Analysing benthic macroinvertebrate community changes along a pollution gradient: A framework for the development of biotic indices

The present study used a new model to analyse macroinvertebrate community changes along an organic pollution gradient in the River Trent system, U.K. The model divides community changes into four types, three of which are further differentiated into two sub-types. These type and sub-type variations are of different ecological significance. The results showed that as water quality deteriorated, species loss, the average abundance of sample-specific species and the average maximum ratio of in-common species abundance increased substantially, while the numbers of persisting species were reduced rapidly. However, polluted sites were also found to gain some tolerant species, particularly at slightly polluted sites. The abilities of several commonly used biotic indices to summarise these changes were compared. The design of the Chandler score system appeared to be more effective than the other systems examined. The Chandler-ASPT was modified by multiplying by log S (species richness/the number of key taxa) to improve its sensitivity over the 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.