Temporal Evolution of Spatial Structure In Soil Carbon Stocks.

Soil variability is the result of soil formation factors. Soil formation factors, conditioned by physiography and geomorphology, determine the processes that determine soil properties in a given space.  The existence of spatially distributed processes controlling factors would lead to the conclusion that systematic variation in soil properties is possible.  Reclaimed minesoils are an ideal settings to study the time-dependant change in soil properties (soil chronosequence) due the possibility of knowing with a high degree of certainty the soils age (time since reclamation), the geologic origin of the parent material, weather, vegetation (reclamation practices), and relief.  The objective of our research was to assess the effect of time since reclamation on the spatial structure of soil organic carbon (SOC), bulk density (BD) and soil carbon stock in a reclaimed minesoil chronosequence. Our hypothesis is that in a soil chronosequence, the spatial structure of SOC, BD, and soil carbon stock, will develop as soil age increases, due to the establishment of a gradual systematic variability. Three northern West Virginia minesoils were selected along a well-defined reclamation chronosequence (one (1), four (4), and twenty one (21) years post-reclamation). At each mine site 0 to 5 cm depth soil samples were collected for SOC and BD in an irregular 7 m by 5 m grid. Measured SOC, BD, and calculated soil carbon stock, were analyzed using variogram analysis to characterize their spatial structure.  A spherical model provided the best fit to the isotropic variograms of SOC concentrations (g/kg), BD (kg/m³) and SOC stocks (Mg C ha^-1).  Spatial analysis for the all the selected variables showed that as the minesoil age increased, short distance variability (nugget) decreased, total sill increased, spatial dependence increased (nugget/sill ratios decreased), and a better fit to a spherical model (higher R², lowest RMSE) was observed.  Results support our hypothesis, and indicate the development of a gradual systematic variability in soil properties as a function of time.