عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Phytoplankton identification, density and dispersal assessment were conducted from June to October 2005 in Lar Reservoir. Samples were taken by simple plankton net (30rm mesh size) and by Ruttner from different depths (0, 5, 10, 20, 30m) and then fixed with formalin 4%. We used inverted microscope in the laboratory to study the samples.
We distinguished 34 genera of phytoplanktons consisting of 7 Phyla. Number of genera for Bacillariophyta was 11, for Euglenophyta was 1, for Chlorophyta was 11, for Cyanophyta was 5, for Pyrrophyta was 3, for Cryptophyta 1 and for Chrysophyta was 2. Phylum Bacillariophyta was dominant comprising 82.83% of phytoplankton population annually.
Cyclotella, Navicula and Nitzchia were the dominant genera. Phylum Chlorophyta was second in dominance and consisted of Oocystis, Pediastrum, Scenedesmus and Chlorella genera altogether sharing 12.89% of the total phytoplankton frequency. Chrysophyta with genera Dinobryon. and Malomonas had a frequency of 2.21%, Cyanophyta with Genera Anabaena, Oscillatoria and Gleocapsa comprised 1.32% of the total frequency, Pyrrophyta with genera Cyratium, and Peridinium had a frequency of 0.52%, Euglenophyta with genus Euglena had a frequency of 0.13% and Cryptophyta with genus Cryptomonas had a frequency of 0.08%.
In all sampling months, the highest mean density belonged to Phylum Bacillariophyta with 10,770,666±21.571 individuals per liter of water. Also, in all seasons, the most dominant genus of the Phylum Bacillariophyta was Cyclotella. Phylum Chlorophyta came second in numbers, with a mean density of 2927000±39.573 individuals per liter of water. The dominant genera of this Phylum were Oocystis, Pediastrum, Scenedesmus and Chlorella.
Non-parametric Kruskal-Wallis and Mann-Whitney analyses showed that Phytoplankton frequency in different stations and months were statistically different (P<0.05). No significant statistical difference was found between different depths (P>0.05).