THE ASSESSMENT OF WATER-QUALITY IN THE ARTOIS-PICARDIE WATER BASIN (FRANCE) BY THE USE OF DIATOM INDEXES

The performance of six diatom indices to evaluate water quality has be en studied in the Artois-Picardie water basin. Results show that all o f them satisfactorily assess organic pollution which is the main pheno menon responsible for the degradation of water quality throughout the year. However, only the Specific Pollution Sensitivity Index (SPI), th e Generic Diatom Index (GDI) and the Commission of Economical Communit y Index (CEC) show significant correlations with the ionic strength (e xpressed by chlorides, sulphates and conductivity) and eutrophication (expressed by chlorophyll and nitrates). Diatom indices do not integra te chemical parameters in the same way. Best correlations are obtained through simultaneous or average chemical analyses whereas for other p arameters, best correlations are noted with chemical analyses carried out just before diatom sampling. Tests performed on different chemical data sets show that it is possible to make a realistic estimation of water quality during the summer in the Artois-Picardie water basin by using SPI in September.