Patterns of succession between bloom-forming cyanobacteria Aphanizomenon flos-aquae and Microcystis and related environmental factors in large, shallow Dianchi Lake, China

The succession amongst different cyanobacteria genera remains understudied and poorly understood as much of the focus has been on mono-specific blooms. The spring-summer succession between Aphanizomenon flos-aquae and Microcystis and its underlying mechanism were investigated from 2009 to 2012 in hypereutrophic Dianchi Lake in China. Regularly, A. flos-aquae grows rapidly and forms bloom in March at water temperatures around 15A degrees C, followed by Microcystis blooming around 18A degrees C in April. Since 2010, the pattern of succession has changed, featuring an increase of Microcystis but decrease of A. flos-aquae biovolume, leading to near disappearance of A. flos-aquae in 2012. Coincidently, there was a sharp increase of nitrogen concentration in 2010, going up to 5.67 mg/l in 2011, and a big increase in the mass ratio of TN to TP from 13.6 in 2009 to 21.1 in 2011. We hypothesized that temperature is the most influential factor governing the initiation of rapid growth and succession between A. flos-aquae and Microcystis, while increase of TN and/or ratio of TN to TP may trigger the decline and disappearance of A. flos-aquae, time of recruitment, and the population dynamics of Microcystis. Our findings are not only meaningful to the understanding of the cyanobacterial bloom mechanism but also to the management of shallow eutrophic lakes.