1. Macro-invertebrate species lists were obtained for 268 sites on forty-one river systems throughout Great Britain by qualitative sampling in spring, summer and autumn. Information on twenty-eight environmental variables was also collated for each site. The sites were ordinated on the basis of their species content using detrended correspondence analysis (DCA) and classified by two-way indicator species analysis (TWINSPAN). Correlation coefficients between ordination scores and single environmental variables indicated that Axis 1 distinguished between types of rivers and Axis 2 reflected variation along the length of rivers. A preliminary classification of sites into sixteen groups has been proposed, together with a key which allows new sites to be classified. Information on the species and environmental features which characterize each group is also presented.2. Multiple discriminant analysis (MDA) was employed to predict the group membership of the 268 sites using the twenty-eight environmental variables. 76.1% of sites were classified correctly. An independent assessment of predictive ability using forty test sites yielded a 50% success rate. Predictive ability was higher for the classification presented in this paper than in fifteen additional classifications produced using data from single seasons and/or different taxonomic treatments.3. TWINSPAN and MDA were found to be useful approaches to the classification of running-water sites by their macro-invertebrate fauna and the prediction of community type (as indicated by the occurrence of species in the sites comprising the group) using environmental variables. Extension of the scope of the classification, coupled with the use of additional environmental variables to increase predictive ability, is now in progress.
River InVenebrate Prediction And Classification System (RIVPACS) is a software package developed by the Institute of Freshwater Ecology (IFE) for assessing the biological quahty of rivers in the United Kingdom. The system can be used to generate site-specific predictions ofthe macroinvertebrate fauna to be expected in the absence of major environmental stress. Each prediction is based on a small number of environmental features that are used to characterize the site. The fauna predicted can then be compared with the fauna observed at the same site. This offers a procedure for evaluating biological quality with application in river management both at the local level and for national surveys. Close collaboration between the IFE team and biologists in the water industry during the project had a beneficial influence on the operational development of the system.A second feature of RIVPACS is the national classification of sites, based on the macroinvertebrate fauna. Although the classification is currently a pre-requisite for the prediction system, it also has intrinsic value because newly sampled sites of high biological quality can be placed within the national framework, based on their macroinvertebrate fauna. This facility is of interest to the statutory nature conservation bodies as an element in their site appraisal procedures.The predictive component of the current version of the system (RIVPACS II) was used in the 1990 River Quality Survey to assess the biological quality of almost 9000 sites throughout the United Kingdom. Further developmental work is now under way to provide a more comprehensive version of the system for the 1995 survey.
SUMMARY. 1. A procedure has been developed which uses environmental data to predict the probabilities of macro‐invertebrate taxa occurring at running‐water sites in Great Britain.
2. Biological, physical and chemical data were collected from twenty‐ one sites on three river systems in order to evaluate the procedure.
3. For most sites the number and type of taxa recorded, using a standard sampling programme, were very close to those predicted using twenty‐eight environmental variables.
4. Comparison with other studies at the same sites showed that most taxa whose probability of occurrence was ≥0.5 could be found with more intensive sampling.
5. Reducing the number of variables used in making the predictions from twenty‐eight to five resulted in only a slight loss of predictive accuracy.
6. Combinations of chemical and physical variables gave better predictions than equivalent numbers of physical variables only but the latter may be more appropriate where chemical pollution is known, or suspected to occur.
7. The procedure is of practical value in the detection and assessment of pollution.
8. It may also be used to explore patterns in the structure and functioning of stream communities.
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