The response of periphytic algal assemblages to disturbances - field study in a temperate floodplain lake

Temporal variations in periphytic algal communities were studied in Lake Sakadaš, a part of a Danubian floodplain known as Kopački Rit Nature Park. An in situ investigation was performed using artificial substrata (glass slides) exposed in the lake in two study series, spring and summer, and incubated until the winter 2010. Due to the extremely high and long-lasting spring-summer flooding, the physical and chemical environment significantly varied, and metaphyton and macrophytes were spread along the lake. Based on the non-metric multidimensional scaling, three phases were identified in the periphytic algal development. The initial accrual phase, in both spring and summer series, was characterized by the continuous increase in periphyton biomass (dry weight, organic weight, and ash-weigh), chlorophyll concentrations, and algal abundance. Diatom successions from low-profile species (Stephanodiscus) to the stalk-forming species (Gomphonema, Encyonema) with a tendency towards vertical overgrowth characterized periphyton communities in spring. Rapid development of filamentous green algae (Oedogonium sp.) characterized periphyton accrual in summer. Huge stands of metaphyton and macrophytes acted as a disturbance to periphytic algal accrual. Shading and mechanical injuries together with high grazing pressure led to a periphyton loss phases. Resetting of the algal community to an earlier stage of development, with diatoms firmly attached to the substrata (e.g. Epithemia, Cocconeis) shows periphyton response to disturbance. The cessation of hydrological perturbations created an opportunity for periphyton development and the rapid accrual of algal communities occurred in autumn. In conclusion, the complexity of environmental changes caused by extreme flooding can significantly influence development of periphytic algal communities in a temperate floodplain. Further investigations are necessary to elucidate very complex interactions between periphyton and other aquatic biocenoses in river-floodplain systems.