A Year-round Investigation On Microcystin Variants Of Microcystis Bloom And Their Relationship To Environmental Factors

A year-rounded investigation on biomass of Microcystis bloom, physiochemical factors and microcystin contents was conducted. Also, the inhibitory test of microcystin on algae-lying bacteria was carried out. On the basis of quantitative analysis of 3 microcystin variants: MC-LR, MC-RR and MC-YR by HPLC, the relationships between microcystin and biomass, water temperature and nutrients (i.e. N, P) were discussed. The result shows: Microcystis produced all 3 variants of microcystin, but the content of MC-RR was much larger than MC-LR and MC-YR. In most cases, MC-YR content was rather low for HPLC analysis. For one of the eutrophic ponds surveyed, MC-RR and MC-LR presented rising tendency throughout the bloom in the year. The toxicity peaks always lagged the growth peaks, furthermore, the greater the biomass, the longer the lagging days. Both MC-RR and MC-LR gave rise to their maximum value at the end of every single bloom and soon after a new bloom began. In general, the ratio of MC-RR and MC-LR remained comparatively constant during every bloom, but no obvious change characteristic was observed on MC-YR content. In the discussion, in was found that toxin-producing of Microcystis was related to biomass, nutrients and water temperature. It was suggested that the ecological function of toxin-producing was most likely inhibiting the growth of other organisms so as to resuming growth of Microcystis and further, forming a new bloom. Concretely, the growth of bacteria taking advantage of nutrients after cell broken of Microcystis was inhibited by maximal microcystins, thus, it was superior for the algae to uptake the released nutrients and recovered from the compacting environments. The inhibitory results of algae-lying bacteria under laboratory conditions positively supported the suggestion above.