Invertebrate Monitoring

To assess the ecological health of the invertebrate communities in a river, samples are collected using a standardised method and the organisms found are identified to the level of taxonomic family or species.

In addition, the approximate abundance of each group found in the sample is also recorded and this combined data is used to calculate so‐called biotic indices, which are used to draw conclusions about the condition of the river and to make comparisons between sites on the same or different rivers.

For their statutory assessments of river condition for the EU Water Framework Directive, the resulting data is entered into a software package called the River InVertebrate Prediction and Classification System (RIVPACS), which was developed by the Institute of Freshwater Ecology (IFE).

The RIVPACS package takes physical and geographical information recorded about the sample site and makes a prediction of the invertebrate assemblage that is ‘expected’ to occur in a river of that type in that geographic location. This predicted score is then compared with the score that was actually recorded from the river sample taken to calculate the Ecological Quality Ratio (EQR) for the site. The EQR score is then used as an indicator of the ecological health of the river for its Water Framework Directive (WFD) invertebrate classification.

The current biotic index used for the WFD Invertebrate Classification is termed the ‘average score per taxon’ (ASPT) index. The power of invertebrate assessment as an indicator of river condition and for identifying what pressures are causing aquatic ecosystem degradation, has, in recent years, been further increased by the development of several new indices. These indices, which include the Proportion of Sediment‐sensitive Invertebrates (PSI) index and the SPEcies At Risk from Pesticides (SPEARPESTICIDES) index, allow the impacts of these specific pollutants on the invertebrate communities living in the river to be evaluated.