Effective dilution rate to suppress the risk of Microcystis blooms in Lake Tega, Japan, based on a competitive growth simulation model

Although water transfer as an efficient method to improve water quality and control Microcystis blooms in lakes has been executed for several decades, few studies have examined effective dilution rates depending on various water qualities. Therefore, to clarify the effective dilution rate to suppress Microcystis blooms, a competitive growth simulation model developed for eutrophic conditions was utilized. A competition experiment between Microcystis sp. and Cyclotella meneghiniana under limited phosphorus and sufficient nitrogen concentration was conducted to investigate the mechanism of dilution effect and verify the broad applicability of the simulation model. Experimental results revealed that there was no remarkable discrepancy in Microcystis sp. cell density among different dilution groups (p>0.05), while C. meneghiniana cell density was significantly different between groups (p<0.05). The accuracy of the simulation model under limited phosphorus as well as sufficient nitrogen concentration was verified by comparing the simulated value with experimental results. Based on the simulated results, it was suggested that a dilution rate of over 13.3% can suppress Microcystis blooms effectively in Lake Tega, Japan, as a case study. The predicted data was also compared with the actual data collected over years in Lake Tega, and its effectiveness has been confirmed.