The Role of Wetland Processes in the Global Carbon Cycle and Climate Change

Although carbon storage in wetland soils has long been recognized as an important component of global carbon budgets and future climate change scenarios, very little work has been done to consider the role of current and restored wetlands carbon processes in the global carbon cycle. Peat deposits in the world's wetlands, particularly in boreal and tropical regions, are substantial storages of carbon (C) in the lithosphere. Of the total storage of carbon in earth's soils of 1,400 to 2,500 Pg-C, anywhere from 20 to 30 percent of that is stored in wetlands. These deep peat deposits, if disturbed could contribute significantly to worldwide atmospheric CO₂ levels, depending on rates of draining and oxidation of the peat deposits due to climate change and human development. While much attention has been recently paid to the ability of coastal wetlands (mangroves, salt marshes, and sea grass beds) to sequester carbon (the concept is known as "blue carbon"), less attention has been paid to the ability of inland wetlands, particularly on a global scale, to sequester carbon, even though these wetlands comprise 95% of the world's wetlands. Part of the reason is because these freshwater wetlands often have significant emissions of greenhouse gases, particularly methane. Our paper provides an updated analysis of the balance between carbon sequestration and methane emissions in natural, created, and restored wetlands around the world, as well as illustrating models and previous studies that have attempted to balance these two fluxes to determine the net effect of wetlands on both carbon balances and net radiative forcing. Our studies show that most wetlands are net sinks of radiative forcing; exceptions to this are some degrading boreal and tropical wetlands that have been drained and have become net sources of carbon dioxide.