Aquatic vegetation in two pre-alpine lakes of different trophic levels (Lake Bled and Lake Bohinj): Vegetation development from the aspect of bioindication

Abstract

The two lakes studied have some common characteristics as are origin and geological age, however apparent differences can be recognised in morphometry, hydrology, physico-chemical characteristics of water, type of watershed and management approach. Lake Bled is smaller and located in the middle of an urban surroundings. Intensive eutrophication has been an outstanding process in this century, accompanied occasionally with algal bloom. Two restoration measures were introduced to improve the state of the ecosystem but the equilibrium is still fragile. Consequently, aquatic vegetation was subject to constant changes in species composition, their abundance, frequency and depth of distribution. The other ecosystem, which is Lake Bohinj is located in natural surroundings of the Triglav National Park. It is considered as a mesotrophic lake. Littoral is for the most part well developed and in some parts abundantly colonised with macrophytes. Changes in communities were not as obvious and radical as in Lake Bled. In 1994, an outstanding increase in biomass of Myriophyllum spicatum, visible with regards to abundance and frequency, was a common phenomenon to both lakes. The bioindicating value of macrophytes has been estimated on a basis of plant strategy which was developed as an answer to the environmental changes in the past. Alternations on other structural and functional levels which also reflect the trophic state can be predicted from the development of macrophytes. © Société botanique de France 1995.