Rivers are spatially and temporally heterogeneous systems susceptible to changes caused by anthropogenic influences. These can significantly alter water quality and river communities, including macrophytes, which are involved in nutrient cycling, energy flow and sedimentation processes and provide habitats for other organisms. The presence, abundance, and distribution of macrophytes can thus serve as indicators of the state of aquatic ecosystems. Rivers that flow (partly) underground are particularly susceptible to (human) impacts from the hinterland due to their lower self-purification capacity. Using a modified RCE (Riparian, Channel, and Environmental Inventory) method, we classified the sections of the Rak River as first or second RCE quality class, and the sections of the Obrh River as second or third RCE quality class. According to the River Macrophyte Index (RMI), the ecological status of the sections of both rivers was assessed as moderate, good or very good, except for the first section of the Obrh, the status of which was assessed
as poor. The ecomorphological preservation of both rivers and suitable conditions for macrophyte growth contribute to the high species diversity observed in both rivers: a total of 36 taxa were recorded in the Obrh and 38 in the Rak. In the latter, the presence of Myriophyllum verticillatum L. was recorded for the first time. Almost a third of the species present in each of the rivers are listed on the Slovenian Red list of threatened pteridophytes and seed plants, which supports the evidence of their high naturalness and underlines the importance of appropriate management of karst watercourses.
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