B. Papp szerk.: Studia Botanica Hungarica 32. 2001 (Budapest, 2001)

Buczkó, Krisztina; Rajczy, Miklós: Changes of attached diatoms in a dead arm of the Danube between 1992-1999 at Ásványráró (Szigetköz section)

About the effect of duckweed invasion Duckweed often form dense homogeneous mats on the water surface all over Hungary. We failed to find any Hungarian publication about the attached algae on duckweed. It is not too surprising, because the study of periphyton is usually neglected, perhaps partly due to methodological problems. In the case of small plants like duckweed the collection of periphyton is more difficult and the application of usual methods (scraping or brushing the coatings) is impossible. We have not found reports on attached algae living under the duckweed carpet either. GOLDSBOROUGH (1993) studied the diatoms living on common duckweed (Lemna minor) in Canada. In spite of the geographical distance he also found Achnanthes hungarica as a dominant taxon from midsummer to autumn. He established that Achnanthes hungarica was found in more than 90% on the air/water boundary (GOLDSBOROUGH 1993). It would be hard to know whether the occurrence of Achnanthes hungarica (and maybe Navicula cf. saprophila) is connected with the presence and density of duckweed. We know a reference of Hustedt who in the beginning of the 20th century commented on the occurrence of A. hungarica as "anscheinend mit Vorliebe an Lemna" (HUSTEDT 1930). It would also be interesting to explore other water bodies in Hungary and see if duckweed and their algal epiphytes coexist or not. We plan further study in different rivers and lakes in Hungary, where duckweed is common and to study the diatoms living on them. * * * Acknowledgements -The study was supported by the Hungarian Ministry for Environment and Regional Policy. The biomonitoring of the Szigetköz section of the Danube has been co-ordinated by the Expert Group of the Hungarian Academy of Sciences. Thanks to Antal Schmidt for revising the manuscript. REFERENCES ÁCS, E. and BUCZKÓ, K. ( 1996): The changes of relative importance value ofperiphytic algal taxa in Szigetköz section of River Danube (Hungary). - In: BERCZIK, Á. (ed.): 31. Konferenz der IAD, Baja - Ungarn 1996, Limnologische Berichte. Donau 1996, Band I. Wissenschaftliche Referate. MTA ÖBKI Magyar Dunakutató Állomás, Vácrátót/Göd, pp. 441-446. BUCZKÓ, K. (1999): Szemelvények a szigetközi algamonitoring eredményeiből (1991-1998). (Some results of the algological monitoring at Szigetköz (1991-1998).) - In: LÁNG, I., BANCZEROWSKI, J. and BERCZIK, Á. (eds): A Szigetköz környezeti állapotáról. MTA Szigetközi Munkacsoport, Budapest, pp. 79-86.