Effect of Fe and EDTA on Freshwater Cyanobacteria Bloom Formation

Due to the fact that not all eutrophic lakes have cyanobacteria blooms, we hypothesized Fe may be another important limiting factor which regulates cyanobacteria bloom formation. We tested the hypothesis by batch cultures of bloom-forming Cyanobacterium,Microcystis aeruginosawith different ethylenediaminetetraacetic acid (EDTA)-Fe concentrations (0.5–6.0 mg/L), three levels of initial biomass, and excessive N and P (N = 4.2 mg/L, P = 0.186 mg/L) to simulate dynamically a cyanobacteria bloom in eutrophic conditions. The effect of EDTA and Fe uptake kinetics byM. aeruginosawere also examined. Results showedM. aeruginosagrowth rate positively correlated with EDTA-Fe concentration and negatively correlated with biomass. Maximal biomass ofM. aeruginosawas determined by Fe availability and initial biomass. EDTA could decrease both Fe availability and toxicity. Based on experimental results, a conceptual model of how Fe availability regulates cyanobacterial biomass in eutrophic lakes was developed. This study demonstrated bioavailable Fe is a potential limiting factor in eutrophic lakes that should be included in eutrophication management strategies.Keywords:Microcystis;eutrophication control;freshwater;Fe availability