Effects of hydrogen peroxide on cyanobacterial blooms

Cyanobacterial blooms often cause ecological and economic damage to recreational waters and drinking water reservoirs around the world. In addition, toxins produced by cyanobacteria can be directly harmful to many organisms. Attempts to reduce nutrient inputs into lakes, which is the preferred long-term solution, have proven to be challenging. Consequently, there is a demand for sustainable emergency measures that rapidly reduce cyanobacterial blooms. Hydrogen peroxide (H₂O₂) is a good candidate for short-term treatments, as it has a stronger effect on cyanobacteria than eukaryotic phytoplankton and degrades to water and oxygen without leaving chemical traces behind.
This PhD thesis aims to further increase our knowledge about the efficacy of H₂O₂ treatments and their effects on other organisms in the ecosystem. Our laboratory experiments show that high light intensities in the presence of H₂O₂ lead to photoinhibition and cell damage, which makes the H₂O₂ treatments more effective. At low light conditions, nutrient limitation caused cyanobacteria to be less sensitive to H₂O₂. Treatments of entire lakes showed that H₂O₂ rapidly suppressed cyanobacterial blooms. Cyanobacteria were indeed much more sensitive to H₂O₂ than eukaryotic phytoplankton and the cyanotoxins, released by the lysing cyanobacterial blooms, declined in the subsequent days. Rotifers were frequently impacted, while other zooplankton groups (cladocerans and copepods) were less sensitive to H₂O₂. Microbial community analysis showed that H₂O₂ induced short-term changes in the microbial community, followed by subsequent resilience and recovery. These findings and several recommendations for H₂O₂ treatments of cyanobacterial blooms are discussed in this thesis.