Occurrence and habitat preference of aquatic macrophytes in a large river channel

Abstract

This paper explores correlations between macrophyte occurrence and environmental characteristics recorded in a more than 350 rkm long segment of the main Danube channel in Hungary. The selected river section belongs entirely to the lowland part of the Middle Danube, but it is separated into the mostly gravelly upper and the sandy lower river sections. Two markedly different groups of macrophytes correlated with this separation; the mostly perennial, rooting species (Myriophyllum spicatum, Potamogeton crispus, P. nodosus, P. pectinatus, P. perfoliatus and Zannichellia palustris) preferred the gravelly habitats, while the non-rooting, free-floating macrophytes (Ceratophyllum demersum, Lemna minor, Salvinia natans and Spirodela polyrhiza) occurred mainly in the sandy stretches. Based on current velocity and Secchi transparency, these stretches seemed to provide “more lotic” and “rather lentic” habitats. Data evaluation also revealed that the closer are the river stretches to a water course discharging upstream the more free-floating aquatic plants occur in the main Danube channel.