Relationship between environmental factors and the formation of cyanobacterial blooms in a eutrophic pond in central Japan
Yamamoto, Yoshimasa; Tsukada, Hajime; Matsuzawa, Yuko
The development of cyanobacterial blooms in a small eutrophic pond was monitored in 2006. Microcystis was the dominant genus in the study pond from May to October. Water temperature seemed to be largely responsible for the increase in Microcystis; recruitment of the colonies from the sediment and the growth of recruited colonies at high temperatures seemed to be particularly important in bloom formation. The ratio of total nitrogen (TN) to total phosphorus (TP) fell in May and remained low until November, implying a strong relationship between the formation of cyanobacterial blooms and low TN:TP ratios. High levels of chlorophyll a, as an indicator of cyanobacterial biomass, were associated with low TN:TP ratios, i.e. below 9.2 by mass. Significant correlations of the concentration of chlorophyll a with TN and TP concentrations during the period of cyanobacterial blooms imply that cyanobacterial intracellular nitrogen and phosphorus strongly regulate the water TN:TP ratio. Results of this study thus indicate that a low TN:TP ratio is attributed to cyanobacterial blooms.