Distribution of epilithic diatoms in the Savinja River flowing through an urban landscape

The catchment area in urban and agricultural landscapes is greatly influenced by human activities that reflect also in physical and chemical characteristics of water as well as in species diversity in waterbodies. The diversity and the species composition of epilithic diatom communities in the Savinja River, as well as basic environmental parameters were analysed. Sampling sites were selected in reaches subjected to different influences from the catchment area and with different physical and chemical characteristics. Samples were collected at the site where the Savinja River enters the urban area of the town Celje, at the end of urban landscape and downstream of the Celje waste water treatment plant outflow. The most common and dominant diatom species in the periphyton community was Achnanthes biasolettiana. Other common diatom taxa that were found in all samples and at least in one sample exceeded relative abundance of 10% were Nitzschia fonticola, Amphora pediculus and Nitzschia dissipata. The results of the redundancy analyses (RDA) revealed that the variance of the epilithic diatom community was explained by O2 saturation (35%) and saprobic index (33% of TVE). Diatom species richness was positively correlated with O2 saturation. Shannon-Wiener diversity index was positively correlated with saprobic index values based on all algae and trophic index calculated on the base of diatoms indicating a relatively low organic matter and nutrient input into the river system. The results showed that no significant changes in epilithic diatom species composition and no negative impacts on diversity of epilithic diatom community in the Savinja River were detected on its flow through the urban landscape. Moreover, changes between the seasons were more evident than changes between sampling sites, confirming the importance of sampling date for monitoring.