4.2 Biological assessment of river quality

4.2 Biological assessment of river quality

Almost all aquatic plant or animal communities, be it micro- or macroscopic, may provide information on the quality of its environment. The community most commonly used in river quality investigations is that of the larger readily visible invertebrate animals colonizing the substrata of all rivers; such animals are collectively referred to as macroinvertebrates of which the main constituents are young aquatic stages of insects. Within this bottom dwelling community the sensitivity and tolerance to pollution of the various constituents vary considerably from species to species. Some species are, for example, very sensitive to reductions in dissolved oxygen and will not be found in areas where oxygen levels are not consistently high. A characteristic feature of polluted environments is a reduction in overall community diversity and an increase in the density of tolerant species. The composition of a macroinvertebrate community at any point in a river therefore reflects the average water quality at that particular point. For this reason macroinvertebrates are widely used in the assessment of river quality.

In the European countries there is a long tradition for assessment of river quality on the basis of macroinvertebrate studies. However, these assessments have primarily been made by local organizations responsible for managing and monitoring specific rivers. In some countries these activities have developed into national surveys of the biological quality of the main rivers (Table 4.2.1). These national surveys are generally based on the results collected by local authorities in accordance with harmonized and standardized procedures (eg. sampling methods, criteria for site selection, classification schemes, etc.). Most of the other countries do not have separate national monitoring programmes for biological assessment of river quality (Table 4.2.1). In some countries macroinvertebrate studies are, included in the general chemical river monitoring programme, macroinvertebrate investigations being, however, restricted to relatively few sampling sites.

Table 4.2.1: Biological assessment of river water quality

National surveys to assess the biological quality of rivers

The specific biological monitoring surveys are usually made in connection with national classification of river quality. Austria, Germany, Luxembourg, Ireland and the United Kingdom have assessed rivers quality at two to five year intervals since the 1970s, while Belgium and Spain initiated similar activities in the 1980s. In 1992, the Netherlands added a biological subprogramme to their inland water monitoring programme MWTL and since 1989 Denmark has annually been collecting all the biological classification grades from the Danish counties. In Portugal, biological assessment (Saprobic system) is undertaken in a number of separate investigations.

Table 4.2.2: National river monitoring programmes based on assessment of biological river quality.

MINVERT: studies of macroinvertebrate community; MiFAUNA: microfauna; MiFLORA: microflora; MAPHYT: macrophyte

The established monitoring networks generally include numerous sampling sites. The UK network and the Irish network, for instance, include around 10,000 and 3,000 sampling sites, respectively. Sites are generally located in all main rivers and reflect the full range of quality conditions of each particular river. The sampling methods used differ and sampling frequency varies among the countries (Table 4.2.2). Additional information on the various methods used for river quality classification can be found in Newman (1988), who made a more comprehensive evaluation of the different classification schemes used in the EU Member States.

In the UK and Germany local authorities, ie. the National River Authority regions and River Purification Boards in the UK, and the Länder in Germany, do the actual sampling and analysis, and special, organised task forces collect the summary results from the local organizations for national evaluation and reporting. In Ireland, by contrast, the biological assessment monitoring programme is carried out by one institution, namely the Environmental Protection Agency. The results are generally published in the form of reports including tables listing the length of rivers assigned to the various grades and river quality maps.

Biological assessment in connection with general national river monitoring programmes

The biological assessment in connection with general river monitoring programmes (eg. AU-R1, DK-R1, FR-R1, and SE-R2/R3) includes one or two annual investigations of macroinvertebrate communities at fixed sampling sites (Table 4.2.3). Additionally, some monitoring programmes include studies of periphyton, macrophytes and fish.

Table 4.2.3: Biological assessment of river quality in connection with general national river monitoring programmes.