Diatom diversity and ecological status of the Lasovacka and Lenovacka streams near Zajecar: consideration of WFD implementation in Serbia

The development and improvement of the monitoring system of rivers according to the requirements of the Water Framework Directive (WFD) is essential for all European states because assigning a wrong ecological status class (misclassification) to a water body can have significant economic consequences. In order to point out some of the key issues of WFD implementation in Serbia, we conducted a one-year study of the composition and abundance of diatoms in the phytobenthos in two streams, the Lasovacka and Lenovacka, in eastern Serbia. The physicochemical quality elements were also used in the assessment of their ecological status. The diatom community exhibited a higher species richness in the Lasovacka (88 taxa) than in the Lenovacka stream (63 taxa). Such a detailed study enabled us to record some of the rare taxa, e.g. Caloneis budensis in the Lasovacka, which was the first finding of this species in Serbia. The Lasovacka and Lenovacka streams were downgraded to moderate and poor ecological status, respectively, because of the high nitrogen load. Since the monitoring results based on the diatom indices resulted in the assignment of two streams to a good ecological status, the possible reason for the mismatch between the biological and physicochemical quality elements could be due to the lack of analysis of benthic invertebrate fauna or the application of diatom indices that are insufficiently sensitive to the specific environmental pressure. The results of this study show that conducting a comprehensive ecological investigation of rivers within the framework of the WFD in Serbia is urgently needed