Wetlands sequester carbon from the atmosphere through plant photosynthesis and by acting as sediment traps for runoff. Carbon is held in the living vegetation as well as in litter, peats, organic soils, and sediments that have built up, in some instances, over thousands of years. Wetland soils are anoxic (oxygen-poor), and therefore slow decomposition and lead to the accumulation of organic matter. The magnitude of storage depends upon wetland type and size, vegetation, the depth of wetland soils, groundwater and nutrient levels, pH, and other factors. Wetland soils also store carbon that washes in from upland areas, through soil erosion or movement of leaves and tree debris. Wetlands also release carbon both through natural, seasonal changes and, more drastically, when their equilibrium is affected by human interference.1
With wetlands holding large amounts of carbon, the fate of existing wetlands is a factor in predicting carbon emissions. The loss of an existing wetland means not only the loss of that particular carbon sink, but also that the carbon stored in that wetland will be released.
"Wetlands sequester some of the largest stores of carbon on the planet, but when disturbed or warmed, they release the three major heat-trapping greenhouse gases (GHGs), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Rising planetary temperatures are causing a positive feedback from warming wetlands and thawing permafrost that is accelerating global warming."2
The Extent of Carbon Storage in U.S. Wetlands
A recent study based on field data from the 2011 National Wetland Condition Assessment finds that wetlands in the conterminous United States store a total of 11.52 billion metric tons of carbon, much of which is within soils deeper than 30 cm. Freshwater inland wetlands, in part due to their substantial acreage, hold nearly ten times more carbon than tidal coastal wetlands.3 The study found that wetlands in forested regions of the East and Upper Midwest store the most carbon, accounting for nearly half the wetland carbon in the United States.
Research studies agree that carbon storage is enhanced in wet systems. Best practices for protecting carbon stores1 include:
- Stopping or reducing wetland drainage and other land and water management practices that lead to dewatering of wetlands
- Controlling fires in wetlands
- Allowing natural revegetation to occur in wetlands or replanting vegetation to prevent proliferation of invasive species due to climate change
- Controlling peat harvesting and other practices that remove carbon from wetlands.
1 Kusler, J. and J. Christie. 2011. Wetlands and Carbon Storage and Carbon Sequestration. White Paper: Reducing Climate Change Impacts and Promoting Fish and Wildlife: Findings and Recommendations for Biological Carbon Storage and Sequestering. Association of Fish and Wildlife Agencies and the Association of State Wetland Managers.
2 Moomaw, W.R., Chmura, G.L., Davies, G.T. et al. 2018. Wetlands In a Changing Climate: Science, Policy and Management. Wetlands 38:183-205.
3 Nahlik, A.M. and M.S. Fennessy. 2016. Carbon Storage in U.S. Wetlands. Nature Communications 7:13835.