Phytoplankton Trophic Index (PTI. A new pan-European phytoplankton taxonomic index (PTI) has been developed that can be used as a common metric for several GIGs, or as a national metric for the 2nd phase of Intercalibration, for those countries that still lack such a metric in their national assessment system. As for many existing national metrics, the new PTI index is developed from trophic scores of phytoplankton taxa along the eutrophication gradient. This pan-European PTI, however, uses data from 1656 lakes from 19 countries providing comprehensive gradients for modelling species responses. The PTI metric shows a very significant relationship to total phosphorus (r2 = 0.667 in all lakes) (Figure 3.1-1). As well as ‘global’ index scores derived from the whole dataset, GIG-specific index scores have been produced. Provisional reference conditions and boundary values have also been established for one lake type, and the metric will become available soon in the WP database.
