`Assessing the biological quality of fresh waters: RIVPACS and other techniques', edited by John F. Wright, David W. Sutcliffe and Mike T. Furse.
`Assessing the biological quality of fresh waters: RIVPACS and other techniques', edited by John F. Wright, David W. Sutcliffe and Mike T. Furse. Published by the Freshwater Biological Association, Ambleside, June 2000. ISBN 0 900386 62 2. 400 pages. Price £40 softback, £60 hardback (including p. & p.).

 

RIVPACS - Calculating Biotic Indices

The expected probabilities of occurrence and expected abundance predicted by the RIVPACS type approach can be used to derive estimates of the expected values of practically any index. The simplest example is the expected number of taxa which is equal to the sum of the site-specific expected probabilities of occurrence (expressed as fraction, not as a percentage) of all the individual taxa.

At present, RIVPACS in the UK predicts the fauna to be expected in a test site, and calculates taxon richness and BMWP-related indices from this information, but RIVPACS is not constrained to calculate only BMWP-related indices; indeed it can calculate many others. By incorporation of carefully selected peer-reviewed indices, and the development of new ones where necessary, RIVPACS could calculate expected values for any index and therefore offer diagnosis of the likely causes of deviation from reference site predictions.

 

New diagnostic indices are being added to RIVPACS at present. Among these are the new AWIC score (Acid Waters Indicator Community) and the LIFE (Lotic-invertebrate Index for Flow Evaluation) score. The existing BMWP-related indices are designed to detect the impacts of organic pollution, while taxon richness is a non-specific index of general deterioration in diversity. The LIFE score will allow for sites that are suffering from persistent low-flows to be identified. The AWIC score will pick out sites with macroinvertebrate communities typical of low-pH waters.

Many scientists in the United States argue that a range of indices provide the best overall assessment of biological water quality. Yet it is clear in the US that, because they do not use a RIVPACS type approach, the behaviour of their indices is strongly influenced by natural physical gradients. Therefore, the addition of more diagnostic indices to RIVPACS probably provides the best of both worlds, whereby diagnostic power is maximised by the use of a variety of indices, but the target value for each index is standardised by stream type specific predictions.