Biological quality assessment of three French Alpine lakes (Lake Annecy, Lake Crop, Lake Grand Domenon) using the Lake Biotic Index (LBI)

Abstract

The Lake Biotic Index (VERNEAUX et al. 2004 a), a new lake biological quality assessment method based on the bathymetric distribution of macroinvertebrate assemblages, was applied to three reference French lakes having different geomorphological characteristics (altitude, size, geology, maximum depth). The Lake Biotic Index (LBI) is interpreted through its two sub-indices; one is a littoral quantitative index (littoral biotic index: Bl which considers the littoral taxon richness and the littoral density per m 2 ) related to lake trophic potential, the second (taxon deficit index: Df) is a qualitative index reflecting the relative loss of taxon richness between littoral and deep zones in relation to the lake's ability to transfer available matter up to consumers (trophic functioning). The results show a great impact of the geomorphological characteristics of the lakes on the reference LBI values (from 12/20 to 18.5/20) due only to different littoral macroinvertebrate biodiversities. Lake Annecy, a great lake situated 457 m a. s. on calcareous substratum, showed a much higher Bl value (62.6) than the two other lakes (Lake Crop Bl: 26.2, Lake Grand-Domenon Bl: 26.4) which are small lakes located at high altitudes on siliceous substratum. Concerning the qualitative index Df, no differences were observed between the three lakes which obtained high Df values (Lake Annecy Df: 0.9/1, Lakes Crop and Grand-Domenon Df: 1/1). It can therefore be concluded that the geomorphological factors considered did not affect the efficiency of lake trophic functioning.