engleski

Colonization of periphytic algae in the Danubian floodplain

Colonization processes of periphytic algae in the endangered and very complex river-floodplain systems of large European rivers have not yet been fully investigated. During the period April -August 2008, colonization of algae on glass slides (vertically oriented and placed 25 cm below the water surface) was investigated in Lake Sakadaš, a permanent water body within the Kopački Rit Nature Park, one of the biggest preserved Danubian floodplains. During the investigated period, different hydrological conditions altered the values of physical and chemical parameters of lake water: depth (6, 50 - 8, 30 m), transparency (0, 72 - 3, 20 m), total nitrogen (0, 10 - 3, 70 mg/L) and total phosphorus (0, 04 - 0, 33 mg/L). Total periphyton biomass (dry weight, organic weight) continuously increased during the investigated period, particularly from July when the invasive species Dreissena polymorpha (Pallas, 1771) comprised the largest portion of total periphyton biomass. Based on autotrophic index, periphyton communities were characterized as autotrophic at the beginning of the colonization, while heterotrophic communities prevailed from July till the end of the experiment. A total of 199 algal taxa were detected in periphytic communities, varied from 55 taxa during the first week to 94 taxa in the thirteenth week of colonization. The Simpson's diversity index values show that the beginning of colonization was characterized by higher diversity due to the colonization of new species, while from the seventh week, gradual domination of several algal species within the periphytic community has been detected. Cyanobacteria comprised the 90% of the total abundance during the first week with well developed species belonging to the genera Phormidium, Aphanocapsa and Gloeocapsa. From the second week till the end of the investigated period various diatom species prevailed. Firstly, the periphyton was dominated by the species of higher biovolume (genera Fragilaria, Melosira, Gomphonema) while in the later phase the species of smaller biovolume (genera Achnanthes, Cymbella, Amphora, Navicula) dominated. Algal abundance reached maximum value(614 x 103individuals/cm2) during the sixth week of exposition. Stabilization of the periphytic community in the seventh week of colonization, indicate the possible influence of the flood dynamics on the colonization processes.

Periphyton; artificial substrates; diatoms

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