Tropical wetland methane emissions - processes and predictions: TropMethane

Two-thirds of global methane emissions from wetlands originate in the tropics, but this estimate is uncertain and our ability to predict variation in 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 peatland research site in Panama with data from ongoing or published research from peatlands in the Republic of Congo, Indonesia, and Peru. Together, this information will allow us to improve models of methane fluxes from tropical wetlands, and therefore refine estimates of future global climate change.

Methane emissions are strongly controlled by the amount of oxygen and inputs of organic substrates needed for methane production by soil microbes. As oxygen levels increase, methane emissions decline as bacteria convert methane to carbon dioxide and because oxygen is toxic to methane producing microorganisms. This reduces climate warming because methane is a more potent greenhouse gas than carbon dioxide. This research will quantify the extent to which oxygen in the peat controls microbial production and consumption of methane in tropical wetlands. We will quantify the environmental and microbial controls of methane oxidation and net methane fluxes through field measurements and experiments. For example, we will determine the extent to which microbial oxidation of methane to carbon dioxide is stimulated by oxygen release from the roots and by transport of atmospheric oxygen into the peat soil. The transport of atmospheric oxygen into the peat could occur through water table draw-down or by oxygenated rainwater flowing into the peat. We will therefore quantify the oxygen inputs related to these processes in the field. Furthermore, trees can stimulate methane production by releasing organic carbon compounds from their roots into waterlogged peat, so we will also measure labile compounds released from roots and plant litter. To establish relationships between oxygen inputs and methane fluxes we will manipulate the water table and mimic root oxygen inputs to quantify how oxygen inputs affect methane fluxes. We will also conduct stable isotope labelling to determine rates of methane oxidation under controlled laboratory conditions and in the field. We will include this information into an existing peatland model, which will then be linked to 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.