ABSTRACT: The relative importance of growth versus loss rates of picocyanobacteria (PC) and the influence of physical and chemical variables on their in situ abundance were examined during summer 2000 in 48 lakes in Quebec, Ontario and New York State. The lakes were selected based on their trophic state. For the resulting range in total phosphorus (TP) (1 to 42 µg l^-1), PC abundance varied from <10² ml^-1 in a eutrophic lake dominated by a cyanobacterial bloom to over 10⁵ ml^-1 in oligotrophic and more mesotrophic lakes. Growth rates on average exceeded loss rates in the lakes with maximum rates of 1.93 and 1.25 d^-1, respectively, as estimated using a selective metabolic inhibitor method. On average the doubling time of PC was about 1.7 d. Growth rates were positively correlated with loss rates in the lakes. The multiple regression model that explained the most variation in PC abundance included SRP, loss rates, conductivity and the ratio of total Kjeldahl nitrogen (TKN) to TP. The results suggest that biotic control of the abundance of PC may be as important as abiotic control. However, the model could only explain 44% of the variation in PC abundance among the lakes. This could be in part the result of considering PC as one ecological group when in fact considerable diversity is likely present among freshwater PC.

KEY WORDS: Picocyanobacteria · Lake trophy · Growth rate · Loss rate · Grazing · Selective metabolic inhibitor technique

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Published in AME Vol. 27, No. 1 (2002) on February 18
Print ISSN: 0948-3055; Online ISSN: 1616-1564. Copyright © Inter-Research, Oldendorf/Luhe, 2002