A computer-based development of the Biological Monitoring Working Party score system incorporating abundance rating, site type and indicator value

A method of deriving BMWP (Biological Monitoring Working Party) scores and indicator values that incorporates the effects of abundance rating and site type is presented. This is an extension of earlier work by the authors, which reappraised overal BMWP family scores using biological data from the 1990 River Quality Survey of England and Wales. The method is only briefly explained but its formulation in mathematical terms is fully documented. Full details are given of the overall, site-related and site-abundance-related derived scores and indicator values of 34 selected families. New definitions of average score per taxon (ASPT) based on the derived scores and indicator values are presented, and the potential impact of these on existing BMWP site scores and ASPTs is briefly examined via two examples. Some interesting variations in the derived scores with respect to site type and abundance rating are noted, and explanations of these are given from an ecological point of view. It is concluded that the method described offers a means of significantly improving the reliability and hence utility of the BMWP score system.