THE RELATIONSHIP BETWEEN MACROPHYTE VEGETATION AND HABITAT FACTORS ALONG A MIDDLE-SIZE EUROPEAN RIVER POLISH JOURNAL OF ECOLOGY

ABSTRACT: The influence of habitat factors on macrophytes distribution was studied along the Hron river – one of the longest Slovakian rivers (length 298 km; average flow rate – 56 m3 s-1 near the outfall into the Danube) and important tribu-tary of the Danube river. Along the river bed, 19 sections were selected according to approximately regular distances and with and without apparent industrial or agricultural influence. Each river sec-tion was 500 m in lenght, and was divided into 5 subsections with a constant length of 100 m. In each subsection, the abundance of all macrophytes was assessed using a five-level scale, from rare to very abundant (Plant Mass Estimate, PME), and habitat factors were measured or assessed. Only one side of river bed was assessed except the upper part, where plants occur across the river bed and therefore the whole river bed was assessed. PME data were transformed into “plant quantity ” using the function y = x3 (y – “plant quantity”, x – PME; cf. Kohler and Janauer 1995) and their nu-merical derivatives were calculated for each river section. These are: the Relative Plant Mass – RPM (percentage of “plant quantity ” of each species weighted by the river section length, formula (1) and the Mean Mass Total – MMT (index of mean PME of each species with regard to the full length of the river section, formula (2). Species richness of macrophytes (hydrophytes) is low; only 11 spe-cies were found. More than 50 % of river sections contain only filamentous algae, Rhynchostegiu