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 (HO) concentration and antioxidant activities of catalase (CAT) and superoxide dismutase (SOD). HO concentrations decreased to 30 µmol m s of PAR, then increased with higher PAR intensities. Regarding P concentrations, HO concentrations (nmol L) generally decreased with increasing P concentrations. SOD and CAT activities were proportionate to the HO protein. No HO concentrations detected outside cells indicated the biological production of HO, and the accumulated HO concentration inside cells was parameterized with HO concentration protein. With over 30 µmol m s of PAR, HO concentration protein had a similar increasing trend with PAR intensity, independently of P concentration. Meanwhile, with increasing P concentration, HO protein decreased in a similar pattern regardless of PAR intensity. Protein content decreased with gradually increasing HO up to 4 nmol HO mg protein, which provides a threshold to restrict the growth of cyanobacteria. With these results, an empirical formula-protein (mg L) = - 192Log((HO/protein)/4.1), where HO/protein (nmol mg) = - 0.312PAR/(50 + PAR)*((25/PAR) + 1)*Log(P/133,100), as a function of total phosphorus concentration, P (µg L)-was developed to obtain the cyanobacteria biomass.