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Sunlight breaks down dissolved organic matter (DOM) in lakes and streams to produce carbon dioxide (a greenhouse gas). The efficiency of this process depends on light exposure, the aromatic content of DOM (i.e., Ar–C), and dissolved iron (Fe). 

ABSTRACT Here, we report on the raw and coassembled metatranscriptomes of 39 Lake Erie surface (1.0 m) water samples collected over a 2-day diel period encompassing episodic weather and bloom events. Preliminary taxonomic annotations and read mappings revealed thatMicrocystisspp. accounted for up to ~47% of the transcriptionally active community. 

In Lake Erie, toxin-forming harmful algal blooms (HABs) occur following high concentrations of hydrogen peroxide (H 2 O 2 ). Correlation between H 2 O 2 concentrations and HABs revealed knowledge gaps on the controls of H 2 O 2 production in Lake Erie. One way H 2 O 2 is produced is upon absorption of sunlight by the chromophoric fraction of dissolved organic matter (CDOM). Rates of this photochemical production of H 2 O 2 may increase in proportion to the apparent quantum yield of H 2 O 2 ( Φ H 2 O 2 ,λ ) from CDOM. However, the Φ H 2 O 2 ,λ for H 2 O 2 production from CDOM remains too poorly constrained to predict the magnitude and range of photochemically produced H 2 O 2 , particularly in freshwaters like Lake Erie. To address this knowledge gap, the Φ H 2 O 2 ,λ was measured approximately biweekly from June–September 2019 in the western basin of Lake Erie along with supporting analyses ( e.g. , CDOM concentration and composition). The average Φ H 2 O 2 ,λ in Lake Erie was within previously reported ranges. However, the Φ H 2 O 2 ,λ varied 5-fold in space and time. The highest Φ H 2 O 2 ,λ was observed in the Maumee River, a tributary of Lake Erie. In nearshore waters of Lake Erie, the Φ H 2 O 2 ,λ decreased about five-fold from June through September. Integration of the controls of photochemical production of H 2 O 2 in Lake Erie show that the variability in rates of photochemical H 2 O 2 production was predominantly due to the Φ H 2 O 2 ,λ . In offshore waters, CDOM concentration also strongly influenced photochemical H 2 O 2 production. Together, the results confirm prior work suggesting that photochemical production of H 2 O 2 contributes but likely cannot account for all the H 2 O 2 associated with HABs in Lake Erie. 

Methane (CH4) concentrations were measured in dissolved organic carbon (DOC) leachates of permafrost soils collected from the frozen permafrost layer at five sites underlying tussock tundra or wet sedge vegetation on the North Slope of Alaska during the summers of 2018 and 2019. 

Leachates of dissolved organic carbon (DOC) from permafrost soils were prepared from soils collected from the North Slope of Alaska in 2018 and 2022. Soil leachates were then either kept in the dark or exposed to light from LEDs at 305 nm (UV) and 405 nm (visible), and then inoculated with native microbial communities and incubated. At the start of the biological incubations, single replicates of the DOC after dark or light treatment and inoculation were assigned accession numbers and analyzed for 14C and 13C at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility. At the end of the biological incubations, duplicates of the dissolved inorganic carbon (DIC) in those waters were assigned accession numbers and analyzed for 14C and 13C at the NOSAMS facility. 

Dissolved organic carbon (DOC) was leached from permafrost soils near the Toolik Field Station in the Alaskan Arctic. Daily rates of sunlight absorption by chromophoric dissolved organic matter (CDOM) from the permafrost soil leachates over the water column depth of an arctic headwater stream were quantified. 

Dissolved organic carbon (DOC) was leached from permafrost soils near the Toolik Field Station in the Alaskan Arctic, either kept in the dark or exposed to light treatments, and then incubated with native permafrost microbial communities. The radiocarbon (14C) and stable carbon (13C) isotopic compositions of the initial DOC present in the dark or light-exposed permafrost soil leachates and the carbon dioxide (CO2) produced by microbial respiration of dark or light-exposed permafrost DOC were quantified. 

Dissolved organic carbon (DOC) was leached from permafrost soils collected from the frozen permafrost layer at four sites underlying tussock tundra or wet sedge tundra vegetation and from both undisturbed soil and a thermokarst failure on the North Slope of Alaska during the summers of 2018 and 2022. 

ABSTRACT In the oligotrophic oceans, key autotrophs depend on “helper” bacteria to reduce oxidative stress from hydrogen peroxide (H 2 O 2 ) in the extracellular environment. H 2 O 2 is also a ubiquitous stressor in freshwaters, but the effects of H 2 O 2 on autotrophs and their interactions with bacteria are less well understood in freshwaters. Naturally occurring H 2 O 2 in freshwater systems is proposed to impact the proportion of microcystin-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 H 2 O 2 concentrations and the microbes responsible for H 2 O 2 decomposition in freshwater cyanobacterial blooms are unknown. To address these knowledge gaps, we used metagenomics and metatranscriptomics to track the presence and expression of genes for H 2 O 2 decomposition by microbes during a cyanobacterial bloom in western Lake Erie in the summer of 2014. katG encodes the key enzyme for decomposing extracellular H 2 O 2 but was absent in most Microcystis cells. katG transcript relative abundance was dominated by heterotrophic bacteria. In axenic Microcystis cultures, an H 2 O 2 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 H 2 O 2 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 (H 2 O 2 ) 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 H 2 O 2 decomposition are unexplored in CHABs. This study shows that some strains of bloom-forming freshwater cyanobacteria benefit from detoxification of H 2 O 2 by associated heterotrophic bacteria, which may impact bloom development.