An ecological study on dynamics of toxic Microcystis blooms in a eutrophic park pond, Wuhan, China

<正> The results of ecological investigation of Microcystis blooms and their toxicity in a eutrophic park pond (where the annual average of total nitrogen and total phosphorus was 6.1 mg·L-1 and 1. 79 mg·L-1, respectively) are presented. The blooms were mainly contributed by M. aeruginosa occurring in the period from May to October when water temperature ranged from 16 to 33℃ . Three remarkable growth peaks of Microcystis during the period were observed with chlorophyll a level of 0. 73 mg· L-1 ,1.44 mg·L-1 , and 1.30 mg· L-1 , respectively. The blooms were independent of phosphorus, but highly dependent on ammonium. A level of ammonium of 9. 5 mg· L-1 could trigger the outbreak of the bloom, while that below 0. 89 mg· L-1 could inhibit its formation. In other words, ammonium in higher concentrations could promote blooming, while that in lower concentrations could be inhibitory. Microcystis toxicity tended to increase with the blooming process, but the toxic peaks lagged behind their corresponding gr