National river classification schemes

Generic metadata

Classification

Identification

River classification schemes are often designed to give an indication of the extent of pollution. There are many different types of schemes. Some are based solely on chemical and general physico-chemical parameters (for example, pH, dissolved oxygen, ammonium and biochemical oxygen demand), some on biological indices (usually based on macro-invertebrates) and some on a combination. Although all the countries have different schemes they give a general indication of river quality, particularly whether according to a country's scheme there has been an improvement or not.

None of the classification schemes meet the requirements of the water framework directive and hence there is at present no information enabling a direct assessment of the situation in relation to the objectives of the directive. Different types of schemes cannot be quantitatively compared hence Figure 2.2 is divided into three types (biological, physico-chemical, combined). Some countries have more than one national classification scheme and so results for each scheme are shown separately, for example England and Wales has a physico-chemical scheme and a biological scheme. This separation into types of scheme also illustrates that whilst one scheme may show an improvement in quality, another may show deterioration for example, the UK (Northern Ireland) chemical scheme showed an improvement whilst the biological scheme showed a deterioration. This was because the biological scheme reflects a degradation in habitat quality as well as changes in water quality.

The majority of river classification schemes show an improvement in quality reflecting the effects of reduced pollution by human activities on the aquatic environment. Figure 2.3 shows the percentage of rivers classified as less than good. There are large differences with countries such as the Czech Republic, Latvia and Poland having relatively large, and UK relatively small percentages less than good quality. However, there is a wide variation in the length of national rivers included in classification schemes. The average length of river classified was only about 30 % of the total length of river in the country. This means that the real picture can be very different from the one presented here.