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)

The algological studies of the Danube river have a long history, marked by results of several authors. Nowadays we have to emphasise the works of K. T. Kiss (e.g. KISS 1999), who especially studies the phytoplankton. E. Acs deals with the periphytic algae of the river (e.g. SZABÓ et al. 2001). A. Schmidt and G. Fehér study the southern stretch of the Hungarian Danube including the side arms (SCHMIDT 1996). E. Tevanné Bartalis published results on the research of algae living in side arms at the Szigetköz before the diversion of the Danube took place (TEVANNÉ BARTALIS 1978). MATERIAL AND METHODS Study area. The Szigetköz is a big island of the Danube, situated in northwest Hungary, where the river enters the Carpathian Basin (Fig. 1 ). This island is bounded by themain arm of the river (Old Danube) and the Moson Danube. It is 52 km long, on average 7-8 km wide and its surface totals at 375 square kilometres. Here the big, quick flowing river is divided into several smaller arms, forming a multiple branch system. The dead arm of our study is situated in the biggest, still existing Hungarian branch system near the village of Ásványráró. It is connected only with a narrow channel to one of the main arms of the branch system. Consequently, it has a direct junction with the flowing water at its lower end but actually the river never flows through it. The Danube is the only river in Hungary that has a complex and extended branch system. Thus the Szigetköz is one of the most remarkable and rare habitats of Hungary. It has been strongly affected by the construction of the Gabcikovo Water Project. N Fig. 2. The detailed map of the Ásványráró branch system with the other sampling points of biomonitoring. The investigated locations in the dead arm are a2 and a3.