Tropical hydroelectric reservoirs are recognized hotspots for greenhouse gas emissions, yet the role of submerged forests in these emissions remains poorly understood. In this study, we investigated the contribution of standing dead trees and their associated epixylic biofilms to methane (CH 4 ) and carbon dioxide (CO 2 ) emissions in the permanently stratified Petit Saut reservoir, French Guiana. We conducted in situ measurem...

Aquatic sediments represent a key component for understanding CH 4 dynamics and emission to the atmosphere. Once produced in the sediments, CH 4 is released either by diffusion at the sediment–water interface or by bubbling out to the atmosphere when total gas pressure in the sediment exceeds local ambient pressure due to high CH 4 production. Although bubbling is one of the dominant CH 4 emission pathways in lakes, direct mea...

Summary Lake methane (CH 4 ) emissions are largely controlled by aerobic methane‐oxidizing bacteria (MOB) which mostly belong to the classes Alpha‐ and Gammaproteobacteria (Alpha‐ and Gamma‐MOB). Despite the known metabolic and ecological differences between the two MOB groups, their main environmental drivers and their relative contribution to CH 4 oxidation rates across lakes remain unknown. Here, we quantified the two MOB g...

Aerobic methanotrophic bacteria (methanotrophs) use methane as a source of carbon and energy, thereby mitigating net methane emissions from natural sources. Methanotrophs represent a widespread and phylogenetically complex guild, yet the biogeography of this functional group and the factors that explain the taxonomic structure of the methanotrophic assemblage are still poorly understood. Here, we used high‐throughput sequencin...

Methane (CH 4 ) emissions from aquatic systems should be coupled to CH 4 production, and thus a temperature‐dependent process, yet recent evidence suggests that modeling CH 4 emissions may be more complex due to the biotic and abiotic processes influencing emissions. We studied the magnitude and regulation of two CH 4 pathways—ebullition and diffusion—from 10 shallow ponds and 3 lakes in Québec. Ebullitive fluxes in ponds aver...

Lakes are a major component of boreal landscapes, and whereas lake CO 2 emissions are recognized as a major component of regional C budgets, there is still much uncertainty associated to lake CH 4 fluxes. Here, we present a large‐scale study of the magnitude and regulation of boreal lake summer diffusive CH 4 fluxes, and their contribution to total lake carbon (C) emissions, based on in situ measurements of concentration and f...

We performed a series of gas exchange measurements in 12 diverse aquatic systems to develop the direct relationship between near‐surface turbulence and gas transfer velocity. The relationship was log‐linear, explained 78% of the variation in instantaneous gas transfer velocities, and was valid over a range of turbulent energy dissipation rates spanning about two orders of magnitude. Unlike wind‐based relationships, our model i...

Natural fires annually decimate up to 1% of the forested area in the boreal region of Québec, and represent a major structuring force in the region, creating a mosaic of watersheds characterized by large variations in vegetation structure and composition. Here, we investigate the possible connections between this fire‐induced watershed heterogeneity and lake metabolism and CO 2 dynamics. Plankton respiration, and water–air CO...

We explore the role of lakes in carbon cycling and global climate, examine the mechanisms influencing carbon pools and transformations in lakes, and discuss how the metabolism of carbon in the inland waters is likely to change in response to climate. Furthermore, we project changes as global climate change in the abundance and spatial distribution of lakes in the biosphere, and we revise the estimate for the global extent of c...

Dissolved organic carbon (DOC) is a key parameter in lakes that can affect numerous features, including microbial metabolism, light climate, acidity, and primary production. In an attempt to understand the factors that regulate DOC in lakes, we assembled a large database (7,514 lakes from 6 continents) of DOC concentrations and other parameters that characterize the conditions in the lakes, the catchment, the soil, and the cli...

Characterizing dissolved organic matter (DOM) composition remains a major unresolved problem in aquatic ecology and is one of the key impediments to developing a good understanding of DOM production and consumption by heterotrophic bacteria. Fluorescence spectroscopy has been proposed as a promising method for characterizing DOM, but few links have been demonstrated between DOM fluorescence and DOM composition or the processes...

We investigated bacterial responses to variations in dissolved organic carbon (DOC) and nutrient availability by a comparative analysis of bacterial metabolism in lakes ranging from oligotrophic to eutrophic. Bacterial growth, respiration, and growth efficiency were quantified in lake water dilution cultures performed in 20 lakes located in eastern Quebec, Canada, which varied with respect to both DOC and nutrient concentratio...