![]() ![]() The latter occurs under peculiar conditions, being referred to the sudden release of CH 4 either accumulated due to water stratification or trapped by ice formation. Once released from bottom sediments, CH 4 can upwardly move through the water column and reach the atmosphere via different pathways, including molecular diffusion, ebullition and storage flux, e.g. Microbial methanogenesis within surface aquatic systems mainly occurs in bottom anoxic sediments, where fresh organic matter accumulates from litterfall, dead plant materials and root exudates, e.g.,, although CH 4 production was also observed under aerobic conditions, e.g. Nevertheless, these estimates are still affected by large uncertainties, mainly because it is not clear how the physico-biogeochemical factors regulate the release of GHGs from aquatic reservoirs to the atmosphere. , aquatic ecosystems are currently responsible for half of global CH 4 emissions to the atmosphere and their contribution is destined to increase as a consequence of global warming and human alterations. The causes of such impressive CH 4 increment are not fully understood and may include both increasing emissions from anthropogenic sources and/or natural ecosystems and a decline in the oxidative capacity of the atmosphere. Its concentration in air is nearly three times higher than that recorded in 1750, with a stepwise increasing trend characterized by a relatively stable period from 2000 to 2007 and a renewed and rapid growth since 2007. Recently, methane has been receiving increased attention since it is the second-most important GHG in the atmosphere, with a global warming potential 28 times higher than that of CO 2 over a 100-year time frame. Methane emissions from wetlands are also augmented by climate change, shifts in the hydrological regime, eutrophication processes or more in general by processes that support anaerobic conditions in shallow waters, e.g. Nevertheless, degraded ecosystems may rapidly turn from carbon sinks to major sources of greenhouse gases (GHGs), releasing high amounts of CH 4 and CO 2 produced by microbial decomposition of organic matter, e.g. Among them, coastal wetlands play a key role in sequestering and storing blue carbon from oceans. According to Lal, wetlands store 20–30% of terrestrial carbon at global scale. Among surface aquatic systems, wetlands are highly productive ecosystems capable of sequestering large amounts of carbon from the atmosphere through photosynthetic activity, which is then stored in biomass and sediments. Accordingly, attention is increasingly being devoted to studying the contribution of water reservoirs to climate change and understanding feedback mechanisms related to global warming of aquatic ecosystems, e.g. Nevertheless, they play a crucial role in the global carbon cycle, as they regulate the transport of terrestrial carbon between lands and seas. ![]() ![]() Surface aquatic systems only cover a small fraction of global land surface. This evidence suggests that the highest CH 4 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. Our data show that the magnitude of CH 4 diffusive emission was controlled by CH 4 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 O 2 contents, respectively. Both wetlands were recognized as net sources of CH 4 to the atmosphere. In this work, CH 4 and CO 2 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 Phragmites australis 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. Several knowledge gaps exist on how environmental drivers shape CH 4 emissions from these ecosystems, posing challenges in upscaling efforts to estimate global emissions from waterbodies. Wetlands are hotspots of CH 4 emissions to the atmosphere, mainly sustained by microbial decomposition of organic matter in anoxic sediments. ![]()
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