Indices of zooplankton community as valuable tools in assessing the trophic state and water quality of eutrophic lakes: long term study of Lake Võrtsjärv

On the basis of long-term (1964-2011) research, we tested the hypothesis that the zooplankton community has a highly indicative value in assessing the ecosystem and trophic state of water bodies. Basing on the results of our study and taking into account relevant data from numerous zooplankton studies, we can conclude that the zooplankton measures deserving to be used as indicators in the monitoring of Lake Võrtsjärv (and other similar eutrophic water bodies) could be the following: i) indicatory species of eutrophic waters [Anuraeopsis fissa (Gosse), Keratella tecta (Gosse), Trichocerca rousseleti (Voigt), Chydorus sphaericus (O. F. Müller), Bosmina longirostris (O. F. Müller)]; ii) indicatory species of oligo-mesotrophic waters [Conochilus unicornis Rousselet, Kellicottia longispina (Kellicott), Ploesoma hudsoni (Imhof), Bosmina berolinensis Imhof, Eudiaptomus gracilis (Sars)]; iii) number and diversity of species; iv) mean zooplankter weight, mean cladoceran weight, mean rotifer weight and mean copepod weight; v) rotifer abundance; vi) the share (%) of rotifers in total zooplankton abundance; vii) the ratio of abundance of large cladocerans to abundance of all cladocerans (N_LargeClad/N_Clad); viii) the ratio of calanoid copepod abundance to cyclopoid copepod abundance (N_Cal/N_Cycl); ix) the ratio of crustacean abundance to rotifer abundance (N_Crust/N_Rot ). The results of our study show that several zooplankton parameters are among the biological quality elements (BQE) deserving to be included in the Water Frame Directive system.