## 5 Conclusions  
Porta and Massaciuccoli Lakes were recognized as net sources of CH4 and CO2 to the atmosphere, with measured CO2 eq emissions to the atmosphere up to 183 g CO2 eq m\({}^{-2}\) day\({}^{-1}\). The magnitude of CH4 diffusive emission at the water-air interface was strictly dependent on the balance between CH4 production and consumption rates. Methane consumption, mostly due to aerobic methanothrophy, was influenced by dissolved O2 contents, which, in turn, were related to the water column depth and stratification/mixing processes. The latter were likely governed by winds, lake morphology and vegetation, with reed beds acting as barriers to water movements and favoring the development of stagnant and hypoxic conditions in surface waters. Methane production rates were affected by both seasonal variations, due to the temperature dependence of microbial activity and quality and quantity of organic matter. In fact, evidence from both lakes suggested that the highest CH4 diffusive fluxes were sustained by the presence of reed beds providing shelter from the wind and ensuring a large availability of labile organic matter. Accordingly, the \(\Phi\)CH4 values in sites proximal to reed beds were up to two orders of magnitude higher than those measured in open waters. The results of this study highlighted that magnitude of CH4 diffusive emissions across wetland systems is strongly site-dependent and shaped by local environmental conditions, which might highly be variable in both time and space. Hence, the sampling strategies, timing and site selection have to be carefully evaluated since they might largely affect the estimation of overall CH4 diffusive emissions even within a single wetland system. Efforts to increase both spatial and temporal resolution of CH4 diffusive flux measurements to evaluate the diverse environmental conditions characterizing wetland landscapes are to be considered. Promising opportunities are offered by integrating traditional CH4 diffusive flux measurements with the deployment of low-cost CH4 sensors in flux chambers [89]. Nevertheless, the CH4 diffusive fluxes measured in this study, largely exceeding those reported in literature (Figure 4), indicate that a relevant portion of CH4 emissions from surface aquatic systems at global scale is likely missing in carbon budgets, with relevant implications for Earth system and climate models. It is to be pointed out that the investigated sites did not include areas with higher density of reed beds where the \(\Phi\)CH4 values might be even greater. Moreover, the CH4 emissions associated with plant litter in wetlands are expected to increase in the near future as a consequence of both eutrophication processes and climate change [3]. Moreover, the relationship between RDBS  
Figure 8: \(\xi^{13}\)C-CH4 (in% vs. V-PDB) vs. CH4 (in mmol/L) binary diagram for samples collected from Massaciuccoli Lake. Symbols as in Figure 1b. The Rayleigh fractionation evolution curve for CH4 oxidation to CO2 related to methanotrophic activity, as described in the text, is also reported (dashed line). and CH\({}_{4}\) diffusive fluxes is particularly alarming, considering that wetlands are among the most threatened ecosystems on Earth, drawing attention to the urgent need to protect and restore wetland ecological functioning. Conceptualization, S.V. and F.T. ; methodology, S.V. and F.T. ; formal analysis, S.V., F.C., M.L. and A.R. ; investigation, S.V., F.C., M.L., A.R., F.T., J.C. and O.V. ; resources, B.V.; data curation, F.T. and F.C. ; writing--original draft preparation, S.V. ; writing--review and editing, F.T., J.C., A.R., F.C. and O.V. ; visualization, S.V. ; supervision, B.V.; project administration, S.V. and O.V. ; funding acquisition, O.V. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The authors want to thank [PERSON] (WWF) for their support during sampling and measuring campaigns.