engleski

Diatom assemblages along freshwater course of a karstic river Krka, Croatia

The aim of this study was to determine the differences in diatom community at the spring (below Krčići waterfalls), middle (at Roški waterfall) and the end of freshwater flow (waterfall Skradinski buk) of a karstic River Krka during summer period of 2002. Plexi slides were placed at the beginning of May and sampled every 2 weeks. Four separate sides of the plexi slides were considered: outer and inner sides of slides under the influence of the flow and those protected from the flow. Altogether 72 samples were collected and analyzed. All samples were fixed with formaldehyde, diatoms counted on centimeter grid and then digested and fixed onto permanent slides for identification and relative abundance counts. During the investigation period, 80 diatom species were identified. The most abundant species at all three sites were species of geni Achnanthidium Kützing and Planothidium Round et L.Bukhtiyarova. At the beginning of colonization period the most abundant species belonged to geni Achnanthidium, Diatoma Bory and Fragilaria Lyngbye. Longer colonization periods were characterized with increased abundances of centric planktonic species belonging to geni Cyclotella Kützing and Stephanodiscus Ehrenberg. Cluster and MDS analyses performed on abundance data set revealed five distinctive groups with sampling site being the main and colonization time secondary separation factor. There were no notable differences in diatom community depending on side and influence of river flow. Diatom assemblages along relatively short (49km) karstic river Krka were characterized by typical small periphytic (mostly monoraphid and biraphid) species while small centric planktonic diatoms that appeared with high abundances on two sites with lower water velocity were main species differentiating between sites with higher and lower flow.

diatoms; assemblages; karst

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