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 (H(2)O(2)) concentration and antioxidant activities of catalase (CAT) and superoxide dismutase (SOD). H(2)O(2) concentrations decreased to 30 µmol m(−2) s(−1) of PAR, then increased with higher PAR intensities. Regarding P concentrations, H(2)O(2) concentrations (nmol L(−1)) generally decreased with increasing P concentrations. SOD and CAT activities were proportionate to the H(2)O(2) protein(−1). No H(2)O(2) concentrations detected outside cells indicated the biological production of H(2)O(2), and the accumulated H(2)O(2) concentration inside cells was parameterized with H(2)O(2) concentration protein(−1). With over 30 µmol m(−2) s(−1) of PAR, H(2)O(2) concentration protein(−1) had a similar increasing trend with PAR intensity, independently of P concentration. Meanwhile, with increasing P concentration, H(2)O(2) protein(−1) decreased in a similar pattern regardless of PAR intensity. Protein content decreased with gradually increasing H(2)O(2) up to 4 nmol H(2)O(2) 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((H(2)O(2)/protein)/4.1), where H(2)O(2)/protein (nmol mg(−1)) = − 0.312*PAR(2)/(50(2) + PAR(2))*((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.