Abstract
Hydrogen peroxide (H2O2) can be used as an emergency method to selectively suppress cyanobacterial blooms in lakes and drinking water reservoirs. However, it is largely unknown how environmental parameters alter the effectiveness of H2O2 treatments. In this study, the toxic cyanobacterial strain Microcystis aeruginosa PCC 7806 was treated with a range of H2O2 concentrations (0 to 10 mg/L), while being exposed to different light intensities and light colors. H2O2 treatments caused a stronger decline of the photosynthetic yield in high light than in low light or in the dark, and also a stronger decline in orange than in blue light. Our results are consistent with the hypothesis that H2O2 causes major damage at photosystem II (PSII) and interferes with PSII repair, which makes cells more sensitive to photoinhibition. Furthermore, H2O2 treatments caused a decrease in cell size and an increase in extracellular microcystin concentrations, indicative of leakage from disrupted cells. Our findings imply that even low H2O2 concentrations of 1–2 mg/L can be highly effective, if cyanobacteria are exposed to high light intensities. We therefore recommend performing lake treatments during sunny days, when a low H2O2 dosage is sufficient to suppress cyanobacteria, and may help to minimize impacts on non-target organisms.
Highlights
Cyanobacteria can develop dense blooms in eutrophic lakes and reservoirs [1,2]
The decline of the photosynthetic vitality was strongly dependent on both the H2 O2 dosage and the light intensity
An addition of mg/L H2 O2 in the dark caused only a 30% decline in photosynthetic vitality (Figure 1E), whereas the addition of 1 mg/L H2 O2 at a light intensity of 150 μmol photons·m−2 ·s−1 caused a complete decline of the photosynthetic vitality to zero within 2.5 h (Figure 1A)
Summary
Cyanobacteria can develop dense blooms in eutrophic lakes and reservoirs [1,2]. Many of the bloom-forming cyanobacteria, such as Microcystis aeruginosa, can produce secondary metabolites that are toxic to plants, invertebrates and vertebrates, including birds and mammals [3,4,5]. Toxic cyanobacteria can be a human health risk, especially in bathing waters or drinking water supplies [6,7,8]. Toxic cyanobacterial blooms may interfere with the intake of water by drinking water companies, and lead to the closure of recreational lakes, sometimes with large socioeconomic consequences [9,10,11,12]. The most sustainable solution to prevent bloom formation of toxic cyanobacteria is a reduction of nutrient inputs, phosphorus (P) and nitrogen (N), into lakes
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