Makrophyten-Verbreitung und Standortqualität im eutrophen Björka-Kävlinge-Fluss (Skåne, Südschweden)

AbstractThe aquatic macrophyte vegetation of the Björka-Kävlinge River (Skåne, South Sweden, Fig. 1) was investigated in 1997 and 1998. By nature, this river has a meso- to eutrophic character. Furthermore, the river has a high structural running water quality and a high species diversity over long distances. Its catchment area is dominated by agriculture and characterized by fertile calcareous soils. 219 river sections of 100–500 m length (overall length 69,950 m = 85.7% of the whole river length) between Vollsjöby and the mouth of the river into the Baltic Sea were cartographically recorded and investigated (Fig. 2).In these sections all vascular hydrophytes, amphiphytes, helophytes and some haptophytes were recorded. For the vegetation survey and evaluation of the results the methods described in Kohler & Janauer (1995) were used. The “index species” of the “limes scanicus” (H. & G. Weimarck 1985) Butomus umbellatus, Sium latifolium and others with their wide area of distribution are characteristic plants for this river type. Some plant species groups, resp. some species, show characteristic distribution patterns in the course of the river: Hildenbrandia rivularis group, Potamogeton lucens group, Zostera marina group etc. Due to the species features a classification of four floristic-ecological river zones was made (zones A to D).The distribution of the macrophyte species was also characterized by a set of quantitative parameters which are “Relative Range Length”, “Average Plant Quantity” and “Average Quantitiy Index”, respectively (Figs. 3–5). Both, the plant distribution as well as the sequences of the floristic zones are less to be seen as a consequence of a trophic gradient, but as a consequence of different river dynamics of velocity of flow, sediment quality as well as of salt water influence. The diagnostic features also served to determine the relation between plant distribution and environmental factors (shading, cattle grazing). Hildenbrandia rivularis mainly occurs in shaded areas, Elodea canadensis in unshaded ones. In sections influenced by cattle tracks there is an increased occurrence of Alopecurus geniculatus, Agrostis stolonifera and Glyceria fluitans.The reasons for the high species diversity of this eutrophic river are a relatively high water quality, a high amount of habitat structures, a variety of vegetational structures and various land use patterns in the surrounding area. Recommendations for the preservation and the improvement of the ecological conditions are made. For the conservation of the biological diversity of the river, hydraulic engineering measures should be avoided. Along considerable river sections suffering from cattle grazing, vegetation could be achieved by partial exclusion of the cattle, and in some sections buffer zones along the river should be established