The aim of the research was to determine the abundance and distribution of macrophyte taxa in the Ljubljanica River. Field work was performed in August 2019, when macrophytes were optimally developed. We divided the river into 19 sections. In each section we measured physical and chemical parameters, assessed environmental parameters of the ecosystem and assessed presence and abundance of macrophyte taxa. We also collected water samples for chemical analysis in the laboratory evenly along the river at 12 sites. The abundance of macrophytes was evaluated according to the Kohler 5-step scale, and the environmental parameters were evaluated using the Slovenian version of the Riparian, Channel and Environmental (RCE) method. Habitat parameters were evaluated only in sections where water samples were also taken. We determined the amount of orthophosphates, nitrates and ammonium in the water samples. Analysis of nutrients was performed in the laboratory at the Department of Ecology and Environmental Protection. We recorded 34 macrophyte taxa in the river, which were distributed differently along the Ljubljanica River. The dominant taxa with the highest abundance were Callitriche sp., Elodea canadensis, and Sparganium emersum. The abundance and diversity of macrophytes decreased because of the changes in environmental parameters in the lower part where the Ljubljanica flows through the city of Ljubljana. The river bed through Ljubljana is channelled, the banks are modified, and the riparian vegetation is removed. According to the RCE, environmental conditions are degraded along the river and the most degraded sections are located in the city Ljubljana.
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