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Hydrogen peroxide is a reactive oxygen species (ROS) naturally occurring at low levels in aquatic environments and production varies widely across different ecosystems. Oxygenic photosynthesis generates hydrogen peroxide as a byproduct, of which some portion can be released to ambient water. However, few studies have examined hydrogen peroxide dynamics in relation to cyanobacterial harmful algal blooms (cHABs). A year-long investigation of algal succession and hydrogen peroxide dynamics was conducted at the Caloosahatchee River, Florida, USA. We aimed to identify potential biological mechanisms responsible for elevated hydrogen peroxide production during cHAB events through the exploration of the freshwater microbial metatranscriptome. Hydrogen peroxide concentrations were elevated from February to September of 2021 when cyanobacteria were active and abundant. We observed one Microcystis cHAB event in spring and one in winter. Both had distinct nutrient uptake and cyanotoxin gene expression patterns. While meaningful levels of microcystin were only detected during periods of elevated hydrogen peroxide, cyanopeptolin was by far the most expressed cyanotoxin during the spring bloom when hydrogen peroxide was at its yearly maxima. Gene expressions of five microbial enzymes (Rubisco, superoxide dismutase, cytochrome b 559, pyruvate oxidase, and NADH dehydrogenase) positively correlated to hydrogen peroxide concentrations. Additionally, there was higher nitrogen-fixing gene (nifDKH) expression by filamentous cyanobacteria after the spring bloom but no secondary bloom formation occurred. Overall, elevated environmental hydrogen peroxide concentrations were linked to cyanobacterial dominance and greater expression of specific enzymes in the photosynthesis of cyanobacteria. This implicates cyanobacterial photosynthesis and growth results in increased hydrogen peroxide generation as reflected in measured environmental concentrations. [Display omitted] • Hydrogen peroxide dynamics coincided with annual cyanobacterial growth pattern. • Hydrogen peroxide surge during cHAB events coincided with high Rubisco expression. • Microcystis gene expression decreased by 98% after bloom formation. • Highest cyanobacterial nitrogen fixation expressions occurred after cHAB event. • High cyanopeptolin gene expressions by Microcystis during hydrogen peroxide maxima. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • 490 μM hydrogen peroxide treatment selectively suppressed dominant bloom species. • Succession to picocyanobacteria within 3 days of hydrogen peroxide treatment. • Microcystis phylotypes exhibited different sensitivity to hydrogen peroxide. [ABSTRACT FROM AUTHOR]

• 90% Florida grapefruits are affected by Huanglongbing (HLB) which causes the accumulation of bitter naringin. • Macroporous resins effectively adsorbed bitter naringin and tasteless narirutin from the juice. • Debittering by adsorption partially removed limonoids and furanocoumarins from the juice. • Taste panel evaluation of bitterness correlated with naringin content in the juice. • Half-debittered juice and untreated juice was ranked as the most and least preferred, respectively. About 90% of grapefruit in Florida are affected by Huanglongbing (HLB). HLB negatively affects the organoleptic properties of grapefruit juice because affected trees overproduce bitter secondary-metabolites, mostly naringin. The objective of this research was to remove naringin from HLB-affected grapefruit juice using microporous-adsorbents and to investigate how debittering affected narirutin, limonoids, bergamottin, and consumer acceptability. The adsorption kinetics of naringin on seven adsorbent resins obeyed pseudo-second order. PAD550 and PAD600 showed better static adsorption/desorption. Adsorption-isotherms on these resins were better fitted on Temkin-Pyzhev-model. On a fixed-bed-column packed with PAD550 resin, a slower loading rate increased its breakthrough volume before naringin in effluent reached its taste-threshold. In addition to naringin being reduced to below its taste-threshold, debittering significantly decreased the content of limonin, nomilin, and bergamottin. A consumer taste panel rated debittered and half-debittered juices higher for overall acceptability than the untreated. The half-debittered juice was ranked the most preferred while untreated was the least preferred. [ABSTRACT FROM AUTHOR]

• High levels of H 2 O 2 were detected in some freshwater bodies in southwest Florida. • The microelectrode technique was useful to determining freshwater H 2 O 2 concentrations. • Hydrogen peroxide levels were associated with cyanobacterial bloom conditions. • We did not find any correlation between H 2 O 2 and microcystin concentrations. Hydrogen peroxide is widely recognized as the most stable of the reactive oxygen species (ROS) produced by both biotic and abiotic pathways in natural waters. Its high reactivity in mediating redox transformations may, directly or indirectly, affect aquatic ecosystem functions, including primary productivity. However, environmental interactions between photoautotrophs, particularly cyanobacteria, and hydrogen peroxide are poorly understood. To gain a better understanding of hydrogen peroxide and cyanobacterial interactions, we determined the hydrogen peroxide concentrations in the presence and absence of cyanobacterial blooms in southwest Florida. Hydrogen peroxide concentrations were determined using a fast response amperometric hydrogen peroxide microelectrode. Our measurements ranged from 0 to 5.3 µM in freshwater bodies (ponds, lakes and the Caloosahatchee River) and 0 to 92.9 µM in rainwater. In general, hydrogen peroxide levels were highly associated with cyanobacterial bloom conditions, indicating the potential role of cyanobacteria in hydrogen peroxide production in freshwater. To determine the potential biodegradation of hydrogen peroxide during sample transportation in the dark condition, water samples were passed through 0.2 µm pore size filters immediately after sampling and compared with unfiltered water samples in the laboratory. We found that filtered water samples retained higher concentrations of hydrogen peroxide than unfiltered samples with a mean biodegradation rate of 44 ± 10.6 nmol/h. Out of a total of 26 samples, only one unfiltered sample showed a higher hydrogen peroxide concentration than the filtered samples. Overall, our study found the microelectrode technique could accurately measure hydrogen peroxide concentrations in the samples from various freshwater bodies. This measurement method revealed that hydrogen peroxide concentrations vary with temporal and spatial dynamics of cyanobacterial blooms. [ABSTRACT FROM AUTHOR]

