Different impact of flood dynamics on the development of culturable planktonic and biofilm bacteria in floodplain lake

Floodplains are lateral river extensions in which lotic, semi-lotic and lentic habitats are formed resulting in high habitat heterogeniety. Consequently biota development is highely influenced by its location within the floodplain and by the hydrological cycle. In the present paper the development of planktonic and biofilm bacteria associated with artificial substrates were investigated in the floodplain lake of the Danube River (Lake Sakadas, Croatia) during different hydrological situations. The aim of the study was to investigate if there was any difference in the bacterial development between two compartments - plankton and biofilm, and how the floods influence these communities. The samples were taken monthly (July.November 2007) from surface and bottom water layer (plankton) and exposed glass slides (biofilm) at two sampling stations. For these purposes bacterial abundance was estimated by the determination of number of colony forming units (CFUs). The development of bacterioplankton was equal between the sites and had its maximum at the time of falling water after the flood pulse. Bacterioplankton abundance correlated significantly with water properties, and it had predictable dynamics comparable with the previous results established in the same floodplain area (Kopacki Rit). The development of biofilm bacteria differed between the sites, and had its maximum prior to the flood pulse, or during the flood. The abundance of attached bacteria correlated with biofilm biomass while it was not significantly correlated with the water properties. Such results describe different development of planktonic and biofilm bacteria. Biofilm bacteria are more independent, compared to bacterioplankton, from the floodplain hydrology.