Vertical migration patterns of different phytoplankton species were examined during a summer bloom period in Dianchi Lake, China. The ratio of the mean crowding to mean density (x*/x) and mean residence depth (MRD) was used to quantitatively evaluate the distribution patterns. The effects of wind velocity and water column temperature differences on the vertical distribution patterns of Microcystis aeruginosa, Aphanizomenonflos-aquae, and total phytoplankton were then investigated. Over 5 days (July 16-20, 2013), abundant of Microcystis aeruginosa (1.10 ± 0.40 9 10 9 cells/L), Aphanizomenonflos-aquae (5.11 ± 1.38 9 10 7 cells/L), and total phytoplankton (1.24 ± 0.40 9 10 9 cells/L, 239.63 ± 79.26 lg/LChl-a, n = 64) were found throughout the water column. Values of x*/x and MRD showed that Microcystis aeruginosa aggregated on the water surface during the calm morning [wind velocity (WV) \2 m/s], and distributed uniformly in the windy afternoon (WV [2-3 m/s). Aphanizomenonflosaquae tended to be randomly distributed for most of the time. Wind velocity was significantly correlated with the x*/x and MRD of Microcystis aeruginosa (P \ 0.05), but not with those of Aphanizomenonflos-aquae. Meanwhile, the effects of thermal differentiation on the vertical distributions of all species were not significant. Therefore, the vertical distributions of Microcystis aeruginosa may be determined by wind velocity rather than thermal differentiation in Dianchi Lake.

To identify a botanical algicide and elucidate the response of cyanobacteria to the extract from higher plants, the effects of garlic and garlic-derived diallyl trisulfide on Microcystis aeruginosa were studied. Effects were evaluated by changes in cell density, chlorophyll a, maximum effective quantum yield (Fv/Fm), effective quantum yield (YII), non-photochemical quenching (NPQ), and rapid light curves of M. aeruginosa. In addition, alkaline phosphatase activity (APA) was measured when M. aeruginosa was incubated with diallyl trisulfide. Results indicated that the inhibition by garlic and diallyl trisulfide was significant. The 120-h 50 % effective concentrations of garlic and diallyl trisulfide (EC50) were 0.75 g L(-1) and 2.84 mg L(-1), respectively. Moreover, the inhibitory rate increased with increasing concentration and the growth of M. aeruginosa was inhibited by 90.0 % at the highest concentrations. We also show that the response of M. aeruginosa to stress could involve both impairment of the photosynthetic center PSII and alteration of APA. For example, at high garlic concentration (2.0 g L(-1)), Fv/Fm significantly decreased from 0.501 to 0.084 (p < 0.05) after 120 h of exposure. Furthermore, the total APA was significantly decreased by exposure to a high diallyl trisulfide concentration after 24 h exposure. As new algal inhibitors, there are several advantages for their utilization, such as being common, cheap, non-toxic, and with high efficiency. It would be meaningful to further research on garlic as an environmentally friendly algicide.

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Atmospheric particulate matter (APM), commonly seen and widely excited in environment, appears great enough to influence the biochemical processes in aquatic microorganisms and phytoplankton. Understanding the response of cyanobacteria to various factors is fundamental for eutrophication control. To clarify the response of cyanobacteria to APM, the effects of PM, PM, and PM on Microcystis aeruginosa were researched. Variabilities in cell density, chlorophyll a, soluble protein, malondialdehyde, extracellular activity, and kinetic parameters of alkaline phosphatase were evaluated by lab-cultured experiments. Results showed that the PM had a slight stimulation impact on the growth and enhanced both of the 48- and 72-h extracellular alkaline phosphatase activity (APA), the affinity of alkaline phosphatase for substrate, and the 72-h maximum enzymatic reaction velocity (V). Moreover, the stimulations in extracellular APA and V enhanced with the increasing exposure concentrations. We also found there were no obvious distinctions on the effects of growth and alkaline phosphatase in M. aeruginosa between PM and PM exposure groups. Obviously, inhibitory effects on growth existed in 4.0 and 8.0 mg/L PM and 8.0 mg/L PM at 120 h. Furthermore, PM and PM exerted inhibitory effects on the extracellular APA during the 72-h exposure. Simultaneously, the V was notably inhibited and the affinity of alkaline phosphatase for substrate was more inseparable compared with control in PM and PM treatments. Nevertheless, the inhibitors in extracellular APA and kinetic parameters were unrelated to PM and PM exposure concentrations. Two-way ANOVA results revealed that there were significant interactions between exposure concentration and diameter of APM on the 120-h cell density, soluble protein content, APA, and 72 h APA of M. aeruginosa. These results in our study would be meaningful to further researches on relationships between APM deposition and cyanobacterial bloom.

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