• Eukaryotic algae sharply increased when the water discharge increased. • Synechococcus and Cyanobium dominated in phytoplankton communities. • Phytoplankton dynamics influence the natural abundance of H 2 O 2. • A H 2 O 2 peak was found when Dolichospermum dominance was ended, and Microcystis increased. • A high correlation was found between H 2 O 2 and microcystin (r = 0.83, p < 0.01). Phytoplankton communities are major primary producers in the aquatic realm and are responsible for shaping aquatic ecosystems. The dynamics of algal blooms could be determined by a succession of variable taxonomic groups, which are altered based on complex environmental factors such as nutrient availability and hydraulic factors. In-river structures potentially increase the occurrence of harmful algal blooms (HABs) by increasing water residence time and deteriorating water quality. How flowing water stimulates cell growth and affects the population dynamics of phytoplankton communities is a prioritized question that needs to be addressed for water management tactics. The goal of this study was to determine if an interaction between water flow and water chemistry is present, furthermore, to determine the relationship among phytoplankton community successions in the Caloosahatchee River, a subtropical river strongly influenced by human-controlled water discharge patterns from Lake Okeechobee. Particularly we focused on how phytoplankton community shifts influence the natural abundance of hydrogen peroxide, the most stable reactive oxygen species and a byproduct of oxidative photosynthesis. High-throughput amplicon sequencing using universal primers amplify 23S rRNA gene in cyanobacteria and eukaryotic algal plastids revealed that Synechococcus and Cyanobium were the dominant cyanobacterial genera and their relative abundance ranged between 19.5 and 95.3% of the whole community throughout the monitoring period. Their relative abundance declined when the water discharge increased. On the contrary, the relative abundance of eukaryotic algae sharply increased after water discharge increased. As water temperature increased in May, initially dominant Dolichospermum decreased as Microcystis increased. When Microcystis declined other filamentous cyanobacteria such as Geitlerinema, Pseudanabaena , and Prochlorothreix increased in their relative abundances. Interestingly, a peak of extracellular hydrogen peroxide was observed when Dolichospermum dominance was ended, and M. aeruginosa numbers increased. Overall, phytoplankton communities were strongly impacted by human-induced water discharge patterns. [ABSTRACT FROM AUTHOR]

Microphytobenthic communities play a significant role in nutrient modulation, sediment stabilization, and primary production in seagrass beds, which provide various ecosystem services. We hypothesized that microphytobenthic communities in sediments of chronically oil-exposed seagrass beds will exhibit increased resiliency to stressors associated with oil exposure as opposed to seagrass beds never exposed to oil spills. We prepared 14-liter seawater mesocosms, each containing a submersed macrophyte Ruppia maritima collected from the Chandeleur Islands, Louisiana, and Estero Bay, Florida. Mesocosms were initially exposed to 50% water-accommodated oil fractions (WAF) and subsequently diluted by 50% with daily artificial seawater exchanges over 8 days to simulate tidal dilution. High-throughput amplicon sequencing based on 23S rRNA gene targeting cyanobacteria and chloroplasts of eukaryotic microphytobenthos was conducted to assess the impact of oiling on microphytobenthic communities with additional assessment via microscopy. High-throughput sequencing in combination with traditional microscopic analysis provided a robust examination in which both methods roughly complemented each other. Distinct succession patterns were detected in benthic algal communities of chronically oil-exposed (Louisiana) versus unexposed (Florida) seagrass bed sediments. The impact of oiling in microphytobenthos across all samples showed that benthic diatoms dominated all algal communities with sample percentages ranging from 42 to 97%, followed by cyanobacteria (2 to 50%). It is noteworthy that drastic changes in microphytobenthic community structure in terms of the larger taxonomic level were not observed, rather change occurred at the phylotype level. These results were also confirmed by microscopy. Similarity percentages (SIMPER) analysis identified seven phylotypes (Cyanobacteria, Bacillariophyceae, and Mediophyceae) in the Louisiana samples and one phylotype (Bacillariophyceae) in the Florida samples that increased in relative sequence abundance after oil exposure. The detailed phylotype analysis identifying sentinel microphytobenthic indicators provides a base for future research on benthic microalgae response to ecosystem disturbance., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier B.V.)