Methane Fluxes of Vegetated Areas in Natural Freshwater Ecosystems: Assessments and Global Significance

Freshwater ecosystems, including wetlands, lakes, and running waters, are estimated to contribute roughly 40% to global emissions of methane (CH4), a highly potent greenhouse gas. The emission of CH4 to the atmosphere entails the diffusive, ebullitive, and plant-mediated pathway. The latter, in particular, has been largely understudied and is neither well understood nor quantified. We have conducted a semi-quantitative literature review to (i) provide a synthesis of the different ways vegetated habitats can influence CH4 dynamics (i.e., production, consumption, and transport) in freshwater ecosystems, (ii) provide an overview of methods applied to study the fluxes from vegetated habitats, and (iii) summarize the existing data on CH4 fluxes associated to different types of vegetated habitats and their range of variation. Finally, we discuss the implications of CH4 fluxes associated with aquatic vegetated habitats for current estimates of aquatic CH4 emissions at the global scale. We identified 13 different aspects in which plants impact CH4 dynamics (three related to gaseous CH4 flux pathways) and ten approaches used to study and quantify fluxes from vegetated habitats. The variability of the fluxes from vegetated areas was very high, varying from -454.4 mg CH4 m-2 d-1 (uptake) to 2882.4 mg CH4 m-2 d-1 (emission). This synthesis highlights the need to incorporate vegetated habitats into CH4 emission budgets from natural freshwater ecosystems and further identifies understudied research aspects and relevant future research directions.