COMMUNITY COMPOSITION AND SENSITIVITY OF PERIPHYTON TO ATRAZINE IN FLOWING WATERS - THE ROLE OF ENVIRONMENTAL-FACTORS

The relationship between environmental variables, community compositio n and the sensitivity of periphyton on artificial substrata to the her bicide atrazine (EC50 values obtained by concentration-effect curves o f photosynthesis to atrazine) was studied for 20 stream and river site s on a latitudinal gradient across Europe (Sweden, The Netherlands, Sp ain). Sensitivity to atrazine was higher in the Swedish than in the Sp anish or Dutch sites. Direct gradient analyses were used to relate dia tom taxa and algal groups with environmental variables. A first redund ancy analysis (RDA) based on diatom taxa showed a pollution gradient ( atrazine and nutrient concentration) associated to diatom taxa that ar e indicators of different degrees of pollution. A second RDA based on algal groups showed that diatom-dominated communities corresponded bot h to sites at higher altitudes and less industrialized areas and to si tes with higher atrazine concentration; Cyanobacteria were the most co mmon in industrial areas, whereas Chlorophyceae dominated in sites wit h high water temperature and alkalinity. Linear regression analyses we re applied to find the relationship between the ordination axes obtain ed and the EC50 values. First axes of both RDA showed significant or m arginally significant relationship with atrazine sensitivity. Regressi on analyses for the Spanish sites indicated that the sensitivity to at razine was related with light conditions (EC50 was positively correlat ed with light) and the percentage of different algal groups (EC50 was positively correlated with the percentage of diatoms and negatively co rrelated with the percentage of green algae). The results indicating t hat differences in sensitivity are related to environmental variables such as light, nutrients or atrazine concentration, permitted us to id entify biological indicators of sensitivity to atrazine in lotic syste ms: Bacillariophyceae-dominated periphyton communities were more toler ant than Chlorophyceae and Chrysophyceae-dominated communities. In add ition, diatom taxa found to be tolerant to atrazine in this study have been considered in the literature to be tolerant to organic pollution .