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We analyzed lower water column redox-sensitive and bio-relevant (Al, Fe, Mn) micronutrient data between 2018 and 2019 to assess spatial and seasonal variability within Lake of the Woods (LoW) as they relate to continued eutrophication and water quality issues. The sediment–water interface represents a dynamic linkage between the sediment and overlying water column, dominated by diffusive flux and particulate resuspension. The complexity of LoW basins, shoreline extent, and underlying geology (situated on both the Canadian Shield and Glacial Lake Agassiz Lakebed sediments) creates variable water quality conditions, with cyanobacterial and harmful algal blooms (cHABs) particularly prevalent in the southern basins. We used a multivariate approach to differentiate basins within LoW, to better understand potential mechanisms underlying eutrophication and cHAB development. A unique signature of redox-sensitive metals was observed above the lakebed suggesting differential impacts of diffusive flux and resuspension dynamics, with significantly different micronutrient signatures between locations on vs off the Canadian Shield. The basins on the Glacial Lake Agassiz lakebed including Big Traverse, Little Traverse, Morson and Bishop were statistically comparable (p > 0.05), and significantly different from those on the Canadian Shield (p < 0.05). Correlations between bio-relevant element vanadium (element potentially used in nitrogen fixation) and chlorophyll-a), suggest potential elemental drivers of cyanobacterial ecology in LoW. An integration of multi-disciplinary research may serve to better address water quality issues as they relate to underlying geology and improve monitoring programs into the future to further delineate the physical-biogeochemical processes differentially impacting basins within LoW. [ABSTRACT FROM AUTHOR]

In the oligotrophic oceans, key autotrophs depend on "helper" bacteria to reduce oxidative stress from hydrogen peroxide (H2O2) in the extracellular environment. H2O2 is also a ubiquitous stressor in freshwaters, but the effects of H2O2 on autotrophs and their interactions with bacteria are less well understood in freshwaters. Naturally occurring H2O2 in freshwater systems is proposed to impact the proportion of microcys-tin-producing (toxic) and non-microcystin-producing (nontoxic) Microcystis in blooms, which influences toxin concentrations and human health impacts. However, how different strains of Microcystis respond to naturally occurring H2O2 concentrations and the microbes responsible for H2O2 decomposition in freshwater cyanobacterial blooms are unknown. To address these knowledge gaps, we used metagenomics and metatranscrip-tomics to track the presence and expression of genes for H2O2 decomposition by microbes during a cyanobacterial bloom in western Lake Erie in the summer of 2014. katG encodes the key enzyme for decomposing extracellular H2O2 but was absent in most Microcystis cells. katG transcript relative abundance was dominated by heterotrophic bacteria. In axenic Microcystis cultures, an H2O2 scavenger (pyruvate) significantly improved growth rates of one toxic strain while other toxic and nontoxic strains were unaffected. These results indicate that heterotrophic bacteria play a key role in H2O2 decomposition in Microcystis blooms and suggest that their activity may affect the fitness of some Microcystis strains and thus the strain composition of Microcystis blooms but not along a toxic versus nontoxic dichotomy. IMPORTANCE Cyanobacterial harmful algal blooms (CHABs) threaten freshwater ecosystems globally through the production of toxins. Toxin production by cyanobacterial species and strains during CHABs varies widely over time and space, but the ecological drivers of the succession of toxin-producing species remain unclear. Hydrogen peroxide (H2O2) is ubiquitous in natural waters, inhibits microbial growth, and may determine the relative proportions of Microcystis strains during blooms. However, the mechanisms and organismal interactions involved in H2O2 decomposition are unexplored in CHABs. This study shows that some strains of bloom-forming freshwater cyanobacteria benefit from detoxification of H2O2 by associated heterotrophic bacteria, which may impact bloom development. [ABSTRACT FROM AUTHOR]

Cyanobacteria are diverse, complex and a unique group of microorganisms that inhabit a wide variety of environments. Contrarily to continental areas, studies on cyanobacteria in islands are scarce and need to be reinforced, since climate change impacts are expected to be harsher in islands, due to their geographical isolation and higher exposition to external influences. Here we present a review of the occurrence of cyanobacteria and cyanotoxins in inland and coastal ecosystems in the Atlantic Ocean islands. These microorganisms were reported from diverse habitats, including saline thermal lakes Iceland), freshwater lakes, terrestrial habitats (Azores, Cuba), and marine coastal areas, either planktonic (Madeira, Canary Islands, Cape Verde) or associated to plants and corals (Brazil, Caribbean Sea). Most of cyanobacteria were reported from freshwaters but some species were found in different habitats. Species richness also varied between islands, with higher number in islands located in temperate regions, and the number of common taxa was low (1-3%). Several toxic species and different types of cyanotoxins were also reported in the Atlantic islands, which are expected to increase with climate change. Mitigation measures should be considered to avoid cyanotoxins risks to environmental and public health. This works shows the great potential of Atlantic islands for cyanobacteria taxonomic, ecological and biogeography research, but more studies are needed with emphasis on less studied islands and habitats and using novel approaches as molecular systematics tools. Furthermore, such studies are of paramount importance for environmental conservation and management strategies, especially facing climate changes. [ABSTRACT FROM AUTHOR]

To identify key factors that control primary production (P.P.) and trigger cyanobacterial harmful algal blooms (cHABs), we investigated spatio-temporal variations in P.P. in a continuous weir system in the Nakdong River once or twice a month from April to October 2018. P.P. was measured through an in-situ incubation experiment using a 13C tracer. Relative proportion of pigment-based phytoplankton composition was calculated by the CHEMTAX program based on pigment analysis using a high-performance liquid chromatography (HPLC). P.P. was higher in spring (1130 ± 1140 mg C m−2 d−1) and summer (1060 ± 814 mg C m−2 d−1) than autumn (180 ± 220 mg C m−2 d−1), and tended to increase downstream. P.P. was negatively related to PO43− (r = −0.41, p < 0.01) due to utilization by phytoplankton during the spring and summer when it was high. The relative proportion of pigment-based cyanobacteria (mainly Microcystis sp.) was positively correlated with water temperature (r = 0.79, p < 0.01) and hydraulic retention time (HRT, r = 0.67, p < 0.01), suggesting that these two factors should affect cHABs in summer. Therefore, to control HRT could be one of the solutions for reducing cHABs in a continuous weir system. [ABSTRACT FROM AUTHOR]