Vegetation of running waters in Southwestern Germany—pristine conditions and human impact

Abstract

Summary The aquatic vegetation of 44 calcareous streams of a moraine (Oberschwaben) and a Karst landscape (Schwäbisch Alb) in Southwestern Germany, encompassing approximately 10 000 km2, was mapped from 1987 to 1990. A DCA-ordination revealed floristic differences between the “Oberschwaben” streams and the “Schwäbisch Alb” streams. The main differences found were as follows: Groenlandia densa and Hippuris vulgaris occurred in many of the upper reaches and sources of Karst streams but were almost completely absent from the “Oberschwaben” streams. Elodea canadensis, Zannichellia palustris and Potamogeton pectinatus were abundant in most of the moraine streams but were uncommon in the Karst streams. The Danube was characterized by the dominance of Ranunculus fluitans and the sparse occurrence of rhitral species. A comparison of the present vegetation patterns with patterns recorded prior to the 1960's revealed a considerable change on a landscape scale. Species richness decreased in most of the streams and stream sections. Zannichellia palustris and Ranunculus trichophyllus x fluitans expanded their distributions, whereas other species, particularly broadleaved pondweeds and Hippuris vulgaris, showed a strong decline. These floristic changes were brought about by the extensive eutrophication of most of the running waters in the 1960's and early 1970's and partly by channelisation, which was carried out mainly in the early 20th century.