Deriving Alaska Carbon Stocks from SSURGO Data.

A comprehensive inventory of soil carbon stocks for soils of the United States is important for helping to derive global carbon accounting.  Total soil organic carbon (SOC) for the contiguous 48 states has been estimated from the Soil Survey Geographic (SSURGO) database of the National Cooperative Soil Survey to be 65 petagrams to a one-meter soil depth). It is widely recognized that arctic and sub-arctic regions may significantly contribute to global carbon stocks.  Recently, the National Park Service and the Natural Resources Conservation Service (NRCS) completed interagency soil mapping in Alaska of Denali National Park (DENA) and Yukon Charley Rivers National Preserve (YUCH). The soil mapping of DENA and YUCH encompassed 3.5 million hectares at a scale of 1:63,360, and included 3,071 geo-referenced field observations along hundreds of transects that are stored in a relational database. From the most recent park SOC data and SSURGO data of 10 additional well distributed and diverse soil surveys, we estimate SOC to be 187 Mg/ha  in Alaska. Soil depths up to 2 m were included in the Alaska calculation due to the extent of deep, cold, wet, organic soils. A deep carbon stock calculation is important if used to estimate subsidence and carbon release to the atmosphere as thermokarst landscapes expand due to climate change. A coarse extrapolation to the entire areal extent of Alaska equates to 34 petagrams of SOC.  Alaska is about one fifth of the areal extent of the lower 48 states, and by this estimate, contains about one third of the estimated total SOC of 49 states (not including Hawaii). These SSURGO-based SOC stocks will allow comparison to future estimates derived from the NRCS Rapid Carbon Assessment program which was recently completed for the contiguous 48 states and is currently on-going in Alaska and Hawaii.  Further refinement can also be made of the SSURGO estimates as additional federal and private lands are mapped in the state.