Lake phytoplankton metrics proposed by the EC WISER Project for ecological quality assessment of European lakes are shown to be robust metrics. Latest results from the WISER pan-European field campaign reveal that variability in metric scores is largely due to variability between lakes and is significantly related to differences in eutrophication pressure (total phosphorus concentrations). Differences in locations around a lake, or sampling and analytical variability, only account for a small proportion of the variability in metric scores. These results are especially true for four candidate phytoplankton metrics being considered for Intercalibration: chlorophyll, PTI, MFGI and cyanobacteria abundance, for which >85% of the variability in metric scores was attributed between lakes and total phosphorus concentration was the best single predictor of variation in these metrics. Although, much among-lake metric variation still remained unexplained by the available environmental data, we conclude that these four proposed metrics are sufficiently robust metrics for ecological status assessment and are suitable for adoption in the Intercalibration process
