Distribution of the Macrophyte Communities in the Danube Reflects River Serial Discontinuity

Abstract

The Danube is the second-longest river in Europe that is subjected to various man-made alterations, including those related to hydro-power plants. We surveyed and analyzed the presence and abundance of macrophytes in the main channel from 2582 river kilometers (rkm) to 171 rkm. We also assessed selected habitat parameters in the sampled river stretches. Sixty-eight different plant species were recorded along the entire course. Among neophytes, we found Elodea nuttallii, E. canadensis, Vallisneriaspiralis and Azolla filiculoides. Based on similarity analysis, we distinguished 15 plant communities, most of which were defined as associations, which were classified into 5 alliances and represented three vegetation classes, namely vegetation of rooted hydrophytes Potamogetonetea, the vegetation of pleustophytes Lemnetea and vegetation of marshes Phragmitetea. The number and abundance of plant species, as well as plant communities recorded in single stretches, varied along the course. Canonical correspondence analysis (CCA) revealed that environmental parameters explained 21% of plant species composition. CCA runs with neophytes explained 41% of the variance, and current velocity, water transparency, species number and bank structure were significant variables. The present study revealed that the free-running sections of the river are poor in number and abundance of plant species, whereas impounded reaches mainly show an opposite result.

Hydrology-Shaped Plant Communities: Diversity and Ecological Function

“…Waterlogged or flooded soil can become an inhospitable environment, which excludes the majority of species, while in the remaining species, it triggers the expression of various traits and mechanisms that enable survival despite oxygen shortage in the root zone. In addition, moving water masses as waves or current present a physical factor preventing successful colonization of certain communities [7,14]. Thus, when various factors shaping the plant communities are assessed [6] according to their importance, a hydrological regime often overrides all other environmental factors, also altering the pattern of regionality, which is generally accepted in biogeography [7].…”

“…In addition, moving water masses as waves or current present a physical factor preventing successful colonization of certain communities [7,14]. Thus, when various factors shaping the plant communities are assessed [6] according to their importance, a hydrological regime often overrides all other environmental factors, also altering the pattern of regionality, which is generally accepted in biogeography [7].…”

“…The Danube River is the second-longest river in Europe that is subjected to various human-made alterations, including those related to hydro-power plants. The extensive study of Janauer et al [7] is a unique compilation of knowledge on macrophyte species, aquatic plant communities, and their habitat preferences in the Danube main channel from 2582 river kilometers (rkm) to 171 rkm. The authors recorded 89 different aquatic macrophyte species along the entire course-among them, neophytes Elodea nuttallii, E. canadensis, Vallisneria spiralis, and Azolla filiculoides-and distinguished 15 plant communities, which were classified into five alliances and represented vegetation classes-namely, rooted hydrophytes Potamogetonetea, pleustophytes Lemnetea, and helophytes Phragmitetea.…”

The Danube: On the Environmental History, Present, and Future of a Great European River

“…Higher plants (11-28% cover) are mostly restricted to impounded sections, and in the lower Danube sections, primarily submerged-floating and free-floating plants were found due to lower transparency and flow velocity (Sommerwerk et al 2009). The distribution of macrophyte communities is related to engineering measures and differences in river streteches (Gyosheva et al 2020, Janauer et al 2021. Recent surveys provide an overview on wetland macrophytes in the Danube Delta (Niculescu et al 2020).…”

Distribution of Vascular Plant Communities in Slovenian Watercourses

“…500 m intervals. A similar approach, but with 1000 m stretches, was used in the macrophyte survey of the Danube River [48]. Macrophyte surveys were performed from the bank of the stream, by wading in the stream or from a boat, using a rake with hooks.…”