MACROPHYTES FROM LAKES IN THE EASTERN PYRENEES - COMMUNITY COMPOSITION AND ORDINATION IN RELATION TO ENVIRONMENTAL-FACTORS

1. Thirty-six species of macrophytes (fourteen flowering plants, two q uillworts, sixteen mosses and liverworts, and two algae) were collecte d in an extensive survey of 116 high mountain lakes in the eastern Pyr enees. Seventy per cent of the lakes showed macrophyte development. 2. The isoetids (Isoetes lacustris, Isoetes setacea and Subularia aquati ca) were the dominant growth form, although the natopotamid Sparganium angusifolium was the most widespread species. Potamids (Potamogeton s pp., Ranunculus spp.), the alga Nitella gr. opaca and some mosses (War nstorfia exannulata, Sphagnum denticulatum) were often present. 3. A m ultivariate ordination analysis (RDA-redundancy analysis) revealed tha t water chemistry, altitude and vegetation cover of the catchment, and nutrient availability are major environmental factors associated with macrophyte distribution along the eastern Pyrenean lakes. Isoetids pr evailed in softwater oligotrophic lakes, potamids in relatively hardwa ter oligotrophic lakes, and Potamogeton natans and Callitriche palustr is in small and eutrophic water bodies affected by the presence of cat tle.