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3.1.3 RIVPACS prediction of indices

If you can predict the invertebrate community (ie species and actual value of the index. The same proportional reduction
their abundances) using RIVPACS, you can predict the value in index value represents the same level of damage,
of biotic indices. Indeed, early versions of RIVPACS did that whatever the actual index value or river type. Because
literally by calculating the predicted value of indices from the the River Communities Project was based on unpolluted
predicted list of species (or the families that they belonged ‘natural’ rivers, chosen to be the best examples of their
to) and their abundances. The current version of RIVPACS type, RIVPACS would be capable of predicting the value
does this directly, see Section 3.2. of biotic indices expected under natural, un-impacted,
conditions. Because the environmental data that was
In 1979, the Biological Monitoring Working Party concluded collected described the natural abiotic conditions of the
that predictions from RIVPACS could be used to overcome site, predictions from RIVPACS are site-specific.
the problem of reporting invertebrate quality in different
rivers in a comparable way for the national river quality Biotic indices expressed as the proportional fraction or
surveys. A biotic index expressed as the fraction of the ratio of observed value to predicted value are known as
value that it should have under natural conditions would be O/E values or EQIs (Environmental Quality Indices):
comparable regardless of the impact of river type on the

observed value of index
EQI =
value of index predicted by RIVPACS

The same value of EQI represents the same degree of degradation in the biological community, regardless of stream type.
Unfortunately, RIVPACS was not sufficiently developed for it to be used for the 1980 national river quality survey, the results of
which were reported as plain BMWP-scores (Figure 3.6). It was not until the 1990 survey that RIVPACS could be used.

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