Report on fitting the Italian national method for the evaluation of the ecological quality of lake waterbodies using benthic diatoms (EPI-L) in the "phytobenthos cross-GIG" intercalibration exercise

When the Cross-GIG phytobenthos intercalibration exercise was carried out, there was no specific Italian national method for the evaluation of the ecological quality of lake waterbodies using benthic diatoms. It was assumed that the common intercalibration metric could be used to replace the national method. However, during the exercise itself it became evident that the common metrics was not strongly correlated to the trophic pressure in the Italian lakes. As a consequence, a new method was developed, namely EPI-L, on the basis of data collected by Environmental Agencies and Research Institutes in 80 lakes covering a long trophic gradient in both the Alpine and Mediterranean ecoregion. This reports aims to evaluate to compare the value of the class boundaries of EPI-L with those agreed in the inter-GIG intercalibration exercise following the "Instruction manual to fit new or revised national classifications to the completed IC exercise". Lake quality classification should be carried out at the biological quality element (BQE) level. However, no intercalibration exercise was carried out for the "macrophyte and phytobenthos" BQE. For this reason, this report will only deal with the phytoplankton subelement.