolerance.

References

BAZERQUE (M.F.), LAVILLE (H.), & BROUQUET (Y.). 1989.- Biological quality assessment in two rivers of the northen plain of France (Picardie) with special reference to Chironomid and Diatom indices. Acta Biol. Debr. Oecol. Hung., 3 : 29-39.

EULIN (A.), GRUARIN (C.), LAVILLE (H.) & LE COHU (R.). 1993.- Evaluation de la qualité de l'eau de la Garonne par référence spéciale aux indices diatomiques et chironomidien. Annls Limnol., 29(2-4) : 269-279.

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