In addition to its Phase I regional greenhouse gas (GHG) emissions inventory, the South Dakota School of Mines and Technology (SDSMT), under Karen Updegraff, modeled terrestrial carbon fluxes (CO2 release and sequestration) for agricultural lands in the Partnership’s core states (ID, MT, SD, and WY).
Agricultural Sink Data
Agricultural sink modeling relied on climate, soil ,and land use data, all represented as continuous surfaces and summarized by county.
One hundred and eight years of climate data from National Climate Data Center station records were averaged for each of up to 10 climate zones in each state so as to produce zone-average files. In addition, zone-specific statistical data on climate variability were used to simulate climate after 2003.
Soil texture grids derived from SSURGO or STATSGO soil databases were developed for eachstate, then statistically aggregated to approximately 20 representative soil texture classes.
Land management data were extracted from the 1997 Census of Agriculture and from the Conservation Technology Information Center. These data were compiled on a county-level basis and are summarized in Table 1.
The CENTURY Model
Agricultural sequestration potential was estimated by applying results of the CENTURY model, a point-based protocol for predicting carbon stock changes, over counties in accord with alternative land management scenarios. Initially, the sets of point-based predictions are generated based on unique combinations between different management scenarios, climatic zones and soil texture classes. These results are then applied across individual counties, respective to the relevant climatic zone and to the extent of within-county management class areas as estimated in proportion to areas of within-county soil texture classes. To obtain the county-level estimated annual soil carbon flux rates, predicted carbon stock changes were then summed across all management classes within each county (Fig.1).
Figure 1. Current estimated annual soil carbon fluxes in Big Sky core states (ID, MT, SD, and WY).
GIS-based modeling has enabled the iterative exploration of effects from changes to the status quo in land use/management such as altered rates of no-till adoption or CRP enrollment. The CENTURY model has already afforded significant insights into the spatially-variable prospects for terrestrial sequestration; as one general example, results have confirmed that South Dakota (the state with by far the largest area of harvested cropland) offers the largest potential for terrestrial sink enhancement due to improved agricultural land management, particularly through conversion to no-till. Estimates of sequestration potential for a limited suite of scenarios have been included in the Big Sky Carbon Data Libraries and are represented in respective static maps in the map gallery.
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