Macrophyte-based assessment of lakes - A contribution to the implementation of the European water framework directive in Germany

The European Water Framework Directive requires ecological status classification and monitoring of surface and ground water bodies using biological indicators. To fulfill the demands of the Directive, a macrophyte-based assessment system was developed for application on four lake site types in Germany. Biological lake site types were established using differences in characteristic macrophyte communities, reflecting ecoregion, Ca²⁺ content, mixis and morphology. Ecological status classification of lake sites is based on macrophyte abundance along 275 transects in 95 natural German lakes and the calculation of a reference index value, in some cases supplemented by submerged vegetation data. The reference index quantifies the deviation of species composition and abundance from reference conditions and classifies sites to one of the five ecological quality classes specified in the Directive. Based on an example of Lake Chiemsee, Germany, the possibilities for a wholelake assessment are discussed.