, Volume 633, Issue 1, pp 197-211

First online:

Assessment of the ecological status of European surface waters: a work in progress

  • Peeter NõgesAffiliated withInstitute for Environment and Sustainability, Joint Research CentreCentre for Limnology, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences Email author 
  • , Wouter van de BundAffiliated withInstitute for Environment and Sustainability, Joint Research Centre
  • , Ana Cristina CardosoAffiliated withInstitute for Environment and Sustainability, Joint Research Centre
  • , Angelo G. SoliminiAffiliated withInstitute for Environment and Sustainability, Joint Research CentreDepartment of Experimental Medicine, Sapienza University of Rome
  • , Anna-Stiina HeiskanenAffiliated withInstitute for Environment and Sustainability, Joint Research CentreMarine Research Centre, Finnish Environment Institute (SYKE), Research Programme for the Protection of the Baltic Sea

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The ‘normative definitions’ of ecological water quality classes given by the Water Framework Directive (WFD) are narrative descriptions of the conditions present in water bodies of different qualities relative to reference conditions found in unimpacted sites. In order to fill these descriptions with a more solid content, the definitions have been a subject of intensive development of quantitative methodologies for ecological status assessment as well as for rules and criteria for setting of reference conditions and ecological status boundaries for classification of water bodies. In this article, we recall the basic principles of the WFD that sometimes have been overlooked and point out some gaps remained and problems arisen during the ongoing implementation of the directive. Defining type-specific reference conditions for water bodies and finding biological metrics that sensitively reflect only the anthropogenic deviations from those conditions are the biggest challenges that the ecological status assessment faces. So far, there is no guarantee that reference conditions are comparable across EU Member States due to a lack of common criteria, which need still to be elaborated. Defining site-specific reference conditions instead of type specific is a novel approach that allows for minimizing uncertainties introduced by applying broad types. Search for new metrics has led to a real boom of multimetric indices which ought to be the adequate tool to measure the multiple human impairments but which should pass a thorough check before being included in monitoring programs. Curiously, some biological indices constructed as surrogates for chemistry (especially nutrients) start ‘living their own life’ and continue indicating the disturbance when the controlling factors change. This shows the obvious advantage of biological indicators against chemical ones. New challenges to WFD implementation are brought about by the need to consider the effects of alien species and climate change in the assessment framework, and by the nonlinear dose—response relationships dominating in biological systems. Attempts to diminish uncertainties in quality assessment have become a new labour-intensive field for researchers.


Water Framework Directive Intercalibration Multimetric index Biological indicators One out/all out principle