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| Earth Resources Observation and Science (EROS) |
Assessing Carbon Stocks in Soils
USGS/EROS scientists are combining remote sensing datasets with detailed soil characterization databases to assess soil carbon stocks throughout the United States. SOC assessments can be used in modeling how soil carbon changes in response to terrestrial disturbances and other factors. Examples of products developed in this regard include:
A series of maps using the State Soil Geographic (STATSGO) database illustrates the calculation of the stock of soil organic carbon in the United States, accounting for the influence of soil depth, rock content, bulk density, and carbon intensity. Maps show the amount of soil carbon for a sequence of depth intervals. For example, 22.1 Pg C of the 61.9 Pg C in the conterminous United States are in the top 20 cm of the soil profile. The influences of soil forming factors on present carbon stocks have been evaluated, categorizing carbon contents by topographic position, soil slope, climate regime, glacial influence, and the interactions of such factors. Knowledge of carbon stocks forms a basis for a more complete modeling of the dynamics of the carbon cycle and the implications of human influences on the pedosphere and related global systems.
Currently, there is a pressing need to better understand changes in SOC and how such changes influence the net flux of carbon to or from the atmosphere. Some land use changes, such as converting grassland to agriculture or removing forests, tend to release SOC to the atmosphere. Other changes, such as restoring degraded lands, may lead to carbon sequestration (movement of carbon from the atmosphere into soils). The Department of the Interior (DOI) has jurisdiction influencing approximately 22 percent of the Nation's land area. SOC maps for all DOI lands were created using the State Soil Geographic Database (STATSGO) and other data sets.
Site-specific pedon data to recalculate the soil carbon for the North Slope of Alaska. This linking of measured point data to the general soil maps provides a method to improve the scientific rigor of the U.S. carbon stock estimates, and represents a 'Proof of Concept' for applying the method nationwide. It is interesting to note that just 2 measurements at Pt. Barrow account for nearly 2.7 petagrams of soil carbon stocks, indicating that additional sampling in this area would greatly reduce the uncertainty of the estimates.
A dataset of changes in population and agricultural land for the conterminous United States has been created that spans more than 200 years and contains more spatial detail than has been previously available. It shows, at the county level, the history of population (1790-1997) and that of agricultural development (1850-1997). The dataset was created to provide data on the timing of land conversion as an input to dynamic models of the carbon cycle, although many other applications are possible in the physical, biological, and social sciences.
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