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Ecological status and intercalibration

The general objective of the WFD is to achieve ‘good status’ for all surface waters by 2015. ‘Good status’ means both ‘good ecological status’ and ‘good chemical status’.

The so called "intercalibration exercise" is a key element in making this general environmental objective operational in a harmonised way throughout the EU. The following paragraphs describe the assessment of ecological status and how 'good ecological status' is intercalibrated in the EU.  

Assessment of water status in the WFD

The WFD classification scheme for water quality includes five status classes: high, good, moderate, poor and bad.

‘High status’ is defined as the biological, chemical and morphological conditions associated with no or very low human pressure. This is also called the ‘reference condition’ as it is the best status achievable - the benchmark. These reference conditions are type-specific, so they are different for different types of rivers, lakes or coastal waters so as to take into account the broad diversity of ecological regions in Europe.

Assessment of quality is based on the extent of deviation from these reference conditions, following the definitions in the Directive. ‘Good status’ means ‘slight’ deviation, ‘moderate status’ means ‘moderate’ deviation, and so on. The definition of ecological status takes into account specific aspects of the biological quality elements, for example “composition and abundance of aquatic flora” or “composition, abundance and age structure of fish fauna” (see WFD Annex V Section 1.1 for the complete list). These definitions are expanded in Annex V to the WFD.

The intercalibration exercise

The intercalibration exercise is referred to in the Directive (Annex V section 1.4.1). Its objective is to harmonise the understanding of ‘good ecological status’ in all Member States, and to ensure that this common understanding is consistent with the definitions of the Directive.

Intercalibration is a complex task that takes into account current scientific knowledge about the structure and functioning of aquatic ecosystems, and how human activities influence them. The process of defining ‘good ecological status’ does not take account of socio-economic factors. These are covered by the exemptions to the general objectives (see Environmental objectives and exemptions).

Although the WFD defines which biological elements must be taken into account when assessing ecological status, it leaves the Member States flexible to define the details of their own assessment system. That is why the purpose of intercalibration is not to harmonise assessment systems, but only their results.

The intercalibration register of sites

The first step in the intercalibration exercise was to select sites representing ecological status at the boundaries between the “high” and “good” and between the “good” and “moderate” classifications. The selection was made by Member States in 2003 and 2004 on the basis of their understanding of good ecological status. On 19 September 2005, the Commission published the register of sites in a Commission Decision published in the Official Journal of the EU.

Organisation of the work

The intercalibration work is led by the dedicated Working Group on Ecological Status under the WFD Common Implementation Strategy, and the technical work is coordinated by the European Commission’s Joint Research Centre (JRC) in Ispra, Italy. The intercalibration exercise is carried out within 14 Geographical Intercalibration Groups (GIGs). These are groups of Member States that share ecological types of rivers, lakes and coastal/transitional waters, and can thus compare monitoring results between themselves. Examples of river, lakes and coastal GIGs are “Mediterranean rivers”, “Northern lakes” or “North-East Atlantic”. More than 500 experts from all 28 Member States, and Norway, are actively participating in the work.

Results of the intercalibration exercise

To define “good ecological status”, the intercalibration exercise defines the upper and lower boundaries of good ecological status, i.e. the “high-good” and the “good-moderate” boundaries. The outcome of the intercalibration exercise establishes the boundaries of good ecological status applicable to all national classification systems.

The intercalibration is carried out at the level of the biological quality elements, comparing the classification results of the national monitoring systems for each biological element and for each common surface water body type among Member States within the same GIG. Some biological quality elements that have been intercalibrated are e.g. macroinvertebrates in different types of rivers or phytoplankton in different types of lakes. 

Two phases of intercalibration exercise have been completed and their results were published in a Commission Decision of 20 September 2013 published in the Official Journal of the EU.

In these two phases of intercalibration it was not possible to intercalibrate all biological quality elements in all water categories. The existing gaps are due mainly to the lack of development of WFD compliant national assessment methods and the lack of data for some quality elements, especially in transitional and coastal waters. The intercalibration exercise will therefore be continued in a third phase in order to achieve comparable and WFD consistent class boundaries for all biological quality elements by end 2016. This will also allow for these results to be included in a new Decision and to be used in the third river basin planning cycle.

More information

You can also read about this process in Water note Waternote 7 : Intercalibration - a common scale for Europes waters

The JRC CIRCA Information exchange platform provides more technical information on the intercalibration exercise.

Among others, the following documents can be downloaded from there:

This is the first Guidance Document on Intercalibration produced in 2003. It sets out the principles for developing the exercise and explores possible problems and solutions. Guidance is also given on the selection of sites to form the intercalibration network.

This document contains descriptions of the agreed common intercalibration types of rivers, lakes, and transitional and coastal waters, as well as the pressures, and quality elements that will be subject to intercalibration. It describes how the Geographical Intercalibration Groups (GIGs) will be organised, specifying which type is present in which country.

This guidance document follows on from Intercalibration Guidance Document No. 6 by providing an overview of the key principles of the intercalibration process, and the options for carrying out the exercise. It summarises what should be in the final intercalibration report, explains how to organise the work, and gives the required timetables. The document also includes a framework for deriving class boundary values consistent with the WFD normative definitions, as this is the precursor of the Boundary Setting Protocol that is used by the GIGs.

This document contains a detailed analysis of the final register of sites as published in the Commission Decision of 19 September 2005 (see above).

This draft technical document serves as a template for reporting the boundary setting work within the GIGs. It will be reviewed in the light of conclusions from the first GIGs applications in 2006.