We studied the structure and population dynamics of zooplankton assemblages in the water bodies (eu-, para-, plesiopotamal and conjunctive water bodies) of a temperate floodplain during flood events. Here we report differences in the species composition of these water bodies in the two stages of flood pulses: rising vs. receding. During the receding period the proportion of larger and tychoplanktonic species increased. Similarity among zooplankton assemblages of these floodplain water bodies increased during the rising and decreased during the receding period. Species richness, diversity and population density values of zooplankton assemblages increased during the receding period in all types of water bodies except the eupotamal. The guild ratio of rotifer assemblages showed characteristic, but somewhat ambiguous changes. We conclude that the hydrological regime affects the structure and dynamics of zooplankton assemblages on the floodplain. IntroductionSpatial and temporal variability induces high productivity and biodiversity in terrestrial and aquatic components of the river-floodplain systems (SHIEL et al., 1998;ARMITAGE et al., 2003). Understanding the ecological functions of natural river-floodplain systems is important to establish criteria to protect the biota of these sites (BERCZIK and BUZETZKY, 2006). Introduction of the Flood Pulse Concept (JUNK et al., 1989) stimulated renewed interest in the connection between large rivers and their floodplains; since then numerous studies have focused on the zooplankton of large rivers. These efforts have indicated that inshore retention and hydrological connectivity are a major determinant of zooplankton assembly (HEIN et al., 1999;BARANYI et al., 2002;RECKENDORFER et al., 1999;ZIMMERMANN-TIMM et al., 2007). In contrast, most hydro-ecological research projects on large rivers and their floodplains focus just on fish and/or benthic invertebrate assemblages, thus neglecting the importance of zooplankton communities in the food-web of river-floodplain systems. Concomitantly an assessment of their suitability as a biomonitoring tool is also neglected (BORJA et al., 2008;RESH, 2008

The Gemenc floodplain of the Danube possesses numerous side arms and backwaters. The aim of my study was to explore connections between hydrological events and diversity patterns of the planktonic rotifer assemblages of these water bodies. During the study period (2002)(2003)(2004)(2005)(2006)(2007)(2008) 75 taxa of rotifers were found. Generally, the water bodies of the floodplain had more diverse rotifer assemblages than the main arm. At low and medium water levels diversity was highest in the parapotamal water bodies. This result may be explained by the intermediate disturbance hypothesis. At high water levels the highest biodiversities shifted to the plesiopotamal. Biodiversity, dominance, and evenness correlated with water flow and temperature. Patterns of biodiversity seem to be determined by the water level of the main arm; therefore the water regime appears to provide pronounced temporal variability in the hydro-ecology of the floodplain.

13In forested floodplain ecosystems, leaf litter represents an important energy source for aquatic 14 organisms, and its decomposition is a key ecosystem process. In this paper, we investigate the