WETLANDS ALONG THE RIVER DANUBE – PHYTOPLANKTON DIVERSITY AND ECOLOGY

Biodiversity, management and protection of wetlands (more than 30 wetlands sites) along the River Danube from the Upper Section (Austria) till the Danube Delta (Romania) were analyzed in the frame of the international project BIOWETMAN. The results of the comparative study of phytoplankton showed that phytoplankton biodiversity and seasonal successions varied significantly due to the wetland type. Under highly changeable and unstable conditions in the temporary wetlands (e.g. Murtvo Blato, Pischene, Dyulova bara) which are heavily overgrown with aquatic and swamp vegetation, low phytoplankton biodiversity and biomass were established. Phytoplankton seasonal sequences in the side-arms (e.g. Regelsbrunn) are basically similar to those found in most large rivers with temperate hydrological regimes: year-round predominance of diatoms, blooming in spring and autumn, and a mixed population of Chlorophyceae and diatoms during summer. Phytoplankton development in floodplain lakes (e.g. Sakadaš, Srebarna, Gorgostel, Erenciuc and Rosu) depends on the influence of riverine water. Bacillariophyceae dominance occurs during the open hydrological connection with the main river channel, while a long-lasting Cyanoprokaryota bloom characterize summer and early autumn conditions of the hydrological isolation from the river. Results obtained by comparative research of the Danubian wetlands clearly show that phytoplankton dynamics in all investigated types of wetlands are hydrology-driven.