Learn More About Biological Carbon Sequestration

Biological Carbon Sequestration

As USGS summarizes, biological carbon sequestration refers to the assimilation and storage of atmospheric carbon in vegetation, soils, woody products, and aquatic environments. Fluxes of carbon dioxide and other greenhouse gases (GHG) in ecosystems are a function of natural ecosystem processes and anthropogenic activities.  The U.S. Department of the Interior (DOI) has developed a methodology  to measure and assess carbon storage, carbon sequestration, and fluxes of three principal GHG – CO2, methane (CH4), and nitrous oxide (N2O) – for the Nation’s ecosystems An assessment methodology has been developed to fulfill the first part of the EISA requirements. The national assessment for biological carbon sequestration and GHG fluxes is ongoing. You can find more information on the assessment, including publications and data results here.

Terrestrial Carbon Sequestration

Terrestrial ecosystems in the United States are globally significant carbon sinks. In the conterminous United States, forests cover about 246 million hectares, with an additional 52 million hectares in Alaska. Forests are a considerable carbon sink in the U.S., but can be highly variable in their annual carbon-storage capacity due to natural disturbances and land use decisions. Fire, for example, is a disturbance that affects a forest’s carbon storage and has effects of both releasing CO2 and CH4 back into the atmosphere and strengthening forest ecosystem’s ability to increase sequestration over long-term.

Croplands are also significant carbon pools, but store carbon differently than forests. Because of annual harvest, the accumulation of carbon in crops is short-lived, so much of the carbon is returned to the soil. Management practices, such as no-till agriculture, can affect the amount of carbon sequestered back into the soil by leaving a substantial amount of crop residue to slowly decompose and become part of the soil organic matter. Other factors to determine sequestration rates, as well as fluctuations in N2O emissions, are fertilization, crop type, and soil-drainage capacity.

Grasslands/shrublands are very similar to croplands in that most of the carbon stock is stored in the soil. While grasslands/shrublands can be net sinks for carbon, the capacity to store carbon varies across the landscape and is subject to grazing intensity and woody encroachment in landscape. The USGS’ LandCarbon project provides a national assessment of ecosystem carbon sequestration and greenhouse gas fluxes.

Aquatic Carbon Sequestration

Wetlands are transitional areas between uplands and aquatic ecosystems and are generally inundated periodically or permanently with water, or have saturated soils and support vegetation adapted to anaerobic conditions. Most of the carbon is stored in the soil, but both woody and nonwoody vegetation and sediments contribute to the sequestration of carbon in wetlands. Carbon is lost from wetlands through methanogenesis (the formation of methane by microbes known as methanogens), in anaerobic soils and through oxidation of organic matter when wetlands are drained. Only about 48% of the original wetland area in the United States still exists, with about 70 million acres in the conterminous U.S. and 43 million more acres in Alaska. Restore America’s Estuaries (RAE) has launched a methodology for aquatic carbon sequestration, or “blue carbon“. Restoration projects that qualify include:

  • Removing tidal barriers
  • Improving water quality, particularly to increase seagrass extent
  • Management of organic soils such as subsidence reversal
  • Rewetting of drained wetlands
  • Lowering of water levels on impounded wetlands
  • Wetland creation through beneficial use of dredged material
  • Restoring salinity conditions
  • Revegetation
  • Combinations of the above

By expanding conservation and restoration efforts on land and in aquatic systems, conservation managers can make significant contributions to climate change mitigation efforts while accomplishing compatible stewardship objectives.

For additional mapping and carbon sequestration data, visit LandCarbon.org, which features data products designed to support national (all states) estimations and projections of carbon stocks and sequestration in ecosystems, and regional (EPA ecoregions) science and land management applications. Featured papers include: