Impact of anthropogenic transformations on the vegetation of selected abiotic types of rivers in two ecoregions (Southern Poland)

The quality of water in rivers is declining worldwide due to anthropogenic activities. This phenomenon may be exacerbated by climate change and population growth. We hypothesised that both physical and chemical parameters of water, which reflect the differences in the underlying geology and anthropogenic transformations, are the most important characteristics to explain the distribution of macrophytes in rivers. In the present study, we analysed the effect of anthropogenic transformation on the structure of macrophytes in eight rivers within the river basins of the Vistula and Oder Rivers (Southern Poland). A canonical correspondence analysis showed that conductivity, altitude, natural features of rivers and adjacent land use, which are indicated by the values of the Hydromorphological Diversity Index (WRH), and medium sand were the most important factors that affected the distribution of macrophytes. The eurytopic species, including invasive alien species, were negatively correlated with the WRH index and positively correlated with high conductivity. An increase in the conductivity led to a loss of vegetation diversity and caused the replacement of freshwater species with brackish or salt-resistant species. Salinity of 2.96–5.16 PSU decreased the number of macrophyte taxa by over 30% in the rivers as compared to salinity of 0.45–0.64 PSU. Because very few studies have investigated the effect of salinity on macrophytes, further research is needed to explain this phenomenon. We therefore suggest extensive use of hydromorphological indices in studies on the distribution of macrophytes in rivers.