Limnetica 34

Before establishing the ecological status of lakes, the Water Framework Directive requires their classification in types. Typically, the development of a typology has been based on abiotic variables. However, for the typology to have validity, the classification of lakes should be corroborated with the biological communities in the bodies of water. In this study, to develop a biologically relevant typology, the natural variability of the macrophyte communities in mountain lakes and ponds was evaluated. The use of functional groups of macrophytes as an alternative to the taxonomic approach was also evaluated. Thirty-one reference mountain lakes and ponds, located in the northwest quadrant of the Iberian Peninsula, were included in the study. The functional groups of macrophytes were based on the inorganic source of carbon used in photosynthesis. The typology developed from the functional groups was more conclusive than the classification derived from the taxonomic data. The primary determinants of the variability in the composition of the functional groups of macrophytes among the different types of lakes were the changes in the pH and in the orthophosphate concentration related to the decomposition of macrophytes. The submerged macrophytes dominated in the lakes with low concentrations of orthophosphate and the highest levels of alkalinity. In the lakes with lower pH values, the floating-leaved macrophytes were the dominant plants when the phosphorus concentration was higher, whereas at intermediate concentrations of phosphorus, the bryophytes and isoetids were more abundant; these two lake types were differentiated because of the dominance of the bryophytes in those lakes with higher acidity.