Original paper

Benthic diatom flora in a small Hungarian tributary of River Danube (Rakos-stream)

Szabó, Katalin; Kiss, Keve T.; Ector, Luc; Kecskés, Mihály; Ács, Éva

Abstract

The Rákos-stream is a small stream near Budapest (Hungary). The water of the stream is considerably polluted with communal and industrial wastewaters. In May and September 2001 benthic diatom samples were collected along the stream, in May from the surface of available water plants and gravel. In September samples from the side of the concrete bed of the stream were also gathered. Diatoms were identified and their relative abundances were determined in each sample. The diatom indices SLA, L&M, IBD, IPS, EPI-D and CEE were calculated using the software ,,Omnidia", which has been developed in France for the purpose of water quality analysis with benthic diatoms. The Shannon-Weaver diversity values were calculated for each association and the data were clustered by Czekanowski and Jaccard indices. The aim of the study was to draw some conclusions on the water quality and to give a floristical overview of benthic diatom flora, since algological observations were previously not made on this stream.The quality of the water based on benthic diatoms is good near the source of the stream, moderate near the mouth and polluted on the middle reach. The diversity values increase from the source towards the mouth. The cluster dendrograms showed that the similarity of benthic diatom associations is firstly influenced by the sampling point, and then by the seasonality. The sampled substratum has less influence. Some very interesting species for Hungary were found. The planktic centric species Thalassiosira duostra was observed in our samples, in greater individual numbers on the most polluted reaches of the stream. Cyclotella distinguenda was noticed at several points (this is the first occurrence of this species in Hungary). Diadesmis confervacea was identified in some samples (it is the third occurrence of this species in Hungary). This species is supposed to be an invasive diatom, which has until recently been considered as a mainly tropical taxon. Finally, Navicula microrhombus was found in fairly great relative abundance at several points in the Rákos-stream (this is also the first occurrence of this species in Hungary).

Keywords

benthic diatomstaxonomical compositiondiversityrelative abundancewater quality