Rooted macrophytes reduce sediment <scp> CH ₄ </scp> storage and net production: An experimental approach using a novel scanning method

Abstract Methane (CH 4 ) emissions from freshwater ecosystems are significant but rarely quantified in vegetated zones. We assessed the influence of five macrophyte species that root in the sediment differing in growth form and root biomass on CH 4 emissions and sediment gas storage. Using a novel scanning method, we visualized sediment bubbles and root structures over time. Macrophyte growth form influenced diffusive as well as ebullitive emissions. Bubbles occupied a smaller volume in vegetated sediments (~ 19%) than in control treatments (~ 53%). Extensive root systems were associated with reduced sediment CH 4 accumulation, likely due to enhanced CH 4 oxidation and/or transport. Total CH 4 production was lower in vegetated (~ 54 mg CH 4 m −2 d −1 ) than in control treatments (103 mg CH 4 m −2 d −1 ), of which a substantial part was stored in sediment bubbles. Our findings highlight the importance of including changes in sediment CH 4 storage in CH 4 budgets and demonstrate how macrophyte characteristics shape CH 4 dynamics.