A generic index of diatom assemblages as bioindicator of pollution in the Keelung River of Taiwan

The Keelung River (Taiwan) is heavily polluted by domestic, industrial and agricultural wastes. Water quality, particularly in ammonium, nitrite, silicate, and turbidity, negatively correlated with dissolved oxygen. A generic index (GI) – the ratio of abundance of Achnanthes, Cocconeis and Cymbella, to that of Cyclotella, Melosira and Nitzschia – was used to measure changes the diatom assemblages. GI values correlated well the saprobic index, diatom assemblage index, composite river water quality index and species richness of insects. It correlated less well with the trophic diatom index and distribution of fish in the river, suggesting that GI was more indicative of organic pollution than of eutrophication. Data from two of other Taiwanese rivers were used to test the applicability of GI. As in the Keelung River, GI correlated well with the saprobity index, diatom assemblage index and river water quality index.