Impact of urbanization-driven changes of the riverbeds on its ecological status evidenced by diatom communities – The negative side of the Anthropocene

Abstract

Hydromorphological transformations, which are characteristic of the Anthropocene epoch display a strong negative impact on urban water ecosystems. Therefore, there is a need to take action to minimize their negative effect when planning spatial development of urban areas. Interference in the natural course of a river alters its conditions and harming aquatic organisms. Our study concerned the assessment of differences in the structure of diatom communities between transformed streams and the river located outside the city, with unaltered hydromorphological conditions. The analysis of physicochemical parameters of studied streams revealed that the reference river located outside the urban area is characterized by stable physicochemical parameters along its flow, whilst urban streams display moderate differences related to the degree of transformation. The biodiversity assessed by the Shannon and Simpson indices of transformed rivers displayed significantly lower values when compared with the river located outside the city. Furthermore, the nMDS analysis showed differences in diatom communities related to the degree of stream transformation, but PCA analysis identified additionally pH reaction, DOC, and N-NO3- concentration as the main factors responsible for the discrimination of compared diatom communities. On the other hand, two-factor PERMANOVA on combined environmental data, i.e., sampling location and degree of hydromorphological transformation confirmed statistically significant differences between analyzed samples. Hydromorphological modifications influenced diatom biodiversity, what reflected in the ecological status of streams. The negative impact of anthropogenic changes on aquatic ecosystems was best assessed by the IPS index, which assigned urban streams' ecological status from poor to bad level. The assessment of the negative impact of hydromorphological transformations of urban streams on their ecological status is visible by comparing them with the reference ecosystem. This allows us to determine the direction for the regeneration of urban streams. Restoration procedures will not return a heavily degraded river to its natural state immediately but knowing the degree of difference from the reference state can minimize them.

Keywords

• Anthropocene
• Hydromorphological transformation
• Urban area
• Diatoms
• Bioassessment