L. Forró szerk.: Miscellanea Zoologica Hungarica 9. 1994 (Budapest, 1994)
Csányi, B.: The macrozoobenthon community of the Danube between Rajka and Budapest
MISCELLANEA Tomus 9. ZOOLOGICA 1994 HUNGARICA p. 105-116 The macrozoobenthon community of the Danube between Rajka and Budapest by B. Csányi (Received July 19, 1994) Abstract: The ecological state of the Danube river in the impact area of the Slovakian Hydroelectric Barrage System was studied between 1987 and 1993. As a part of the hydrobiological survey of the water bodies, the macrozoobenthon community was investigated focusing mainly on the faunal description of the upper Hungarian Danube in order to collect basic ecological data. Qualitative community structure data were used for the multivariate analysis to identify characteristic sections of the river. One identical stretch of the upper Hungarian Danube is formed by four sampling sites situated in the Szigetköz area. Gradual increase of laxon number is characteristic downstream until Budapest where the richest community was detected. Key words: macrozoobenthon fauna, community structure, multivariate analysis Introduction The investigated upper stretch of the Hungarian Danube impacted by the Slovakian water barrage system has two different major sections. The Szigetköz flood-plain just after the Hungarian border contains numerous different types of water bodies including the main river arm (50 km) itself. The following Danube River (140 km) has rather uniform large river channel along its whole length with a faster section passing the Visegrád Mountains (Danube Bend) at 60 km upstream of Budapest. The first 50 km section of the main river arm is characterized by strong current and high water velocities, due to larger bed-slope values (20-50 cm/km). An extended side-arm system, developed by river regulating activity, follows the main Danube forming the active flood plain. The side-arms receive direct surface inflow from the Danube only above 2300 m 3 /sec due to the upstream inlets, having stabilized level by rock fill dams. The hydrogeological history of the area and the development of dead arms, old meanders, marshlands, more or less stagnant water bodies due to river engineering is discussed by Göcsei (1979) in details. Channels for irrigation and drainage and gravel mine lakes are isolated by flood protecting embankments from the active flood plain. Their actual water-level and groundwater supply is determined by the hydrological situation. The sharp decrease of the slope after Gönyü results in slower current velocities. In a natural river-bed where dredging and bank protection works take place nowadays, regulation and stabilization of the original channel was carried out during the last century.
