Abstract Accurately quantifying air–sea CO 2 exchange remains a central challenge for the measurement, reporting, and verification (MRV) of marine carbon dioxide removal. I apply direct eddy covariance measurements of CO 2 fluxes at a macroalgae‐dominated coast to compile the first gas transfer velocity ( k 660 ) parameterization for such a habitat. k 660 exhibited a quadratic dependence on wind speed of the form: . Random forest analysis showed that wind speed and wind‐wave interaction control k 660 at high wind speed, and a suite of drivers enhance k 660 under calm conditions, generating a non‐zero intercept with significant impacts for CO 2 flux modelling. A simulated macroalgal marine carbon dioxide removal intervention demonstrated the sensitivity of removals to k 660 uncertainty, via its effect on CO 2 equilibration timescale, with variation across k 660 models causing shifts comparable to those by operational emissions. Finally, a new framework embedding site‐specific equilibration dynamics into marine carbon dioxide removal accounting is presented, offering an understandable and defensible tool for measurement, reporting, and verification.

Seasonal variations and the biological drivers underlying the methane paradox in freshwater lakes are poorly understood. Here, we investigated the relationship between subsurface methane inventories and phytoplankton in two peri-Alpine lakes across different seasons. Surface waters of both lakes were consistently saturated in methane, with maxima reaching 570 and 205 nmol L−1 during summer in the metalimnion of lakes Mondsee and Attersee, respectively. Methane concentrations were positively correlated with phytoplankton abundance in meso-oligotrophic lake Mondsee but not in ultra-oligotrophic lake Attersee. However, although phytoplankton peaked in abundance at the methane maxima in Mondsee, incubation experiments with 13C-labeled bicarbonate revealed negligible methane production from primary productivity. Instead, our results suggest that phytoplankton might only be indirectly involved in methane production through alternative pathways, or by providing precursor compounds to other members of the microbial community in these oligotrophic lakes.

Abstract Given the limited understanding of discrepancies in responses of diatoms to ocean acidification (OA), we comparatively investigated the physiological and transcriptional performances of a diatom Thalassiosira weissflogii acclimated to OA (pH t drop of 0.35–0.41) between day and night periods. We found that OA enhanced its specific growth rate (up to 10%) in the light period by upregulating light reaction, Calvin cycle and H + pumps to cope with the decreased pH. On the other hand, OA reduced its apparent specific growth rate (14%) in the dark period due to additive pH drop caused by OA‐enhanced respiratory CO 2 release. In the dark period, the cells could not effectively cope with the decreased pH since H + pumps were downregulated. Consequently, OA did not affect cell growth during a 24 h diel cycle. These findings suggest that daytime positive and night negative effects of OA on diatoms could be responsible for differential results observed under different conditions, with implications for possible seasonal and latitudinal effects of OA.

Abstract Species invasions are among the most important environmental problems facing freshwater ecosystems this century, contributing to biodiversity loss and changes in ecosystem function. Freshwater lakes are an important component of the global carbon cycle and a key source of atmospheric greenhouse gases, yet the consequences of species invasions on gas emissions remain poorly understood. In this study, we analyzed greenhouse gas emissions from shallow lakes invaded by one of the world's most damaging invasive species, the common carp. We show that lakes with invasive carp had lower methane emissions despite increased eutrophication, contradicting the well‐established assumption that methane emissions from lakes increase with nutrient levels and productivity. Lakes with carp had reduced sediment phosphorus concentrations, likely due to bioturbation, which correlated with lower methane emissions. Given the widespread and global nature of carp invasion, carp may have the potential to alter carbon and nutrient cycling at large scales.

Reservoirs are globally important sources of greenhouse gases, but the magnitude of their emissions is highly uncertain. Here, we present data for 146 reservoirs from two surveys of reservoir methane and carbon dioxide emissions, one at the regional scale in the midwestern United States and one at the national scale in the United States, plus data from two hand-picked sites in Washington and Puerto Rico. At all reservoirs, ebullitive and diffusive emissions and basic physicochemistry were measured at 15-55 locations during one 22 to 64-h period during the summers of 2016-2023, with four reservoirs revisited a second time. Contemporaneous water chemistry measurements were made at one or two locations in each reservoir. The dataset consists of two geospatial files and seven CSV files containing greenhouse gas emissions, water chemistry, morphology, and other relevant data. To date, these data comprise the largest multi-reservoir emissions dataset assembled using consistent measurement methods.

Abstract Satellite‐based earth observation is a robust tool for tracking change in ecosystems. While terrestrially focused applications of remote sensing have empowered wide adoption for research and management, remote sensing of inland aquatic ecosystems remains comparably nascent. This divergence, in part, stems from the lack of standardized, accessible, and near real‐time remotely sensed surface reflectance, atmospherically corrected for aquatic environments. To date, surface reflectance products at national scales and with minimal latency are typically designed exclusively for terrestrial environments. Rectifying this situation can be accomplished by applying aquatic‐focused atmospheric correction algorithms independent of those used for terrestrial ecosystems. As a first step to filling this data gap, we present the first national scale, dynamically updated, analysis‐ready, aquatic reflectance dataset for inland water derived from Sentinel‐2 for the conterminous United States.

Abstract Seawater contains small biomolecules, or metabolites, that are highly labile components of dissolved organic matter (DOM). Marine microbes interact by exchanging metabolites, thus shaping marine microbial ecology, DOM composition, and global carbon cycling. To better constrain one set of microbe‐metabolite interactions, we cultured the marine gammaproteobacterium Alteromonas macleodii MIT1002 on a range of compounds excreted by a sympatric cyanobacterium, Prochlorococcus . Alteromonas macleodii MIT1002 could metabolize the branched‐chain amino acids leucine, isoleucine, and valine, as well as 3‐methyl‐2‐oxobutanoic acid (a branched‐chain ketoacid intermediate of valine metabolism), but not thymidine, kynurenine, 4‐hydroxybenzoic acid, nor the other branched‐chain ketoacids. The utilization of branched‐chain amino acids indicates that A. macleodii MIT1002 can metabolize each corresponding ketoacid, suggesting that transporter specificity underlies the observed substrate specificity for 3‐methyl‐2‐oxobutanoic acid. These experiments show that even subtle changes in chemical structure can result in different microbial interactions and different fates for dissolved metabolites.

Abstract All organisms contain carbon, nitrogen, and phosphorus in widely ranging amounts and proportions. Integrating existing datasets enables quantification of this variation at global scales. Such efforts could leverage ecological stoichiometry theory, the study of elemental supply and imbalances in ecological interactions, to connect ecological drivers and taxonomic constraints to ecosystem structure and function. Towards this goal, we developed the Limnology Stoichiometric Traits of Organisms In their Chemical Habitats (Limno‐STOICH) database. The Limno‐STOICH database includes 51,576 observations of organismal elemental stoichiometry from >3100 rivers, lakes, wetlands, and other aquatic ecosystem sites on seven continents, derived from 190+ sources. It also includes extensive spatial and temporal metadata to link elemental stoichiometry with ecosystem type, trophic status, etc., and information on organismal data (body size, taxonomic classifications, stable isotope composition) and water physicochemical parameters. The Limno‐STOICH database sets the stage for significant applications across food web ecology, evolutionary ecology, biogeochemistry, and other disciplines.