Beeinflusst die Strukturgüte von Fließgewässern das Vorkommen von Makrophyten?

Does the Structural Quality of Running Waters Affect the Occurrence of Macrophytes? The morphological structure plays, besides e.g. nutrient concentration, an important role for the integrated assessment of running waters. This paper focuses on the relationship between structural quality and macrophyte vegetation. During summer 2000 structural quality according to LAWA, macrophyte vegetation, and selected habitat parameters were recorded in 135 mapping sections in running waters in Southern Germany. In streams of high structural diversity, generally higher species richness is expected than in rivers of low diversity of habitats. However, no significant differences in macrophyte species richness were detected between different classes of structural quality. In contrast, bryophytes alone showed a significant decrease in species richness with degradation of structural quality. The number of species of other macrophytes increased, respectively. The relationship between occurrence of macrophytes, structural quality, and other environmental variables was analysed using canonical correspondence analysis. Rivers of high structural quality mostly showed high flowing velocities and were heavily shaded. These environmental conditions, which characterize river types of mountainous regions, were predominantly tolerated by bryophytes. Vascular plants and charophytes generally prefer slowly flowing and unshaded habitats. River types exhibiting these environmental conditions often are more influenced by human activities and are more structurally degraded, respectively. With respect to these fundamental differences between river types, species richness of macrophytes and class of structural quality are not correlated when all types of rivers are taken into account. Type‐specific ecomorphological parameters, which conceal the differences in species richness caused by structural quality, are discussed. Structural degraded rivers can provide good environmental conditions for vascular plants and charophytes. To predict macrophyte species richness from structural quality, a differentiation of river types is essential.