title: Fate of methane in aquatic systems dominated by free-floating plants.
abstract: Worldwide the area of free-floating plants is increasing, which can be expected to alter methane (CH4) emissions from aquatic systems in several ways. A large proportion of the CH4produced may become oxidized below the plants due to the accumulation of CH4as a result of a decrease in the diffusive water-atmosphere flux and the entrapment of part of the ebullitive CH4, in combination with suitable conditions for methane oxidizing (MOX) bacteria in the aerobic rhizosphere. We used a set of essays to test this hypothesis and to explore the effect of different densities for three widespread free-floating species: Azolla filiculoides, Salvinia natans, and Eichhornia crassipes. The gas exchange velocity, proportion of CH4bubbles trapped by the plants, occurrence of radial oxygen loss from roots, and MOX rates on the roots were assessed. We subsequently used the outcome of these experiments to parameterize a simple model. With this model we estimated the proportion of the produced CH4that is oxidized, for different plant species and different densities. We found that in a shallow (1 m) system up to 70% of the CH4produced may become oxidized as a result of a strong decrease in gas exchange combined with high MOX activity of the rhizosphere microbiome. As floating plants also are likely to increase CH4production by organic matter production, especially when their presence induces anaerobic conditions, the overall effect on CH4emission will strongly depend on local conditions. This explains the contrasting effects of floating plants on CH4emissions in literature as reviewed here. As the effect of floating plants on CH4emissions, including the high MOX rates we show here, can be substantial, there is an urgent need to consider this impact when assessing greenhouse gas budgets.
authors.affiliation: Department of Aquatic Ecology and Environmental Biology, Institute for Water and Wetland Research, Radboud University, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands. Electronic address: s.kosten@science.ru.nl.
authors.forename: Sarian
authors.initials: S
authors.lastname: Kosten
authors.affiliation: Department of Aquatic Ecology and Environmental Biology, Institute for Water and Wetland Research, Radboud University, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands.
authors.forename: Marcia
authors.initials: M
authors.lastname: Piñeiro
authors.affiliation: Department of Aquatic Ecology and Environmental Biology, Institute for Water and Wetland Research, Radboud University, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands.
authors.forename: Eefje
authors.initials: E
authors.lastname: de Goede
authors.affiliation: Department of Aquatic Ecology and Water Quality Management, P.O. Box 47, 6700AA, Wageningen University, Wageningen, The Netherlands.
authors.forename: Jeroen
authors.initials: J
authors.lastname: de Klein
authors.affiliation: Department of Aquatic Ecology and Environmental Biology, Institute for Water and Wetland Research, Radboud University, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands.
authors.forename: Leon P M
authors.initials: LPM
authors.lastname: Lamers
authors.affiliation: Department of Microbiology, Institute for Water and Wetland Research, Radboud University, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands.
authors.forename: Katharina
authors.initials: K
authors.lastname: Ettwig
mesh_terms: D017752:Greenhouse Effect; D008697:Methane; D010100:Oxygen; D010944:Plants; D058441:Rhizosphere
chemical_list: D008697:Methane; D010100:Oxygen
keywords: Free-floating plants; Gas exchange velocity; Greenhouse gas; Methane emission; Methane oxidation; Rhizosphere