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The biologic carbon sequestration assessment program (LandCarbon) investigates ecosystem carbon cycle problems and develops carbon management science and monitoring methods.
Specifically, LandCarbon is focused on the following research areas:
- Synthesize and assess current and potential carbon balance (stocks and fluxes) in major terrestrial and aquatic ecosystems
- Evaluate the effects of both natural and anthropogenic driving forces on ecosystem carbon balance and greenhouse gas fluxes
- Develop carbon monitoring methods and capabilities
- Conduct research and provide science support for increasing carbon sequestration in land management policies and practices
Since 2010, the USGS has:
- Released a methodology for the national assessment of biologic carbon sequestration (USGS Scientific Investigations Report 5233)
- Completed the assessment for the conterminous United States divided into three regional reports (USGS Professional Papers 1787- Great Plains, 1797- Western US, and 1804- Eastern US), and Alaska and Hawaii separately
- Developed and released a LandCarbon website for data distribution and visualization.
Additionally, a number of research papers have been published in leading journals by USGS and academic scientists supported by the program.
Going forward, the new focus of the program is in two priority areas:
- Synthesis and assessment linking ecosystem carbon balance with natural and anthropogenic processes as well as carbon management
- Carbon sequestration application studies in support of Department of the Interior land management decision making
The USGS investigates the amount of carbon burial, emissions, and export taking place in the aquatic ecosystems of the United States. Data analysis and modeling are used to identify the controls on greenhouse gas emissions from lakes and rivers, as well as the magnitude of carbon burial in sediments. Linkages between land use and carbon cycling in nearby aquatic habitats are being characterized in order to understand the effects of human activity such as agriculture and development on aquatic carbon cycling. Carbon export to the coastal ocean is also being quantified, and ecosystem models will describe the movement of continental carbon exports through the coastal food web.
Inland aquatic ecosystems (rivers, lakes, ponds, and reservoirs) play several important roles in the carbon cycle. Carbon that has been fixed via terrestrial primary production and processed in the soil is exported to surface water as both organic and mineral carbon compounds. In the aquatic environment, organic carbon compounds are respired (converted to CO2) by bacteria. This process can lead to a greater concentration of CO2 in the water than in the air (supersaturation), which results in "degassing", or emission of CO2 to the atmosphere. At the same time, plants and algae in aquatic ecosystems take up CO2 for photosynthesis. As it moves through the food web, most of this carbon is ultimately converted back to CO2 by respiration, but some of it can be buried in sediments. Anaerobic decomposition of carbon buried in sediments can create CH4, another greenhouse gas, which can also escape to the atmosphere. River systems transport carbon, originating from both terrestrial and aquatic systems, to the coastal ocean, where it is then further processed (emitted as greenhouse gases, buried in sediments, or transported offshore).
Carbon Sequestration Assessment
According to the newly completed the 2nd State of Carbon Cycle Report (), Terrestrial and aquatic ecosystems in the United States are a significant carbon sinks, taking up approximately a quarter of the nation’s CO2 emissions. The ecosystem carbon sink can be highly variable over space and time due to natural disturbances and land use decisions (Goodale and others, 2002)). 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 a forest ecosystem's ability to increase sequestration over the long-term. USGS conducts synthesis and assessment of carbon sequestration processes and long-term balances of major ecosystems including forests, croplands, grasslands, and wetlands in relation to both natural and anthropogenic driving forces.
Ecosystem Disturbances – Wildland Fire
Ecosystem disturbance modeling and emission estimation produces spatially-explicit forecasts of fire patterns, and the resulting greenhouse gas emissions for U.S biomes. At the heart of the approach is a series of statistical and process-based models, coded in C++, that simulate processes of fire ignition, spread, and emissions. Patterns of historic ignitions are characterized using logistic regressions that relate ignition location to daily fuel moisture conditions, as well as, vegetation type and urban extent. These ignition models are used to determine when and where ignitions are located under stable or changing climate scenarios. Once ignitions are located, the area burned is determined by allowing each ignition to spread using the minimum travel time algorithm. After fire spread is complete, emissions are calculated using the FOFEM and CONSUME models.
Vegetation, fuels, daily weather, and fuel moisture data are critical to disturbance simulations. Vegetation and fuels data are provided by the LANDFIRE project. The daily weather data we use have 12 km spatial resolution and span from 1950 to 2010. For future climate-change scenarios, we randomly resample annual sequences of historic daily weather and rescale them to match the monthly means provided by downscaled climate-change forecasts. Fuel moistures and fire behavior indices are calculated for both historic and forecast daily weather using the National Fire Danger Rating System and then used as predictor variables for ignition locations, fire spread, and fire emissions.
Future Scenarios and land use modeling
To study potential changes in land use, land cover and land management in the future United States, USGS has incorporated probable scenarios as defined by the Intergovernmental Panel on Climate Change (IPCC) in its fourth and fifth assessment reports (AR4 and AR5), which lists major driving forces of future emissions, including changes in demographic, technological and economic developments. To be able to incorporate these scenario assumptions into ongoing research and to produce nationally and regionally unique future potential land use and land cover scenarios, data on historical land-cover change from USGS and information derived from a global integrated assessment model are used in conjunction with expert analysis to 1) downscale scenario narrative storylines to national and sub-national scales, and 2) develop quantitative regional projections of LULC change for major land-use sectors of the conterminous United States. Results of this process are a set of quantitative future scenarios for specific land use and land cover classes, unique at both national and regional scales.
There are large uncertainties in how land and climate systems will evolve and interact to shape future ecosystem carbon dynamics. To address this uncertainty, we developed the Land-Use and Carbon Scenario Simulator (LUCAS) to track changes in land use, land cover, land management, and disturbance, and their impact on ecosystem carbon storage and flux. The LUCAS model combines a state-and-transition simulation model (STSM) for modeling land-change with a stock and flow model for modeling carbon dynamics, within a scenario-based framework. These two models were developed in conjunction within the ST-SIM modeling environment to provide a complete package for testing a range of future scenarios of land-use change and their impacts on carbon dynamics. Land-use change scenarios developed from the Intergovernmental Panel on Climate Change's (IPCC) Special Report on Emission Scenarios (SRES), and Representative Concentration Pathways (RCPs), as well as scenarios developed from historical land-use change datasets that include a range of mitigation and adaptation policies can be applied in the model.