caa a22 4500 445891874 CHVBK 20180317145619.0 cr unu---uuuuu 170323e20110201xx s 000 0 eng 10.1007/s10750-010-0414-5 doi (NATIONALLICENCE)springer-10.1007/s10750-010-0414-5 Why do phytoplankton species composition and "traditional” water quality parameters indicate different ecological status of a large shallow lake? [Elektronische Daten] [Lea Tuvikene, Tiina Nõges, Peeter Nõges] Long-term data on phytoplankton species composition in large and shallow Lake Võrtsjärv indicated a sharp deterioration of the ecological status at the end of the 1970s. The more traditional water quality indicators, such as the concentrations of nutrients and chlorophyll a, phytoplankton biomass, and Secchi depth, failed to capture this tipping point or even showed an improvement of the status at that time. As the shift coincided with a large increase of the lake's water level (WL), we hypothesized that direct effect of the changing WL on traditional water quality indicators might have blurred the picture. We removed statistically the direct effect of the WL and the seasonality from the traditional water quality indicators in order to minimize the effects of natural variability. The average of the standardised water quality indicators, used as a proxy for the ecological status, distinguished a period of fast eutrophication in the first half of the 1970s (not captured by the phytoplankton species index), a fast improvement at the end of the 1970s (when the species index showed deterioration) followed by a continuous deterioration trend (when the species index remained rather constant). The causes of this inconsistency are discussed in the light of the alternative stable states theory and the priority of biotic indicators stipulated by the EU Water Framework Directive. Springer Science+Business Media B.V., 2010 Water Framework Directive nationallicence Phytoplankton taxonomic index nationallicence Trophic state indicators nationallicence Long-term data nationallicence High natural variability nationallicence Alternative stable states nationallicence Tuvikene Lea Centre for Limnology, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, 61117, Rannu, Tartumaa, Estonia aut Nõges Tiina Centre for Limnology, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, 61117, Rannu, Tartumaa, Estonia aut Nõges Peeter Centre for Limnology, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, 61117, Rannu, Tartumaa, Estonia aut Hydrobiologia Springer Netherlands 660/1(2011-02-01), 3-15 0018-8158 660:1<3 2011 660 10750 https://doi.org/10.1007/s10750-010-0414-5 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10750-010-0414-5 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Tuvikene Lea Centre for Limnology, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, 61117, Rannu, Tartumaa, Estonia aut NATIONALLICENCE 700 1- Nõges Tiina Centre for Limnology, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, 61117, Rannu, Tartumaa, Estonia aut NATIONALLICENCE 700 1- Nõges Peeter Centre for Limnology, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, 61117, Rannu, Tartumaa, Estonia aut NATIONALLICENCE 773 0- Hydrobiologia Springer Netherlands 660/1(2011-02-01), 3-15 0018-8158 660:1<3 2011 660 10750 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer