Effect of hydrogen peroxide on natural phytoplankton and bacterioplankton in a drinking water reservoir: Mesocosm-scale study

The use of coagulant and natural soil to control cyanobacterial blooms in a tropical reservoir

Cyanobacterial blooms have been a growing problem in water bodies and attracted attention from researcher and water companies worldwide. Different treatment methods have been researched and applied either inside water treatment plants or directly into reservoirs. We tested a combination of coagulants, polyaluminium chloride (PAC) and iron(III) chloride (FeCl3), and ballasts, luvisol (LUV) and planosol (PLAN), known as the 'Floc and Sink' technique, to remove positively buoyant cyanobacteria from a tropical reservoir water. Response Surface Methodology (RSM) based on Central Composite Design (CCD) was used to optimize the two reaction variables - coagulant dosage (x1) and ballast dosage (x2) to remove the response variables: chlorophyll-a, turbidity, true color, and organic matter. Results showed that the combination of LUV with PAC effectively reduced the concentration of the response variables, while PLAN was ineffective in removing cyanobacteria when combined to PAC or FeCl3. Furthermore, FeCl3 presented poorer floc formation and lower removal efficiency compared to PAC. This study may contribute to the theoretical and practical knowledge of the algal biomass removal for mitigating eutrophication trough different dosages of coagulants and ballasts.

Molecular mechanisms underlying sodium percarbonate treatment suppress the recovery and growth of Pseudanabaena sp. in early spring

Increasing frequency and intensity of cyanobacterial blooms in water sources is a growing global issue. Algicides are usually implemented in summer or autumn when blooms break out, however, the blooms will form again when algicide's concentration declines to a certain extent. Preventing the recovery and growth of cyanobacteria in early spring may be conducive to abatement of the blooms in summer or autumn. In this study solid sodium percarbonate (SPC) was used as an algicide to suppress recovery and growth of Pseudanabaena sp., a common odour-producing cyanobacterium, in early spring (12 °C). Results showed that 3.0 and 6.0 mg/L SPC were able to kill most of the algal cells after 12 h treatment at 12 °C, and the residual cells gradually died during the re-cultivation period at 25 °C. As a control, although SPC also caused most of algal cells to lyse at 25 °C, regrowth of cells was found during the period of re-cultivation at 25 °C. Transcriptomic analysis revealed that the dysregulated genes were strongly associated with translation and photosynthesis after SPC treatment. All differentially expressed unigenes related to translation and photosynthesis were down-regulated after SPC oxidation at 12 °C, whereas key genes associated with translation and photosynthesis were upregulated after SPC treatment at 25 °C.

The secondary outbreak risk and mechanisms of Microcystis aeruginosa after H2O2 treatment

The secondary outbreak of cyanobacteria after algicide treatment has been a serious problem to water ecosystems. Hydrogen peroxide (H2O2) is an algaecide widely used in practice, but similar re-bloom problems are inevitably encountered. Our work found that Microcystis aeruginosa (M. aeruginosa) temporarily hibernates after H2O2 treatment, but there is still a risk of secondary outbreaks. Interestingly, the dormant period was as long as 20 and 28 days in 5 mg L-1 and 20 mg L-1 H2O2 treatment groups, respectively, but the photosynthetic activity was both restored much earlier (within 14 days). Subsequently, a quantitative imaging flow cytometry-based method was constructed and confirmed that the re-bloom had undergone two stages including first recovery and then re-division. The expression of ftsZ and fabZ genes showed that M. aeruginosa had active transcription processes related to cell division protein and fatty acid synthesis during the dormancy stat. Furthermore, metabolomics suggested that the recovery of M. aeruginosa was mainly by activating folate and salicylic acid synthesis pathways, which promoted environmental stress resistance, DNA synthesis, and cell membrane repair. This study reported the comprehensive mechanisms of secondary outbreak of M. aeruginosa after H2O2 treatment. The findings suggest that optimizing the dosage and frequency of H2O2, as well as exploring the potential use of salicylic acid and folic acid inhibitors, could be promising directions for future algal control strategies.

Unraveling the ecological mechanisms of Aluminum on microbial community succession in epiphytic biofilms on Vallisneria natans leaves: Novel insights from microbial interactions

The extensive use of aluminum (Al) poses an escalating ecological risk to aquatic ecosystems. The epiphytic biofilm on submerged plant leaves plays a crucial role in the regulation nutrient cycling and energy flow within aquatic environments. Here, we conducted a mesocosm experiment aimed at elucidating the impact of different Al concentrations (0, 0.6, 1.2, 2.0 mg/L) on microbial communities in epiphytic biofilms on Vallisneria natans. At 1.2 mg/L, the highest biofilms thickness (101.94 µm) was observed. Al treatment at 2.0 mg/L significantly reduced bacterial diversity, while micro-eukaryotic diversity increased. Pseudomonadota and Bacteroidota decreased, whereas Cyanobacteriota increased at 1.2 mg/L and 2.0 mg/L. At 1.2 and 2.0 mg/L. Furthermore, Al at concentrations of 1.2 and 2.0 mg/L enhanced the bacterial network complexity, while micro-eukaryotic networks showed reduced complexity. An increase in positive correlations among microbial co-occurrence patterns from 49.51% (CK) to 57.05% (2.0 mg/L) was indicative of augmented microbial cooperation under Al stress. The shift in keystone taxa with increasing Al concentration pointed to alterations in the functional dynamics of microbial communities. Additionally, Al treatments induced antioxidant responses in V. natans, elevating leaf reactive oxygen species (ROS) content. This study highlights the critical need to control appropriate concentration Al concentrations to preserve microbial diversity, sustain ecological functions, and enhance lake remediation in aquatic ecosystems.

Microbial Community Response to Granular Peroxide-Based Algaecide Treatment of a Cyanobacterial Harmful Algal Bloom in Lake Okeechobee, Florida (USA)

Cyanobacterial harmful algal blooms (cyanoHABs) occur in fresh water globally. These can degrade water quality and produce toxins, resulting in ecological and economic damages. Thus, short-term management methods (i.e., algaecides) are necessary to rapidly mitigate the negative impacts of cyanoHABs. In this study, we assess the efficacy of a hydrogen peroxide-based algaecide (PAK® 27) on a Microcystis dominated bloom which occurred within the Pahokee Marina on Lake Okeechobee, Florida, USA. We observed a significant reduction in chlorophyll a (96.81%), phycocyanin (93.17%), and Microcystis cell counts (99.92%), and a substantial reduction in microcystins (86.7%) 48 h after treatment (HAT). Additionally, there was a significant shift in bacterial community structure 48 HAT, which coincided with an increase in the relative abundance of photosynthetic protists. These results indicate that hydrogen peroxide-based algaecides are an effective treatment method for cyanoHAB control and highlight their effects on non-target microorganisms (i.e., bacteria and protists).

Synechococcus dominance induced after hydrogen peroxide treatment of Microcystis bloom in the Caloosahatchee River, Florida

Few field trials examining hydrogen peroxide as a cyanobacterial harmful algal bloom (cHAB) treatment have been conducted in subtropical and tropical regions. None have been tested in Florida, home to Lake Okeechobee and downstream waterways which periodically experience Microcystis bloom events. To investigate treatment effects in Florida, we applied a 490 μM (16.7 mg/L; 0.0015%) hydrogen peroxide spray to a minor bloom of Microcystis aeruginosa on the downstream side of Franklin Lock and Dam in the Caloosahatchee River. Although hydrogen peroxide decreased to background level one day post-treatment, succession was observed in phytoplankton community amplicon sequencing. The relative abundance of Microcystis decreased on day 3 by 86%, whereas the picocyanobacteria Synechococcus became dominant, increasing by 77% on day 3 and by 173% on day 14 to 57% of the phytoplankton community. Metatranscriptomics revealed Synechococcus likely benefitted from the antioxidant defense of upregulated peroxiredoxin, peroxidase/catalase, and rubrerythrin expressions immediately after treatment, and upregulated nitrate transport and urease to take advantage of available nitrogen. Our results indicated hydrogen peroxide induces succession of the phytoplankton community from Microcystis to non-toxic picocyanobacteria and could be used for selective suppression of harmful cyanobacteria.

Quorum sensing signal autoinducer-2 promotes hydrogen peroxide degradation in water by Gram-positive bacteria

Hydrogen peroxide is widely used to remedy bacterial and parasitic infections, but its excessive use will cause severe damage to aquatic animals. Moreover, there is no safe, efficient and low-cost method to degrade residual hydrogen peroxide in water. Here we developed a hydrogen peroxide removal mechanism by which autoinducer-2 (AI-2), a quorum sensing signal molecule that can promote the hydrogen peroxide degradation by Gram-positive bacteria. Here, we investigated the promotion effect of AI-2 on hydrogen peroxide degradation by Deinococcus sp. Y35 and the response of the antioxidant system. We further sought to understand the key mechanism underlying the promotion effect of AI-2 on hydrogen peroxide degradation is that, AI-2 contributed to the resistance of strain Y35 to oxidative stress induced by hydrogen peroxide, and altered membrane permeability of strain Y35 that allowed more hydrogen peroxide to enter bacterial cells and be degraded. Additionally, AI-2 can also encourage multiple Gram-positive bacteria to degrade hydrogen peroxide. Accordingly, our study serves as a reference for the regulation mechanism of the signal molecule AI-2 and provides the development of new strategies for hydrogen peroxide degradation.

Bacterial community shifts induced by high concentration hydrogen peroxide treatment of Microcystis bloom in a mesocosm study

Hydrogen peroxide has gained popularity as an environmentally friendly treatment for cyanobacterial harmful algal blooms (cHABs) that takes advantage of oxidative stress sensitivity in cyanobacteria at controlled concentrations. Higher concentrations of hydrogen peroxide treatments may seem appealing for more severe cHABs but there is currently little understanding of the environmental impacts of this approach. Of specific concern is the associated microbial community, which may play key roles in the succession/recovery process post-treatment. To better understand impacts of a high concentration treatment on non-target microbial communities, we applied a hydrogen peroxide spray equating to a total volume concentration of 14 mM (473 mg/L, 0.04%) to 250 L mesocosms containing Microcystis bloom biomass, monitoring treatment and control mesocosms for 4 days. Cyanobacteria dominated control mesocosms throughout the experiment while treatment mesocosms experienced a 99% reduction, as determined by bacterial amplicon sequencing, and a 92% reduction in bacterial cell density within 1 day post-treatment. Only the bacterial community exhibited signs of regrowth, with a fold change of 9.2 bacterial cell density from day 1 to day 2. Recovery consisted of succession by Planctomycetota (47%) and Gammaproteobacteria (17%), which were likely resilient due to passive cell component compartmentalization and rapid upregulation of dnaK and groEL oxidative stress genes, respectively. The altered microbiome retained beneficial functionality of microcystin degradation through a currently recognized but unidentified pathway in Gammaproteobacteria, resulting in a 70% reduction coinciding with bacterial regrowth. There was also an 81% reduction of both total nitrogen and phosphorus, as compared to 91 and 93% in the control, respectively, due to high expressions of genes related to nitrogen (argH, carB, glts, glnA) and phosphorus (pntAB, phoB, pstSCB) cycling. Overall, we found a portion of the bacterial community was resilient to the high-concentration hydrogen peroxide treatment, resulting in Planctomycetota and Gammaproteobacteria dominance. This high-concentration treatment may be suitable to rapidly end cHABs which have already negatively impacted the aquatic environment rather than allow them to persist.

Periodic Addition of Glucose Suppressed Cyanobacterial Abundance in Additive Lake Water Samples during the Entire Bloom Season

Previously, we showed that prophylactic addition of glucose to Harsha Lake water samples could inhibit cyanobacteria growth, at least for a short period of time. The current study tested cyanobacterial control with glucose for the entire Harsha Lake bloom season. Water samples (1000 ml) were collected weekly from Harsha Lake during the algal-bloom season starting June 9 and lasting until August 24, 2022. To each of two 7-liter polypropylene containers, 500 ml of Harsha Lake water was added, and the containers were placed in a controlled environment chamber. To one container labeled "Treated," 0.15 g of glucose was added, and nothing was added to the container labeled "Control." After that, three 25 ml samples from each container were collected and used for 16S rRNA gene sequencing each week. Then 1000 ml of Harsha Lake water was newly collected each week, with 500 ml added to each container, along with the addition of 0.15 g glucose to the "Treated" container. Sequencing data were used to examine differences in the composition of bacterial communities between Treated and Control containers. Treatment with glucose altered the microbial communities by 1) reducing taxonomic diversity, 2) largely eliminating cyanobacterial taxa, and 3) increasing the relative abundance of subsets of non-cyanobacterial taxa (such as Proteobacteria and Actinobacteriota). These effects were observed across time despite weekly inputs derived directly from Lake water. The addition of glucose to a container receiving weekly additions of Lake water suppressed the cyanobacterial populations during the entire summer bloom season. The glucose appears to stimulate the diversity of certain bacterial taxa at the expense of the cyanobacteria.

Unleashing the power of acetylacetone: Effective control of harmful cyanobacterial blooms with ecological safety

Harmful algal blooms resulting from eutrophication pose a severe threat to human health. Acetylacetone (AA) has emerged as a potential chemical for combatting cyanobacterial blooms, but its real-world application remains limited. In this study, we conducted a 42-day evaluation of AA's effectiveness in controlling blooms in river water, with a focus on the interplay between ecological community structure, organism functional traits, and water quality. At a concentration of 0.2 mM, AA effectively suppressed the growth of Cyanobacteria (88 %), Bacteroidia (49 %), and Alphaproteobacteria (52 %), while promoting the abundance of Gammaproteobacteria (5.0 times) and Actinobacteria (7.2 times) that are associated with the degradation of organic matter. Notably, after dosing of AA, the OD680 (0.07 ± 0.02) and turbidity (8.6 ± 2.1) remained at a satisfactory level. AA induced significant disruptions in two photosynthesis and two biosynthesis pathways (P < 0.05), while simultaneously enriching eight pathways of xenobiotics biodegradation and metabolism. This enrichment facilitated the reduction of organic pollutants and supported improved water quality. Importantly, AA treatment decreased the abundance of two macrolide-related antibiotic resistance genes (ARGs), ereA and vatE, while slightly increased the abundance of two aminoglycoside-related ARGs, aacA and strB. Overall, our findings establish AA as an efficient and durable algicide with favorable ecological safety. Moreover, this work contributes to the development of effective strategies for maintaining and restoring the health and resilience of aquatic ecosystems impacted by harmful algal blooms.

Effect of luminescent materials on the biochemistry, ultrastructure, and rhizobial microbiota of Spirodela polyrhiza

Fluorescent materials and technologies have become widely used in scientific research, and due to the ability to convert light wavelengths, their application to photosynthetic organisms can affect their development by altering light quality. However, the impacts of fluorescent materials on aquatic plants and their environmental risks remain unclear. To assess the effects of luminescent materials on floating aquatic macrophytes and their rhizosphere microorganisms, 4-(di-p-tolylamino)benzaldehyde-A (DTB-A) and 4-(di-p-tolylamino)benzaldehyde-M (DTB-M) (emitting blue-green and orange-red light, respectively) were added individually and jointly to Spirodela polyrhiza cultures and set at different concentrations (1, 10, and 100 μM). Both DTB-A and DTB-M exhibited phytotoxicity, which increased with concentration under separate treatment. Moreover, the combined group exhibited obvious stress relief at 10 μM compared to the individually treated group. Fluorescence imaging showed that DTB-A and DTB-M were able to enter the cell matrix and organelles of plant leaves and roots. Peroxidation induced cellular damage, contributing to a decrease in superoxide dismutase (SOD) and peroxidase (POD) activities and malondialdehyde (MDA) accumulation. Decomposition of organelle structures, starch accumulation in chloroplasts, and plasmolysis were observed under the ultrastructure, disrupting photosynthetic pigment content and photosynthesis. DTB-A and DTB-M exposure resulted in growth inhibition, dry weight loss, and leaf yellowing in S. polyrhiza. A total of 3519 Operational Taxonomic Units (OTUs) were identified in the rhizosphere microbiome. The microbial communities were dominated by Alphaproteobacteria, Oxyphotobacteria, and Gammaproteobacteria, with the abundance and diversity varied significantly among treatment groups according to Shannon, Simpson, and Chao1 indices. This study revealed the stress defense response of S. polyrhiza to DTB-A and DTB-M exposures, which provides a broader perspective for the bioremediation of pollutants using aquatic plants and supports the further development of fluorescent materials for applications.

Impact of artificial mixing and oxygenation on bacteria in a water transfer reservoir: Community succession and the role in water quality improvement

Artificial mixing and oxygenation induced by water-lifting aerations (WLAs) have the potential to improve water quality in reservoirs. However, there is a limited understanding of the bacterial community composition, assembly, and mechanisms behind water quality improvement under the influence of WLAs, especially in a water transfer reservoir. Here, the dynamics and relationship between water quality, bacterial diversity, and composition during the pre-operation, in-operation, and post-operation stages of WLAs were analyzed using high-throughput sequencing technology to explore the effects of artificially regulated bacteria on water quality improvement. WLAs operation led to the elimination of water stratification, significant bottom oxygenation, and reduction in nutrient concentrations. In addition, the operation of WLAs significantly changed the bacterial community composition, with an increase in richness, negligible difference in diversity, and a significant increase in the abundance of species with pollutant degradation functions, resulting in a shift from stochastic to deterministic processes of the bacterial community assembly. As a result, enhancement of the dominant bacteria responsible for organic matter degradation and denitrification and suppression of the emergence of algae-related bacteria were observed during the WLAs operation, and the ecosystem stability improved. Multiple analyses indicated a direct correlation between artificial mixing and oxygenation; changes in the bacterial community; and the reduction of nitrogen, phosphorus, and permanganate index in the water column. This study provides novel insights into in situ water quality enhancement and a valuable reference for understanding bacterial change patterns under artificially intervened conditions in water transfer reservoirs.

Control of cyanobacterial bloom and purification of bloom-laden water by sequential electro-oxidation and electro-oxidation-coagulation

The outbreaks of cyanobacterial blooms have caused severe threat to aquatic ecosystem and public health. In this work, electrochemical technology with RuO2/IrO2/Ti (RIT) or/and Al as anode for cyanobacterial bloom control and simultaneous water purification were studied. Compared with RIT-Al and Al electrodes, RIT exhibited the highest effects on bloom algae inactivation and inhibition of algae regrowth. Live/dead analysis, SEM, intracellular reactive oxygen species (ROS) and antioxidant system activities revealed that RIT could disintegrate bloom flocs and damage embedded algal cells due to high intensity of oxidation. With the lysis of cyanobacterial bloom, high content of intracellular compounds containing organic carbon, nitrogen and phosphorus released, necessitating water quality restoration. In the subsequent water purification process, RIT-Al overtook RIT and Al in removal of organic and nutrient pollutants due to the complex effects of electro-oxidation, coagulation, co-precipitation, electro-nitrification and electro-denitrification. Therefore, sequential electro-oxidation and electro-oxidation-coagulation process was an effective method for control cyanobacteria bloom and simultaneous removal of DOM, microcystin-LR (MC-LR), nitrogen and phosphorus, which is a promising technology.

The apoptosis of Chlorella vulgaris and the release of intracellular organic matter under metalimnetic oxygen minimum conditions

Metalimnetic oxygen minimum (MOM) is a frequent occurrence in lakes and reservoirs, and its formation is related to the blooming and apoptosis of algae. In this study, the apoptosis mechanism of Chlorella vulgaris (C. vulgaris) and the release of intracellular organic matter (IOM) under different MOM conditions were analyzed by changing the dissolved oxygen (DO) (7.0 mg/L, 3.0 mg/L, and 0.3 mg/L) and water pressure (0.3 MPa and normal pressure). The integrity and auto-fluorescence of algae cells decreased rapidly in the first 8 days, and then stabilized gradually during the development of MOM. Compared with that of water pressures, DO had a significant effect on the activity of algal cells, and higher initial DO levels (3.0 mg/L and 7.0 mg/L) accelerated the lysis of algal cells. The integrity of algae cells decreased to 28.8 %, 31.8 % and 56.6 % at the initial DO of 7 mg/L, 3 mg/L and 0.3 mg/L under 0.3 MPa, respectively. Meanwhile, the concentration of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) continued to increase and reached their maximum at 8 or 12 days, respectively, due to the IOM release caused by algal cell rupture, and then gradually decreased due to microbial degradation. Consistent with the results of membrane integrity, the highest DOC and DON concentrations were found at higher initial DO conditions. By parallel factor analysis, the change in total organic matter fluorescence intensity was consistent with DOC, once again increasing in the first 8 days and then gradually decreasing. The increased humic-like component, which is related to higher aromaticity, led to the monotonic increase of HAAFPs and THMFPs. However, the released IOM of C. vulgaris had lower N-DBPFPs, with TCNMFP predominating primarily. In summary, these results shed new lights on exploring the apoptosis of algae and the release of IOM during the development of MOM.

Broad spectrum and species specificity of plant allelochemicals 1,2-benzenediol and 3-indoleacrylic acid against marine and freshwater harmful algae

Allelochemicals derived from plants have shown great potential in mitigating harmful algal blooms (HABs), although different algal species can respond differently to these chemicals. Therefore, we first investigated the allelopathic effects of two newly identified plant-derived allelochemicals, 1,2-benzenediol (1,2-BD) and 3-indoleacrylic acid (3-IDC), on six algal species. Then we further evaluated the allelopathic responses of two bloom-forming species, Microcystis aeruginosa FACHB-905 and Heterosigma akashiwo to 1,2-BD. Results showed that 1,2-BD had a broader antialgal spectrum than 3-IDC. Allelopathic response analysis indicated that 1,2-BD consistently and stably inhibit the growth of M. aeruginosa FACHB-905, with inhibitory mechanism being disruption of photosynthetic activity, overwhelming of the antioxidant system and activation of programmed cell death (PCD). H. akashiwo displayed resistance to 1,2-BD during exposure, and the growth inhibition was mainly attributed to PCD. Therefore, the species-specific allelopathic responses provide new insights for controlling HABs using 1,2-BD and 3-IDC.

Phytoplankton interspecific interactions modified by symbiotic fungi and bacterial metabolites under environmentally relevant hydrogen peroxide concentrations stress

Hydrogen peroxide (H2O2), which accumulates in water and triggers oxidative stress for aquatic microbes, has been shown to have profound impacts on planktonic microbial community dynamics including cyanobacterial bloom formation. Yet, potential effects of H2O2 on interspecific relationships of phytoplankton-microbe symbiotic interactions remain unclear. Here, we investigated effects of environmentally relevant H2O2 concentrations on interspecific microbial relationships in algae-microbe symbiosis. Microbes play a crucial role in the competition between M. aeruginosa and Chlorella vulgaris at low H2O2 concentrations (∼400 nM), in which fungi and bacteria protect Microcystis aeruginosa from oxidative stress. Moreover, H2O2 stimulated the synthesis and release of extracellular microcystin-LR from Microcystis aeruginosa, while intracellular microcystin-LR concentrations remained at a relatively constant level. In the presence of H2O2, loss of organoheterocyclic compounds, organic acids and ketones contributed to the growth of M. aeruginosa, but the reduction of vitamins inhibited it. Regulation of interspecific relationships by H2O2 is achieved by its action on fungal species and bacterial secretory metabolites. This study explored the response of phytoplankton interspecific relationships in symbiotic phytoplankton-microbe interactions to environmentally relevant H2O2 concentrations stress, providing a theoretical basis for understanding the formation of harmful-algae blooming and impact of photochemical properties of water on aquatic ecological safety and stability.

Long-range hydrophobic force enhanced interfacial photocatalysis for the submerged surface anti-biofouling

Developing anti-biofouling and anti-biofilm techniques is of great importance for protecting water-contact surfaces. In this study, we developed a novel double-layer system consisting of a bottom immobilized TiO2 nanoflower arrays (TNFs) unit and an upper superhydrophobic (SHB) coating along with the assistance of nanobubbles (NBs), which can significantly elevate the interfacial oxygen level by establishing the long-range hydrophobic force between NBs and SHB and effectively maximize the photocatalytic reaction brought by the bottom TNFs. The developed NBs-SHB/TNFs system demonstrated the highest bulk chemical oxygen demand (COD) reduction efficiency at approximately 80% and achieved significant E. coli and Chlorella sp. inhibition efficiencies of 5.38 and 1.99 logs. Meanwhile, the system showed a sevenfold higher resistance to biofilm formation when testing in a wastewater matrix using a wildly collected biofilm seeding solution. These findings provide insights for implementing nanobubble-integrated techniques for submerged surface protection.

In situ H2O2 treatment of blue-green algae contaminated reservoirs causes significant improvement in drinking water treatability

The evaluation of water quality improvement brought about by in situ treatment of eutrophic water bodies, especially those used for human supply is a challenging task since each water system responds differently. To overcome this challenge, we applied exploratory factor analysis (EFA) to understand the effects of using hydrogen peroxide (H₂O₂) on eutrophic water used as a drinking water supply. This analysis was used to identify the main factors that described the water treatability after exposing blue-green algae (cyanobacteria) contaminated raw water to H₂O₂ at both 5 and 10 mg L^-1. Cyanobacterial chlorophyll-a was undetectable following the application of both concentrations of H₂O₂ after four days, while not causing relevant changes to green algae and diatoms chlorophyll-a concentrations. EFA demonstrated that the main factors affected by both H₂O₂ concentrations were turbidity, pH, and cyanobacterial chlorophyll-a concentration, which are important variables for a drinking water treatment plant. The H₂O₂ caused significant improvement in water treatability by decreasing those three variables. Finally, the use of EFA was demonstrated to be a promising tool in identifying which limnological variables are most relevant concerning the efficacy of water treatment, which in turn can make water quality monitoring more efficient and less costly.

Inactivation of Microcystis aeruginosa by H2O2 generated from a carbon black polytetrafluoroethylene gas diffusion electrode in electrolysis by low-amperage electric current

Frequent outbreaks of cyanobacterial blooms have seriously threatened aquatic ecological environments and human health. Electrolysis by low-amperage electric current is effective for algae inactivation; however, it has no selectivity. Hydrogen peroxide (H₂O₂) is considered to be an efficient and selective suppressor of algae. Therefore, it is necessary to develop an electrode that can generate H₂O₂ to improve electrolysis technology. In this study, a carbon black polytetrafluoroethylene gas diffusion electrode (C-PTFE GDE) with good stability was prepared by a simple adhesive coating method. Then, the inactivation of Microcystis aeruginosa was conducted with electrolysis by low-amperage electric current using Ti/RuO₂ as the anode and C-PTFE GDE as the cathode. When the electrode spacing was 4 cm, the current density was 20 mA cm^-2, and the gas flow was 0.4 L min^-1, 85% of the algae could be inactivated in 20 min. Comparing the inactivation effect of the electric field and electrogenerated oxidants, it was found that electrolysis more rapidly and strongly inactivated algae when an electric field existed. However, electrogenerated oxidants dominated algae inactivation. The concentration of H₂O₂ was as high as 58 mg L^-1, while the concentration of chlorines was only 0.57 mg L^-1, and the generation rate of H₂O₂ was 65 times that of chlorines. Consequently, electrogenerated oxidants dominated by H₂O₂ attacked photosystem II of the algae and caused oxidative damage to membrane lipids, affecting the photosynthetic capacity. Eventually, most of the algae were inactivated. The study suggested that C-PTFE GDE was promising for the inactivation of Microcystis aeruginosa in this electrochemical system.

Repeated hydrogen peroxide dosing briefly reduces cyanobacterial blooms and microcystin while increasing fecal bacteria indicators in a eutrophic pond

This study explored the effects of H₂O₂ on Cyanobacteria and non-target microbes using fluorometry, microscopy, flow cytometry, and high throughput DNA sequencing of the 16S rRNA gene during a series of mesocosm and whole-ecosystem experiments in a eutrophic pond in NY, USA. The addition of H₂O₂ (8 mg/L) significantly reduced Cyanobacteria concentrations during a majority of experiments (66%; 6 of 9) and significantly increased eukaryotic green and unicellular brown algae in 78% and 45% of experiments, respectively. While heterotrophic bacteria declined significantly following H₂O₂ addition in all experiments, bacteria indicative of potential fecal contamination (Escherichia coli, Enterococcus, fecal coliform bacteria) consistently and significantly increased in response to H₂O₂, evidencing a form of 'pollution swapping'. H₂O₂ more effectively reduced Cyanobacteria in enclosed mesocosms compared to whole-ecosystem applications. Ten whole-pond H₂O₂ applications over a two-year period temporarily reduced cyanobacterial levels but never reduced concentrations below bloom thresholds and populations always rebounded in two weeks or less. The bacterial phyla of Cyanobacteria, Actinobacteria, and Planctomycetes were the most negatively impacted by H₂O₂. Microcystis was always reduced by H₂O₂, as was the toxin microcystin, but Microcystis remained dominant even after repeated H₂O₂ treatments. Although H₂O₂ favored the growth of eukaryotic algae over potentially harmful Cyanobacteria, the inability of H₂O₂ to end cyanobacterial blooms in this eutrophic waterbody suggests it is a non-ideal mitigation approach in high biomass ecosystems and should be used judiciously due to potential negative impacts on non-target organisms and promotion of bacteria indicative of fecal contamination.

Complex effects of dissolved organic matter, temperature, and initial bloom density on the efficacy of hydrogen peroxide to control cyanobacteria

Harmful cyanobacterial blooms plague reservoirs and lakes used for a variety of purposes, such as recreation and drinking water. Chemical controls are frequently used to mitigate the occurrence of cyanobacterial blooms given that many are fast-acting and effective at reducing cyanobacterial abundance. Recent research has identified hydrogen peroxide (H₂O₂) as an environmentally friendly alternative to algaecides that have typically been used, such as copper sulfate. To build on past studies, these experiments sought to further understand how well H₂O₂ treatments reduce cyanobacteria in complex eutrophic conditions, as well as to assess treatment effects on a non-target phytoplankter, a green alga. We assessed the effectiveness of H₂O₂ (at treatments of 2-16 mg L^-1) under varying environmental conditions in a controlled laboratory setting, including (1) dissolved organic matter (DOM) concentrations (humic acid; 0-60 mg L^-1), (2) temperature (20, 25, and 32 °C), and (3) initial algal biomass (chlorophyll-a; 82-371 µg L^-1). In contrast to our expectations, neither DOM concentration nor temperature meaningfully impacted the effectiveness of H₂O₂ at reducing cyanobacteria. However, initial algal biomass as well as H₂O₂ treatment dose greatly influenced the effectiveness of the algaecide on cyanobacteria. Treatments of ≥ 8 mg H₂O₂ L^-1 on algal biomass were significantly buffered with higher DOM and lower temperature, and the biological significance of these findings should be explored further. Across all experiments, H₂O₂ concentrations of 0.03-0.12 mg H₂O₂ L^-1 µg chlorophyll L^-1 were effective at significantly reducing cyanobacteria with varying effects on algal biomass. Thus, water resource managers are encouraged to consider how ambient levels of phytoplankton biomass may affect the ability of H₂O₂ to control cyanobacterial blooms prior to treatment.

Solar-driven semi-conductor photocatalytic water treatment (TiO2, g-C3N4, and TiO2+g-C3N4) of cyanotoxins: Proof-of-concept study with microcystin-LR

Cyanobacteria and their toxins are a threat to drinking water safety as increasingly cyanobacterial blooms (mass occurrences) occur in lakes and reservoirs all over the world. Photocatalytic removal of cyanotoxins by solar light active catalysts is a promising way to purify water at relatively low cost compared to modifying existing infrastructure. We have established a facile and low-cost method to obtain TiO₂ and g-C₃N₄ coated floating photocatalysts using recycled glass beads. g-C₃N₄ coated and TiO₂+g-C₃N₄ co-coated beads were able to completely remove microcystin-LR in artificial fresh water under both natural and simulated solar light irradiation without agitation in less than 2 h. TiO₂ coated beads achieved complete removal within 8 h of irradiation. TiO₂+g-C₃N₄ beads were more effective than g-C₃N₄ beads as demonstrated by the increase reaction rate with reaction constants, 0.0485 min^-1 compared to 0.0264 min^-1 respectively, with TiO₂ alone found to be considerably slower 0.0072 min^-1. g-C₃N₄ based photocatalysts showed a similar degradation pathway to TiO₂ based photocatalysts by attacking the C6-C7 double bond on the Adda side chain.

Mitigation of Marine Dinoflagellates Using Hydrogen Peroxide (H2O2) Increases Toxicity towards Epithelial Gill Cells

Hydrogen peroxide (H₂O₂) has been shown to efficiently remove toxic microalgae from enclosed ballast waters and brackish lakes. In this study, in vitro experiments were conducted to assess the side effects of mitigating toxic and non-toxic dinoflagellates with H₂O₂. Five H₂O₂ concentrations (50 to 1000 ppm) were used to control the cell abundances of the toxic dinoflagellates Alexandrium catenella and Karenia selliformis and the non-toxic dinoflagellates Lepidodinium chlorophorum and Prorocentrum micans. Photosynthetic efficiency and staining dye measurements showed the high efficiency of H₂O₂ for mitigating all dinoflagellate species at only 50 ppm. In a bioassay carried out to test cytotoxicity using the cell line RTgill-W1, control experiments (only H₂O₂) showed cytotoxicity in a concentration- and time- (0 to 24 h) dependent manner. The toxic dinoflagellates, especially K. selliformis, showed basal cytotoxicity that increased with the application of hydrogen peroxide. Unexpectedly, the application of a low H₂O₂ concentration increased toxicity, even when mitigating non-toxic dinoflagellates. This study suggests that the fatty acid composition of toxic and non-toxic dinoflagellate species can yield toxic aldehyde cocktails after lipoperoxidation with H₂O₂ that can persist in water for days with different half-lives. Further studies are needed to understand the role of lipoperoxidation products as acute mediators of disease and death in aquatic environments.

Effective Early Treatment of Microcystis Exponential Growth and Microcystin Production with Hydrogen Peroxide and Hydroxyapatite

Mitigating cyanotoxin production is essential to protecting aquatic ecosystems and public health. However, current harmful cyanobacterial bloom (HCB) control strategies have significant shortcomings. Because predicting HCBs is difficult, current HCB control strategies are employed when heavy HCBs have already occurred. Our pilot study developed an effective HCB prediction approach that is employed before exponential cyanobacterial growth and massive cyanotoxin production can occur. We used a quantitative polymerase chain reaction (qPCR) assay targeting the toxin-encoding gene mcyA to signal the timing of treatment. When control measures were applied at an early growth stage or one week before the exponential growth of Microcystis aeruginosa (predicted by qPCR signals), both hydrogen peroxide (H2O2) and the adsorbent hydroxyapatite (HAP) effectively stopped M. aeruginosa growth and microcystin (MC) production. Treatment with either H2O2 (10 mg·L-1) or HAP (40 µm particles at 2.5 g·L-1) significantly reduced both mcyA gene copies and MC levels compared with the control in a dose-dependent manner. While both treatments reduced MC levels similarly, HAP showed a greater ability to reduce mcyA gene abundance. Under laboratory culture conditions, H2O2 and HAP also prevented MC production when applied at the early stages of the bloom when mcyA gene abundance was below 105 copies·mL-1.

Treatment of the red tide dinoflagellate Karenia brevis and brevetoxins using USEPA-registered algaecides

The effectiveness of USEPA-registered algaecides for managing algae in lakes and reservoirs has been extensively evaluated in laboratory studies, mesocosm studies and in situ treatment. However, the use of these algaecides in marine environments for the management of dinoflagellates and associated toxins remains largely unknown. Karenia brevis is a toxic dinoflagellate that causes red tides in the Gulf of Mexico. In this study, we investigated the efficacy of six USEPA-registered algaecides, three copper-based and three peroxide-based, on treating toxic K. brevis with a natural bloom density (1.79 × 10⁷ cells/L). Our results indicate that the application of as low as 0.31-0.34 mg Cu/L led to a significant decrease of K. brevis cells within 24 h after treatment, while peroxide-based algaecides required a relatively higher concentration for the effective removal of K. brevis cells (4.89-7.08 mg H₂O₂/L), but still lower than maximum label rate. Total brevetoxin levels 72 h after treatment revealed that 1.00 mg Cu/L for Algimycin® PWF, 6.48 mg H₂O₂/L for PAK® 27 and 7.08 mg H₂O₂/L for Oximycin® P5 had the greatest impact on decreasing toxin levels. The correlation analysis showed that brevetoxin reduction rate was significantly positively related with the peroxide-based algaecide exposure concentration, which is caused by the oxidation of hydroxyl radicals produced by hydrogen peroxide. The degradation dynamics of the three peroxide-based algaecides revealed that salinity, microorganisms and organic matter (≥ 0.2 μm) impact the stability of hydrogen peroxide, and Oximycin® P5 showed the highest stability among tested peroxide-based algaecides with a degradation rate of 0.467 mg/d in natural seawater. Hence, our laboratory work provided new insights into potential emergency treatment methods for immediate mitigation of K. brevis and brevetoxins. More work on the fate and persistence of algaecide active ingredients and phycotoxins, effects of site characteristics, and pilot studies on marine non-targets are still needed before safe application of this method for HABs in marine systems.

Suppressing cyanobacterial dominance by UV-LED TiO2-photocatalysis in a drinking water reservoir: A mesocosm study

Cyanobacteria and their toxic secondary metabolites present challenges for water treatment globally. In this study we have assessed TiO₂ immobilized onto recycled foamed glass beads by a facile calcination method, combined in treatment units with 365 nm UV-LEDs. The treatment system was deployed in mesocosms within a eutrophic Brazilian drinking water reservoir. The treatment units were deployed for 7 days and suppressed cyanobacterial abundance by 85% while at the same time enhancing other water quality parameters; turbidity and transparency improved by 40 and 81% respectively. Genomic analysis of the microbiota in the treated mesocosms revealed that the composition of the cyanobacterial community was affected and the abundance of Bacteroidetes and Proteobacteria increased during cyanobacterial suppression. The effect of the treatment on zooplankton and other eukaryotes was also monitored. The abundance of zooplankton decreased while Chrysophyte and Alveolata loadings increased. The results of this proof-of-concept study demonstrate the potential for full-scale, in-reservoir application of advanced oxidation processes as complementary water treatment processes.

Sensitivity of phytoplankton, zooplankton and macroinvertebrates to hydrogen peroxide treatments of cyanobacterial blooms

Addition of hydrogen peroxide (H₂O₂) is a promising method to acutely suppress cyanobacterial blooms in lakes. However, a reliable H₂O₂ risk assessment to identify potential effects on non-target species is currently hampered by a lack of appropriate ecotoxicity data. The aim of the present study was therefore to quantify the responses of a wide diversity of freshwater phytoplankton, zooplankton and macroinvertebrates to H₂O₂ treatments of cyanobacterial blooms. To this end, we applied a multifaceted approach. First, we investigated the 24-h toxicity of H₂O₂ to three cyanobacteria (Planktothrix agardhii, Microcystis aeruginosa, Anabaena sp.) and 23 non-target species (six green algae, eight zooplankton and nine macroinvertebrate taxa), using EC₅₀ values based on photosynthetic yield for phytoplankton and LC₅₀ values based on mortality for the other organisms. The most sensitive species included all three cyanobacterial taxa, but also the rotifer Brachionus calyciflores and the cladocerans Ceriodaphnia dubia and Daphnia pulex. Next, the EC₅₀ and LC₅₀ values obtained from the laboratory toxicity tests were used to construct a species sensitivity distribution (SSD) for H₂O₂. Finally, the species predicted to be at risk by the SSD were compared with the responses of phytoplankton, zooplankton and macroinvertebrates to two whole-lake treatments with H₂O₂. The predictions of the laboratory-based SSD matched well with the responses of the different taxa to H₂O₂ in the lake. The first lake treatment, with a relatively low H₂O₂ concentration and short residence time, successfully suppressed cyanobacteria without major effects on non-target species. The second lake treatment had a higher H₂O₂ concentration with a longer residence time, which resulted in partial suppression of cyanobacteria, but also in a major collapse of rotifers and decreased abundance of small cladocerans. Our results thus revealed a trade-off between the successful suppression of cyanobacteria at the expense of adverse effects on part of the zooplankton community. This delicate balance strongly depends on the applied H₂O₂ dosage and may affect the decision whether to treat a lake or not.

Community succession during the preventive control of cyanobacterial bloom by hydrogen peroxide in an aquatic microcosm

Hydrogen peroxide (H₂O₂) is an environmentally friendly algaecide with good prospects for cyanobacterial bloom control. In this study, 0.2-1.5 mg L^-1 of H₂O₂ was applied to an aquatic microcosm containing cyanobacteria, bacteria, and eukaryotic phytoplankton at the early cyanobacterial growth stage·H₂O₂ generated hormesis in cyanobacteria at 0.2 mg L^-1; significantly (p < 0.05) inhibited cyanobacterial growth, cyanobacterial photosynthesis, and microcystin production at 0.5-1.5 mg L^-1; and effectively prevented the formation of cyanobacterial bloom without generating adverse effects on eukaryotic phytoplankton at 1.0 and 1.5 mg L^-1. Application of 0.5-1.5 mg L^-1 H₂O₂ directly inhibited the abundance of five typical bloom-forming cyanobacterial genera (Microcystis, Anabeana, Synechococcus, Nostoc, and Oscillatoria), which were negatively correlated with four bacterial genera (Actinotalea, Flavobacterium, Fluviicola, and Exiguobacterium) and five eukaryotic phytoplankton genera (Cyclotella, Desmodesmus, Dinobryon, Fragilaria, and Mychonastes) and positively correlated with six proteobacterial genera (Brevundimonas, Devosia, Limnohabitans, Porphyrobacter, Pseudomonas, and Rhodobacter). After application of 1.0 and 1.5 mg L^-1 H₂O₂ for 15 days, H₂O₂-treated groups showed significantly (p < 0.05) different prokaryotic community structures from that of the control group at the bloom stage (15th day), while eukaryotic community structures in H₂O₂-treated groups remained stable and showed high similarity with that of the control group at a non-bloom stage (5th day). Application of low-dose H₂O₂ during the early cyanobacterial growth stage could effectively prevent the formation of cyanobacterial blooms without disrupting non-target organisms.

The Effects of Algaecides and Herbicides on a Nuisance Microcystis wesenbergii-Dominated Bloom

Microcystis-dominated cyanobacterial harmful algal blooms (cyanoHABs) are a reoccurring problem globally, resulting in widespread economic and health impacts. As public awareness of the risks of blooms increases, there is an urgent need for studies on both short-term and long-term management of cyanoHABs. In order to provide science-based best management practices and treatment options, we tested various concentrations and combinations of USEPA-registered algaecides and herbicides on a Microcystis wesenbergii-dominated bloom. The bloom material was exposed to fifteen different algaecides, herbicides, or combinations, using four different concentrations. Cell abundance and morphology as well as microscopic analyses were undertaken at the time of collection and 72 h post-treatment. Overall, the effectiveness of the chemicals varied with the most efficacious treatments being SeClear®, and a combination of Hydrothol® 191 and GreenClean® Liquid 5.0, both of which resulted in a significant decrease at all tested concentrations after 72 h. Interestingly, Microcystis wesenbergii is more resistant to algaecides than M. aeruginosa. Results from this study provide valuable data for treating cyanoHABs and show the varied efficacy of different algaecidal formulations.

