Characterizing Multi-Scale Variation of Soil Organic Carbon in the United States.

To characterize the spatial variation of soil carbon at a single spatial scale may be too simplistic due to the fact that soil carbon forming and evolving processes are controlled by various factors that operate simultaneously at multiple scales. There is a lack in knowledge on the multi-scale variation of soil carbon that extends over multiple escalating spatial scales including large region, continental, and global applications. The goal of this study was to identify the key characteristics of soil carbon variation across multiple scales (fine scale – 500m*500m study area in Florida, regional scale – Florida, and continental scale - the conterminous U.S.). Soil samples were taken across the three scales in the topsoil (0-20 cm). Soil organic carbon (SOC) was measured using dry combustion method on a Shimatzu TOC analyzers. Factorial kriging analysis was applied to SOC to identify the hierarchy of the spatial variation of SOC. The fractal analysis was conducted to delineate the multi-fractal feature of SOC variation and to identify the critical tipping points at which the SOC variation structure changes significantly. Results demonstrate that the SOC variability has a pronounced spatially hierarchical structure in terms of spatial autocorrelation range, sill, and nugget, suggesting that SOC variation is scale-dependent. The SOC variability across multiple scales shows multi-fractal characteristics. These results advance our understanding of the spatial variation of SOC in the Southeastern US and its correlation with scales. Incorporating scale-dependent measurements and modeling of SOC concentration in large region assessments is profoundly important to accurately quantify distribution patterns and soil carbon sinks/sources.