Diatom assemblages and water quality assessment in the Duero Basin (NW Spain)

Abstract

n order to determine water quality status in the Duero basin (NW Spain), epilithic diatom samples were collected and analyzed in 137 stations in August 2004 following normalized standard protocols. The floristic particularities of the diatom assemblages in the basin are discussed. A total of 429 diatom taxa were identified in the basin and 90 taxa (21%) were new for the Iberian Peninsula. Especially noticeable was the presence of Achnanthidium rivulare, only known until now from North America. Ordination revealed the existence of five species assemblages related t 3-o the following environmental factors: 5-Day Biochemical Oxygen Demand (BOD ), [PO ], and conductivity. Light and scanning electron microscopymicrographs are provide5d for s 4ome common, infrequent or exotic diatom species present in the Duero basin. Three diatom indices (Specific Pollution Index SPI, European Index CEC and Biological Diatom Index BDI) were applied. All of them correlated significantly with water physical and chemical variables, but SPI achieved the best correlations, and is therefore recommended as the reference diatom index for this Mediterranean basin.