Photocatalytic inactivation of algae in a fluidized bed photoreactor with an external magnetic field

Practical applications of photocatalysis in algae removal often involve the use of photoreactors, which can be of many different configurations. In this study, a fluidized bed photoreactor (FBPR) with an external magnetic field was designed and constructed to achieve algae inactivation continuously and stably. Magnetic photocatalyst ZnFe₂O₄/Ag₃PO₄/g-C₃N₄ attached to Fe₃O₄ aggregate, was dispersed and fixed at the bottom of the reactor to form a flower-like structure, which can not only increase the effective irradiation area of the photocatalyst, but also enhances mass transfer by inducing flow disturbance. Under the optimal operating conditions, i.e., 0.04 m/s flow rate, 200 mT magnetic field strength, and 0.025 g photocatalyst loading, the photoreactor can effectively remove algae cells within 6 h. During the continuous operation experiment, the quality of the magnetic photocatalyst and aggregate did not decrease significantly, and there was still a 90% removal efficiency after 18 h of continuous operation. Furthermore, in the experiment where humic acid was added to simulate actual water environment, certain advantages can still be observed with the FBPR. As a continuous reactor using a magnetic photocatalyst, the FBPR has the characteristics of high availability, low cost, and low energy consumption.

Evaluation of a Peroxide-Based Algaecide for Cyanobacteria Control: A Mesocosm Trial in Lake Okeechobee, FL, USA

A 72 h small-scale trial was conducted in enclosed mesocosms in the Lake Okeechobee waterway to evaluate the effectiveness of a USEPA-registered peroxide-based algaecide (formulated as sodium carbonate peroxyhydrate) for controlling a natural cyanobacteria population. Mesocosms were initially subjected to either no algaecide or the maximum label rate of 10 mg H2O2·L−1. A subset of mesocosms were then subjected to a sequential application of 5 mg H2O2·L−1 at 48 h after initial treatment. Following application, peroxide concentrations rapidly decreased and were undetectable by 48 h. At 24 h after treatment, significant decreases in all biomass indicators were observed (compared to untreated mesocosms), including extracted chlorophyll a, microscopic counts (total phytoplankton and total cyanobacteria), and cyanobacteria-specific 16S rRNA gene copies by over 71%. Although peroxide treatment reduced cyanobacteria biomass, there was no change in overall community structure and the remaining population was still dominated by cyanobacteria (>90%). After 48 h exposure, some biomass recovered in single application mesocosms resulting in only a 32–45% reduction in biomass. Repeated peroxide dosing resulted in the greatest efficacy, which had a sustained (60–91%) decrease in all biomass indicators for the entire study. While a single application of the peroxide was effective in the first 24 h, a sequential treatment is likely necessary to sustain efficacy when using this approach to manage cyanobacteria in the field. Results of this study support that this peroxide-based algaecide is a strong candidate to continue with scalable field trials to assess its potential future utility for operational management programs in the Lake Okeechobee waterway.

Differential Effect of Hydroxen Peroxide οn Toxic Cyanobacteria of Hypertrophic Mediterranean Waterbodies

Cyanobacterial blooms have been known since ancient times; however, they are currently increasing globally. Human and ecological health risks posed by harmful cyanobacterial blooms have been recorded around the world. These risks are mainly associated with their ability to affect the ecosystem chain by different mechanisms like the production of cyanotoxins, especially microcystins. Their expansion and their harmful effects have led many researchers to seek techniques and strategies to control them. Among them, hydrogen peroxide could be a promising tool against cyanobacteria and cyanotoxins and it is well-established as an environmentally friendly oxidizing agent because of its rapid decomposition into oxygen and water. The aim of the present study was to evaluate the effect of hydrogen peroxide on phytoplankton from two hypertrophic waterbodies in Greece. The effect of hydrogen peroxide on concentration of microcystins found in the waterbodies was also studied. Treatment with 4 mg/L hydrogen peroxide was applied to water samples originated from the waterbodies and Cyanobacterial composition and biomass, phycocyanin, chlorophyll-a, and intra-cellular and total microcystin concentrations were studied. Cyanobacterial biomass and phycocyanin was reduced significantly after the application of 4 mg/L hydrogen peroxide in water treatment experiments while chlorophytes and extra-cellular microcystin concentrations were increased. Raphidiopsis (Cylindrospermopsis) raciborskii was the most affected cyanobacterial species after treatment of the water of the Karla Reservoir in comparison to Aphanizomenon favaloroi, Planktolyngbya limnetica, and Chroococcus sp. Furthermore, Microcystis aeruginosa was more resistant to the treatment of Pamvotis lake water in comparison with Microcystis wesenbergii and Microcystis panniformis. Our study showed that hydrogen peroxide differentially impacts the members of the phytoplankton community, affecting, thus, its overall efficacy. Different effects of hydrogen peroxide treatment were observed among cyanobacerial genera as well as among cyanobacterial species of the same genus. Different effects could be the result of the different resistance mechanisms of each genus or species to hydrogen peroxide. Hydrogen peroxide could be used as a treatment for the mitigation of cyanobacterial blooms in a waterbody; however, the biotic and abiotic characteristics of the waterbody should be considered.

Resilience of Microbial Communities after Hydrogen Peroxide Treatment of a Eutrophic Lake to Suppress Harmful Cyanobacterial Blooms

Applying low concentrations of hydrogen peroxide (H₂O₂) to lakes is an emerging method to mitigate harmful cyanobacterial blooms. While cyanobacteria are very sensitive to H₂O₂, little is known about the impacts of these H₂O₂ treatments on other members of the microbial community. In this study, we investigated changes in microbial community composition during two lake treatments with low H₂O₂ concentrations (target: 2.5 mg L⁻¹) and in two series of controlled lake incubations. The results show that the H₂O₂ treatments effectively suppressed the dominant cyanobacteria Aphanizomenon klebahnii, Dolichospermum sp. and, to a lesser extent, Planktothrix agardhii. Microbial community analysis revealed that several Proteobacteria (e.g., Alteromonadales, Pseudomonadales, Rhodobacterales) profited from the treatments, whereas some bacterial taxa declined (e.g., Verrucomicrobia). In particular, the taxa known to be resistant to oxidative stress (e.g., Rheinheimera) strongly increased in relative abundance during the first 24 h after H₂O₂ addition, but subsequently declined again. Alpha and beta diversity showed a temporary decline but recovered within a few days, demonstrating resilience of the microbial community. The predicted functionality of the microbial community revealed a temporary increase of anti-ROS defenses and glycoside hydrolases but otherwise remained stable throughout the treatments. We conclude that the use of low concentrations of H₂O₂ to suppress cyanobacterial blooms provides a short-term pulse disturbance but is not detrimental to lake microbial communities and their ecosystem functioning.