Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling

Vertical Soil Carbon Distributions in the Contiguous United States: Effects of Land Cover and History of Cultivation

Thursday, December 17, 2015 - 13:55 to 14:10
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Soils contain the largest pool of carbon in most terrestrial ecosystems. The vertical distribution of these large carbon pools contains important information about the factors affecting soil formation and soil organic matter preservation. In addition, the depth distribution of organic matter is associated with its stability and resilience to climatic and ecological changes. We fit the vertical distribution soil organic carbon (SOC) concentration using an exponential model in order to calculate empirical parameters Z*, representing the characteristic vertical scale of the decline in SOC concentration with depth, and Csurf, representing the approximate SOC concentration in the uppermost layer of mineral soil. A higher value of Z* indicates a longer vertical scale, and therefore a slower decline with depth. This calculation was applied to a set of over 28,000 soil profiles in the coterminous United States. Limiting the analysis to fits with an r2>0.9 yielded more than 15,000 estimates of Z* and Csurf from soil profiles representing a variety of different ecosystems. We used this large dataset to test hypotheses related to the impacts of soil type, ecosystem type, and land use history on soil carbon stocks and vertical distributions. SOC concentration near the surface and its rate of decline with depth were both strongly dependent on land use, with cultivated soils having the lowest Csurf and highest Z* and forest soils having the highest Csurf and lowest Z*. These effects were more pronounced in forest soil orders (alfisols and spodosols) than in prairie soil orders (mollisols). Cultivation lowered SOC concentrations throughout the soil profile, and these effects were visible in currently forested ecosystems with a history of cultivation, indicating that the effects were persistent after reforestation. These results will be useful for both assessing land use effects on soil carbon stocks and evaluating ecosystem

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