Peatland Carbon Cycling

Peat bogs are significant contributors to the global carbon cycle, acting as large repositories of atmospheric carbon and containing over one third of the organic carbon in global soils. Emissions of methane (CH4) and carbon dioxide (CO2) greenhouse gases occur primarily by two processes: methanogenesis and methane oxidation.

Methanogenesis is the process by which CH4 is produced, which thereafter can be oxidized by methanotrophs or released into the atmosphere. CH4 is largely produced by methanogens performing anaerobic fermentation of carbohydrate substrates. Methanotrophic bacteria are largely responsible for the oxidation of CH4 to CO2. Methane oxidation tends to occur at oxic-anoxic interfaces since methane-oxidizing bacteria are restricted to soil depths and areas in which oxygen is present. Vascular plants expand the oxic zone just beneath the peat surface by producing oxygen from oxygenic photosynthesis, which increases rates of bacterial respiration and methane oxidation. Methanotrophs are crucial for efficient recycling of both methane from decaying plants and oxygen from photosynthesis.

Carbon Budget

There is growing interest in the annual CO2 and CH4 budgets of peatlands. Such budgeting is required for calculating the radiative forcing effect of peatlands on climate. The radiative forcing of different greenhouse gases (GHG) can be calculated using the concept of global warming potential (GWP) as defined by the Intergovernmental Panel on Climate Change (IPCC), and is usually expressed in terms of carbon dioxide equivalents (CO2-e). CH4 is a much more potent GHG than CO2 and correspondingly has a higher GWP. It is currently estimated that CH4 is 28 times more potent than CO2 over a 100-year timeframe.  Although in mass terms peatland CH4 fluxes typically represent < 10% of the combined CO2 and CH4 budget, they assume much greater importance when considered in CO2-e terms. Dissolved organic carbon (DOC) and particulate organic carbon (POC) are also important parts of any peatland carbon budget, as these components may later be mineralised and released as CH4 and CO2 from water bodies.

Climate Change

Atmospheric concentrations of CH4 under future climate change are uncertain. This is in part because many climate-sensitive ecosystems (including peatlands) release both CH4 and CO2 and it is unknown how these systems will partition future releases of carbon to the atmosphere. Understanding where and how climate change could affect peatlands  is vital to implement appropriate conservation and restoration policies that will preserve the world’s peatlands. But until now, very little is known about what climate change could do to these ecosystems.

 

 

 

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