RESUMO
To support the basic data for forecast of algal blooms, circadian vertical migration experiment was carried out in the Daning River Bay of the Three Gorges Reservoir in July, 2011. The results were as follows: in this period, different algal species were found in the Daning River Bay, including cyanobacteria, green algae, dinoflagellates and diatoms etc; the distribution of algal cells was uneven, 72.5%-76.2% of algal cells aggregated at 0.5-4.0 m water depths from 10:00 AM to 10:00 AM next day, but 7.5%-16.3% of algal cells aggregated at 0-0.5 m. Morisita's indexes (MI) of algal cells were from 1.41 to 1.97 in day time, and from 1.17 to 1.55 at night. Morisita's indexes of chlorophyll a(Chla)were from 1.31 to 1.59 in day time, and from 1.17 to 1.39 at night. The vertical migration also occurred at 0.5-4.0 m water depths. The algal density was not significantly related with the concentrations of nutrient except that of dissolved total phosphorus (DTP) (r = 0.89). The algal density was also influenced by water temperature (WT), pH and specific conductance (SPC), and the correlation coefficients were 0.96, 0.97 and -0.99, respectively.