Tropical wetland methane emissions - processes and predictions: TropMethane

Summary
Two-thirds of global methane emissions from wetlands originate in the tropics, but this estimate is uncertain and our ability to predict methane emissions from tropical wetland remains rudimentary. Furthermore, we do not know how methane emissions will respond to climate change. In this project we will address this knowledge gap by combining new mechanistic information from our existing long term wetland research site in Panama with data from ongoing or published research from wetlands in the Republic of Congo, Indonesia, and Peru. This project targets two processes that are important controls of methane fluxes: methane oxidation and methane production linked to root exudates. This project will measure these processes and associated environmental and microbial drivers in the field. We will then use this data to incorporate both of these processes in large scale models to estimate net methane emissions from tropical wetlands.

Oxygen levels in the saturated soils of wetlands can increase due to the water table falling, inputs from oxygenated rainfall and from roots. As oxygen levels increase, methane emissions decline as bacteria convert methane to carbon dioxide, and because oxygen is toxic to methane-producing microorganisms. This research will quantify the extent to which oxygen in the soil controls microbial production and consumption of methane in tropical wetlands. The substrate availability from decaying organic matter and labile organic compounds released from roots affect methane production, linking methane production both to the organic matter in the soil and root exudates. In this project, we will determine the amounts and types root exudate inputs from trees to improve our understanding of how trees affect methane production in wetlands. For example, we will collect water samples from the root zone to determine the different organic compounds present, and compare these results between different tree species. To develop a full understanding of the different processes impacting methane fluxes we will carry out detailed measurement of environmental and microbial controls of methane oxidation, production and net emissions. In our field work, we will determine the extent to which microbial oxidation of methane is increased by experimental simulation of root oxygen inputs and water table draw down. We will also conduct stable isotope labelling experiments to determine rates of methane oxidation and production by microbes directly in the field. We will include this information into an existing wetland methane emissions model and integrate this into JULES - a large-scale ecosystem model that forms a component of UK Met Office climate model. This will enable us to predict methane emissions from tropical wetlands and how these will respond to climate change. The project is an important step toward the representation of methane emissions from tropical wetlands in global climate models.