An appraisal on methane emissions from wetlands based on direct estimates and theoretical computations: the case of Lake Porta wetland, northern Tuscany (Italy)

Methane (CH4) emissions to the atmosphere are a rising concern affecting the Earth’s climate. Among natural sources, wetlands contribute to 30% of global CH4 emissions, making flux assessment from these environments pivotal. Any attempt to establish a theoretical estimate of gas flux from aquatic ecosystems should address the rate of gas exchange between the air-water interface, a process commonly modelled as driven by two variables: the difference in gas concentration between water and air and the gas transfer velocity (k). The magnitude of gas exchange, thus the value of k, has been shown to be related to wind speed, a parameter through which k is calculable. In this study, diffusive CH4 fluxes were measured at Lake Porta, a coastal wetland in northern Tuscany (Italy), adopting the floating static chamber (FSC) method. Two field campaigns were carried out in March and July 2021 to evaluate the influence of seasonal variations. As the measured data showed that significant amounts of CH4 are emitted into the air, the fluxes were compared with those obtained from theoretical computations based on empirical relationships from literature where k values were achieved experimentally. The results show coherent trends in the measured and calculated fluxes, with a regular shift related to the assumptions the authors made in determining the k coefficient. This study offers a methodologic approach on both empiric and theoretical estimates of greenhouse gas fluxes from aquatic ecosystems, which may be critical for future climate change scenarios.