Effects of environmental factors on the seasonally change of phytoplanktonpopulations in a closed freshwater pond

The effect of environmental factors affecting the population dynamic of phy toplankton population was studied seasonally in a closed freshwater pond wi th the natural water of Lake Kasumigaura, Japan. The predominant phytoplank ton species in the pond were classified as Oscillatoria tenuis, Synedra uln a, Chlamydomonas cingulata and Cyclotella kutzingiana, with dominant specie s of Melosira italica, Synechococcus sp. and Cryptomonas ovata. The most im portant limiting factor for filament length and cell size of most of the ph ytoplankton community was temperature. Availability of most nutrients had p rofound effects on the phytoplankton growth as nonlimiting factors. Based o n our results, it is suggested that cell cycle progression was also tempora lly regulated by a multiplicity of external factors such as temperature, nu trients, dissolved oxygen (DO) and pH. At high pH and high temperature, con sistent increase of cell division of some phytoplanketers such as Synedra, Cyclotella, Chlamydomonas and Melosira occurs, and there also may be specie s-specific responses for other species of phytoplankters. In addition, the cell divisions of phytoplankters are differentially regulated in different phytoplankton species. (C) 2001 Elsevier Science Ltd. All rights reserved.