Estimation of effective dilution rate to inhibit cyanobacterial blooms based on a novel competitive growth model -Case study in Lake Tega, Japan

Abstract

Although water transfer as a functional method to improve water quality and control cyanobacterial blooms in lakes has been used for several decades, there was few studies examining effective dilution rate depending on various water qualities in lakes. It would be due to the scarcity of water transfer execution in fields. Therefore, in order to clarify the optimum dilution rate to suppress cyanobacterial blooms, the competitive growth model based on the Droop model and the Lotka-Volterra model developed for eutrophic conditions was used. First, to verify the wide applicability of the simulation model, a competitive culture experiment between Microcystis sp. and Cyclotella meneghiniana under limited phosphorus and sufficient nitrogen concentration was conducted, then the cell densities of the two species were predicted by using the simulation model. Results of the competitive experiment revealed that there was no significant discrepancy in the growth of Microcystis sp. cell among different dilution groups (p＞0.05), while that of Cyclotella meneghiniana had significant discrepancy between groups (p＜0.05), and the accuracy of the simulation model under limited phosphorus concentration was verified. Based on these results, an exact effective dilution rate for the inhibition of Microcystis blooms in Lake Tega, Japan, was suggested by this novel simulation model. When the dilution rate reaches 13.3%, the Microcystis blooms will hard to occur. The predicted data were also compared with the actual data collected over years in Lake Tega, and its effectiveness has been confirmed.