A phytoplankton trophic index to assess the status of lakes for the Water Framework Directive

Abstract

Despite improvements in waste water treatment systems, the impact of anthropogenic nutrient sources remains a key issue for the management of European lakes. The Water Framework Directive provides a mechanism through which progress can be made on this issue. The Directive requires a classification of the ecological status of phytoplankton which includes an assessment of taxonomic composition. In this paper we present a composition metric, the Plankton Trophic Index, that was developed in the WISER EU FP7 project and demonstrate how it has been used to compare national phytoplankton classification systems in Northern and Central Europe. The metric was deerived from sumaer phytoplankton data from 1795 lakes, summarised by genus covering 20 European countries. We show that it is significantly related to total phosphorus concentrations, but that it is alos sensitive to alkalinity, lake size and climatic variables. Through the use of country specific reference values for the index we demonstrate that it is significantly related to othrt national phytoplankton assessment systems and illustrate for a sinngle lake type how it was used to intercalibrate Water Framework Directive boundaries for different countries.