Methodology

3.1.     Basis for classification of ecological status

3.1.1.      Principles on classification of ecological status or potential

The WFD defines “good ecological status” in terms a healthy ecosystem based upon classification of the biological elements (phytoplankton, phytobenthos, benthic fauna and fish) and supporting hydromorphological, physico-chemical quality elements and non-priority pollutants. Biological elements are especially important, since they reflect the quality of water and disturbance of environment over longer period of time. The ecological status is reported for each water body. Water bodies are classified by assessment systems developed for the different water  categories (river, lake, transitional and coastal waters) and  the different natural type characteristics within each water category..

WFD has different requirements for natural waters and for artificial or heavily modified waters. ‘Artificial water bodies’ are those, created by human activity (e.g. an artificial lagoon in the area where there was naturally no water before). ‘Heavily modified water bodies’ (HMWB) are waters, where significant human induced physical alterations have changed  of their hydro-geomorphological character to the extent that habitats are negatively affected (e.g. large harbours, hydropower reservoirs, major reductions of natural river flow, etc.). For natural water bodes the ecological status is standard for classification, while for heavily modified and artificial water bodies the ecological potential should be determined. Member States will need to meet the good ecological potential (GEP) criterion for ecosystems of HMWBs and AWBs rather than good ecological status as for natural water bodies.  The objective of GEP is similar to good status but takes into account the constraints imposed by social and/or economic uses. 

The ecological status classification scheme 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 in order to take into account the broad variation of ecological conditions in Europe.

The Directive requires that the overall ecological status of a water body be determined by the results for the biological or physicochemical quality element with the worst class determined by any of the biological quality elements. This is called the “one out - all out” principle.

At “good” ecological status, none of the biological quality elements can be more than slightly altered from their reference conditions. At “moderate” status, one or more of the biological elements may be moderately altered. At poor status, the alterations to one or more biological quality elements are major and, at bad status, there are severe alterations such that a large proportion of the reference biological community is absent.

The class boundaries for the biological classification tools are expressed as ecological quality ratios (EQRs). EQRs are a means of expressing class boundaries on a common scale from zero to one. The boundary EQR values represent particular degrees of deviation from the corresponding reference values. High status is represented by values relatively close to one (i.e. little or no deviation) and bad status by values relatively close to zero (i.e. substantial deviation).

The process of ecological classifications is described in Figure 3.1.