Hydrogen peroxide can be a plausible biomarker in cyanobacterial bloom treatment.

The effect of combined stresses, photoinhibition, and nutrient depletion on the oxidative stress of cyanobacteria was measured in laboratory experiments to develop the biomass prediction model. Phormidium ambiguum was exposed to various photosynthetically active radiation (PAR) intensities and phosphorous (P) concentrations with fixed nitrogen concentrations. The samples were subjected to stress assays by detecting the hydrogen peroxide (H2O2) concentration and antioxidant activities of catalase (CAT) and superoxide dismutase (SOD). H2O2 concentrations decreased to 30 µmol m-2 s-1 of PAR, then increased with higher PAR intensities. Regarding P concentrations, H2O2 concentrations (nmol L-1) generally decreased with increasing P concentrations. SOD and CAT activities were proportionate to the H2O2 protein-1. No H2O2 concentrations detected outside cells indicated the biological production of H2O2, and the accumulated H2O2 concentration inside cells was parameterized with H2O2 concentration protein-1. With over 30 µmol m-2 s-1 of PAR, H2O2 concentration protein-1 had a similar increasing trend with PAR intensity, independently of P concentration. Meanwhile, with increasing P concentration, H2O2 protein-1 decreased in a similar pattern regardless of PAR intensity. Protein content decreased with gradually increasing H2O2 up to 4 nmol H2O2 mg-1 protein, which provides a threshold to restrict the growth of cyanobacteria. With these results, an empirical formula-protein (mg L-1) = - 192*Log((H2O2/protein)/4.1), where H2O2/protein (nmol mg-1) = - 0.312*PAR2/(502 + PAR2)*((25/PAR)4 + 1)*Log(P/133,100), as a function of total phosphorus concentration, P (µg L-1)-was developed to obtain the cyanobacteria biomass.