Abstract
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 aeruginosa with 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 by M. aeruginosa were also examined. Results showed M. aeruginosa growth rate positively correlated with EDTA-Fe concentration and negatively correlated with biomass. Maximal biomass of M. aeruginosa was 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.
Highlights
The presence of cyanobacteria blooms in freshwater is one of the most serious ecological problems in the world [1]
Biomass and growth rate of M. aeruginosa in almost all treatments positively correlated with ethylenediaminetetraacetic acid (EDTA)-Fe concentration (0.5–6.0 mg/L) (Figure 2A and Figure S1, Table S3)
Main results from three experiments were that: that: (i) M. aeruginosa growth rate positively correlated with EDTA-Fe concentration and negatively
Summary
The presence of cyanobacteria blooms in freshwater is one of the most serious ecological problems in the world [1]. It causes water discoloration, foul odors and tastes, deoxygenation of bottom waters (hypoxia and anoxia), toxicity, fish kills, and food web alterations. With increasing anthropogenic nutrient loading (cultural eutrophication), phytoplankton become P and N saturated, i.e., their growth rate and biomass are insensitive to changes in P or N concentration. The work by Auer verified that the eutrophic waters of southern Green Bay, western Lake Erie, and nearshore Lake Ontario are nutrient saturated and insensitive to P reduction [9]. Something other than P or N regulates phytoplankton biomass in eutrophic lakes
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