engleski

The influence of flooding on colonization of peryphitic algae in a Danubian floodplain lake(Croatia)

The colonization of periphytic algae was studied in a shallow floodplain lake situated in the area of the Kopački Rit Nature Park (Croatia), one of the largest conserved floodplains of the Danube River. An in situ experiment was done in the summer (July-August) of 2010 using artificial substrata (glass slides vertically oriented and placed 20 cm below the water surface), in order to examine the short-time changes in algal community composition during the early phase of periphyton formation. The experiment was started at the end of the flood pulse which began in June. A long-lasting high flood pulse began at the end of July and lasted till the end of the experiment. PCA analysis showed significant changes of the physical and chemical water parameters as a consequence of the inflow of Danube floodwater. The BIOENV sub module showed a maximum correlation between environmental factors and algal species abundance data of 0.592, with water depth (6.51 - 8.66 m), nitrite (0.004 - 0.02 mgl-1), total nitrogen (0.67 - 5.81 mg l-1) and Danube water level (2.12 - 5.26 m) being the factors that mostly influenced algal species composition and abundance at all samplings. The periphyton formation was initiated on the first day of deployment due to the rapid formation of bacterial biofilm. Altogether, 214 algal taxa were identified during the investigated period. The number of algal taxa continuously increased from 38 taxa on the first day of colonization to 134 taxa on day 27. A stable algal community was achieved on day 18, as shown by the MacArthur-Wilson equilibrium model. According to the cluster and NMDS analysis based on qualitative composition and abundance of periphytic algal assemblages, the following sequences of periphyton colonization can be defined: the initial colonization (days 1-3), the intermediate phase (days 6-15) and the late phase (days 18-42). Initial colonization was characterized by species in polysaccharide matrix, Aphanocapsa delicatissima W. West et G. S. West and Asterococus superubs (Cienk.) Scherff. being attached directly to the substrata. The small stalk- forming, Characiopsis acuta (A.Br.) Borzi and a large filamentous green alga Cladophora glomerata (L.) Kütz., C-selected species, were significant during the intermediate phase in the conditions of stable, nutrient rich habitat. Oedogonium sp., an upright filamentous green taxa with heterotrichous holdfast cells, offered an additional substratum for small Characium as well as for Gomphonema species during the late phase of periphyton colonization in the conditions of flooding. In such an unstable habitat, the dominant diatom species was G. parvulum (Kütz.) Kütz., known as R-selected species with a high resistance to removal. In spite of the fact that the cohesive filaments of Oedogonium sp. can protect the periphyton communities from the total removal during the flooding, the significant decrease of algal abundance and total periphyton biomass was established on day 36. Intensive development of metaphyton and macrophyte vegetation in the conditions of long-lasting flood caused mechanical injuries of periphyton. Subsequently, in periphyton which had lost a considerable amount of its biomass, the dominant diatom species was Achnanthidium minutissimum (Kütz.) Czar, an early colonist of denuded habitats, indicating on recolonization process. According to all given results it is evident that the flooding caused environmental disturbance which can significantly influence the periphyton colonization.

flooding; periphyton; artificial substratum; algae; colonization

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