Abstract
Experiments with different phytoplankton densities in lake samples showed that a high biomass increases the rate of hydrogen peroxide (HP) degradation and decreases the effectiveness of HP in the selective suppression of dominant cyanobacteria. However, selective application of HP requires usage of low doses only, accordingly this defines the limits for use in lake mitigation. To acquire insight into the impact of HP on other phytoplankton species, we have followed the succession of three phytoplankton groups in lake samples that were treated with different concentrations of HP using a taxa-specific fluorescence emission test. This fast assay reports relatively well on coarse changes in the phytoplankton community; the measured data and the counts from microscopical analysis of the phytoplankton matched quite well. The test was used to pursue HP application in a Planktothrix agardhii-dominated lake sample and displayed a promising shift in the phytoplankton community in only a few weeks. From a low-diversity community, a change to a status with a significantly higher diversity and increased abundance of eukaryotic phytoplankton species was established. Experiments in which treated samples were re-inoculated with original P. agardhii-rich lake water demonstrated prolonged suppression of cyanobacteria, and displayed a remarkable stability of the newly developed post-HP treatment state of the phytoplankton community.
Highlights
In recent years the nuisance of harmful algae has increased rather than decreased (Stumpf et al, 2012; Michalak et al, 2013; Ai et al, 2015; Paerl et al, 2015), because of eutrophication; climate change and rising carbon dioxide concentrations in the atmosphere make cyanobacteria thrive and contribute to their dominance (Paerl and Huisman, 2008; Carey et al, 2012; Abbreviations: HP, hydrogen peroxide, H2O2Combatting cyanobacteria with hydrogen peroxideVerspagen et al, 2014)
After 24 h, all HP was degraded in the concentrated water sample, except for the highest dose of 50 mg·L−1, which was still present at 6.3 mg·L−1 HP and of the similar start concentration the diluted water sample still contained 24.9 mg·L−1 HP after 24 h
The original lake sample showed no more traces of added HP below 5 mg·L−1 after 24 h; but of the dose of 10 mg·L−1 1.8 mg·L−1 HP was still present (Figure 2B)
Summary
In recent years the nuisance of harmful algae has increased rather than decreased (Stumpf et al, 2012; Michalak et al, 2013; Ai et al, 2015; Paerl et al, 2015), because of eutrophication; climate change and rising carbon dioxide concentrations in the atmosphere make cyanobacteria thrive and contribute to their dominance (Paerl and Huisman, 2008; Carey et al, 2012; Abbreviations: HP, hydrogen peroxide, H2O2Combatting cyanobacteria with hydrogen peroxideVerspagen et al, 2014). In invasive lake mitigation technology, diverse methods are available for the termination of harmful cyanobacterial blooms, but many are not selective, may leave traces of added chemicals behind, and often do not comply with the desirable selectivity to not overly damage lake-ecology. An example of the latter is the use of cyanocidal or cyanostatic agents like copper sulfate; a range of extracted biological agents or unrefined products, such as barley or rice straw, has been used (for a review see Jancula and Marsalek, 2011). Artificial deep mixing (Visser et al, 1996; Huisman et al, 2004) and flushing (see Verspagen et al, 2006 and references therein) of lakes have been successfully applied in the reduction of cyanobacterial blooms
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