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)

Table 2 (continued) 1992 1995 1996 1997 1998 1999 Nitzschia inconspicua Grun. 3 Nitzschia levidensis (W. Smith) Grun. 1 Nitzschia linearis (Agardh) W. Smith 2 2 1 4 Nitzschia palea (Kütz.) W. Smith 2 2 6 Nitzschia pellucida Grun. 1 Nitzschia recta Hantzsch 1 1 3 1 5 Nitzschia sigmoidea (Nitzsch) W. Smith 1 Nitzschia sinuata var. delongei (Grun.) Lange-Bert. 1 Nitzschia sinuata var. tabellaria (Grun.) Grun. 1 Nitzschia sublinearis Hust. 2 Nitzschia small 1 1 2 2 6 Nitzschia sp. (spine-like) 1 1 Pinnularia viridis (Nitzsch) Ehr. 1 Pinnularia sp. 1 Rhoicosphaenia abbreviata (Agardh) Lange-Bert. 4 4 3 1 2 Rhopalodia gibba (Ehr.) O. F. Müller 4 and Cocconeis placentula. Almost every sample contained a few valves belonging to Centrales. We gave constancy 4 Gomphonema parvulum and Amphora pediculus. The following 8 taxa had constancy 3: Cymbella silesiaca, Fragilaria capucina var. mesolepta, Fragilaria ulna, Navicula cryptocephala, Rhoicosphaenia abbreviata, Fragilaria ulna var. acus, Nitzschia frustulum, and Nitzschia dissipata. Naturally most taxa (82 by number) had constancy 1; 14 of these occurred in two samples, and 37 taxa were found only in one sample. On Figure 3 we present the result of PCA. The isolation of the samples collected in 1999 is conspicuous. The biplot clearly shows that Cocconeis placentula, Navicula cf. saprophila and Achnanthes hungarica caused this isolation. Cocconeis placentula is a very common, well known species all over the Danube. Its abundance increases usually from spring to autumn (BUCZKO 2001). Recently in a side arm of the Danube at Soroksár the abundance of the Cocconeis placentula on reed was also studied by Szabó et al. (SZABÓ et al. 2001). They found that the abundance of Cocconeis placentula increased from the water sur-