A hitchhiker's guide to European lake ecological assessment and intercalibration

The Water Framework Directive is the first international legislation to require European countries to
establish comparable ecological assessment schemes for their freshwaters. A key element in harmonising
quality classification within and between Europe’s river basins is an “Intercalibration” exercise, stipulated
by the WFD, to ensure that the good status boundaries in all of the biological assessment methods correspond
to similar levels of anthropogenic pressure. In this article, we provide a comprehensive overview
of this international comparison, focusing on the assessment schemes developed for freshwater lakes.
Out of 82 lake ecological assessment methods reported for the comparison, 62 were successfully intercalibrated
and included in the EC Decision on intercalibration, with a high proportion of phytoplankton
(18), macrophyte (17) and benthic fauna (13) assessment methods. All the lake assessment methods are
reviewed in this article, including the results of intercalibration. Furthermore, the current gaps and way
forward to reach consistent management objectives for European lakes are discussed.