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Wetlands are hotspots of CH₄ emissions to the atmosphere, mainly sustained by microbial decomposition of organic matter in anoxic sediments. Several knowledge gaps exist on how environmental drivers shape CH₄ emissions from these ecosystems, posing challenges in upscaling efforts to estimate global emissions from waterbodies. In this work, CH₄ and CO₂ diffusive fluxes, along with chemical and isotopic composition of dissolved ionic and gaseous species, were determined from two wetlands of Tuscany (Italy): (i) Porta Lake, a small wetland largely invaded by <i>Phragmites australis</i> reeds experiencing reed die-back syndrome, and (ii) Massaciuccoli Lake, a wide marsh area including open-water basins and channels affected by seawater intrusion and eutrophication. Both wetlands were recognized as net sources of CH₄ to the atmosphere. Our data show that the magnitude of CH₄ diffusive emission was controlled by CH₄ production and consumption rates, being mostly governed by (i) water temperature and availability of labile carbon substrates and (ii) water column depth, wind exposure and dissolved O₂ contents, respectively. This evidence suggests that the highest CH₄ diffusive fluxes were sustained by reed beds, providing a large availability of organic matter supporting acetoclastic methanogenesis, with relevant implications for global carbon budget and future climate models.