CENTURY

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CENTURY Soil Carbon model

CENTURY Soil Carbon model has been used by the LCZO to understand the distribution of soil carbon across Luquillo watersheds.

Model Category: Numerical

CENTURY Soil Carbon model has been used by the LCZO to understand the distribution of soil carbon across Luquillo watersheds.

Abstract from Johnson K, Scatena F.N., Silver W.L. 2011 "Atypical soil carbon distribution across a tropical steepland forest catena" Catena 87:391-397

Soil organic carbon (SOC) in a humid subtropical forest in Puerto Rico is higher at ridge locations compared to
valleys, and therefore opposite to what is commonly observed in other forested hillslope catenas. To better
understand the spatial distribution of SOC in this system, plots previously characterized by topographic
position, vegetation type and stand age were related to soil depth and SOC. Additional factors were also
investigated, including topographically-related differences in litter dynamics and soil chemistry. To
investigate the influence of litter dynamics, the Century soil organic model was parameterized to simulate
the effect of substituting valley species for ridge species. Soil chemical controls on C concentrations were
investigated with multiple linear regression models using iron, aluminum and clay variables. Deeper soils
were associated with indicators of higher landscape stability (older tabonuco stands established on ridges and
slopes), while shallower soils persisted in more disturbed areas (younger non-tabonuco stands in valleys and
on slopes). Soil depth alone accounted for 77% of the observed difference in the mean 0 to 60 cmSOC between
ridge soils (deeper) and valley soils (shallower). The remaining differences in SOC were due to additional
factors that lowered C concentrations at valley locations in the 0 to 10 cm pool. Model simulations showed a
slight decrease in SOC when lower litter C:N was substituted for higher litter C:N, but the effects of different
woody inputs on SOC were unclear. Multiple linear regression models with ammonium oxalate extractable
iron and aluminum, dithionite–citrate-extractable iron and aluminum, and clay contents explained as much
as 74% of the variation in C concentrations, and indicated that organo-mineral complexation may be more
limited in poorly developed valley soils. Thus, topography both directly and indirectly affects SOC pools
through a variety of inter-related processes that are often not quantified or captured in terrestrial carbon models.