engleski

Biocenotical Structure of Phytoplankton Communities in two Mediterranean Shallow Lakes

Long-term phytoplankton study was carried out in two Mediterranean shallow lakes Ponikve (surface area 70 km2, max. depth 6 m, mean depth 2, 4 m, catchment&#8217 ; s 35 km2 ) and Njivice (surface area 35 km2, max. depth 9 m, mean depth 4 m, catchment&#8217 ; s 20 km2 ) on island Krk. The lakes are usable for inhabitants of the island. Biocenotical structure of phytoplankton communities was investigated be-monthly during 1994/95, 1997/98. and 2000/01. Chlorophyll a concentration, phytoplankton biovolumes and species compositions are used for trophic level and water quality. Phytoplankton was sampled on tree vertical profiles in Ponikve and two vertical profiles in Njivice. Water was filtered through a 25 &#956 ; m plantonic net and samples for chemical analyses were taken simultaneously. The number of phytoplankton cells was estimated by using algae chambers. The species composition revealed 72 taxa with Bacillariophyceae and Chlorophyceae as best represented. Dinophyceae and Cyanobacteria were moderately represented. Seasonal and vertical distribution of the total phytoplankton abundance and biomass were significantly different between seasons and lakes, and were highly influenced by hydrological parameters. On the basis of indicator species, both lakes characterizes the water of first to second class levels of water purity, but indicates that Ponikve has already become a mesotrophic stagnant water while Njivice slowly altered from a mesotrophic to a eutrophic character.

phytoplankton; trophy level; water quality; Mediterranean shallow lakes

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