ANALYZING BENTHIC MACROINVERTEBRATE COMMUNITY CHANGES ALONG A POLLUTION GRADIENT - A FRAMEWORK FOR THE DEVELOPMENT OF BIOTIC INDEXES

The present study used a new model to analyse macroinvertebrate commun ity changes along an organic pollution gradient in the River Trent sys tem, U.K. The model divides community changes into four types, three o f which are further differentiated into two sub-types. These type and sub-type variations are of different ecological significance. The resu lts showed that as water quality deteriorated, species loss, the avera ge abundance of sample-specific species and the average maximum ratio of in-common species abundance increased substantially, while the numb ers of persisting species were reduced rapidly. However, polluted site s were also found to gain some tolerant species, particularly at sligh tly polluted sites. The abilities of several commonly used biotic indi ces to summarise these changes were compared. The design of the Chandl er score system appeared to be more effective than the other systems e xamined. The Chandler-ASPT was modified by multiplying by log S (speci es richness/the number of key taxa) to improve its sensitivity over th e lower range of water quality while retaining its effectiveness over the upper range of water quality. The modified index was tested using a published data set. (C) 1997 Elsevier Science Ltd.