Definition Of Seasonal Phytoplankton Events For Analysis Of Long TermData Fiom Coastal Waters Of The Southern Baltic Sea With Respect To TheRequirements Of The European Water Framework Directive

The key feature of the European Water Framework Directive (EU-WFD) is to measure water quality with respect to ecological categories, i.e. in terms of the community structure and functioning of natural ecosystems. For the use of phytoplankton data in comparative ecosystem assessment it is important to compare similar seasonal phytoplankton stages since phytoplankton runs through different succession stages throughout the year, all characterised by differences in biomass and taxonomical composition. In this paper calculable seasonal markers are suggested from the analysis of a long term data set indicating important successional stages at different types of coastal waters in the southern Baltic Sea. In order to test the applicability of the temporal markers for water quality assessment, phytoplankton biomass was calculated for the defined seasonal events and compared to annual mean biomass calculations. While the calculation of the annual mean failed to indicate different trophic states, the event based biomass calculation showed clear differences between sampling sites, reflecting the pronounced differences between the stations concerning their nutrient regime. Thus, the proposed phytoplankton event definition is a recommendable tool for the application of biological metrics in evaluating coastal ecosystems with respect to the needs of the EU-WFD.