Competitive growth characteristics between Microcystis aeruginosa and Cyclotella sp. accompanying changes in river water inflow and their simulation model

Abstract

Summary When the water quality in Lake Tega was the worst among Japanese lakes in the 1970s, cyanobacteria (mainly the genus Microcystis) were observed to be the dominant species in the summer. Since 2000, for water quality improvement, a large amount of the Tone River water was discharged into Lake Tega, resulting in an improvement in the water quality together with transition of algal dominant species from cyanobacteria to diatoms (mainly the genus Cyclotella). Although several factors including nutrient concentration and daily renewal rate (d) could have been related to the succession of algal dominant species, these effects have not been understood very well. This study investigated the effects of the daily renewal rate and nitrate‐nitrogen (hereafter nitrogen) concentration (N) on the competition between the cyanobacterium Microcystis aeruginosa and the diatom Cyclotella sp. through monoculture and monoxenic culture experiments. Based on the experimental results, a simulation model was constructed to predict the competitive growth pattern of each species. Monoxenic culture experiments showed that M . aeruginosa outcompeted Cyclotella sp. under conditions of N = 0.5 (1.0 mg‐N L−1) and d = 5, 15, and 20%. The domination of M . aeruginosa could be attributed to smaller values for the half‐saturation constant and the minimum nitrogen cell quota for this species with respect to Cyclotella sp. However, Cyclotella sp., possessing higher values of nitrogen cell quota and nitrogen uptake rate, dominated by an increasing nitrogen concentration (N = 1.0 mg L−1) and daily renewal rate (d = 30%). The competitive growth patterns of M . aeruginosa and Cyclotella sp. could roughly be predicted by the simulation model. These results suggested that the daily renewal rate as well as the nitrogen concentration, could affect the competition and be influential factors as to which species dominates between M . aeruginosa and Cyclotella sp.

Blue light irradiation increases the relative abundance of the diatom Nitzschia palea in co‐culture with cyanobacterium Microcystis aeruginosa

“…For instance, Wyman and Fay (1986) and Tan et al (2020) used BG-11 medium at different concentrations, suggesting that the available nutrient concentrations must have differed between the studies. The growth rate follows the Droop equation, which is a model affected by the intracellular content, and the nutrient uptake rate is calculated using the Michaelis-Menten equation, which is affected by the nutrient concentration in the medium (Ducobu et al, 1998;Mikawa et al, 2016). Since the halfsaturation constant for nutrient uptake is usually smaller than the concentration of the medium, it is considered that the growth rate does not differ depending on the type of medium unless the nutrient is depleted.…”

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

“…The accuracy of a previous model (Mikawa et al 2016) tended to decrease under high nutrient concentrations. In the previous model, the limiting nutrient was determined as the relationship between the mass ratio of minimum cell quota of assimilated N:P (the optimum N:P ratio) and the external dissolved N:P mass ratio.…”

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

“…The accuracy of Mikawa's model [16] tended to decrease under high nutrient concentrations. Because the growth rate term of the model was formulated based on the Droop equation, the growth rate values in a longer period would be close to μ max , which led to the excess of cell densities.…”

“…However, the predicted cell density still had a discrepancy compared with the actual cell density in Lake Tega, due to the shortcoming of the simulation model, especially its overestimation of algal cell density. In order to modify the overestimation problem of algal cell density in this model [16], an improved model has been developed by Chujo et al [4] , by introducing a growth limitation term from Lotka-Volterra model into the previous model. The developed model presented a more accurate prediction of growth patterns of co-cultured cyanobacteria and diatom, under high nitrogen and phosphorus concentrations.…”