Abstract
We investigated the optical and hydraulic conditions of cyanobacteria growth using the field observation data for two reservoirs in Japan. When the buoyancy frequency (N2) is greater than O(10-4)(s-2) - O(10-3)(s-2), the populations of PC type Phormidium and Microcystis increase, however, for N2 values less than that, the population of PE type Phormidium increases. From a theoretical analysis using the Wedderburn number (W), it is considered that the above level of N2 is estimated as the critical condition for vertical mixing of density stratification. Therefore, it is assumed that two antenna pigments types, that is PC and PE, of Phormidium have different suitable hydraulic conditions. Furthermore the hydraulic stability requirement for large-colony cyanobacteria that form water bloom can be estimated based on N2.
