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The colonization of periphytic algae in a temperate floodplain was studied in Lake Sakadasš, a part of a fluvial floodplain along the Danube River. An in situ investigation, using artificial substrata, was started after extremely high spring flooding and was carried out during long-lasting summer floods (July-August 2010). The physical and chemical environment was variable and large stands of metaphyton, submersed and floating macrophytes were spread along the lake. The periphyton development was initiated on the first day of exposition and algal abundance increased exponentially till day 27. Directional changes in the relative abundance of algal species, shown by the results of the non-metric multidimensional scaling, indicate a pattern of short-term sequences in algal colonization. The initial attachment of planktonic cyanobacteria and unicellular diatoms (initial phase, days 1-3) to the biofilm matrix was followed by the development of the filamentous chlorophytes, Cladophora glomerata and Oedogonium spp. (intermediate phase, days 6-15) and then by stalk-forming diatoms particularly Gomphonema spp. (late phase, days 18-33). According to the redundancy analyses, water temperature and oscillations of Danube water level that define the flooding pattern had the most significant influence on algal colonization. Flood-induced spreading of metaphyton firstly supported the rapid progress of algal colonization towards a climax community, while later, metaphyton together with macrophytes disrupted algal community by increasing the mechanical injuries, shading and grazing pressure. Consequently, algal abundance and community structure were returned to the intermediate phase of colonization. [ABSTRACT FROM AUTHOR]

During the past decade, basic hydrological conditions of a floodplain lake in the middle Danube section have been altered with long-lasting extremely high flooding. The objective of the paper is to show the effectiveness of the functional approach to explain phytoplankton changes associated with hydrological events. Intensity and duration of flooding were qualified as the primary cause for the changes of functional groups. Flooding phase was characterised by diatoms ( B, C, D, P, T) tolerant to water column mixing. Due to the dilution and washout effect their biomass was low during the long-lasting flooding despite their input from the river. Co-occurrence of coccoid green algae ( X1, J, F) was associated with turbid and mixed waters. High-nutrient concentrations and water column stability during the long-term dry conditions led to the dominance and high biomass of cyanobacteria. Low-nitrogen H1 group was particularly sensitive to stress caused by flooding, while filamentous N-fixing ( S) and non N-fixing species ( S1) showed tolerance to short-term flooding. The development of euglenoids and dinoflagellates ( W1, W2, L) was also associated with dry conditions and seasonal changes in autumn. The functional classification allows representing of the hydrological phases which characterise the phytoplankton succession in highly disturbed river-floodplain systems. [ABSTRACT FROM AUTHOR]

There are several conflicting hypothesis that deal with the influence of flooding in the natural river–floodplain systems. According to the Flood Pulse Concept, the flood pulses are not considered to be a disturbance, while some recent studies have proven that floods can be a disturbance factor of phytoplankton development. In order to test whether flooding acts as a disturbance factor in the shallow Danubian floodplain lake (Lake Sakadaš), phytoplankton dynamics was investigated during two different hydrological years—extremely dry (2003) without flooding and usually flooded (2004). A total of 18 phytoplankton functional groups were established. The sequence of phytoplankton seasonality can be summarized P/D → E (W1, W2) → C/P (only in potamophase) → S2/H1/SN/S1 → W1/W2 → P/D. The canonical correspondence analysis (CCA) demonstrated that the water level was a significant environmental variable in 2004. Due to the higher total biomass of Bacillariophyceae established under potamophase conditions, floodings in the early spring seem to be a stimulating factor for phytoplankton development. On the other hand, the flood pulses in May and June had dilution effects on nutrients, so that a significantly lower phytoplankton biomass was established indicating that flooding pulses can be regarded as a disturbance event. Such conditions supported diatom development (D, P, C species) and prolonged its dominance in the total phytoplankton biomass. A long-lasting Cyanoprokaryota bloom (various filamentous species—S1, S2, SN and H1 representatives) with very high biomass characterized the limnophase (dry conditions) in summer and autumn of both years. In-lake variables (lake morphology, internal loadings of nutrients from sediments, light conditions) seem to be important for the appearance of Cyanoprokaryota bloom. The equilibrium phase was found during the Cyanoprokaryota bloom only in the extremely... [ABSTRACT FROM AUTHOR]