COMPARATIVE PERFORMANCE OF BENTHIC DIATOM INDEXES USED TO ASSESS RIVER WATER-QUALITY

The performance of five types of benthic diatom index (four quantitati ve methods and a zoning system) to evaluate water quality was tested i n rivers in England and Scotland. Significant correlations were observ ed between the four quantitative indices examined. In the case of SPI (Specific Pollution sensitivity Index) and GDI (Generic Diatom Index), over 80% of the variation in GDI was explained by a bivariate regress ion on SPI. Samples taken from six sites at four different times of ye ar showed no significant influence of season on any of the indices. Th e zoning system led to a similar assessment of organic pollution as th e SPI and GDI indices, but it was sometimes difficult to determine the zone. This method showed no obvious advantages over the quantitative indices. The high correlation between values for indices based on spec ies and those on genera suggests that for routine monitoring, recognit ion to the generic level is adequate.